Regional warming around West Antarctica, including the Antarctic Peninsula, is related to the retreat of glaciers that has resulted in significant ice mass loss in recent decades (De Angelis and Skvarca, 2003). Large icebergs (> 18.5 km long) originating from ice shelves in the Ross and Weddell Seas (Scambos et al., 2000) are attributed primarily to major loss events in these regions. Once free, icebergs become entrained in the counterclockwise Antarctic Coastal Current (Figure 1), eventually entering a strong northward flow in the Northwest Weddell Sea. We examined free-drifting icebergs in the Atlantic sector of the Southern Ocean in December 2005, aboard ARSV Laurence M. Gould, and in June 2008 and March/April 2009, aboard RVIB Nathaniel B. Palmer. Prior to these studies, little information was available about the effects of icebergs on the pelagic realm. On these cruises, we investigated the "iceberg ecosystem" (Smith et al., 2007; Smith, 2011) to assess the degree to which icebergs are (1) hotspots of biological activity across multiple trophic levels, and (2) focal points for enhanced export of organic carbon to the deep sea. An important focus of this work was to examine the fundamental mechanisms by which icebergs affect the pelagic ecosystem, including physical disruption and effects on the availability of critical nutrients (e.g., iron, nitrate).

Knowledge of iceberg locations is important for safety reasons as well as for understanding many geophysical and biological processes. Originally designed to measure wind speed and direction over the ocean, SeaWinds is a microwave scatterometer that operates at 13.4GHz (Ku-band) on the QuikSCAT satellite. Radar measurements from SeaWinds are collected and processed on a daily basis using resolution-enhancement techniques to produce daily radar images. Because icebergs scatter microwave energy more than sea ice and sea water, icebergs are detected as high-backscatter targets surrounded by lower-backscatter regions in daily SeaWinds images. As a result, iceberg positions are determined in real-time and a time-series of iceberg positions is maintained in an Antarctic iceberg database by Brigham Young University's Microwave Earth Remote Sensing (MERS) laboratory. Since SeaWinds operates independent of both solar illumination and cloud cover and has a large daily spatial coverage, this paper demonstrates that SeaWinds is an excellent platform to detect and track large tabular icebergs. These icebergs are generally larger than 5km and are typically characterized as a rough ice plateau above the surrounding sea water or sea ice. The number of icebergs tracked in the MERS Antarctic iceberg database is found to be generally greater than the number of icebergs tracked by the National Ice Center. The movement patterns of all icebergs detected by SeaWinds are also analyzed and 90% of icebergs are found to travel a counter-clockwise path around Antarctica and accumulate in the Weddell and Scotia Seas. Iceberg detection and tracking is demonstrated via multiple case studies that highlight icebergs C-19a and A-22a using the MERS database and through real-time operational support of the 2005, 2008, and 2009 NSF Antarctic cruises. Iceberg positions are validated by using collocated high-resolution satellite imagery and by navigating the NSF ships to physically intercept several large tabular icebergs in the Weddell and Scotia Seas.

From 1999 to 2009, the SeaWinds scatterometer has been used to detect and track large Antarctic icebergs on a daily basis. Here, we develop an automated estimation algorithm to supplement iceberg position reports with estimates of the iceberg's major axis length, minor axis length, and angle of orientation. A maximum-likelihood objective function that relates measured backscatter to model-based simulated backscatter is developed. The utility of the estimation approach is analyzed in simulation and via a case study of iceberg A22a. Subsequent results agree with and supplement reports compiled by the United States National Ice Center.

QuikSCAT tracking of Antarctic icebergs is discussed, and iceberg movement trends are illustrated. Iceberg melting factors are explored and a backscatter time-series is presented. Interactions between ice-berg and sea ice are examined using QuikSCAT data. To improve QuikSCAT sea ice mapping capability, a threshold algorithm to detect polynyas is developed. The 2006-2007 Antarctic ablation season is analyzed and correlations between polynya formation and sea ice melting are explored. General sea ice melting patterns are discussed, and statistics are derived from QuikSCAT's life mission and compared with SSM/I measurements. This study finds that while average Antarctic sea ice coverage is increasing, minimum sea ice extent is decreasing.

The SeaWinds on QuikSCAT scatterometer measures near surface ocean winds using radar backscatter values and a geophysical model function. QuikSCAT data is limited in coastal regions due to land contamination of the backscatter measurements. However, wind retrieval in near coastal areas can be successfully accomplished by estimating the amount of land contamination in the backscatter measurements and eliminating measurements which exceed a specified threshold. In order to accurately assess the amount of land contamination in a given measurement, a detailed knowledge of the antenna spatial response is required. The land contribution ratio is used as the contamination metric and is calculated using the spatial response of each QuikSCAT measurement. The land contamination threshold changes during wind retrieval as a function of wind conditions in the local area which allows retrieval closer to the coast as wind speeds increase. To ameliorate processing time the QuikSCAT spatial response is calculated and tabulated prior to wind retrieval. Subjective comparisons to estimated coastal winds show that determining a land contamination threshold using the percent land contribution metric provides accurate wind retrieval up to 25km closer to the coast than. current methods. As a result wind speeds can be accurately retrieved as close as 2.5km from the coast.