Radionuclide measurements in sediments and water of the Kara Sea

In this report, the results of a 2000-2001 radiogeoecological investigation are presented for the region of the Ob and Yenisei estuaries and the adjacent Kara Sea. In order to study the behaviour and migration of Cs, Sr and Pu radionuclides in a river - sea system experimental research on the distribution of these radionuclides in the water column and surface sediments has been carried out. In addition, the role of suspended and dissolved organic matter on the behaviour of radionuclides in water solutions has been studied. The 137Cs and 239,240Pu concentrations in the upper 0-2cm layer of the sediments varied between 1,4 and 50,0 Bq/kg, with a mean of 12,4 Bq/kg, and between 0,065-1,96 Bq/kg, with a mean of 0,62 Bq/kg, respectively. There is a direct relationship of a specific radioactivity of 137Cs and 239,240Pu in the sediments and the content of clay fraction. The 137Cs, 90Sr and 239,240Pu concentrations in the water samples varied between 0,4 and 7,0 Bq/m**3 (mean of 3,6 Bq/m**3), 0,4 and 9,7 Bq/m**3 (mean of 3,3 Bq/m**3), and 0,01-0,3 Bq/m**3 (mean of 0,02 Bq/m**3), respectively. In the water samples the concentration of the water-soluble species l37Cs increases with increasing salinity, whereas the concentration of the 90Sr-radionuclide decreases with increasing salinity. This may be related to the physico-chemical behaviour of these radionuclides in water solutions and the influence of several sources on radioactive pollution in this basin. In sea water the suspended matter may absorb up to 10% 137Cs, 90Sr and 239,240Pu, in river water samples these values may reach 15-30%. More than 50% 90Sr and 239,240Pu is able to form complexes with dissolved organic matter. This effect is smaller in saline water. The comparison of the data of 137Cs radioactivity in the surface sediments in 1995 and 2000-2001 showed that the level of radioactivity has decreased.

(Table S1) Carbon and oxygen isotope values, and Mn and Sr concentrations of Early Jurassic sediments

For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ~2 per mil at the Sinemurian-Pliensbachian boundary, and a positive excursion of ~2 per mil in the Late Pliensbachian. The Sinemurian-Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic-rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian-Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large-scale, long-term and small-scale, short-duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.

Organic carbon isotope ratios of sea surface sediments and sea-ice from the Amerasian Continental shelf

Organic matter origins are inferred from carbon isotope ratios (delta13C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in delta13C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment delta13C, OC/N, and delta15N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C3 plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C4 and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment delta13C values (-16.5 to -13.6 per mil) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial-interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO2 and pCO2 in the Arctic Basin halocline.

The South Atlantic carbon isotope record of planktic foraminifera

We reviewed the paleoceanographic application of the carbon isotope composition of planktic foraminifera. Major controls on the distribution of d13C of dissolved CO2 (d13CSCO2) in the modern ocean are photosynthesis-respiration cycle, isotopic fractionation during air-sea exchange, and circulation. The carbon isotope composition of surface waters is not recorded without perturbations by planktic foraminifera. Besides d13CSCO2 of the surrounding seawater, the d13C composition of planktic foraminifera is affected by vital effects, the water depth of calcification and postdepositional dissolution. We compared several high-resolution (>10cm/ka) carbon isotope records from the Southern Ocean, the Benguela upwelling system, and the tropical Atlantic. In the Southern Ocean, carbon isotope values are about 1.2 per mil lower during the LGM and up to 1.7 per mil lower during the last deglaciation, when compared to the Holocene. These depletions might be explained with a combination of a subsurface nutrient enrichment and reduced air-sea exchange due to an increased stratification of surface waters. In the Benguela Upwelling system, waters originating in the south are upwelled. While the deglacial minimum is transferred and recorded in its full extent in the d13C record of Globigerina bulloides, glacial values show only little changes. This might suggest, that the lower glacial d13C values of high-latitude surface waters are not upwelled off Namibia, or that G. bulloides records post-upwelling conditions, when increased seasonal production has already increased surface-water d13C. Synchronous to the d13C depletions in high latitudes, low d13C values were recorded in Globigerinoides sacculifer during the LGM and during the last deglaciation in the nutrient-depleted western equatorial Atlantic. Hence, part of the glacial-interglacial variability presumably transferred from high to low latitudes seems to be related to changes in thermodynamic fractionation. The variability in d13C is lowest in the northernmost core M35003-4 from the eastern Caribbean, implying that the Antarctic Intermediate Water might have acted as a conduit to transfer the deglacial minimum to tropical surface waters.

(Table T1) Dissolved sulfide concentration and d34S of dissolved sulfate and sulfide in pore waters of ODP Leg 204

We report dissolved sulfide sulfur concentrations and the sulfur isotopic composition of dissolved sulfate and sulfide in pore waters from sediments collected during Ocean Drilling Program Leg 204. Porewater sulfate is depleted rapidly as the depth to the sulfate/methane interface (SMI) occurs between 4.5 and 11 meters below seafloor at flank and basin locations. Dissolved sulfide concentration reaches values as high as 11.3 mM in Hole 1251E. Otherwise, peak sulfide concentrations lie between 3.2 and 6.1 mM and occur immediately above the SMI. The sulfur isotopic composition of interstitial sulfate generally becomes enriched in 34S with increasing sediment depth. Peak d34S-SO4 values occur just above the SMI and reach up to 53.1 per mil Vienna Canyon Diablo Troilite (VCDT) in Hole 1247B. d34S-Sigma HS values generally parallel the trend of d34S-SO4 values but are more depleted in 34S relative to sulfate, with values from -12.7 per mil to 19.3 per mil VCDT. Curvilinear sulfate profiles and carbon isotopic composition of total dissolved carbon dioxide at flank and basin sites strongly suggest that sulfate depletion is controlled by oxidation of sedimentary organic matter, despite the presence of methane gas hydrates in underlying sediments. Preliminary data from sulfur species are consistent with this interpretation for Leg 204 sediments at sites not located on or near the crest of Hydrate Ridge.

Age model and chemistry of sediment core STK7 from Steisslinger See

Stable isotope records for carbon and oxygen in bulk carbonates, carbon in bulk organic matter, and for total and chromium-reducible sulfur in a lacustrine sediment core from Lake Steisslingen (Southwest Germany) show several distinct and abrupt shifts during the last 15,000 years. Variations in the isotopic composition of authigenic carbonates indicate two major phases in the lake history. In the pre-Holocene, the hydrological budget of the lake was apparently stable. Variations of delta18O values of authigenic carbonates were, therefore, dominantly controlled by temperature changes. A decrease in the delta18Ocarb values of about 2 per mil at the Allerød/Younger Dryas transition is interpreted as a drop in mean annual air temperatures of approximately 5°C. An abrupt temperature increase of a similar magnitude is inferred at the Younger Dryas/Preboreal boundary. Throughout most of the Holocene, the isotopic composition of authigenic carbonates was influenced by marked changes in the hydrological budget of the lake. A major positive excursion in the delta13Ccarb and delta18Ocarb values at the beginning of the Atlantic and a smaller one in the Preboreal were related to evaporation effects, which indicate that dry climatic conditions must have prevailed at that time. A simultaneous increase in delta13C values of bulk organic matter at the beginning of the Atlantic suggests a high level of productivity in the lake. As a consequence, aqueous sulfate became limited as indicated by variations in the delta34S values of total and chromium-reducible sedimentary sulfur. Therefore, we conclude that the beginning of the Atlantic was characterized not only by dry but also by warm climatic conditions, which triggered a higher productivity in the lake. In the Subatlantic sediments, large variations in carbon, oxygen, and sulfur isotope ratios were observed as a result of human activities, causing considerable perturbations in the biogeochemical element cycling of Lake Steisslingen. Results obtained by the study of the continuous 15 ka record of Lake Steisslingen document clearly that isotopic proxy data from lacustrine sediments can provide useful information on environmental and climatic changes of local, regional, and in the case of the Younger Dryas event, of even hemispherical significance.

Combined effects of ocean acidification and light or nitrogen availabilities on 13C fractionation in marine dinoflagellates

Along with increasing oceanic CO2 concentrations, enhanced stratification constrains phytoplankton to shallower upper mixed layers with altered light regimes and nutrient concentrations. Here, we investigate the effects of elevated pCO2 in combination with light or nitrogen-limitation on 13C fractionation (epsilon p) in four dinoflagellate species. We cultured Gonyaulax spinifera and Protoceratium reticulatum in dilute batches under low-light (LL) and high-light (HL) conditions, and grew Alexandrium fundyense and Scrippsiella trochoidea in nitrogen-limited continuous cultures (LN) and nitrogen-replete batches (HN). The observed CO2-dependency of epsilon p remained unaffected by the availability of light for both G. spinifera and P. reticulatum, though at HL epsilon p was consistently lower by about 2.7 per mil over the tested CO2 range for P. reticulatum. This may reflect increased uptake of (13C-enriched) bicarbonate fueled by increased ATP production under HL conditions. The observed CO2-dependency of epsilon p disappeared under LN conditions in both A. fundyense and S. trochoidea. The generally higher epsilon p under LN may be associated with lower organic carbon production rates and/or higher ATP:NADPH ratios. CO2-dependent epsilon p under non-limiting conditions has been observed in several dinoflagellate species, showing potential for a new CO2-proxy. Our results however demonstrate that light- and nitrogen-limitation also affect epsilon p, thereby illustrating the need to carefully consider prevailing environmental conditions.

(Figure 4) Stable carbon isotopic values and relative contents of biphytanes and sugars from sediment sample from the Peru margin and from the Pakistan margin

Glycolipids are prominent constituents in the membranes of cells from all domains of life. For example, diglycosyl-glycerol dibiphytanyl glycerol tetraethers (2Gly-GDGTs) are associated with methanotrophic ANME-1 archaea and heterotrophic benthic archaea, two archaeal groups of global biogeochemical importance. The hydrophobic biphytane moieties of 2Gly-GDGTs from these two uncultivated archaeal groups exhibit distinct carbon isotopic compositions. To explore whether the isotopic compositions of the sugar headgroups provide additional information on the metabolism of their producers, we developed a procedure to analyze the d13C values of glycosidic headgroups. Successful determination was achieved by (1) monitoring the contamination from free sugars during lipid extraction and preparation, (2) optimizing the hydrolytic conditions for glycolipids, and (3) derivatizing the resulting sugars into aldononitrile acetate derivatives, which are stable enough to withstand a subsequent column purification step. First results of d13C values of sugars cleaved from 2Gly-GDGTs in two marine sediment samples, one containing predominantly ANME-1 archaea and the other benthic archaea, were obtained and compared with the d13C values of the corresponding biphytanes. In both samples the dominant sugar headgroups were enriched in 13C relative to the corresponding major biphytane. This 13C enrichment was significantly larger in the putative major glycolipids from ANME-1 archaea (~15 per mil) than in those from benthic archaea (<7 per mil). This method opens a new analytical window for the examination of carbon isotopic relationships between sugars and lipids in uncultivated organisms.

Oceanographic data, oxygen and methane concentrations, and C-CH4 isotope ratios measured at Jaco Scar

Methane (CH4) concentrations and CH4 stable carbon isotopic composition (d13CCH4) were investigated in the water column within Jaco Scar. It is one of several scars formed by massive slides resulting from the subduction of seamounts offshore Costa Rica, a process that can open up structural and stratigraphical pathways for migrating CH4. The release of large amounts of CH4 into the adjacent water column was discovered at the outcropping lowermost sedimentary sequence of the hanging wall in the northwest corner of Jaco Scar, where concentrations reached up to 1,500 nmol L-1. There CH4-rich fluids seeping from the sedimentary sequence stimulate both growth and activity of a dense chemosynthetic community. Additional point sources supplying CH4 at lower concentrations were identified in density layers above and below the main plume from light carbon isotope ratios. The injected CH4 is most likely a mixture of microbial and thermogenic CH4 as suggested by d13CCH4 values between -50 and -62 per mil Vienna Pee Dee Belemnite. This CH4 spreads along isopycnal surfaces throughout the whole area of the scar, and the concentrations decrease due to mixing with ocean water and microbial oxidation. The supply of CH4 appears to be persistent as repeatedly high CH4 concentrations were found within the scar over 6 years. The maximum CH4 concentration and average excess CH4 concentration at Jaco Scar indicate that CH4 seepage from scars might be as significant as seepage from other tectonic structures in the marine realm. Hence, taking into account the global abundance of scars, such structures might constitute a substantial, hitherto unconsidered contribution to natural CH4 sources at the seafloor.

(Table 2) Carbonate chemistry and isotopes from northern Cascadia margin samples

Most authigenic carbonates previously recovered from the Cascadia slope have 87Sr/86Sr signatures that reflect shallow precipitation in equilibrium with coeval seawater. There is also evidence for carbonate formation supported by fluids that have been modified by reactions with the incoming Juan de Fuca plate (87Sr/86Sr = 0.7071; Teichert et al., 2005, doi:10.1016/j.epsl.2005.08.002) or with terrigenous turbidites (87Sr/86Sr = 0.70975 to 0.71279; Sample et al., 1993, doi:10.1130/0091-7613(1993)021<0507:CCICFF>2.3.CO;2). We report on the strontium isotopic composition of carbonates and fluids from IODP Site U1329 and nearby Barkley Canyon (offshore Vancouver Island), which have strontium isotope ratios as low as 0.70539. Whereas the strontium and oxygen isotopic compositions of carbonates from paleoseeps in the uplifted Coast Range forearc indicate formation in ambient bottom seawater, several samples from the Pysht/Sooke Fm. show a 87Sr-depleted signal (87Sr/86Sr = 0.70494 and 0.70511) similar to that of the anomalous Site U1329 and Barkley Canyon carbonates. Our data, when analyzed in the context of published elemental and isotopic composition of these carbonates (Joseph et al., 2012, doi:10.1016/j.palaeo.2013.01.012 ), point to two formation mechanisms: 1) shallow precipitation driven by the anaerobic oxidation of methane (AOM) with d13C values as low as -50 per mil and contemporaneous 87Sr/86Sr seawater ratios, and 2) carbonate precipitation driven by fluids that have circulated through the oceanic crust, which are depleted in 87Sr. Carbonates formed from the second mechanism precipitate both at depth and at sites of deep-sourced fluid seepage on the seafloor. The 87Sr-depleted carbonates and pore fluids found at Barkley Canyon represent migration of a deep, exotic fluid similar to that found in high permeability conglomerate layers at 188 mbsf of Site U1329, and which may have fed paleoseeps in the Pysht/Sooke Fm. These exotic fluids likely reflect interaction with the 52-57 Ma igneous Crescent Terrane, which supplies fluids with high calcium, manganese and strontium enriched in the non-radiogenic nucleide. Tectonic compression and dehydration reactions then force these fluids updip, where they pick up the thermogenic hydrocarbons and 13C-enriched dissolved inorganic carbon that are manifested in fluids and carbonates sampled at Barkley Canyon and at Site U1329. The Crescent Terrane may have sourced cold seeps in this margin since at least the late Oligocene.

(Appendix) Carbon and nitrogen isotope ratios of ODP Site 160-964

Nitrogen isotopes of chlorins, degradation products of chlorophyll, reflect the isotopic composition of nutrient N utilized by marine phytoplankton communities. Here we show that in sediments of the eastern Mediterranean Pleistocene and Holocene, values of d15N for chlorins and total nitrogen vary in concert, with a consistent offset of ~5 per mil reflecting the fractionation imparted during chlorophyll biosynthesis. Samples from the Integrated Ocean Drilling Program Sites 964 and 969 were analyzed at a sampling resolution of ~4-10 cm, clustered around sapropel events 2, 3, 4 and 5 (~100-170 ka). In low organic content sediments, chlorin values of ~0 per mil coincident with total nitrogen values of ~+ 5 per mil indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment. In sapropel horizons, the chlorin and total nitrogen values are 5 per mil more negative (~-5 per mil and ~ 0 per mil, respectively), resembling previously-reported, modern-day water-column particulates (~0 per mil). We suggest that nutrient conditions in the Eastern Mediterranean correspond to three scenarios and that the similarity between sapropel and modern-day bulk d15N is coincidental. Organic-poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of Atlantic-sourced nitrate. Sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine P fluxes to surface waters. Present-day conditions are dominated by anthropogenic N sources. These scenarios agree with a model of sapropel formation in which stratification caused by increased fresh-water inputs led to N fixation due to P:N nutrient imbalance. Enhanced production combined with stratification promoted and maintained anoxic deep waters, consequently increasing organic matter preservation. Such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans.

n-alkane carbon isotope ratios in plants and recent lake sediments from Cameroon

Trees and shrubs in tropical Africa use the C3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n-alkanes (e.g., n-C27 to n-C33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n-alkane d13C values are often used to reconstruct past C3/C4 composition of vegetation, assuming that the relative proportions of C3 and C4 leaf waxes reflect the relative proportions of C3 and C4 plants. We have compared the d13C values of n-alkanes from modern C3 and C4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C3 vegetation cover (fC3) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C3-dominated rain forest by C4-dominated savanna. The C3 plants analysed were characterised by substantially higher abundances of n-C29 alkanes and by substantially lower abundances of n-C33 alkanes than the C4 plants. Furthermore, the sedimentary d13C values of n-C29 and n-C31 alkanes from recent lake sediments in Cameroon (-37.4 per mil to -26.5 per mil) were generally within the range of d13C values for C3 plants, even when from sites where C4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C3 and C4 vegetation cover when using the d13C values of sedimentary n-alkanes, overestimating the proportion of C3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C3 and C4 plants. We therefore tested a set of non-linear binary mixing models using d13C values from both C3 and C4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the fC3 values as the minimum and maximum d13C values are approached, and a hyperbolic function that takes into account the differences between C3 and C4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed d13C values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert d13C measurements on sedimentary n-alkanes directly into reconstructions of C3 vegetation cover.

Molecular hydrogen (H2) mixing ratio and stable isotopic composition (dD) at the Cabauw tall tower in the Netherlands (2008-2012)

Measurements of the stable isotopic composition (dD(H2) or dD) of atmospheric molecular hydrogen (H2) are a useful addition to mixing ratio (X(H2)) measurements for understanding the atmospheric H2 cycle. dD datasets published so far consist mostly of observations at background locations. We complement these with observations from the Cabauw tall tower at the CESAR site, situated in a densely populated region of the Netherlands. Our measurements show a large anthropogenic influence on the local H2 cycle, with frequently occurring pollution events that are characterized by X(H2) values that reach up to 1 ppm and low dD values. An isotopic source signature analysis yields an apparent source signature below -400 per mil, which is much more D-depleted than the fossil fuel combustion source signature commonly used in H2 budget studies. Two diurnal cycles that were sampled at a suburban site near London also show a more D-depleted source signature (-340 per mil), though not as extremely depleted as at Cabauw. The source signature of the Northwest European vehicle fleet may have shifted to somewhat lower values due to changes in vehicle technology and driving conditions. Even so, the surprisingly depleted apparent source signature at Cabauw requires additional explanation; microbial H2 production seems the most likely cause. The Cabauw tower site also allowed us to sample vertical profiles. We found no decrease in (H2) at lower sampling levels (20 and 60m) with respect to higher sampling levels (120 and 200m). There was a significant shift to lower median dD values at the lower levels. This confirms the limited role of soil uptake around Cabauw, and again points to microbial H2 production during an extended growing season, as well as to possible differences in average fossil fuel combustion source signature between the different footprint areas of the sampling levels. So, although knowledge of the background cycle of H2 has improved over the last decade, surprising features come to light when a non-background location is studied, revealing remaining gaps in our understanding.

Particle fluxes of the bathypelagic sediment trap CVOO-3 in the eastern tropical North Atlantic for the period December 2009 until May 2011

Particle fluxes at the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic for the period December 2009 until May 2011 are discussed based on bathypelagic sediment trap time-series data collected at 1290 and 3439 m water depth. The typically oligotrophic particle flux pattern with weak seasonality is modified by the appearance of a highly productive and low oxygen (minimum concentration below 2 µmol kg**-1 at 40 m depth) anticyclonic modewater eddy (ACME) in winter 2010. The eddy passage was accompanied by unusually high mass fluxes of up to 151 mg m**-2 d**-1, lasting from December 2009 to May 2010. Distinct biogenic silica (BSi) and organic carbon flux peaks of ~15 and 13.3 mg m**-2 d**-1, respectively, were observed in February-March 2010 when the eddy approached the CVOO. The flux of the lithogenic component, mostly mineral dust, was well correlated with that of organic carbon, in particular in the deep trap samples, suggesting a tight coupling. The lithogenic ballasting obviously resulted in high particle settling rates and, thus, a fast transfer of epi-/meso-pelagic signatures to the bathypelagic traps. We suspect that the two- to three-fold increase in particle fluxes with depth as well as the tight coupling of mineral dust and organic carbon in the deep trap samples might be explained by particle focusing processes within the deeper part of the eddy. Molar C : N ratios of organic matter during the ACME passage were around 18 and 25 for the upper and lower trap samples, respectively. This suggests that some productivity under nutrient (nitrate) limitation occurred in the euphotic zone of the eddy in the beginning of 2010 or that a local nitrogen recycling took place. The d15N record showed a decrease from 5.21 to 3.11 per mil from January to March 2010, while the organic carbon and nitrogen fluxes increased. The causes of enhanced sedimentation from the eddy in February/March 2010 remain elusive, but nutrient depletion and/or an increased availability of dust as a ballast mineral for organic-rich aggregates might have contributed. Rapid remineralisation of sinking organic-rich particles could have contributed to oxygen depletion at shallow depth. Although the eddy formed in the West African coastal area in summer 2009, no indications of coastal flux signatures (e.g. from diatoms) were found in the sediment trap samples, confirming the assumption that the suboxia developed within the eddy en route. However, we could not detect biomarkers indicative of the presence of anammox (anaerobic ammonia oxidation) bacteria or green sulfur bacteria thriving in photic zone suboxia/hypoxia, i.e. ladderane fatty acids and isorenieratene derivatives, respectively. This could indicate that suboxic conditions in the eddy had recently developed and/or the respective bacterial stocks had not yet reached detection thresholds. Another explanation is that the fast-sinking organic-rich particles produced in the surface layer did not interact with bacteria from the suboxic zone below. Carbonate fluxes dropped from -52 to 21.4 mg m**-2 d**-1 from January to February 2010, respectively, mainly due to reduced contribution of shallow-dwelling planktonic foraminifera and pteropods. The deep-dwelling foraminifera Globorotalia menardii, however, showed a major flux peak in February 2010, most probably due to the suboxia/hypoxia. The low oxygen conditions forced at least some zooplankton to reduce diel vertical migration. Reduced "flux feeding" by zooplankton in the epipelagic could have contributed to the enhanced fluxes of organic materials to the bathypelagic traps during the eddy passage. Further studies are required on eddy-induced particle production and preservation processes and particle focusing.

Boron isotope composition and seawater characteristics of cold water scleratinian corals

The boron isotope systematics has been determined for azooxanthellate scleractinian corals from a wide range of both deep-sea and shallow-water environments. The aragonitic coral species, Caryophyllia smithii, Desmophyllum dianthus, Enallopsammia rostrata, Lophelia pertusa, and Madrepora oculata, are all found to have relatively high d11B compositions ranging from 23.2 per mil to 28.7 per mil. These values lie substantially above the pH-dependent inorganic seawater borate equilibrium curve, indicative of strong up-regulation of pH of the internal calcifying fluid (pH(cf)), being elevated by ~0.6-0.8 units (Delta pH) relative to ambient seawater. In contrast, the deep-sea calcitic coral Corallium sp. has a significantly lower d11B composition of 15.5 per mil, with a corresponding lower Delta pH value of ~0.3 units, reflecting the importance of mineralogical control on biological pH up-regulation. The solitary coral D. dianthus was sampled over a wide range of seawater pH(T) and shows an approximate linear correlation with Delta pH(Desmo) = 6.43 - 0.71 pH(T) (r**2 = 0.79). An improved correlation is however found with the closely related parameter of seawater aragonite saturation state, where Delta pH(Desmo) = 1.09 - 0.14 Omega(arag) (r**2 = 0.95), indicating the important control that carbonate saturation state has on calcification. The ability to up-regulate internal pH(cf), and consequently Omega(cf), of the calcifying fluid is therefore a process present in both azooxanthellate and zooxanthellate aragonitic corals, and is attributed to the action of Ca2+ -ATPase in modulating the proton gradient between seawater and the site of calcification. These findings also show that the boron isotopic compositions (d11Bcarb) of aragonitic corals are highly systematic and consistent with direct uptake of the borate species within the biologically controlled extracellular calcifying medium.