Evolution of the Cook Ice Cap (Kerguelen Islands) between the last centuries and 2100 ce based on cosmogenic dating and glacio-climatic modelling

Abstract

The Cook Ice Cap (CIC) on the sub-Antarctic Kerguelen Islands recently experienced extremely negative surface mass balance. Further deglaciation could have important impacts on endemic and invasive fauna and flora. To put this exceptional glacier evolution into a multi-centennial-scale context, we refined the evolution of the CIC over the last millennium, investigated the associated climate conditions and explored its potential evolution by 2100 ce. A glaciological model, constrained by cosmic ray exposure dating of moraines, historical documents and recent direct mass balance observations, was used to simulate the ice-cap extents during different phases of advance and retreat between the last millennium and 2100 ce. Cosmogenic dating suggests glacial advance around the early Little Ice Age (LIA), consistent with findings from other sub-Antarctic studies, and the rather cold and humid conditions brought about by the negative phase of the Southern Annular Mode (SAM). This study contributes to our currently limited understanding of palaeoclimate for the early LIA in the southern Indian Ocean. Glaciological modelling and observations confirm the recent decrease in CIC extent linked to the intensification of the SAM. Although affected by large uncertainties, future simulations suggest a complete disappearance of CIC by the end of the century.

New cosmogenic nuclide constraints on Late Glacial and Holocene glacier fluctuations in the sub-Antarctic Indian Ocean (Kerguelen Islands, 49°S)

“…The western part of the main Kerguelen island, Grande Terre, hosts the warm-based Cook Ice Cap (CIC; 1050 m a.s.l. ), which covered ~ 400 km 2 in 2020 (Verfaillie et al, 2021). Several other smaller glaciated areas are also located on the Rallier du Baty Peninsula in the southwest of the archipelago, on the Gallieni Peninsula in the south, and on the Presqu'île de la Société de Géographie north of CIC (Fig.…”

“…(Charton et al, 2020). Finally, 36 Cl ages from moraines deposited by Ampere Glacier, an outlet glacier of CIC, reveal -albeit with some scatter -the occurrence of at least two advances of the Ampere Glacier during the last millennium (Jomelli et al, 2017;Verfaillie et al, 2021). One is attributed to the beginning of the Little Ice Age (Solomina et al, 2016), and used to constrain a glaciological model that simulated the extent of the Cook Ice Cap during this period (Verfaillie et al, 2021).…”

“…Since the 1960s, glaciers at Kerguelen have experienced dramatic wastage, with the surface area of the CIC expected to disappear by 2100 CE (Verfaillie et al, 2021). This is explained by decreasing precipitation mainly attributed to the high index Southern Annular Mode (SAM+) (Thompson et al, 2011;Verfaillie et al, 2015;Favier et al, 2016) and to the longterm increase in atmospheric temperatures (Verfaillie et al, 2021).…”

“…Since the 1960s, glaciers at Kerguelen have experienced dramatic wastage, with the surface area of the CIC expected to disappear by 2100 CE (Verfaillie et al, 2021). This is explained by decreasing precipitation mainly attributed to the high index Southern Annular Mode (SAM+) (Thompson et al, 2011;Verfaillie et al, 2015;Favier et al, 2016) and to the longterm increase in atmospheric temperatures (Verfaillie et al, 2021). Mass and energy balance conducted on the CIC reveals that temperature impacts the precipitation phase and the equilibrium line altitude, through changes in the elevation of the 0°C isotherm and therefore of the rain/snow limit with impacts on both the snow accumulation amount and the glacier surface albedo (Favier et al, 2016).…”

“…Existing studies on Kerguelen glaciers document their fluctuations from Marine Isotopic Stage 3 (MIS-3; 60 -25 ka) to the last millennium (section 2.2; Jomelli et al, 2017Jomelli et al, , 2018Charton et al, 2020;Verfaillie et al, 2021). However, knowledge of the evolution of glaciers at Kerguelen from the end of the Late Glacial (19.0 -11.7 ka) to the Late Holocene (4 -0 ka) remains limited.…”