Central American wind jets create seasonally low pH and saturation states in Gulf of Tehuantepec

Pressure gradients between the Gulf of Mexico and the Tropical Eastern Pacific Ocean drive intense, intermittent northerly winds through gaps in the mountainous Central American isthmus. These wind jets have long been known to influence oceanographic conditions in the eastern tropical Pacific, from striking remote sensing images that show the effect of these northerly winds on sea surface temperature and wind speeds (http://www-po.coas.oregonstate.edu/~poa/www-po/research/po/research/windjets/). In the center of the Gulf of Tehuantepec, located in the Mexican tropical Pacific, temperatures can drop as much as 8°C during “norte” or “Tehuano” wind events (with speeds above 10 m s-1) from November to March, forming a strip of cold water that can stretch more than 400 km away from the coast and more than 200 km wide.

However, intense winds also make direct oceanographic observations particularly challenging. This study reports the first quantitative information on the carbonate chemistry in the Gulf of Tehuantepec, from a coastal survey cruise that occurred shortly after the Tehuano winds relaxed (April 2013). The authors observed high levels of inorganic carbon, with ~1000 µatm pCO2 (partial pressure of carbon dioxide), and aragonite saturation state and pH values as low as approximately 1.1 and 7.5, respectively. These challenging conditions are comparable to those observed on the West Coast Ocean Acidification cruises, on which scientists from NOAA’s Pacific Marine Environmental Laboratory and Mexico have collaborated since 2007 (See http://www.pmel.noaa.gov/pubs/outstand/feel3087/figs.shtm).

The findings reported in this paper suggest that the Gulf of Tehuantepec is a major source of CO2into the atmosphere, and should be included in carbon inventories. The estimated carbon dioxide fluxes are the highest reported for the Mexican Pacific and rank second across the Tropical Eastern Pacific, even when determined under post-Tehuano conditions. The results of this study highlight the importance of regions whose dynamics are dominated by wind jets in the global carbon balance.

But from the ecology point of view, the presence of coral reefs in the region raises several questions: how do they survive in such conditions? Have organisms living in the Gulf of Tehuantepec developed adaptative strategies to withstand these conditions? If they have indeed adapted, this region could serve as a window into the future under an ocean acidification scenario, since many of the pH values reported here are lower than those predicted to occur in tropical regions by year 2100 (7.7). To understand these processes, further studies are needed, focusing on the variability of the carbonate system in the Gulf of Tehuantepec at different spatial and temporal scales, as well as studies on the exposure of various native organisms to these conditions, in order to deepen our understanding of how pH and aragonite saturation state influence coral reef-building species and other calcifying organisms that inhabit Gulf of Tehuantepec coastal ecosystems.