The Antarctic Peninsula's Response to Holocene Climate Variability: Controls on Glacial Stability and Implications for Future Change
Minzoni, Becky Lynn
Anderson, John B
Doctor of Philosophy
The Antarctic Peninsula is one of the most rapidly changing regions in the Cryosphere, with 87% of its glaciers receding and several ice shelves catastrophically collapsing since observations began in the 1960’s. These substantial, well-documented changes in the ice landscape have caused concern for the mass balance of the Antarctic Peninsula Ice Cap. To better understand the significance of these recent changes, I have assimilated a massive database of new and published marine sedimentary records spanning the Holocene Epoch (the last 11.5 kyrs). The database includes 9 coastal embayments with expanded sedimentary packages and well-dated cores. Each site represents an end-member in the wide range of Antarctic Peninsula oceanography, orography, meteorology, and glacial drainage basin characteristics. Multi-proxy analysis, including sedimentology, geochemistry, and micropaleontology, was conducted at each site to reconstruct glacial history at centennial-scale resolution on par with ice-core data. The coastal sites were then compared in the context published ice-core paleoclimate, paleoceanographic, and glaciological records. The first of these sites, Herbert-Croft Fjord, provides an unparalleled opportunity to compare the marine sediment record with a related ice-core in an Antarctic maritime setting. Herbert-Croft Fjord is the southernmost embayment studied on the eastern side of the Antarctic Peninsula and represents an end-member with a cold, dry atmosphere and cold, saline ocean mass. The record from Herbert-Croft Fjord indicates grounded ice receded quickly and early in the Holocene, followed by a floating ice phase that collapsed 10 ± 2.4 calendar kyrs before present (cal kyr BP, where present day is 1950 A.D.) and never re-advanced. The fjord remained open and productive during the prolonged warm intervals of the Mid Holocene, and began to experience greater glacial influence and sea ice cover during Late Holocene cooling, a period termed the Neoglacial. The second site, Ferrero Bay of the Amundsen Sea, is the southernmost end-member on the western side of the Antarctic Peninsula and represents a truly polar coastal setting. Grounded ice receded from the deep basin much earlier than expected, ~10.7 cal kyr BP, due to warm deep water masses that under-melted the extended ice sheet during the Early Holocene. Ferrero Bay was then covered by the extensive Cosgrove Ice Shelf, which remained stable during the Mid Holocene Hypsithermal and did not recede to its current position until ~2.0 cal kyr BP, coincident with Neoglacial cooling. Thus, Ferrero Bay and the Cosgrove Ice Shelf were starkly out of phase with the northern peninsula sites and apparently were not sensitive to Holocene climate variability but rather to impinging warm ocean currents, which are observed in Ferrero Bay today. Comparison of 9 coastal sites, including Herbert-Croft Fjord, Ferrero Bay, and several other embayments of various local settings, shows highly variable glacial response to Early Holocene warming, with difference in response onset of ± 4.2 kyrs and difference in duration of ± 2.5 kyrs. The Mid Holocene was less variable, with the onset of moderately cooler conditions varying by ± 1.7 kyrs and difference in duration of this epidosde of ± 1.9 kyrs. The Late Holocene Neoglacial by contrast was synchronous with difference in onset and duration of ± 0.7 kyrs and ± 0.7 kyrs, respectively. Later historic events of shorter duration, such as the Little Ice Age, were more synchronous with differences in onset and duration of ± 0.3 kyrs and ± 0.2 kyrs, respectively. Regional glacial behavior became more synchronous during the Holocene as the glaciers and their drainage basins became progressively smaller, rendering them more sensitive to climate change and less influenced by various local forcings such as ocean temperature, basin bathymetry, and precipitation differences. The increase in glacier sensitivity helps explain the current widespread glacial recession in response to the rapid regional warming of ~3.5° C over the last century.
Antarctica; Holocene climate; glacimarine sediment; polar diatoms; glacial stability