Beyond Surface Level: Evaluating Spatial Incongruencies in High‐Resolution Bottom Temperature Trends for the Gulf of Mexico, 1996–2012

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ABSTRACT Semi‐enclosed seas present complex and nonlinear challenges to understanding climate impacts on fisheries because continental margins restrict poleward movement by taxa seeking to maintain preferred temperatures. The Gulf of Mexico (GoM), a semi‐enclosed, marginal sea surrounded by the North American continent, supports many economically and ecologically important demersal species. A comprehensive assessment of GoM demersal environments is vital to understanding and predicting potential distribution shifts by such taxa. Here we present a Gulf‐wide, interannual spatial evaluation of bottom temperature trends between 1996‐2012. We validated and used bottom temperature products from a regional reanalysis with 24‐h temporal and 1/25° spatial resolution (33,159 grid cells and 6209 days). Ordinary least‐squares and autoregressive models estimated temporal trends and uncertainty, and optimized hot spot analyses identified spatial locales of anomalies. Bottom water cooling occurred along the West Florida Shelf, Florida Keys, northwest Cuba, and the Tamaulipas‐Veracruz Shelf. Warming trends dominated the Bay of Campeche and Louisiana–Texas Shelf. Highest warming and cooling rates were 0.25 (± 0.011)°C year−1 (uncertainty as 95% confidence; located in the Campeche subregion) and −0.12 (± 0.015)°C year−1 (located in the Florida Keys), respectively. Increased duration of Loop Current impingement on the “pressure point” near the Dry Tortugas may drive the observed cooling trends in the eastern GoM, whereas warming trends likely arise from mixing of shallow surface waters. This study highlights the importance of spatiotemporal bottom temperature analyses in complex semi‐enclosed seas where bottom temperature trends may be counterfactual to the long‐term surface warming narrative.

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