Abstract
Abstract. Knowing when sea ice will open is crucial, notably for scientific deployments. This was particularly obvious when the Weddell Polynya, a large opening in the winter Southern Ocean sea ice, unexpectedly re-appeared in 2016. As no precursor had been detected, observations were limited to chance autonomous sensors, and the exact cause of the opening could not be determined accurately. We investigate here whether the signature of the vertical ocean motions or that of the leads, which ultimately re-open the polynya, are detectable in spaceborne infrared temperature before the polynya opens. From the full historical sea ice concentration record, we find 30 polynyas starting from 1980. Then, using the full time series of the spaceborne infrared Advanced Very High Resolution Radiometer, we determine that these events can be detected in the 2 weeks before the polynya opens as a reduction in the variance of the data. For the three commonly used infrared brightness temperature bands, the 15 d sum and 15 d standard deviation of their area median and maximum are systematically lower than the climatology when a polynya will open. Moreover, by comparing the infrared brightness temperature to atmospheric reanalysis, hydrographic mooring data, and autonomous profilers, we find that temporal oscillations in one band and the decrease in the difference between bands may be used as proxies for upwelling of warm water and presence of leads, respectively, albeit with caution. Therefore, although infrared data are strongly limited by their horizontal resolution and sensitivity to clouds, they could be used for studying ocean or atmosphere preconditioning of polynyas in the historical record.
Highlights
Global changes in the sea ice cover, of which the continuous decrease in summer Arctic sea ice since satellite observations began in the 1970s is the most dramatic example (Stocker et al, 2014; Notz and Stroeve, 2016), lead to a development in exploitation of ice-infested waters in both hemispheres (Meier et al, 2014; Schillat et al, 2016)
By comparing the infrared brightness temperature to atmospheric reanalysis, hydrographic mooring data, and autonomous profilers, we find that temporal oscillations in one band and the decrease in the difference between bands may be used as proxies for upwelling of warm water and presence of leads, respectively, albeit with caution
When salinity data are available, we find positive correlations between T4 and the salinity measured by the mooring (Table B2), which further indicates that variations in T4 mirror variations in warm and salty Circumpolar Deep Water (CDW)
Summary
Global changes in the sea ice cover, of which the continuous decrease in summer Arctic sea ice since satellite observations began in the 1970s is the most dramatic example (Stocker et al, 2014; Notz and Stroeve, 2016), lead to a development in exploitation of ice-infested waters in both hemispheres (Meier et al, 2014; Schillat et al, 2016). For planning purposes, early detection of sea ice opening is urgently needed. In 2016, the most famous opening in the Antarctic sea ice, the Weddell Polynya (Carsey, 1980), re-appeared for the first time in over a decade (Swart et al, 2018). Two autonomous profilers were drifting over the polynya region as it was opening (Campbell et al, 2019), but these are the only in situ data ever collected during one of its openings. Knowing of such upcoming re-opening, even if it is but a few days in advance, would allow for potentially re-routing autonomous sensors or nearby expeditions and obtaining precious data
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