Trends of Anthropogenic Dissolved Inorganic Carbon in the Northwest Atlantic Ocean Estimated Using a State Space Model

Abstract
The northwest Atlantic Ocean is an important sink for carbon dioxide produced by anthropogenic activities. However the strong seasonal variability in the surface waters paired with the sparse and summer biased observations of ocean carbon makes it difficult to capture a full picture of its temporal variations throughout the water column. We aim to improve the estimation of temporal trends of dissolved inorganic carbon (DIC) due to anthropogenic sources using a new statistical approach: a time series generalization of the extended multiple linear regression (eMLR) method. Anthropogenic increase of northwest Atlantic DIC in the surface waters is hard to quantify due to the strong, natural seasonal variations of DIC. We address this by separating DIC into its seasonal, natural and anthropogenic components. Ocean carbon data is often collected in the summer, creating a summer bias, however using monthly averaged data made our results less susceptible to the strong summer bias in the available data. Variations in waters below 1000m have usually been analysed on decadal time scales, but our monthly analysis showed the anthropogenic carbon component had a sudden change in 2000 from stationary to an increasing trend at the same rate as the waters above. All depths layers had similar rates of anthropogenic increase of ∼0.57μmol kg−1 year−1, and our uncertainty levels are smaller than with eMLR results. Integration throughout the water column (0-3500m) gives an anthropogenic carbon storage rate of 1.37 ± 0.57 mol m−2 year−1, which is consistent with other published estimates.

Citation
Boteler, C., Dowd, M., Oliver, E. C. J., Krainski, E. T., & Wallace, D. W. R. (2023). Trends of Anthropogenic Dissolved Inorganic Carbon in the Northwest Atlantic Ocean Estimated Using a State Space Model. Journal of Geophysical Research: Oceans. Portico. https://doi.org/10.1029/2022jc019483

Acknowledgements
We would like to acknowledge Lorenza Raimondi and Dariia Atamanchuk for their many helpful discussions about the eMLR method and anthropogenic carbon. Funding for this research was provided by the Ocean Frontier Institute and from a Nova Scotia Graduate Scholarship.

Publisher
American Geophysical Union (AGU)

Journal
Journal of Geophysical Research: Oceans

DOI
10.1029/2022jc019483

Additional Links
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JC019483

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