Abstract
We show an annual overview of the sea-air CO2 exchanges and primary drivers in the Gerlache Strait, a hotspot for climate change that is ecologically important in the northern Antarctic Peninsula. In autumn and winter, episodic upwelling events increase the remineralized carbon in the sea surface, leading the region to act as a moderate or strong CO2 source to the atmosphere of up to 40 mmol m–2 day–1. During summer and late spring, photosynthesis decreases the CO2 partial pressure in the surface seawater, enhancing ocean CO2 uptake, which reaches values higher than − 40 mmol m–2 day–1. Thus, autumn/winter CO2 outgassing is nearly balanced by an only 4-month period of intense ocean CO2 ingassing during summer/spring. Hence, the estimated annual net sea-air CO2 flux from 2002 to 2017 was 1.24 ± 4.33 mmol m–2 day–1, opposing the common CO2 sink behaviour observed in other coastal regions around Antarctica. The main drivers of changes in the surface CO2 system in this region were total dissolved inorganic carbon and total alkalinity, revealing dominant influences of both physical and biological processes. These findings demonstrate the importance of Antarctica coastal zones as summer carbon sinks and emphasize the need to better understand local/regional seasonal sensitivity to the net CO2 flux effect on the Southern Ocean carbon cycle, especially considering the impacts caused by climate change.
Highlights
The investigation of Antarctic coastal regions has long been neglected because they are difficult to access[1,2,3,4], especially during periods other than the austral s ummer[5,6,7,8]
The intensity of this behaviour is marked by high interannual variability, since the summer C O2 fluxes in the Gerlache Strait, for example, oscillate between periods of strong C O2 sink (i.e., < − 12 mmol m–2 day–1) and sea-air near-equilibrium conditions at inter-annual scales[15]
Even when Antarctic coastal regions do not behave as a strong CO2 sink, they take up CO2 in the summer[15], eventual episodes of C O2 outgassing can o ccur[20]
Summary
The investigation of Antarctic coastal regions has long been neglected because they are difficult to access[1,2,3,4], especially during periods other than the austral s ummer[5,6,7,8] This occurs because of most of the year, i.e., from April to November, these regions are almost completely or completely covered by sea ice[9,10]. Understanding the annual budget of sea-air C O2 exchanges remains a c hallenge[4,24] This is true for the Gerlache Strait and likely other major embayments around the Antarctic coasts, since it remains unclear whether this C O2 sink behaviour persists throughout the year or is balanced in other seasons. The rapid effects of climate c hange[24,28,38], a recent increase in glacial meltwater d ischarge[39], and likely the advection of both organic and anthropogenic carbon around the N AP21,40,41 have influenced the coupled physical-biological processes changing the carbon biogeochemistry across the entire western Antarctic Peninsula shelf r egion[28,39]
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