Organic properties of sediments and amino acids in iterstitial waters of ODP Holes 111-677A and 111-678B

The basement at Ocean Drilling Program (ODP) Sites 677 and 678 originated from the Galapagos spreading center of the Costa Rica Rift and has moved about 200 km over the last 6 m.y. (Fig. 1) (Shipboard Scientific Party, 1987, 1988; Scientific Drilling Party, 1987). Sediments about 300 m thick cover basement so young that basal sediments at Sites 677 and 678 have been reheated up to 60?-70?C at Site 677 and altered to limestone and/or chert (Shipboard Scientific Party, 1988). Sediments from both sites indicate (1) a high sedimentation rate (about 48 m/m.y.) and (2) biogenic silica and carbonate as the main constituents of sediments (Table 1) (Shipboard Scientific Party, 1988). Heatflow observations and measurements of interstitial water chemistry around the sites show that Site 677 is in a lower heatflow zone (166 mW/m**2; 1°12.14'N, 83°44.22'W) whereas Site 678 is located in a zone of higher heat flow (250 mW/m**2; 1°13.01'N, 83°43.39'W) (Langseth et al., 1988; Shipboard Scientific Party, 1988). In the flank hydrothermal systems, circulating solution is moving upward through the sedimentary column in zones of higher heat flow while it is moving downward in zones of lower heat flow (Anderson and Skilbeck, 1981). The chemistry of the interstitial waters is modified by several processes such as (1) diagenetic reactions and (2) advective and (3) diffusive transports of dissolved constituents. Analyses of Ca2+ and Mg2+ in interstitial waters from Sites 677 and 678 show that their profiles are mainly controlled by advective transport (Shipboard Scientific Party, 1988). In contrast, the interstitial-water profiles for NH4+, Si, and PO4[3-] are highly affected by reactions in the sediments. Site 677 offers a good opportunity to investigate amino acids in the interstitial waters because sediments of similar compositions have been deposited at constant rates of sedimentation. There are few previous works on amino acid distributions in interstitial waters (Henrichs and Parrington, 1979; Michaelis et al., 1982; Henrichs et al., 1984; Henrichs and Farrington, 1987; Ishizuka et al., 1988). In this chapter, we report (1) Rock-Eval analysis and (2) the composition of total hydrolyzable and dissolved free amino acids (THAA and DFAA, respectively) in the interstitial waters. Our objectives are to discuss (1) the possible origin of organic materials, (2) the characteristics of THAA and DFAA, and (3) their relationships in interstitial waters.

Organic geochemistry on surface sediments from the Laptev Sea

Sediment samples from the Laptev Sea, taken during the 1993 RV Polarstern expedition ARK IX/4 and the RV Ivan Kireyev expedition TRANSDRIFT I, were investigated for the amount and composition of their organic carbon fractions. Of major interest was the identification of different processes controlling organic carbon deposition (i.e. terrigenous supply vs. surface water productivity). Long-chain unsaturated alkenones derived from prymnesiophytes, and fatty acids derived from diatoms and dinoflagellates, were analysed by means of gas chromatography and mass spectrometry. First results on the distribution of these biomarkers in surface sediments indicate that the surface water productivity signal is well preserved in the sediment data. This is shown by the distribution of the 16:1(n-7) and 20:5(n-3) fatty acids indicative for diatoms, and the excellent correlation with the chlorophyll a concentrations in the surface water masses and the biogenic-opal content and increased hydrogen indices of the sediments. The high concentration of these unsaturated fatty acids in shallow water sediments shows the recent deposition of the organic material. In deep-sea sediments, on the other hand, the concentrations are low. This decreased content is typical for phytoplankton material which has been degraded by microorganisms or autoxidation. In general, the alkenone concentrations are very low, suggesting low production rates by prymnesiophytes. Only at one station from the lower continental margin influenced by the inflow of Atlantic water masses, were some higher amounts of alkenones determined. Long-chain n-alkanes as well as high C/N ratios and low hydrogen indices indicate the importance of (fluvial) supply of terrigenous organic matter.

Ether lipids in deep sea and swamp sediments

Methanogen ether lipids have been quantified in sediments from a Florida swamp and the Atlantic ocean. Swamp cores containing acyclic and monocyclic isopranyl ethers are clearly differentiated from deep sea sediments which also contain bicyclic compounds. A concentration maximum near the bottom of the sulfate reducing zone in deep sea sediments may reflect a biogeochemical system in which methanogenesis and sulfate reduction are coupled by the process of methane oxidation. Lipid diagenesis is evident in the deep sea sediments. Species zonation, possibly caused by oxygen sensitivity, is detected in the relative lipid abundances in swamp sediments.

Benthic anammox and dentrification rates measured in a slurry incubation experiments at four different stations in the Arabian Sea off Pakistan during the METEOR cruise M74/2 in 2007

Vertical distributions of benthic denitrification and anammox rates within the sediment were estimated from slurry incubation experiments. Rates were used to calculate the contribution of anammox and denitrification to the total N-loss. Briefly, MUC sediment cores were sliced in 2 cm intervals and the sediment was diluted and incubated with degassed bottom water in a gas tight bag. After pre-incubating the bags for 2 h, 15N-labeled substrates were injected into the bags and the slurries were thoroughly mixed. Incubations were performed in the dark at in situ temperatures. The N2 isotope ratio (28N2, 29N2, and 30N2) was determined by gas chromatography-isotopic ratio mass spectrometry (VG Optima, Micromass) and calculated according to Kuypers et al. (2005) and Holtappels et al. (2011), respectively.Furthermore, total organic carbon and nitrogen concentrations were measured of core sediment layers corresponding to those used for rate measurements. Concentrations of organic carbon and nitrogen were determined by combustion/gas chromatography (Carlo Erba NA-1500 CNS analyzer) of dried sediment samples after acidification. The same sediment layer were also used to extract nucleic acids. The concentrations of the DNA in the samples were measured spectrophotometrically with a NanoDrop instrument (Thermo Fisher Scientific Inc.). The biomarker functional gene nirS, encoding the cd1-containing nitrite reductase, for both denitrifiers and marine anammox bacteria were quantified with real-time PCR, using the primers cd3aF/R3cd (5'-GTSAACGTSAAGGARACSGG-3' (Michotey et al., 2000)/5'-GASTTCGGRTGSGTCTTGA-3'; Throback et al., 2004) and Scnir372F/Scnir845R (5'-TGTAGCCAGCATTGTAGCGT-3'/5'-TCAAGCCAGACCCATTTGCT-3'; Lam et al., 2009).