Depletion of Oxygen in the Bothnian Sea Since the Mid-1950s

Glider observations conducted between 2016 and 2021 were combined with shipborne surveys from the 1950s through 2010s to provide critically important information about changes in Bothnian Sea. Particularly, we evaluated rate of warming freshening several layers basin showed that 0.3°C/decade upper 25m was sufficient explain ~40% oxygen depletion since mid-1950s. This driven by limited saturation surface mixed layer (SML), caused a (related) weakening flux during spring blooms. Below SML, role decreased less than 30%, whereas became increasingly via establishing stronger stratification reduced local ventilation across basin’s halocline. The observed values this study are not critical for ecological system However, presented trends towards should be considered as an early warning sign future projections levels Sea suggest further severe losses dissolved next decades. Thus, enhancement both observational networks current physical biogeochemical models is high priority if mitigate potential impact loss develop reliable monitoring