1. Western Pacific Warm Pool Warming and Salinity Front Expansion Since 1821 Reconstructed From Paired Coral δ18O, Sr/Ca, and Reconstructed δ18Osw.
- Author
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Todorović, Sara, Wu, Henry C., Linsley, Braddock K., Kuhnert, Henning, Menkes, Christophe, Isbjakowa, Albina, and Dissard, Delphine
- Subjects
EFFECT of human beings on climate change ,OCEAN temperature ,SEAWATER salinity ,THERMAL stresses ,CLIMATE change - Abstract
The Southwest Pacific region is of great importance to global climate variability, but instrumental climate observations before the 1980s lack in numbers and quality. Despite efforts in complementing instrumental records with proxy sea surface temperature (SST) and sea surface salinity (SSS) reconstructions based on coral Sr/Ca and δ18Osw records, few of them are longer than a century. This study introduces a northwestern extension to the existing records of South Pacific coral study sites with monthly‐resolved Sr/Ca, δ18O, and δ18Osw reconstructions from Rotuma dating back to 1821. Additionally, we present new monthly‐resolved Sr/Ca and reconstructed δ18Osw from a coral from Tonga dating back to 1848. Results reveal 1.5°C warming in the Western Pacific Warm Pool, while the adjacent coral from Tonga shows 1°C warming over the twentieth century. The Rotuma Sr/Ca record reveals thermal stress events impacting the Sr/Ca‐SST relationship in the following months. Coral δ18Osw results reveal significant freshening of 0.45 Sp (practical salinity unit) in Tonga since the early twentieth century, suggesting the southeastward expansion of the South Pacific Convergence Zone salinity front. The δ18Osw inferred SSS provides a valuable extension into the past considering the short and inconsistent instrumental records available. This study demonstrates the utility of coral‐based reconstructions in capturing long‐term and regional climate variations in the Southwest Pacific and the necessity of expanding replicated studies to other underrepresented areas to enhance our understanding of regional climate dynamics. Plain Language Summary: The Southwest Pacific has limited historical climate data. This makes studying anthropogenic climate change, and how it is changing our oceans, very challenging. This study addresses this gap by using massive tropical corals from Rotuma and Tonga to reconstruct climatic key parameters back to the mid‐1800s. Our findings show that the Western Pacific Warm Pool (WPWP) has warmed by 1.2°C, much more than the adjacent subtropical waters around Tonga (0.5°C) between 1850 and 1998. The Rotuma coral record is one of the rare long records from the WPWP area where the average annual temperatures are very high (29°C). It reveals the coral was repeatedly affected by temperature stress, and probably unreported bleaching episodes throughout history. We also observe a significant freshening of 0.45 Sp in Tonga, indicating that fresher waters from the South Pacific Convergence Zone are spreading southeastward. Our coral‐derived records provide valuable historical perspectives in the absence of consistent instrumental records. Our study emphasizes the reliability of coral‐based reconstructions as indicators of local to regional conditions in the Southwest Pacific and the need for more research to better understand and address climate variability of this key area for Pacific‐wide climate. Key Points: Rotuma coral Sr/Ca and δ18Osw records provide the first reconstructions of surface seawater temperature and salinity from this locationCoral Sr/Ca‐SST shows long‐term warming in the Southwest Pacific, with higher rates in the Western Pacific Warm Pool, compared to subtropicsδ18Osw‐SSS reconstruction from Tonga shows significant long‐term freshening [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
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