Harold W. Borns

Late Quaternary Marine Invasion in Maine: Its Chronology and Associated Crustal Movement

Recession of the ice margin at a rate of 0.3 km/yr or more in coastal areas in central Maine between 13,000 and 12,700 yr B.P. resulted in a large-scale marine submergence of this region. Isostatic uplift brought the region above sea level by 12,100 yr B.P. Model calculations show the existence of an inland sea in the later stages of emergence. The chronology of these events is given by 14 C dates on shells and seaweed from the Presumpscot Formation. Several criteria applied indicate age reliability of the shell dates within a few hundred years. 14 C ages of the earliest grown organic material in kettles often lag behind the time of deglaciation.

Ice Elevation Near the West Antarctic Ice Sheet Divide During the Last Glaciation

[1] Interior ice elevations of the West Antarctic Ice Sheet (WAIS) during the last glaciation, which can serve as benchmarks for ice-sheet models, are largely unconstrained. Here we report past ice elevation data from the Ohio Range, located near the WAIS divide and the onset region of the Mercer Ice Stream. Cosmogenic exposure ages of glacial erratics that record a WAIS highstand 125 m above the present surface date to 11.5 ka. The deglacial chronology prohibits an interior WAIS contribution to meltwater pulse 1A. Our observational data of ice elevation changes compare well with predictions of a thermomechanical icesheet model that incorporates very low basal shear stress downstream of the present day grounding line. We conclude that ice streams in the Ross Sea Embayment had thin, lowslope profiles during the last glaciation and interior WAIS ice elevations during this period were several hundred meters lower than previous reconstructions. Citation: Ackert, R. P., Jr., S. Mukhopadhyay, B. R. Parizek, and H. W. Borns (2007), Ice elevation near the West Antarctic Ice Sheet divide during the Last Glaciation, Geophys. Res. Lett., 34, L21506, doi:10.1029/ 2007GL031412.

Crustal warping in coastal Maine

A multidisciplinary study of crustal movements in coastal Maine has shown that parts of the state9s coastal zone are subsiding. This subsidence is associated with seismic activity that has persisted locally since at least the 1800s. Bedrock structural studies have not produced evidence of major Holocene faulting, but measured horizontal rock strains may be related to Mesozoic graben development in the adjacent Gulf of Maine. The crustal down warping is most apparent in eastern Maine, where releveling data indicate a modern subsidence rate of as much as 9 mm/yr. The anomalously rapid sea-level rise resulting from this subsidence has caused erosion and submergence of archeological sites and historical man-made structures. However, the altitudes of glaciomarine deltas and the distribution of dated archeological sites show that the present subsidence rates have not persisted throughout Holocene time.

The deglaciation of Maine, U.S.A.

The glacial geology of Maine records the northward recession of the Late Wisconsinan Laurentide Ice Sheet, followed by development of a residual ice cap in the Maine-Quebec border region due to marine transgression of the St. Lawrence Lowland in Canada. The pattern of deglaciation across southern Maine has been reconstructed from numerous end moraines, deltas and submarine fans deposited during marine transgression of the coastal lowland. Inland from the marine limit, a less-detailed sequence of deglaciation is recorded by striation patterns, meltwater channels, scattered moraines and waterlain deposits that constrain the trend of the ice margin. There is no evidence that the northern Maine ice cap extended as far south-west as the Boundary Mountains and New Hampshire border. Newly-obtained radiocarbon ages from marine and terrestrial ice-proximal environments have improved the chronology of glacial recession in Maine. Many of these ages were obtained by coring Late-glacial sediments beneath ponds and lakes. Data from this study show that the state was deglaciated between about 14.5 and 10.0 ka BP (14C years). The coastal moraine belt in southern Maine was deposited by oscillatory ice-margin retreat during the cold pre-Bolling time. Rapid ice recession to northern Maine then occurred between 13 and 11 ka BP, during the warmer Bolling/Allerod chronozones. Radiocarbon-dated pond sediments in western and northern Maine show lithological evidence of Younger Dryas climatic cooling and persistence of the northern ice cap into Younger Dryas time. A large discrepancy still exists between radiocarbon ages of deglaciation in coastal south-western Maine and the timing of ice retreat indicated by New England varve records in areas to the west. Part of this problem may stem from the uncertainty of reservoir corrections applied to the radiocarbon ages of marine organics.

Younger Dryas deglaciation of Scotland driven by warming summers

Significance Resolving the full manifestation of past abrupt climate change is key to understanding the processes driving and propagating these events. As a principal component of global heat transport, the North Atlantic Ocean also is susceptible to rapid disruptions of meridional overturning circulation and thus widely invoked as a cause of abrupt climate variability in the Northern Hemisphere. We assess the impact of one such North Atlantic cold event—the Younger Dryas Stadial—on an adjacent ice mass and show that, rather than instigating a return to glacial conditions, this abrupt climate event was characterized by deglaciation. We suggest this pattern indicates summertime warming during the Younger Dryas, potentially as a function of enhanced seasonality in the North Atlantic. The Younger Dryas Stadial (YDS; ∼12,900–11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial–interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159–1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS.

Quaternary glaciation, west-central Maine

The highlands of west-central Maine, including the Longfellow and Boundary Mountains, were overridden at least twice, probably three times, by a continental ice sheet during Wisconsinan time. These episodes are indicated by at least five widely separated exposures displaying two-drift sequences composed of thick lodgment tills separated by glaciolacustrine and fluvial sediment. Radiocarbon dates on an intertill pollen- and wood-bearing deposit at New Sharon, Maine, record a major nonglacial interval that ended more than 52,000 B.P. The last ice sheet, actively building end moraines along the Maine coast 13,500 yr ago, had thinned, separated, stagnated, and dissipated over the Longfellow and Boundary Mountains at least by 12,500 B.P. Contemporaneous stagnation, throughout and southeast of the mountains, is evidenced by the distribution and volume of ice-contact stratified drift. Coupled with this is the lack of evidence for receding active ice margins associated with either the Laurentide Ice Sheet or a late-glacial locally centered ice cap suggested by some workers. In addition, the highest cirques in the study area, floored at approximately 930 m, reveal no evidence of reactivation during and subsequent to the dissipation of the last ice sheet.

Late Glacial Ice-Wedge Casts in Northern Nova Scotia, Canada

Ice-wedge casts in northern Nova Scotia and the relation of the casts to the outwash that contains them indicate that the ice wedges formed in a permafrost environment after the accumulation of the outwash. This permafrost environment is tentatively correlated with pollen zone L-3 of the Gillis Lake deposit, Cape Breton Island, Nova Scotia, and with the Valders time of the midcontinental sequence.

Late-Glacial Stratigraphy of a Northern Part of the Kennebec River Valley, Western Maine

The late-glacial stratigraphy of the northern part of the Kennebec River valley of Maine indicates the following sequence of events. (1) As the last extensive ice sheet dissipated in Maine, the sea inundated parts of the deglaciated and isostatically depressed region and deposited the Presumpscot Formation. (2) During emergence, outwash of the Embden Formation was gradationally deposited on the Presumpscot Formation. (3) As emergence progressed, the Embden and Presumpscot Formations were deeply incised by the early Kennebec River. (4) Outwash (?) of the North Anson Formation was later deposited within this incision. The geologic sequence of events, radiocarbon dates in the area, and correlation of events of the Maine, Quebec, New Brunswick, and Nova Scotia region suggest that the last extensive ice sheet to cover the region dissipated more rapidly in eastern Maine and New Brunswick than in the highlands of New Hampshire and western Maine. The data also suggest that ice persisted in the highlands during the time of the Cary-Port Huron Interstade, perhaps dissipating during the time of the Port Huron- Valders Interstade of the mid-continental sequence. These highlands probably later became a center for ice accumulation and radial outflow. This ice cap probably grew synchronously with the main Valders ice sheet to the north, with cirque glaciers on Mount Katahdin, Maine, and with the ice cap in southwestern Nova Scotia.

THE HIRUNDO ARCHAEOLOGICAL PROJECT ‐ AN INTERDISCIPLINARY APPROACH TO CENTRAL MAINE PREHISTORY*

The Hirundo Archaeological project is designed to examine the interrelationships between prehistoric man and his environment in central Maine in an inland setting. The project involves, but is not restricted to, members of the Institute for Quaternary Studies at the University of Maine, Orono. Although much of the fieldwork is completed, there remains a great deal of analysis before any final statements can be made. The authors have been involved since the inception of the project in 197 1. Robert G . MacKay and David Sanger have supervised the excavation and site analysis; Harold W. Borns, Jr. has directed the geological studies, and Ronald B. Davis has supervised the paleoecological aspects. The project has been coordinated by Sanger. Financial support has come from the National Geographic Society, the Hazel Smith Fund, and the University of Maine, Orono. Radiocarbon dates have been provided by the Smithsonian Institution through the efforts of Robert Stuckenrath. We would also like to acknowledge the cooperation of the landowners, Mr. J. Oliver Larouche of the Hirundo site, and Mr. K. Young of the Young site. With few exceptions, research in Maine has been dominated by the search and interpretation of the red ochre burials (the so-called “Red Paint” people), and the excavation of coastal sites, usually shell middens occupied during the winter. To provide some balance, we decided in the fall of 1971 to develop an inland project in the hopes of learning more about a neglected part of the seasonal activities, and at the same time focus on habitation components related to the mortuary complex termed the “Moorehead burial tradition.”’ Scientists capable of reconstructing the terrestrial paleoenvironments were invited to participate in order to provide a necessary background against which prehistoric man can be examined. The Hirundo site and locality is situated in central Maine in the Pushaw Lake region, which is drained by Pushaw Stream to the Penobscot River ( F I G U R E 1). The site was discovered by MacKay in 1971 following a tip from an amateur. Limited to a few days at the end of the field season, MacKay’s crew tested the site, putting down pits between trees in the heavily wooded area. Those initial pits indicated a multicomponent site suffering little or no man-inflicted damage.

Younger Dryas Paleoenvironments and Ice Dynamics in Northern Maine: A Multi-Proxy, Case History

Abstract Geological evidence for modeled Younger Dryas ice expansion in northern Maine is assessed in conjunction with temperature and precipitation estimates from chironomids and pollen, and plant macrofossil and lake-level analyses from lake sediment. Pollen and chironomid temperature and precipitation transfer-function estimates for the Allerød warming period indicate colder winters, precipitation levels half that of modern times, and summer temperatures near modern levels. The combination of cold winters and low precipitation prevented forest establishment in northern Maine along the Maine/New Brunswick border. While winter temperatures and precipitation remained stable, summer temperatures decreased as much as 7.5 °C during the Younger Dryas stadial, forcing a shift from shrub-dominated to sedge-dominated tundra. Summer and winter temperatures, as well as annual precipitation, increased rapidly at the Holocene onset.