Reconstructing intermediate and deep water formation in the North Pacific during the last deglaciation

The Pacific Ocean is nearly twice the volume of the Atlantic Ocean, but the role and response of the Pacific in climate change is less well known. Future changes in atmospheric circulation may affect northward heat transport, and yet there is “low confidence” in the Intergovernmental Panel on Climate Change (IPCC) 2023 report about how this mechanism could impact modern climate change.

Another unresolved issue is the long-term potential to store carbon in the deep Pacific, which is affected by ocean circulation rates and the timescales with which waters are isolated from the atmosphere. Although circulation is slow in the Pacific today, it may have been faster during the transition out of the last ice age (18,000- 10,000-years ago), specifically during times when circulation in the Atlantic collapsed or was reduced substantially.

This work will use existing marine sediment cores and geochemical measurements collected from the Pacific Ocean and explore how and why circulation in the Pacific and the Atlantic may have alternated in strength in the past. Results will provide useful benchmarks for how the Pacific Ocean might respond to climate change in the future. This work will also provide learning and professional development opportunities for a graduate student and undergraduate students and opportunities for engagement with the public in fundamental climate science research.

This project will reconstruct intermediate and deep circulation in the North Pacific over the past 25,000-years by generating new stable isotope (d18O, d13C) and trace element data (Cd/Ca) from benthic foraminifera across a depth transect from the Northeast Pacific. These data will subsequently be combined to calculate the air-sea component of d13C (d13CAS), a novel and promising water mass tracer for this region.

The first hypothesis will ground truth d13CAS in this region and test the viability of the two benthic foraminifera, Cibicidoides and Uvigerina, as natural archives. The second part of the project endeavors to integrate the d13CAS calculation over the last deglaciation, in lieu of the current approach with distinct Holocene and LGM equations. The third hypothesis will test the influence of sea ice expansion and contraction on the signature d13CAS of the water masses NPIW and SSW over the last deglaciation.

Finally, in the fourth part of the project, the team will test if the Atlantic and Pacific Meridional Overturning Circulation were antiphased during millennial scale events in the deglaciation.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.