Voss, M. Baltic Sea Research Institute, +49/381/5197440
Montoya, J. Georgia Institute of Technology, email@example.com
NITROGEN ISOTOPE PATTERNS IN THE OXYGEN DEFICIENT WATERS OF THE EASTERN TROPICAL Pacific Ocean (ETNP)
We have measured the stable nitrogen isotope composition of an extensive set of samples of particulate matter (PM) and seawater nitrate collected during October/November 1997 along the Californian and Mexican coastline from 24 deg. N to 11,5 deg. N. These samples were obtained in conjunction with experimental measurements of denitrification and other N cycle processes, providing a robust biogeochemical context for our natural abundance data. PM and the filtrate was analysed for stable nitrogen isotope composition.
At the northern end of our study area, the delta-15N of PM ranged between 5 and 7 per mil in the upper 2000 m of the water column, values that are very similar to those reported from other parts of the open ocean. In general, delta-15N values were elevated within the oxygen minimum zone. In contrast, we found elevated values and a strong relationship between the oxygen deficiency, nitrate concentration and the 15N stable isotope content of the nitrate at mid-depths within the oxygen minimum zone. The delta 15N of nitrate was highest, with values up to 16 permill, where oxygen concentrations are were below 1 micromol per liter. This pattern is consistent with an overall fractionation factor of 13 per mil in a zone of high denitrification activity centered slightly below the minimum in nitrate concentration.
Day: Tuesday, Feb. 2
Location: Sweeney Center