Seasonal Variations and Drivers of Surface Ocean pCO₂ in the Seasonal Ice Zone of the Eastern Indian Sector, Southern Ocean

Abstract

To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80–150°E, south of 60°S), we measured ocean surface temperature, salinity, total alkalinity (TA), the partial pressure of carbon dioxide (pCO2), and concentrations of chlorophyll‐a (chl a), dissolved inorganic carbon (DIC), and nutrients during the KY18 survey (December 2018–January 2019). The sea–air CO2 flux in this region was −8.3 ± 12.7 mmol m−2 day−1 (−92.1 to +10.6 mmol m−2 day−1). The ocean was therefore a weak CO2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO2 from winter to summer (δpCO2) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO2 in the western part (80–110°E) of the study area was mainly driven by biological activity, which decreased pCO2 from December to early January, and in the eastern part (110–150°E) by temperature, which increased pCO2 from January to February. We also examined the changes in the CO2 concentrations (xCO2) over time by comparing data from 1996 with our data (2018–2019). The oceanic and atmospheric xCO2 increased by 23 and 45 ppm in 23 years, respectively. These changes of ocean xCO2 were mainly driven by an increase in CO2 uptake from the atmosphere as a result of the rise in atmospheric xCO2 and increase in biological activity associated with the change in the water‐mass distribution.

Storm‐Driven pCO2 Feedback Weakens the Response of Air‐Sea CO2 Fluxes in the Sub‐Antarctic Southern Ocean

“…The variability in ΔpCO 2 is controlled by the air‐sea gradient of pCO 2sea with negative values implying the ingassing of CO 2 . Across the SO, the contribution made by pCO 2air variability to ΔpCO 2 is relatively low (1–4 μatm, Tozawa et al., 2022), compared to the seasonal to intra‐seasonal variability in pCO 2sea (10–100 μatm, Gregor et al., 2018; Mongwe et al., 2016). Furthermore, while storm linked drop (rise) in atmospheric pressure can decrease (increase) the pCO 2air significantly, it also increases (decreases) pCO 2sea (Text S3 in Supporting Information ), resulting in the net impact of the atmospheric pressure on ΔpCO 2 to be insignificant.…”

“…The variability in ΔpCO 2 is controlled by the air-sea gradient of pCO 2sea with negative values implying the ingassing of CO 2 . Across the SO, the contribution made by pCO 2air variability to ΔpCO 2 is relatively low (1-4 μatm, Tozawa et al, 2022), compared to the seasonal to intra-seasonal variability in pCO 2sea (10-100 μatm, (mol m 2 hr 1 ) as observed by the Wave Glider (FCO 2_storm , in black) and the storm-filtered FCO 2 (FCO 2_storm-filtered in blue) calculated from hourly k w and pre-storm ∆pCO 2 (dashed orange line), for the duration of three spring storms events Sp4, Sp5, and Sp6 (27 September 2015-9 October 2015). Gregor et al, 2018;Mongwe et al, 2016).…”

Global Ocean pCO2 Variation Regimes: Spatial Patterns and the Emergence of a Hybrid Regime

“…The thermodynamic effect of temperature on the solubility of dissolved CO 2 gives rise to a 4.23% change in p CO 2 per 1°C temperature change in isochemical conditions (Takahashi et al., 1993). The non‐thermal effect regulates ocean p CO 2 by biological production and consumption of CO 2 , ocean mixing processes, and freshwater inputs (Chierici et al., 2006; Lüger et al., 2004; Tozawa et al., 2022). However, it is challenging to directly diagnose these individual physical and biological processes from limited observations other than by approximating them within an idealized framework (Anderson et al., 2000; Chierici et al., 2006; Nomura et al., 2014).…”

“…Most previous studies of p CO 2 variability have been regionally based, using in‐situ observations that are limited in space and time (e.g., Nickford et al., 2022; Prend et al., 2022; Sutton et al., 2017; Tozawa et al., 2022). Globally, Takahashi et al.…”

Quantitative Assessment of Factors Contributing to Variations in Sea Surface pCO2 in the Pacific Sector of the Arctic Ocean

“…Our assessment of factors was based on Tozawa et al. (2022), who estimated the variation in p CO 2 due to changes in water temperature, freshwater inflow, and biological activity in the Southern Ocean. However, because the Arctic Ocean differs from the Southern Ocean in terms of both water depth and freshwater supply, their methods needed to be modified.…”