Après avoir presque écrasé la vulnérable plateforme glaciaire de Brunt, un groupe d’icebergs antarctiques s’installe pour l’hiver austral.
A l’été 2019, un faille qui a commencé à s’accélérer à travers la plateforme glaciaire de Brunt menaçait de libérer un iceberg d’environ deux fois la taille de la ville de New York. Mais alors qu’un autre été antarctique touche à sa fin, la plate-forme de glace continue obstinément de tenir bon. Elle a même échappé – jusqu’à présent – aux collisions avec de nombreux icebergs qui dérivaient à proximité et menaçaient d’écraser la plate-forme comme une boule de démolition glacée.
Tout au long de l’été austral 2021-22, les icebergs de l’est de la mer de Weddell ont dérivé vers le sud avec le courant côtier antarctique. L’iceberg A-23A – actuellement le plus grand iceberg du monde – a flotté librement après s’être détaché du plancher océanique où il était “échoué” (coincé) depuis des décennies. Et en janvier 2022, l’iceberg D-28 a contourné la langue du glacier Stancomb-Wills, flottant à environ 4 300 kilomètres (2 600 miles) de l’endroit où il s’est détaché de la plate-forme de glace Amery en 2019.
Un pot-pourri de grands bergs a fini par converger près de la plate-forme de glace Brunt. L’image ci-dessus, acquise le 6 mars 2022 avec le spectroradiomètre imageur à résolution modérée (MODIS) sur ;” data-gt-translate-attributes=”[{” attribute=””>NASA’s Aqua satellite, shows the bergs as they neared the end of their summer migration.
The drift of the icebergs has slowed as daylight hours have waned and temperatures have dropped, allowing sea ice to start growing in earnest on the Weddell Sea. The bergs will eventually become fully encased in seasonal sea ice for the austral winter. But for now, their enormous size makes them effective bulldozers, still capable of plowing through the sea ice and leaving paths of open water behind them. Notice also the striking cloud bands near the sides of icebergs D-31A and D-28. These are likely the result of vortices in the air produced by the edges of the thick, table-like bergs.
More bands of clouds are visible north of the bergs. Clouds like these, known as cloud streets or convective roll clouds, often line up when strong, cold winds blow over comparatively warm ocean water. In this instance, the air blowing off Antarctica was “quite cold,” according to Bart Geerts, an atmospheric scientist at University of Wyoming. Geerts inferred from the ERA5, a reanalysis product from the European Centre for Medium-Range Weather Forecasts (ECMWF), that the winds that day were blowing from the southwest and would have been about -20°C (-4°F).
The relative warmth of seawater behind the icebergs and within leads in the sea ice is apparent in the second image, acquired on March 6 by the Landsat 8 satellite. The image is false-color, created by blending data from the satellite’s Operational Land Imager (for detail and texture) and its Thermal Infrared Sensor (TIRS). The warmest areas (yellow, orange, and red) depict open water and thin, newly formed sea ice. The coldest areas (blue and white) are older, thicker ice, including the icebergs and broken ice rubble in their paths.
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, and MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Kathryn Hansen with image interpretation by Christopher Shuman, NASA/UMBC, and Bart Geerts, University of Wyoming.