NOAA/WDS Paleoclimatology - Northern Galapagos Coral Sr/Ca and Mg/Ca Data from 1985-2014 CE

Coral Sr/Ca records have been widely used to reconstruct and understand past sea surface temperature (SST) variability in the tropical Pacific. However, in the eastern equatorial Pacific, coral growth conditions are marginal and strong El Niño events have led to high mortality, limiting opportunities for coral Sr/Ca-based SST reconstructions. In this study, we present two ~25 year Sr/Ca and Mg/Ca records measured on modern Porites lobata from Wolf and Darwin Islands in the northern Galapagos. In these records, we confirm the well-established relationship between Sr/Ca and SST and investigate the impact of heat stress on this relationship. We demonstrate a weakened relationship between Sr/Ca and SST after a major 9C Degree Heating Months) heat stress event, with a larger response in the Wolf core. However, removing this anomalous period does not improve reconstruction statistics. These results confirm that coral Sr/Ca is a reliable SST proxy in this region, although it can respond adversely to unusual heat stress. Nevertheless, we find that excluding data after the 1997-1998 El Niño event from the calibration reduces the SST reconstruction error slightly. Therefore, noise in Sr/Ca-SST calibrations may be reduced by removing data immediately following large heat extremes.

珊瑚Sr/Ca记录已被广泛用于重建并解析热带太平洋过去的海表温度（sea surface temperature, SST）变化。然而在东赤道太平洋区域，珊瑚生长条件较为严苛，强厄尔尼诺（El Niño）事件曾造成大规模珊瑚死亡，极大限制了基于珊瑚Sr/Ca的SST重建研究机遇。本研究针对加拉帕戈斯群岛北部的沃尔夫岛与达尔文岛的现代叶状滨珊瑚（Porites lobata）样品，构建了两组时长约25年的Sr/Ca与Mg/Ca记录。基于该系列记录，我们验证了学界已公认的Sr/Ca与SST之间的关联关系，并探究了热胁迫对该关联的影响。研究表明，在一次主要的9℃热月度数（Degree Heating Months）热胁迫事件后，Sr/Ca与SST之间的关联出现弱化，且沃尔夫岛珊瑚岩芯的响应更为显著。然而，移除该异常时段并未提升重建结果的统计性能。上述结果证实，尽管珊瑚Sr/Ca记录可能会对异常热胁迫产生非预期响应，但该区域的珊瑚Sr/Ca仍不失为可靠的SST代用指标（proxy）。尽管如此，我们发现若从校准（calibration）过程中剔除1997-1998年厄尔尼诺事件后的相关数据，可小幅降低SST重建误差。因此，通过移除极端热事件发生后的即时观测数据，或可降低Sr/Ca-SST校准过程中的噪声干扰。