HR: 0800h
AN: PP41A-0630    [Abstracts]
TI: Glacial diatom-bound 15N/14N records from the Antarctic Zone of the Southern Ocean
AU: * Robinson, R S
EM: rebeccar@princeton.edu
AF: Department of Geosciences Princeton University, Guyot Hall Washington Rd., Princeton, NJ 08544 United States
AU: Sigman, D M
EM: sigman@princeton.edu
AF: Department of Geosciences Princeton University, Guyot Hall Washington Rd., Princeton, NJ 08544 United States
AB: The potential role of Southern Ocean surface conditions in glacial/interglacial atmospheric CO{_2} changes was noted several decades ago, but a consensus view of their importance has yet to be reached. The overturning and deep ocean ventilation that occurs in the currently macronutrient-rich Antarctic Zone releases deeply sequestered CO{_2} to the atmosphere, making it of particular interest with regard to glacial/interglacial carbon cycle changes. Here we present three downcore records of diatom-bound δ¹⁵N as a proxy for nutrient consumption in the Antarctic surface, one each from the Atlantic, Indian, and Pacific sectors. In the Indian sector (MD84-552), glacial diatom-bound δ¹⁵N is slightly (1-2 ‰) elevated relative to the Holocene. In the Atlantic (RC13-259) and Pacific (NP9802-5GC) sectors, diatom-bound δ¹⁵N is significantly elevated (4-10 ‰) during the coldest episodes of the glacial periods (MIS 2 and 4) relative to the Holocene and the warmer stages of the glacial. At face value, these data suggest significant yet spatially variable degrees of enhanced nutrient consumption during the last ice age. As opal accumulation and other indicators suggest that export production was reduced at each of these sites during glacial times, these data appear to support previous suggestions of reduced macronutrient supply to the glacial Antarctic surface, through stratification of the upper water column. The large zonal differences in the degree and of δ{¹5}N change may be related to surface ocean hydrography. Both the Atlantic and Pacific core locations lie within the seasonal sea ice zone, whereas the Indian Sector core is within the modern permanently open ocean zone. While the seasonal ice zone provides an ideal location for extensive drawdown of nutrients (e.g., stable surface layer, micronutrients from summertime sea ice melt), these δ¹⁵N changes cannot yet be attributed uniquely to nutrient consumption changes, especially because of their large amplitude. Several alternative explanations for these large-amplitude changes will be explored.
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005