The Ocean CO₂ Sink in the Canadian Arctic Archipelago: A Present‐Day Budget and Past Trends Due to Climate Change

Abstract

Arctic shelf seas are highly heterogeneous, making it difficult to accurately account for their role in regional and global air‐sea CO2 exchange budgets. Here we estimate the CO2 sink in the Canadian Arctic Archipelago (CAA) based on empirical relationships that account for spatiotemporal variations in the sea surface partial pressure of CO2 (pCO2sw) as a function of seasonal sea ice cycles. During the open water season from 2010 to 2016, the CAA acted as a net oceanic sink with an average CO2 flux of −7.7 ± 4 Tg C/year. This sink is significantly smaller than previous estimates for the CAA, emphasizing the importance of properly accounting for seasonal and spatial variability on Arctic shelves. Applying our analysis to a 37‐year record of sea ice conditions, we calculate an increase in the open water CO2 sink by ~150% (a trend of ~ −1.3 Tg C/decade), associated with sea ice loss and higher wind speeds.

Impact of Vertical Mixing on Summertime Net Community Production in Canadian Arctic and Subarctic Waters: Insights From In Situ Measurements and Numerical Simulations

“…(2020), who identified an important role of terrestrially‐derived DOC remineralization in driving summertime CO 2 accumulation in HB waters. Our findings in the QMG are also consistent with Ahmed and Else (2019), who observed CO 2 outgassing in the QMG during the time of our 2015 sampling.…”

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Arctic and Subarctic oceanic waters contain highly-productive ecosystems that contribute significantly to the global air-sea exchange of carbon dioxide (e.g., Ahmed & Else, 2019;Fennel et al, 2018). Strong variability in these ecosystems is driven, in part, by seasonal cycles in marine primary production (PP) associated with large-amplitude changes in mixed layer (ML) nutrient inventories, solar irradiance, and sea ice dynamics (R. Ji et al, 2013;Tremblay et al, 2015).

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Tidal mixing of estuarine and coastal waters in the Western English Channel controls spatial and temporal variability in seawater CO<sub>2</sub>

“…The latest version of SOCAT (v2021), contains ~32.7 million pCO 2 measurements, with the majority (~>75%) of data collected in the open ocean (Laruelle et al, 2018). The carbon cycle in continental shelf waters has been extensively studied in recent years (Laruelle et al, 2018;Robbins et al, 2018;Kahl et al, 2017;Ahmed and Else, 2019;Laruelle et al, 2017b;Kitidis et al, 2019;Fennel et al, 2019). Whilst the surface area of coastal, estuarine and continental shelf waters make up 7.5% of global waters (~2.7 x 10 7 km 2 ) (Cai, 2011), continental shelves alone have been shown to take up a substantial proportion 0.20-0.25 Pg C yr -1 (8-10%) of global ocean uptake (Laruelle et al, 2018;Chen et al, 2013;Cai, 2011;Bauer et al, 2013;Laruelle et al, 2014).…”

Reply on RC1

“…The latest version of SOCAT (v2021), contains ~32.7 million pCO 2 measurements, with the majority (~>75%) of data collected in the open ocean (Laruelle et al, 2018). The carbon cycle in continental shelf waters has been extensively studied in recent years (Laruelle et al, 2018;Robbins et al, 2018;Kahl et al, 2017;Ahmed and Else, 2019;Laruelle et al, 2017b;Kitidis et al, 2019;Fennel et al, 2019). Whilst the surface area of coastal, estuarine and continental shelf waters make up 7.5% of global waters (~2.7 x 10 7 km 2 ) (Cai, 2011), continental shelves alone have been shown to take up a substantial proportion 0.20-0.25 Pg C yr -1 (8-10%) of global ocean uptake (Laruelle et al, 2018;Chen et al, 2013;Cai, 2011;Bauer et al, 2013;Laruelle et al, 2014).…”