Köhn, E. E., Münnich, M., Vogt, M., Desmet, F., & Gruber, N. (2022). Strong Habitat Compression by Extreme Shoaling Events of Hypoxic Waters in the Eastern Pacific. Journal of Geophysical Research: Oceans, 127(6), e2022JC018429. https://doi.org/10.1029/2022JC018429
The global ocean is currently losing oxygen. Consequently, marine organisms that require oxygen are increasingly confined to the well-oxygenated surface ocean above the gradually shoaling sub-surface “hypoxic” waters, that is, waters with insufficiently low oxygen concentrations. On top of this long-term trend, internal variability causes the hypoxic waters to intermittently shoal and induce Transient Habitat Reduction Extreme Events (THREEs). THREEs may change biogeochemical processes or alter entire ecosystem structures for weeks to months. To investigate when and where THREEs occur, a simulation of the Eastern Pacific (EP) from 1979 to 2016 was performed. The authors find that EP THREEs are mainly associated with the El Niño-Southern Oscillation, the seasonal cycle, and mesoscale eddies. At low latitudes, THREEs compress the habitat by up to 50%–70% (locally over 80%). Furthermore, 71% of THREEs go along with a shoaling of waters with extremely low pH conditions. Hence, during these THREEs marine organisms face compounding extremes. This study establishes a basis for studying the effects of THREEs in the open ocean. THREEs can provide a window into the future, as the long-term oxygen loss might transform current “extreme” conditions into the future normal state.
Policy relevant message
At low latitudes, Transient Habitat Reduction Extreme Events (THREEs) compress the habitat by up to 50%–70% (locally over 80%). Furthermore, 71% of THREEs go along with a shoaling of waters with extremely low pH conditions. Hence, during these THREEs marine organisms face compounding extremes.