Presenter: Xinping Hu (Harte Research Instiute for Gulf of Mexico Studies, Texas A&M University-Corpus Christi)

Description:
Most of open ocean surface waters have similar acidification rates that trail the atmospheric CO₂ increase. Marginal seas are surrounded by land masses from which freshwater input may introduce abundant nutrients, hence productivity in the near coastal areas is high. Meanwhile, strong interactions between ocean currents, benthic topography, and wind forcing result in complex hydrodynamics. Therefore, acidification in marginals seas may show distinct characteristics compared to the open ocean. Gulf of Mexico is the largest marginal sea in North America and understanding the dynamics and temporal trend of acidification is limited. Two summer cruises, Gulf of Mexico and East Coast Carbon (GOMECC-1) and Gulf of Mexico Ecosystem and Carbon (GOMECC-3), which were conducted 10 years apart (2007 and 2017), showed significant decreases in pH (up to -0.12 pH units) and aragonite saturation state (up to -0.7) in the subsurface waters along the shelf-slope break in the northwestern Gulf. This type of large change could pose potential risks to the rich warmwater reef systems inhabiting this oligotrophic outer shelf region. However, it is unclear whether these two “snapshots” reflect gradual changes in the carbonate chemistry, or if temporal fluctuation also played a role. Additional data from follow-up non-summer cruises will be incorporated into the historical dataset for analyses of both temporal trends and seasonal fluctuations.