(Table T1) Amino acid ratios and concentrations in interstitial waters of seven ODP Leg 201 sites

Proteins and their amino acid building blocks form a major group of biomolecules in all organisms. In the sedimentary environment, proteins and amino acids have two sources: (1) soft tissues and detritus and (2) biotic skeletal structures, dominantly from calcium carbonate-secreting organisms. The focus of this report is on D/L ratios and concentrations of selected amino acids in interstitial waters collected during ODP Leg 201. The Peru margin sites are generally low in carbonates, whereas the open-ocean sites are more carbonate rich. Seifert et al. (1990, doi:10.2973/odp.proc.sr.112.152.1990) reported amino acid concentrations in interstitial waters from Site 681 (ODP Leg 112) comparable to Leg 201 Site 1229.

Benthic organic carbon flux and oxygen penetration depth in the Southern Ocean

For the investigation of organic carbon fluxes reaching the seafloor, oxygen microprofiles were measured at 145 sites in different sub-regions of the Southern Ocean. At eleven sites, an in situ oxygen microprofiler was deployed for the measurement of oxygen profiles and the calculation of organic carbon fluxes. At four sites, both in situ and ex situ data were determined for high latitudes. Based on this dataset as well as on previous published data, a relationship was established for the estimation of fluxes derived by ex situ measured O2 profiles. The fluxes of labile organic matter range from 0.5 to 37.1 mgC m**2/day. The high values determined by in situ measurements were observed in the Polar Front region (water depth of more than 4290 m) and are comparable to organic matter fluxes observed for high-productivity, upwelling areas like off West Africa. The oxygen penetration depth, which reflects the long-term organic matter flux to the sediment, was correlated with assemblages of key diatom species. In the Scotia Sea (~3000 m water depth), oxygen penetration depths of less than 15 cm were observed, indicating high benthic organic carbon fluxes. In contrast, the oxic zone extends down to several decimeters in abyssal sediments of the Weddell Sea and the southeastern South Atlantic. The regional pattern of organic carbon fluxes derived from micro-sensor data suggest that episodic and seasonal sedimentation pulses are important for the carbon supply to the seafloor of the deep Southern Ocean.

Organic carbon flux and remineralization in surface sediments

Organic carbon fluxes through the sediment/water interface in the high-latitude North Atlantic were calculated from oxygen microprofiles. A wire-operated in situ oxygen bottom profiler was deployed, and oxygen profiles were also measured onboard (ex situ). Diffusive oxygen fluxes, obtained by fitting exponential functions to the oxygen profiles, were translated into organic carbon fluxes and organic carbon degradation rates. The mean Corg input to the abyssal plain sediments of the Norwegian and Greenland Seas was found to be 1.9 mg C/m**2/d. Typical values at the seasonally ice-covered East Greenland continental margin are between 1.3 and 10.9 mg C/m**2/d (mean 3.7 mg C/m**2/d), whereas fluxes on the East Greenland shelf are considerably higher, 9.1-22.5 mg C/m**2/d. On the Norwegian continental slope Corg fluxes of 3.3-13.9 mg C/m**2/d (mean 6.5 mg C/m**2/d) were found. Fluxes are considerably higher here compared to stations on the East Greenland slope at similar water depths. By repeated occupation of three sites off southern Norway in 1997 the temporal variability of diffusive O2 fluxes was found to be quite low. The seasonal signal of primary and export production from the upper water column appears to be strongly damped at the seafloor. Degradation rates of 0.004-1.1 mg C/cm**3/a at the sediment surface were calculated from the oxygen profiles. First-order degradation constants, obtained from Corg degradation rates and sediment organic carbon content, are in the range 0.03-0.6/a. Thus, the corresponding mean lifetime of organic carbon lies between 1.7 and 33.2 years, which also suggests that seasonal variations in Corg flux are small. The data presented here characterize the Norwegian and Greenland Seas as oligotrophic and relatively low organic carbon deep-sea environments.

Analytical results of 19 amino acid analyses from Unit 3.1 of sediment core CRP-1 (Table 1)

Amino acid-based geochronological analyses were carried out on fossil mollusc shell and foraminifera from Unit 3.1, Cape Roberts Project core CRP-1. Ratios of D-alloIsoleucine to L-Isoleucine (D/L) were measured from 19 fossil samples using cation exchange High Performance Liquid Chromatography (HPLC) methods. Preliminary interpretation of these results suggest that Unit 3.1 contains carbonate fossils having multiple ages. The interpreted ages have a bimodal distribution between ~220 Ka (Quaternary) and ~2.4 Ma (Pliocene). However, these results lack a comprehensive regional and taxonomic context for amino acid studies in Antarctica and therefore should be regarded as preliminary age estimates of fossil shell ages.

Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic

The occurrence of mesoscale eddies that develop suboxic environments at shallow depth (about 40-100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, with the use of moorings, under water gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). During the survey the eddy core showed oxygen concentrations as low as 5 µmol kg-1 with a pH of around 7.6 at approximately 100 m depth. Correspondingly, the aragonite saturation level dropped to 1 at the same depth, thereby creating unfavorable conditions for calcifying organisms. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate organic matter and dissolved organic matter (POM and DOM), generally showed elevated concentrations in the surface mixed layer (0-70 m), with DOM also accumulating beneath the oxygen minimum. With the use of reference data from the upwelling region where these eddies are formed, the oxygen utilization rate was calculated by determining oxygen consumption through the remineralization of organic matter. Inside the core, we found these rates were almost 1 order of magnitude higher (apparent oxygen utilization rate (aOUR); 0.26 µmol kg-1 day-1) than typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC), were around 0.19 to 0.23 g C m-2 day-1 at 100 m depth, clearly exceeding fluxes typical for an oligotrophic open-ocean setting. The observations support the view that the oxygen-depleted eddies can be viewed as isolated, westwards propagating upwelling systems of their own, thereby represent re-occurring alien biogeochemical environments in the ETNA.

Particle flux studies of sediment traps from the northern and equatorial Indian Ocean

The Asian monsoon system governs seasonality and fundamental environmental characteristics in the study area from which two distinct peculiarities are most notable: upwelling and convective mixing in the Arabian Sea and low surface salinity and stratification in the Bay of Bengal due to high riverine input and monsoonal precipitation. The respective oceanography sets the framework for nutrient availability and productivity. Upwelling ensures high nitrate concentration with temporal/spatial Si limitation; freshwater-induced stratification leads to reduced nitrogen input from the subsurface but Si enrichment in surface waters. Ultimately, both environments support high abundance of diatoms, which play a central role in the export of organic matter. It is speculated that, additional to eddy pumping, nitrogen fixation is a source of N in stratified waters and contributes to the low-d15N signal in sinking particles formed under riverine impact. Organic carbon fluxes are best correlated to opal but not to carbonate, which is explained by low foraminiferal carbonate fluxes within the river-impacted systems. This observation points to the necessity of differentiating between carbonate sources for carbon flux modeling. As evident from a compilation of previously published and new data on labile organic matter composition (amino acids and carbohydrates), organic matter fluxes are mainly driven by direct input from marine production, except the site off Pakistan where sedimentary input of (marine) organic matter is dominant during the NE monsoon. The explanation of apparently different organic carbon export efficiency calls for further investigations of, for example, food web structure and water column processes.

Hydrostatic pressure affects aggregate transformation and organic carbon transport: in and beyond the twilight zone: Experiment December 2010

This work aimed to explore evaluated the effects of the increased of hydrostatic pressure on a defined bacterial community on aggregates formed from an axenic culture of marine diatoms by simulating sedimentation to the deep sea by increase of hydrostatic pressure up to 30 bar (equivalent to 3000 m water depth) against control at ambient surface pressure. Our hypothesis was that microbial colonization and community composition and thus microbial OM turnover is greatly affected by changes in hydrostatic pressure during sinking to the deep ocean.

Distribution of major carbon pools in a cyanobacterial mat from Salin de Giraud, Camargue, France

The fine-scale depth distribution of major carbon pools and their stable carbon isotopic signatures (d13C) were determined in a cyanobacterial mat (Salin-de-Giraud, Camargue, France) to study early diagenetic alterations and the carbon preservation potential in hypersaline mat ecosystems. Particular emphasis was placed on the geochemical role of extracellular polymeric substances (EPS). Total carbon (Ctot), organic carbon (Corg), total nitrogen (Ntot), total hydrolysable amino acids (THAA), carbohydrates, cyanobacteria-derived hydrocarbons (8-methylhexadecane, n-heptadec-5-ene, n-heptadecane) and EPS showed highest concentrations in the top millimetre of the mat and decreased with depth. The hydrocarbons attributed to cyanobacteria showed the strongest decrease in concentration with depth. This correlated well with the depth profiles of oxygenic photosynthesis and oxygen, which were detected in the top 0.6 and 1.05 mm, respectively, at a high down-welling irradiance (1441 µmol photons m**-2 s**-1). At depths beneath the surface layer, the Corg was composed mainly of amino acids and carbohydrates. A resistance towards microbial degradation could have resulted from interactions with diverse functional groups present in biopolymers (EPS) and with minerals deposited in the mat. A 13C enrichment with depth for the total carbon pool (Ctot) was observed, with d13C values ranging from -16.3 permil at the surface to -11.3 permil at 9-10 mm depth. Total lipids depicted a d13C value of -17.2 permil in the top millimetre and then became depleted in 13C with depth (-21.7 to -23.3 permil). The d13C value of EPS varied only slightly with depth (-16.1 to -17.3 permil) and closely followed the d13C value of Corg at depths beneath 4 mm. The EPS represents an organic carbon pool of preservation potential during early stages of diagenesis in recent cyanobacterial mats as a result of a variety of possible interactions. Their analyses might improve our understanding of fossilized microbial remains from mat ecosystems.

Molecular dissolved organic matter composition and environmental parameters from a laboratory incubation study

Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years. The composition of this refractory DOM (RDOM) exhibits a molecular signature which is ubiquitously detected in the deep oceans. Surprisingly efficient microbial transformation of labile into RDOM was shown experimentally, implying that microorganisms produce far more RDOM than needed to sustain the global pool. By assessing the microbial formation and transformation of DOM in unprecedented molecular detail for 3 years, we show that most of the newly formed RDOM is molecularly different from deep sea RDOM. Only <0.4% of the net community production was channeled into RDOM molecularly undistinguishable from deep sea DOM. Our study provides novel experimentally derived molecular evidence and data for global models on the production, turnover and accumulation of marine DOM.

Organic compounds in sediments and pore waters of ODP Sites 117-723 and 117-724

Total organic carbon, amino compounds, and carbohydrates were measured in pore waters and sediments of Pliocene to Pleistocene age from Sites 723 and 724 (ODP Leg 117) to evaluate (1) relationships between organic matter in the sediment and in the pore water, (2) the imprint of lithological variations on the abundance and contribution of organic substances, (3) degradation of amino compounds and carbohydrates with time and/or depth, and (4) the dependence of the ammonia concentration in the pore water on the degradation of amino compounds in the sediment. Total organic carbon concentrations (TOC) of the investigated sediment samples range from 0.9% to 8.7%, and total nitrogen concentrations (TN) from 0.1% to 0.5%. Up to 4.9% of the TOC is contributed by hydrolyzable amino acids (THAA) which are present in amounts between 1.1 and 21.3 µmol/g dry sediment and decrease strongly downhole. Hydrolyzable carbohydrates (THCHO) were found in concentrations from 1.3 to 6.6 ?mol/g sediment constituting between 0.1% and 2.0% of the TOC. Differences between the distribution patterns of monomers in Sites 723 and 724 indicate higher terrigenous influence for Site 724 and, furthermore, enhanced input of organic matter that is relatively resistant to microbial degradation. Lithologically distinct facies close to the Pliocene/Pleistocene boundary yield different organic matter compositions. Laminated horizons seem to correspond with enhanced amounts of biogenic siliceous material and minor microbiological degradation. Total amounts of dissolved organic carbon (DOC) in pore waters vary between 11 and 131 mg/L. Concentrations of DOC as well as of dissolved amino compounds and carbohydrates appear to be related to microbial activity and/or associated redox zones and not so much to the abundance of organic matter in the sediments. Distributions of amino acids and monosaccharides in pore waters show a general enrichment in relatively stable components in comparison to those of the sediments. Nevertheless, the same trend appears between amino acids present in the sediments from Sites 723 and 724 as well as between amino acids in pore waters from these two sites, indicating a direct relation between the dissolved and the sedimentary organic fractions. Different ammonia concentrations in the pore waters of Sites 723 and 724 seem to be related to enhanced release of ammonia from degradation of amino compounds in Site 723.