Content uploaded by Andrey V. Gebruk
Author content
All content in this area was uploaded by Andrey V. Gebruk on Jul 27, 2020
Content may be subject to copyright.
Methane gas Seeps Along the Oxic/Anoxic Gradient in the Black Sea: Manifestations, Biogenic Sediment Compounds and Preliminary Results on Benthic Ecology
Abstract
. Sediment parameters (grain size, organic content, chloroplastic pigments, Adenylates, Potential hydrolytic activity and electron transport system activity) and benthic biota were studied in methane seep area south-west of the Crimean Peninsula in the Black Sea over a depth range from 60 to 260m. A control transect with similar depths was performed in an adjacent nonseep area. Methane seepage in this region occurs from 35 to ˜ 85m depth, passing the oxic anoxic interface zone at 130 to 180m. The methane seep areas were characterized by abundant carbonate precipitates which occurred in various shapes from small, flat structures to tall chimneys with increasing anoxia. The carbonates were associated with distinct bacterial mats. Most of the measured biochemical parameters in the sediment were quite similar in the seep and nonseep areas. The content of organic matter was higher and grain size was more uniform in the nonseep areas. However, the seep areas were charaterized by highter proportions of the larger fauna (size classes 0.5–1 mm and ≥ 1mm) as well as increased total numbers of benthic fauna in the suboxic and upper anoxic zone. The animals did not show any seep-specific adaptations. In addition to methane seepage, highly variable hydrochemical and sedimentary conditions on the lower shelf and upper slope may also play an important role in structuring the composition and distribution of the benthic fauna.
... The formation of authigenic carbonates as a result of continuous and widespread seafloor seepage of methane (cf. Ritger et al., 1987) has been described in detail from numerous localities of the Black Sea including the Romanian, Ukrainian, and Crimean shelves, and the eastern Black Sea (Shnukov et al., 1995;Luth et al., 1999;Peckmann et al., 2001;Mazzini et al., 2004;Reitner et al., 2005;Bahr et al., 2009Bahr et al., , 2010. Black Sea seeps provide niches on the seafloor for diverse chemosynthesis-based microbial communities, whose metabolisms produce voluminous amounts of authigenic carbonate including spectacular build-ups growing up to several meters from the seafloor into the anoxic water column (Michaelis et al., 2002). ...
... Seep carbonates analyzed for this study were collected from the Ukrainian Shelf in the northwestern Black Sea located to the west of the Crimean Peninsula, and from the Dolgovskoy Mound located in the northern Black Sea (Fig. 1). The former locality was investigated by two research cruises in 1993 and 1994 that conducted hydro-acoustic surveys, analyses of sediment geochemistry, and faunal analyses in the Dnjeper Canyon region southwest of the Crimean Peninsula (Luth et al., 1999). The Ukrainian Shelf features hundreds of active seepage sites that occur along the shelf edge at water depths between 30 and 800 meters (Ivanov et al., 1991). ...
... The Ukrainian Shelf features hundreds of active seepage sites that occur along the shelf edge at water depths between 30 and 800 meters (Ivanov et al., 1991). Subsequent detailed investigations discovered active microbial communities, methane-derived seep carbonates, and the presence of seep-endemic benthic chemosynthetic communities (Lein et al., 1995;Pimenov et al., 1997;Luth et al., 1999). The methane seeps from the Ukrainian Shelf region are located at the deeper end of the permanent halocline that separates the brackish oxygenated surface waters from the deeper, anoxic, highly saline waters below a water depth of about 200 meters (Sorokin, 1982;Oguz and Besiktepe, 1999). ...
Trace elements are widely used to constrain environmental conditions and biogeochemical processes through geologic time. Authigenic carbonates in particular are a reliable archive due to their ability to take up and store trace elements over long periods of time. This comparative study presents new data on the effect of ambient redox conditions on trace element distributions in authigenic seep carbonates forming in different geochemical and hydrographic environments. Carbonates from shallow and deep-sea hydrocarbon seeps of the Black Sea are compared to seepage sites from the northern Gulf of Mexico and the northern South China Sea, revealing that trace element inventories are to some extent site-specific and depend on carbonate mineralogy. Strongly euxinic conditions at Black Sea deep-water seeps favor the formation of low-magnesium calcite, whereas fluctuating redox conditions favors aragonite cement precipitation. The trends in mineralogy are accompanied by distinct enrichments and depletions of specific trace elements including uranium, iron, and manganese. Aragonite cements exhibit lower magnesium to strontium ratios and manganese contents than their low-magnesium calcite counterparts. Moreover, trace elements in Black Sea carbonates are enriched in barium, manganese, zinc, and nickel, and are depleted in iron. The new trace element data suggest that the presence of dissolved sulfide influences carbonate mineralogy, and, accordingly, trace element speciation and content. The results of this study have implications for trace element-based paleoenvironment reconstructions beyond seep environments, and may initiate a reassessment of authigenic carbonates as a trace element archive, in particular for carbonates from ancient and modern euxinic environments.
... Sequence S3 is characterized by the presence of paleochannels that frequently have gas deposits (Fig. 4, Giagante et al., 2008). Evidence of acoustic turbidity has been recorded in sediments at gas concentrations lower than 1% whereas acoustic blanking evidence is related to larger gas concentrations in sediments (Magariñoz-Alvarez et al., 2002). The most important controlling factor of gas accumulation, both in lateral and vertical sense, is stratigraphy (Magariñoz-Alvarez et al., 2002;Weschenfelder et al., 2016). ...
... Evidence of acoustic turbidity has been recorded in sediments at gas concentrations lower than 1% whereas acoustic blanking evidence is related to larger gas concentrations in sediments (Magariñoz-Alvarez et al., 2002). The most important controlling factor of gas accumulation, both in lateral and vertical sense, is stratigraphy (Magariñoz-Alvarez et al., 2002;Weschenfelder et al., 2016). The seismic stratigraphic column in the inner zone of BBE estuary is characterized by five Late Pleistocene-Holocene seismic sequences (Aliotta et al., 2014), which have been described following the order of their Fig. 4. Shallow gas was found in sequence S5 and originated from sequence S3. ...
... Although Dando et al. (1994) study performed in Denmark and Judd et al. (2002) study performed in England were both carried out at shallow depths, they are hardly comparable with ours because they were conducted in beach and intertidal environments with gas seepages and methane-derived carbonate cementation. Most of the studies on the benthic effects of gassy sediments report enrichment in diversity as a result of the presence of hard sediments (Dando and Hovland, 1992;Jensen et al., 1992;Dando et al., 1994) or a benthic methane-dependent fauna (Dando et al., 1991a;Luth et al., 1999). However, in gas seepages from an intertidal area of Torry Bay, Judd et al. (2002) observed that seepages seem to have no effects on faunal composition and diversity. ...
... Cavity/conduit-fillings, such as those here described from limestone blocks of the Stirone River, are good sites for microbial recovery. In methane-derived, modern carbonates from the Black Sea shelf microcavities and conduits, similar to those recovered from the Stirone limestones, are filled or lined by abundant microbial aggregates that are mostly assigned to orders of methanogenic bacteria (Luth et al., 1999;Peckmann et al., 2001). We interpret the described fossil structures as the ancient counterparts of these extant microbial communities. ...
... We interpret the described fossil structures as the ancient counterparts of these extant microbial communities. The suggested capability of methane-metabolizing archaea to induce carbonate precipitation via anaerobic oxidation of methane (see discussion in Luth et al., 1999) may convincingly link, in the fossil example discussed here, microbes mineralized in carbonate phases and conduits. Further evidence of anaerobic conditions is the abundance of pyrite (especially around the conduits), probably derived from bacterial sulphatereduction. ...
Chemosynthetic-generated (non-hydrothermal) geological bodies abound on Earth since at least the Paleozoic and mostly derive from hydrocarbon gases such as methane, which is the main component of gas hydrates. Because of the abundance of hydrocarbons in the Solar System, it is likely that methane degassing, perhaps stored as hydrate, can occur in other planetary bodies apart from Earth. Similarly to what is described on Earth, where present and past chemoautotrophically-based communities belong to peculiar "island" ecosystems associated with methane or sulfide-rich fluids source, other planetary bodies (especially Mars) may have harbored extinct biota in such environments. This assumption is based on the independence of modern chemosynthetic biota from Earth-like ambient conditions, such as free oxygen and light, as well as the presence of microbial communities that are only sustained by the products of cold seepage. In cold seep-derived carbonate bodies from Morocco and Italy we have described microbial structures from different geologic age and environmental settings. Three-dimensional stromatolite structures, mineralized into iron oxides (hematite), are extensively recovered in recrystallized authigenic carbonates of Silurian age (Morocco), and are attributed to Beggiatoa-like colonies similar to those that abound in present-day areas with active hydrocarbon seepage. Well-preserved microbial structures in form of mucilage and three-dimensional webs have also been isolated from upper Tertiary, methane-derived carbonates (Italy). These structures are contained in cement phases that form irregular calcite layers partially filling voids and pre-existing gas conduits. They are interpreted as derived from anaerobic bacterial oxidation of methane, and a further evidence of anaerobic conditions is the abundance of pyrite of a probable bacterial sulfate-reduction derivation. Microbial morphologies of different nature can therefore be preserved and detected in mineral compounds embedded in methane-derived carbonate phases. Thus, because the size of these terrestrial geologic bodies produced by cold gases can be sufficiently large to be detectable by remote-sensing techniques, they would appear as reliable terrestrial analogues supplied with exobiological potential.
... Flora: none. Selective literature: Luth et al., 1995Luth et al., , 1998Luth et al., , 1999 Peckmann et al., 2001; Wenzhofer et al., 2002; Micu ,2008. Correspondence with Palearctic Habitats: PAL.CLASS.: 11.26: Communities of marine invertebrates and algae colonizing the bottom and sides of caves situated under the sea or the sublittoral part of caves having an entirely, periodically or partly submerged opening. ...
... There are 5 Natura 2000 elemental habitats in the reserve of which more important are: 5. Methanogenic submerged structures from Sfantu Gheorghe (ROSCI0237). Present in the NW Black Sea between 35 and 784m of depth, the methanogenic carbonate structures extend well beyond the oxic/anoxic interface characteristic for this sea (Luth et Luth, 1995, Lutz et al., 1998, Luth et al., 1999, Peckmann et al., 2001, Wenzhofer et al., 2002). The shallowest methane seeps occur off the Danube Delta Biosphere Reserve, which offers the opportunity of an integrated management. ...
... The most plausible explanation of the observed patterns in mineral phase and element composition of the cements may lie in the unique seawater chemistry of the Black Sea. The Black Sea exhibits sulphidic conditions from a water depth below 100 m, and sulphide concentration increases with depth reaching more than 400 lM at about 2000 m water depth (Luth et al., 1999;Neretin et al., 2001;Hiscock & Millero, 2006;Eckert et al., 2013). Sulphide is a significant factor that controls the composition of Mg-bearing Ca carbonate minerals. ...
Climate change poses a significant challenge for life on Earth. Different climate modes have been shown to come along with changes of the magnesium/calcium (Mg/Ca) ratio of seawater, and such changes are believed to control the primary mineral phase of marine authigenic carbonates. However, factors controlling marine carbonate phases other than seawater Mg/Ca ratios exist. Fibrous cements forming at methane seeps in the Black Sea provide new insight into the factors governing elemental and mineral phase compositions of fibrous carbonates. In this study, the distribution of aragonite and fibrous Mg calcite cements from three seep sites in the Black Sea is described as a function of water depth. The Mg/Ca ratio of seawater, as well as the ratio in shallow pore water, is close to four at the examined sites. Fibrous Mg calcite postdated aragonite cement in seep carbonates from shallow water depth of 120 to 190 m, whereas Mg calcite is the only cement at a greater depth of ca 2000 m. The primary formation of fibrous Mg calcite is confirmed by its zonation under cathodoluminescence, crystal morphologies agreeing with competitive growth, uniformly distributed MgCO 3 contents and precipitation in equilibrium with local conditions calculated from δ ¹⁸ O values. The MgCO 3 contents (4.5 to 12.2 mol%) are negatively correlated with δ ¹³ C values, indicating that the incorporation of Mg into the calcite crystal structure was favoured by high concentrations of sulphide generated by sulphate‐driven anaerobic oxidation of methane. Unlike open oceanic basins, stratification in the Black Sea leads to euxinic conditions in the deeper water column, favouring fibrous Mg calcite formation. This observation is consistent with sulphide catalysis as a critical agent for the formation of low‐Mg calcite to very high‐Mg calcite at high Mg/Ca ratios and is possibly relevant to carbonate cements forming during times of oceanic euxinia.
... They mostly belong to two main groups. A first one deals with deposits formed below the water-sediments interface as porous plates of carbonate-cemented sediments, irregular crusts, smooth lenticular concretions, flat pancake-shaped deposits, and large metricsized tabular constructions (Luth et al., 1999;Peckmann et al., 2001;Lein et al., 2002;Michaelis et al., 2002). A different situation is observed where carbonates can grow in the water column, forming high accumulations and, in some places, tower-like constructions that can reach several meters in height Lein et al., 2002;Michaelis et al., 2002). ...
... The present ANME lipid analysis supports this interpretation by revealing extremely 13 C-depleted branched-chain amino acids and isoprenoid lipids ( Fig. 3; Supplementary Fig. S4). 44 . Please see the Supplementary Movie S1 for methane venting from carbonate chimneys. ...
Abstract Oceanic methane from global deep-sea sediment is largely consumed through microbially mediated sulfate-coupled oxidation, resulting in 13C-depleted cell biomass of anaerobic methanotrophic archaea (ANME). The general ecological importance of subseafloor ANME has been well recognized in the last two decades. However, the crucial biochemical pathways for the overall anaerobic oxidation of methane (AOM) still remain enigmatic. Here, methanotrophic pathways were analyzed to trace 13C-depleted amino acid biosynthesis in two clades of ANME (ANME-1 and ANME-2) from the Black Sea. Compound-specific analysis of ANME-dominated microbial mats showed a significant 13C-depletion trend in association with increasing carbon numbers in protein-derived amino acid families (e.g., the pyruvate family in the order of alanine, valine, isoleucine and leucine was down to −114‰). This result indicates a stepwise elongation of 13C-depleted carbon during amino acid biosynthesis. The overall results suggest that intracellular protein amino acids and the most 13C-depleted signature of leucine, which has a specific branched-chain structure, are potentially propagated as isoprenoid precursor molecules into archaeal biosynthesis, resulting in the extremely 13C- and 14C-depleted nature of ANME cells in the deep microbial oasis.
... The analyses of cores retrieved in active seeps located in the innermost part of the San Simón Bay (inner area), indicate that the up-ward migration of methane associated to seeps and pockmarks increases the methane concentration in the SRZ (Martínez-Carreño, 2015). Similar results were also noted by Ivanov et al. (1998) and Luth et al. (1999) in the Black Sea sediments. Martens and Klump (1980) suggested that in coastal sediment with high organic matter sedimentation rates, the SRZ would not be efficient enough to trap all the methane flux, and the methane could reach the sediment surface by diffusion or facilitated by bioirrigation or ebullition. ...
High-resolution seismic profiles, gravity core analysis and radiocarbon data have been used to identify the factors behind the methane production and free gas accumulation in the Ría de Vigo. Lithological and geochemical parameters (sulfate and methane concentration) from seventeen gravity cores were analyzed to characterize the sediment of the ria. The distribution of methane-charged sediments is mainly controlled by the quantity and quality of organic matter. Geochemical analyses reveal minimum methane concentrations ranging between 1 µM to 1 mM in sediments located outside the acoustic gas field, while gas-bearing sediments, show methane concentrations up to 5 mM.
Analysis of NOAA 11 satellite images (April-August 1993) and CTD measurements carried out from aboard the R/V Akvanavt on June 16-17, 1993, over the continental slope west of Sevastopol, showed that two anticyclonic eddies can exist together without coalescing in the 0-to 300-m layer. One of the eddies was a quasi-stationary one, while the other had a comparatively short lifetime (1.5 months). The diameters of the eddies were 90 and 55 km, respectively. Collapse of the less intensive anticyclone occurred when it was displaced to the shelf area by a quasi-stationary eddy. The formation of a cyclone north of the anticyclonic pair of eddies when they draw together leads to the appearance of counterflow streams between the eddies of different signs both in the upper layer (0-150 m) and at greater depths with the core of the stream located at a depth of 150 m. This facilitates horizontal exchange between the shelf and the open part of the sea.
Hydrocarbon-based communities occur in connection with gas-related seabed features, pockmarks and 'mottled' seabed. Sediments beneath the larger patches of 'mottled' seabed are gas-charged and it is assumed that slow seepage (micro-seepage) of pore-water and hydrocarbons occurs from these. The distribution of the benthos, nekton, and plankton associated with 'mottled' seabed in the Tommeliten area and specific pockmarks in the Holene and Gullfaks areas was studied by video-tape recordings. Besides the faunal elements, biogenic sedimentary structures were recorded.
We report the first discovery and sampling of a methane-hydrogen sulfide rich “cold seep” from the Makran accretionary prism off Pakistan (Arabian Sea). A variety of cm- to m-scale pockmarks and gas seepage structures were identified from underwater TV-photo sled profiles crossing the oxygen minimum zone (OMZ), related to highresolution seismic (PARASOUND) records. From the seeps isotopically light, bacterially formed methane is emanating that is partly oxidized to HCO3− in the bacterial sulfate reduction zone. This results in the precipitation of irregular dark-gray to black crusts of indurated authigenic carbonates, mainly cryptocrystalline magnesian calcite and Ca-rich dolomite, near the sediment/seawater interface within the OMZ. Downcore, the crusts grade into hemipelagic carbonate-poor silty clays with transitional lithologies in between. Similar to the pockmark carbonates from the Oregon margin and in the North Sea, the authigenic carbonates are extremely depleted in 13C (δ13Ccarbonate < − 40%.). This suggests that they were derived from bacterial methane (δ13Cmethane: − 77.8%.) that was oxidized under anaerobic conditions. The authigenic carbonates are associated with white fluffy mats of chemoautotrophic H2S-oxidizing bacteria.Small pockmarks appear to be concentrated at small-scale escarpments, suggesting focussed fault-controlled pore fluid expulsion due to the tectonic dewatering and degassing of the accretionary prism, whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes.
Exploration of the northern Peruvian subduction zone with the French submersible 'Nautile' has revealed benthic communities dominated by new species of vesicomyid bivalves (Calyptogena spp. and Vesicomya sp.) sustained by methane-rich fluid expulsion all along the continental margin, between depths of 5140 and 2630 m. Videoscopic studies of 25 dives ('Nautiperc' cruise 1991) allowed us to describe the distribution of these biological communities at different spatial scales. At large scale, the communities are associated with fluid expulsion along the major tectonic features (scarps, canyons) of the margin. At a smaller scale on the scarps, the distribution of the communities appears to be controlled by fluid expulsion along local fracturation features such as joints, faults and small-scale scars. Eight dives were made at one particular geological structure, the Middle Slope Scarp (the scar of a large debris avalanche) where numerous clam beds have been discovered. The spatial distribution of the chemosynthetic communities on this scarp indicates extensive fluid expulsion, but the low clam densities and low faunal diversity in clam beds and the presence of dead beds suggest fluid expulsion is temporally irregular. An exceptionally large clam field was observed at the bend of this scarp at the intersection of 2 faults. It extends for about 1000 m(2) with the biomass of bivalves as high as 30 kg m(-2) wet weight without shells. A strong and regular fluid flow, estimated at 400 m yr(-1), is required at this location to generate such a high chemosynthetic primary production. Temperature anomalies in the sediment were measured in situ in the main field and compared to clam density. The distribution of the bivalves at the metre scale is likely related to local variations in fluid flow and in fluid expulsion patterns controlled by the nature of the subsurface sediment. Exceptionally large and densely distributed serpulids (Neovermilia n. sp.) were arranged in clumps of 20 to 30 m(2), and covered 200 m(2) of the field. Their abundance may be related to the filtration of chemoautotrophic free-living bacteria. Another 22 non-symbiotic species displaying various trophic strategies have been sampled or observed, and 5 are still undescribed new species. The resulting community structure is more complex than in other subduction systems described so far.
The results of measurements of the concentrations of Cs-137 and Co-60 in the bottom sediments of the northwestern part of the Black Sea indicate the inhomogenity of their distribution both over the studied area and over the core depth. The intermittency of the layers with different concentration of radionuclides in the cores reflects the active horizontal movements and redistribution of sediments on the shelf and continental slope. As a result, the sedimentary layers, dated by the Chernobyl mark as seven years old, were found in the 5- to 7-cm depth layer from the sediment surface. The maximum Cs-137 concentration in the surface sedimentary layer on the shelf was 42 mBq/g. The maximum Co-60 concentration of 1320 mBq/g was due to a hot particle. No correlation was found between the Cs-137 and the Co-60 contents.
The bottom water in local areas of Limfjorden (Denmark) frequently becomes anoxic during warm summer periods. The water may be stagnant for one to several weeks due to stratification in temperature and salinity. The anoxia stimulates the anaerobic metabolism in the sediment and H2 S accumulates. Normally the H2 S does not penetrate up into the bottom water because the ferric iron pool functions as a buffer binding the transient excess of sulfide as FeS and perhaps FeS2. Benthic animals react to the lack of oxygen by creeping out of the mud and may survive lying on the mud surface. Mussel beds increase the benthic respiration per m2 ten fold and thereby enhance oxygen depletion of the bottom water. Their high metabolic rate may thus regulate the size of the mussel beds to the limit at which animals in the center become choked. A survey is presented of the frequency and distribution of anoxia which leads to mass mortality of the bottom fauna in Limfjorden. Due to the seasonal oxygen depletion, the composition of the benthic community is in some areas regulated by alternating sequences of extinction and recolonization. /// Донная вода в некоторых участках Лимфъорден (Дания) часто становится бескислородной во время жаркого летного периода. Вода может бытъ стоячей в течение одной или несколъких неделъ в резулътате стратификации по температуре и солености. Отсутствие кислорода стимулирует анаэробный метаболизм в осадке и аккумуляцию H2 S. Обычно H2 S не проникает в донную воду в резулътате того, что железистый пул функционирует как буфер, связывающий избыток сулъфидов FeS и вероятно FeS2. Бентосные животные реагируют на отсутствие кислорода тем, что они выходят из ила и переживают этот пернод на его поверхности. Скопления моллюсков повышают респирацию бентоса в 10 раз, но таким образом увеличивают кислородное истощение в донной воде. Их высокая метаболическая активностъ может таким образом регулироватъ размеры агрегаций до пределов, за которыми животные задыхаются в цетре. Дан обзор частоты и характера распространения кислородного истощения, которое приводит к массовой гибели донной фауны в Лимфъорден. В резулътате сезонного кислородного истощения сгруктура бентосного сообщества в некоторых участках регулируется путем последователъной смены вымирания и реколонизации организмов.
Satellite and in situ data are utilized to investigate the mesoscale dynamics of the Black Sea boundary current system with special emphasis on aspects of transport and productivity. The satellite data are especially helpful in capturing rapid sub-mesoscale motions insufficiently resolved by the in situ measurements.Various forms of isolated features, including dipole eddies and river plumes, are identified in the satellite images. Unstable flow structures at these sites appear to transport materials and momentum across the continental shelf. Species differentiation and competition are evident along the boundary current system and at the frontal regions during the development of early summer productivity.A time series of Coastal Zone Colour Scanner (CZCS) images indicate dynamical modulation of the springtime surface productivity in the southern Black Sea. Unstable meandering motions generated at Sakarya Canyon propagate east with speeds of ∼10–15 km d−1. Within weeks, a turbulent jet is created which separates from the coast, covering the entire southwestern sector. The nutrients driving the phytoplankton production (mainly Emiliana huxleyi) of the current system evidently originate from fluvial discharge entering from the northwestern region including the Danube river. The productivity pattern develops in early summer when the Danube inflow is at its peak, and through meandering motions spreads into an area several times wider than the continental shelf.In 1980, the CZCS data, and in 1991 and 1992, the Advanced Very High Resolution Radiometer (AVHRR) data indicate patches of upwelling along the west Anatolian coastline between Sakarya Canyon and Cape İnce (Ince Burun) in summer. The upwelling phenomenon is outstanding because it occurs on a coast where normally the surface convergence near the coast implies downwelling, and under conditions of unfavorable winds.In 1992, the hydrographic data indicated the upwelling to be the result of a surface divergence of the boundary current, and sequences of satellite data indicate the role of transient dynamics. The in situ data showed the upwelling centres to be devoid of phytoplankton as well as fish eggs and larvae.The AVHRR and in situ hydrographic data in winter 1990 indicate cold water is formed over the entire western Black Sea continental shelf. The band of cold water decreases in width as it moves south and impinges on the headland at Baba Burnu, where it undergoes a sudden expansion. The maximum winter phytoplankton bloom sampled during the same period indicates explosive populations of diatoms following the band of cold water.
Sediments off northwest Africa were assayed for activity of the respiratory electron transport system (ETS) and for primary amino nitrogen. ETS activities were used to compute respiratory oxygen consumption, carbon oxidation, and nitrate reduction rates. Activities were correlated with depth of the water column, and their longshore distribution resembled that of euphotic zone phytoplankton productivity. Protein concentrations were closely correlated with ETS activities. Carbon biomass was calculated from protein and compared with other computed values. The carbon oxidation rates accounted for 13% of the region's primary production.