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Reduced CaCO 3 Flux to the Seafloor and Weaker Bottom Current Speeds Curtail Benthic CaCO 3 Dissolution Over the 21st Century
Author(s) -
Sulpis Olivier,
Dufour Carolina O.,
Trossman David S.,
Fassbender Andrea J.,
Arbic Brian K.,
Boudreau Bernard P.,
Dunne John P.,
Mucci Alfonso
Publication year - 2019
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2019gb006230
Subject(s) - seafloor spreading , benthic zone , bottom water , dissolution , geology , oceanography , abyssal zone , sediment , flux (metallurgy) , antarctic bottom water , deep sea , seabed , environmental science , calcite , ocean current , current (fluid) , mineralogy , geomorphology , chemistry , organic chemistry
Results from a range of Earth System and climate models of various resolution run under high‐CO 2 emission scenarios challenge the paradigm that seafloor CaCO 3 dissolution will grow in extent and intensify as ocean acidification develops over the next century. Under the “business as usual,” RCP8.5 scenario, CaCO 3 dissolution increases in some areas of the deep ocean, such as the eastern central Pacific Ocean, but is projected to decrease in the Northern Pacific and abyssal Atlantic Ocean by the year 2100. The flux of CaCO 3 to the seafloor and bottom‐current speeds, both of which are expected to decrease globally through the 21st century, govern changes in benthic CaCO 3 dissolution rates over 53% and 31% of the dissolving seafloor, respectively. Below the calcite compensation depth, a reduced CaCO 3 flux to the CaCO 3 ‐free seabed modulates the amount of CaCO 3 material dissolved at the sediment‐water interface. Slower bottom‐water circulation leads to thicker diffusive boundary layers above the sediment bed and a consequent stronger transport barrier to CaCO 3 dissolution. While all investigated models predict a weakening of bottom current speeds over most of the seafloor by the end of the 21st century, strong discrepancies exist in the magnitude of the predicted speeds. Overall, the poor performance of most models in reproducing modern bottom‐water velocities and CaCO 3 rain rates coupled with the existence of large disparities in predicted bottom‐water chemistry across models hampers our ability to robustly estimate the magnitude and temporal evolution of anthropogenic CaCO 3 dissolution rates and the associated anthropogenic CO 2 neutralization.