@article {2982,
	title = {Relative sea-level data preclude major late Holocene ice-mass change in Pine Island Bay},
	journal = {Nature Geoscience},
	volume = {15},
	year = {2022},
	month = {06/2022},
	pages = {568-573},
	abstract = {The rapidly retreating Thwaites and Pine Island glaciers together dominate present-day ice loss from the West Antarctic Ice Sheet and are implicated in runaway deglaciation scenarios. Knowledge of whether these glaciers were substantially smaller in the mid-Holocene and subsequently recovered to their present extents is important for assessing whether current ice recession is irreversible. Here we reconstruct relative sea-level change from radiocarbon-dated raised beaches at sites immediately seawards of these glaciers, allowing us to examine the response of the earth to loading and unloading of ice in the Amundsen Sea region. We find that relative sea level fell steadily over the past 5.5 kyr without rate changes that would characterize large-scale ice re-expansion. Moreover, current bedrock uplift rates are an order of magnitude greater than the rate of long-term relative sea-level fall, suggesting a change in regional crustal unloading and implying that the present deglaciation may be unprecedented in the past 5.5 kyr. While we cannot preclude minor grounding-line fluctuations, our data are explained most easily by early Holocene deglaciation followed by relatively stable ice positions until recent times and imply that Thwaites and Pine Island glaciers have not been substantially smaller than present during the past 5.5 kyr.},
	doi = {10.1038/s41561-022-00961-y},
	url = {https://www.nature.com/articles/s41561-022-00961-y},
	author = {Braddock, Scott and Hall, Brenda L. and Johnson, Joanne S. and Balco, Greg and Spoth, Meghan and Whitehouse, Pippa L. and Campbell, Seth and Goehring, Brent M. and Rood, Dylan H. and Woodward, John}
}
@article {johnson_review_2022,
	title = {Review article: Existing and potential evidence for Holocene grounding line retreat and readvance in Antarctica},
	journal = {The Cryosphere},
	volume = {16},
	number = {5},
	year = {2022},
	note = {Publisher: Copernicus GmbH},
	month = {05/2022},
	pages = {1543{\textendash}1562},
	abstract = {Widespread existing geological records from above the modern ice sheet surface and outboard of the current ice margin show that the Antarctic Ice Sheet (AIS) was much more extensive at the Last Glacial Maximum (\~{}20 ka) than at present. However, whether it was ever smaller than present during the last few millennia, and (if so) by how much, is known only for a few locations because direct evidence lies within or beneath the ice sheet, which is challenging to access. Here, we describe how retreat and readvance (henceforth {\textquotedblleft}readvance{\textquotedblright}) of AIS grounding lines during the Holocene could be detected and quantified using subglacial bedrock, subglacial sediments, marine sediment cores, relative sea-level (RSL) records, geodetic observations, radar data, and ice cores. Of these, only subglacial bedrock and subglacial sediments can provide direct evidence for readvance. Marine archives are of limited utility because readvance commonly covers evidence of earlier retreat. Nevertheless, stratigraphic transitions documenting change in environment may provide support for direct evidence from subglacial records, as can the presence of transgressions in RSL records, and isostatic subsidence. With independent age control, ice structure revealed by radar can be used to infer past changes in ice flow and geometry, and therefore potential readvance. Since ice cores capture changes in surface mass balance, elevation, and atmospheric and oceanic circulation that are known to drive grounding line migration, they also have potential for identifying readvance. A multidisciplinary approach is likely to provide the strongest evidence for or against a smaller-than-present AIS in the Holocene.},
	issn = {1994-0416},
	doi = {10.5194/tc-16-1543-2022},
	url = {https://tc.copernicus.org/articles/16/1543/2022/},
	author = {Johnson, Joanne S. and Venturelli, Ryan A. and Balco, Greg and Allen, Claire S. and Braddock, Scott and Campbell, Seth and Goehring, Brent M. and Hall, Brenda L. and Neff, Peter D. and Nichols, Keir A. and Rood, Dylan H. and Thomas, Elizabeth R. and Woodward, John}
}
@article {2646,
	title = {Abrupt mid-Holocene ice loss in the western Weddell Sea Embayment of Antarctica},
	journal = {Earth and Planetary Science Letters},
	volume = {518},
	year = {2019},
	month = {Jan-07-2019},
	pages = {127 - 135},
	abstract = {The glacial history of the westernmost Weddell Sea sector of Antarctica since the Last Glacial Maximum is virtually unknown, and yet it has been identified as critical for improving reliability of glacio-isostatic adjustment models that are required to correct satellite-derived estimates of ice sheet mass balance. Better knowledge of the glacial history of this region is also important for validating ice sheet models that are used to predict future contribution of the Antarctic ice sheet to sea level rise. Here we present a new Holocene deglacial chronology from a site on the Lassiter Coast of the Antarctic Peninsula, which is situated in the western Weddell Sea sector. Samples from 12 erratic cobbles and 18 bedrock surfaces from a series of presently-exposed ridges were analysed for cosmogenic Be-10 exposure dating, and a smaller suite of 7 bedrock samples for in situ C-14 dating. The resulting Be-10 ages are predominantly in the range 80-690 ka, whereas bedrock yielded much younger in situ C-14 ages, in the range 6.0-7.5 ka for samples collected from 138-385 m above the modern ice surface. From these we infer that the ice sheet experienced a period of abrupt thinning over a short time interval (no more than 2700 years) in the mid-Holocene, resulting in lowering of its surface by at least 250 m. Any late Holocene change in ice sheet thickness - such as re-advance, postulated by several modelling studies - must lie below the present ice sheet surface. The substantial difference in exposure ages derived from Be-10 and C-14 dating for the same samples additionally implies ubiquitous Be-10 inheritance acquired during ice-free periods prior to the last deglaciation, an interpretation that is consistent with our glacial-geomorphological field observations for former cold-based ice cover. The results of this study provide evidence for an episode of abrupt ice sheet surface lowering in the mid-Holocene, similar in rate, timing and magnitude to at least two other locations in Antarctica.},
	keywords = {Antarctica, cosmogenic dating in situ 14C, Holocene, Weddell Sea ice sheet},
	issn = {0012821X},
	doi = {10.1016/j.epsl.2019.05.002},
	url = {https://www.sciencedirect.com/science/article/pii/S0012821X19302638},
	author = {Johnson, Joanne S. and Nichols, Keir A. and Goehring, Brent M. and Balco, Greg and Schaefer, Joerg M.}
}
@article {2793,
	title = {Glacial geology and cosmogenic-nuclide exposure ages from the Tucker Glacier - Whitehall Glacier confluence, northern Victoria Land, Antarctica},
	journal = {American Journal of Science},
	volume = {319},
	year = {2019},
	month = {Oct-04-2019},
	pages = {255 - 286},
	abstract = {We describe glacial-geological observations and cosmogenic-nuclide exposure ages from the vicinity of the present grounding line of Tucker Glacier, a large alpine glacier flowing from the mountains of northern Victoria Land, East Antarctica, into the outer Ross Sea. These data are relevant for constraining the extent of ice sheet expansion and retreat in the Ross Sea, and associated eustatic sea level impact, between the Last Glacial Maximum (LGM) and the present. In addition, a terrestrial geological record of ice thickness change from this region could provide evidence for or against the hypothesis that rapid eustatic sea-level rise during meltwater pulse 1A ({\textquotedblleft}MWP-1A{\textquotedblright}) at 14.6 ka was in part the result of rapid, large-scale thinning or breakup of a marine-based portion of the LGM ice sheet in the outer Ross Sea. Glacial-geological observations, exposure ages on glacial deposits, and a novel application of in-situ-produced cosmogenic 14C in quartz-bearing bedrock to identify the limits of LGM ice cover in the absence of direct geomorphic evidence, show that Tucker Glacier near its present grounding line was 300 to 350 m thicker than present during the LGM and thinned steadily between 17 to 5 ka. The largest possible rapid thickness change in the time period 14 to 15 ka that could be accommodated by the exposure-age data is \~{}50 m, which is a small fraction of that predicted for the western Ross Sea by model simulations of the Antarctic contribution to MWP-1A. There do exist possible scenarios in which hypothesized marine ice sheet collapse in the outer Ross Sea during MWP-1A might not be recorded by ice thickness changes at Tucker Glacier. However, our record of ice thickness changes spanning this time period is the closest such record to the outer Ross Sea that is likely to exist, and it agrees with all exposure-age deglaciation chronologies from other regions of the Ross embayment in providing no evidence for such an event.},
	keywords = {Antarctica, cosmogenic-nuclide geochemistry, exposure-dating, glacial geology, Last glacial maximum, Ross Sea, Tucker Glacier, Victoria Land},
	issn = {0002-9599},
	doi = {10.2475/04.2019.01},
	url = {http://www.ajsonline.org/lookup/doi/10.2475/04.2019.01},
	author = {Balco, Greg and Todd, Claire and Goehring, Brent M. and Moening-Swanson, Isaac and Nichols, Keir}
}
@article {2794,
	title = {New Last Glacial Maximum ice thickness constraints for the Weddell Sea Embayment, Antarctica},
	journal = {The Cryosphere},
	volume = {13},
	year = {2019},
	month = {Jan-01-2019},
	pages = {2935 - 2951},
	abstract = {We describe new Last Glacial Maximum (LGM) ice thickness constraints for three locations spanning the Weddell Sea Embayment (WSE) of Antarctica. Samples collected from the Shackleton Range, Pensacola Mountains, and the Lassiter Coast constrain the LGM thickness of the Slessor Glacier, Foundation Ice Stream, and grounded ice proximal to the modern Ronne Ice Shelf edge on the Antarctic Peninsula, respectively. Previous attempts to reconstruct LGM-to-present ice thickness changes around the WSE used measurements of long-lived cosmogenic nuclides, primarily Be-10. An absence of post-LGM apparent exposure ages at many sites led to LGM thickness reconstructions that were spatially highly variable and inconsistent with flow line modelling. Estimates for the contribution of the ice sheet occupying the WSE at the LGM to global sea level since deglaciation vary by an order of magnitude, from 1.4 to 14.1m of sea level equivalent. Here we use a short-lived cosmogenic nuclide, in situ-produced C-14, which is less susceptible to inheritance problems than Be-10 and other long-lived nuclides. We use in situ C-14 to evaluate the possibility that sites with no post-LGM exposure ages are biased by cosmogenic nuclide inheritance due to surface preservation by cold-based ice and non-deposition of LGM-aged drift. Our measurements show that the Slessor Glacier was between 310 and up to 655m thicker than present at the LGM. The Foundation Ice Stream was at least 800m thicker, and ice on the Lassiter Coast was at least 385m thicker than present at the LGM. With evidence for LGM thickening at all of our study sites, our in situ C-14 measurements indicate that the long-lived nuclide measurements of previous studies were influenced by cosmogenic nuclide inheritance. Our inferred LGM configuration, which is primarily based on minimum ice thickness constraints and thus does not constrain an upper limit, indicates a relatively modest contribution to sea level rise since the LGM of < 4.6 m, and possibly as little as < 1.5 m.},
	doi = {10.5194/tc-13-2935-2019},
	url = {http://nora.nerc.ac.uk/id/eprint/526081/},
	author = {Nichols, Keir A. and Goehring, Brent M. and Balco, Greg and Johnson, Joanne S. and Hein, Andrew S. and Todd, Claire}
}
@article {444,
	title = {Regional beryllium-10 production rate calibration for late-glacial northeastern North America},
	journal = {Quaternary Geochronology},
	volume = {4},
	year = {2009},
	note = {id: 2034; PT: J; UT: WOS:000265163500003},
	pages = {93-107},
	abstract = {The major uncertainty in relating cosmogenic-nuclide exposure ages to ages measured by other dating methods comes from extrapolating nuclide production rates measured at globally scattered calibration sites to the sites of unknown age that are to be dated. This uncertainty can be reduced by locating production rate calibration sites that are similar in location and age to the sites to be dated. We use this strategy to reconcile exposure age and radiocarbon deglaciation chronologies for northeastern North America by compiling (10)Be production rate calibration measurements from independently dated late-glacial and early Holocene ice-marginal landforms in this region. 10Be production rates measured at these sites are 6-12\% lower than predicted by the commonly accepted global 10Be calibration data set used with any published production rate scaling scheme. In addition, the regional calibration data set shows significantly less internal scatter than the global calibration data set. Thus, this calibration data set can be used to improve both the precision and accuracy of exposure dating of regional late-glacial events. For example, if the global calibration data set is used to calculate exposure ages, the exposure-age deglaciation chronology for central New England is inconsistent with the deglaciation chronology inferred from radiocarbon dating and varve stratigraphy. We show that using the regional data set instead makes the exposure age and radiocarbon chronologies consistent. This increases confidence in correlating exposure ages of ice-marginal landforms in northeastern North America with glacial and climate events dated by other means. (c) 2008 Elsevier Ltd. All rights reserved.},
	issn = {1871-1014},
	doi = {10.1016/j.quageo.2008.09.001},
	author = {Balco, Greg and Briner, Jason and Finkel, Robert C. and Rayburn, John A. and Ridge, John C. and Schaefer, Joerg M.}
}
