Storm‐induced upwelling of high pCO₂ waters onto the continental shelf of the western Arctic Ocean and implications for carbonate mineral saturation states

Abstract

The carbon system of the western Arctic Ocean is undergoing a rapid transition as sea ice extent and thickness decline. These processes are dynamically forcing the region, with unknown consequences for CO2 fluxes and carbonate mineral saturation states, particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors. In October 2011, persistent wind‐driven upwelling occurred in open water along the continental shelf of the Beaufort Sea in the western Arctic Ocean. During this time, cold (<−1.2°C), salty (>32.4) halocline water—supersaturated with respect to atmospheric CO2 (pCO2 > 550 μatm) and undersaturated in aragonite (Ωaragonite < 1.0) was transported onto the Beaufort shelf. A single 10‐day event led to the outgassing of 0.18–0.54 Tg‐C and caused aragonite undersaturations throughout the water column over the shelf. If we assume a conservative estimate of four such upwelling events each year, then the annual flux to the atmosphere would be 0.72–2.16 Tg‐C, which is approximately the total annual sink of CO2 in the Beaufort Sea from primary production. Although a natural process, these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region, and could have significant impacts on regional carbon budgets. As sea ice retreat continues and storms increase in frequency and intensity, further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable.

Responses in Arctic marine carbon cycle processes: conceptual scenarios and implications for ecosystem function

“…This is also likely to prevent high rates of F P,NC . Furthermore, in some areas, upwelling events, through changes in the atmospheric forcing and storm events, have been found to bring high pCO 2 , from biological remineralization in deep water, to the surface, causing localized outgassing of CO 2 and lowered saturation state conditions in the SW (Mathis et al 2012).…”

“…That said, an increase in food quality has also been shown to counter potential impacts of acidification (e.g., Seibel et al 2012). However, acidification may be of more concern for benthic organisms, in particular in shelf regions that are already experiencing undersaturated conditions, for example, the PiS (Mathis et al 2012). The well coupled pelagicÁbenthic exchange in the PiS means higher trophic Oceanic influence Major changes in sea-ice regime (switch from × Coastal erosion, organic matter fluxes (see river influences) All, especially CB 2, 7 multi-year cover to seasonal ice cover) × Vertical mixing, nutrient supply, F A,NP C drawdown in SW. C cycling × Vertical mixing, ¡ euphotic zone, ¡ F A,NP ¡ C drawdown in SW. ¡ C cycling × ¡ Ice cover, light availability, F A,NP C drawdown in SW. C cycling × Gas-exchange opportunities Changes to C gas exchange × Changes in freshwater delivery Changes to C gas exchange × Disturbed formation of cold water masses Changes to C pump and export Wassmann & Reigstad 2011;3.…”

Late winter biogeochemical conditions under sea ice in the Canadian High Arctic

“…Therefore, because of the relatively low pCO 2 under the ice in our study*lower than other recorded winter and early spring values )*we could expect a rapid CO 2 uptake from the atmosphere into the ocean, if the shear zone between drifting ice and the stationary, land-fast ice developed into flaw leads and polynyas, a phenomenon typical of this area of the Arctic (Carmack & Wassmann 2006). A pH T , calcite and aragonite saturation state minimum occurred in this data set at around 100 m. This midwater column minimum in pH T and saturation state has also been observed in the Arctic Ocean on a number of previous occasions and was thought to exist because of remineralization of organic matter either directly in the subsurface layer or through vertical transport (seasonal upwelling events) of carbon Shadwick et al 2011;Lansard et al 2012;Mathis et al 2012). Although the observations by and Mathis et al (2012) were only made in the spring or summer periods and were thought to be a seasonally induced phenomenon ).…”

“…A pH T , calcite and aragonite saturation state minimum occurred in this data set at around 100 m. This midwater column minimum in pH T and saturation state has also been observed in the Arctic Ocean on a number of previous occasions and was thought to exist because of remineralization of organic matter either directly in the subsurface layer or through vertical transport (seasonal upwelling events) of carbon Shadwick et al 2011;Lansard et al 2012;Mathis et al 2012). Although the observations by and Mathis et al (2012) were only made in the spring or summer periods and were thought to be a seasonally induced phenomenon ). Shadwick et al (2011) and Lansard et al (2012) confirmed that the phenomenon persists throughout the winter, which is consistent with the results from this study.…”

Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

“…In some cases, they have been shown to be a net sink of CO 2 (e.g., Bates, 2006;Shadwick et al, 2011a;Else et al, 2013;Anderson & Macdonald, 2015), while at other times are shown to be areas of increased upwelling activity and sources of CO 2 to the atmosphere (e.g., Williams et al, 2008;Mathis et al, 2012;Pickart et al, 2013b). Quantification of these sources or sinks and understanding the effects on the biogeochemistry of shelf regions is important to gain a better understanding of how and where carbon is stored and moved in 5 these high latitude areas.…”