Marine habitat use and feeding ecology of introduced anadromous brown trout at the colonization front of the sub-Antarctic Kerguelen archipelago

In 1954, brown trout were introduced to the Kerguelen archipelago (49°S, 70°E), a pristine, sub-Antarctic environment previously devoid of native freshwater fishes. Trout began spreading rapidly via coastal waters to colonize adjacent watersheds, however, recent and unexpectedly the spread has slowed. To better understand the ecology of the brown trout here, and why their expansion has slowed, we documented the marine habitat use, foraging ecology, and environmental conditions experienced over one year by 50 acoustically tagged individuals at the colonization front. Trout mainly utilized the marine habitat proximate to their tagging site, ranging no further than 7 km and not entering any uncolonized watersheds. Nutritional indicators showed that trout were in good condition at the time of tagging. Stomach contents and isotope signatures in muscle of additional trout revealed a diet of amphipods (68%), fish (23%), isopods (6%), and zooplankton (6%). The small migration distances observed, presence of suitable habitat, and rich local foraging opportunities suggest that trout can achieve their resource needs close to their home rivers. This may explain why the expansion of brown trout at Kerguelen has slowed.

Evolution of a debris-covered glacier in the Kerguelen Archipelago (49°S, 69°E) over the past 15,000 years constrained by in situ cosmogenic 36Cl dating

<p>Debris-covered glaciers constitute a substantial part of the worldwide cryosphere (Scherler et al. 2018). However, their long-term response to multi-millennial climate variability has rarely been studied, in particular in the Southern Hemisphere. The presence of both debris-covered and debris-free glaciers on Kerguelen Archipelago (49°S, 69°E) offers therefore an excellent opportunity to investigate and compare long-term evolution of these two types of glaciers. To do so, we used the cosmogenic <sup>36</sup>Cl surface dating method on moraine boulders that allows to establish temporal constraints of glacier oscillation. We provide here the first Late Glacial and Holocene glacier chronology of a still active debris-covered glacier from the archipelago: the Gentil Glacier. Results show that the Gentil Glacier advanced once at ~14.3 ka, i.e. during the Late Glacial (19.0 – 11.6 ka), and re-advanced during the Late Holocene at ~2.6 ka (Charton et al., 2020). Both debris-covered and debris-free glaciers experienced a broadly synchronous advance during the Late Glacial, that may be assigned to the Antarctic Cold Reversal event (14.5 – 12.9 ka) (Jomelli et al., 2017; 2018). This suggests that both types (debris-covered and debris-free) of glaciers at Kerguelen were sensitive to large amplitude temperature fluctuations recorded in Antarctic ice cores (WAIS divide Project Members, 2013), associated with increased precipitations (Van der Putten, 2015). However, during the Late Holocene, the advance at about ~2.6 ka was not observed on other glaciers and seems to be a specific response of the debris-covered Gentil Glacier, either related to distinct ice dynamics or an individual response to precipitation changes.</p><p> </p><p> </p><p>Charton et al., 2020 : Ant. Sci. 1-13</p><p>Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144</p><p>Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123</p><p>Scherler et al., 2018 : GRL. 45, 11,798-11,805</p><p>Van der Putten et al., 2015 : Quat. Sci. Rev. 122, 142-157</p><p>WAIS Divide Project Members, 2013: Nature. 500, 440-444</p>

New Late Glacial and Holocene 36Cl and 10Be moraine chronologies from sub-Antarctic Kerguelen Archipelago

<p>The Kerguelen Archipelago (49°S, 69°E) is an excellent location for the study of multi-millennial glacier fluctuations, since it is the largest still glaciated emerged area (552 km<sup>2 </sup>in 2001) in the sub-Antarctic sector of the Indian Ocean, where many glacio-geomorphological formations such as moraines may be dated. To investigate the so-far little-known Late Glacial and the Holocene glacier fluctuations in Kerguelen, we apply cosmogenic nuclide dating of moraines in 3 glacial valleys: Val Travers valley, Ampere glacier valley and Arago glacier valley. We use in situ <sup>36</sup>Cl dating of the basaltic moraine boulders at the first two sites, and <sup>10</sup>Be dating of the quartz-bearing syenite boulders at the third site. The new <sup>36</sup>Cl and <sup>10</sup>Be exposure ages provide time constraints over the last 17,000 years. A glacial advance was highlighted during the Late Glacial at 14.4 ± 1.4 ka ago, probably linked to the Antarctic Cold Reversal event. These results are consistent with those previously obtained on the archipelago (Jomelli et al., 2017, 2018; Charton et al., 2020) and more generally those from other the sub-Antarctic regions (<em>e.g.</em> Sagredo et al., 2018). This suggests that all glaciers at this latitude were broadly sensitive to this specific climatic signal. No Early nor Mid Holocene advances were evidenced in Kerguelen glacier evolution during the Holocene due to missing moraines that may have formed in these specific periods. Radiocarbon-dated peat, published in the 1990s, provides evidence of less extensive glacier extents during the Early Holocene than during the Late Holocene (Frenot et al., 1997). Finally, glaciers seem to have re-advanced only during the Late Holocene, especially within the last millennium, at ⁓1 ka, ⁓620 years and ⁓390 years (Verfaillie et al., submitted). A comparison of this new dataset with the available <sup>10</sup>Be ages from other sub-Antarctic regions allows for the identification of 3 different glacier evolution patterns during the Holocene. The glacial fluctuations experienced by Kerguelen glaciers seems particularly uncommon, and are likely due to its singular location in the Southern Indian Ocean. Finally, climatic factors that may explain the Kerguelen glacier evolution (temperature, precipitation) are discussed. To this end, we investigate the chronology of glacier advance/retreat periods with <em>(i)</em> the variation in atmospheric temperatures recorded in ice cores in Antarctica and <em>(ii)</em> the variation in precipitation (Southern Westerly Winds, Southern Annular Mode).</p><p>Charton et al., 2020 : Ant. Sci. 1-13</p><p>Frenot et al., 1997 : C.R. Acad. Sci. Paris Life Sciences 320, 567-573</p><p>Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144</p><p>Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123</p><p>Sagredo et al., 2018 : Quat Sci. Rev. 188, 160-166</p><p>Verfaillie et al., submitted</p>

Exploring the microdiversity within marine bacterial taxa: Towards an integrated biogeography in the Southern Ocean

The phylogeography traditionally correlates the genetic relationships among individuals within a macroorganism species, to their spatial distribution. Most microbial phylogeographic studies so far have been restricted to narrow geographical regions, mainly focusing on isolated strains, either obtained by culture or single-strain natural enrichments. However, the laborious culture-based methodology imposes a low number of studied individuals, leading to poor resolution of haplotype frequency estimation, making difficult a realistic evaluation of the genetic structure of natural microbial populations in the environment.To tackle this limitation, we present a new approach to unravel the phylogeographic patterns of bacteria combining (i) community-wide survey by 16S rRNA gene metabarcoding, (ii) intra-species resolution through the oligotyping method, and (iii) genetic and phylogeographic indices, as well as migration parameters, estimated from populational molecular data as traditionally developed for macroorganisms as models.As a proof-of-concept, we applied this methodology to the bacterial genus Spirochaeta, classically reported as a gut endosymbiont of various invertebrates inhabiting the Southern Ocean (SO), but also described in marine sediment and in open waters. For this purpose, we centered our sampling into three biogeographic provinces of the SO; maritime Antarctica (King George Island), sub-Antarctic Islands (Kerguelen archipelago) and Patagonia in southern South America. Each targeted OTU was chaLRracterized by substantial intrapopulation microdiversity, a significant genetic differentiation and a robust phylogeographic structure among the three distant biogeographic provinces. Patterns of gene flow in Spirochaeta populations support the role of the Antarctic Polar Front (APF) as a biogeographic barrier to bacterial dispersal between Antarctic and sub-Antarctic provinces. Conversely, the Antarctic Circumpolar Current (ACC) appears as the main driver of connectivity between geographically distant sub-Antarctic areas such as Patagonia and Kerguelen archipelago, and between Kerguelen archipelago and maritime Antarctica. Additionnally, we found that historical processes (drift and dispersal limitation) together govern up to 86% of the spatial turnover among Spirochaeta populations. Overall, our approach represents a substantial first attempt to bridge the gap between microbial and macrobial ecology by unifying the way to study phylogeography. We revealed that strong congruency with macroorganisms patterns at the populational level shaped by the same oceanographic structures and ecological processes.

Cosmogenic Be-10 surface exposure data from the Sub-Antarctic Kerguelen Archipelago

<p>The Kerguelen archipelago (around 49°S 69°E) is the emerged part of the Kerguelen Plateau, a large igneous province in the southwestern Indian Ocean. Information on past climatic and environmental conditions in the region is vital for understanding the past behaviour of the southern westerly winds. The cross-disciplinary project SOUTHSPERE seeks to investigate past variations in this weather system through reconstruction of temporal and spatial glacier variability from lake records and glacial landforms N and NE of the Cook Ice Cap. Reliable and accurate chronological control is crucial in this context.</p><p>Surface exposure dating of glacial geomorphological features S and SE of the Cook Ice Cap has previously been done using in situcosmogenic Cl-36 [1, 2]. Solifluction and gelifraction processes appear very active in our field area, as do aeolian erosion. Also, highly variable geochemical composition of the basalts and associated intrusions, as well as the degree and type of metamorphosis, lead to strong lithology-dependant weathering and erosion rates, as evident from differential weathering reliefs on cm and m scales. The very active surface environment constitutes a challenge for obtaining accurate surface exposure ages.</p><p>In the NW part of the archipelago, basaltic lava units altered by meteoric-hydrothermal fluids contain a wide variety of secondary silicate and carbonate minerals [3]. In settings where quartz-filled geodes and fractures in the basalt are located in favourable positions on bedrock and boulder surfaces, analysis of Be-10 in euhedral and microcrystalline quartz offers a means of validating in situ Cl-36 surface exposure ages. Moreover, multi-nuclide analysis would open up for a wide range of process and landscape development studies on this young archipelago. Percolation of hydrothermal fluids in fractures and geodes is probably related to the intrusion of younger (15-5 Ma) subvolcanic rocks [see 3 and references therein]. A meteoric source of the fluids would imply that the secondary silicates contain meteoric Be-10. As meteoric production is greater than in situ production, this may represent a problem for utilising in situ Be-10 for surface exposure dating. If secondary silicate formation occurred early, rather than late in the intrusive phase, complete radioactive decay of the meteoric Be-10 component is expected prior to surface exposure.</p><p>110 rock samples were collected for surface exposure dating with in situ cosmogenic nuclides during a field campaign in November and December 2019. Here we present the first Be-10 data from rock surfaces of glacially transported boulders and exposed bedrock.</p><p>[1] Jomelli et al. 2017. Quaternary Science Reviews 162, 128-144.</p><p>[2] Jomelli et al. 2018. Quaternary Science Reviews 183, 110-123.</p><p>[3] Renac et al. 2010. European Journal of Mineralogy 22, 215-234.</p>

Geomorphological analysis of a sub-Antarctic valley under deglaciation: the Guynemer basin, Kerguelen Archipelago (49°S), Southern Indian Ocean

<p>Located in the southern part of the Indian Ocean (49°S), the Kerguelen Archipelago is the largest of the sub-Antarctic islands with an area of ​​around 7,200 km<sup>2</sup>. With a volcanic origin, its main island Grande Terre is partly covered by the Cook ice Cap which rises above 1000 m a.s.l. Numerous glaciers flow towards deep fjords especially from the ice cap. Their total surface area decreased by 21 % between 1963 and 2001, from 703 to 552 km<sup>2</sup> [1]. This high retreat rate was associated with an increase in air temperature and a decrease in precipitation potentially associated with a modification of the westerlies' regime. The archipelago has so far been the subject of very little geomorphological work, while thirty cosmogenic nuclide dates distributed on the archipelago allow a first insight in the deglaciation with ages between 41.9 ± 4.4 and 0.7 ± 0.37 ka [2].</p><p>Within the PALAS expedition (PAleoclimate from LAke Sediments) carried out in November and December 2019 on several lakes located between the ice cap and the Peninsula of the Société de la Géographie, we mapped the geomorphology of several valleys. Here we present the mapping results and analysis of the Guynemer basin located downstream the Guynemer Peak (1088 m a.s.l.). Located c. 10 km north of the Cook Ice Cap, its slopes mainly consist of frost-shattered debris interspersed with rocky escarpments, but the basin still contains a small glacier (<1.5 km<sup>2</sup>) at the foot of the east face of the peak. This face has several small hanging glaciers, one of which showing signs of destabilization. An upper Guynemer Lake resulting from the glacial over-deepening (0.5 km<sup>2</sup>; 245 m a.s.l.) is separated from the lower Guynemer Lake (1.5 km<sup>2</sup>; 121 m a.s.l.) by a rock step, a gorge and a wide delta incised by several channels. The mapped sector has many glacial inheritances, from the cirque which contains the upper lake to a frontal moraine that is partly damming the lower lake. Several dozens of morainic ridges have been recognized, corresponding at least to 6 or 7 main stages, from possibly early Holocene or Lateglacial to the 1960s. Surface exposure dating of moraines and erratic boulders in the coming months will supply a detailed chronology of the glacier fluctuations.</p><p> </p><p>[1] Berthier et al. (2009). Journal of Geophysical Research - Earth Surface, 114: F3.</p><p>[2] Jomelli et al. (2018). Quaternary Science Reviews, 183: 110-123.</p>

Etablishing the first continuous Holocene tephrostratigraphy on Kerguelen Archipelago, subantarctic Indian Oean

<p>Here we present the first Holocene-long continuous chronology of volcanic eruptions on Kerguelen archipelago, where no evidence of Holocene volcanic activity has been published so far. Our chronicle is based upon sedimentological, chronological and geochemical data form two sediment cores, taken in two different depocenters of a large lake, Lake Armor, located ca. 70 km away from the archipelago’s potentially active volcanic area. This allowed us to confidently attribute the origin of pumice-rich or ash-rich layers to contemporaneous volcanic eruptions. Altogther eight main eruptions, as well as three secondary ones, were here documented and dated, among which the youngest occurred during the Middle Age, between 890 and 980 AD. The oldest eruption is also by far the strongest one and deposited more  than 1.2m of up-to 3cm large pumices, 70 km away from the volcanic edifice. It occurred at the very beginnning of the Holocene (11 ka cal. BP), suggesting a climatic control after glacial retreat upon volcanic activity. Additionnal evidences from lake sediment and geological outcrops, both close to Lake Armor and in remote areas over Kerguelen mainland, open the future possibility of a better reconstruction of major eruptions deposit spreading and thus an assessment of their intensity. This established chronostratigraphy will be useful to synchronise paleoenvironment record at least at the scale of the archipelago as well as in surrounding marine areas where Holocene climate reconstructions are particularly sparse.</p>

A brief survey of bryological studies in the Subantarctic, including Macrocoma tenue (Orthotrichaceae), a moss genus and species newly found in Îles Kerguelen

Studies on the bryophyte flora of the Southern Ocean islands and in the Antarctic are briefly reviewed and the current state of knowledge of the moss flora of Îles Kerguelen is discussed. <em>Macrocoma tenue</em> (Hook. &amp; Grev.) Vitt is recorded from the Îles Kerguelen archipelago and this constitutes the first record of the genus <em>Macrocoma</em> (Müll. Hal.) Grout from the Subantarctic. The local plants of the species are characterized and illustrated and their ecology is discussed. Global distribution of <em>M. tenue</em> is reviewed and mapped. It is suggested that the type subspecies of <em>M. tenue</em> is a Gondwanan relictual taxon, which could have evolved on this supercontinent prior to its break-up and, subsequently, it reached Îles Kerguelen where it survived during the Pleistocene glacial epoch.