Biomarkers in surface sediments from the Ob and Yenisei estuaries and the southern Kara Sea

Organic-geochemical bulk parameter (Total organic carbon contents, C/N ratios and d13Corg values), biogenic opal and biomarkers (n-alkanes, fatty acids, sterols and amino acids) were determined in surface sediments from the Ob and Yenisei estuaries and the adjacent southern Kara Sea. Maximum TOC contents were determined in both estuaries, reaching up to 3 %. Relatively high C/N ratios around 10, light d13Corg values of -26.5 per mil (Yenisei) and -28 to -28.7 per mil (Ob), and maximum concentrations of long-chain n-alkanes of up to about 10 µg/g Sed clearly show the predominance of terrigenous organic matter in the sediments from the estuaries. Towards the open Kara Sea, all p arameters indicate a decrease in terrigenous organic carbon. Brassicasterol as well as the short-chain n-alkanes parallel this trend, suggesting that these biomarkers are probably also related to a terrigenous (fresh-water phytoplankton) source. Amino acid spectra show characteristic trends from the Yenisei Estuary to the open Kara Sea revealing increasing state of degradation. Sedimentary organic matter in the Yenisei Estuary is relatively less degraded compared to the Ob Estuary and the open Kara Sea.

Miocene to Pliocene calcareous nannofossil biostratigraphy at ODP Leg 117 Sites 1088 and 1090, Southern Ocean

The calcareous nannofossil biostratigraphy of ODP Leg 177 Sites 1088 and 1090 (Subantarctic sector from the Atlantic Ocean) is discussed. Most nannofossil zonal boundaries of Martini (1971) and Okada and Bukry (1980) were recognized for the studied mid-high-latitude sediments. Conventional low-latitude marker species such as Amaurolithus spp., Discoaster spp., Triquetrorhabdulus spp., Ceratolithus spp. were recorded as rare and scattered, which impeded the development of a detailed nannofossil biostratigraphic zonation of some Miocene and Pliocene intervals. Because of the absence of some primary biostratigraphic marker species, additional second-order bioevents, such as the first occurrence of Calcidiscus macintyrei and the last occurrence of Coccolithus miopelagicus, have been used to approximate the base of zones NN7 and NN8, respectively. Several disconformities disturbing the Pliocene and Miocene intervals of Site 1090 could be determined based on nannofossil distribution although the occurrence of intervals with dissolved nannofloras and low species diversity prevented a reliable age assignment. An acme of small Gephyrocapsa was recognized near the lower/middle Pliocene boundary, close to the NN15-NN16 zonal boundary, presenting an event for further improvement of the calcareous nannofossil biostratigraphy of this interval time. The first occurrence of Pseudoemiliania lacunosa (>4 µm) occurs close to this interval, representing a fairly reliable event to approximate the base of NN15 zone when other biozonal events are absent. A paracme of R. pseudoumbilicus (>7 µm) was detected in the lower Pliocene NN12 and in the upper Miocene NN11. These temporary absences of the species seem to be isochronous between high-latitude and low-middle-latitude areas.

Biogenic flux and primary production of sediment traps in the Atlantic and the Southern Ocean

Fluxes of organic carbon normalised to a depth of 1000 m from 18 sites in the Atlantic and the Southern Ocean are presented, comprising nine biogeochemical provinces as defined by Longhurst et al. (1995. Journal of Plankton Research 17, 1245-1271). For comparison with primary production, we used a recent compilation of primary production values derived from CZCS data (Antoine et al., 1996. Global Biogeochemical Cycles 10, 57-69). In most cases, the seasonal patterns stood reasonably well in accordance with the carbon fluxes. Particularly, organic carbon flux records from two coastal sites off northwest and southwest Africa displayed a more distinct correlation to the primary production in sectors (1 x 1°) which are situated closer to the coastal environments. This was primarily caused by large upwelling filaments streaming far offshore, resulting in a cross-shelf carbon transport. With respect to primary production, organic carbon export to a water depth of 1000 m, and the fraction of primary production exported to a depth of 1000 m (export fraction=EF1000), we were able to distinguish between: (1) the coastal environments with highest values (EF1000=1.75-2.0%), (2) the eastern equatorial upwelling area with moderately high values (EF1000=0.8-1.1%), (3) and the subtropical oligotrophic gyres that yielded lowest values (EF1000=0.6%). Carbon export in the Southern Ocean was low to moderate, and the EF1000 value seems to be quite low in general. Annual organic carbon fluxes were proportional to primary production, and the export fraction EF1000 increased with primary production up to 350 gCm**-2 yr**-1. Latitudinal variations in primary production were reflected in the carbon flux pattern. A high temporal variability of primary production rates and a pronounced seasonality of carbon export were observed in the polar environments, in particular in coastal domains, although primary production (according to Antoine et al., 1996. Global Biogeochemical Cycles 10, 57-69), carbon fluxes, and the export fraction remained at low.

Quantification and molecular characterization of dissolved organic sulfur in water samples obtained during POLARSTERN cruise ANT-XXV (PS73) to the East Atlantic and the Southern Ocean

Although sulfur is an essential element for marine primary production and critical for climate processes, little is known about the oceanic pool of non-volatile dissolved organic sulfur (DOS). We present a basin-scale distribution of solid phase extractable DOS in the East Atlantic Ocean and the Atlantic sector of the Southern Ocean. While molar DOS versus dissolved organic nitrogen (DON) ratios of 0.11 ± 0.024 in Atlantic surface water resembled phytoplankton stoichiometry (S/N ~ 0.08), increasing dissolved organic carbon (DOC) versus DOS ratios and decreasing methionine-S yield demonstrated selective DOS removal and active involvement in marine biogeochemical cycles. Based on stoichiometric estimates, the minimum global inventory of marine DOS is 6.7 Pg S, exceeding all other marine organic sulfur reservoirs by an order of magnitude.