Abstract
Abstract. Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA<1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area.
Highlights
Ocean acidification and its repercussions on marine ecosystems constitute an important consequence of the ongoing rise in atmospheric carbon dioxide (CO2) concentrations
It is important to note that the mean regional values we report for the Canada Basin may be skewed by the higher density of stations located along the Mackenzie Shelf and that our sample size for Baffin Bay consists of only six stations
The discrepancy between SP and total alkalinity (TA) values observed at the surface and in most of the water column of the Canada Basin (CB), Canadian Arctic Archipelago (CAA) and Baffin Bay (BB) clearly illustrates the change in water mass regime west of Lancaster Sound, while dissolved inorganic carbon (DIC), which is strongly affected by biological activity, shows a less prominent spatial pattern
Summary
Ocean acidification and its repercussions on marine ecosystems constitute an important consequence of the ongoing rise in atmospheric carbon dioxide (CO2) concentrations. Atmospheric carbon dioxide uptake by the surface oceans has well-defined impacts on seawater chemistry, including a decrease of pH resulting from the dissociation of carbonic acid (H2CO3), the product of the reaction between water and dissolved CO2. A large fraction of the hydrogen ions released by this reaction is neutralized by carbonate ions (CO23−), leading to a decrease of their concentration and, concomitantly, the saturation state of seawater with respect to the carbonate minerals calcite and aragonite. A. Beaupré-Laperrière et al.: The recent state and variability of the carbonate system where square brackets denote concentrations and KS∗P is the stoichiometric solubility product of calcite or aragonite, the two most common marine CaCO3 polymorphs, at a given temperature, pressure and salinity
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