Biogeochemical timescales of climate change onset and recovery in the
North Atlantic interior under rapid atmospheric CO2 forcing
Abstract
Anthropogenic climate change footprints in the ocean go beyond the mixed
layer depth, with considerable impacts throughout mesopelagic and
deep-ocean ecosystems. Yet, little is known about the timing of these
environmental changes, their spatial extent, and the associated
timescales of recovery in the ocean interior when strong mitigation
strategies are involved. Here, we simulate idealized rapid climate
change and mitigation scenarios using the Norwegian Earth System Model
(NorESM) to investigate timescales of climate change onset and recovery
and the extent of change in the North Atlantic (NAtl) interior relative
to Pre-industrial (PI) variability across a suite of environmental
drivers (Temperature – T; pH; Dissolved Oxygen – DO; Apparent Oxygen
Utilization - AOU; Export Production - EP; and Calcite saturation state
- Ωc). We show that, below the subsurface domains,
responses of these drivers are asymmetric and detached from the
anthropogenic forcing with large spatial variations. Vast regions of the
interior NAtl experience detectable anthropogenic signal significantly
earlier and over a longer period than those projected for the
subsurface. In contrast to surface domains, the NAtl interior remains
largely warmer relative to PI (up to +50%) following the mitigation
scenario, with anomalously lower EP, pH and Ωc (up to
-20%) south of 30°N. Oxygenation in the upper mesopelagic of up to
+20% is simulated, mainly driven by a decrease in consumption during
remineralization. Our study highlights the need for long-term commitment
focused on pelagic and deep-water ecosystem monitoring to fully
understand the impact of anthropogenic climate change on the North
Atlantic biogeochemistry.