CS08 Biogeochemical Cycles
Date: Monday, June 10, 2002
Time: 4:00:00 PM
Location: Saanich
 
Lopez-VeneroniD, Instituto Mexicano del Petroleo, Mexico City, Mexico, dglopez@imp.mx
Cifuentes, L, A, Texas A&M University, College Station, USA, lcifuentes@ocean.tamu.edu
 
RELATIVE CONTRIBUTIONS OF RIVERINE AND UPWELLED NITROGEN TO THE NW GULF OF MEXICO CONTINENTAL SHELF
image
An estimate of the relative riverine and oceanic N contributions to the NW Gulf of Mexico was obtained based on stable isotopes of dissolved, particulate and sedimentary N (DIN, PN and SN) from various seasons. The spatial distribution of d15N-PN in the shelf followed a mixing line between river and slope N inputs, with about an equal contribution of each endmember at the 30 m isobath. Endmember d15N-nitrate values were 8.5 permil for Mississippi River outflow and 1.7 permil for upwelled Gulf water. Shelf d15N-PN values further decreased from the Mississippi River's outflow to the west in accordance to the shelf's westward circulation pattern. The 50 m isobath separated the inner and outer shelves, dominated respectively by N mineralization and net N uptake. Although enhanced N cycling occurs at the inner shelf, the relative linearity of both 15N-PN and 15N-SN between the two N endmembers suggests that upwelled water supplies N to about two thirds of the shelf.