@article {2688,
	title = {Holocene temperature and landscape history of southwest Greenland inferred from isotope and geochemical lake sediment proxies},
	journal = {Quaternary Science Reviews},
	volume = {239},
	year = {2020},
	month = {Jan-07-2020},
	pages = {106358},
	abstract = {Terrestrial temperature reconstructions from the ice-free margins of Greenland are critical for constraining the sensitivity of the Greenland ice sheet to past climate change. Numerous investigations have clarified the glacial history of southwest Greenland in recent decades; however, very few local quantitative temperature reconstructions exist as context for changes in the cryosphere. We examine sedimentary records from two lakes south of Nuuk, Greenland (informally named lakes T1 and T2), and investigate millennial scale Holocene climate change using a multi-proxy approach. Changes in X-Ray fluorescence spectroscopy (XRF), δ15N, δ13C and biogenic silica concentrations of bulk lake sediments mark the transition from a marine environment to isolated lakes as relative sea level fell in the early Holocene. δ18O values of subfossil insects (chironomids) from lakes T1 and T2 decreased by 2{\textendash}3{\textperthousand} from c. 8.8 ka BP (minimum limiting age for the onset of lacustrine sediment deposition in lake T2; ka BP = thousands of years before 1950) to 1 ka BP. Existing isotope-independent temperature reconstructions from the west coast of Greenland suggest that these changes in δ18O values accompanied gradual cooling of 2{\textendash}4 {\textdegree}C, concomitant with decreasing summer insolation. There is widespread regional evidence that this cooling resulted in progressive regrowth of local glaciers and of the ice sheet. The regional consensus on the magnitude of this temperature change indicates that the local, modern modeled temperature - precipitation δ18O relationship cannot be used to quantify millennial-scale temperature changes at these sites through the Holocene. This reinforces that studies utilizing δ18O-based proxies to infer temperature change should carefully assess local isotope-temperature relationships over space and time.},
	keywords = {Chironomids, glaciers, Greenland, Isolation basins, lake sediments, oxygen isotopes, Paleotemperatures, Stable isotopes},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2020.106358},
	url = {https://www.sciencedirect.com/science/article/pii/S0277379120303206},
	author = {Lasher, G. Everett and Axford, Yarrow and Masterson, Andrew L. and Berman, Karalyn and Larocca, Laura J.}
}
@article {2689,
	title = {Local glaciers record delayed peak Holocene warmth in south Greenland},
	journal = {Quaternary Science Reviews},
	volume = {241},
	year = {2020},
	month = {Jan-08-2020},
	pages = {106421},
	abstract = {Local glaciers and ice caps (GICs) respond sensitively and quickly, on the scale of decades to centuries, to climate variations. Continuous records of past fluctuations in GIC size provide information on the timing and magnitude of Holocene climate shifts, and a longer-term perspective on 21st century glacier retreat. Although there is broad-scale agreement on millennial-scale trends in Holocene climate variability and fluctuations in local GICs in Greenland, regional variations are only loosely constrained. Here we present three Holocene proglacial lake sediment records from South Greenland, an area with abundant local glaciers but few Holocene-length paleoclimate records. In addition, we use geospatial analysis to model past equilibrium-line altitudes (ELAs) and thereby constrain the magnitude of ablation-season temperature change during the warmest and coolest periods of the Holocene. Physical and geochemical sedimentary characteristics show that two of the proglacial lakes continued to receive glacial meltwater input until \~{}7.3 and \~{}7.1 ka BP. The survival of local glaciers implies that South Greenland remained relatively cool, and that summer temperatures gradually warmed, but did not warm well beyond 1.2 {\textdegree}C above present in the early Holocene. In the mid-Holocene, from \~{}7.1 to 5.5 ka BP, organic sedimentation at these two sites indicates that local glaciers became very small, or more likely melted away completely. The glaciers within the third lake{\textquoteright}s catchment melted away prior to \~{}5.2 ka BP, as sediments deposited earlier in the Holocene could not be dated at this site. We estimate that summer temperatures increased by at least 1.2{\textendash}1.8 {\textdegree}C above present by \~{}7.3{\textendash}7.1 ka BP. Our results are consistent with other observations that suggest a north-to-south gradient in the timing of Holocene thermal maximum conditions, with southern Greenland experiencing a delayed warming relative to other regions in Greenland. As summer temperatures cooled in the Neoglacial, our records show that sustained glacier regrowth began \~{}3.1 ka BP with glaciers in the southernmost catchment, which at present, receive the most precipitation. In the other two catchments, which host smaller glaciers in a drier environment, regrowth began at \~{}1.3 and \~{}1.2 ka BP, the timing of which is in agreement with other glacial records from the Arctic Atlantic region. Local glaciers reached their maximum late Holocene extents during a cooler, second phase of the Little Ice Age (LIA) \~{}0.2-0.1 ka BP, that we estimate was at least 0.4{\textendash}0.9 {\textdegree}C cooler than present. Overall, these findings improve understanding of the spatio-temporal dynamics of Holocene glacier and climate change in Greenland, potentially yielding valuable information about their future response.},
	keywords = {Equilibrium-line altitudes, Greenland, Holocene thermal maximum, lake sediments, Little ice age, Mountain glaciers, Paleotemperatures},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2020.106421},
	url = {https://www.sciencedirect.com/science/article/pii/S0277379120303838},
	author = {Larocca, Laura J. and Axford, Yarrow and Bj{\o}rk, Anders A. and Lasher, G. Everett and Brooks, Jeremy P.}
}
@article {2687,
	title = {Medieval warmth confirmed at the Norse Eastern Settlement in Greenland},
	journal = {Geology},
	volume = {47},
	year = {2019},
	month = {Jan-03-2019},
	pages = {267 - 270},
	abstract = {Recent work has documented glacier advances in West Greenland coincident with the Medieval Climate Anomaly (MCA) and warmth across much of northern Europe. The North Atlantic Oscillation (NAO) has been invoked to explain antiphasing of temperatures between these North Atlantic regions. Historical and model observations suggest negative correlation between the mode of NAO and both temperature and δ18O values of precipitation over much of Greenland. We test for a hypothesized positive NAO mode and associated cool conditions during the MCA in South Greenland within the Norse Eastern Settlement by reconstructing δ18O values of precipitation at subcentennial resolution over the past 3000 yr using aquatic insect subfossils preserved in lake sediments. More positive δ18O values are found between 900 and 1400 CE, indicating a period of warmth in South Greenland superimposed on late Holocene insolation-forced Neoglacial cooling, and thus not supporting a positive NAO anomaly during the MCA. Highly variable δ18O values record an unstable climate at the end of the MCA, preceding Norse abandonment of Greenland. The spatial pattern of paleoclimate in this region supports proposals that North Atlantic subpolar ocean currents modulated South Greenland{\textquoteright}s climate over the past 3000 yr, particularly during the MCA. Terrestrial climate in the Labrador Sea and Baffin Bay regions may be spatially heterogeneous on centennial time scales due in part to the influence of the subpolar gyre.},
	issn = {0091-7613},
	doi = {10.1130/G45833.110.1130/2019096},
	url = {https://pubs.geoscienceworld.org/gsa/geology/article/47/3/267/568708/Medieval-warmth-confirmed-at-the-Norse-Easternhttps://pubs.geoscienceworld.org/gsa/geology/article-pdf/47/3/267/4650216/267.pdfhttps://www.geosociety.org/datarepository/2019096},
	author = {Lasher, G. Everett and Axford, Yarrow}
}
@article {2601,
	title = {Holocene temperatures and isotopes of precipitation in Northwest Greenland recorded in lacustrine organic materials},
	journal = {Quaternary Science Reviews},
	volume = {170},
	year = {2017},
	month = {Jan-08-2017},
	pages = {45 - 55},
	abstract = {Reconstructions of Holocene lake water isotopic composition based upon subfossil aquatic organic material offer new insights into Arctic
climate. We present quantitative estimates of warmth during the Holocene Thermal Maximum in northwest Greenland, inferred from oxygen isotopes of chironomid head capsules and aquatic moss preserved in lake sediments. delta O-18 values of chironomids from surface sediments of multiple Greenland lakes indicate that these subfossil remains record the delta O-18 values of the lake water in which they grow. Our lake water delta O-18 reconstruction is supported by downcore agreement with delta O-18 values in aquatic moss and chironomid remains. delta O-18 of both organic materials from Secret Lake decrease after 4 ka (ka = thousands of years ago) by 3 parts per thousand into the Neoglacial. We argue that lake water at Secret Lake primarily reflects precipitation delta O-18 values, which is strongly correlated with air temperature in NW Greenland, and that this signal is biased towards summer and early autumn conditions. Other factors may have influenced Secret Lake delta O-18 values through the Holocene, including evaporation of lake water and changing seasonality and source of precipitation. The maximum early Holocene summer and early autumn-biased temperature anomaly at Secret Lake is 2.5-4 degrees C warmer than present from 7.7 (the beginning of our record) to similar to 6 ka. The maximum late Holocene cold anomaly (which includes the Little Ice Age) is 1.5-3 degrees C colder than present. These ranges of possible temperature anomalies reflect uncertainty in the delta O-18 temperature relationship for precipitation at the study site through the Holocene. (C) 2017 Elsevier Ltd. All rights reserved.},
	keywords = {Chironomids, Greenland, Holocene, paleoclimatology, paleolimnology, Stable isotopes},
	issn = {02773791},
	doi = {10.1016/j.quascirev.2017.06.016},
	url = {http://linkinghub.elsevier.com/retrieve/pii/S0277379116305650http://api.elsevier.com/content/article/PII:S0277379116305650?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0277379116305650?httpAccept=text/plain},
	author = {Lasher, G. Everett and Axford, Yarrow and McFarlin, Jamie M. and Kelly, Meredith A. and Osterberg, Erich C. and Berkelhammer, Max B.}
}
