HR: 1400h
AN: OS23F-08    [Abstracts]
TI: The Stable Nitrogen Isotope Composition of Particulate Matter of Eastern Tropical Pacific Surface Waters During the Boreal Spring
AU: * López-Veneroni, D
EM: dglopez@imp.mx
AF: Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, Edificio 24-111, México, DF , Mexico
AB: The stable nitrogen isotope composition (¹⁵N/¹⁴N-PN relative to air N₂) of surface-water particulate matter (> 0.7 μm) was measured along approximately one-degree intervals at WOCE P18 line of the Eastern Tropical Pacific Ocean between 15°S to 23°N, 103°/110°W, in April of 1994. This line intersected segments of the equatorial surface current systems (North and South Equatorial Currents, and the Equatorial Countercurrent). The δ¹⁵N-PN values in each of these features reflect N- nutrient availability to the photic zone. Near the Equator, surface waters were nitrate-sufficient (up to 6.7 μM), and δ¹⁵N-PN values were usually 0 to 5 ‰ as a result of fractionation during uptake of surplus upwelled nitrate. South of the Equator an enrichment value (ε) for nitrate uptake was calculated to be 3.8 ‰ during the depletion of equatorially-upwelled water. δ¹⁵N-PN values at the nutrient-depleted North Equatorial Current (NEC) averaged 7.2 ‰, which should resemble the isotopic composition of incoming nitrate from subsurface waters. At the NEC's northern limit, surface δ¹⁵N-PN values were isotopically enriched (16 ‰) which is consistent with the input of subsurface ¹⁵N-enriched NO₃^- from the oxygen minimum zone. This surface distribution is similar to that reported by others for the austral spring farther west and the Tropical North Pacific oxygen minimum zone near the Mexican coastline and suggests a constancy of processes determining the nitrogen isotopic composition of the region both in space and time.
DE: 0469 Nitrogen cycling
DE: 4231 Equatorial oceanography
DE: 4273 Physical and biogeochemical interactions
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4870 Stable isotopes (0454, 1041)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly