CPP-02. Edge of Antarctica: Two Differing Perspectives on Where Ice and Water Mix

Abstract
The marginal ice zone, or MIZ, is that band of the sea ice cover where sea ice concentration ramps up from open ocean (0%) to “close pack”, or 70%-80% ice concentration. It is “The region of an ice cover which is affected by waves and swell penetrating into the ice from the open ocean” (WMO Sea Ice Nomenclature). The MIZ marks a region of rapid change in atmospheric and oceanographic profiles of temperature, pressure, and other parameters, and of energy exchange between the ocean and atmosphere. Researchers want to know how wide the MIZ is, and how that may be changing over time. The U.S. National Ice Center Marginal Ice Zone product enables MIZ research. To create the product, analysts draw the 1/10 and 8/10 ice concentration contours on GIS workstations aided by satellite imagery, derived satellite products, and buoy data. Manual analysis allows USNIC sea ice experts to draw on experience and use contextual information like local weather and climate. The daily MIZ product offers spatial resolution and accuracy unmatched by the passive microwave-derived sea ice concentration products commonly used by researchers. These products often fail to detect ice when it is newly forming and thin, or present at low concentrations. Ice concentration tends to be underestimated, especially in the melt season. Yet there have been decades of study using PM products. They offer consistency and are well documented. Before turning to a product of manual analysis, researchers will want to know how it compares with more familiar data. An analysis compared USNIC MIZ product contours with 10% and 80% contours from the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration for February 2018 through June 2020 in the Antarctic ocean (Figure 1). In general, the MIZ product 1/10 and 8/10 contours were north of the CDR 10% and 80% contours. There was little overlap of the MIZ bands mapped by the two products. The width of the MIZ band measured by the CDR tended to be much wider than that of the USNIC product. In our short record, seasonal variations in these differences were apparent. A similar analysis using Arctic charts suggests hemispheric differences. For example, in the northern hemisphere the MIZ bands mapped by the two products overlapped considerably. U.S. National Ice Center Daily Marginal Ice Zone Products, Version 1 is available from the National Snow and Ice Data Center in shapefile, Google Earth KMZ, and ASCII formats, beginning in September 2004 in the Arctic and January 2010 in the Antarctic. We hope our preliminary analysis sparks interest in using the USNIC MIZ product for research. This poster was first presented at the January 2021 AMS meeting.