Sudden Emergence of a Shallow Aragonite Saturation Horizon in the Southern Ocean
Abstract
Models project that with current CO2 emission rates, the Southern Ocean surface will be undersaturated with respect to aragonite by the end of the 21st century, resulting in widespread impacts on biogeochemistry and ocean ecosystems. Particularly concerning is the health of aragonitic organisms, such as pteropods, which can dominate surface water communities in polar regions. Here, we quantify the depth of the present-day Southern Ocean aragonite saturation horizon using hydrographic and ocean carbon chemistry observations and track its evolution over the next century using output from a large ensemble of simulations with a single Earth System Model. A new, shallow aragonite saturation horizon emerges in many locations in the Southern Ocean between now and the end of the century. While the emergence of this new horizon is captured by all ensemble members, internal climate variability may affect the year of emergence; thus, its detection may have been overlooked by ensemble average analysis in the past. The emergence of the new horizon is driven by the slow accumulation of anthropogenic CO2 in the thermocline of the Southern Ocean, where the carbonate ion concentration exhibits a local minimum and approaches undersaturation. The new horizon is apparent under the RCP4.5 emission-stabilizing scenario, as well, indicating an inevitable change. Our results suggest that there will be a sudden decrease in the volume of suitable habitat for aragonitic organisms.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53K2538N
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL