Surface Water CO2 variability in the Gulf of Mexico (1996\u20132017)

Andrea K Kealoha,Robert D Hetland,Kristen M Thyng,Derek P Manzello,Kathryn E F Shamberger,Niall C Slowey,Ian C Enochs,Steven F Dimarco

doi:10.1038/s41598-020-68924-0

Abstract

Approximately 380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO2) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean CO2 Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal CO2 dynamics from 1996 to 2017. An empirical orthogonal function (EOF) was used to derive the main drivers of spatial and temporal variability in the dataset. In open and coastal waters, drivers were identified as a biological component linked to riverine water, and temperature seasonality. Air-sea flux estimates indicate the GoM open (− 0.06 ± 0.45 mol C m−2 year−1) and coastal (− 0.03 ± 1.83 mol C m−2 year−1) ocean are approximately neutral in terms of an annual source or sink for atmospheric CO2. Surface water pCO2 in the northwest and southeast GoM open ocean is increasing (1.63 ± 0.63 µatm year−1 and 1.70 ± 0.14 µatm year−1, respectively) at rates comparable to those measured at long-term ocean time-series stations. The average annual increase in coastal CO2 was 3.20 ± 1.47 µatm year-1 for the northwestern GoM and 2.35 ± 0.82 µatm year−1 for the west Florida Shelf. However, surface CO2 in the central (coastal and open) GoM, which is influenced by Mississippi and Atchafalaya River outflow, remained fairly stable over this time period.

Highlights

380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO2) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean C O2 Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal C O2 dynamics from 1996 to 2017
Summer (Jun–Sep: ~ 166,000) and spring (Mar–May: ~ 117,000) seasons account for 75% of the dataset with far fewer measurements collected during the winter (Dec–Feb: ~ 56,000) and fall (Oct–Nov: ~ 42,000) seasons (Fig. 1 and Table S1), leading to potential biases in the annual flux calculations and seasonal cycle characterizations
The empirical orthogonal function (EOF) analysis suggests that organic production associated with freshwater input is the primary driver of variability in the open ocean dataset (Figure S9)

Summary

Introduction

380,000 underway measurements of sea surface salinity, temperature, and carbon dioxide (CO2) in the Gulf of Mexico (GoM) were compiled from the Surface Ocean C O2 Atlas (SOCAT) to provide a comprehensive observational analysis of spatiotemporal C O2 dynamics from 1996 to 2017. Oceanic absorption of atmospheric CO2 leads to an increase in seawater partial pressure of C O2 (pCO2), and a decrease in seawater pH and calcium carbonate ( CaCO3) saturation state (Ω)[2,3]. This process, termed ocean acidification, has numerous negative consequences for marine organisms, especially those that form C aCO3 skeletons and shells (e.g. corals and shellfish), including a reduction in biogenic calcification and an increase in C aCO3 dissolution[4,5,6,7,8]. Shelf surface water CO2 and DIC are lower than offshore levels, with the lowest concentrations observed on the Louisiana shelf near the Scientific Reports | (2020) 10:12279

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