The Benthic B/Ca Record at Site 806: New Constraints on the Temperature of the West Pacific Warm Pool and the “El Padre” State in the Pliocene
The Benthic B/Ca Record at Site 806: New Constraints on the Temperature of the West Pacific Warm Pool and the “El Padre” State in the Pliocene
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DOI：
10.1029/2019pa003812
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发表时间：
2020-09
影响因子：
3.5
通讯作者：
S. White;A. Ravelo
中科院分区：
文献类型：
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作者：
S. White;A. Ravelo
西太平洋暖池（WPWP）在上新世期间对pCO2增加的响应是一个关键的模型验证目标。不同的温度指标显示了不同的趋势：有孔虫的Mg/Ca海表温度（SST）记录显示上新世的WPWP温度比今天低1.2℃（Wara等，2005,https://doi.org/10.1126/science.1112596），而TEX86研究发现了降温趋势，并声称上新世的WPWP温度比今天高（Zhang等，2014,https://doi.org/10.1126/science.1246172）。我们将重点放在理解Mg/Ca数据的偏差作为约束上新世WPWP温度的最佳方法上。对有孔虫Mg/Ca的非热控制作用最强的是海水和溶蚀。溶解作用对Mg/Ca温度有较低的偏倚，这取决于Δ[CO32−]，即方解石饱和所需的碳酸盐离子浓度的差值。因此，上新世代用物的差异可能源于Δ[CO32−]随时间的变化。为了限制溶解变化对Mg/Ca数据的影响，我们收集了0-5.5 Ma的WPWP中底栖有孔虫B/Ca数据（Δ[CO32−]的代理）。我们没有发现Δ[CO32−]的长期趋势，但在上新世中期至早期平均时，有孔虫溶解阈值以上和以下的变化产生了~0.4°C的冷偏。海水Mg/Ca的变化在上新世Mg/Ca资料中造成了~0.6°C的冷偏。在考虑这些偏差后，我们发现上新世的WPWP比全新世晚期低~0.1°C，范围在- 0.5°C到+0.5°C之间，包括所有不确定性。我们的重建显示，上新世热带太平洋的东西温度梯度比今天低得多，支持永久的El Niño - like“El Padre”状态。
The West Pacific Warm Pool (WPWP)'s response to increased pCO2 during the Pliocene is a key model validation target. Different temperature proxies show different trends: The foraminiferal Mg/Ca sea surface temperature (SST) record shows Pliocene WPWP temperatures ~1.2°C cooler than today (Wara et al., 2005, https://doi.org/10.1126/science.1112596), whereas a TEX86 study finds a cooling trend and claims the Pliocene WPWP was warmer than today (Zhang et al., 2014, https://doi.org/10.1126/science.1246172). We focus on understanding biases in Mg/Ca data as the best way to constrain the temperature of the Pliocene WPWP. The strongest nonthermal controls on foraminiferal Mg/Ca are Mg/Ca of seawater and dissolution. Dissolution, which imparts a cool bias to Mg/Ca temperatures, depends on Δ[CO32−], the difference from the carbonate ion concentration needed for calcite saturation. Thus, Pliocene proxy discrepancies might stem from varying Δ[CO32−] over time. To constrain the effect of changing dissolution on the Mg/Ca data, we collected benthic foraminiferal B/Ca data (a proxy for Δ[CO32−]) from the WPWP spanning 0–5.5 Ma. We find no long‐term trend in Δ[CO32−], but variations above and below the threshold of foraminiferal dissolution yield an ~0.4°C cold bias when averaged over the middle to early Pliocene. Changes in seawater Mg/Ca create an ~0.6°C cold bias in the Pliocene Mg/Ca data. After accounting for these biases, we find that the Pliocene WPWP was ~0.1°C cooler than the late Holocene, ranging from −0.5°C to +0.5°C including all uncertainties. Our reconstruction shows a much lower east‐west temperature gradient in the Pliocene tropical Pacific than today, supporting a permanent El Niño‐like “El Padre” state.