Search

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 Galápagos. 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 (Degree Heating Months 9°C‐months) heat stress event during the 1997–1998 El Niño, with a larger response in the Wolf core. However, removing data that covers the 1997–1998 El Niño from calibration does not improve reconstruction statistics. Nevertheless, we find that excluding data after the 1997–1998 El Niño event from the calibration reduces the SST reconstruction error slightly. These results confirm that coral Sr/Ca is a reliable SST proxy in this region, although it can respond adversely to unusual heat stress. We suggest that noise in Sr/Ca‐SST calibrations may be reduced by removing data immediately following large heat extremes. Plain Language Summary: The ratio of strontium to calcium (Sr/Ca) in reef‐building coral skeletons has long been recognized to covary with the seawater temperature in which the corals grew and has been measured in many corals to understand past temperature changes. However, there are few examples from the eastern equatorial Pacific, an important region that drives variations in the climate system. Furthermore, this ratio might not reflect temperature as reliably after a heat stress event because of the physiological impacts on calcification processes. To test if Sr/Ca in corals from this region can reflect past temperature reliably and if this coral "thermometer" is compromised by heat stress, we analyze two coral records from the northern Galápagos. We find that Sr/Ca in these corals reflect temperature, but their relationship is weaker following heat stress and during the 21st century portion of our coral records. Although the heat stress event itself does not affect how well we can infer past temperature, using data after the event to establish the Sr/Ca‐temperature relationship impacts the accuracy of temperature reconstruction. Our results demonstrate that excluding post‐heat stress periods from the intervals during which these chemistry‐climate relationships are developed may reduce the uncertainty of the resulting temperature reconstructions. Key Points: We present Sr/Ca and Mg/Ca measurements of two corals from the northern Galápagos, spanning 25–30 years following the 1982‐3 El Niño eventIn the faster‐growing colony, the Sr/Ca‐SST relationship weakens after heat stressExcluding data after the heat stress event from proxy calibration improves temperature reconstruction statistics [ABSTRACT FROM AUTHOR]

In light of rapid environmental change, quantifying the contribution of regional‐ and local‐scale drivers of coral persistence is necessary to characterize fully the resilience of coral reef systems. To assess multiscale responses to thermal perturbation of corals in the Coral Triangle (CT), we developed a spatially explicit metacommunity model with coral–algal competition, including seasonal larval dispersal and external spatiotemporal forcing. We tested coral sensitivity in 2,083 reefs across the CT region and surrounding areas under potential future temperature regimes, with and without interannual climate variability, exploring a range of 0.5–2.0°C overall increase in temperature in the system by 2054. We found that among future projections, reef survival probability and mean percent coral cover over time were largely determined by the presence or absence of interannual sea surface temperature (SST) extremes as well as absolute temperature increase. Overall, reefs that experienced SST time series that were filtered to remove interannual variability had approximately double the chance of survival than reefs subjected to unfiltered SST. By the end of the forecast period, the inclusion of thermal anomalies was equivalent to an increase of at least 0.5°C in SST projections without anomalies. Change in percent coral cover varied widely across the region within temperature scenarios, with some reefs experiencing local extinction while others remaining relatively unchanged. Sink strength and current thermal stress threshold were found to be significant drivers of these patterns, highlighting the importance of processes that underlie larval connectivity and bleaching sensitivity in coral networks. [ABSTRACT FROM AUTHOR]

Abstract: Models and observations disagree regarding sea surface temperature (SST) trends in the eastern tropical Pacific. We present a new Sr/Ca‐SST record that spans 1940–2010 from two Wolf Island corals (northern Galápagos). Trend analysis of the Wolf record shows significant warming on multiple timescales, which is also present in several other records and gridded instrumental products. Together, these data sets suggest that most of the eastern tropical Pacific has warmed over the twentieth century. In contrast, recent decades have been characterized by warming during boreal spring and summer (especially north of the equator), and subtropical cooling during boreal fall and winter (especially south of the equator). These SST trends are consistent with the effects of radiative forcing, mitigated by cooling due to wind forcing during boreal winter, as well as intensified upwelling and a strengthened Equatorial Undercurrent. [ABSTRACT FROM AUTHOR]