Oxygen Depletion in Arctic Lakes: Circumpolar Trends, Biogeochemical Processes, and Implications of Climate Change.

Polar amplification of climate change has the potential to cause large‐scale shifts in the dissolved oxygen (DO) dynamics of Arctic lakes, with implications for fish survival, greenhouse gas production, and drinking water quality. While DO is also a sentinel of environmental changes of physical, chemical, and biological nature (e.g., ice cover, temperature, dissolved organic carbon, photosynthesis, and respiration), no synthesis exists of current knowledge of DO dynamics across the diverse freshwater systems of the Arctic. We thus conducted a systematic review of the literature that yielded DO data from 167 sites north of the Subarctic limit (based on vegetation zones), spanning 76 years and including 40 sites with time series. The compilation revealed insufficient observations for adequate representativeness of oxygen dynamics over Arctic ecosystem gradients. We described the main processes controlling DO budgets of Arctic lakes and tested relationships of summer oxygen depletion with maximum depth and latitude. The meta‐analysis showed that most sites with low O2 concentrations were shallow (<10 m) and situated toward the southern end of the latitudinal gradient. Permanently stratified lakes with deep, perennially anoxic basins were located toward the northern end of the gradient. By way of a conceptual model, we identified the direct and indirect drivers and mechanisms that lead to changes in oxygen budgets in the context of the warming Arctic. This comprehensive update on available data allowed us to suggest future research directions and recommend the use of moored instruments for continuous all‐season observations, combined with modeling, remote sensing, and paleo‐reconstructions. Plain Language Summary: Lakes are dominant features of the Arctic landscape, and they have great cultural and environmental significance. The amplified effects of global warming observed in the Arctic represent a threat to the integrity of these systems. Levels of dissolved oxygen (DO) in lake water have implications for fish survival, greenhouse gas production, and drinking water quality. To summarize the state of knowledge about DO in Arctic lakes, we reviewed literature and extracted data from 167 sites. We describe the main processes known to control the oxygen balance and classified the lakes according to their bottom oxygen concentrations during summer. Most lakes that had low oxygen were shallow and situated toward the southern part of our study region. Lakes that never mix, and thus preserve permanent oxygen depletion in their deep waters, were located toward the northern end of the gradient. With a conceptual model, we illustrate how climate change is likely to influence oxygen balance by the way of direct and indirect drivers. We suggest future research directions including the collection of continuous data throughout all seasons, modeling, remote sensing, and studies of sediment cores to reconstruct past conditions. Key Points: Our systematic review located oxygen data in the Arctic from 167 field sites spanning 76 years, including 40 lakes with time‐seriesMeta‐analysis showed that summer oxygen depletion occurred mostly in shallow lakes toward the southern end of the latitudinal gradientWe formulated conceptual models of oxygen sinks and sources relevant to Arctic lakes and their responses to ongoing climate change [ABSTRACT FROM AUTHOR]