No warming in the eastern Gulf of Mexico since 1845 recorded by a Siderastrea siderea coral from Cuba

Changes in the surface ocean pH and temperature caused by the uptake of anthropogenic CO₂ are posing a threat to calcifying marine organisms. Recent studies have observed significant impacts on coral reef ecosystems with impaired carbonate skeletal growth and decreased calcification due to acidifying oceans. The current coverage of observations for the northwestern Cuban coastal waters provides an incomplete picture of natural climate variability over interannual to interdecadal timescales, showing the need for high resolution climate archives. Cuba is situated between densely populated landmasses of North and South America offering a unique environment to study multiple aspects of anthropogenic activity across the region as well as their interconnectivity. Sub-seasonally resolved sea surface temperature (SST), δ¹⁸O of seawater, and carbonate chemistry parameters were reconstructed from a massive Siderastrea siderea coral from Cuba’s northwestern coast through a multi-proxy approach since the preindustrial era. Trace element ratios as proxies of SST indicate no significant increase in temperature over the past 160 years since 1845. Over the same time period, coral skeletal δ¹¹B ratio decreased by ca. 1.6 ‰, translating into a decrease of 0.1 on the pH scale, reflecting the acidification of the northwestern Cuban coastal waters. Furthermore, an accelerating depletion of coral δ¹³C from the 1850s to 2005 of 1.5 ‰ demonstrates the changes in seawater CO₂ with an anthropogenic imprint due to increased fossil fuel combustion. Further investigation and the comparison to trace elements indicate possible baseline shifts in regional seawater carbonate chemistry that has been affected by anthropogenic activity.