CMI Annual Report 2021

For the first time, the researchers found a consistent response
across models, which was lacking in prior work. ESMs project a
robust expansion of low oxygenated waters (Figure 12.1c), but a
slight contraction of the volume of the OMZ core waters
(Figure 12.1b). While thermal changes lead to a relatively
homogeneous oxygen loss (warming waters reduce oxygen
solubility), the team found that non-thermal changes dictate
the switch from core contraction to broader OMZ expansion.
The OMZ expansion can be attributed to a slowing down of the
tropical ocean circulation that supplies oxygen to the OMZ,
while the core contraction is associated with both a change in
ocean turbulent mixing and a decline in biological production
and respiration (Busecke et al., 2022).
Figure 12.1a-c.
(a) Global map of
oxygen distribution
at 300-500m water
depth in the world
ocean (Source:
GEOMAR).
(b-c) Projected
evolution of the
tropical Pacific
OMZ core (O 2