Ocean carbonate system variability in the North Atlantic Subpolar surface water (1993-2017)
The North Atlantic is one of the major ocean sinks for natural and anthropogenic atmospheric CO 2. Given the variability of the circulation, convective processes or warming-cooling recognized in the high latitudes in this region , a better understanding of the CO 2 sink temporal variability and asso...
Published in: | Biogeosciences |
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Main Authors: | , , , , , , |
Other Authors: | , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2020
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Subjects: | |
Online Access: | https://hal.archives-ouvertes.fr/hal-02573889 https://hal.archives-ouvertes.fr/hal-02573889/document https://hal.archives-ouvertes.fr/hal-02573889/file/Leseurre-bg-17-2553-2020.pdf https://doi.org/10.5194/bg-17-2553-2020 |
Summary: | The North Atlantic is one of the major ocean sinks for natural and anthropogenic atmospheric CO 2. Given the variability of the circulation, convective processes or warming-cooling recognized in the high latitudes in this region , a better understanding of the CO 2 sink temporal variability and associated acidification needs a close inspection of seasonal, interannual to multidecadal observations. In this study, we investigate the evolution of CO 2 uptake and ocean acidification in the North Atlantic Subpolar Gyre (50-64 • N) using repeated observations collected over the last 3 decades in the framework of the long-term monitoring program SURATLANT (SURveillance de l'ATLANTique). Over the full period (1993-2017) pH decreases (−0.0017 yr −1) and fugacity of CO 2 (f CO 2) increases (+1.70 µatm yr −1). The trend of f CO 2 in surface water is slightly less than the atmospheric rate (+1.96 µatm yr −1). This is mainly due to dissolved inorganic carbon (DIC) increase associated with the anthropogenic signal. However, over shorter periods (4-10 years) and depending on the season, we detect significant variability investigated in more detail in this study. Data obtained between 1993 and 1997 suggest a rapid increase in f CO 2 in summer (up to +14 µatm yr −1) that was driven by a significant warming and an increase in DIC for a short period. Similar f CO 2 trends are observed between 2001 and 2007 during both summer and winter, but, without significant warming detected, these trends are mainly explained by an increase in DIC and a decrease in alkalinity. This also leads to a pH decrease but with contrasting trends depending on the region and season (between −0.006 and −0.013 yr −1). Conversely , data obtained during the last decade (2008-2017) in summer show a cooling of surface waters and an increase in alkalinity, leading to a strong decrease in surface f CO 2 (between −4.4 and −2.3 µatm yr −1 i.e., the ocean CO 2 sink increases). Surprisingly, during summer, pH increases up to +0.0052 yr −1 in the southern subpolar ... |
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