Abstract
Antarctic sea ice formation is strongly influenced by polynyas occurring in austral winter. The sea ice production of Ross Ice Shelf Polynya (RISP) located in the Ross Sea is the highest among coastal polynyas around the Southern Ocean. In this paper, daily sea ice production distribution of RISP in wintertime is estimated during 2003–2015, and the spatial and temporal trends of ice production are explored. Moreover, the sensitivity of the ice production model to parameterization is tested. To define the extent of RISP, this study uses sea ice concentration (SIC) maps mainly derived from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSRE) and the Advanced Microwave Scanning Radiometer 2 (AMSR2) by ARTIST (Arctic Radiation and Turbulence Interaction Study) sea ice algorithm (ASI) and constrains the ice production estimation to areas with SIC less than 75%. ERA-Interim reanalysis meteorological data are applied to a thermodynamic model to estimate daily ice production distribution between April and October during 2003–2015 for the open water fractions within the polynya. This estimation is conducted under the assumption that the meteorological data represent the reality. We further analyzed the spatial variability, monthly trend, and interannual trend for wintertime of the total RISP sea ice production. The results show that the ocean surface produces ice at a high rate within the distance of 20–30 km from the ice shelf front. In most high production areas, the ice production significantly increases. Some local regions show a contrarily significant decreasing trend as a result of ice shelf expansion and iceberg events. The monthly total RISP ice production ranges from 14 to 76 km3, showing substantial fluctuations in each month during 2003–2015. The seasonal variation of each year also shows substantial fluctuations. The wintertime total ice productions of RISP for 2003–2015 range 164–313 km3 with an average of 219 km3, showing no obvious temporal trend. More importantly, we conducted ten sensitivity tests, aiming to illustrate the sensitivity of the ice production model to parameterization. The output of the ice production model is sensitive to the value of the bulk transfer coefficients ( C s and C e ), latent heat of sea ice fusion ( L f ), and the threshold of SIC for RISP extent definition. C s and C e have the greatest influence, leading to a variation of average wintertime total RISP ice production results as high as 87.1%. A set of optimal local parameter values are recommended, including C s and C e = 0.002 and L f = 2.79 × 105 J·kg−1. L f is calculated by the salinity and temperature of sea ice, the value of which may lead to potential influence to the value of L f and the following ice production results.
Highlights
Polynyas are isolated areas of open water and thin ice within the ice pack in a polar region [1].They occur predictably, often at the same geographical location in winter [2,3]
The Ross Ice Shelf Polynya (RISP) and ice production occurs along the Ross Ice Shelf, in a shape of a long strip
A high ice production rate is observed in regions less than 20–30 km from the Ross Ice Shelf front
Summary
Polynyas are isolated areas of open water and thin ice within the ice pack in a polar region [1]. They occur predictably, often at the same geographical location in winter [2,3]. As coastal polynyas are forced by winter winds, the underlying warm water is exposed to cold air. The heat flux entering the polynya area brought by upwelling warm water is sufficient to prevent new ice formation. Latent heat polynyas play a much more important role in polar sea ice production than sensible heat polynyas [6]
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