A controversial aspect of Pliocene (5.3–2.6 Ma) climate is whether El Niño‐like (El Padre) conditions, characterized by a reduced trans‐equatorial sea‐surface temperature (SST) gradient, prevailed across the Pacific. Evidence for El Padre is chiefly based on reconstructions of sea‐surface conditions derived from the oxygen isotope (δ¹⁸O) and Mg/Ca compositions of shells belonging to the planktic foraminifer Trilobatus sacculifer. However, fossil shells of this species are a mixture of multiple carbonate phases—pre‐gametogenic, gametogenic (reproductive), and diagenetic calcites—that formed under different physiological and/or environmental conditions and are averaged in conventional whole‐shell analyses. Through in situ measurements of micrometer‐scale domains within Pliocene‐aged shells of T. sacculifer from Ocean Drilling Program Site 806 in the western equatorial Pacific, we show that the δ¹⁸O of gametogenic calcite is 0.6–0.8‰ higher than pre‐gametogenic calcite, while the Mg/Ca ratios of these two phases are the same. Both the whole‐shell and pre‐gametogenic Mg/Ca records indicate that average early Pliocene SSTs were ~1°C warmer than modern, with present‐day SSTs being established during the latest Pliocene and early Pleistocene (~3.0–2.0 Ma). The measurement of multiple calcite phases by whole‐shell δ¹⁸O analyses masks a late Pliocene to earliest Pleistocene (3.6–2.2 Ma) decrease in seawater δ¹⁸O (δ¹⁸O_sw) values reconstructed from in situ pre‐gametogenic δ¹⁸O and Mg/Ca measurements. Our novel δ¹⁸O_sw record indicates that sea‐surface salinities in the west Pacific warm pool were higher than modern prior to ~3.5 Ma, which is consistent with more arid conditions under an El Padre state.

中文翻译：

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使用化石浮游有孔虫壳的原位微分析重建上新世西太平洋暖池水文气候

上新世（5.3-2.6 Ma）气候的一个有争议的方面是整个太平洋地区是否普遍存在着以减少的越赤道海面温度（SST）梯度为特征的厄尔尼诺现象（El Padre）。的El帕德瑞证据主要基于来自所述氧同位素衍生（δ海面状况重建¹⁸属于浮游有孔虫O）和壳的镁/钙组合物Trilobatus sacculifer。但是，该物种的化石壳是多种碳酸盐相的混合物-配子前，配子体（生殖）和成岩方解石，它们是在不同的生理和/或环境条件下形成的，并在常规全壳分析中取平均值。通过在上新世老年壳内微米级域的现场测量T. sacculifer来自大洋钻探计划网站806在赤道西太平洋，我们表明δ ¹⁸配子方解石的O比配子前的方解石高0.6-0.8‰，而这两个相的Mg / Ca之比相同。整个壳期和配子发生前的Mg / Ca记录均表明，上新世早期平均SST比现代温度高约1°C，目前的SST建立在最新的上新世和更新世早期（〜3.0-2.0 Ma）。通过全-壳多方解石相的δ测量¹⁸ Ô分析口罩一晚上新世到最早更新世（3.6-2.2马）减少海水中δ ¹⁸ O（δ ¹⁸ ö _SW）值从原位重建预δ配子¹⁸ ö和Mg / Ca测量。我们的新δ ¹⁸ Ø _SW 记录表明，在约3.5 Ma之前，西太平洋暖池中的海面盐度高于现代，这与帕德（El Padre）州的干旱条件相一致。