Description: Calmette Bay within Marguerite Bay along the western side of the Antarctic Peninsula contains one of the most continuous flights of raised beaches described to date in Antarctica. Raised beaches extend to 40.8 m above sea level (masl) and are thought to reflect glacial isostatic adjustment due to the retreat of the Antarctic Peninsula Ice Sheet. Using optically stimulated luminescence (OSL), we dated quartz extracts from cobble surfaces buried in raised beaches at Calmette Bay. The beaches are separated into upper and lower beaches based on OSL ages, geomorphology, and sedimentary fabric. The two sets of beaches are separated by a prominent scarp. One of our OSL ages from the upper beaches dates to 9.3 thousand years ago (ka; as of 1950) consistent with previous extrapolation of sea-level data and the time of ice retreat from inner Marguerite Bay. However, four of the seven ages from the upper beaches date to the timing of glaciation. We interpret these ages to represent reworking of beaches deposited prior to the Last Glacial Maximum (LGM) by advancing and retreating LGM ice. Ages from the lower beaches record relative sea-level fall due to Holocene glacial-isostatic adjustment. We suggest a Holocene marine limit of 21.7 masl with an age of 5.5-7.3 ka based on OSL ages from Calmette Bay and other sea-level constraints in the area. A marine limit at 21.7 masl implies half as much relative sea-level change in Marguerite Bay during the Holocene as suggested by previous sea-level reconstructions. No evidence for a relative sea-level signature of neoglacial events, such as a decrease followed by an increase in RSL fall due to ice advance and retreat associated with the Little Ice Age, is found within Marguerite Bay indicating either: (1) no significant neoglacial advances occurred within Marguerite Bay; (2) rheological heterogeneity allows part of the Antarctic Peninsula (i.e. the South Shetland Islands) to respond to rapid ice mass changes while other regions are incapable of responding to short-lived ice advances; or (3) the magnitude of neoglacial events within Marguerite Bay is too small to resolve through relative sea-level reconstructions. Although the application of reconstructing sea-level histories using OSL-dated raised beach deposits provides a better understanding of the timing and nature of relative sea-level change in Marguerite Bay, we highlight possible problems associated with using raised beaches as sea-level indices due to post-depositional reworking by storm waves.

Description: Most current methods of reconstructing past sea levels within Antarctica rely on radiocarbon dating. However, radiocarbon dating is limited by the availability of material for dating and problems inherent with radiocarbon reservoirs in Antarctic marine systems. Here we report on the success of a new approach to dating raised beach deposits in Antarctica for the purpose of reconstructing past sea levels. This new approach is the use of optically stimulated luminescence (OSL) on quartz-grains obtained from the underside of cobbles within raised beaches and boulder pavements. We obtained eight OSL dates from three sites along the shores of Maxwell Bay in the South Shetland Islands of the Antarctic Peninsula. These dates are internally consistent and fit well with previously published radiocarbon ages obtained from the same deposits. In addition, when the technique was applied to a modern beach, it resulted in an age of zero. Our results suggest that this method will provide a valuable tool in the reconstruction of past sea levels in Antarctica and other coarse-grained beach deposits across the globe.

Description: The timing of the most recent Neoglacial advance in the Antarctic Peninsula is important for establishing global climate teleconnections and providing important post-glacial rebound corrections to gravity-based satellite measurements of ice loss. However, obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent Neoglacial advance in Antarctica has been hampered by the lack of historical records and the difficulty of dating materials in Antarctica. Here we use a new approach to dating flights of raised beaches in the South Shetland Islands of the northern Antarctic Peninsula to bracket the age of a Neoglacial advance that occurred between 1500 and 1700 AD, broadly synchronous with compilations for the timing of the Little Ice Age in the northern hemisphere. Our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent Neoglacial advance. In addition, these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the South Shetland Islands. We use a Maxwell viscoelastic model of glacial-isostatic adjustment (GIA) to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent Neoglacial advance. Our rebound model suggests that the subsequent melting of an additional 16-22% increase in the volume of ice within the South Shetland Islands would result in a subsequent uplift rate of 12.5 mm/yr that lasted until 1840 AD resulting in a cumulative uplift of 2.5 m. This uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent Neoglacial advance along the South Shetland Islands and falls within the range of uplift rates from similar settings such as Alaska.

Description: These grainsize data were collected by a BetterSize S3 Plus Particle Analyzer at the University of Virginia, organized in the spreadsheet by site. Each sample has a unique row with differential percentages of the binned grainsize data output in microns. Code to plot these data was developed by Dr. Allison Lepp and is available upon request to Dr. Marion McKenzie.

Description: These grainsize data were collected by a BetterSize S3 Plus Particle Analyzer at the University of Virginia, organized in the spreadsheet by site. Each sample has a unique row with differential percentages of the binned grainsize data output in microns. Code to plot these data was developed by Dr. Allison Lepp and is available upon request to Dr. Marion McKenzie.

Description: This file includes columns for dry and wet weight of sediments as well as calculated moisture content in percent. Moisture content was calculated by subtracting the dry weight from the wet weight, dividing by the dry weight and multiplying by 100. Sample dry weight was collected after oven drying at 60 degrees Celsius for 48 hours.

Description: These trace element data were collected by a Niton XLF X-ray fluorescence machine (units in ppm), while magnetic susceptibility (MS) data (units in SI) were collected using a Bartington MS2 meter. Within the spreadsheet, this data is organized by site and each sample has a unique row of data. This spreadsheet also lists the difference between "field" labels (in centimeters from the beach) and "lab" labels (in centimeters from the top of the column) presented in the associated manuscript. Code to plot these data is available upon request to Dr. Marion McKenzie.

Description: These trace element data were collected by a Niton XLF X-ray fluorescence machine (units in ppm), while magnetic susceptibility (MS) data (units in SI) were collected using a Bartington MS2 meter. Within the spreadsheet, this data is organized by site and each sample has a unique row of data. This spreadsheet also lists the difference between "field" labels (in centimeters from the beach) and "lab" labels (in centimeters from the top of the column) presented in the associated manuscript. Code to plot these data is available upon request to Dr. Marion McKenzie.

Description: These trace element data were collected by a Niton XLF X-ray fluorescence machine (units in ppm), while magnetic susceptibility (MS) data (units in SI) were collected using a Bartington MS2 meter. Within the spreadsheet, this data is organized by site and each sample has a unique row of data. This spreadsheet also lists the difference between "field" labels (in centimeters from the beach) and "lab" labels (in centimeters from the top of the column) presented in the associated manuscript. Code to plot these data is available upon request to Dr. Marion McKenzie.