@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 {2792,
	title = {Isolation of quartz for cosmogenic in situ 14C analysis},
	journal = {Geochronology},
	volume = {1},
	year = {2019},
	month = {Jan-01-2019},
	pages = {43 - 52},
	abstract = {Froth flotation is a commonly used procedure for separating feldspars and micas from quartz for the preparation of quartz mineral separates to carry out cosmogenic nuclide analysis. Whilst extracting carbon from quartz we observed in situ carbon-14 (14C) concentrations which were anomalously high and in excess of theoretical geological maximum concentrations. Further etching of sample material reduced carbon yields and 14C concentrations, yet the latter remained unrealistically high. When quartz from the original whole rock sample was isolated in our laboratory, we observed even lower carbon yields and geologically plausible in situ 14C concentrations. After ruling out unlikely geological scenarios and systematic measurement issues, we decided to investigate the quartz isolation procedure as a potential source of 14C contamination. We hypothesised that laurylamine (dodecylamine), an organic compound used as part of the froth flotation procedure, elevates 14C concentrations if residual laurylamine is present. We demonstrate that laurylamine has a 14C modern carbon source and thus has the potential to influence in situ 14C measurements if present in minute but measurable quantities. Furthermore, we show that insufficient sample etching results in contaminant 14C persisting through the step heating of quartz that is subsequently collected with the in situ component released at 1100 oC. We demonstrate that froth flotation contaminates in situ 14C measurements. We provide guidelines for the preparation of quartz based on methods developed in our laboratory and demonstrate that all froth-flotation-derived carbon and 14C is removed when applied. We recommend that the procedures presented be used at a minimum when using froth flotation to isolate quartz for in situ 14C measurements.},
	doi = {10.5194/gchron-1-43-2019},
	url = {https://gchron.copernicus.org/articles/1/43/2019/},
	author = {Nichols, Keir A. and Goehring, Brent M.}
}
@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}
}
