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The timing and dynamics of deglaciation of the Newfoundland Ice Sheet (NIS) represents a complex and poorly resolved portion of the North American Ice Sheet Complex. Establishing the flow dynamics [...]

Archaeological sites in the Canadian Arctic often contain substantial quantities of marine mammal bones and in some cases completely lack terrestrial mammal bones. A distrust of radiocarbon (14C) dates on marine mammal bones among Arctic archaeologists has caused many sites to be insufficiently dated. The goal of this study was to investigate the marine reservoir effect on Atlantic walrus in the Foxe Basin region of the Canadian Arctic through a two-pronged approach: dating of live-harvested specimens of known age collected prior to AD 1955 and dating of pairs of animal remains (walrus and caribou) from stratigraphically contemporaneous levels within archaeological features. 14C dates on pre-bomb, live-harvested walrus indicate that a ΔR value of 160±50 yr be used in calibrating dates on walrus from this region. These results differed significantly from a similar set of pre-bomb mollusks, which argues against applying mollusk-based corrections to marine mammals. The results of comparative dating of caribou and walrus from archaeological features provided maximum estimates of reservoir ages that were more varied than the directly measured ages. Although about half of inferred ΔR values overlap the museum specimen results, the others indicate that the assumption of contemporaneity does not hold true. [ABSTRACT FROM AUTHOR]

Throughout northern Canada, live-collected, pre-bomb, deposit-feeding marine molluscs from calcareous sediments yield greater apparent radiocarbon ages than do suspension feeders. We explore the size of this effect in a set of 57 paired datings of deposit feeders, mainly Portlandia arctica, and suspension feeders, mainly Hiatella arctica and Mya truncata, collected from both calcareous and non-calcareous Holocene sediments. Deposit feeders from calcareous sediments are older than their suspension-feeding counterparts by as much as 2240±130 14 C years. This is attributed to the uptake of 'old' bicarbonate derived from calcareous bedrock. The age discrepancy between suspension and deposit feeders in calcareous terrain is non-systematic in space and time, thereby invalidating the application of a correction. In contrast, the age comparisons are concordant at sites located on the Precambrian Shield. In terrestrial environments underlain by carbonate, previous acceptance of dates on deposit feeders led to erroneous interpretations of deglaciation and relative sea-level history, in both the North American and the Eurasian Arctic. This has prompted several researchers to exclude deposit feeders from their late Quaternary reconstructions. The same chronological problem of deposit-feeding molluscs now needs to be more widely acknowledged by the marine community. [ABSTRACT FROM AUTHOR]

This study addresses the timing and causes of the Holocene population expansion of Fagus sylvatica at two sites in the southern Prealps (Italy): Lago di Fimon and Lago Piccolo di Avigliana. At both sites pollen and microcharcoal have been analysed at high temporal resolution. The impact of humans and of fire on the forest dynamics is tested by means of time-series analysis and the influence of climatic change has been inferred from summer temperature and precipitation reconstructions in the Alps. The time intervals during which the population expansion of F. sylvatica occurred (ie, phases during which population doubling times were shortest) is determined by fitting linear regressions through the ln-transformed Fagus pollen-accumulation rate (ln(PAR)). At Lago di Fimon, the population expansion of F. sylvatica occurred at 7300-6400 cal. yr BP (FIM I). After a marked decline the population re-expanded at 5500-4700 cal. yr BP (FIM II). At Lago Piccolo di Avigliana F. sylvatica expanded c. 5300-4600 cal. yr BP (AVP I). Time-series analyses show that Fagus expanded after forest fires decreased during FIM I, and human impact likely contributed to the F. sylvatica population expansions at the two sites during FIM II and AVP I. The comparison with independent climatic records suggests that favourable climatic conditions (eg, cool and wet) were a determining factor. Our study suggests that the expansion of F. sylvatica populations has been triggered by more than one single factor alone. [ABSTRACT FROM AUTHOR]

Changes according to elevation in frequencies of naturally stranded bowhead whale (Balaena mysticetus) remains on Holocene beaches in theCanadian Arctic Archipelago (CAA) closely parallel previously reported temporal changes in frequencies of independently radiocarbon-datedbowhead remains from these same beaches. Specifically, on the basis of emergence curves determined for 10 localities surveyed in the CAA,stranded whale remains tend to be relatively common in beaches dating to approximately 2500-5500 B.P. and those older than 8000 B.P., butrelatively rare in beaches dating to 0-2500 B.P. and 5500-8000 B.P. The former beaches apparently developed primarily during periods of relatively ice-free summer conditions, while the latter developed during periods of relatively pervasive summer sea ice that prevented bowheads from entering the region. Length-based mortality profiles of thestranded whale assemblages suggest that random processes, such as ice entrapment, were responsible for the death of most whales found on these beaches. [ABSTRACT FROM AUTHOR]

During the last deglaciation of North America, huge proglacial lakes formed along the southern margin of the Laurentide Ice Sheet. The largest of these was glacial Lake Agassiz, which formed about 11.7 14C kyr and drained into Hudson Bay about 7.7 14C kyr (8.45 cal kyr). Overflow from these lakes was variably directed to the Mississippi, St. Lawrence and Mackenzie drainage systems and it is thought that switches in routing were accompanied by a response in ocean circulation that produced abrupt climate events. When the ice dam across Hudson Bay finally was breached, a massive flood drained Lake Agassiz, which was routed through Hudson Strait to the Labrador Sea. In terms of stored water volume the largest reservoir was associated with the Kinoje´vis level of Lake Agassiz. For this maximum filling, the impounded water volume available to produce floods is estimated as 40,000–151,000 km3, depending on the location of the ice margin and route used. The timing of this rapid release of stored freshwater just precedes the early Holocene cooling event at 8.2 cal kyr BP. We use the Spring–Hutter theory to simulate flood hydrographs for floods that originate in subglacial drainage conduits and find that flood magnitude and duration are ∼5 Sv and ∼0.5 yr. Multiple fillings and floods are possible as are single floods having a complex multipulse structure. Modelling results suggest that the outburst flood from Lake Agassiz may have terminated before the lake surface elevation dropped to sea level and that the flood ended when a stable drainage channel was established, connecting Lake Agassiz to the Tyrrell Sea. [Copyright &y& Elsevier]