Ice Age‐Holocene Similarity of Foraminifera‐Bound Nitrogen Isotope Ratios in the Eastern Equatorial Pacific
Ice Age‐Holocene Similarity of Foraminifera‐Bound Nitrogen Isotope Ratios in the Eastern Equatorial Pacific
复制标题
DOI：
10.1029/2020pa004063
复制
发表时间：
2021-04
影响因子：
3.5
通讯作者：
A. Studer;F. Mekik;H. Ren;M. Hain;S. Oleynik;A. Martínez-García;G. Haug;D. Sigman
中科院分区：
文献类型：
--
作者：
A. Studer;F. Mekik;H. Ren;M. Hain;S. Oleynik;A. Martínez-García;G. Haug;D. Sigman
东热带太平洋（ETP）回溯至末次冰川期的整体沉积物δ15N记录通常表现为低冰川δ15N，然后是去冰期δ15N最大值，随后逐渐下降到全新世晚期δ15N，通常高于末次冰川期（LGM）。LGM较低的δ15N被解释为反映了水柱反硝化作用的冰期减少。本文报道了近35 ka来赤道东太平洋（EEP）两个沉积物岩心中Neogloboquadrina duterte和Neogloboquadrina incompta两种有孔虫壳结合氮同位素（FB - δ15N）的测量结果，它们的整体沉积物δ15N均具有典型的LGM -全新世增加。FB‐δ15N与整体沉积物δ15N相比，在LGM期间没有显示较低的δ15N。相反，FB‐δ15N记录以去冰期δ15N最大值为主，与LGM值和全新世值相当。大块沉积物记录的低LGM δ15N可能是人为的，可能与LGM期间较大的外源N输入和/或较弱的沉积成岩作用有关。新的数据提出了以前推断的冰川减少ETP水柱反硝化的可能性是不正确的。对重建冰期条件和地球化学盒模式输出的回顾为这种可能性提供了机制支持。然而，赤道海洋环流和覆盖两个核心站点的富硝酸盐地表水允许其他可能的解释，要求在非赤道ETP站点进行复制。
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.