The evolution of the Patagonian Ice Sheet from 35 ka to the Present Day (PATICE)

Abstract

<p>We present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronostratigraphic data. PATICE includes 58,823 landforms and 1,669 ages, and extends from 38°S to 55°S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka (synchronous with the “Little Ice Age”) and 2011 AD. At 35 ka, the PIS covered of 492.6 x10<sup>3 </sup>km<sup>2</sup>, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent at 33 – 28 ka from 38°S to 48°S, and earlier, around 47 ka from 48°S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation at 21 – 18 ka, followed by rapid deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at 14 – 13 ka, 11 ka, 5 – 6 ka, 1 – 2 ka, and 0.2 ka. We suggest that 20<sup>th</sup> century glacial recession is occurring faster than at any time documented during the Holocene. </p>

Southward migration of the Southern Hemisphere westerly winds corresponds with warming climate over centennial timescales

“…in NZ fjords 36,37 ) or sustained (e.g., Patagonian glacier fluctuations 53 ), cool periods, such as the LIA, have been associated with increased rainfall. For example, in Patagonia, many records show cooler and wetter conditions beginning around c. 1450-1500 CE, associated with increased effective precipitation recorded in lakes 33,[54][55][56] and glacier advances 53,57 . Colder and wetter conditions are also seen in New Zealand and Australia during the LIA [58][59][60] .…”

The submerged footprint of Perito Moreno glacier

“…It is possible that moraines of the mid-Holocene are much more widespread in Patagonia, but the limited number of studies performed and the possibility that these have been re-occupied by glaciers make these reconstructions very uncertain 11 . Similar mid-Holocene advances have been observed at this time in the sub-Antarctic islands 36 and in New Zealand 37 , 38 .…”

“…There is evidence that calving glaciers have not been responding directly to climate this century, their behavior being more closely controlled by trough geometry and topography than by climate 10 . This is because a strong influence of topography and water depth is expected in influencing ice marginal positions and retreat dynamics 11 . For the case of Perito Moreno, it has been demonstrated that seasonal ice-front variations would be primary due to frontal ablation (subaqueous melting), which is correlated with seasonal lake water temperature variations 12 .…”

“…Most of the present landscape of the Patagonia region is the result of the glacial modification during the Pleistocene and Holocene, when the glaciers expanded their fronts towards the east 22 – 24 . A recent reconstruction of the Patagonia ice-sheet made at 5 kyr intervals, and based on a compilation of available geomorphological data and recalibrated ages 11 indicate that this region has responded to climate signals observed in Antarctica (e.g., the Antarctic Cold Reversal), and also that variations in the core of the Southern Westerly Winds played a role in driving glacier advance and recession in function of both the timings and their latitudinal locations.…”

Holocene glacier history of northeastern Cordillera Darwin, southernmost South America (55°S)

“…Yet additional paleoclimate records are justified for several reasons. First, records of paleoglacier activity in Cordillera Darwin could provide insights to solve apparent differences regarding the magnitude/timing of glacial fluctuations during the Antarctic Cold Reversal (ACR; 14.5-12.9 ka; e.g., McCulloch et al, 2005b;Hall et al, 2013Hall et al, , 2019Menounos et al, 2013;Fernández et al, 2017;Davies et al, 2020). Second, a detailed understanding of the Holocene glacier history of this region is lacking in general with exceptions (e.g., Strelin et al, 2008;Menounos et al, 2013Menounos et al, , 2020Hall et al, 2019).…”