PP52B-07:
Glacial-to-interglacial Changes in Nitrate Supply and Consumption in the Subarctic North Pacific from Microfossil-bound N Isotopes at Two Trophic Levels
Friday, 19 December 2014: 11:50 AM
Haojia Abby Ren1, Daniel Mikhail Sigman2, Anja Studer2, Sascha Serno3, Robert F Anderson4, Gisela Winckler3, Sergey Oleynik2, Rainer Gersonde5 and Gerald Hermann Haug6, (1)Department of Geoscience, National Taiwan University, Taipei, Taiwan, (2)Princeton University, Princeton, NJ, United States, (3)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (4)Lamont-Doherty Earth Obs, Palisades, NY, United States, (5)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (6)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland
Abstract:
The modern subarctic North Pacific constitutes one of the high-nutrient-low-chlorophyll regions of the modern ocean, where nitrate is perennially abundant at the surface. In a sediment core from the western subarctic North Pacific (SNP), we report the foraminifera-bound δ15N (FB-δ15N, in Neogloboquadrina pachyderma and Globigerina bulloides) and diatom-bound d15N (DB-δ15N) back to the last glacial maximum (LGM), to infer past changes in the degree of surface nitrate consumption. The δ15N of all recorders is higher during the LGM, indicating more complete nitrate consumption over the course of the spring-to-summer maximum in phytoplankton growth. N. pachyderma FB-δ15N is similar to DB-d15N in the Holocene but 2.3‰ higher than DB-δ15N during the LGM, a difference that is consistent with reduced wintertime nitrate supply during the LGM. Unlike DB-δ15N, FB-δ15N does not decrease from the LGM into HS1, which supports the previous suggestion that the HS1 DB-δ15N drop is due to contamination by sponge spicules. FB-δ15N decreases in the latter half of the Bolling/Allerod (B/A) warm period, rises weakly during the Younger Dryas (YD) cold period, followed by a decline into the mid-Holocene. The FB-δ15N records, together with changes in the biogenic flux reconstructed from this site, suggest that the coupling between cold climate and reduced nitrate supply that characterizes the LGM-to-Holocene difference also applied to the deglacial events. The indications for this coupling are strengthened by a correction of the FB- and DB-δ15N data for denitrification-driven increases in the δ15N of subsurface nitrate during the B/A and post-YD period.
