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1. Introduction
The end Cretaceous mass extinction was associated with a severe disruption of marine productivity (Birch
etal., 2016; Coxall etal.,2006; D’Hondt etal.,1998; Hsü & Mckenzie,1985; Zachos etal., 1989). A reduc-
tion in sunlight received at Earth's surface caused by dust, soot, and sulfate aerosols ejected by the Chicxulub
impact resulted in a reduction in photosynthesis which is thought to have led to the collapse of marine food webs
(Alvarez etal.,1980; D’Hondt etal.,1998). Models show that the reduction in insolation lasted only a few years
after the impact (Alegret etal.,2022; Artemieva & Morgan,2020; Artemieva etal.,2017; Bardeen etal.,2017;
Brugger etal.,2017; Toon etal.,1997), removing the proximal external stress on marine primary producers and
clearing the way for the recovery of primary production. How, exactly, marine productivity recovered has been a
focus of K-Pg boundary research for decades; the K-Pg mass extinction represents a geologically unique disrup-
tion of marine ecosystems, perhaps the only major event in Earth history which happened faster than modern
climate change and environmental disruption. Modern oceans are likely on the verge of a major reorganization of
dominant plankton types due to warming, acidification, and changes in circulation and ventilation patterns (e.g.,
Barton etal.,2016; Jonkers etal.,2019), and primary production is expected to decline 20% due to warming
Abstract The global heterogeneity in export productivity after the Cretaceous-Paleogene (K-Pg) mass
extinction is well documented, with some sites showing no change on geologic timescales, some demonstrating
sustained decline, and a few showing a somewhat surprising increase. However, observational data come from
sites so widespread that a key outstanding question is the geographic scale of changes in export productivity,
and whether similar environments (e.g., open ocean gyres) responded similarly or whether heterogeneity is
unrelated to environment. To address this, we developed three new Ba/Ti export productivity records from sites
in the Gulf of Mexico and Caribbean which, combined with published data from a fourth site in the Chicxulub
Crater itself, allow us to reconstruct regional changes in post K-Pg export productivity for the first time. We
find that, on a regional scale, export productivity change was homogenous, with all four sites showing a ∼300
Kyr period of elevated export production just after the boundary, followed by a longer period of decline.
Interestingly, this interval of elevated export production appears to coincide with the post K-Pg global micrite
layer, which is thought to at least partially have been produced by blooms of carbonate-producing cyanobacteria
and other picophytoplankton. Global comparison of sites shows that elevated export productivity appears to
have been most common in oligotrophic gyres, which suggests that changing plankton ecology evidenced by the
micrite layer altered the biological pump, leading to a temporary increase in export production in these settings.
Plain Language Summary Primary producers are the base of the food chain; this group was
severely damaged by the environmental effects associated with the Cretaceous-Paleogene mass extinction.
Determining how primary production recovered after this calamity is an important foundation for understanding
how ecosystems recovered. Most previous work has focused on a process called export production, whereby
organic carbon produced by phytoplankton is transferred to the ocean interior (some of which sinks to the
seafloor and is buried). This work has shown that although most parts of the ocean recorded a decline in export
production after the extinction event, some regions actually showed an increase. However, it was not clear on
what geographic scale these differences occurred, or what caused them. We generated three new records of
export production from a single region, the Gulf of Mexico/Caribbean Sea, and found a consistent increase in
export production at each site for the same period of time after the extinction event. Comparison with other sites
with increased export production shows that many are from open ocean gyres, suggesting that these regions
were predisposed to increased export production in the earliest Paleocene because they were characterized by
low productivity prior to the extinction.
LOWERY AND BRALOWER
© 2022. American Geophysical Union.
All Rights Reserved.
Elevated Post K-Pg Export Productivity in the Gulf of Mexico
and Caribbean
Christopher M. Lowery1 and Timothy J. Bralower2
1University of Texas Institute for Geophysics, Austin, TX, USA, 2Pennsylvania State University, University Park, PA, USA
Key Points:
• Post K-Pg export productivity was
elevated across the Caribbean-Gulf of
Mexico region for ∼300 Kyr
• At sites with a clearly defined micrite
layer, the end of micrite deposition
coincides with the top of the highest
productivity interval
• Elevated post K-Pg export
productivity appears to be a feature
of oligotrophic low latitude open
ocean sites
Correspondence to:
C. M. Lowery,
cmlowery@utexas.edu
Citation:
Lowery, C. M., & Bralower, T. J. (2022).
Elevated post K-Pg export productivity
in the Gulf of Mexico and Caribbean.
Paleoceanography and Paleoclimatology,
37, e2021PA004400. https://doi.
org/10.1029/2021PA004400
Received 9 DEC 2021
Accepted 24 AUG 2022
Author Contributions:
Conceptualization: Christopher M.
Lowery
Data curation: Christopher M. Lowery
Formal analysis: Christopher M.
Lowery, Timothy J. Bralower
Investigation: Christopher M. Lowery,
Timothy J. Bralower
Methodology: Christopher M. Lowery
Resources: Christopher M. Lowery
Validation: Christopher M. Lowery
Visualization: Christopher M. Lowery
Writing – original draft: Christopher
M. Lowery
Writing – review & editing: Christopher
M. Lowery, Timothy J. Bralower
10.1029/2021PA004400
RESEARCH ARTICLE
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(Moore etal.,2018). The earliest Paleocene provides a window into understanding how such ecological changes
may impact food webs and marine carbon burial.
Of course, we can't observe ancient primary production in the euphotic zone directly, so most work on the
collapse and recovery of productivity after the K-Pg boundary has focused on sedimentary records of export
production (the transfer of particulate organic matter (POM) from the euphotic zone to the deep sea; e.g., Passow
& Carlson,2012)). The movement of POM from the euphotic zone to the seafloor is complicated and can be
divided into a series of steps, all of which are influenced by different processes. Most net primary production
(NPP) occurs in the euphotic zone (dependent on sunlight penetration but typically defined as 0–100 or 200m
water depth; Passow & Carlson,2012), and most POM is remineralized in these near surface waters. The precise
amount varies by region and season, but typically ∼90% of NPP is consumed and recycled before it can sink out
of the euphotic zone. The movement of POM out of the euphotic zone is what biological oceanographers define
as “export flux” or “export productivity” (Passow & Carlson,2012). Paleoceanographers typically use the latter
term to refer to the whole process by which POM is buried in the sediments. However, here we follow the biolog-
ical oceanographers and use “export productivity” to refer to this initial sinking out of surface waters, mainly
because this is the process that can be tracked in ancient sediments by biogenic barium concentration—see below.
As POM continues sinking through the mesopelagic zone (typically defined as 100–1,000m water depth; Passow
& Carlson,2012) it is subject to grazing by mesopelagic organisms of all sizes, which gradually break down long
chain organic carbon molecules to their constituent inorganic carbon molecules, turning POM into dissolved
organic carbon and then dissolved inorganic carbon (e.g., Boyd & Trull,2007). The amount of remineralization
in the mesopelagic zone is controlled by the rate at which the POM is sinking (i.e., how long it is exposed to
mesopelagic grazers), the composition of the grazing ecosystem, and the quality of the organic carbon (i.e., is
it labile and easy to degrade or refractory and more difficult to break down) (e.g., Buesseler & Boyd,2009;
Henson etal.,2012). POM which sinks below the mesopelagic zone is effectively removed from the short-term
carbon cycle, and so the export of organic matter below 1,000m is often referred to as “sequestration flux” (e.g.,
Passow & Carlson,2012) or “transfer efficiency” (Henson etal.,2012). By this point, most remineralization has
occurred, but POM sinking out of the mesopelagic zone has traveled through less than one third of the average
depth of the ocean, and additional remineralization occurs all the way to (and at) the seafloor, before surviving
POM is buried and removed from the carbon cycle on geologic time scales (referred to as “burial flux” by Griffith
etal.[2021]). The amount of NPP that reaches the deep sea varies by region and is largely controlled by plankton
ecology (Henson etal.,2012), but on the whole only 1%–3% of modern NPP reaches the deep ocean or sediments
(e.g., de la Rocha and Passow,2007; Griffith etal.,2021; Müller & Suess,1979).
Initial reconstructions of productivity change across the K-Pg boundary focused on carbonate proxies, specifically
carbonate mass accumulation rates and carbon stable isotopes (e.g., Hsü & Mckenzie,1985; Zachos etal.,1989).
A drop in carbonate mass accumulation rate in the deep sea has been observed at many boundary sites across the
globe, and is interpreted to represent a reduction in the production of carbonate by pelagic calcifiers like calcar-
eous nannoplankton and planktic foraminifera (e.g., D’Hondt etal.,1998), both of which suffered severe (>90%
species diversity) extinction at the K-Pg boundary (e.g., Bown,2005; Fraass etal.,2015; Lowery etal., 2020;
Thierstein, 1982). The most striking carbonate proxy response, though, is the collapse of the δ
13C gradient
between the surface ocean and the deep sea (Alegret etal.,2012; Birch etal.,2016; Coxall etal.,2006; D’Hondt
etal.,1998; Esmeray-Senlet etal.,2015; Zachos & Arthur,1986; Zachos etal.,1989). In the modern ocean (and
likely since phytoplankton first evolved) the sinking of
12C-rich organic matter depletes the surface ocean and
enriches the seafloor in that light isotope, resulting in an isotopic gradient from surface to seafloor. This gradient
collapsed at the Cretaceous-Paleogene (K-Pg) boundary (e.g., Hsü etal.,1982; Kump,1991), reflecting a reduc-
tion in export production and a weakening of the biological pump for 1.8 Myr (Birch etal.,2016,2021). Taking
into account observed changes in planktic foraminifer ecology and physiology (which account for a portion of the
change in the δ
13C gradient—Birch etal.,2016,2021), modeling suggests that a ∼50% decrease in the amount
of organic carbon exported from the euphotic zone, from 10% of NPP to 5%, would account for the observed
collapse of the δ
13C gradient (D’Hondt etal.,1998; Henehan etal.,2019).
The continued flux of some organic matter to the deep ocean is confirmed by fossil data which indicate a lack
of extinction in some groups of pelagic fishes (Doyle & Riedel,1979; Sibert & Norris, 2015) and deep sea
benthic foraminifera (e.g., Alegret & Thomas,2005, 2007, 2009; Alegret et al., 2012, 2021; Culver,2003;
Thomas, 1990). Meanwhile, geochemical data indicate a rapid recovery of primary producers (Sepúlveda
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etal., 2009,2019). One of the most striking features of the benthic foraminiferal record at the K-Pg boundary
is its global variability. Although no major extinction occurred, assemblage compositions shifted at many sites
(e.g., Alegret etal., 2012,2021; Culver,2003). At some localities, benthic foraminifer assemblages indicate a
reduction in the flux of organic matter to the seafloor, but others show no significant change across the boundary,
and some actually indicate an increase in organic matter flux (e.g., Alegret & Thomas,2005,2007,2009; Alegret
etal.,2012,2021).
In practice, it is difficult to use carbon isotope gradients to reconstruct post K-Pg export production in geographic
detail. Isotopic analysis of planktic and benthic foraminifera requires well-preserved carbonate material, other-
wise diagenetic overprinting will obscure the signal. Localities with well-preserved 66-Myr-old foraminifera
are not particularly common, and thus carbon isotope gradients have only been produced from a handful of
well-studied sites like Walvis Ridge (Alegret etal.,2012; Birch etal.,2016,2021; Coxall etal.,2006; D'Hondt
etal.,1998; Hsü & Mckenzie,1985; Hsü etal.,1982), Shatsky Rise (Coxall etal.,2006; Zachos & Arthur,1986;
Zachos etal.,1989), J-Anomaly Ridge (Zachos & Arthur,1986), and São Paulo Plateau (Zachos & Arthur,1986).
While these sites have all yielded high quality data that have fundamentally changed our understanding of K-Pg
recovery, they only cover a small part of the ocean.
For this reason, additional proxies not dependent on pristine microfossil preservation are necessary. Benthic
foraminifera, which track burial flux of POM, are one such proxy, and another is based on barium. Biogenic
barium concentration in marine sediments (where it is commonly preserved as barite—BaSO4) has been shown
to correlate with export production in the modern and ancient ocean (Dymond etal.,1992; Eagle etal., 2003;
Francois etal.,1995; Paytan & Griffith,2007) and is not subject to the same diagenetic effects as carbon isotopes.
Like so many other proxies, though, studies have shown that the relationship between the measurement (biogenic
barium) and the thing for which it is a proxy (export production) is not quite straight forward. Carter etal. (2020)
provide a good review of the processes which can affect the formation, burial, and preservation of marine barite.
Here we summarize the most important processes that impact the reconstruction of changes in export production
across the K/Pg boundary.
Although marine barite is linked to export production, Ba can also be sourced from detrital settings, and the
Ba content can vary from source area to source area (e.g., Carter etal.,2020), so elemental Ba data need to be
normalized against a terrigenous element like titanium or aluminum to control for any possible detrital barium
component (e.g., Bains etal.,2000; Dymond et al.,1992; Griffith & Paytan,2012; Paytan & Griffith,2007;
Paytan etal.,1996). Most marine barite formation occurs between 200 and 600m water depth, where most organic
matter remineralization occurs (Carter etal.,2020; Martinez-Ruiz etal.,2020), and so biogenic Ba production
tracks “export flux” or the amount of POM which sinks below the euphotic zone (see above). However, Ba
formation is probably mediated by bacteria which consume oxygen during remineralization of POM, which
means that increased bacterial production could lead to increased barite formation (e.g., Dehairs etal.,2008;
Jacquet etal.,2011; Planchon etal.,2013) without a change in export production. This microbial activity can be
influenced by organic matter quality, temperature (as warmer temperatures result in increased bacterial metabolic
rates), and the composition of the microbial ecosystem itself (Carter etal.,2020). Ba production is thus (mostly)
correlated directly to the export flux of POM, but the ocean is undersaturated in barite, which means that 70% of
particulate barite (and more in anoxic regions) dissolves in the water column and the upper few cm of the sedi-
ments before it is buried (Carter etal.,2020). This means that the replacement of one watermass with another of
a different Ba
2+ saturation state could lead to a change in barite accumulation which could be misinterpreted as a
change in export flux (e.g., Carter etal.,2020; Paytan etal.,2007).
These caveats make it difficult to directly extrapolate from Ba flux to absolute values of export flux in mass of
organic carbon per unit time, particularly all the way back in the Paleocene, but if major variables (terrigenous
flux, water mass changes) are controlled for, then marine barite can provide important insights to changes in
export flux. Hull and Norris(2011) used XRF-derived Ba/Ti and Ba/Fe ratios from five K-Pg boundary sites to
bolster the export productivity record of benthic foraminifera, and demonstrated that changes in export produc-
tion across the boundary were indeed geographically heterogeneous, with some sites showing an increase in
export production after the boundary.
Understanding geographic heterogeneity in export production is necessary to understand the overall recovery
of marine primary producers after the K-Pg boundary. In particular, the calcareous nannoplankton, which have
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the best fossil record among primary producers in the early Paleocene, exhibit geographic heterogeneity in
their post K-Pg recovery (Jiang etal.,2010; Jones et al.,2019; Schueth et al.,2015). Post-extinction calcare-
ous nannoplankton assemblages are characterized by a dominance of “disaster taxa,” chiefly Braarudosphaera
and Cervisiella, which eventually give way to a succession of acme events as new Paleocene genera appear
and briefly dominate the assemblage (Bown,2005; Gibbs etal.,2020; Jones et al.,2019). Gibbs et al.(2020)
found that some of the survivors and earliest new genera have adaptations which indicate a mixotrophic lifestyle
(i.e., they supplemented photosynthesis by ingesting small prey like bacteria); later incoming taxa lack these
adaptations, indicating changing trophic conditions (specifically the under exploitation of small prey species
following the extinction of many heterotrophic plankton) may have played a role in nannoplankton recovery
(Gibbs etal.,2020). The timing of these acme events is geographically variable, and at sites with elevated export
productivity after the K-Pg (Shatsky Rise and Chicxulub Crater), it is coincident with an observed decline in
export production (Jones etal.,2019). In the ocean today, eutrophic waters tend to be dominated by a few taxa
best suited to take advantage of widely available food, while oligotrophic waters tend to have much higher diver-
sity with greater degrees of specialization (e.g., Hallock,1987). Jones etal.(2019) hypothesized that the recov-
ery of primary producer assemblages (and by extension the ecosystems which they supported) after the K-Pg is
similarly linked to nutrient state controlled by the recovery of the biological pump, but the linkages are not well
understood and a better picture of export productivity trends is a necessary first step.
Unfortunately, geographic trends in early Paleocene export productivity are still poorly known. Modeling by
Henehan etal.(2019) indicated that typically oligotrophic gyre environments in the North and South Pacific
Oceans, the Arctic Ocean, and northern Indian Ocean, would have experienced increased export productivity in a
scenario in which global average export productivity declined 50% (in line with estimates of post-K-Pg declines
in export production; D’Hondt etal.,1998; Henehan etal.,2019). However, these modeling results are currently
unconstrained by data, and sites with observed increases in post-extinction export production (e.g., Shatsky Rise
Site 1209; Hull & Norris,2011) are close to, but fall outside of, modeled areas of increased post-extinction export
production. Hull and Norris(2011) represents a significant improvement in observations of export productivity
trends, but are limited to the ocean basin scale: for example, Shatsky Rise in the North Pacific compared to São
Paulo Plateau in the South Atlantic compared to Maud Rise in the Southern Ocean. This is a good starting place
but leaves open the question of the scale of heterogeneity. Do regions exhibit similar trends (implying an ocean-
ographic driver of variability) or do sites vary even within a region (implying that variability is driven by local
effects or is just stochastic)? To address this question, we developed three Ba/Ti datasets from the Gulf of Mexico
and Caribbean at Deep Sea Drilling Project (DSDP) Site 95 and Ocean Drilling Program (ODP) Sites 999 and
1001, which we combined with published data from International Ocean Discovery Program (IODP) Site M0077
in the Chicxulub Crater (Lowery etal., 2021) to produce the first regional-scale study (∼1,700km) of export
productivity after the K-Pg. This region was modeled to have been characterized by low export production in the
latest Cretaceous (Henehan etal.,2019) and thus may be predicted to have exhibited increased export produc-
tion after the boundary. We found that earliest Danian export productivity is elevated at all Gulf of Mexico and
Caribbean sites and that an initial reduction in export production occurs ∼300 Kyr after the boundary at all sites,
indicating that export productivity trends were homogeneous at a regional scale.
1.1. Study Sites
We looked at three scientific ocean drilling sites in the greater Caribbean region with a well-preserved K-Pg
boundary interval and compared them to published XRF data from IODP Site M0077 in the Chicxulub Crater
(Figure 1). An additional site, DSDP Site 536, below the Campeche Escarpment in the southeastern Gulf
of Mexico (Buffler et al., 1984), was considered but rejected because a preliminary examination of planktic
foraminifera in the nominally lowermost Paleocene cores found a mix of biozones ranging from the Cretaceous to
the late Paleocene, indicating significant reworking and/or drilling disturbance, suggesting that XRF data would
be untrustworthy. All four sites appear to have been at roughly bathyal water depths in the earliest Danian (Buffler
etal.,1984; Lowery etal.,2018; Sigurdsson etal.,1997; Worzel etal.,1973). These tropical/subtropical sites are
characterized by pelagic carbonate deposition throughout the study interval.
Deep Sea Drilling Project Site 95, drilled in 1970 on the northeasterly margin of the Yucatan Platform on the Campe-
che Escarpment (Worzel etal.,1973), contains the correct order of planktic foraminifer biozones and decent preserva-
tion in a mostly complete section overlying the K-Pg impact layer. The Chicxulub impact (and associated earthquakes,
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tsunami, and seiche waves) caused widespread mass-wasting across the Gulf of Mexico, resulting in K-Pg boundary
deposits 10–100s of m thick (e.g., Bralower etal.,1998; Denne etal.,2013; Sanford etal.,2016). Site 95, due to its
perched position on the edge of the Yucatan Platform, only has ∼3m of reworked Cretaceous material and impact
debris (Figure2a). The top of the K-Pg boundary layer occurs at the top of Core 13. This is not the K-Pg boundary
per se, because the base of the Paleocene is defined at its Global Stratotype Section and Point at El Kef, Tunisia, as
the lowest occurrence of impact material, which means that the Cretaceous ended at “the moment of the meteorite
impact” (Molina etal.,2006). The impact layer in the Gulf of Mexico is thus technically earliest Danian in age.
Site 1001 was drilled in 1995-6 during ODP Leg 165, and is located on the Hess Escarpment on the Nicaragua Rise
(Figure1). Shipboard biostratigraphy placed the K-Pg boundary between Core 1001A-38R-CC and 1001A-39R-1
(Figure2b). Unlike the thick K-Pg boundary deposits in the Gulf of Mexico, here the whole interval is just a few
cm thick. Maastrichtian limestone is overlain by a 1cm thick dark greenish gray clay, which is in turn overlain by
a 3.5cm bluish gray claystone containing 1mm scale dark green spheroids interpreted to be tektites (Sigurdsson
etal.,1997). This tektite layer is turn overlain by a 3.5cm medium gray to greenish gray claystone which contains
shocked quartz (Sigurdsson etal.,1997). The boundary sequence, identified on the basis of biostratigraphy and
impact debris, is overlain by a 4cm thick light gray limestone assigned to planktic foraminifer Biozones P0/Pα
undifferentiated, based on thin section analysis (the zones are undifferentiated because the biostratigraphers were
not confident in their ability to identify the taxon differentiating the zones, Parvularugoglobigerina eugubina,
in thin section; Sigurdsson etal.,1997). Shipboard biostratigraphy in the Paleocene is of poor quality due to the
extremely poor preservation of fossil material in the indurated limestone. A magnetic polarity timescale was
published for Site 1001 by Louvel and Galbrun(2000) based on whole core scans and single samples, as well
as a downhole wireline tool called the Geological High-sensitivity Magnetic Tool, and the resulting magnetic
reversal timescale means that Site 1001 has the best age model of the sites examined here. Although Hole 1001B
recovered a more complete boundary section than Hole 1001A (Figure2b), Hole 1001B has a number of coring
gaps in both the uppermost Cretaceous and the early Paleocene, so XRF scans were conducted on Hole 1001A.
Site 999 was also drilled in 1995-6 during Leg 165 and is located on Kogi Rise in the Colombian Basin (Figure1).
Shipboard biostratigraphy placed the K-Pg boundary near the boundary between Cores 999B-59R and 999B-60R
(Figure2c). The highest occurrence of common Maastrichtian calcareous nannoplankton was observed in Sample
999B-60R-1 10cm, and that of Maastrichtian planktic foraminifera in a thin section in Sample 999B-60R-1
1–21cm (Sigurdsson etal.,1997). The few foraminifera observed in thin section between Samples 999B-59R-CC
15cm (the base of the core catcher) and 999B-60R-1 1cm were composed primarily of survivor species Guem-
belitria cretacea (Sigurdsson etal.,1997). The shipboard biostratigraphers were not confident that tiny trochos-
piral specimens observed in the same sample were or were not P. eugubina and thus conservatively assigned
this interval to Zones P0/Pα undifferentiated (Sigurdsson etal.,1997). The bases of Zones P1a (top of P.eugu-
bina), P1b (base of Subbotina triloculinoides), and P2 (base of Praemurica uncinata) were identified shipboard
(Sigurdsson etal., 1997) and form the basis for the age model used here, although the latter two are of lower
Figure 1. (a) Global plate tectonic reconstruction from 66Ma showing location of our study area (in red) and other notable sites discussed in this paper (in orange).
Gray areas are continental blocks, terranes, and plateaus; map from ODSN generated at https://www.odsn.de/odsn/services/paleomap/paleomap.html. (b) Regional map
showing position of our study sites around the time of the K-Pg Boundary. Map modified after Pindell and Barrett(1990) and Snedden etal.(2021). Black indicates
land and gray indicates continental platforms.
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confidence. We washed and examined samples from Site 999 to see if we could refine the shipboard age model
but poor microfossil preservation in the indurated limestone material prevented us from adding anything new.
A white indurated limestone overlies the highest Cretaceous nannoplankton observed in Core 60, and the base
of Section 59R-CC contains a 1mm thick claystone. Comparison of the recovered core and borehole images
collected by the formation microscanner tool reveals that this claystone is ∼9cm thick in the borehole, and thus
∼8cm of this unit were not recovered (Sigurdsson etal.,1997). It seems reasonable to assume that this missing
interval is equivalent to the 8cm of ejecta-bearing claystones described at Site 1001. The claystone is overlain
by 10cm thick mottled blue limestone described by shipboard scientists as having the appearance of “Roquefort
Blue Cheese” and assigned to planktic foraminifer Zones P0/Pα (Sigurdsson etal.,1997). This white limestone is
a common feature of K-Pg boundary sections in the deep sea, and is comprised of micrite (i.e., microcrystalline
calcite; Bralower etal.,2020). Although the white limestone only extends 10cm above the boundary, Bralower
etal.(2020) observed micrite at Site 999 over a total thickness of 2.42m. A 2m coring gap occurs at the base
of Core 999B-58R in planktic foraminifer Zone P1a. Micrite was also identified at Site 1001 but it was limited
to the core catcher of core 1001A-38R, which contains a few discontinuous bits of rubble and a large void space
(Figure2b), so Bralower etal.(2020) considered the observed 17cm interval to be a minimum.
2. Methods
We scanned the cores at the XRF Core Scanning Lab at the IODP GCR at Texas A&M University in College
Station, TX. The archive halves of selected cores were scraped to ensure a fresh face of the core for scanning, and,
Figure 2. Stratigraphic sections showing lithostratigraphy, core scan photographs, and images of the K-Pg boundary of the studied intervals from DSDP Hole 95, ODP
Hole 1001A, and ODP Hole 999B. Lithostratigraphy follows shipboard descriptions Worzel etal.(1973) for Site 95 and Sigurdsson etal.(1997) for Sites 999 and 1001.
Core scan photographs were collected at the Gulf Coast Repository at the same time XRF data were collected (except for the photograph of the K-Pg boundary in Hole
1001B, which is from the ODP photo archives). Mbsf, meters below sea floor; PFZ, Planktic Foraminifer Zone; Lith., lithology; PMag, Paleomagnetic polarity; E.
Campanian, Early Campanian; Maas., Maastrichtian; G. elevata, Globotruncanita elevata; A.m. and A. mayaroensis, Abathomphalus mayaroensis.
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in the case of the softer sediments of Site 95, to ensure a flat surface for the XRF core scanner (the split surface
was generally smooth in the unlithified cores from Site 95 but decades in shrink wrap added a bit of texture in
some places). Lithified sections from Sites 999 and 1001 were likewise scraped and leveled within the core liner
to ensure a flat horizontal surface. Cores were then covered with 4μm thick Ultralene film to prevent sediment
from sticking to the scanner.
Cores were scanned on an Avaatech XRF Core Scanner at two excitation conditions focused on different element
groups. The first scan was at 10kVp with no filter to analyze major and minor elements (Al, Si, K, Ca, Ti, Mn,
Fe, Cr, P, S, and Mg) and the second was at 50kVp with a Cu filter to analyze heavier trace elements (Sr, Rb, Zr,
and Ba). Scan resolution was set depending on relative distance above the K-Pg boundary, based on low resolu-
tion shipboard biostratigraphy. Core sections within Zone Pα or the lower part of Zone P1a (very roughly, within
∼500 Kyr after the boundary) were scanned at 1 or 2cm steps, and sections below the boundary and >500 Kyr
after the boundary were scanned at 5cm steps. Some steps were skipped or moved based on visual examination
of the core before scanning (e.g., to avoid cracks or uneven surfaces). Laboratory standards were run at the begin-
ning and end of each day to monitor instrumental performance.
Raw spectral data were processed into peak areas in the lab and exported as count data using the software program
bAxil. Quality control of processed data was carried out using the following parameters: (a) throughput (samples
with values <150,000 cps, which indicates a gap between the sensor and the core, were removed); (b) Argon peak
(samples with positive Ar values, indicating that the sensor was measuring ambient air, were removed); and (c)
standard deviation (samples with elemental peaks of Ba or Ti within 2 standard deviations of zero were removed).
To improve the age model for this study we analyzed planktic foraminifera from Site 95 at a resolution of up to
5cm. Lightly lithified samples were gently broken into cm-sized pieces using a mortar and pestle. All samples
were soaked in a solution of hydrogen peroxide and borax for at least 48hr and then washed over a 45μm sieve to
ensure capture of typically very small early Paleocene taxa; the sieve was soaked in methylene blue dye between
samples to mark contaminants. Finally, samples were dried overnight in an oven. Samples were examined for
presence/absence of key marker species on a Zeiss Discovery.V8 light microscope. Species concepts follow
those of Olsson etal.(1999); biozones are the Wade etal.(2011) update of the Paleocene biozonation scheme
published by Berggren and Pearson(2005) and calibrated to the timescale of Gradstein etal.(2012).
3. Results
3.1. Biostratigraphy
Sediment at Site 95 is comprised of firm but unlithified calcareous ooze that yielded fairly well preserved material.
We examined 25 samples from Cores 11 to 13 to identify and refine the boundaries between planktic foraminifer
biozones. An obvious lithologic change occurs in Section 95-13R-3 at 24cm (397.92 mbsf). Samples below this
level are composed of mixed Cretaceous species remobilized by impact-induced seismic disturbance and tsunami,
termed the K-Pg Boundary Cocktail (Bralower etal.,1998). From Sample 95-13R-2, 139cm to Sample 95-13R-3,
24cm (397.76–397.92 mbsf), the core is mottled and contains some signs of drilling disturbance (biscuiting, soft
sediment deformation). Samples taken within what we interpret to be the biscuits, however, contain mostly Creta-
ceous species until 95-13R-3, 0–2cm (397.70 mbsf), where the survivor species Guembelitria cretacea starts to
become more common; this level is assigned to the base of Zone P0. The lowest occurrence of P.eugubina, which
defines the base of Zone Pα, is found just above this level, in Sample 95-13R-2 130–132cm (397.5 mbsf). The
highest occurrence of P.eugubina, which marks the base of Zone P1a, occurs in sample 95-13R-1 130cm (396.60
mbsf). Most of Zone P1a falls within a coring gap, but Zone Pα and the portion of Zone P1a preserved here
contain abundant calcispheres, the resting cyst of calcareous dinoflagellates. Above the coring gap between Cores
95-12R and 13R, the bases of Zone P1b (lowest occurrence of S. triloculinoides) and Zone P1c (lowest occur-
rence of Globanomalina compressa) are both present. The base of Zone P2 (P. uncinata) is missing in another
coring gap between Cores 11R and 12R, and the age model from the base of Zone P1c to the coring gap is based
on extrapolating the sedimentation rate from Zone P1b; this method suggests that most of Zone P1c is present.
3.2. Ba/Ti
A key underlying assumption in the use of XRF scan data to reconstruct changes in biogenic Ba is that there is
no change in the Ba/Ti value of terrigenous material delivered to the site. The extensive volcanism documented
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in the Caribbean region throughout the early Cenozoic (Sigurdsson etal.,1997) could be a source of discrete or
diffuse tephra deposition to the study sites which may vary through time and alter that ratio. Thus, we have plotted
Ba from Site 999 and 1001 against Rb and Zr, which are enriched in volcanogenic minerals of the regional type of
volcanism. Both Zr and Rb show weak positive correlation with Ba at Site 999 (Figures3a and3b) and a slightly
less-weak positive correlation with Ba at Site 1001 (Figures3c and3d). This is to be expected, as any volcanic ash
would have introduced more detrital Ba in the record. However, when we normalize Ba against Ti and compare
this to Rb and Zr at both sites, the positive correlation goes away (Figures3e–3h). To demonstrate how overall
changes in lithology affect Ba counts, we plotted Ba against Ca (any decrease in Ca in a pelagic setting above
the lysocline is likely due to dilution by terrigenous material). At both sites, there is a weak negative correlation
between Ca and Ba (Figures3i and3j). This is what we'd expect, as dilution of pelagic Ca by terrigenous material
would introduce detrital Ba; this is why we normalize Ba to a terrigenous element like Ti. Overall, the relation-
ship between Ca and Ba is not very strong, likely because overall terrigenous content in these pelagic carbonates
is very low. We conclude that the Ba/Ti values at these sites do not reflect changes in terrigenous flux from either
volcanism or other sources, and are thus primarily driven by changes in export productivity (Figure4).
3.2.1. Site M0077
Data from the Chicxulub Crater have been published (Lowery etal.,2018,2021) but contain several interesting
trends that should be summarized here. The highest Ba/Ti values in the study interval are found in the lowermost
Paleocene, representing the first ∼320 Kyr after the impact (Figure4). At that point, there is a sharp drop in Ba/Ti
values, followed by a steady decline from moderate values to a minimum about 1.2 Myr after the K-Pg boundary,
at which point values stabilize and remain low with some small-scale variability. Interestingly, this transition
Figure 3. Crossplots of Rb, Zr, and Ca with Ba and Ba/Ti from Sites 999 and 1001. R
2 values showing correlation (or lack thereof) for each parameter are included on
the plots.
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around 1.2 Myr post-impact coincides with turnover in the calcareous nannoplankton ecosystem, as disaster taxa
began to give way to acmes of new Paleocene taxa (Jones etal.,2019; Lowery etal.,2021).
3.2.2. Site 95
Ba/Ti values at Site 95 are also highest in the lowermost Paleocene, with a peak around the Pα/P1a zonal bound-
ary and a sharp drop off ∼340 Kyr after the impact (Figure4). A difference of 20 Kyr between two sites whose
age models are entirely based on biostratigraphy is basically within error and we feel comfortable assuming that
this drop was contemporaneous with the one observed at Chicxulub Crater Site M0077. Approximately 300 Kyr
of the record in the middle of Zone P1a is erased by a coring gap, but above this level Ba/Ti values trend lower
until about 1.1 Myr after the K-Pg boundary. Values then remain low until about 1.6 Myr post-impact and finally
increase somewhat, varying through the rest of the record.
3.2.3. Site 1001
Site 1001 is the first of our sites in which there are data for the uppermost Cretaceous, and (above a gap where
the boundary layer is mostly missing) Ba/Ti values increase in the Danian relative to the Maastrichtian (Figure4).
Although there is no obvious large peak like in the two Gulf of Mexico sites, there is an interval of overall higher
values lasting to ∼280 Kyr after the impact. Above this level, values are much more variable than in the Gulf of
Mexico but there is still a clear downward trend to a nadir around 1.4 Myr after the K-Pg boundary, above which
point values increase slightly and vary a little bit for the rest of the record.
3.2.4. Site 999
Site 999 is the southernmost site, and the most distal from the Chicxulub impact crater. Ba/Ti values are very
low directly above the boundary layer, quickly increasing through the lower part of Zone Pα (Figure4). Higher
values after this brief recovery interval do not exceed the Ba/Ti values observed in the uppermost Cretaceous,
but they are much higher than subsequent Paleocene values (with the exception of a brief peak around 2 Myr
Figure 4. Barium-Titanium export productivity proxy data for IODP Site M0077, DSDP Site 95, and ODP Sites 1001 and 999. Individual datapoints are gray circles,
thick black lines is a 5-point moving average. Red line indicates the K-Pg boundary (or the top of the boundary interval in the case of Sites M0077 and 95), blue line
indicates the thickness of the micrite layer identified at each site by Bralower etal.(2020), and the green dashed line indicates the top of the interval of highest export
productivity at each site. PFZ: Planktic Foraminifer Zone (after Wade etal.,2011); A. maya.: Abathomphalus mayaroensis.
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after the K-Pg boundary). Once again, values decreased sharply approximately 320 Kyr post-impact followed by
gradually declining values. The very poor quality of the biostratigraphy in this core (the Pα/P1a zonal boundary
marker is the only reliable datum) makes it difficult to determine the timing of this decline and whether the
increase observed below the coring gap occurred just 600 Kyr after the boundary or much later. While we do not
place much confidence in the ages above this level, we are confident in age control in the key interval above the
boundary, specifically the highest occurrence of P.eugubina (Pα/P1a zonal boundary).
4. Discussion
4.1. Regional Homogeneity of Post K-Pg Export Production
The most striking feature of the four export productivity records presented here, and the key result of this inves-
tigation, is the consistent occurrence of relatively elevated Ba/Ti values in the earliest Paleocene. Interestingly,
this is in line with trends from other sites in oligotrophic regions like the North Pacific Gyre. Three other open
ocean sites have evidence of increased export productivity in the earliest Danian: the North Pacific Shatsky Rise
and Hess Rise (Alegret & Thomas,2005,2009; Hull & Norris,2011), and the mid-latitude South Pacific sections
around Marlborough, South Island, New Zealand (Hollis etal., 1995, 2003). The high export productivity at
Marlborough appears to be the result of increased upwelling along the continental margin (Hollis etal.,2003).
Shatsky Rise and Hess Rise, though, are open ocean sites on roughly the same paleolatitude as our study area
and were generally oligotrophic during this time interval (e.g., Deprez etal.,2017; Henehan etal.,2019). It is
tempting to interpret the Ba/Ti data as elevated export production in the earliest Paleocene at all of these sites, in
contrast with the overall global trend of reduced export production. But first we need to rule out other possible
explanations.
As discussed above, there is no evidence that changes in terrigenous Ba/Ti values influence the record at our
Caribbean sites, and this could not explain how the same trend could be extended to the Gulf of Mexico and North
Pacific sites. Likewise, we do not think transient (100-Kyr-scale) changes in intermediate or deep water masses
affecting barite dissolution rates make sense across such widely dispersed sites. The most likely explanations
must be related to the oligotrophic gyres themselves, either oceanographic changes in the gyres or, more likely,
ecological changes in the populations of phytoplankton and/or grazers in these gyres.
There are several possible mechanisms which could drive an increase in marine barite production while export
production is kept steady. Different groups of plankton incorporate different amounts of Ba into their biomass. For
example, coccolithophores have less Ba in their cells than diatoms, which in turn have less Ba in their cells than
chrysophytes (gold algae), which have less Ba than chlorophytes (green algae) (e.g., Paytan & Griffith,2007).
Calcareous nannoplankton suffered a severe extinction at the K-Pg, and if they were briefly replaced in olig-
otrophic gyres by any of these other groups, the biogenic Ba flux to the seafloor would increase even if export
production held steady. Alternatively (or additionally), an increase in temperature or a shift in bacterial ecology
at mesopelagic depths could have increased bacterial remineralization and thus barite production. A reduction in
the abundance of grazers which break apart sinking POM or an increase in ballasting or the formation of aggre-
gates (which have the effect of making POM sink more quickly) may have increased the amount of POM which
sank below the mesopelagic zone and to the seafloor. However, such a change wouldn't necessarily be expressed
by increased biogenic barium, since marine barite formation is a byproduct of the remineralization of organic
matter (Dehairs etal.,2008; Jacquet etal.,2011; Planchon etal.,2013) and quickly sinking POM has less time to
remineralize. On the other hand, a more robust grazer community at mesopelagic depths may have broken apart
more POM, slowed sinking and increased the time it was exposed to remineralization. Many of these change
(mesopelagic temperature increase, shifts in the grazer community or toward phytoplankton with higher Ba
abundance in their cells) are impossible to test with existing paleoceanographic tools. What we can do, though,
is look to other parts of the biological pump and see if they indicate whether the observed increase in Ba/Ti was
indeed related to export productivity.
Benthic foraminiferal accumulation rate and assemblages provide additional export productivity information at
these sites. Benthic foraminifera, which are responsive to the amount and quality of organic matter that reaches
the seafloor, record a different part of the biological pump than biogenic barium, which is formed during the
remineralization of organic matter at mesopelagic depths. Indeed, these two proxies can sometimes show oppo-
site trends (e.g., Griffith etal.,2021), which can help us determine if our observations are the result of increased
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export production or some other process. At Site M0077 in the Chicxulub Crater, elevated Ba/Ti values are asso-
ciated with an interval of higher benthic foraminiferal abundance, indicating increased export production was
associated with increased food supply to the seafloor (Lowery etal.,2021). We don't have benthic foraminifera
data from Site 95 because it is difficult to tell reworked benthics from in situ ones, and we don't have benthic
foraminifera from Sites 999 and 1001 because of overall poor preservation of microfossils. On Shatsky Rise in
the North Pacific gyre benthic foraminifera from Site 1210 (from Alegret & Thomas,2009) and barium proxy
data from the adjacent Site 577 (from Hull & Norris,2011) are elevated for roughly the first 100 Kyr after the
extinction. On Hess Rise, also in the North Pacific gyre, no barium data exist but benthic foraminifera at Site
465 indicate a peak in post K-Pg burial flux within 100 Kyr of the boundary (within planktic foraminifer Zone
Pα) (Alegret & Thomas,2005). At the three sites with both Ba and benthic foraminifer data, they both indi-
cate increased transport of POM out of the euphotic zone and to the seafloor; we therefore interpret the Ba/Ti
data at all our sites as primarily recording an increase in export productivity.
In the Gulf of Mexico and Caribbean, the interval of highest export production ends right around the Pα/P1a
zonal boundary at each site, roughly 300 Kyr after the K-Pg boundary, followed by a general decline over the next
million years or so. The precise features vary from site to site; notably, the prominent early peak observed in the
Gulf of Mexico (Sites M0077 and 95) is absent in the Caribbean cores (Sites 999 and 1001). Likewise, Site 999
records very low values immediately above the K-Pg boundary followed by a rapid recovery that is not evident at
any of the other sites. Finally, the timing of the sharp decline of these high productivity intervals varies by a few
tens of kyrs between sites. Because the age models are based on biostratigraphy or paleomagnetic reversals, with
no higher resolution techniques like orbital chronology, it is impossible to say whether these differences are real
or merely artifacts of the limits of the age models. These are superficial differences, though, and a clear overall
trend exists that export productivity was elevated across Gulf of Mexico and Caribbean (a distance of ∼1,700km)
for ∼300 Kyr after the K-Pg mass extinction, and began to decline thereafter.
The observed homogeneity in regional export productivity in the earliest Paleocene provides important context
for previous observations of global-scale heterogeneity determined with the Ba proxy. Previous work had shown
major differences in the amount of organic matter remineralized in the mesopelagic zone between ocean basins,
with an increase in export production in the middle of the North Pacific, a decline in the western North Atlantic,
western South Atlantic, and Southern Ocean, and no change in the eastern South Atlantic (Hull & Norris,2011).
Those sites are widely separated and represent different oceanographic environments (oligotrophic gyres, west-
ern boundary currents, eastern boundary currents). With only one site in each region, it is hard to know whether
these observations are indicative of regional trends or more limited, local change. With the discovery that open
ocean sites within the Gulf of Mexico/Caribbean all exhibit the same trends (and, interestingly, the local change
in benthic foraminiferal diversity in nearshore environments Gulf of Mexico is also lower than many other sites;
Alegret etal.,2022), we can be more confident that previously observed regional differences are real, and there-
fore conclude that oligotrophic open ocean sites were prone to increased export production immediately after
the K-Pg boundary, as suggested by Henehan etal. (2019). But what was the driver for this increased export
production?
4.2. Drivers of Post-Extinction Export Productivity
In the modern ocean, oligotrophic gyres are typically dominated (in terms of biomass) by picophytoplankton
(0.2–2.0 μm in size) like cyanobacteria and algae, but larger nano and micro phytoplankton (2–20μm and
>20μm, respectively), though less numerous, account for the majority of productivity measured in incubation
experiments (e.g., Marañón etal.,2003). Because picophytoplankton have no physical fossil record, we cannot
say for sure whether this was the case at the end of the Cretaceous, but this seems like a safe assumption.
A switch from calcareous nannoplankton, the dominant phytoplankton of the Cretaceous (Bown, 2005) to
smaller phytoplankton like cyanobacteria and chlorophyte algae would serve to reduce export flux globally and
retain more nutrients in the euphotic zone, because smaller cell sizes sink more slowly and are less likely to
be consumed by zooplankton and packaged in fecal pellets, or bunch together in aggregates (de la Rocha and
Passow,2007; Legendre & Michaud,1998, although it should be noted that some modeling studies dispute the
role of plankton size on export magnitude, e.g., Fakhraee etal.,2020). Henehan etal.(2019) pointed out that in
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oligotrophic regions, this post-extinction increase in nutrients could actually lead to an increase in primary and/
or export productivity.
But how would NPP dominated by picophytoplankton lead to increased export production? After all, if export
increased then there would be a mechanism to remove nutrients from the euphotic zone and NPP would
necessarily decrease. Yet our work and that of others has found that high export production was maintained in
typically oligotrophic regions for 100–300 Kyr (Alegret & Thomas,2005,2009; Alegret etal.,2012,2022; Hull
& Norris,2011). To explain this dichotomy, we suggest that POM exported from the euphotic zone became more
refractory. The continuous remineralization of very small POM in the euphotic zone is termed the “microbial
loop,” and the only POM that manages to sink out of the euphotic zone is more refractory and difficult to metab-
olize (de la Rocha & Passow, 2007; Legendre & Michaud,1998). This refractory organic matter is less likely
to be completely remineralized by grazers as it sinks through intermediate depths, which would result in less
marine barite formation and lower Ba contents. However, if NPP increased after the K-Pg boundary at these sites
as a result of the loss of larger phytoplankton, then the export of refractory POM may have increased, as would
the amount of barite formation from that POM. Thus, even if only a small fraction of the refractory POM was
remineralized, the overall increase in POM sinking below the euphotic zone would have elevated total reminer-
alization and barite production. This also would explain why food supply increased to the seafloor, as evidenced
by increases in benthic foraminifera.
An alternate explanation could be the occurrence of blooms of specific groups of phytoplankton with barium-rich
cells or which favor barite formation. For example, in the modern ocean Phaetocystis is a common haptophyte
which secretes extracellular polymers which form aggregates that speed sinking and enhance export production
(e.g., Verity etal., 2007). These polymers may also play a key role in marine barite formation as nucleation
sites (Martinez-Ruiz etal., 2020). Acantharians have barium-rich skeletons and are known to form blooms in
oligotrophic regions (e.g., Decelle etal.,2012) but, like the other groups, do not typically fossilize. Blooms of
plankton like these may serve to increase export to the seafloor and also increase marine barite production with-
out necessarily relying on a stronger microbial loop in the euphotic zone. While we currently lack direct evidence
of blooms of non-fossilizing phytoplankton like these groups, more work is required to provide a clear answer to
this question. But we can see some evidence for ecosystem changes associated with increased export productivity
after the K-Pg.
4.3. Evidence of Ecosystem Changes
The second-most striking feature of our data is that at two of the sites studied (Sites 95 and 999) the interval
of high export productivity ∼300 Kyr after the boundary coincides almost exactly with well-defined intervals
of microcrystalline calcite (“micrite”). The widespread deposition of micrite in marine settings after the K-Pg
boundary was documented by Bralower etal.(2020), and proposed to have been primarily formed by micro-
bial blooms. The structure of individual micrite crystals is similar to that produced by various cyanobacteria
(Bralower etal., 2020) and the micrite layer itself at several sites is associated with elevated biomarkers for
photosynthetic bacteria and eukaryotic algae (Bralower etal.,2020; Schaefer etal.,2020; Sepúlveda etal.,2009).
Some portion of the global micrite layer was also likely formed by the backreaction of CaO or CaOH vaporized
by the Chicxulub impact, but this process would have been limited to the years after the impact as ejecta fell out
of the atmosphere (Bralower etal.,2020) and wouldn't explain micrite deposition over ∼300 Kyr.
Extensive recrystallization of carbonate material at Site M0077 obscures the micrite record at that location. At
Site M0077, abundant micrite is limited to a zone of good preservation which includes the “Transitional Unit”
at the top of the K-Pg boundary layer (Morgan etal.,2017) and an overlying layer of green marlstone dated to
the base of planktic foraminifer Zone Pα (Bralower etal.,2020). Above this, in the overlying white limestone
layer, poor preservation prevents the consistent identification of micrite, and so the top of the micrite layer is not
identified. At Site 1001, coring gaps in the boundary interval in Hole 1001B limit the identification of the micrite
layer to a minimum thickness (17cm, Bralower etal.,2020). Thus, we have two sites showing a clear deposition
of micrite ending at the same stratigraphic position (Sites 95 and 999), and two other sites with insufficient data
to determine the relative timing (Sites M0077 and 1001).
None of the published Pacific sites which show an increase in post-K-Pg export production have both Ba/Ti
data and micrite data (although we can compare nearby sites 1210 and 577—see below). Micrite is enriched
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at Shatsky Rise Site 1209 over a 6cm interval above the boundary, and at 1210 over a 7cm interval above the
boundary (Bralower etal.,2020), associated with the ∼100 Kyr peak in benthic foraminifer proxies for burial flux
(Alegret & Thomas,2009) and the ∼100 Kyr interval of elevated Ba/Ti at nearby Site 577 (Hull & Norris,2011).
At Hess Rise Site 465, micrite is enriched over a 24cm interval above the boundary (Bralower etal.,2020), and
benthic foraminifera likewise show a peak in burial flux in this interval (Alegret & Thomas,2005). It is important
to point out that foraminifer samples at both Sites 465 and 1210 were taken at a 10cm resolution (Alegret &
Thomas,2005,2009) so a precise tie between the decline in export productivity and the end of micrite deposition
is impossible to make.
Although various types of “ballast,” including calcite plankton shells, have been thought to influence export
production in the modern ocean (Armstrong etal.,2001; Francois etal.,2002), it does not seem likely that micrite
itself, or more specifically the cyanobacteria that produced it, is the cause of increased export production in the
earliest Paleocene. Micrite is abundant at many sites which did not experience elevated export production after
the K-Pg. For example, Blake Nose Site 1049, which experienced either a decline or no change in export produc-
tion after the boundary (Alegret & Thomas,2004), has a 30cm thick micrite layer. Walvis Ridge Site 1262, which
similarly experienced no change in post-extinction export production based on benthic foraminifera (Alegret &
Thomas,2007), has a 1.82m thick micrite layer. All told, Bralower etal.(2020) identified micrite layers at 31
sites globally; of these, only five record elevated export production in the early Danian based on available proxies.
All of these sites are in open ocean settings which are predisposed to oligotrophy.
The general association of the micrite layer (indicating dominance of microbial primary producers) with the
elevated post-impact export production across Pacific and Caribbean/Gulf of Mexico sites suggests that a
post-extinction dominance of picophytoplankton is the primary mechanism driving elevated export productivity
at previously oligotrophic parts of the open ocean in the earliest Paleocene.
The dominance of picophytoplankton may have been the proximal cause of elevated post K-Pg export production
in tropical open ocean waters, but it is important to note that the timing was different between the Caribbean
and the central Pacific. The period of highest export production dropped off ∼300 Kyr after the K-Pg in the
Gulf of Mexico and Caribbean but much earlier at Shatsky and Hess Rises, that is, after ∼100 Kyr (Alegret &
Thomas,2005,2009; Hull & Norris,2011). This is in line with previous results which indicate a global diachrone-
ity in the turnover of calcareous nannoplankton assemblages in the earliest Paleocene (Jones etal.,2019), driven
by transition from surface waters characterized by efficient recycling of nutrients due to the prevalence of pico-
phytoplankton feeding the microbial loop, to surface waters characterized by less efficient recycling of nutrients
caused by greater export of larger plankton out of the euphotic zone (Jones etal.,2019; Lowery etal., 2021).
At Shatsky Rise, disaster assemblages of calcareous nannoplankton gave way to acmes of Paleocene taxa soon
after the K-Pg (Alvarez etal.,2019; Jones etal.,2019). On the other hand, disaster taxa in the Chicxulub Crater
continued until the final decline in export productivity about a million years after the K-Pg (Jones etal.,2019),
and at Site 999, disaster taxa continued at least into Zone P1a >300 Kyr after the K-Pg (Sigurdsson etal.,1997).
Whether the recovery in calcareous nannoplankton caused the observed change in export production or if a reduc-
tion in export production spurred the local diversification of calcareous nannoplankton remains an open question.
5. Conclusions
Our XRF-derived Ba/Ti export productivity proxy data from the Gulf of Mexico and Caribbean show a post
K-Pg peak in export productivity across the region, with an interval of high values lasting for ∼300 Kyr after the
boundary, then declining values for another ∼700 Kyr. This is a major improvement on previous compilations
of earliest Paleocene export productivity, which showed that post-extinction changes in export production were
globally heterogeneous on an ocean basin scale. Our results show that broad regions followed similar trends. In
particular, we find that most elevated export production in the earliest Danian occurred tropical open ocean sites
(Shatsky Rise, Hess Rise, and our Caribbean/Gulf of Mexico sites) which were oligotrophic at the end of the
Cretaceous (Henehan etal.,2019).
At sites with elevated export production and at which preservation makes such observations possible, the post
K-Pg global micrite layer corresponds to the interval of elevated export production. We interpret this as evidence
that the dominance of picophytoplankton like cyanobacteria and chlorophyte algae, which appear to have been
responsible for the micrite deposition (Bralower etal., 2020), altered the dynamics of the biological pump to
increase recycling of organic matter in the euphotic zone. Enhanced recycling of organic matter left only refrac-
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tory material, which is more difficult to recycle, to be exported from the euphotic zone. Because it is refractory,
this organic matter would have been more likely to sink through the water column than more labile material
exported under normal conditions. In typically oligotrophic environments, this slight increase in efficiency of
the biologic pump could have resulted in overall higher export production; as larger phytoplankton recovered and
more labile organic matter was exported and grazed, enhanced export production would have subsided.
More datasets from a wider range of latitudes and ocean basins are needed to build a more complete picture of
post K-Pg export production to more fully understand how the marine biosphere recovered from the most recent
major mass extinction.
Data Availability Statement
XRF core scan data and age models are archived at the NCEI Paleoclimate Database (Lowery,2021).
References
Alegret, L., Arreguin-Rodriguez, G., & Thomas, E. (2022). Oceanic productivity after the Cretaceous/Paleogene impact: Where do we stand?
The view from the deep. In C. Koeberl, P. Claeys, & A. Montanari (Eds.), From the Guajira Desert to the Apennines, and from Mediterranean
Microplates to the Mexican Killer Asteroid: Honoring the Career of Walter Alvarez, Geological Society of America Special Paper (Vol. 557).
https://doi.org/10.1130/2022.2557(21)
Alegret, L., Arreguín-Rodríguez, G. J., Trasviña-Moreno, C. A., & Thomas, E. (2021). Turnover and stability in the deep sea: Benthic foraminif-
era as tracers of Paleogene global change. Global and Planetary Change, 196, 103372. https://doi.org/10.1016/j.gloplacha.2020.103372
Alegret, L., & Thomas, E. (2004). Benthic foraminifera and environmental turnover across the Cretaceous/Paleogene boundary at Blake Nose
(ODP Hole 1049C, Northwestern Atlantic). Palaeogeography, Palaeoclimatology, Palaeoecology, 208(1–2), 59–83. https://doi.org/10.1016/j.
palaeo.2004.02.028
Alegret, L., & Thomas, E. (2005). Cretaceous/Paleogene boundary bathyal paleo-environments in the central North Pacific (DSDP Site 465), the
Northwestern Atlantic (ODP Site 1049), the Gulf of Mexico and the Tethys: The benthic foraminiferal record. Palaeogeography, Palaeoclima-
tology, Palaeoecology, 224(1–3), 53–82. https://doi.org/10.1016/j.palaeo.2005.03.031
Alegret, L., & Thomas, E. (2007). Deep-sea environments across the Cretaceous/Paleogene boundary in the eastern South Atlantic Ocean (ODP
leg 208, Walvis Ridge). Marine Micropaleontology, 64(1–2), 1–17. https://doi.org/10.1016/j.marmicro.2006.12.003
Alegret, L., & Thomas, E. (2009). Food supply to the seafloor in the Pacific Ocean after the Cretaceous/Paleogene boundary event. Marine
Micropaleontology, 73(1–2), 105–116. https://doi.org/10.1016/j.marmicro.2009.07.005
Alegret, L., Thomas, E., & Lohmann, K. C. (2012). End-Cretaceous marine mass extinction not caused by productivity collapse. Proceedings of
the National Academy of Sciences, 109(3), 728–732. https://doi.org/10.1073/pnas.1110601109
Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V. (1980). Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, 208(4448),
1095–1108. https://doi.org/10.1126/science.208.4448.1095
Alvarez, S. A., Gibbs, S. J., Bown, P. R., Kim, H., Sheward, R. M., & Ridgwell, A. (2019). Diversity decoupled from ecosystem function and
resilience during mass extinction recovery. Nature, 574(7777), 242–245. https://doi.org/10.1038/s41586-019-1590-8
Armstrong, R. A., Lee, C., Hedges, J. I., Honjo, S., & Wakeham, S. G. (2001). A new, mechanistic model for organic carbon fluxes in the ocean
based on the quantitative association of POC with ballast minerals. Deep Sea Research Part II: Topical Studies in Oceanography, 49(1–3),
219–236. https://doi.org/10.1016/s0967-0645(01)00101-1
Artemieva, N., & Morgan, J. (2020). Global K-Pg layer deposited from a dust cloud. Geophysical Research Letters, 47(6), e2019GL086562.
https://doi.org/10.1029/2019gl086562
Artemieva, N., Morgan, J., & Expedition 364 Science Party. (2017). Quantifying the release of climate-active gases by large meteorite impacts
with a case study of Chicxulub. Geophysical Research Letters, 44(20), 10–180. https://doi.org/10.1002/2017gl074879
Bains, S., Norris, R. D., Corfield, R. M., & Faul, K. L. (2000). Termination of global warmth at the Palaeocene/Eocene boundary through produc-
tivity feedback. Nature, 407(6801), 171–174. https://doi.org/10.1038/35025035
Bardeen, C. G., Garcia, R. R., Toon, O. B., & Conley, A. J. (2017). On transient climate change at the Cretaceous−Paleogene boundary
due to atmospheric soot injections. Proceedings of the National Academy of Sciences, 114(36), E7415–E7424. https://doi.org/10.1073/
pnas.1708980114
Barton, A. D., Irwin, A. J., Finkel, Z. V., & Stock, C. A. (2016). Anthropogenic climate change drives shift and shuffle in North Atlantic phyto-
plankton communities. Proceedings of the National Academy of Sciences, 113(11), 2964–2969. https://doi.org/10.1073/pnas.1519080113
Berggren, W. A., & Pearson, P.N. (2005). A revised tropical to subtropical Paleogene planktonic foraminiferal zonation. Journal of Foraminiferal
Research, 35(4), 279–298. https://doi.org/10.2113/35.4.279
Birch, H., Schmidt, D. N., Coxall, H. K., Kroon, D., & Ridgwell, A. (2021). Ecosystem function after the K/Pg extinction: Decoupling of marine
carbon pump and diversity. Proceedings of the Royal Society B, 288(1953), 20210863. https://doi.org/10.1098/rspb.2021.0863
Birch, H. S., Coxall, H. K., Pearson, P. N., Kroon, D., & Schmidt, D. N. (2016). Partial collapse of the marine carbon pump after the
Cretaceous-Paleogene boundary. Geology, 44(4), 287–290. https://doi.org/10.1130/g37581.1
Bown, P. (2005). Selective calcareous nannoplankton survivorship at the Cretaceous-Tertiary boundary. Geology, 33(8), 653–656. https://doi.
org/10.1130/g21566ar.1
Boyd, P.W., & Trull, T. W. (2007). Understanding the export of biogenic particles in oceanic waters: Is there consensus? Progress in Oceanog-
raphy, 72(4), 276–312. https://doi.org/10.1016/j.pocean.2006.10.007
Bralower, T. J., Cosmidis, J., Heaney, P.J., Kump, L. R., Morgan, J. V., Harper, D. T., etal. (2020). Origin of a global carbonate layer deposited
in the aftermath of the Cretaceous-Paleogene boundary impact. Earth and Planetary Science Letters, 548, 116476. https://doi.org/10.1016/j.
epsl.2020.116476
Bralower, T. J., Paull, C. K., & Mark Leckie, R. (1998). The Cretaceous-Tertiary boundary cocktail: Chicxulub impact triggers margin collapse
and extensive sediment gravity flows. Geology, 26(4), 331–334. https://doi.org/10.1130/0091-7613(1998)026<0331:tctbcc>2.3.co;2
Acknowledgments
We are grateful for insightful reviews
by Ellen Thomas and an anonymous
reviewer, both of which substantially
improved this manuscript. We are also
grateful to Brian LeVay and Mackenzie
Schoemann of the IODP GCR at Texas
A&M University for their assistance
with XRF core scanning, the staff of the
GCR for sending samples from Sites 95
and 536 for biostratigraphic analysis, and
Vinny Percuoco at the GCR for providing
high resolution photograph for the K-Pg
boundary in Hole 1001B. We are also
grateful to Ryan Weber and Calvin
Gordon of PaleoData, Inc., for their assis-
tance preparing samples from Site 999
and 1001 for biostratigraphic analysis.
Paleoceanography and Paleoclimatology
LOWERY AND BRALOWER
10.1029/2021PA004400
15 of 17
Brugger, J., Feulner, G., & Petri, S. (2017). Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of
the Cretaceous. Geophysical Research Letters, 44(1), 419–427. https://doi.org/10.1002/2016gl072241
Buesseler, K. O., & Boyd, P.W. (2009). Shedding light on processes that control particle export and flux attenuation in the twilight zone of the
open ocean. Limnology and Oceanography, 54(4), 1210–1232. https://doi.org/10.4319/lo.2009.54.4.1210
Buffler, R. T., Schlager, W., & Pisciotto, K. A. (1984). Initial Reports of the Deep Sea Drilling Project (Vol. 77). https://doi.org/10.2973/dsdp.
proc.77.1984
Carter, S. C., Paytan, A., & Griffith, E. M. (2020). Toward an improved understanding of the marine barium cycle and the application of marine
barite as a paleoproductivity proxy. Minerals, 10(5), 421.
Coxall, H. K., D'Hondt, S., & Zachos, J. C. (2006). Pelagic evolution and environmental recovery after the Cretaceous-Paleogene mass extinction.
Geology, 34(4), 297–300. https://doi.org/10.1130/g21702.1
Culver, S. J. (2003). Benthic foraminifera across the Cretaceous–Tertiary (K–T) boundary: A review. Marine Micropaleontology, 47(3–4),
177–226. https://doi.org/10.1016/s0377-8398(02)00117-2
Decelle, J., Probert, I., Bittner, L., Desdevises, Y., Colin, S., de Vargas, C., etal. (2012). An original mode of symbiosis in open ocean plankton.
Proceedings of the National Academy of Sciences, 109(44), 18000–18005. https://doi.org/10.1073/pnas.1212303109
Dehairs, F., Jacquet, S., Savoye, N., Van Mooy, B. A., Buesseler, K. O., Bishop, J. K. B., etal. (2008). Barium in twilight zone suspended matter
as a potential proxy for particulate organic carbon remineralization: Results for the North Pacific. Deep Sea Research Part II: Topical Studies
in Oceanography, 55(14–15), 1673–1683. https://doi.org/10.1016/j.dsr2.2008.04.020
de la Rocha, C. L., & Passow, U. (2007). Factors influencing the sinking of POC and the efficiency of the biological carbon pump. Deep Sea
Research Part II: Topical Studies in Oceanography, 54(5–7), 639–658. https://doi.org/10.1016/j.dsr2.2007.01.004
Denne, R. A., Scott, E. D., Eickhoff, D. P., Kaiser, J. S., Hill, R. J., & Spaw, J. M. (2013). Massive Cretaceous-Paleogene boundary deposit,
deep-water Gulf of Mexico: New evidence for widespread Chicxulub-induced slope failure. Geology, 41(9), 983–986. https://doi.org/10.1130/
g34503.1
Deprez, A., Jehle, S., Bornemann, A., & Speijer, R. P. (2017). Pronounced biotic and environmental change across the latest Danian warm-
ing event (LDE) at Shatsky Rise, Pacific Ocean (ODP Site 1210). Marine Micropaleontology, 137, 31–45. https://doi.org/10.1016/j.
marmicro.2017.10.001
D'Hondt, S., Donaghay, P., Zachos, J. C., Luttenberg, D., & Lindinger, M. (1998). Organic carbon fluxes and ecological recovery from the
Cretaceous-Tertiary mass extinction. Science, 282(5387), 276–279. https://doi.org/10.1126/science.282.5387.276
Doyle, P.S., & Riedel, W. R. (1979). Ichthyoliths: Present status of taxonomy and stratigraphy of microscopic fish skeletal debris. Scripps Insti-
tution of Oceanography, University of California at San Diego.
Dymond, J., Suess, E., & Lyle, M. (1992). Barium in deep-sea sediment: A geochemical proxy for paleoproductivity. Paleoceanography, 7(2),
163–181. https://doi.org/10.1029/92pa00181
Eagle, M., Paytan, A., Arrigo, K. R., van Dijken, G., & Murray, R. W. (2003). A comparison between excess barium and barite as indicators of
carbon export. Paleoceanography, 18(1). https://doi.org/10.1029/2002pa000793
Esmeray-Senlet, S., Wright, J. D., Olsson, R. K., Miller, K. G., Browning, J. V., & Quan, T. M. (2015). Evidence for reduced export productivity
following the Cretaceous/Paleogene mass extinction. Paleoceanography, 30(6), 718–738. https://doi.org/10.1002/2014pa002724
Fakhraee, M., Planavsky, N. J., & Reinhard, C. T. (2020). The role of environmental factors in the long-term evolution of the marine biological
pump. Nature Geoscience, 13(12), 812–816. https://doi.org/10.1038/s41561-020-00660-6
Fraass, A. J., Kelly, D. C., & Peters, S. E. (2015). Macroevolutionary history of the planktic foraminifera. Annual Review of Earth and Planetary
Sciences, 43(1), 139–166. https://doi.org/10.1146/annurev-earth-060614-105059
Francois, R., Honjo, S., Krishfield, R., & Manganini, S. (2002). Factors controlling the flux of organic carbon to the bathypelagic zone of the
ocean. Global Biogeochemical Cycles, 16(4), 34–1. https://doi.org/10.1029/2001gb001722
Francois, R., Honjo, S., Manganini, S. J., & Ravizza, G. E. (1995). Biogenic barium fluxes to the deep sea: Implications for paleoproductivity
reconstruction. Global Biogeochemical Cycles, 9(2), 289–303. https://doi.org/10.1029/95gb00021
Gibbs, S. J., Bown, P.R., Ward, B. A., Alvarez, S. A., Kim, H., Archontikis, O. A., etal. (2020). Algal plankton turn to hunting to survive and
recover from end-Cretaceous impact darkness. Science Advances, 6(44), eabc9123. https://doi.org/10.1126/sciadv.abc9123
Gradstein, F. M., Ogg, J. G., Schmitz, M. D., & Ogg, G. M. (Eds.). (2012). The geologic time scale 2012. Elsevier.
Griffith, E. M., & Paytan, A. (2012). Barite in the ocean–occurrence, geochemistry and palaeoceanographic applications. Sedimentology, 59(6),
1817–1835. https://doi.org/10.1111/j.1365-3091.2012.01327.x
Griffith, E. M., Thomas, E., Lewis, A. R., Penman, D. E., Westerhold, T., & Winguth, A. M. (2021). Bentho-pelagic decoupling: The marine
biological carbon pump during Eocene hyperthermals. Paleoceanography and Paleoclimatology, 36(3), e2020PA004053. https://doi.
org/10.1029/2020pa004053
Hallock, P. (1987). Fluctuations in the trophic resource continuum: A factor in global diversity cycles? Paleoceanography, 2(5), 457–471. https://
doi.org/10.1029/pa002i005p00457
Henehan, M. J., Ridgwell, A., Thomas, E., Zhang, S., Alegret, L., Schmidt, D. N., etal. (2019). Rapid ocean acidification and protracted Earth
system recovery followed the end-Cretaceous Chicxulub impact. Proceedings of the National Academy of Sciences, 116(45), 22500–22504.
https://doi.org/10.1073/pnas.1905989116
Henson, S. A., Sanders, R., & Madsen, E. (2012). Global patterns in efficiency of particulate organic carbon export and transfer to the deep ocean.
Global Biogeochemical Cycles, 26(1). https://doi.org/10.1029/2011gb004099
Hollis, C. J., Rodgers, K. A., & Parker, R. J. (1995). Siliceous plankton bloom in the earliest Tertiary of Marlborough, New Zealand. Geology,
23(9), 835–838. https://doi.org/10.1130/0091-7613(1995)023<0835:spbite>2.3.co;2
Hollis, C. J., Strong, C. P., Rodgers, K. A., & Rogers, K. M. (2003). Paleoenvironmental changes across the Cretaceous/Tertiary boundary at Flax-
bourne River and Woodside Creek, eastern Marlborough, New Zealand. New Zealand Journal of Geology and Geophysics, 46(2), 177–197.
https://doi.org/10.1080/00288306.2003.9515003
Hsü, K. J., He, Q., McKenzie, J. A., Weissert, H., Perch-Nielsen, K., Oberhänsli, H., etal. (1982). Mass mortality and its environmental and
evolutionary consequences. Science, 216(4543), 249–256. https://doi.org/10.1126/science.216.4543.249
Hsü, K. J., & Mckenzie, J. A. (1985). A “Strangelove” ocean in the earliest Tertiary. The carbon cycle and atmospheric CO2: Natural variations
Archean to present (Vol. 32,pp.487–492).
Hull, P.M., & Norris, R. D. (2011). Diverse patterns of ocean export productivity change across the Cretaceous-Paleogene boundary: New
insights from biogenic barium. Paleoceanography, 26(3). https://doi.org/10.1029/2010pa002082
Jacquet, S. H., Dehairs, F., Dumont, I., Becquevort, S., Cavagna, A. J., & Cardinal, D. (2011). Twilight zone organic carbon remineralization
in the Polar Front Zone and Subantarctic Zone south of Tasmania. Deep Sea Research Part II: Topical Studies in Oceanography, 58(21–22),
2222–2234. https://doi.org/10.1016/j.dsr2.2011.05.029
Paleoceanography and Paleoclimatology
LOWERY AND BRALOWER
10.1029/2021PA004400
16 of 17
Jiang, S., Bralower, T. J., Patzkowsky, M. E., Kump, L. R., & Schueth, J. D. (2010). Geographic controls on nannoplankton extinction across the
Cretaceous/Palaeogene boundary. Nature Geoscience, 3(4), 280–285. https://doi.org/10.1038/ngeo775
Jones, H. L., Lowery, C. M., & Bralower, T. J. (2019). Delayed calcareous nannoplankton boom-bust successions in the earliest Paleocene Chicx-
ulub (Mexico) impact crater. Geology, 47(8), 753–756. https://doi.org/10.1130/g46143.1
Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature,
570(7761), 372–375. https://doi.org/10.1038/s41586-019-1230-3
Kump, L. R. (1991). Interpreting carbon-isotope excursions: Strangelove oceans. Geology, 19(4), 299–302. https://doi.org/10.1130/0091-
7613(1991)019<0299:icieso>2.3.co;2
Legendre, L., & Michaud, J. (1998). Flux of biogenic carbon in oceans: Size-dependent regulation by pelagic food webs. Marine Ecology
Progress Series, 164, 1–11. https://doi.org/10.3354/meps164001
Louvel, V., & Galbrun, B. (2000). Magnetic polarity sequences from downhole measurements in ODP holes 998B and 1001A, leg 165, Caribbean
Sea. Marine Geophysical Researches, 21(6), 561–577. https://doi.org/10.1023/a:1004852810281
Lowery, C. M. (2021). NOAA/WDS Paleoclimatology—Gulf of Mexico and Caribbean XRF core scan data from the Early Paleocene. [Dataset].
NOAA National Centers for Environmental Information. https://doi.org/10.25921/g1wy-1d88
Lowery, C. M., Bown, P.R., Fraass, A. J., & Hull, P.M. (2020). Ecological response of plankton to environmental change: Thresholds for extinc-
tion. Annual Review of Earth and Planetary Sciences, 48(1), 403–429. https://doi.org/10.1146/annurev-earth-081619-052818
Lowery, C. M., Bralower, T. J., Owens, J. D., Rodríguez-Tovar, F. J., Jones, H., Smit, J., etal. (2018). Rapid recovery of life at ground zero of the
end-Cretaceous mass extinction. Nature, 558(7709), 288–291. https://doi.org/10.1038/s41586-018-0163-6
Lowery, C. M., Jones, H., Bralower, T. J., Perez Cruz, L., Gebhardt, C., Whalen, M. T., etal. (2021). Early Paleocene paleoceanography and
export productivity in the Chicxulub Crater. Paleoceanography & Paleoclimatology, 36(11), e2021PA004241.
Marañón, E., Behrenfeld, M. J., González, N., Mouriño, B., & Zubkov, M. V. (2003). High variability of primary production in oligotrophic
waters of the Atlantic Ocean: Uncoupling from phytoplankton biomass and size structure. Marine Ecology Progress Series, 257, 1–11. https://
doi.org/10.3354/meps257001
Martinez-Ruiz, F., Paytan, A., Gonzalez-Muñoz, M. T., Jroundi, F., Abad, M. D. M., Lam, P.J., etal. (2020). Barite precipitation on suspended
organic matter in the mesopelagic zone. Frontiers in Earth Science, 8, 567714. https://doi.org/10.3389/feart.2020.567714
Molina, E., Alegret, L., Arenillas, I., Arz, J. A., Gallala, N., Hardenbol, J., etal. (2006). The global boundary stratotype section and point for the
base of the Danian Stage (Paleocene, Paleogene, “Tertiary”, Cenozoic) at El Kef, Tunisia-original definition and revision. Episodes, 29(4),
263–273. https://doi.org/10.18814/epiiugs/2006/v29i4/004
Moore, J. K., Fu, W., Primeau, F., Britten, G. L., Lindsay, K., Long, M., etal. (2018). Sustained climate warming drives declining marine biolog-
ical productivity. Science, 359(6380), 1139–1143. https://doi.org/10.1126/science.aao6379
Morgan, J., Gulick, S., Mellett, C. L., & Green, S. L. (2017). Chicxulub: Drilling the K-Pg impact crater. Proceedings of the International Ocean
Discovery Program, 364. https://doi.org/10.14379/iodp.proc.364.2017
Müller, P.J., & Suess, E. (1979). Productivity, sedimentation rate, and sedimentary organic matter in the oceans—I. Organic carbon preservation.
Deep-Sea Research, Part A: Oceanographic Research Papers, 26(12), 1347–1362. https://doi.org/10.1016/0198-0149(79)90003-7
Olsson, R. K., Berggren, W. A., Hemleben, C., & Huber, B. T. (1999). Atlas of Paleocene planktonic foraminifera. Smithsonian Contributions to
Paleobiology, 85, 1–106. https://doi.org/10.5479/si.00810266.85.1
Passow, U., & Carlson, C. A. (2012). The biological pump in a high CO₂ world. Marine Ecology Progress Series, 470, 249–272. https://doi.
org/10.3354/meps09985
Paytan, A., Averyt, K., Faul, K., Gray, E., & Thomas, E. (2007). Barite accumulation, ocean productivity, and Sr/Ba in barite across the
Paleocene-Eocene Thermal Maximum. Geology, 35(12), 1139–1142. https://doi.org/10.1130/g24162a.1
Paytan, A., & Griffith, E. M. (2007). Marine barite: Recorder of variations in ocean export productivity. Deep Sea Research Part II: Topical
Studies in Oceanography, 54(5–7), 687–705. https://doi.org/10.1016/j.dsr2.2007.01.007
Paytan, A., Kastner, M., & Chavez, F. P. (1996). Glacial to interglacial f luctuations in productivity in the equatorial Pacific as indicated by marine
barite. Science, 274(5291), 1355–1357. https://doi.org/10.1126/science.274.5291.1355
Pindell, J. L., & Barrett, S. F. (1990). Caribbean plate tectonic history. The Caribbean Region (Vol. H,pp.405–432). The Geology of North
America.
Planchon, F., Cavagna, A. J., Cardinal, D., André, L., & Dehairs, F. (2013). Late summer particulate organic carbon export and twilight zone
remineralisation in the Atlantic sector of the Southern Ocean. Biogeosciences, 10(2), 803–820. https://doi.org/10.5194/bg-10-803-2013
Sanford, J. C., Snedden, J. W., & Gulick, S. P. (2016). The Cretaceous-Paleogene boundary deposit in the Gulf of Mexico: Large-scale oceanic basin
response to the Chicxulub impact. Journal of Geophysical Research: Solid Earth, 121(3), 1240–1261. https://doi.org/10.1002/2015jb012615
Schaefer, B., Grice, K., Coolen, M. J., Summons, R. E., Cui, X., Bauersachs, T., etal. (2020). Microbial life in the nascent Chicxulub crater.
Geology, 48(4), 328–332. https://doi.org/10.1130/g46799.1
Schueth, J. D., Bralower, T. J., Jiang, S., & Patzkowsky, M. E. (2015). The role of regional survivor incumbency in the evolutionary recovery
of calcareous nannoplankton from the Cretaceous/Paleogene (K/Pg) mass extinction. Paleobiology, 41(4), 661–679. https://doi.org/10.1017/
pab.2015.28
Sepúlveda, J., Alegret, L., Thomas, E., Haddad, E., Cao, C., & Summons, R. E. (2019). Stable isotope constraints on marine productivity across the
Cretaceous-Paleogene mass extinction. Paleoceanography and Paleoclimatology, 34(7), 1195–1217. https://doi.org/10.1029/2018pa003442
Sepúlveda, J., Wendler, J. E., Summons, R. E., & Hinrichs, K. U. (2009). Rapid resurgence of marine productivity after the Cretaceous-Paleogene
mass extinction. Science, 326(5949), 129–132. https://doi.org/10.1126/science.1176233
Sibert, E. C., & Norris, R. D. (2015). New age of fishes initiated by the Cretaceous−Paleogene mass extinction. Proceedings of the National
Academy of Sciences, 112(28), 8537–8542. https://doi.org/10.1073/pnas.1504985112
Sigurdsson, H., Leckie, R. M., Acton, G. D., Miller, C. M., & Maddox, E. M. (1997). Proceedings of the Ocean Drilling Program, Initial Reports
(Vol. 165). Ocean Drilling Program. https://doi.org/10.2973/odp.proc.ir.165.1997
Snedden, J., Leshyk, V. O., & Kring, D. (2021). Paleogeographic evolution of the Chicxulub Region. Lunar and Planetary Institute Illustration.
Retrieved from https://www.lpi.usra.edu/exploration/training/illustrations/chicxulub-effects/
Thierstein, H. R. (1982). Terminal cretaceous plankton extinctions: A critical assessment. Geological implications of impacts of large asteroids
and comets on the Earth (Vol. 190,pp.385–399).
Thomas, E. (1990). Late Cretaceous-early Eocene mass extinctions in the deep sea. Geological Society of America Special Publication, 247,
481–495.
Toon, O. B., Zahnle, K., Morrison, D., Turco, R. P., & Covey, C. (1997). Environmental perturbations caused by the impacts of asteroids and
comets. Reviews of Geophysics, 35(1), 41–78. https://doi.org/10.1029/96rg03038
Paleoceanography and Paleoclimatology
LOWERY AND BRALOWER
10.1029/2021PA004400
17 of 17
Verity, P. G., Brussaard, C. P., Nejstgaard, J. C., van Leeuwe, M. A., Lancelot, C., & Medlin, L. K. (2007). Current understanding of Phae-
ocystis ecology and biogeochemistry, and perspectives for future research. Biogeochemistry, 83(1), 311–330. https://doi.org/10.1007/
s10533-007-9090-6
Wade, B. S., Pearson, P. N., Berggren, W. A., & Pälike, H. (2011). Review and revision of Cenozoic tropical planktonic foraminiferal biostra-
tigraphy and calibration to the geomagnetic polarity and astronomical time scale. Earth-Science Reviews, 104(1–3), 111–142. https://doi.
org/10.1016/j.earscirev.2010.09.003
Worzel, J. L., Bryant, W., Beall, A. O., Jr., Capo, R., Dickinson, K., Foreman, H. P., etal. (1973). Initial Reports of the Deep Sea Drilling Project
(Vol. 10). U.S. Government Printing Office. https://doi.org/10.2973/dsdp.proc.10.1973
Zachos, J. C., & Arthur, M. A. (1986). Paleoceanography of the Cretaceous/Tertiary boundary event: Inferences from stable isotopic and other
data. Paleoceanography, 1(1), 5–26. https://doi.org/10.1029/pa001i001p00005
Zachos, J. C., Arthur, M. A., & Dean, W. E. (1989). Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/
Tertiary boundary. Nature, 337(6202), 61–64. https://doi.org/10.1038/337061a0
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