Direct Observations of the Role of Lateral Advection of Sea Ice Meltwater in the Onset of Autumn Freeze Up. Issue 2 (18th February 2022)

• Record Type: Journal Article
• Authors: Crews, Laura; Lee, Craig M.; Rainville, Luc; Thomson, Jim
• Is Part Of: Journal of geophysical research. Volume 127:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-18
• Subjects: Arctic Ocean -- Beaufort Sea -- advection -- sea ice meltwater -- freeze up -- mixed layer; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017775
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: In seasonally ice‐free parts of the Arctic Ocean, autumn is characterized by heat loss from the upper ocean to the atmosphere and the onset of freeze up, in which first year sea ice begins to grow in open water areas. The timing of freeze up can be highly spatially variable, complicating efforts to provide accurate sea ice forecasting for marine operations. While melt season anomalies can be used to predict freeze up anomalies in some parts of the Arctic, this one‐dimensional view merits further examination in light of recent work demonstrating the importance of three‐dimensional flows in setting mixed layer properties in marginal ice zones. In this study, we show that horizontal advection of sea ice meltwater hastens freeze up in areas distant from the ice edge. We use nearly 800 temperature and salinity profiles along with satellite imagery collected in the central Beaufort Sea in autumn 2018 to document the roughly 100 km advection of a cold and fresh surface meltwater layer over several weeks. After the meltwater arrived, the mixed layer was cooler and shallower than the mixed layer in adjacent areas unaffected by the meltwater. The cooler and shallower meltwater‐influenced mixed layer promoted earlier ice formation. Within the meltwater‐affected area, advection was nearly as important as heat loss to the atmosphere for seasonally integrated mixed layer heat loss. Plain Language Summary: In large parts of the Arctic Ocean, sea ice melts completely in summer and reforms in autumn in a process known as "freeze up." The timing of freeze up may affect energy exchanges between the ocean and atmosphere, such as occur during storms, as well as impact the sea ice ecosystem. Warming ocean temperatures mean freeze up is occurring later, lengthening the season in which vessels that are not ice‐rated can engage in operations like shipping, resource extraction, and supplying local communities with fuel and cargo. Accurate freeze up forecasting helps ensure these operations are conducted safely. This study uses ocean temperature and salinity data from autonomous vehicles as well as data from satellites to demonstrate how areas that were affected by recent sea ice melt can freeze up early. We observed a cold and fresh footprint of meltwater near sea ice in the Beaufort Sea that flowed away from its original location and altered the upper ocean in neighboring areas. A simple model that simulates the atmosphere's influence on the ocean demonstrates that this meltwater caused the ocean to freeze several days earlier than it otherwise would have by cooling the upper ocean and limiting the depth of ocean mixing. Key Points: High spatial and temporal resolution observations by ship‐based and autonomous instruments in the ice‐free Beaufort Sea are presented Modified meltwater advected about 100 km over several weeks, cooling and shoaling the mixed layer and hastening freeze up by several days Meltwater advection caused nearly as much mixed layer heat loss as was caused by seasonally integrated heat loss to the atmosphere