(Table) Carbon, nitrogen and n-alkane content and isotopic composition of bottom sediments obtained in the East Siberian Sea

The chemical composition of organic matter (Corg, Norg, d13C, d1SN, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Seawater carbonate chemistry, structural and chemical characteristics of the seagrass Thalassia testudinum in an situ CO2 enrichment experiment

Seagrasses commonly display carbon-limited photosynthetic rates. Thus, increases in atmospheric pCO2, and consequentially oceanic CO2(aq) concentrations, may prove beneficial. While addressed in mesocosms, these hypotheses have not been tested in the field with manipulative experimentation. This study examines the effects of in situ CO2(aq) enrichment on the structural and chemical characteristics of the tropical seagrass, Thalassia testudinum. CO2(aq) availability was manipulated for 6 months in clear, open-top chambers within a shallow seagrass meadow in the Florida Keys (USA), reproducing forecasts for the year 2100. Structural characteristics (leaf area, leaf growth, shoot mass, and shoot density) were unresponsive to CO2(aq) enrichment. However, leaf nitrogen and phosphorus content declined on average by 11 and 21 %, respectively. Belowground, non-structural carbohydrates increased by 29 %. These results indicate that increased CO2(aq) availability may primarily alter the chemical composition of seagrasses, influencing both the nutrient status and resilience of these systems.

Sediment and pore water N and d15N concentrations of ODP Holes 202-1234A and 202-1235A

The isotopic composition of nitrogen in pore water ammonium and in sedimentary organic matter (Norg) was measured at Sites 1234 and 1235 in order to evaluate the impact of long-term (>100 k.y.) diagenesis on d15N of preserved organic matter. At both sites, the average d15N of pore water ammonium and Norg are within 0.2 per mil to 0.4 per mil. The small difference is less than the analytical uncertainty, indicating that no significant isotopic fractionation is associated with decomposition of organic matter in these sediments. A mass balance for nitrogen was also computed, indicating that ~20% of the organic matter flux buried below 1.45 meters composite depth (mcd) is degraded between this depth and 40 mcd (Site 1235) to 60 mcd (Site 1234) depth. Two factors determine the absence of isotopic fractionation in these sediments: 1. A high degree of organic matter preservation due to rapid sediment accumulation rates at both sites. 2. The dominance of a marine component in the sedimentary organic matter (with only a small fraction contributed by a terrestrial component).