Ice Age-Holocene Similarity of Foraminifera-Bound Nitrogen Isotope Ratios in the Eastern Equatorial Pacific

Anja S. Studer, Figen Mekik, Haojia Ren, Mathis P. Hain, Sergey Oleynik, Alfredo Martínez-García, Gerald H. Haug, Daniel M. Sigman

Research output: Contribution to journalArticlepeer-review

Abstract

Bulk sediment δ15N records from the eastern tropical Pacific (ETP) extending back to the last ice age most often show low glacial δ15N, then a deglacial δ15N maximum, followed by a gradual decline to a late Holocene δ15N that is typically higher than that of the Last Glacial Maximum (LGM). The lower δ15N of the LGM has been interpreted to reflect an ice age reduction in water column denitrification. We report foraminifera shell-bound nitrogen isotope (FB-δ15N) measurements for the two species Neogloboquadrina dutertrei and Neogloboquadrina incompta over the last 35 ka in two sediment cores from the eastern equatorial Pacific (EEP), both of which have the typical LGM-to-Holocene increase in bulk sediment δ15N. FB-δ15N contrasts with bulk sediment δ15N by not indicating a lower δ15N during the LGM. Instead, the FB-δ15N records are dominated by a deglacial δ15N maximum, with comparable LGM and Holocene values. The lower LGM δ15N of the bulk sediment records may be an artifact, possibly related to greater exogenous N inputs and/or weaker sedimentary diagenesis during the LGM. The new data raise the possibility that the previously inferred glacial reduction in ETP water column denitrification was incorrect. A review of reconstructed ice age conditions and geochemical box model output provides mechanistic support for this possibility. However, equatorial ocean circulation and nitrate-rich surface water overlying both core sites allow for other possible interpretations, calling for replication at non-equatorial ETP sites.

Original languageEnglish (US)
Article numbere2020PA004063
JournalPaleoceanography and Paleoclimatology
Volume36
Issue number5
DOIs
StatePublished - May 2021

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Atmospheric Science
  • Palaeontology

Keywords

  • denitrification
  • Holocene
  • Last Glacial Maximum
  • nitrogen isotopes
  • Pacific Ocean
  • suboxia

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