(Table 1) Stable oxygen isotope ratios of interstitial waters from ODP Sites 164-994 and 164-997

The d18O values of interstitial waters from Site 994 and Site 997 sediments, Blake Ridge, western Atlantic, tend to decrease with depth from 0.3 per mil to -0.5 per mil Standard Mean Ocean Water in the upper 200 mbsf, then fluctuate with significant positive spikes of Delta = 0.2 per mil - 0.5 per mil in the gas hydrate zone (200 to 450 mbsf), and finally increase from -0.4 per mil to -0.2 per mil toward 700 mbsf. Positive shifts of d18O IW in the gas hydrate zone are probably caused by the dissociation of gas hydrates originally contained in sediment cores. Gas hydrates recovered from the sites are enriched in 18O, d18O ranging between 2.7 per mil and 3.5 per mil. d18O values of gas hydrates and ambient interstitial waters give an oxygen isotopic fractionation factor of 1.0034-1.0040 at 12°-16°C and ~31 MPa (3 km below sea level). Based on this fractionation and observed isotopic anomalies in the gas hydrate zone, gas hydrates occupy 6% to 12% of pore-space volume within Blake Ridge sediments.

Organic carbon concentrations and isotope ratios of sediments from the Laptev Sea

Stable carbon isotope ratios in the organic fraction of surface sediments from the Laptev Sea shelf were analyzed in order to study the modern distribution pattern of terrestrial organic matter. The delta13Corg signature of the surface sediments range from -26.6? near the coastal margin to -22.8? in the north towards the outer shelf. Characterizing the possible sources of organic matter by their delta13Corg signature reveals that the terrestrial influence reaches further north in the eastern than in the western Laptev Sea. Downcore records of the delta13Corg, measured on three AMS 14C-dated cores from water depths between 46 and 77 m, specify the spatial and temporal changes in the deposition of terrestrial organic matter on the Laptev Sea shelf during the past 12.7 ka. The major depositional changes of terrestrial organic matter occurred between 11 and 7 ka and comprised the main phase of the southward retreat of the coastline and of the river depocenters due to the postglacial sea level rise.

Sedimentology, age models and stable isotope ratios of sediment cores from the equatorial Pacific

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic d13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic d13C by 0.4-0.5 per mil. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.

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.