Stable oxygen isotope records of different benthic foraminiferal species of core GeoB3004-1 from the western Arabian Sea

The stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western Arabian Sea was determined to evaluate deepwater oxygenation, organic matter remineralization, and early diagenetic processes during the past 190,000 years. The d18O records reveal species-specific metabolic effects, susceptibility to changes in carbonate ion concentration, and supralysoclinal calcite dissolution. The foraminiferal d13C records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon (d13CDIC) and in the microhabitat depth of infaunal species. Maximum d13CDIC offsets between bottom and pore waters ranged between mean values of 0.8 and 1.2% corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2.7 ml/l. Intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well-oxygenated deepwater masses during interglacials. During interglacial maxima the d13C difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes.

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).