Abstract
The Bering Sea is highly vulnerable to ocean acidification (OA) due to naturally cold, poorly buffered waters and ocean mixing processes. Harsh weather conditions within this rapidly changing, geographically remote environment have limited the quantity of carbon chemistry data, thereby hampering efforts to understand underlying spatial-temporal variability and detect long-term trends. We add carbonate chemistry to a regional biogeochemical model of the Bering Sea to explore the underlying mechanisms driving carbon dynamics over a decadal hindcast (2003-2012). The results illustrate that coastal processes generate considerable spatial variability in the biogeochemistry and vulnerability of Bering Sea shelf water to OA. Substantial seasonal biological productivity maintains high supersaturation of aragonite on the outer shelf, whereas riverine freshwater runoff loaded with allochthonous carbon decreases aragonite saturation states (ΩArag) to values below 1 on the inner shelf. Over the entire 2003-2012 model hindcast, annual surface ΩArag decreases by 0.025 – 0.04 units/year due to positive trends in the partial pressure of carbon dioxide (pCO2) in surface waters and dissolved inorganic carbon (DIC). Variability in this trend is driven by an increase in fall phytoplankton productivity and shelf carbon uptake, occurring during a transition from a relatively warm (2003-2005) to cold (2010-2012) temperature regime. Our results illustrate how local biogeochemical processes and climate variability can modify projected rates of OA within a coastal shelf system.
Highlights
The global ocean has absorbed ∼41% of all anthropogenic carbon dioxide (CO2) emissions resulting from the combustion of fossil fuels and industrial processes (Khatiwala et al, 2009), thereby mitigating some of the warming associated with climate change
The model does contain a few previously described biases, including a late sea ice retreat and colder water temperatures in the northern regions (Hermann et al, 2016). This late sea ice retreat delays the timing of the spring bloom and tends to generate somewhat lower total phytoplankton biomass in spring and greater biomass in fall (Ortiz et al, 2016)
The model version used in the present study includes recent corrections to the ice thermodynamics terms, which reduce but do not completely eliminate these biases
Summary
The global ocean has absorbed ∼41% of all anthropogenic carbon dioxide (CO2) emissions resulting from the combustion of fossil fuels and industrial processes (Khatiwala et al, 2009), thereby mitigating some of the warming associated with climate change. Aragonite Saturation State in the Bering Sea. Aragonite Saturation State in the Bering Sea The dissociation of this acid shifts the marine carbonate system, generating a decline in surface pH and reduced carbonate saturation states ( ), a process referred to as ocean acidification (OA). This process is expected to negatively impact the growth and survival of a wide-range of marine organisms, marine calcifiers (Doney et al, 2009; Kroeker et al, 2013). High-latitude regions are vulnerable to this expected change as these waters are already naturally low in carbonate ion concentrations, due to ocean circulation patterns and the effect of colder water temperatures increasing CO2 gas solubility (Fabry et al, 2009)
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