1. Estimating marine carbon uptake in the northeast Pacific using a neural network approach.
- Author
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Duke, Patrick J., Hamme, Roberta C., Ianson, Debby, Landschützer, Peter, Ahmed, Mohamed M. M., Swart, Neil C., and Covert, Paul A.
- Subjects
ATMOSPHERIC carbon dioxide ,MARINE heatwaves ,CARBON emissions ,CARBON dioxide ,INDEPENDENT variables ,PRECIPITATION gauges ,WINTER - Abstract
The global ocean takes up nearly a quarter of anthropogenic CO 2 emissions annually, but the variability in this uptake at regional scales remains poorly understood. Here we use a neural network approach to interpolate sparse observations, creating a monthly gridded seawater partial pressure of CO 2 (p CO 2) data product from January 1998 to December 2019, at 1/12 ∘ × 1/12 ∘ spatial resolution, in the northeast Pacific open ocean, a net sink region. The data product (ANN-NEP; NCEI Accession 0277836) was created from p CO 2 observations within the 2021 version of the Surface Ocean CO 2 Atlas (SOCAT) and a range of predictor variables acting as proxies for processes affecting p CO 2 to create nonlinear relationships to interpolate observations at a spatial resolution 4 times greater than leading global products and with better overall performance. In moving to a higher resolution, we show that the internal division of training data is the most important parameter for reducing overfitting. Using our p CO 2 product, wind speed, and atmospheric CO 2 , we evaluate air–sea CO 2 flux variability. On sub-decadal to decadal timescales, we find that the upwelling strength of the subpolar Alaskan Gyre, driven by large-scale atmospheric forcing, acts as the primary control on air–sea CO 2 flux variability (r2=0.93 , p<0.01). In the northern part of our study region, divergence from atmospheric CO 2 is enhanced by increased local wind stress curl, enhancing upwelling and entrainment of naturally CO 2 -rich subsurface waters, leading to decade-long intervals of strong winter outgassing. During recent Pacific marine heat waves from 2013 on, we find enhanced atmospheric CO 2 uptake (by as much as 45 %) due to limited wintertime entrainment. Our product estimates long-term surface ocean p CO 2 increase at a rate below the atmospheric trend (1.4 ± 0.1 µ atm yr -1) with the slowest increase in the center of the subpolar gyre where there is strong interaction with subsurface waters. This mismatch suggests the northeast Pacific Ocean sink for atmospheric CO 2 may be increasing. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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