Air-sea CO<sub>2</sub> fluxes and the controls on ocean surface <i>p</i>CO<sub>2</sub> seasonal variability in the coastal and open-ocean southwestern Atlantic Ocean: a modeling study

Abstract

Abstract.We use an eddy-resolving, regional ocean biogeochemical model to investigate the main variables and processes responsible for the climatological spatio-temporal variability of pCO 2 and the air-sea CO 2 fluxes in the southwestern Atlantic Ocean. Overall, the region acts as a sink of atmospheric CO 2 south of 30 • S, and is close to equilibrium with the atmospheric CO 2 to the north. On the shelves, the ocean acts as a weak source of CO 2 , except for the mid/outer shelves of Patagonia, which act as sinks. In contrast, the inner shelves and the low latitude open ocean of the southwestern Atlantic represent source regions. Observed nearshoreto-offshore and meridional pCO 2 gradients are well represented by our simulation. A sensitivity analysis shows the importance of the counteracting effects of temperature and dissolved inorganic carbon (DIC) in controlling the seasonal variability of pCO 2 . Biological production and solubility are the main processes regulating pCO 2 , with biological production being particularly important on the shelves. The role of mixing/stratification in modulating DIC, and therefore surface pCO 2 , is shown in a vertical profile at the location of the Ocean Observatories Initiative (OOI) site in the Argentine Basin (42 • S, 42 • W).

A multi-decade record of high-quality <i>f</i>CO<sub>2</sub> data in version 3 of the Surface Ocean CO<sub>2</sub> Atlas (SOCAT)

“…SOCAT data products are used for model-to-data comparison, model evaluation and data assimilation in coupled and ocean-only biogeochemical models. Model-to-data comparisons of surface water f CO 2 have been carried out for seasonal (Tjiputra et al, 2012;Arruda et al, 2015) to multi-year timescales McKinley et al, 2016). In several studies, model data are subsampled to surface ocean pCO 2 observations from SOCAT Tjiputra et al, 2014;Turi et al, 2014).…”

“…A mean annual increase of 1.5 µatm has been estimated in surface ocean f CO 2 (fugacity of CO 2 ) for the period from 1970 to 2007 , which is superimposed on large seasonal variation, here defined as 386 D. C. E. Bakker et al: A multi-decade record of high-quality f CO 2 data the difference between winter and summer values, of, for example, 120 µatm in the seasonally ice covered Southern Ocean and 160 µatm in Georgia Basin (E. M. . The annual increase also occurs against a background of large spatial variation of, for example, 140 µatm in different regions of the Southern Ocean in spring (Bakker et al, 2008; E. M. . Similarly, seasonal variation of 0.04 in surface pH in the subtropical North Atlantic Ocean (González-Dávila et al, 2007) is 20 times the mean annual decrease in surface ocean pH at a rate of −0.002 yr −1 Lauvset et al, 2015).…”

The Spatiotemporal Dynamics of the Sources and Sinks of CO2 in the Global Coastal Ocean

“…In the California Current, the water circulation generated by the strong upwelling is the main control of the pCO 2 seasonality, which is further influenced by the solubility and biological pumps. In the study of Arruda et al (2015) on the Patagonia shelf, the opposite is observed and the solubility and biological pumps govern the seasonality of pCO 2 with only a small contribution from the water circulation. These different contributions to the pCO 2 seasonal variability remain however unknown at the global scale as in coastal seas not under upwelling influence.…”

“…In addition to determining the global coastal carbon sink, we are particularly interested in the seasonal dynamics of the coastal air-sea CO 2 fluxes, as this provides insight into the sensitivity of these fluxes to environmental change. The few studies that attempted to identify and quantify the main processes driving the seasonality of FCO 2 remained, however, regional (Arruda et al, 2015;Frankignoulle & Borges, 2001;Nakaoka et al, 2006;Shadwick et al, 2010Shadwick et al, , 2011Turi et al, 2014;Yasunaka et al, 2016) or were limited to a single oceanic basin (i.e., the Atlantic, Laruelle et al, 2014). In addition, with few exceptions (i.e., Yasunaka et al, 2016), most regional studies focused mainly on the seasonal variability of pCO 2 , neglecting the potentially important contribution of changes in the atmospheric pCO 2 , the gas transfer velocity, and the sea ice coverage.…”

The potential of using remote sensing data to estimate air–sea CO<sub>2</sub> exchange in the Baltic Sea

“…Other studies have calculated FCO 2 across ocean basins using climate databases (Takahashi et al, 2002) or biogeochemical numerical models Arruda et al, 2015). These calculations, however, have failed to provide outputs covering the global coastlines.…”