Glacial-to-interglacial changes in nitrate supply and consumption in the subarctic North Pacific from microfossil-bound N isotopes at two trophic levels

• Published in: Paleoceanography
• Main Authors: Ren, Haojia, Studer, Anja S., Serno, Sascha, Sigman, Daniel M., Winckler, Gisela, Anderson, Robert F., Oleynik, Sergey, Gersonde, Rainer, Haug, Gerald H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Institut für Geowissenschaften; Pacific; Neogloboquadrina pachyderma; Subarctic
• Online Access: https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/index/index/docId/38616; https://doi.org/10.1002/2014PA002765

Reduced nitrate supply to the subarctic North Pacific (SNP) surface during the last ice age has been inferred from coupled changes in diatom-bound delta N-15 (DB-delta N-15), bulk sedimentary delta N-15, and biogenic fluxes. However, the reliability of bulk sedimentary and DB-delta N-15 has been questioned, and a previously reported delta N-15 minimum during Heinrich Stadial 1 (HS1) has proven difficult to explain. In a core from the western SNP, we report the foraminifera-bound delta N-15 (FB-delta N-15) in Neogloboquadrina pachyderma and Globigerina bulloides, comparing them with DB-delta N-15 in the same core over the past 25 kyr. The delta N-15 of all recorders is higher during the Last Glacial Maximum (LGM) than in the Holocene, indicating more complete nitrate consumption. N. pachyderma FB-delta N-15 is similar to DB-delta N-15 in the Holocene but 2.2% higher during the LGM. This difference suggests a greater sensitivity of FB-delta(15)NZ to changes in summertime nitrate drawdown and delta N-15 rise, consistent with a lag of the foraminifera relative to diatoms in reaching their summertime production peak in this highly seasonal environment. Unlike DB-delta N-15, FB-delta N-15 does not decrease from the LGM into HS1, which supports a previous suggestion that the HS1 DB-delta N-15 minimum is due to contamination by sponge spicules. FB-delta N-15 drops in the latter half of the Bolling/Allerod warm period and rises briefly in the Younger Dryas cold period, followed by a decline into the mid-Holocene. The FB-delta N-15 records suggest that the coupling among cold climate, reduced nitrate supply, and more complete nitrate consumption that characterized the LGM also applied to the deglacial cold events.