Altabet, M. A. Center for Marine Science and Technology, U. Mass., maltabet@umassd.edu
Francois, R. A. Woods Hole Oceanographic Inst., rfrancois@whoi.edu

 
NITROGEN AND CARBON ISOTOPIC STUDIES DURING AESOPS: IMPLICATIONS FOR THE PALEOCEANOGRAPHIC RECORD AND MODERN BIOGEOCHEMISTRY IN THE SOUTHERN OCEAN
 
Nitrate drawdown by phytoplankton is found to be the driver for most of the nitrogen isotopic variations observed. Both geographically and seasonally, surface ocean nitrate 15N/14N inversely correlates with nitrate concentration. Rayleigh fractionation plots show that over the entire AESOPS region the fractionation factor for phytoplankton uptake falls between 4 and 6 depending on season. At 63 S, surface nitrate d15N averages about 6 and using average fractionation factors observed, the expected d15N for sinking PN is 1 . Annual average sediment trap d15N is remarkably close (0.5 ) confirming our view of a robust relationship between d15N and nitrate drawdown in this region that is recorded in the sediments. The d13C POM data shows a N-S distribution similar to prior observations. The trap d13C values are seen to generally follow the variations found in surface POM.
 
Day: Friday, Feb. 5
Time: 04:45 - 05:00pm
Location: Sweeney Center
 
Code: SS31FR0445S