Award: OPP-1543012

The aim of this project was to advance our understanding of the ocean processes that modulate glacier retreat along the west Antarctic Peninsula continental shelf, including enhanced understanding of societal implications. The loss of ice currently found on continents is a major driver of global sea level rise. As this ice melts and enters the ocean, it can also impact marine ecosystems by changing the properties (i.e., salinity and temperature) and circulation of coastal waters. The ocean itself plays a critical role in this ice loss as the parts of the glacial ice that is in contact with the ocean (marine terminating glaciers and ice shelves) are melted by relatively warm ocean waters. This project focused on the coastal system west of the Antarctic Peninsula (wAP), where deep ocean temperatures change significantly along the coast as the warm Bellingshausen Sea-influenced central shelf (cWAP) meets the colder Bransfield Strait to the north. While the atmosphere is typically cooler farther south, glaciological evidence indicates that glaciers terminating in the warmer cWAP are retreating faster than those terminating in Bransfield Strait. Social science evidence reveals societal impacts of these changes on conservation practices and policies, tourism, and scientific research itself. We used a combination of existing oceanographic, meteorological, and glaciological data, and the output of a state-of-the-art numerical model of the wAP coastal ocean. We analyzed them to understand the spatial and temporal variability of the along-shore thermal gradients, the processes that modulate them, and how this variability influences glacier retreat along the coast. We generated a new compilation of ocean data for this region and used it to characterize the strong hydrographic gradients along the shelf in what we are calling the Southern Bransfield Front (SBF), which separates the cWAP from Bransfield Strait. We found significant spatial variability in these gradients from the near-shore regions (where glaciers terminate) to the mid- and outer-shelf regions, with colder water generally penetrating farther south closer to the coast. The data also revealed that the along-shore thermal gradients vary by depth and season, with stronger along-shore gradients during the winter, when colder water from the Weddell Sea flows around the tip of the Antarctic Peninsula and enters Bransfield Strait. Analyses of two years of the output of the high-resolution model revealed that the exchange between the warm cWAP shelf and the cold Bransfield Strait regions is strongly seasonal, with warm flow from the cWAP to Bransfield during the summer largely reversing to flooding of the northern cWAP by cold Bransfield Strait water of Weddell Sea origin. The results also suggest significant, wind-driven interannual variability in this exchange process, with enhanced flooding of the cWAP when a dominant large scale climate signal, the Southern Annular Mode, is weaker (negative). This results in the weakening of otherwise upwelling-favorable winds in Bransfield Strait. Our efforts also resulted in significant improvement of an existing, high-resolution numerical model of this region, with the addition of tides and new wind forcing, and a detailed analysis of the performance of the model against observations. The implications of these results include that the along-shore temperature gradients that modulate glacier retreat along the wAP vary significantly in seasonal-to-interannual time scales. Most of the data available for this region comes from the summer, when sea ice is at a minimum, but our results suggest that more efforts should be made to understand the deep water variability during the rest of the year. Moreover, our results challenge the idea that the heat budget of the warm cWAP is fundamentally two-dimensional, with input of warm water from the open ocean being balanced by heat loss to the atmosphere and ice melt. Instead, we show that along-shore exchange cannot be ignored in this region. The northern cWAP, in particular, should be considered a transitional region between Bransfield Strait/Weddell Sea and the Bellingshausen Sea. We also examined how changes in the Antarctic cryosphere has impacted human communities in this polar region. For broader impacts, we updated and maintained a website (https://glaciers.uoregon.edu/) with information and resources (including a compilation of K-12 teaching lessons) of topics related to glaciers & society. A new class on polar ice and society was developed and taught for the first time in Spring 2020, with more than 50 students enrolled. The project also supported the training of a new generation of graduate students and post-doctoral scholars. This included two postdoctoral researchers, five PhD students, and four undergraduate students across four institutions (University of Delaware, University of Oregon, Old Dominion University, and University of South Florida). The work of these students spanned the natural sciences and the interface between the natural and social sciences. These early-career researchers led conference presentations and several of the publications produced by the project. Both postdoctoral researchers were successful in finding permanent academic positions after contributing to the project. Last Modified: 09/28/2021 Submitted by: Mark P Carey