The North American Varve Chronology and Glacial Varve Project

American Journal of Science, 2012

New glacial varve records from long cores combined with records from key surface exposures and new radiocarbon ages have allowed the correction, consolidation, expansion, and calibration of Ernst Antevs' original New England Varve Chronology (NEVC) in the Connecticut Valley of New England, U.S.A. The varve records have been reformulated, with corrections and a new numbering system, as the new North American Varve Chronology (NAVC), which is a continuous 5659-yr varve sequence that spans most of the last deglaciation (18,200-12,500 yr BP) in the northeastern United States. Rates of ice recession for separate intervals terminated by abrupt glacial stillstands and readvances have been determined for western New England. Ice recession history is coupled to varve thickness changes that depict changes in meltwater production in the Connecticut Valley and show the relationship of changes in ablation rate (summer climate variation) to glacial readvances and periods of halted and rapid ice recession (up to 300 m/yr). Comparison of varve thickness records to Greenland ice-core climate records show that after 15,000 yr BP, climate changes of sub-century and longer scales recorded in both records appear identical and synchronous. After 15,000 yr BP, therefore, there was a link between North Atlantic climate and marginal processes of the southeastern sector of the Laurentide Ice Sheet (LIS). Prior to 15,000 yr BP, when the LIS was closer to an equilibrium condition, retreat rates were generally lower and changes in varve thickness and ablation were more subtle, but can still be linked to ice sheet activity. Only weak relationships between varve thickness changes and Greenland climate are evident suggesting that changes in the southeastern LIS during this time may have been significantly influenced by climate patterns unique to the North American continent or ice dynamics.

Géographie physique et Quaternaire, 2000

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The formation of Glacial Lake Hitchcock in western New England during the period in which the Laurentide Ice Sheet retreated out of the northeastern U.S. has allowed for the construction of a chronology of the event. The north-south orientation of the 320 kilometer-long proglacial lake positioned it perpendicular to the southeastern retreating margin of the glacier. This particular spatial relationship between the lake and glacier allowed for the formation of a geophysical record in the landscape of the glacier’s retreat in the form of glacial varves. However, this phenomenon has recorded but a segment of what occurred. Although the Lake Hitchcock varve chronology illustrates the retreat of the southeastern Laurentide Ice Sheet over 300 kilometers and 4,000 years, it offers little insight to the first phases of the glacier’s retreat from its last glacial maximum paralleling Long Island, New York, to the southern terminus of Lake Hitchcock near Middletown, Connecticut, a distance of approximately 80 kilometers. This paper will propose to fill in this gap by pursuing exposure-age dating of moraines, erratics, and bedrock outcrops located in the area between the southern end of Glacial Lake Hitchcock and the boundary of the last glacial maximum of the Laurentide Ice sheet at Long Island. An outline of glacial retreat from New England as it is known will also be presented.

Quaternary Science Reviews, 2020

The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most upto-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 ; 'Quaternary Glaciations e Extent and Chronology, Part II' ). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km 2 , which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of and where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world's largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n ¼ 5195 ages) and estimates of uncertainty for each interval.

Science, 2000

A glacial varve chronology from New England spanning the 4000-year period from 17,500 to 13,500 calendar years before the present was analyzed for evidence of climate variability during the late Pleistocene. The chronology shows a distinct interannual (3 to 5 years) band of enhanced variability suggestive of El Niño-Southern Oscillation (ENSO) teleconnections into North America during the late Pleistocene, when the Laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today. This interannual variability largely disappears by the young end of the 4000-year chronology, with only the highest frequency components (roughly 3-year period) persisting. This record provides evidence of ENSO-like climate variability during near-peak glacial conditions.

Quaternary Science Reviews, 2010

The last glacial maximum (LGM) outline and subsequent retreat pattern (21e7 kyr) of North American ice sheets are reasonably well established. However, the evolution of the ice sheets during their build-up phase towards the LGM between 115 and 21 kyr has remained elusive, making it difficult to verify numerical ice sheet models for this important time interval. In this paper we outline the pre-LGM ice sheet evolution of the Laurentide and Cordilleran ice sheets by using glacial geological and geomorphological records to make a first-order reconstruction of ice sheet extent and flow pattern. We mapped the entire area covered by the Laurentide and Cordilleran ice sheets in Landsat MSS images and approximately 40% of this area in higher resolution Landsat ETMþ images. Mapping in aerial photographs added further detail primarily in Quebec-Labrador, the Cordilleran region, and on Baffin Island. Our analysis includes the recognition of approximately 500 relative-age relationships from crosscutting lineations. Together with previously published striae and till fabric data, these are used as the basis for relative-age assignments of regional flow patterns. For the reconstruction of the most probable ice sheet evolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineating coherent landforms swarms (reflecting flow direction and configuration), and linking these to previously published constraints on relative and absolute chronology. Our results reveal that icedispersal centres in Keewatin and Quebec were dynamically independent for most of pre-LGM time and that a massive Quebec dispersal centre, rivalling the LGM in extent, existed at times when the SW sector of the ice sheet had not yet developed. The oldest flow system in eastern Quebec-Labrador (Atlantic swarm had an ice divide closer to the Labrador coast than later configurations). A northern Keewatin-Central Arctic Ice Sheet existed prior to the LGM, but is poorly chronologically constrained. There is also evidence for older and more easterly Cordilleran Ice Sheet divide locations than those that prevailed during the Late Wisconsinan. In terms of ice sheet build-up dynamics, it appears that "residual" ice caps after warming phases may have played an important role. In particular, the location and size of remnant ice masses at the end of major interstadials, i.e. OIS 5c and 5a, must have been critical for subsequent build-up patterns, because such remnant "uplands" may have fostered much more rapid ice sheet growth than what would have occurred on a fully deglaciated terrain. The ice-sheet configuration during stadials would also be governed largely by the additional topography that such "residual" ice constitutes because of inherent mass balanceetopography feedbacks.

Palaeogeography, Palaeoclimatology, …, 2009

Trace fossils as paleoecological and paleobiogeographical tools in Pleistocene glaciolacustrine sediments have been largely ignored. Combining high resolution varve stratigraphy with trace fossil data can lead to refined paleoenvironmental interpretations during times of rapid climate change. Based on trace fossils from glaciolacustrine varves in the Connecticut and Merrimack River valleys, a new timeline for the reinhabitation of New England by fish and associated invertebrates has been constructed. In addition, it appears that colonization of the recently deglaciated environments occurred in at least four successional stages. If these stages can be recognized elsewhere, it may be possible to accurately model other postglacial migrations using trace fossils and varve chronostratigraphy.

2008

Lithologic, CHIRP (Compressed High Intensity Radar Pulse) sonar, paleomagnetic, stable isotopic and micropaleontological analyses of sediment cores from Lake Champlain (New York, Vermont) were used to determine the age of the post-glacial Champlain Sea marine episode, the timing of salinity changes and their relationship to freshwater discharge from mid-continent glacial lakes. Calibrated radiocarbon ages on plant material provide an improved post-glacial chronology overcoming problems from shell ages caused by carbon reservoir effects up to 1500 yr. The final drainage of glacial Lake Vermont and the inception of marine conditions occurred ∼ 13.1-12.8 ka (kiloannum, calendar years) and a sharp decrease in Champlain Sea salinity from ∼ 25 to 7-8 psu (practical salinity units) occurred approximately 11.4-11.2 ka. Reduced salinity was most likely caused by rapid freshwater inflow eastward from glacial Lake Algonquin into the Champlain Basin. The timing of inferred freshwater event coincides with the widespread climatic cooling called the Preboreal Oscillation.