Anthropogenic-induced variations of the Atlantic Meridional Overturning Circulation (AMOC) and the associated Deep-Water Formation (DWF) are a major concern. Using measurements of triple oxygen isotopes in the deep North Atlantic, we present novel evidence for a dramatic decadal to centennial shift in ocean conditions at the source region of DWF. These measurements suggest a recent decrease in the percentage of photosynthetic O2 derived from the source regions of AMOC in the Nordic Seas compared to the Little Ice Age. 1-D model simulations suggest that a reduction in photosynthetic O2 production can explain the observed decrease. Alternatively, it may indicate a substantial decrease in sea-ice cover and thus increased air-sea gas exchange, bringing the isotopic composition of O2 closer to equilibrium with the atmosphere. Our novel data can serve as a benchmark for climate models.
Bibliographical noteFunding Information:
We thank Dr. Brian King for the opportunity to join the DY040 cruise, and the DY040 crew for all the help and support. We also thank two anonymous reviewers for their constructive comments. This study was supported by The National Science Foundation Grant 1936746 (WMS), and The Israel Science Foundation Grant 325/14, and the Comer Foundation (BL).
© 2023. The Authors.