The Mid-Atlantic Bight Dissolved Inorganic Carbon System Observed in the March 1996 DOE Ocean Margins Program (OMP)—A Baseline Study

Ting-Hsuan Huang,Penny Vlahos,Ernie R Lewis,Wei-Jun Cai,Chen-Tung Arthur Chen,Douglas W R Wallace

doi:10.3389/fmars.2021.629412

Abstract

The United States Department of Energy (DOE)’s Ocean Margins Program (OMP) cruise EN279 in March 1996 provides an important baseline for assessing long-term changes in the carbon cycle and biogeochemistry in the Mid-Atlantic Bight (MAB) as climate and anthropogenic changes have been substantial in this region over the past two decades. The distributions of O2, nutrients, and marine inorganic carbon system parameters are influenced by coastal currents, temperature gradients, and biological production and respiration. On the cross-shelf direction, pH decreases seaward, but carbonate saturation state (ΩArag) does not exhibit a clear trend. In contrast, ΩArag increases from north to south, while pH has no clear spatial patterns in the along-shelf direction. In order to distinguish between the effects of physical mixing of various water masses and those of biological activities on the marine inorganic carbon system, we use the potential temperature-salinity diagram to identify water masses, and differences between observations and theoretical mixing concentrations to measure the non-conservative (primarily biological) effects. Our analysis clearly shows the degree to which ocean margin pH and ΩArag are regulated by biological activities in addition to water mass mixing, gas exchange, and temperature. The correlations among anomalies in dissolved inorganic carbon, phosphate, nitrate, and apparent oxygen utilization agree with known biological stoichiometry. Biological uptake is substantial in nearshore waters and in shelf-slope mixing areas. This work provides valuable baseline information to assess the more recent changes in the marine inorganic carbon system and the status of coastal ocean acidification.

Highlights

Coastal waters link the three main carbon reservoirs: land, ocean, and atmosphere, and are recognized as a major component of the global carbon cycle and budget
The dissolved inorganic carbon (DIC) concentrations were measured using a single operator multi-parameter metabolic analyzer (SOMMA) with a precision of ± 0.06% and an accuracy of ca. ± 2 μmol kg−1, with values checked against Certified Reference Materials (CRM) (Dickson, 2010), and total alkalinity (TA) concentrations were determined with a Metrohm 665 Dosimat titrator and an Orion 720A pH meter with a ROSS glass pH electrode and an Orion double junction Ag, AgCl reference electrode through a nonlinear least squares approach with ±2 μmol kg−1 precision and were corrected with the difference between the CRM stated and analyzed values (Johnson, 1992; Johnson et al, 1993; Department of Energy (DOE), 1994; Jahnke and Verity, 1994; Knap et al, 1996)
The greatest onshore–offshore salinity contrast occurs in the CB and Cape Hatteras (CH) transects due to the large amount of freshwater input from the Chesapeake Bay and the greater influences of the Gulf Stream and slope water at the most offshore stations (Figure 2B)

Summary

Introduction

Coastal waters link the three main carbon reservoirs: land, ocean, and atmosphere, and are recognized as a major component of the global carbon cycle and budget. Terrestrial materials flow into the continental shelf through river plumes and groundwater discharge. Coastal ocean processes such as tides, upwelling, onwelling, and net advective transport are the main physical pathways for terrestrial material exchange with oceanic water. Besides mediating the exchange of carbon among the three main carbon reservoirs, biogeochemical processes, and anthropogenic impacts further compound the complexity of the marine inorganic carbon system in continental margins (Mackenzie et al, 2005; MullerKarger et al, 2005; Jahnke, 2010; Cai, 2011; Bauer et al, 2013)

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Conclusion