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Seminar: Quantifying Canada’s marine carbon budget: Air-sea CO2 fluxes in the Northeast Pacific

Tuesday 24 January 2023

: Microsoft Teams

We're delighted to welcome Patrick Duke, PhD Candidate from the University of Victoria, to host a seminar at Plymouth Marine Laboratory at 12.45pm on Tuesday 24th January.

Currently in his PhD at the University of Victoria in Canada, Patrick Duke studies how the ocean mitigates climate change and is impacted by human emissions. He uses machine learning to create high-resolution regional estimates of air-sea gas exchange of carbon dioxide. His work contributes to establishing a baseline of marine uptake, particularly in dynamic coastal zones, important in ensuring proposed marine carbon dioxide removal projects are real, permanent, measurable, and verifiable. He is also a sustainability leader in his community, focused on training people to combat climate change through art, policy, and innovation.
Quantifying Canada’s marine carbon budget: Air-sea CO2 fluxes in the Northeast Pacific
With the ocean taking up nearly a quarter of anthropogenic emissions annually, there is an urgent need to better understand variability in the marine carbon sink and how it may be shifting under climate change. Here, we use a two-step neural network approach as a method of gap-filling sparse observations to basin wide estimates. We compiled partial pressure of CO2 (pCO2) observations as well as a range of predictor variables including physical oceanographic reanalysis products, and satellite based biological estimates. With the predictor variables acting as proxies for known processes affecting pCO2, we can create non-linear relationships to interpolate observations from 1998-2020 in the Northeast Pacific. Using wind speed and atmospheric CO2, we evaluate spatiotemporal dynamics of carbon uptake from the atmosphere. Focusing on the open ocean, distinct seasonal, interannual, and long-term patterns emerge. Seasonally, strong fluxes in the winter months are dominated by higher winds, with outgassing in the north Alaskan Gyre and uptake in the south. On sub-decadal to decadal scales, we find the circulation strength of the subpolar Alaskan Gyre driven by large-scale atmospheric forcing acts as the primary control on air-sea CO2 flux variability. Local wind stress drives gyre circulation, depressing sea surface height, enhancing upwelling of CO2-rich subsurface waters, leading to decade-long intervals of winter outgassing. When looking at specific events, such as recent Pacific marine heatwaves from 2013, we find enhanced uptake of atmospheric CO2 due to the regional control of the Alaskan Gyre set in a weak upwelling phase. Surface ocean pCO2 long-term trends generally increase at a rate below the atmospheric trend with the largest divergence happening where there is strong interaction with water from depth. This suggests the Northeast Pacific Ocean sink for atmospheric CO2 may be increasing. The insights from such a high-resolution, regional look at marine carbon fluxes are just beginning to be mined, with estimates across the coastal to open ocean continuum next to be resolved. 

The seminar will be hosted at 12.45pm on Tuesday 24th January, through Microsoft Teams.
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