Modeling the Seasonal Ice Zone from the Air: use of repeat aerial hydrographic surveys to constrain a regional ice-ocean model in an area of rapidly evolving ice cover

Abstract:

The Seasonal Ice Zone of the Beaufort Sea is the area of ocean north of Alaska over which sea ice melts and reforms annually. It contains the more narrow, near-edge marginal ice zone (MIZ). Seasonal Ice Zone Reconnaissance Surveys (SIZRS) measure hydrography along two meridional sections using Air eXpendable CTDs (AXCTDs) and Air eXpendable Current Profilers (AXCPs). These surveys take place aboard U.S. Coast Guard Arctic Domain Awareness flights of opportunity during each melt season (June-October) starting in 2012.

The Marginal Ice Zone Modeling and Assimilation System (MIZMAS) is a high-resolution regional ice-ocean model with daily, three-dimensional output encompassing the SIZRS survey area. Direct comparison of the SIZRS data with MIZMAS output as well as with several regional climatologies can constrain the ice-ocean model and help to explain recent changes in subsurface heat content and salinity. For example, observed freshening relative to climatology has been used as a reference to which MIZMAS surface salinity values can be relaxed. MIZMAS may in turn shed light on the physical mechanisms driving the observed freshening.

In addition, use of MIZMAS surface fluxes to drive a one-dimensional mixed layer model gives results close to observations when the model is initialized with SIZRS profiles. Because SIZRS observations range in time from the onset of melt to the onset of Fall freeze-up, the comparison of the one-dimensional model with MIZMAS illustrates the relative roles of local and regional processes in forming near-surface temperature maxima and salinity minima. The SIZRS observations and one-dimensional model are used to constrain MIZMAS estimations of stored subsurface heat while establishing the physical drivers of these temperature and salinity changes.