Influence of terrestrial inputs on continental shelf carbon dioxide

Abstract

Abstract. The US South Atlantic Bight (SAB) is a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. Based on previously published data on sea surface partial pressure of carbon dioxide (pCO2) and new dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) data, a model analysis is presented to identify and quantify the contributions of various terrestrial carbon inputs on SAB sea surface pCO2. After removal of pCO2 variations due to annual temperature variability and air–sea gas exchange from the in situ pCO2, the temperature- and gas-exchange-corrected pCO2 (TG-corrected pCO2) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TG-corrected pCO2 are then calculated. Our findings demonstrate that although additions of CO2 from within shelf waters (i.e., ΔpCO2(shelf)) were the greatest of the three components and underwent the largest seasonal changes, ΔpCO2(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO2 contributions from river (ΔpCO2(river)) and salt marsh (ΔpCO2(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of ΔpCO2(marsh) was about three-fold greater than ΔpCO2(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of pCO2 on the inner shelf. Despite large uncertainties, this study demonstrates the importance of terrestrial inputs, in particular those from coastal wetlands, on coastal ocean CO2 distributions.

Seasonal response of air–water CO<sub>2</sub> exchange along the land–ocean aquatic continuum of the northeast North American coast.

“…None of these estimates, however, fully resolves the seasonality in CO 2 fluxes because temporal coverage of the global data is insufficient. Complex seasonal dynamics of CO 2 exchanges between the atmosphere and individual components of the LOAC have been reported in previous studies which have highlighted the potential importance of the intraannual variability for local and regional CO 2 budgets (e.g., Kempe, 1982;Frankignoulle et al, 1998;Jones and Mulholland, 1998;Degrandpré et al, 2002;Thomas and Schneider, 1999;Wallin et al, 2011;Regnier et al, 2013a;Rawlins et al, 2014). Here, we extend the analysis to the sub-continental scale, and present the spatial and seasonal variability of CO 2 fluxes at the air-water interface (F CO 2 ) for the entire northeast North American LOAC, from streams to the shelf break.…”

“…The steep increase and F CO 2 maximum in spring could be related to the flushing of water from the thawing top soils, which are rich in dissolved organic carbon (DOC) and CO 2 . Additionally, the temperature rise also induces an increase in respiration rates within the water columns (Jones and Mulholland, 1998;Striegl et al, 2012). Rivers and the continental shelf in the North section present synchronized opposite behaviors from winter through spring.…”

Air–sea exchanges of CO<sub>2</sub> in the world's coastal seas

“…Coastal waters receive large inputs of terrestrial material, such as suspended sediments and nutrients in solution or in particulate matter, in organic or inorganic forms and through river and groundwater discharge, as well as by exchange with the atmosphere, the sediments and the open ocean. They therefore tend to show greater temporal and spatial variability than open oceans, and are more affected by human activities (Cameron and Pritchard, 1963;Alongi, 1998;Chen and Tsunogai, 1998;Rabouille et al, 2001;Chen, 2002Chen, , 2003Chen, , 2004Slomp and Van Cappellen, 2004;Beusen et al, 2005;Chavez et al, 2007;Doney et al, 2007;Radach and Patsch, 2007;Peng et al, 2008;Seitzinger et al, 2010;Dürr et al, 2011;Jiang et al, 2013). However, unlike the open oceans, in which millions of observations have been made and the air-sea exchanges of CO 2 have been valued using various developed models (such as by Khatiwala et al, 2013;Schuster et al, 2013;Wanninkhof et al, 2013), coastal waters have been relatively poorly examined.…”

“…The above may be summarized by noting that nutrients from land, which may be transported by rivers or submarine groundwater discharge, or may be atmospheric fallout, markedly affect estuaries and continental shelves (Ittekkot et al, 1991;Cole and Caraco, 2001;Neubauer and Anderson, 2003;Clark et al, 2004;Thomas et al, 2004;Gazeau et al, 2005;Hales et al, 2008;Jiang et al, 2013;Lauerwald et al, 2012). Consequently, estuaries and proximal continental shelves typically sustain high biological productivity (Walsh et al, 1981;Wollast, 1993Wollast, , 1998Cai, 2003), which may draw down CO 2 .…”

Variation pattern of particulate organic carbon and nitrogen in oceans and inland waters

“…Other factors that regulate C/N on a regional scale include microzooplankton (Talmy et al, 2016), heterotrophic 60 microbes (Crawford et al, 2015) and terrestrial organisms (Jiang, 2013). This variation in C/N increases the uncertainty of global carbon and nitrogen estimation (Babbin, 2014).…”