HR: 12:05h
AN: PP32B-08    [Abstracts]
TI: Contributions to bulk sedimentary nitrogen isotope variability in the Eastern Equatorial Pacific
AU: * Robinson, R R
EM: rebeccar@gso.uri.edu
AF: Graduate School of Oceanography, South Ferry Rd, Narragansett, RI 02882, United States
AU: Martinez, P
AF: University Bordeaux 1, Avenue des Facultes, Talence, 33405, France
AB: The surface waters of the Eastern Equatorial Pacific contain a standing nitrate pool due to iron limitation. As a consequence, nitrogen isotopes records from sediments underlying the Eastern Equatorial Pacific have been interpreted as an archive of relative nitrate utilization in the upwelling region and thus, a potential record of changing Fe availability. The nitrogen isotopic composition of the upwelled nitrate was assumed to be constant on glacial-interglacial timescales. However, some proportion of the nitrate in the Eastern Equatorial Pacific passes through the oxygen minimum zone of the Eastern Tropical South Pacific. Active water column denitrification in the oxygen minimum likely imparts a large isotopic signature upon the advecting nitrate pool. Here, a high resolution, well-dated sedimentary N isotope record from Eastern Equatorial Pacific site ODP 1240 is compared to records from the Eastern Pacific margins where variation in sedimentary ¹⁵N/¹⁴N is primarily attributed to changes in regional denitrification rates. Similarity in the magnitude and timing of the N isotope variations suggest that the large-scale glacial-interglacial pattern observed in the sedimentary ¹⁵N/¹⁴N of Eastern Equatorial Pacific sediments reflects variation in regional denitrification rates rather than large-scale changes in demand for nutrients driven by fluctuating availability of iron. Underlying the glacial- scale variations in the Eastern Equatorial Pacific is a longer timescale shift in sedimentary ¹⁵N/¹⁴N that cannot be directly attributed to regional changes in denitrification rate. This shift may reflect an important biogeochemical change within the Equatorial Pacific however, diagenetic artifacts must first be ruled out.
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4926 Glacial
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting