Accuracy and Reproducibility of Coral Sr/Ca SIMS Timeseries in Modern and Fossil Corals
Accuracy and Reproducibility of Coral Sr/Ca SIMS Timeseries in Modern and Fossil Corals
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DOI：
10.1029/2021gc010068
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发表时间：
2021-08
期刊：
影响因子：
3.7
通讯作者：
H. Sayani;K. Cobb;B. Monteleone;Heather Bridges
中科院分区：
文献类型：
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作者：
H. Sayani;K. Cobb;B. Monteleone;Heather Bridges
珊瑚锶钙比(锶/钙)提供了过去海表面温度(SST)的定量估计，从而能够重建平均状态的变化和气候变化，如厄尔尼诺-南方涛动。然而，珊瑚的锶/钙比值很容易受到成岩作用的影响，成岩作用可能带来1-2℃的人工产物，通常与感兴趣的热带气候信号相当。通过二次离子质谱仪(SIMS)进行微尺度采样，对蚀变的珊瑚化石中的主要骨骼物质进行采样，为基于锶/钙的化石珊瑚古温度估计提供亟需的检查。在这项研究中，我们使用了一套来自热带太平洋中部巴尔米拉环礁的现代珊瑚和化石珊瑚，以量化SIMS锶/Ca分析相对于整体锶/钙分析的准确性和重复性。在三个重叠的现代珊瑚样品中，我们在±0.3%(1σ)的范围内重现了整体的锶/钙比值。我们展示了3个月平滑的SIMS珊瑚SR/Ca时间序列和海温之间的高保真度(R=−0.5to−0.8p<；0.5)。对于20世纪早期的年轻珊瑚化石，SIMS的锶/钙时间序列重现了大量的锶/钙时间序列，这与我们对现代珊瑚的研究结果一致。在同一化石珊瑚的一个中等蚀变的剖面上，成岩作用产生了大量的锶/钙估计值，高出0.6mmo1(大致相当于海温中的−6°C人工制品)，SIMS的锶/钙时间序列追踪了仪器性的海温时间序列。我们的结论是，每月对珊瑚生长进行3-4次SIMS分析，可以提供急需的定量检查，以检验化石珊瑚锶/钙对古温度估计的准确性，即使在适度变化的样本中也是如此。
Coral strontium‐to‐calcium ratios (Sr/Ca) provide quantitative estimates of past sea surface temperatures (SST) that allow for the reconstruction of changes in the mean state and climate variations, such as the El Nino‐Southern Oscillation, through time. However, coral Sr/Ca ratios are highly susceptible to diagenesis, which can impart artifacts of 1–2°C that are typically on par with the tropical climate signals of interest. Microscale sampling via Secondary Ion Mass Spectrometry (SIMS) for the sampling of primary skeletal material in altered fossil corals, providing much‐needed checks on fossil coral Sr/Ca‐based paleotemperature estimates. In this study, we employ a set modern and fossil corals from Palmyra Atoll, in the central tropical Pacific, to quantify the accuracy and reproducibility of SIMS Sr/Ca analyses relative to bulk Sr/Ca analyses. In three overlapping modern coral samples, we reproduce bulk Sr/Ca estimates within ±0.3% (1σ). We demonstrate high fidelity between 3‐month smoothed SIMS coral Sr/Ca timeseries and SST (R = −0.5 to −0.8; p < 0.5). For lightly‐altered sections of a young fossil coral from the early‐20th century, SIMS Sr/Ca timeseries reproduce bulk Sr/Ca timeseries, in line with our results from modern corals. Across a moderately‐altered section of the same fossil coral, where diagenesis yields bulk Sr/Ca estimates that are 0.6 mmol too high (roughly equivalent to −6°C artifacts in SST), SIMS Sr/Ca timeseries track instrumental SST timeseries. We conclude that 3–4 SIMS analyses per month of coral growth can provide a much‐needed quantitative check on the accuracy of fossil coral Sr/Ca‐derived estimates of paleotemperature, even in moderately altered samples.