Multi-decadal uptake of carbon dioxide into subtropical mode water of the North Atlantic Ocean

• Published in: Biogeosciences
• Main Author: Bates, N. R.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Bates; North Atlantic; North Atlantic oscillation; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-9-2649-2012; https://www.biogeosciences.net/9/2649/2012/

Natural climate variability impacts the multi-decadal uptake of anthropogenic carbon dioxide ( C ant ) into the North Atlantic Ocean subpolar and subtropical gyres. Previous studies have shown that there is significant uptake of CO 2 into subtropical mode water (STMW) of the North Atlantic. STMW forms south of the Gulf Stream in winter and constitutes the dominant upper-ocean water mass in the subtropical gyre of the North Atlantic Ocean. Observations at the Bermuda Atlantic Time-series Study (BATS) site near Bermuda show an increase in dissolved inorganic carbon (DIC) of +1.51 ± 0.08 μmol kg −1 yr −1 between 1988 and 2011, but also an increase in ocean acidification indicators such as pH at rates (−0.0022 ± 0.0002 yr −1 ) higher than the surface ocean (Bates et al., 2012). It is estimated that the sink of CO 2 into STMW was 0.985 ± 0.018 Pg C (Pg = 10 15 g C) between 1988 and 2011 (70 ± 1.8% of which is due to uptake of C ant ). The sink of CO 2 into the STMW is 20% of the CO 2 uptake in the North Atlantic Ocean between 14°–50° N (Takahashi et al., 2009). However, the STMW sink of CO 2 was strongly coupled to the North Atlantic Oscillation (NAO), with large uptake of CO 2 into STMW during the 1990s during a predominantly NAO positive phase. In contrast, uptake of CO 2 into STMW was much reduced in the 2000s during the NAO neutral/negative phase. Thus, NAO induced variability of the STMW CO 2 sink is important when evaluating multi-decadal changes in North Atlantic Ocean CO 2 sinks.