Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the ocean's external (nonrecycled) nitrogen supply and up to approximately 3% of the annual new marine biological production, approximately 0.3 petagram of carbon per year. This input could account for the production of up to approximately 1.6 teragrams of nitrous oxide (N2O) per year. Although approximately 10% of the ocean's drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

No abstract

Abstract. The late Quaternary history of water-column denitrifcation of the eastern Pacific margins and the Arabian Sea is reconstructed using sedimentary •515N measurements. The •515N values in six piston cores raised from these regions show remarkably similar cyclic variations, being heavy (9-10.5%o) during the interglacials and 2-3%0 lighter during the glacials. This implies that denitrification in these regions decreased substantially during the glacial periods. The glacial decline in denitrification is attributed to reduce• upwelling and flux of organic material through the oxygen minimum zone. Since water-column denitrification in these areas accounts for about half of the fixed-nitrogen loss in the modem ocean, the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods. Because nitrate is a limiting nutrient, oceanic productivity and attendant changes in CO2 may therefore have been modulated on glacial-interglacial timescales by variations in the oceanic NO3-content.

No abstract

No abstract

No abstract

No abstract

O calcite variability in two planktonic foraminiferal species: Globigerinoides ruber, which thrives throughout the year, and Globigerina bulloides, which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing. SSTs in both areas based on Mg/Ca in G. ruber were $3 to 4°C lower during the Last Glacial Maximum (LGM; $21 ka) than today and the Holocene period. The SST records based on G. bulloides also indicate general cooling, down to 18°C in both areas. SSTs in the western Arabian Sea based on G. bulloides were always lower than those based on G. ruber, indicating the presence of strong seasonal temperature contrast during the Holocene and LGM. We interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling (SW monsoon) and winter convective mixing (NE monsoon) in the western Arabian Sea. In the eastern Arabian Sea, G. bulloides-based SSTs were slightly lower (about 1°C) than G. ruber-based SSTs during the Holocene, indicating the almost absence of a seasonal temperature gradient, similar to today. However, a large seasonal temperature contrast occurred during the LGM which favors the assumption that strong NE monsoon winds forced winter upwelling or convective mixing offshore Goa. SST and d18 Ow reconstructions reveal evidence of millennial-scale cycles, particularly in the eastern Arabian Sea. Here, the stadial periods (Northern Hemisphere cold periods such as Younger Dryas and Heinrich events) are marked by increasing SSTs and salty sea surface conditions relative to those during the interstadial periods. Indeed, the d 18Ow record shows evidence of low-saline surface waters during interstadial periods, indicating increased freshwater runoff from the Western Ghats as a consequence of enhanced SW monsoon intensity.