Biologie | Umwelt
Laura Schmutz, 2004 | Basel, BS
It is already known that Thwaites Glacier is one of the fastest-flowing glaciers in West Antarctica, and that its complete retreat could trigger a chain reaction that could lead to the collapse of the entire West Antarctic Ice Sheet, causing sea levels to rise by around 3.5 metres. This paper examines the instability of Thwaites Glacier, the processes controlling its recent dynamic behaviour, and the potential impacts on society. Evidence of instability is derived from satellite images of the ice’s surface movement. Conclusions about the cause of the speed-up are drawn from air and ocean parameters and their correlation. The analysis shows that the origin of Thwaites› instability is not in locally altered conditions, as originally assumed, but in changing air pressure distribution and wind movement in the southern hemisphere, which is largely influenced by man-made climate change.
Introduction
The thesis investigated two hypotheses: (I) Thwaites Glacier is now dynamically unstable and (II) regional changes in air and water temperatures are responsible for contemporary dynamic instability.
Methods
(I) Three pairs of satellite images were chosen to investigate the instability of Thwaites: 1988-89, 2005-06 and 2022-23. The images of each pair were separated by one year, enabling the geographical information systems software QGIS to be used to measure the displacement of particular crevasses seen in each image pair. The large time interval of 16 years between each pair of images serves as a context for capturing the long-term movements reflected in the retreat of the coastline and the disintegration of the glacier. (II) To investigate the cause of the instability, measurements of water temperature and salinity were analysed which had been collected from boreholes drilled through Thwaites› Eastern Ice Shelf at depths of -350 and -790 m below the ice surface between January 2020 and March 2021. Data on air temperature, air pressure and easterly surface wind speed were taken from ERA5, a reanalysis model of global climate and weather. The likelihood of a link between water temperature and easterly wind speeds was determined using Spearman’s rank correlation coefficient.
Results
(I) The results show that crevasses moved 2’950 m yr-1 in 1988-89, 3’020 m yr-1 in 2005-06 and 4’170 m yr-1 in 2022-23. The observed coastal retreat was almost 15 km between 1989 and 2005 and nearly 72 km between 2006 and 2022, with an area loss of about 4’000 km2 of fractured ice between 1988 and 2023. (II) Water measurements at -790 m reveal the presence of warm and saline Antarctic Circumpolar Deep Water (ACDW), which warmed only slightly during the measurement period. Conversely, water measurements taken at -350 m showed significant warming between 2020 and 2021 despite colder temperatures. Consistently low air temperatures and air pressures were observed, accompanied by a strengthening westerly wind pattern. The correlation coefficient between water temperature and easterly wind speeds is -0.59 at -350 m depth and -0.45 at -790 m depth.
Discussion
At a depth of -790 m, the weak correlation attributes the slight warming of the ACDW to anthropogenic climate change. At a depth of -350 m, however, the strong correlation explains the temperature increase by the upwelling of the ACDW. This is caused by a change in air pressure distribution in the southern hemisphere, characterised by the positive Southern Annular Mode which indicates a low-pressure system over Antarctica (Amundsen Sea Low) and related to increased greenhouse gas emissions. Consequently, Southern Westerly Winds have intensified and shifted southwards, forcing warm ACDW beneath the ice shelf and flowing along the inward-sloping terrain where it melts the underside of the ice. The subsequent thinning of the ice shelf reduces the buttressing support of the upstream inland ice, leading to accelerated ice flow, coastal retreat and the discharge of large masses of ice into the sea. Conversely, the consistently negative air temperatures indicate that surface melt has not been responsible for destabilising Thwaites Glacier.
Conclusions
Human-induced warming and upwelling of the ACDW has caused the instability of Thwaites, which, like uncorking a shaken bottle, could suddenly exacerbate the destabilisation of Antarctic ice. In terms of the consequences of associated sea level rise, Thwaites can be declared an undeniable part of the global climate crisis in a world of unequal vulnerability.
Würdigung durch den Experten
Dr. Andrew Tedstone
Laura erforschte die Stabilität des Thwaites-Gletschers in der Antarktis. Sie nutzte Satellitenbilder, um Veränderungen im Fluss des Gletschers in den letzten 30 Jahren zu messen und konnte zeigen, dass der Gletscher bereits instabil ist. Zudem wurden Messungen der Wassertemperatur unter dem Eisschelf und Daten von Klimamodellen verwendet, um mögliche Ursachen für die Instabilität zu identifizieren. Die Arbeit zeichnet sich durch Interdisziplinarität aus (Klima- und Glaziologie, Ozeanographie), vereint verschiedene methodische Ansätze und berücksichtigt die globale Bedeutung des Gletschers.
Prädikat:
sehr gut
Sonderpreis «Sail&Explore» gestiftet von Mare Nostrum
Gymnasium am Münsterplatz, Basel
Lehrerin: Dr. Susanne Eder-Sandtner
