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.

中文翻译：

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赤道东太平洋有孔虫与约束氮同位素比率的冰期-全新世相似性

散装沉积物δ ¹⁵ N条记录从东部热带太平洋（ETP）向后延伸到最后一个冰河时代最经常表现出低冰川δ ¹⁵ N，然后冰消δ ¹⁵ N个最大，随后逐渐下降到晚全新世δ ¹⁵ ñ通常高于上次冰河最大值（LGM）。下部δ ¹⁵的LGM N个被解释为反映在水柱脱氮冰年龄减少。我们报告有孔虫壳结合的氮同位素（FB-δ ¹⁵ N）的测量对于两个物种Neogloboquadrina dutertrei和Neogloboquadrina incompta在过去的35か在从赤道东太平洋（EEP）2个沉淀核，两者都具有在散装沉积物典型LGM-到全新世增加δ ¹⁵ N. FB-δ ^15个Ñ对比散装沉积物δ ¹⁵由N个不是指示下δ ¹⁵在LGM在n个。相反，FB-δ ¹⁵ N个记录是由冰消δ为主的¹⁵ N个最大，具有相当的LGM和全新价值。较低的LGMδ ¹⁵大量沉积物记录中的N个可能是人工产物，可能与LGM期间大量的外源N输入和/或较弱的沉积成岩作用有关。新数据增加了以前推测的ETP水柱反硝化作用的冰川减少作用不正确的可能性。对重建的冰河时期条件和地球化学箱模型输出的回顾为这种可能性提供了机械支持。然而，赤道海洋环流和两个核心站点上空的富含硝酸盐的地表水允许进行其他可能的解释，要求在非赤道ETP站点进行复制。