Glacier extent in sub-Antarctic Kerguelen archipelago from MIS 3 period: Evidence from 36Cl dating
Introduction
Hodgson et al. (2014) published a synthesis of terrestrial and submarine evidence of the extent and timing of the global Last Glacial Maximum (gLGM 26, 500–19, 000 years ago) (Clark et al., 2009) and the onset of deglaciation on the maritime-Antarctic and sub-Antarctic islands in the framework of the Scientific Committee for Antarctic Research (SCAR). Based on the lack of glacier chronologies or indirect evidence of glacier extents from the local LGM (lLGM), Kerguelen archipelago, located in the Indian Ocean (49°S, 69°E; Fig. 1), was classified as an area with a limited lLGM ice extent, but as subject to extensive earlier continental shelf glaciations. The Kerguelen archipelago is, however, the largest currently glaciated area in sub-Antarctic regions with numerous terrestrial glaciers. The Cook Ice Cap (CIC) and smaller glaciers covered a total area of 520 km2 in 2009 (Berthier et al., 2009). These glaciers are known to be very sensitive indicators of climate change in the southern polar region. Favier et al. (2016) showed that the current high wastage of the largest CIC outlet Ampere glacier was driven by atmospheric drying, which was induced by a latitudinal shift of the storm track over the last decades. This latitudinal storm track shift is mainly driven by the Southern Annular Mode, whose positive phase (SAM+) is associated with a belt of low pressure surrounding Antarctica (Thompson and Wallace, 2000, Thompson et al., 2011). In addition, Jomelli et al. (2017) provided chronological evidences of a general glacier retreat since the Late Glacial in Kerguelen and suggested that this glacier retreat was concomitant with warming and snow accumulation decrease in Antarctica, thus demonstrating the sensitivity of the CIC to climate change in the Antarctic region.
Considering this connection between glaciers in Kerguelen and Antarctic climate, new investigations on glacier extensions during and before the lLGM in Kerguelen is particularly relevant. It raises questions regarding their relative pacing with Antarctic climate and ice sheet changes. Moreover, a comparison of several ice core records from West and East Antarctic Ice Sheets revealed distinct variations, pointing to differences in the climate evolution of the Indo-Pacific and Atlantic sectors of Antarctica (Stenni et al., 2010, Stenni et al., 2011). A better knowledge of glacier changes at Kerguelen may be relevant to discussing possible differences in glacier behavior between the Indo-Pacific and Atlantic sectors of sub-Antarctic regions.
To address these issues, a field campaign organized in the framework of two IPEV(Institut Paul Emile Victor) programs (Kesacco and Glacepreker) was conducted focusing on the geomorphology and the chronology of several glacially formed landscapes and deposits at the margin of the CIC with the aim to document the timing and extent of the LGM in Kerguelen. Here, we present 22 new 36Cl cosmic-ray exposure ages obtained from roche moutonnee surfaces, erratics and boulders collected on moraines over the whole extent of the main island.
Section snippets
Study area
The French Kerguelen basaltic archipelago is located in the southern Indian Ocean (49°N, 69°E) about 2000 km north of Antarctica. It is composed of one main island with an area of 6700 km2 and about 300 smaller islands (Fig. 1) emerged from the Kerguelen oceanic plateau about 40 Ma ago. It stretches over a distance of about 150 km. The western part of the archipelago is covered by the CIC, the largest ice cap on this island (410 km2 in 2011, Verfaillie et al., 2015), which is culminating at
Previous glaciological studies on glaciers at Kerguelen
The first glaciological investigations at Kerguelen were realized in the 1970s, during which surface energy and mass balance studies (Poggi, 1977, Vallon, 1977a, Vallon, 1977b, Vallon, 1987) were conducted on Ampere glacier. Additionally, satellite images made it possible to assess CIC wastage over the last decades (Berthier et al., 2009, Verfaillie et al., 2015). During the last six years, new glaciological investigations were conducted at Kerguelen. Ablation stakes were set up in December
Methods
The fieldwork was conducted in different areas of the Kerguelen Islands on the slope east of the CIC in order to complement a previous study (Jomelli et al., 2017) and document earlier glacier extents on the main Island at various altitudes and distances from CIC. Frontal moraines are rare on the main island but erratics and roche moutonnees are very frequent making possible to document past ice extents. Five sites, Peninsule Courbet, Val Studer, Armor Lake, Bontemps valley and Le Belvedere
Erratic boulders deposited far east of CIC
The 36Cl ages range from ∼42 to ∼11 ka (Table 1, Table 2, Table 3, Table 4) with an ∼80% contribution covering the 42–20 ka period. Our dataset can be divided into three groups (erratics, roche moutonnees and moraine landforms) in terms of sampled glacial features and distance from CIC.
The first group is composed of the 13 distant erratic boulders located at Peninsule Courbet and Val Studer.
Peninsule Courbet is the farthest sampling site located about 85 km east of CIC in our study, at an
History of glacier fluctuations at Kerguelen from 41 ka to the late glacial
36Cl cosmic-ray exposure dating of glacial erratics, roches moutonnees and morainic boulders collected at different sites over Kerguelen archipelago provide constraints on the glacier extents on the island from 41 ka to the late glacial period. Erratics from Peninsule Courbet, the farthest site east of CIC provide direct evidence that this part of the main island of Kerguelen was deglaciated ∼41 ka ago (Fig. 13). These erratics most likely do not represent the maximum glacier position and were
Conclusion
Twenty-two cosmogenic 36Cl surface exposure ages were collected from five sites on Kerguelen Archipelago on the eastern slope of the Cook Ice Cap. These samples collected from glacial moraine boulders, erratic boulders and roche moutonnee surfaces made it possible to document changes in glacier extent between 42 ka ago and the late glacial period. The data combined with an earlier record from Kerguelen reveal that glaciers retreated from the maximum extent at ∼41 ka ago. From ∼41 to ∼15 ka,
Author contributions
V.J., D.B., D.V., V.R., C.L. and V.F. conducted the field work on the Island; F.M. produced the cosmogenic data, ASTER Team performed AMS measurements; I.S., V.M., V.R. and V.J. interpreted the cosmogenic ages; A.L. V.J. interpreted the ice core signal; V.J. and I.S. prepared figures and V.J., I.S., V.R., V.F., D.V. and A.L. contributed to writing the paper.
Acknowledgments
This paper was supported by the French INSU LEFE Glacepreker project and by the IPEV Kesaaco 1048 project. The Cl-36 and Cl measurements were performed at the ASTER AMS national facility (CEREGE, Aix-en-Provence) which is supported by the INSU/CNRS, the ANR through the “Projets thématiques d'excellence” program for the “Equipements d'excellence” ASTER-CEREGE action, and IRD. We are thankful for the compositional analyses at SARM/CRPG.
References (47)
- et al.
Regional imprints of millennial variability during the MIS 3 period around Antarctica
Quat. Sci. Rev.
(2012) - et al.
Extensive MIS 3 glaciation in southernmost Patagonia revealed by cosmogenic nuclide dating of outwash sediments
Earth Planet Sci. Lett.
(2015) - et al.
Cross-sections for 36Cl from Ti at Ep = 35–150 MeV: applications to in-situ exposure dating
Nucl. Instrum. Methods Phys. Res., Sect. B
(2000) - et al.
Datation de quelques sédiments tourbeux holocènes et oscillations glaciaires aux Iles Kerguelen
C. R. Acad. Sci.
(1997) Evidence in favour of an extensive ice cover on sub-Antarctic Kerguelen Island during the last glacial
Pal Pal Pal
(1984)- et al.
Terrestrial and marine evidence for the extent and timing of glaciation on the sub-Antarctic islands
Quat. Sci. Rev.
(2014) - et al.
Initial results from isotope dilution for Cl and 36Cl measurements at the PSI/ETH Zurich AMS facility
Nucl. Instrum. Methods Phys. Res., Sect. B
(2004) - et al.
Sub-Antarctic glacier extensions in the Kerguelen region (49°S, Indian Ocean) over the past 24 000 years constrained by 36Cl moraine dating
Quat. Sci. Rev.
(2017) - et al.
Links between Patagonian ice Sheet fluctuations and Antarctic dust variability during the last glacial period (MIS 4-2)
QSR
(2010) - et al.
High-precision 10Be chronology of moraines in the Southern Alps indicates synchronous cooling in Antarctica and New Zealand 42,000 years ago
Earth Planet Sci. Lett.
(2014)