Publisher Summary This chapter reviews that the Late Wisconsinan North American ice sheet complex consisted of three major ice sheets: (1) the Laurentide Ice Sheet, which was centred on the Canadian Shield, but also expanded across the Interior Plains to the west and south, (2) the Cordilleran Ice Sheet, which inundated the western mountain belt between the northernmost co-terminus United States and Beringia, and (3) the Innuitian Ice Sheet, which covered most of the Canadian Arctic Archipelago north of about 7°N latitude. The ice cover over Newfoundland and the Maritime Provinces of Canada is usually referred to as the Appalachian Ice Complex, because ice flowed out from local centres rather than from the Canadian Shield. All of the peripheral ice sheets were confluent at the Last Glacial Maximum (LGM) with the Laurentide Ice Sheet, and the Greenland Ice Sheet was confluent with the Innuitian Ice Sheet. The nucleus of this complex, the Laurentide, comprised three major sectors, the Labrador Sector, the Keewatin Sector, and the Baffin Sector, named for areas of inception mid probable areas of outflow at LGM and located respectively east, west and north of Hudson Bay. The chapter presents revised maps of North American deglaciation at 500-year and finer resolution. These maps represent an updating of a series prepared nearly two decades ago for the INQUA 1987 Congress.

/pdf/an-outline-of-north-american-deglaciation-with-emphasis-on-3350t0jf79.pdf

An outline of North American deglaciation with emphasis on central and northern Canada

Despite recent advances in population genetic theory and empirical research, the extent of genetic differentiation among natural populations of animals remains difficult to predict. We reviewed studies of geographic variation in mitochondrial DNA in seabirds to test the importance of various factors in generating population genetic and phylogeographic structure. The extent of population genetic and phylogeographic structure varies extensively among species. Species fragmented by land or ice invariably exhibit population genetic structure and most also have phylogeographic structure. However, many populations (26 of 37) display genetic structure in the absence of land, suggesting that other barriers to gene flow exist. In these populations, the extent of genetic structure is best explained by nonbreeding distribution: almost all species with two or more population-specific nonbreeding areas (or seasons) have phylogeographic structure, and all species that are resident at or near breeding colonies year-round have population genetic structure. Geographic distance between colonies and foraging range appeared to have a weak influence on the extent of population genetic structure, but little evidence was found for an effect of colony dispersion or population bottlenecks. In two species (Galapagos petrel, Pterodroma phaeopygia, and Xantus's murrelet, Synthliboramphus hypoleucus), population genetic structure, and even phylogeographic structure, exist in the absence of any recognizable physical or nonphysical barrier, suggesting that other selective or behavioural processes such as philopatry may limit gene flow. Retained ancestral variation may be masking barriers to dispersal in some species, especially at high latitudes. Allopatric speciation undoubtedly occurs in this group, but reproductive isolation also appears to have evolved through founder-induced speciation, and there is strong evidence that parapatric and sympatric speciation occur. While many questions remain unanswered, results of the present review should aid conservation efforts by enabling managers to predict the extent of population differentiation in species that have not yet been studied using molecular markers, and, thus, enable the identification of management units and evolutionary significant units for conservation.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-294X.2006.03197.x

Mechanisms of population differentiation in seabirds

Jack pine (Pinus banksiana Lamb.) is a broadly distributed North American conifer and its current range was covered by the Laurentian ice sheet during the last glacial maximum. To infer about the history and postglacial colonization of this boreal species, range-wide genetic variation was assessed using a new and highly variable minisatellite-like marker of the mitochondrial genome. Among the 543 trees analysed, 14 distinct haplotypes were detected, which corresponded to different repeat numbers of the 32-nucleotide minisatellite-like motif. Several haplotypes were rare with limited distribution, suggesting recent mutation events during the Holocene. At the population level, an average of 2.6 haplotypes and a mean haplotype diversity (H) of 0.328 were estimated. Population subdivision of genetic diversity was quite high with G(ST) and R(ST) values of 0.569 and 0.472, respectively. Spatial analyses identified three relatively homogeneous groups of populations presumably representative of genetically distinct glacial populations, one west and one east of the Appalachian Mountains in the United States and a third one presumably on the unglaciated northeastern coastal area in Canada. These results indicate the significant role of the northern part of the US Appalachian Mountains as a factor of vicariance during the ice age. A fourth distinct group of populations was observed in central Quebec where the continental glacier retreated last. It included populations harbouring haplotypes present into the three previous groups, and it had higher level of haplotype diversity per population (H = 0.548) and lower population differentiation (G(ST) = 0.265), which indicates a zone of suture or secondary contact between the migration fronts of the three glacial populations. Introgression from Pinus contorta Dougl. var. latifolia Engelm. was apparent in one western population from Alberta. Altogether, these results indicate that the mitochondrial DNA variation of jack pine is geographically highly structured and it correlates well with large-scale patterns emerging from recent phylogeographical studies of other tree boreal species in North America.

A mitochondrial DNA minisatellite reveals the postglacial history of jack pine (Pinus banksiana), a broad-range North American conifer.

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (δ 18 O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in δ 18 O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM δ 18 O values suggest thick ice frozen to the bed of Hudson Bay.

/pdf/penny-ice-cap-cores-baffin-island-canada-and-the-wisconsinan-3tu6ea7q96.pdf

Penny Ice Cap Cores, Baffin Island, Canada, and the Wisconsinan Foxe Dome Connection: Two States of Hudson Bay Ice Cover

Strontium, neodymium, and lead isotope variations of authigenic and silicate sediment components from the Late Cenozoic Arctic Ocean: Implications for sediment provenance and the source of trace metals in seawater

Paleogeography of northern North America

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Paleogeography of northern North America