A modelling study of temporal and spatial p CO 2 variability on the biologically active and temperature-dominated Scotian Shelf

• Published in: Biogeosciences
• Main Authors: K. Rutherford, K. Fennel, D. Atamanchuk, D. Wallace, H. Thomas
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; North Atlantic
• Online Access: https://doi.org/10.5194/bg-18-6271-2021; https://doaj.org/article/4fbfb3f0a9034adfaa061f9884c12dbf

Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air–sea carbon dioxide (CO 2 ) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO 2 , whereas mid- and high-latitude shelves act as net sinks. Here, we combine a high-resolution regional model with surface water time series and repeat transect observations from the Scotian Shelf, a mid-latitude region in the northwest North Atlantic, to determine what processes are driving the temporal and spatial variability of partial pressure of CO 2 ( p CO 2 ) on a seasonal scale. In contrast to the global trend, the Scotian Shelf acts as a net source. Surface p CO 2 undergoes a strong seasonal cycle with an amplitude of ∼ 200–250 µ atm. These changes are associated with both a strong biological drawdown of dissolved inorganic carbon (DIC) in spring (corresponding to a decrease in p CO 2 of 100–200 µ atm) and pronounced effects of temperature, which ranges from 0 ∘ C in the winter to near 20 ∘ C in the summer, resulting in an increase in p CO 2 of ∼ 200–250 µ atm. Throughout the summer, events with low surface water p CO 2 occur associated with coastal upwelling. This effect of upwelling on p CO 2 is also in contrast to the general assumption that upwelling increases surface p CO 2 by delivering DIC-enriched water to the surface. Aside from these localized events, p CO 2 is relatively uniform across the shelf. Our model agrees with regional observations, reproduces seasonal patterns of p CO 2 , and simulates annual outgassing of CO 2 from the ocean of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M34" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>+</mo><mn mathvariant="normal">1.7</mn><mspace linebreak="nobreak" width="0.125em"/><mo>±</mo><mspace width="0.125em" linebreak="nobreak"/><mn mathvariant="normal">0.2</mn></mrow></math> <svg:svg ...