Abstract
The Canada Basin of the Arctic Ocean is considered the region of the world’s open ocean most susceptible to the Ocean Acidification (OA). This study examines progression of OA in the Canada Basin, focusing on expansion of surface and subsurface aragonite undersaturated waters (USW). Surface USW thickness increased from 0 m in 2003 to 19 ± 2 m in 2019. This change was due to freshening until 2012, and then due to increased uptake of anthropogenic CO2 after 2012. In the subsurface layer, USW thickness increased from 94 ± 6 m in 2003 to 136 ± 11 m in 2019. This change is primarily attributed to OA in upstream shelf regions, driven by increased CO2 uptake and respiration, with some contribution from thickening in the Pacific Winter Water layer. The combined thickening of surface and subsurface USW layers increased the percentage of USW in the 0–250 m water column from 38 ± 3% in 2003 to 62 ± 5% in 2019. Because of the concurrent deepening of the water masses due to the enhanced Beaufort Gyre, the replacement of oversaturated water to USW occurred mostly at the subsurface layer below 190 m. The thickness of the oversaturated layer between surface and subsurface USWs remained almost unchanged. If Beaufort Gyre weakens in the future, it would bring subsurface USW shallower, potentially affecting marine life.
Key Points
- Long-term observations revealed expansion of aragonite undersaturated waters (USW) in the Canada Basin of the Arctic Ocean
- Increase in USW thickness was mainly due to physical processes in the earlier period and biogeochemical processes in the later period
- Although USW thickened in surface and subsurface layers, the thickness of the oversaturated layer between them did not change
Plain Language Summary
The Canada Basin of the Arctic Ocean is particularly vulnerable to a process called Ocean Acidification (OA), which makes the water less suitable for marine life. This study focuses on how OA has been changing in this area, especially the expansion of certain types of problematic water (called “aragonite undersaturated waters” or USW) in the surface and subsurface layers. At the surface, this less hospitable USW has become thicker, going from essentially nothing in 2003 to 19 ± 2 m deep in 2019. This change was due to the water becoming less salty (freshening) and increased absorption of carbon dioxide (CO2). In the subsurface layer, USW also got thicker, increasing from 94 ± 6 m in 2003 to 136 ± 11 m in 2019. This happened because of OA driven by more atmospheric CO2 absorption and increased respiration in the upstream shallow shelf areas. The combined increase in the thickness of these surface and subsurface USW layers means that a larger portion of the water now consists of this less hospitable USW, going from 38 ± 3% in 2003 to 62 ± 5% in 2019. If physical conditions change in the future, the less suitable subsurface water would be brought closer to the surface, potentially impacting marine life.
Yamamoto‐Kawai M., Tsujimoto H., Zhang Y., Zimmermann S. & Williams W., 2025. Vertical expansion of aragonite undersaturated waters in the Canada Basin of the Arctic Ocean from 2003 to 2019. Journal of Geophysical Research: Oceans 130(2): e2024JC021166. doi: 10.1029/2024JC021166. Article (subscription required).
