Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ∼5 Million Years
Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ∼5 Million Years
复制标题
DOI：
10.1029/2020pa004115
复制
发表时间：
2021-08
影响因子：
3.5
通讯作者：
N. Meinicke;M. Reimi;A. Ravelo;A. N. Meckler
中科院分区：
文献类型：
--
作者：
N. Meinicke;M. Reimi;A. Ravelo;A. N. Meckler
印度太平洋暖池（IPWP）在影响热带和全球气候动态方面发挥着至关重要的作用。然而，有一个持续的争议，关于IPWP的表面温度的演变，因为上新世，这是由矛盾的代理证据。使用TEX 86进行的温度重建表明，从上新世到今天，温度逐渐降低了102 °C，而使用南极有孔虫的Mg/Ca研究没有报告任何长期趋势。由于海水化学变化的镁/钙记录的偏见已被建议作为这种代理不匹配的解释。在这里，我们提供了来自两个独立的有孔虫温度代理的数据，Mg/Ca和聚集同位素（Δ47），这些数据是在IPWP中IODP站点U1488的相同样品上测量的。我们重建了混合层和次表层温度，并发现当对海水中Mg/Ca比值的变化进行微小校正时，Mg/Ca和Δ47之间具有很好的一致性。成岩作用可能会影响Δ47，但对现场U1488有孔虫保存的评价表明，这种影响不太可能掩盖数据中的长期趋势。虽然剩余的不确定性使我们无法完全排除特定的假设，但我们的研究增加了证据，表明混合层温度可能没有大幅冷却，而自上新世以来，地下温度冷却得更强烈。以前在TEX 86数据中观察到的大量更新世冷却与将其解释为地表和地下信号相结合时的这一发现一致。
The Indo‐Pacific Warm Pool (IPWP) plays a crucial role in influencing climate dynamics both in the tropics and globally. Yet, there is an ongoing controversy concerning the evolution of surface temperatures in the IPWP since the Pliocene, which is fueled by contradictory proxy evidence. Temperature reconstructions using TEX86 indicate a gradual cooling by ∼2°C from the Pliocene to today while Mg/Ca‐based studies using planktonic foraminifera do not report any long‐term trends. A bias in Mg/Ca records due to seawater chemistry changes has been suggested as an explanation for this proxy mismatch. Here, we present data from two independent foraminifera‐based temperature proxies, Mg/Ca and clumped isotopes (Δ47), measured on the same samples from IODP Site U1488 in the IPWP. We reconstructed mixed layer and subsurface temperatures and find very good agreement among Mg/Ca and Δ47 when applying a minor correction for changing Mg/Ca ratios of seawater. Diagenetic effects could influence Δ47 but the evaluation of foraminifera preservation at Site U1488 suggests that this effect is unlikely to have masked a long‐term trend in the data. While remaining uncertainties prevent us from fully ruling out particular hypotheses, our study adds evidence that mixed layer temperatures likely did not cool substantially, while subsurface temperatures cooled more strongly since the Pliocene. The substantial Pleistocene cooling previously observed in TEX86 data is consistent with this finding when interpreting it as a combined surface and subsurface signal.