Inorganic Carbon and pCO2 Variability During Ice Formation

For details read: DeGrandpre, M. D., Lai, C.‐Z., Timmermans, M.‐L., Krishfield, R. A., Proshutinsky, A., & Torres, D. (2019). Inorganic Carbon and pCO2 Variability During Ice Formation in the Beaufort Gyre of the Canada Basin. Journal of Geophysical Research: Oceans, 124, 4017–4028. https://doi.org/10.1029/ 2019JC015109

Link: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JC015109

When sea ice forms, the dissolved solutes are squeezed out of the ice matrix, forming a dense brine that can sink into deeper water. This process has a potentially important role in the inorganic carbon cycle because dissolved inorganic carbon can sink with the brine, exporting it from the surface ocean and increasing the sea surface CO2 partial pressure (pCO2). We deployed a pCO2 sensor at 30‐m depth in the Canada Basin, the largest of the Arctic Ocean subbasins, that documented an increase in pCO2 during the fall to winter ice formation period. This increase correlated with an increase in salinity over the same time period. A simple model calculation supports that the increase in pCO2 and inorganic carbon is primarily due to ice formation. This finding has important implications for the future inorganic carbon cycle as seasonal ice formation increases due to loss of perennial ice cover in the Arctic. Figures below support these findings.

Figure 1 Beaufort Gyre Observing System mooring locations in the Canada Basin (A, B, D). This study is focused on a pCO2 record collected at ~30‐m depth on Mooring B (78.01°N, 150.00°W, 3,830‐m total water depth). The mooring was deployed on 9 October 2014 and recovered on 29 September 2015 (collecting data for 356 days).

Figure 2 CTD salinity and temperature profiles obtained on deployment (9 October 2014; red) and recovery (29 September 2015; black) at the mooring B deployment location (Figure 1). The mean depth of the CTD, located just below the subsurface float, was 28.5 m, placing the pCO2 sensor at ~30 m (horizontal dashed line). An increase in salinity and temperature were observed over the annual period (Figure 3).

Figure 3 Mooring B time series collected from 9 October 2014 to 29 September 2015. The pCO2 sensor was deployed at 30 m. Temperature and salinity were recorded by the CTD sensor at 28.5 m (see depth record in the fourth panel). Ice draft data are daily averages computed from the upward looking sonar located at 25 m. The sensor depth increased periodically due to strong eddy currents. Note that some of the sensor values are plotted off scale during these periods. The depth record has a split axis to better show the shallow depth excursions. During the ice formation period, the pCO2 increased by ~35 μatm (Figure 3) and salinity increased from 27.2 to 28.5. The mass balance models support that these increases can be primarily attributed to exclusion from growth of ~1.0–1.5 m of ice (Figure 43) during the fall to winter of 2014–2015.

References

References are available at: DeGrandpre, M. D., Lai, C.‐Z., Timmermans, M.‐L., Krishfield, R. A., Proshutinsky, A., & Torres, D. (2019). Inorganic Carbon and pCO2 Variability During Ice Formation in the Beaufort Gyre of the Canada Basin. Journal of Geophysical Research: Oceans, 124, 4017–4028. https://doi.org/10.1029/ 2019JC015109

Link: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JC015109