@article {2981,
	title = {Reconciling the apparent absence of a Last Glacial Maximum alpine glacial advance, Yukon Territory, Canada, through cosmogenic beryllium-10 and carbon-14 measurements},
	journal = {Geochronology},
	volume = {4},
	year = {2022},
	month = {05/2022},
	pages = {311 - 322},
	abstract = {We present a new in situ produced cosmogenic beryllium-10 and carbon-14 nuclide chronology from two sets (outer and inner) of alpine glacier moraines from the Grey Hunter massif of southern Yukon Territory, Canada. The chronology of moraines deposited by alpine glaciers outside the limits of the Last Glacial Maximum (LGM) ice sheets potentially provides a less-ambiguous archive of mass balance, and hence climate, than can be inferred from the extents of ice sheets themselves. Results for both nuclides are inconclusive for the outer moraines, with evidence for pre-LGM deposition (beryllium-10) and Holocene deposition (carbon-14). Beryllium-10 results from the inner moraine are suggestive of canonical LGM deposition but with relatively high scatter. Conversely, in situ carbon-14 results from the inner moraines are tightly clustered and suggestive of terminal Younger Dryas deposition. We explore plausible scenarios leading to the observed differences between nuclides and find that the most parsimonious explanation for the outer moraines is that of pre-LGM deposition, but many of the sampled boulder surfaces were not exhumed from within the moraine until the Holocene. Our results thus imply that the inner and outer moraines sampled pre- and post-date the canonical LGM and that moraines dating to the LGM are lacking likely due to overriding by the subsequent Late Glacial/earliest Holocene advance.},
	doi = {10.5194/gchron-4-311-2022},
	url = {https://gchron.copernicus.org/articles/4/311/2022/},
	author = {Goehring, Brent M. and Menounos, Brian and Osborn, Gerald and Hawkins, Adam and Ward, Brent}
}
@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 {2797,
	title = {Analysis of multiple cosmogenic nuclides constrains Laurentide Ice Sheet history and process on Mt. Mansfield, Vermont{\textquoteright}s highest peak},
	journal = {Quaternary Science Reviews},
	volume = {205},
	year = {2019},
	month = {Jan-02-2019},
	pages = {234 - 246},
	abstract = {Constraining glacial history and process on Mt Mansfield, the highest peak in Vermont (1339 m a.s.l.), provides insight into how the Laurentide Ice Sheet shaped the underlying landscape, when latest Pleistocene ice retreated, and how upland and lowland glacial histories relate. Here, we quantify in situ cosmogenic 10Be in 20 bedrock and boulder surfaces, as well as in situ cosmogenic 14C in three of those surfaces, to assess subglacial erosion and exposure history. Isotopic concentrations indicate that Mt. Mansfield{\textquoteright}s lower elevations (\~{}400{\textendash}1200 m a.s.l.) were deeply eroded by at least several meters during the last glaciation and then deglaciated rapidly; 10Be ages across this elevation span are indistinguishable and average 13.9 {\textpm} 0.6 ka (n = 15), suggesting that 800 m of ice thinning occurred within at most about a millennium. Conversely, the higher elevations (>1200 m a.s.l.) preserve a more complex geomorphic history. Mt. Mansfield{\textquoteright}s summit surfaces contain 10Be from previous periods of exposure, indicating that the mountaintop landscapes were likely preserved beneath cold-based, weakly-erosive glacial ice. Exposure ages from the shorter-lived isotope, 14C, are younger (9.7 and 11.7 ka), suggesting that Mt. Mansfield{\textquoteright}s summit was covered until the early Holocene, perhaps by snowfields, ice carapaces, and/or till. Our findings, in context of previous work, suggest that thinning Laurentide ice flowed through the valleys for at most hundreds of years following deglaciation of the uplands, but that the summit remained shielded by ice or sediment for millennia after the valleys became ice-free.},
	keywords = {Cosmogenic isotopes, erosion, Geochronology, Glaciation, Last glacial maximum, North America, Pleistocene},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2018.12.014},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0277379118307145},
	author = {Corbett, Lee B. and Bierman, Paul R. and Wright, Stephen F. and Shakun, Jeremy D. and Davis, P. Thompson and Goehring, Brent M. and Halsted, Christopher T. and Koester, Alexandria J. and Caffee, Marc W. and Zimmerman, Susan R.}
}
@article {2795,
	title = {The distribution and magnitude of subglacial erosion on millennial timescales at Engabreen, NorwayAbstract},
	journal = {Annals of Glaciology},
	volume = {60},
	year = {2019},
	month = {Jan-12-2019},
	pages = {73 - 81},
	abstract = {We quantify the magnitude of millennial-scale glacial erosion at Engabreen, a temperate glacier in coastal northern Norway, using the in situ cosmogenic nuclides carbon-14 (14C) and beryllium-10 (10Be) in bedrock exposed recently by glacial retreat. Nuclide concentrations show no dependence on distance down or across the valley. As such, resulting Holocene erosion depths along two transects perpendicular to glacier flow are highly variable with no systematic distribution, ranging from 0.10 to 2.95 m. We observed 14C{\textendash}10Be ratios elevated above the production ratio in samples of abraded bedrock, which is counter to the expectation for surfaces covered during the Holocene and exposed only recently. Muon reactions produce nuclides at greater depths than do spallation reactions and 14C at production rates at higher than those of 10Be, resulting in 14C{\textendash}10Be ratios that increase with depth. Therefore, elevated 14C{\textendash}10Be ratios indicate that sampled sites were deeply plucked during recent cover, the Little Ice Age in this case, and then rapidly abraded prior to retreat. Our results suggest that, while glacial erosion can generate a u-shaped valley profile over long periods of time (e.g., 105{\textendash}107 years), the discontinuous nature of glacial plucking produces spatially variable patterns of erosion over shorter millennial timescales.},
	keywords = {Beryllium-10, Carbon-14, cosmogenic nuclides, Engabreen, glacial erosion},
	issn = {0260-3055},
	doi = {10.1017/aog.2019.42},
	url = {https://www.cambridge.org/core/product/identifier/S0260305519000429/type/journal_article},
	author = {Rand, Cari and Goehring, Brent M.}
}
@article {2796,
	title = {A fully automated system for the extraction of in situ cosmogenic carbon-14 in the Tulane University cosmogenic nuclide laboratory},
	journal = {Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms},
	volume = {455},
	year = {2019},
	month = {Jan-09-2019},
	pages = {284 - 292},
	abstract = {During 2015 and culminating in early 2016, we acquired a new Carbon Extraction and Graphitization System (CEGS) from Aeon Laboratories, L.L.C. (hereafter, {\textquotedblleft}Aeon{\textquotedblright}), and adapted it for in situ cosmogenic sample processing. The Tulane University CEGS (TU-CEGS) is fully automated starting from sample insertion into the tube furnace to generation of graphite material ready for accelerator mass spectrometry cathode preparation. The system implements an integrated sequence of sample processing functions: extraction/collection, purification, measurement, and graphite production, which are all integrated into one unified system. The extraction portion is derived from evolving designs of fusions of quartz via lithium metaborate (LiBO2) flux. A critical analysis of system design in concert with analysis of process parameters yield a nearly order of magnitude increase in sample throughput with total samples processed in our laboratory (320 since installation) with consistent process blank levels (0.98 {\textpm} 0.32 {\texttimes} 105 atoms 14C, n = 26) and secondary standard values (0.4953 {\textpm} 0.0012 Fm, n = 8). In this paper we detail system design, process algorithm, and line performance including system blanks and the results from the CRONUS-A (6.12 {\textpm} 0.32 {\texttimes} 105 atoms g-1 14C, n = 13) interlaboratory comparison material.},
	keywords = {Automation, Cosmogenic nuclide, In situ carbon-14},
	issn = {0168583X},
	doi = {10.1016/j.nimb.2019.02.006},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0168583X19300771},
	author = {Goehring, Brent M. and Wilson, Jim and Nichols, Keir}
}
@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 {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}
}
@article {2523,
	title = {Constraining Holocene 10Be production rates in Greenland},
	journal = {Journal of Quaternary Science},
	volume = {27},
	year = {2012},
	month = {Jan-01-2012},
	pages = {2 - 6},
	abstract = {The absence of a production rate calibration experiment on Greenland has limited the ability to link 10Be exposure dating chronologies of ice-margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbr{\ae}, western Greenland, to investigate 10Be production rates. The radiocarbon chronology is inconsistent with the 10Be age calculations based on the current globally averaged 10Be production rate calibration data set, but is consistent with the 10Be production rate calibration data set from north-eastern North America, which includes a calibration site nearby on north-eastern Baffin Island. Based on the best-dated feature available from the Jakobshavn Isbr{\ae} forefield, we derive a 10Be production rate value of 3.98 {\textpm} 0.24 atoms g a-1, using the {\textquoteleft}St{\textquoteright} scaling scheme, which overlaps with recently published reference 10Be production rates. We suggest that these 10Be production rate data, or the very similar data from north-eastern North America, are used on Greenland. Copyright {\textcopyright} 2011 John Wiley \& Sons, Ltd.},
	doi = {10.1002/jqs.1562},
	url = {http://doi.wiley.com/10.1002/jqs.1562},
	author = {Briner, Jason P. and Young, {\'a}s E. and Goehring, Brent M. and Schaefer, Joerg M.}
}
