Sea‐ice conditions in the Ross Sea during spring 1996 as observed on SAR and AVHRR imagery

Abstract

The structure and properties of the sea-ice field in the western Ross Sea during the spring of 1996 are evaluated using data from the ERS-2 Synthetic Aperture Radar (SAR) and the Advanced Very High Resolution Radiometer (AVHRR) sensors. A multispectral classification method enabled separation of six ice types including fast ice, new ice, smooth first-year ice, rough first-year ice, thin new ice/wind roughened open water and glacial ice. In Terra Nova Bay it was observed that the size of the recurring polynya depended strongly on the strength of the consistent offshore winds arising from the strong katabatic wind flow down the Priestley and Reeves Glaciers. It appears that the presence and size of this feature is more dependent on atmospheric than on oceanographic forcing. The Terra Nova Bay Polynya is frequently not ice free, but covered, at least in part, by thin, new sea ice. During katabatic events, rows of new ice, formed in response to Langmuir circulations, are observed oriented perpendicular to the coastline. These structures are swept downstream where, under less turbulent conditions, they consolidate to form pancake ice and thicker ice floes. Elsewhere over the continental shelf sea-ice conditions changed little in over a month, indicating that much of the ice in this area is landfast.RÉSUMÉ [Traduit par la rédaction] On a évalué la structure et les propriétés du champ de glace de mer dans la partie ouest de la mer de Ross au printemps 1996 à partir de données des capteurs du radar à antenne synthétique (SAR) ERS-2 et du radiomètre perfectionné à très haut pouvoir de résolution (AVHRR). Une méthode de classification multispectrale a permis de subdiviser la glace en six types, dont la banquise côtière, la glace nouvelle, la glace de première année à surface lisse, la glace de première année à surface rugueuse, la glace nouvelle mince/eau libre à surface balayée par le vent et glace de glacier. Dans la baie de Terra Nova, on a observé que la taille de la polynie récurrente est largement fonction de la force des vents de terre générés par le vent catabatique en provenance des glaciers Priestley et Reeves. La présence et la taille de cet élément dépend plus du forçage atmosphérique que du forçage océanographique. Souvent, la polynie de la baie de Terra Nova n'est pas libre de glace, mais est plutôt couverte au moins en partie par une mince couche de glace de mer nouvelle. Au cours d'événements catabatiques, on observe des rangées de glace nouvelle qui sont formées en réponse à la circulation de Langmuir et orientées perpendiculairement au trait de côte. Ces structures sont entraînées vers l'aval où, dans des conditions moins turbulentes, elles fusionnent pour former des glaces en crêpes et des floes plus épais. Ailleurs sur la plate-forme continentale, les conditions de glace de mer ont peu changé dans l'espace de plus d'un mois, indiquant que dans cette région, la glace est en grande partie de la banquise côtière.

An Analysis of Near-Surface Winds, Air Temperature, and Cyclone Activity in Terra Nova Bay, Antarctica, from 1993 to 2009

“…Additionally, the polynya is an important area for the production of sea ice, as the denser, saltier water left behind when the ice forms and moves eastward sinks to the bottom of the ocean and adds to the formation of Antarctic Bottom Water (Hauser et al 2002;Kern 2009). Despite the relatively small area of the polynya (during the winter the size varies between 3000 and 7000 km 2 ), the impacts on the climate system are significant, as the formation of Antarctic Bottom Water influences the Southern Ocean thermohaline circulation (Hauser et al 2002).…”

“…Despite the relatively small area of the polynya (during the winter the size varies between 3000 and 7000 km 2 ), the impacts on the climate system are significant, as the formation of Antarctic Bottom Water influences the Southern Ocean thermohaline circulation (Hauser et al 2002).…”

A New Approach for Monitoring the Terra Nova Bay Polynya through MODIS Ice Surface Temperature Imagery and Its Validation during 2010 and 2011 Winter Seasons

“…Even though previous studies estimated TNBP extents up to 7100 km 2 [28] and 8600 km 2 [62], using ENVISAT/ASAR and ERS/SAR products respectively, the observed fluctuations of the open water area within the TNBP are typical, with annual maxima which can exceed 4000-5000 km 2 , e.g., [32,48]. These results also confirm the important effect of the Drygalski Ice Tongue, as it blocks the sea ice advection from the south and frequently represents an upper limit to the TNBP offshore widening (the bay itself measures about 3300 km 2 when considering the glacier tongue length as its longitudinal side).…”

Observations of the atmosphere and surface state over Terra Nova Bay, Antarctica using unmanned aircraft systems

“…These strong winds are responsible for creating a region free of sea ice, adjacent to the coast, which occurs periodically throughout the winter, known as the Terra Nova Bay (TNB) polynya (Kurtz and Bromwich, 1983;Bromwich and Kurtz, 1984;van Woert, 1999;Ciappa et al, 2012). The TNB polynya varies in size from 3000 to 7000 km 2 during the winter (Hauser et al, 2002) and is an important element of the regional climate since strong air-sea coupling occurs over the open water, especially in winter, as cold, dry continental air flows over the relatively warm open water. This air-sea coupling provides a source of heat and moisture for the atmosphere (Knuth and Cassano, 2014).…”