Controls on surface water carbonate chemistry along North American ocean margins

Wei‐Jun Cai ,Joseph E Salisbury,Bror Jönsson,José Martín Hernández-Ayón,Adrienne J Sutton,Richard A Feely,Kumiko Azetsu-Scott,Yongzhi Xu ,Brendan R Carter,Janet J Reimer,Qian Li,Pierre Pepin,Leticia Barbero,Li‐Qing Jiang ,Chris Langdon,Jessica N Cross,Simone R Alin,Rik Wanninkhof,Liang Xue,Andrea J Fassbender,Chen‐Tung Arthur Chen ,Baoshan Chen,N Hussain ,D K Gledhill

doi:10.1038/s41467-020-16530-z

Abstract

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO2 (pCO2) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.

Highlights

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans
The North American Atlantic and Gulf of Mexico (GOM) coastal regions are characterized by broad, shallow shelves influenced on the landward side by rivers and wetlands and on the seaward side by alongshore currents
While data presented here were collected during slightly different summer months on the Atlantic coast (Supplementary Table 1), the spatial patterns of all parameters are consistent for the cruises conducted in 2007, 2012, and 2015, each plotted with a shift in longitude for the purpose of illustration (Fig. 2, Supplementary Table 2)

Summary

Introduction

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Examples of local processes that influence surface water distributions of pCO2, pH, total alkalinity (TA), dissolved inorganic carbon (DIC), and Ωarag in ocean margins include river and wetland inputs, coastal circulation, vertical and lateral mixing, spatial and seasonal temperature variations, the balance of biological production and respiration, and anthropogenic CO2 uptake[23,24,25,26,27,28,29,30]. Subsequent CO2 release to the atmosphere and biological production stimulated by the accompanying upwelled nutrients may increase pH and Ωarag[33] In addition to these driving processes, it is important to understand the influence of temperature on the spatial distributions of carbonate system properties. Coastal currents often bring waters from warm (or cold) locations to cold (or warm) locations, resulting in chemical equilibrium shifts and air–sea gas exchange, both of which are sensitive to temperature change: CO2gas K!0 CO2aq; ð1Þ

Methods

Results

Conclusion