Abstract Project: RAP1223

Agnes Baltzer (CNRS/ Université de Nantes)

Since 2009, we are recording and studying the evolution in the context of climate change of the coastal submarine and land morphology in front of 3 alpine glaciers on the south coast of the Kongsfjorden in Svalbard: the Vestre, the Midtre and theAustre Lovenbreen. We focus our study on the transfer from the continental to the marine domains of sediment supplied by the sub glacial rivers and relayed by a channel network to the submarine prodeltas. Thanks to different programs, realised within the AWIPEV framework (Spistbay 2009, the sailing cruises Sonny2011, Seispitz2012 and C3 (2016-2018)), and the PhD work of Marine Bourriquen (2016-2018), several questions have been explored. Our main results show that 1) glaciers retreat increases water volume and sediment availability by uncovering large areas and generating a contraction of the drainage pattern, 2) the coastal progradation was dominant from 1966 to 1990 but coastal erosion became predominant since 1990 and increased since 2011, illustrating the end of te transitional paraglacial period in the coastal dynamic of the Brøgger peninsula. On the contrary, in the sublittoral area 3) the prodeltas revealed a huge extension (246,000 m ) from 2009 to 2017. These sediment deposits, together with increased fresh water input, already have been observed to have a visible impact on the benthic algae and fauna. Indeed, in 2017, we detected, by sonar imageries and grab samples, new benthic habitats developing on the submarine prodeltas, such as Laminaria seaweeds fields. Moreover, ongoing GPS measurements of the Kongsvegen glacier mass balance ( J. Kholer, person. comm.) show that this glacier has begun to accelerate (KINGSurge project of UNIS-2018-2020) and reached summer velocities of 18m/yr in 2017, suggesting that a full surge is imminent. The associated new sediment and fresh water supplies expected, together with the intensification of the calving processes, is also expected to deeply modify the new benthic habitats.