Declining O2 in the Canada Basin Halocline Consistent With Physical and Biogeochemical Effects of Pacific Summer Water Warming

The Arctic Ocean's Canada Basin (CB) has seen significant changes in ocean properties in the past two decades. A prominent change has been a warming of the Pacific Summer Water (PSW) layer in the central CB. The corresponding change in dissolved oxygen (O-2) is analyzed here to provide additional insight into PSW physics and biology, pathways, and evolution. O-2 observations are analyzed between 2003 and 2021 from the Joint Ocean Ice Study/Beaufort Gyre Observing System (JOIS/BGOS) field program, which samples CB hydrographic and biogeochemical properties. In the central CB, warming of the PSW layer over 2003-2021 has been accompanied by O-2 decreases over this time in the layer. Nutrients and other biogeochemical properties are analyzed to quantify the combined influences of both physical changes and biological changes on the evolution of O-2 concentrations in the CB PSW. In the upper portion of the PSW, O-2 decreases can be entirely accounted for by surface warming (and corresponding decrease in O-2 solubility) of its source waters in the Chukchi Sea region. In the deeper portion of the PSW layer, the observed O-2 changes are larger, and are accounted for by a combination of the decreased solubility effect due to warming, and increased organic matter breakdown in warmer waters. Decreasing O-2 in a warming Arctic Ocean is consonant with O-2 trends in the warming global oceans, and highlights the need for continued observations and analyses.

Automated summary

The Canada Basin in the Arctic Ocean has experienced significant changes in ocean properties, particularly a warming of the Pacific Summer Water layer. This study analyzes the corresponding changes in dissolved oxygen (O-2) to gain insights into the physics, biology, pathways, and evolution of the Pacific Summer Water. O-2 observations from 2003 to 2021 indicate that the warming of the Pacific Summer Water layer is accompanied by a decrease in O-2 concentrations. The combined influences of physical and biological changes on O-2 concentrations in the Pacific Summer Water are assessed through the analysis of nutrients and other biogeochemical properties. Surface warming and decreased solubility account for O-2 decreases in the upper portion of the Pacific Summer Water, while a combination of warming-related solubility decrease and increased organic matter breakdown explain larger O-2 changes in the deeper portion. The decreasing O-2 in the warming Arctic Ocean is consistent with O-2 trends in global warming oceans, emphasizing the importance of continued observations and analyses.