ArticlePDF Available

Alkalinity: The link between anaerobic basins and shallow water carbonates?

Authors:
Stephan Kempe at Technische Universität Darmstadt
Stephan Kempe
Download full-text PDF
Read full-text
Download citation
Content uploaded by Stephan Kempe
Author content
All content in this area was uploaded by Stephan Kempe on Nov 17, 2016
Content may be subject to copyright.
FNotur
w ssenschaflen
Naturwissenschaften 77,426-427 (1990) © Springer-Verlag 1990
Alkalinity: the Link Between Anaerobic Basins and
Shallow Water Carbonates?
S. Kempe
Institut fiir Biogeochemie und Meereschemie der Universit~it, D-2000 Hamburg
Anaerobic ocean basins were common
features in earth history. Today, only
one large anoxic basin exists, the deep
Black Sea (480 000 km3). Massive cal-
careous deposits are often found in
close regional and stratigraphic associa-
tion with deposits of anoxic basins. The
Aptian/Albian and Cenomanian/Tu-
ronian anoxic events were, for ex-
arnaple, accompanied by widespread
epicontinental chalk and reef limestone
deposition.
Therefore, one may ask if there is a
causal relation between the two facies.
In fact, such a connection has been
proposed (e.g., [3, 6]). These models
describe the general implications of
shifting chemoclines and explore con-
sequences of a Ca input, for example,
from hydrothermal sources. Here, I
present an alternative view which sug-
gests that small changes in the concen-
tration of the total dissolved inorganic
carbon
(~]CO2)
could be responsible.
Shifts in ~CO2 affect the supersatura-
tion of CaCO 3 more effectively and
therefore faster than the same change
in Ca because the Ca concentration in
seawater is about ten times that of
~-]CO2.
Anaerobic basins are governed by
sulfate reduction which mineralizes
sinking algal organic matter (i.e., of a
Redfield composition [ 12]):
53 SO42- + C106Hz63OlloN16P ] +
14 H20
53 H2S + 106 HCO~- +
HPO 2- + 16NH 2 + 14 OH- (1)
424 e- are used in the reduction and to
transfer negative charge from sulfate to
bicarbonate. H2S and HCO~- are
426
produced at a molar ratio of 1:2. The
addition of HCO~- increases both
~CO2 and alkalinity (i.e., the sum of
the charges of all anions of weak acids,
HCO~- + CO~-+ H(BO3)- + OH-
etc.).
Turning to the deep Black Sea, we find
that the ratio between H2S and ~CO 2
is higher than 1:2 (Fig. 1). Either HzS
has been removed or HCO~- was gen-
erated in excess to Eq. (1). Both possi-
bilities are realistic. H2S is, in fact, re-
moved by the formation of settling in-
soluble metal (mainly Fe) sulfides, and
CaCO 3 dissolution would increase
~CO 2 and alkalinity.
Probably both processes occur simulta-
neously. Our sediment trap experi-
ments allow one to estimate the FeS2
flux to 690 nag m -2 a ] or ca. 2 % of
--4200
Z
=:L
4000
3800
o
3600
3400
I..--
o:
3200
r I ~ i ~ 2000~
1 oo t T r ~ ! l
0 1 O0 200 300
Sulfide sulfur
[FH]
Fig. 1. Comparison of actual ]~CO2/H2S
molar ratio (points) with the 2:1 ratio of
sulfate reduction (lower line) in the Black
Sea. The hatched area represents excess
~CO 2 gained by either calcite dissolution or
pyrite formation (altered after [12], data by
[11])
Naturwissenschaften 77 (1990)
the total vertical particle flux of 36g
m -2
a-1 (Kempe and Enaeis, unpubl.
EDX data, 1983/84, station 40km
north of Amasra/Turkey). The total
vertical particle flux in the Black Sea is,
however, highly variable seasonally,
interannually, and between different
locations [5]. An average deposition
rate is therefore better estimated from
sediment cores, it amounts to roughly
190g m -2 a- ] [4]. Thus, total FeS 2 flux
may amount to 3.8 g
m -2 a-1
(64mmol
S na -2 a-1). For comparison, Tambiev
[13] estimated the pyrite flux to 2.9g
na- 2 a- 1 (48 mmol m- 2 a- 1). Sulfate
reduction amounts to 2.5 mol m -2 a -1
of which 2.4mol m -2 a-1 are oxidized
again [8]. The remainder, 100mmol
m -2 a-1, minus the pyrite flux created
the present H2S pool (600mol m -2) in
the Black Sea. These figures suggest
that the pyrite flux accounts for the re-
moval of roughly half of the net
production of HzS and must play a key
role in building up excess ~CO2.
The deposition rate of CaCO 3 is ca.
100g m -2 a -1 [4], compared to 7g
m -2 a -1 recorded by sediment trap
(1983/84). This illustrates the size of
medium-term changes in the CaCO3
production in the Black Sea. How
much of the sinking CaCO 3 dissolves is
unknown. At present, possibly none
because the water below a depth of
60m is just saturated with respect to
calcite (unpubl. data), but could have
been corrosive in the recent past. This is
in accordance with the sediment rec-
ord: During the last 1 000 years a coc-
colith carbonate ooze was deposited
(varve counts by Degens et al. [2], and
Hay, pers. comm.). It rests on a marine
sapropel free of carbonate, deposited
5 000- 1000 years •.P., at a time when
the Black Sea was already anoxic but
calcite undersaturated. The observed
~CO2 surplus may also be a relic from
that time.
The ]]CO 2 difference between the oxic
surface layer and the bottom of the
Black Sea is 1 mmol/kg, i.e., five times
larger than in the world oceans
© Springer-Verlag 1990
(0.22 mmol/kg; Fig. 2) [ 1]. Comparing
the ages of anaerobic conditions in the
Black Sea (ca. 5 000 a) with the average
age of deep oceanic waters (ca. 1 000 a)
and taking the different mean depths of
both water bodies into account (factor
of 2) we can tentatively deduce that
~CO 2 accumulation by aerobic and
anaerobic respiration relate like 1 to 2.
Such rates would deplete the sulfate
supply (28mmol/kg) of an oceanic
basin within a few 205 a.
Most striking is, however, that the sur-
face of the Black Sea has a much higher
ECO2 than the world ocean (Fig. 2).
Apparently, ~CO 2 is "leaking" from
below the chemocline to the surface
layer by upwelling and/or eddy diffu-
sion. This shows that the reverse pro-
cess to sulfate reduction, i.e.,
HzS ox-
idation,
HzS + 20 2 --+ SO 2- + 2H + ;
H + +
HCOf --+ H20 +
CO 2
(2)
is not 100 °70 effective to turn all of the
HCOf back to CO2 which would then
degas to the atmosphere. Only if a
sizable part of the sulfide was removed
to sediments or if oxidation produces
elemental S, which sinks back into the
anoxic zone, the alkalinity generated by
sulfate reduction would be charge-bal-
anced by cations and is protected from
degassing.
Whatever the exact reaction pathways
are, the Black Sea managed to increase
its surface ECO2 much above the mix-
ture of the two end members which
deliver water to the Black Sea, i.e.,
Mediterranean water with 2.18 to
2.36mmol/kg [9] and rivers with a dis-
charge weighted average of 1.3
mmol/kg [10].
This high ]~CO2 is, however, paired
with a low Ca 2+ concentration. For Ca,
end-member mixing leads to a much
lower concentration than seawater be-
cause of the low salinity of the Black
Sea. Thus, the ion activity product of
Ocean, surface l
/
0
2.23 &30
Fig. 2. Comparison of ~CO 2 (in mmol/kg)
between the surface and bottom waters of
the world ocean and the Black Sea (data
after [1] and [12] quoted in [12])
Naturwissenschaften 77 (1990)
CO 2
Ca 2÷
k,,,~t k
i
O~ C02
Fig. 3. Scheme of fluxes in the coupled anaerobic basin - epicontinental carbonate platform
model
[Ca2+][CO3 -] in Black Sea surface wa-
ters is comparable to average oceanic
surface water. If, however, the Black
Sea would have an oceanic salinity
(35°/00), then the surface would be
highly supersaturated with respect to
calcite, high enough to possibly cause
spontaneous aragonite formation or to
impede growth of most marine species.
An example of such a high supersatura-
tion environment is the seawater-filled
Satonda Crater lake. There an increase
in carbonate alkalinity to only
3.4mEq/kg proved enough to cause
cyanobacterial stromatolites and ara-
gonite precipitation, and to exclude all
marine biomineralizing species, except
for one gastropod [7]. In Satonda the
logarithmic index of calcite saturation
increased to +0.8 compared to +0.5 in
the Black Sea and to +0.4- +0.6 in
normal sea-surface waters.
The Black Sea shows that stagnation
periods of a few thousand years allow
the generation of high ECO 2 and al-
kalinity not only in anaerobic bottom
waters, but also in aerobic surface wa-
ters. If such waters are then advected to
epicontinental seas, further CO2 is
extracted by phytoplankton and
epiphytes. This causes a CaCO 3 super-
saturation stress, which, in turn, leads
to increased rates of biomineralization
forming either chalks or reef limestones
(Fig. 3). Paleogeographically the Cre-
taceous anaerobic basins were caused
by the opening of the Atlantic and a
high sea level provided for extensive
epicontinental seas. In such a geo-
graphic setting three different modes of
sedimentation can be discerned: 1)
Platform carbonates and basin sedi-
ments can form at the same time but
spatially apart; 2) at the
H2S/O 2
inter-
face alternating columns of anaerobic
sediments and carbonate deposits may
form induced by changes in sea level or
© Springer-Verlag 1990
changes in the depth of the aerobic
layer; and 3) the aeration of the total
basin may cause deep water carbonate
deposits on top of deep-water
anaerobic sediments.
Received March 8 and May 22, 1990
1. Broecker, W., Peng, T.-H.: Tracers in
the Sea. Palisades: Lamont-Doherty
Geol. Observ., Cotumbia Univ. 1982
2. Degens, E. T., Michaelis, W., Garrasi,
C., Mopper, K., Kempe, S., Ittekkot,
V. : N. Jb. Geol. Pal~iont. Mh.
1980
(2),
65
3. Degens, E. T., Stoffers, P.: Nature
263,
22 (1976)
4. Hay, B. J.: Dissertation, Woods Hole
Oceanographic 1987
5. Hay, B. J., Honjo, S., Kempe, S., Ittek-
kot, V., Degens, E. T., Konuk, T.,
Izdar, E.: Deep-Sea Res. (submitted)
6. Kazmierczak, J., 2ttekkot, V., Degens,
E. T.: Pal~ont. Z.
59
(1 -2), 15 (1985)
7. Kempe, S., Kazmierczak, J.: Chem.
Geol. (in press)
8. Lein, A. Yu., Ivanov, M. V., Vainsh-
tein, M. V., in: 2nteractions of Bio-
geochemical Cycles in Aqueous Systems
Pt.7 (Degens, E. T., Kempe, S., Lein,
A., Sorokin, Y., eds.). Mitt. Geol.-Pa-
l~ont. Inst. Univ. Hamburg, SCO-
PE/UNEP Sonderband.
71
(in press)
9. Millero, F., Morse, J., Chen, C.-T.:
Deep-Sea Res.
26A,
1395 (1979)
20. Shimkus, K. M., Trimonis, V. V.: Am.
Ass. Pet. Geol. Mere.
20,
249 (1974)
21. Skopintsev, B. A., et al., in: The Sea,
Vol. 2 (Hill, M.N., ed.). New York:
Wiley Interscience 1966
12. Stumm, W., Morgan, J. J.: Aquatic
Chemistry. New York-London: Wiley
Interscience 1970
23. Tambiev, S. B., in: Particle Flux in the
Ocean (Degens, E. T., Izdar, E.,
Honjo, S., eds.). Mitt. Geol.-Pal~tont.
Inst. Univ. Hamburg, SCOPE/UNEP
Sonderband.
62,
42 (1987)
427
... The formation of seafloor authigenic carbonate cements was common during the Proterozoic, when the seawater was presumably much more oversaturated with respect to carbonates (Grotzinger 1994;Sami & James 1996), as a result of widespread, deep ocean anoxia, which generated additional alkalinity by pyrite burial and/or hydrogen sulphide evasion to the atmosphere (e.g., Kempe 1990;Grotzinger & Knoll 1995;Higgins et al. 2009;Hood & Wallace 2014). ...
... A possible explanation can be based on the widely studied Permian/Triassic extinction event, where a combination of global scale oceanic anoxia (Lau et al. 2016), hydrogen sulphide evasion (Kump et al. 2005) and massive pyrite burial (Berner 2005) may have concurrently caused extensive seawater sulphate anion depletion (Luo et al. 2010). Seawater (anion) charge equilibrium, which requires sulphate−bicarbonate charge transfer, may have resulted in significant increase in alkalinity and DIC = Dissolved Inorganic Carbon (Kempe 1990;Grotzinger & Knoll 1995;Saitoh et al. 2015). Upwelling of highly alkaline waters into shallow shelves potentially caused a rise in carbonate saturation driven by CO 2 degassing or photosynthetic carbon incorporation (e.g., Woods et al. 1999). ...
... The surprising abundance of authigenic carbonates in the Alum Shale facies may be explained by the unusual chemical and hydrodynamic conditions in the basin. The presence of long-standing anoxia and water stagnation in the basin are perfect conditions for carbonate supersaturation and the precipitation of chemogenic CaCO 3 (e.g., Kempe 1990;Kempe & Kaźmierczak 1994;Grotzinger & Knoll 1995;Woods et al. 1999;Kozłowski 2015;Saitoh et al. 2015; Fig. 9). Authigenic carbonate formation may have taken place as a result of a series of chemical reactions in anoxic waters, as discussed below. ...
Authigenic calcium carbonate precipitation in the “bathtub ring” around the anoxic Alum Shale Basin during the Furongian SPICE event (Baltic Basin, northern Poland)
Article
Full-text available
  • Sep 2021
The precipitation of both biotic and abiotic calcium carbonate is of great importance in modern and ancient global biogeochemical cycles. In the present-day oceans, the widespread precipitation of inorganic CaCO3 on the seafloor or in the water column is possible only under extraordinary circumstances. By contrast, in the geological record, authigenic seafloor carbonate cements were widespread in the supersaturated, anoxic oceans of the Precambrian. Widespread authigenic carbonate precipitation ceased by the end of the Neoproterozoic as a consequence of global oceanic oxygenation: in the Phanerozoic, it occurred only during major anoxic events (for example, at the Permian/Triassic boundary) or in restricted, stagnant basins. Here, we present an anomalous record of CaCO3 precipitation from the Cambrian Alum Shale Basin of the Baltica palaeocontinent with Precambrian-like authigenic, seafloor encrusting, crystalline carbonates. The depositional environment of this well-recognized, cool-water, stagnant anoxic basin favoured local carbonate precipitation via the surplus generation of alkalinity in anoxic bottom waters. However, the correlation of the acme of authigenic carbonate formation with the onset and peak of the Steptoean Positive Carbon Isotope Excursion (SPICE) suggests a driver−trigger relation between the two phenomena. On a smaller scale, carbonate authigenic precipitation is manifested by a cement-supported texture of the limestone intercalations in the Alum Shale facies. Instantaneous calcification of the faunal remains, termed here the Snedronningen phenomenon, must have been of great importance in the formation of Orsten-type Konservat Lagerstätten.
View
... The Na, Mg-Cl, HCO 3 subtype is associated with processes that lead to concentration of HCO 3 and Mg 2+ rather than evaporation. The seawater-derived Satonda Lake is concentrated in HCO 3 due to a hydrological process called an alkalinity-pump, i.e., export of alkalinity produced by decomposition of OM in the deepest layers to the surficial layers of the lake (Kempe, 1990). Lakes Atexcac, Vai Lahi and Vai Si′i are not derived from seawater and the enhancement of HCO 3 and Mg 2+ is also attributed to the high pCO 2 and hydrolysis of silicate minerals from volcanic rocks situated around the lakes (Kaźmierczak and Kempe, 2006;Kaźmierczak et al., 2011). ...
... Owing to the great variety of water chemistry in lakes, the processes observed among the lacustrine microbialites are not exclusive to lakes but form part of a continuum that extends across other environments, such as continental tufas (Arp et al., 2010), sabkhas (Bontognali et al., 2010(Bontognali et al., , 2012(Bontognali et al., , 2014, open-marine settings (Visscher et al., 1998;Paerl et al., 2000;Reid et al., 2000;Visscher et al., 2000) and hypersaline soils (Reid et al., 2003a;Reid et al., 2003b;Papineau et al., 2005). Carbonate precipitation occurs in the microbialites when the saturation index of each mineral reaches adequate supersaturation (Kempe, 1990;Arp et al., 2001). Two possible situations occur among the case studies. ...
Modern lacustrine microbialites: Towards a synthesis of aqueous and carbonate geochemistry and mineralogy
Article
  • Sep 2016
  • EARTH-SCI REV
Lacustrine microbialites record evidence of their depositional environments in their morphology, mineralogy and geochemistry. This synthesis reviews geochemical data both for microbialites and lake water for 21 modern lacustrine microbialite occurrences younger than 15,000 years. Although these data are limited, several trends and associations are identified that provide useful criteria to aid interpretation of the environmental settings of ancient analogues. These microbialites are either thrombolites or thrombolitic stromatolites. They form in diverse settings, including karst, volcanic, coastal and inland (athalassic) lakes. Surveyed lakes are mostly closed basins subject to evaporative processes. Lakes vary from stratified to totally mixed examples. The major hydrochemical types include Na-Cl, Ca-SO4, Ca-HCO3 and Soda Lakes. The salinity and alkalinity of the lakes correlates, as expected, with the mode of mineralization, which in turn is reflected in the microstructure of the microbialites. A correlation between the δ13Ccarbonate and the Ca2 +/alkalinity ratio (Ca/Alk) is observed. Generally, lakes with Ca/Alk > 1 are subject to carbonate precipitation driven by either uptake of CO2 that results in a broad range of positive and negative δ13Ccarbonate, or mineralization mediated by sulphate reducing-bacteria in saline to hypersaline environments that results in negative δ13Ccarbonate. Ca/Alk < 1 correlates with positive δ13Ccarbonate. The mineral make-up of the analysed microbialites trends with lake chemistry and place of deposition. Mg/Ca ratios < 0.8 correlate with precipitation of low-Mg calcite (LMC) and low salinity. Extremely high Mg/Ca ratios (> 39) are associated with hydromagnesite. Dolomite, high-Mg calcite (HMC) and monohydrocalcite are associated with the total aqueous concentration of Mg (cMg), occurring only in lakes with cMg > 75 meq/L. Evaporites (e.g., gypsum) are related to high lake water salinities. The absolute concentration of aqueous Si, commonly associated with dissolution of diatom tests, influences precipitation of crystalline and/or amorphous silicates/silica to form microbialites with Si concentrations above 0.54 mmol/L, either as amorphous phases or as minerals such as stevensite and kerolite. Combined, the trends observed in this survey demonstrate that modern lacustrine microbialites can preserve information symptomatic of the environments in which they formed. However, in a limited number of examples this is not the case, as subsequent diagenesis may alter the original mineralogy to a point where the geochemical evidence conserved from the depositional environment is lost. Additionally, some geochemical information may be the product of isolated microenvironments within living biofilms, and thus not necessarily directly related to the chemistry of ambient lake water. Further misleading conclusions would result if the hydrochemistry at the time of study had changed from those prevailing when the microbialites were mineralized. Thus, all the correlations developed in this work represent hypotheses to be tested rather than interpretations to be accepted. This compilation demonstrates how microbialites respond to different lacustrine hydrochemical environments, and is intended to provide a guide for future field studies and laboratory simulations. This review also highlights the general scarcity of trace-element data for lake waters and microbialites. However, some recent studies suggest that lacustrine microbialites may fractionate rare earth elements (REE) during uptake from water whereas marine microbialites appear to record the REE distribution from seawater without modification. This possible difference in REE behaviour could have implications for the interpretation of palaeoenvironmental proxies.
View
... It is believed that rainwater can percolate through the sand dune and bring oxygen to the shallow, fresh groundwaters . In addition, the groundwater TA was higher in the forest than in the upper beach and this may reflect the impact of local redox reac-tions that serve as sources or sinks of alkalinity (Kempe, 1990;Stumm and Morgan, 1996;Abril and Frankignoulle 2001;Thomas et al., 2009). The oxidation of reduced Fe and nitrification of ammonia by oxygen consumes alkalinity (Eqs. ...
Carbon dynamics driven by seawater recirculation and groundwater discharge along a forest-dune-beach continuum of a high-energy meso-macro-tidal sandy coast
Article
  • Oct 2021
  • GEOCHIM COSMOCHIM AC
High-energy tidal beaches are exposed to strong physical forcings. The submarine groundwater discharge (SGD) that occurs in intertidal sandy sediments includes both terrestrial, fresh groundwater flow and seawater recirculation, and plays a significant role in regulating biogeochemical cycles in some coastal zones. In this transition zone between land and sea, complex biogeochemical reactions alter the chemical composition of pore waters that discharge to the coastal ocean. Recent studies highlight that SGD can be a significant source of carbon to the coastal ocean but very few have investigated SGD in high-energy environments. We have characterized the dissolved carbon dynamics in such a high-energy environment (Truc Vert Beach, SW France) through pore-water sampling in key compartments of the SGD system. Dissolved organic carbon (DOC), pH, total alkalinity (TA), and the isotopic composition of dissolved inorganic carbon (δ¹³C-DIC) were measured in pore waters sampled at regular intervals between 2011 and 2014 in the intertidal zone of the beach, the mixing zone of the subterranean estuary (STE), and the freshwater aquifer upstream from the beach. Results reveal that SGD exports dissolved carbon mostly as DIC to the Aquitaine coast, some of which originates from the aerobic respiration of marine organic matter within the beach aquifer. This is highlighted by the reverse spatial trend of DOC, which is consumed, and DIC, which is produced. Saline pore waters expelled from the beach through tidally-driven recirculation of seawater provide about 4400 tons of carbon per year to the coastal zone of the 240-kmlong Aquitaine sandy coast. Terrestrial groundwater, characterized by high pCO2 values, is also a significant contributor to the DIC flux to the coastal ocean (16,200 tons per year). This flux is abated by CO2 evasion in the upper beach, at the onset of the salinity gradient in the STE, and within the surficial freshwater aquifer along the forest-beach transect below the coastal foredune. Accordingly, the DIC:TA ratio evolves to below 1, suggesting that this SGD increases the buffer capacity of coastal seawater against acidification. This study demonstrates that high-energy beaches are active vectors of DIC from the land to the coastal ocean as well as significant sources of CO2 to the atmosphere, and must therefore be taken into consideration in SGD carbon budgets.
View
... High concentrations of TA and DIC in hypoxic/anoxic river waters TA is generally considered as a relative conservative property of natural waters (Kempe 1990;Wolf-Gladrow et al. 2007). In estuaries, TA generally shows a linear distribution versus the salinity following conservative mixing. ...
Greenhouse gas emissions (CO2 and CH4) and inorganic carbon behavior in an urban highly polluted tropical coastal lagoon (SE, Brazil)
Article
Full-text available
  • Jul 2021
  • ENVIRON SCI POLLUT R
Increasing eutrophication of coastal waters generates disturbances in greenhouse gas (GHG) concentrations and emissions to the atmosphere that are still poorly documented, particularly in the tropics. Here, we investigated the concentrations and diffusive fluxes of carbon dioxide (CO2) and methane (CH4) in the urban-dominated Jacarepagua Lagoon Complex (JLC) in Southeastern Brazil. This lagoonal complex receives highly polluted freshwater and shows frequent occurrences of anoxia and hypoxia and dense phytoplankton blooms. Between 2017 and 2018, four spatial surveys were performed (dry and wet conditions), with sampling in the river waters that drain the urban watershed and in the lagoon waters with increasing salinities. Strong oxygen depletion was found in the rivers, associated with extremely high values of partial pressure of CO2 (pCO2; up to 20,417 ppmv) and CH4 concentrations (up to 288,572 nmol L−1). These high GHG concentrations are attributed to organic matter degradation from untreated domestic effluents mediated by aerobic and anaerobic processes, with concomitant production of total alkalinity (TA) and dissolved inorganic carbon (DIC). In the lagoon, GHG concentrations decreased mainly due to dilution with seawater and degassing. In addition, the phytoplankton growth and CH4 oxidation apparently consumed some CO2 and CH4, respectively. TA concentrations showed a marked minimum at salinity of ~20 compared to the two freshwater and marine end members, indicating processes of re-oxidation of inorganic reduced species from the low-salinity region, such as ammonia, iron, and/or sulfides. Diffusive emissions of gases from the entire lagoon ranged from 22 to 48 mmol C m−2 d−1 for CO2 and from 2.2 to 16.5 mmol C m−2 d−1 for CH4. This later value is among the highest documented in coastal waters. In terms of global warming potential (GWP) and CO2 equivalent emissions (CO2-eq), the diffusive emissions of CH4 were higher than those of CO2. These results highlight that highly polluted coastal ecosystems are hotspots of GHG emissions to the atmosphere, which may become increasingly significant in future global carbon budgets.
View
... The carbonate suspensoids appear most abundantly in semi-isolated marine anoxic stratified basins (Degens and Stoffers 1976). In the recent anoxic fjords and marine lakes (filled with marine water), the effects of the absence (or limited presence) of skeletal calcifiers concur with the effective production of additional alkalinity by anaerobic degradation of OM, coupled with sulfate reduction and pyrite formation (Black 1933;Kempe 1990;Kempe and Kaźmierczak 1994;Lalou 1957). ...
Marine snow and epipelagic suspensoids in the Reda carbonates and a pronounced mid-Ludfordian (Silurian) CIE in the axis of the Baltic Basin (Poland)
Article
Full-text available
  • Sep 2020
The mid-Ludfordian pronounced, positive carbon isotope excursion (CIE), coincident with the Lau/kozlowskii extinction event, has been widely studied so far in shallow-water, carbonate successions, whereas its deep-water record remains insufficiently known. The aim of this research is to reconstruct the sedimentary environments and the palaeoredox conditions in the axial part of the Baltic-Podolian Basin during the event. For these purposes , the Pasłęk IG-1 core section has been examined using microfacies analysis, framboid pyrite diameter and carbon isotope measurements. The prelude to the event records an increased influx of detrital dolomite interpreted as eolian dust, coupled with a pronounced decrease in the diameter of the pyrite framboids, indicating persistent euxinic conditions across the event. The event climax is recorded as the Reda Member and consists of calcisiltites, composed of calcite microcrystals ('sparoids'), which are interpreted as suspensoids induced by phytoplankton blooms in the hipersaturation conditions present in the epipelagic layer of the basin. Both the prelude and climax facies show lamination, interpreted as having resulted from periodical settling of marine snow, combined with hydraulic sorting within a 'benthic flocculent layer', which additionally may be responsible for a low organic matter preservation rate due to methanogenic decomposition. Contrary to the observed basinward CIE decline in the benthic carbonates in the basin, the Reda Member records an extremely positive CIE (up to 8.25‰). Given the pelagic origin of the sparoids, the CIE seems to record surface-water carbon isotope ratios. This points to a large carbon isotope gradient and kinetic fractionation between surface and bottom waters during the mid-Ludfordian event in a strongly stratified basin. The Reda facies-isotope anomaly is regarded as undoubtedly globally triggered, but amplified by the stratified and euxinic conditions in the partly isolated, Baltic-Podolian basin. Hence, the common interpretation of the basin record as representative for the global ocean needs to be treated with great caution.
View
... Increase in pCO 2 (as 448 well as DIP and NH 4 + ) downslope the cross-shore transect (Fig. 5) clearly indicated that more 449 products from organic matter mineralization accumulated in the lower part of the beach. The related 450 increase in TA downslope suggests that the part of anaerobic processes in organic matter oxidation 451 was higher in the lower beach, as anaerobic processes create alkalinity (Kempe, 1990 studied transects covered oxic to anoxic redox-conditions as it has been described for other beaches 497 (e.g. Reckhardt et al., 2015). ...
Biogeochemistry in an intertidal pocket beach
Article
  • Jul 2020
Sandy beaches are places of active organic matter mineralization due to water renewal providing organic matter and electron acceptors in the porous and permeable sands. Recycled biogenic compounds are efficiently transferred to the coastal marine environment via wave and tidal-driven advective flows. The biogeochemical processes in beach aquifers were mainly studied in semi enclosed systems with low tidal amplitude, and with a connection to continental aquifers contributing to solute fluxes to the coast from terrestrial groundwater. We present here the study of a pocket beach isolated from terrestrial aquifers with a high tidal amplitude and a medium energy wave regime. In situ measurements, cross-shore profiles and vertical sampling were conducted during several tidal cycles in spring and autumn. Cross-shore transects, obtained at low tide from holes that represent a mixture of the upper 20 cm of the water saturated zone, showed concentration gradients of redox and recycled compounds. Increase in pCO2, dissolved phosphate and ammonium concentrations downslope revealed that more products from organic matter mineralization accumulated in the lower beach. The related increase in total alkalinity downslope indicated that the part of anaerobic processes in organic matter oxidation was higher in the lower beach. Concentration and δ¹³C of dissolved inorganic carbon in pore waters suggested that the carbon mineralized in pore waters came from marine plant debris that were mixed with the sand. Continuous probe records of dissolved oxygen saturation and vertical profiles revealed a tidally-driven dynamics of pore water in the first centimetres of the lower beach aquifer. Ventilation of pore waters corresponded to wave pumping and swash-induced infiltration of seawater in the upper 10–20 cm of sediment. Nutrients and reduced compounds produced through organic matter mineralization remained stored in pore water below the layer disturbed by wave. The flux of these components to seawater is possible when this interface is eroded, for example when wave energy increases after a less energetic period. The low extension of the studied aquifer, typical of pocket beaches, limits the connection with continental groundwater. Both tidally-driven and wave-driven recirculation of seawater allows pocket beaches to be efficient bioreactors for marine organic matter mineralization. As such, they provide the coastal environment with recycled nutrients, and not new nutrients.
View
... Cryogenian ice-covered oceans were probably low productivity, because photosynthesis in the marine realm was greatly diminished (Hawes et al., 2018). In the modern Black Sea, a low-productivity anoxic deep basin, the alkalinity production rate is~100 g/(m 2 ·yr) or~164 g/ (m 2 ·yr) CaCO 3 (Kempe, 1990), which, scaled up, would equate with an alkalinity production rate of~3.6 × 10 16 g/yr for Cryogenian anoxic deep oceans. ...
View
Entrapment and transformation of post-bloom radiolarians in cyanobacterial mats as a factor enhancing the formation of black cherts in the Early Silurian sea
Article
  • Feb 2020
Black radiolarian cherts are widespread in the lithological records of the Silurian; however, the processes governing their formation remain unclear. Analyses of Early Silurian cherts of Poland have revealed that they are composed of degraded remains of cyanobacterial mats enclosing variable numbers of dissolved radiolarian tests. In optical and scanning electron microscope (SEM) images, this cyanobacterial necromass, containing entrapped radiolarians and forming massive or laminated cherty deposits, exhibits a complex taphonomic and diagenetic history. These cyanobacterial mats underwent syndepositional to early diagenetic silicification in a peculiar environment which was highly enriched with dissolved silica, due mainly to a massive deposition of opaline tests of post-bloom radiolarians, which settled on mats covering large areas of the sea bottom. It is assumed that precipitation of the chert precursor silica occurred in the highly porous mats and, to a great extent, was governed by the activity of sulfate-reducing bacteria (SRB), which resulted in changes in pH in the mat profile. This process was a key factor governing the dissolution of the radiolarian tests and subsequent reprecipitation of dissolved radiolarian silica in the mats' microenvironment. Photosynthesis carried out by cyanobacteria and the decompositional activity of sulfate-reducing bacteria resulted in: i) a shift of the oxygen gradient below the mat, and ii) strong pH fluctuation within the mat profile. During the first stage of bacterial degradation of the cyanobacterial necromass (SRB I stage), an increase in pH caused dissolution of the radiolarian tests. During the second stage of bacterial degradation (SRB II stage), as the decomposition of organic matter proceeded, a significant amount of organic acid was produced, causing a reduction in pH in the mat interior. Presumably this triggered rapid silica precipitation from the pore waters, which were highly saturated with silica. The availability of radiolarian tests and the rate of their dissolution was therefore a key factor governing the rate of silicification in Early Silurian cyanobacterial mats.
View
The interaction of recovery and environmental conditions: An analysis of the outer shelf edge of western North America during the Early Triassic
Article
  • Jan 2019
  • PALAEOGEOGR PALAEOCL
Biotic recovery from the Permian-Triassic mass extinction was complex and uneven, with prior studies typically revealing a long, drawn-out recovery that was either delayed for some interval, or was subdued and stepwise in nature. Examples of rapid recovery at the outcrop scale cloud this narrative and point to the importance of environmental stresses in determining the timing and shape of recovery. The Union Wash Formation at the Darwin locality (east-central California) contains at least 3 recovery intervals that terminate with the onset of deleterious conditions and therefore offers a means to examine the relationship between environmental stress and recovery. The first recovery is manifested as bioturbated (ii = 5–6), shallow marine micritic limestones that contain small diameter (2–4 mm) Thalassinoides burrows that form complex networks. This interval is overlain by 650.5 m of laminated mudstone that signal deleterious environmental conditions. The second recovery interval begins directly above seafloor precipitate-bearing micritic limestones that make up the lowermost 130 m of the upper member of the Union Wash Formation and is marked by the occurrence of a 3 m-thick interval containing sphinctozoan sponges, an intervening ~1 m-thick laminated (ii = 1) micritic limestone, and an overlying, 5 m-thick bivalve-rich and bioturbated calcareous siltstone (ii = 4–5) that contains Chrondrites trace fossils. This interval is overlain by 18 m of laminated green shale (ii = 1) that signifies another incursion of anoxic waters. The third recovery interval is represented by a 30 m-thick unit that includes beds of micritic limestone, fossiliferous limestone containing transported fossil grains (including bivalves, microgastropods, sphinctozoan sponges, microgastropods, flat clams, and terebratulid brachiopods), flat pebble conglomerate and vermicular limestone. The results of this study, therefore, point to an uneven recovery within the Union Wash Formation, in which an initially robust recovery in the lower member deteriorated across the remainder of the study section. Areas exposed to persistent environmental stress, therefore, demonstrate protracted and complex recoveries. Study localities located within the habitable zone instead exhibit accelerated recoveries during the post-extinction interval and are indicative of an environmental bias in the form of persistent favorable conditions. The most accurate measures of post – extinction recovery, therefore, are those that examine biotic trends over a broad geographic area, and, as a result, incorporate the role of environmental stress in determining when and how life recovered from the Permian – Triassic mass extinction.
View
View
Biocalification through time: environmental challenge and cellular response
Article
Full-text available
  • Jun 1985
A concept explaining biocalcification as a form of calcium detoxification is advanced using geochemical and paleontological criteria. The first appearence of calcareous skeletons at the turn of the Precambrian/Cambrian is interpreted as a biotic response to a gradual rise of Ca2+ in world ocean resulting in Ca2+ stress environments in shelf areas. Periodic appearance in the Phanerozoic record of heavily calcified marine biota, absent or relic in modern seas, suggests considerable temporal fluctuations of calcium concentrations in the ancient ocean. Temporal changes in Ca2+ and mineral nutrient contents in the environment can thus be seen as overriding factors in the evolution of organisms.
View
View
View
Stratified waters as a key to the past
Article
  • Aug 1976
Density stratification in lakes and oceans generate anoxic conditions below the pycnocline, and sediment facies mirror this development. A comparison of modern sediments deposited in stratified and non-stratified waters with sediments formed since the Cambrian reveals that the ancient sea has been stratified a number of times.
View
The carbonate system in the western Mediterranean Sea
Article
  • Dec 1979
  • Deep Sea Res
Measurements of the pH and total alkalinity have been made on waters collected in the western Mediterranean Sea. These results have been used to examine the elements of the carbonate system, HCO3−, CO32−, CO2, ΣCO2, PCO2, and specific alkalinity. The saturation of Mediterranean Gibraltar is supersaturated with respect to calcium carbonate. Our results for the saturation state (Ω) for Mediterranean waters are in good agreement with the results of Alekin (Geochemistry, 206, 239–242, 1972) and those calculated from the GEOSECS (Geochemical Ocean Sections) test station in the eastern Mediterranean. The saturation state of calcite and aragonite in deep Mediterranean waters in higher than that of deep North Atlantic waters.
View
Tracers in the Sea. Palisades: Lamont-Doherty Geol. Observ., Cotumbia Univ
  • Jan 1982
  • W Broecker
  • T.-H Peng
Broecker, W., Peng, T.-H.: Tracers in the Sea. Palisades: Lamont-Doherty Geol. Observ., Cotumbia Univ. 1982
  • Jan 1976
  • NATURE
  • E T Degens
  • P Stoffers
Degens, E. T., Stoffers, P.: Nature 263, 22 (1976)
  • Jan 1985
  • 15
  • J Kazmierczak
  • V Degens
Kazmierczak, J., 2ttekkot, V., Degens, E. T.: Pal~ont. Z. 59 (1 -2), 15 (1985)
  • Jan 1974
  • 249
  • K M Shimkus
  • V V Trimonis
Shimkus, K. M., Trimonis, V. V.: Am. Ass. Pet. Geol. Mere. 20, 249 (1974)
in: Interactions of Biogeochemical Cycles in Aqueous Systems Pt
  • A Lein
  • Yu
  • M V Ivanov
  • M V Vainshtein