Discussion and conclusion

The results presented here substantiate work elsewhere in Canada and Fennoscandia where data are showing that relict landscapes that lack erosional or depositional evidence of glaciation were actually glaciated as recently as the last global glacial maximum. In the Long Range Mountains of western Newfoundland we use TCN in three ways to document that:

1 deglaciation of the highland summits was approximately coeval or slightly preceded the last deglaciation of thicker ice in the bounding fjord valleys based on radiocarbon age-estimates (on land and offshore, Batterson & Catto, 2001);

2 that despite being glaciated, the summit surfaces have retained an isotopic record of exposure prior to the last glaciation, which means that glacial erosion on the summits was less than 2 m;

3 ratios of 26Al/10Be show that the cosmic ray exposure of summit bedrock surfaces was interrupted at least once in the long histories, but that the valleys (zone 'A') and valley walls

(many of the zone 'B' surfaces) have apparently been continuously exposed since deglaciation.

Of several explanations that have been posed to counter the interpretation of refugia on ice-free coastal highlands from the biological evidence, there are two that are appropriate for western Newfoundland.

1 The species are isolated today because they are adapted only to the specific ecosystems these summits provide (relative to the adjacent regions, the summits are cold, have wet but evenly distributed annual precipitation, low snow volumes and thin sediment cover).

2 These few species survived the last glaciation(s) in cliff habitats along coasts or between ice caps and valley glaciers that may have remained ice-free during most of the glaciation and subsequently expanded to the summit surfaces.

The latter explanation is not feasible if the entire Long Range Mountains were covered by the Laurentide Ice Sheet flowing from the west (another remaining debate). Clearly additional isotope measurements are needed to substantiate this small dataset for western Newfoundland. More importantly, we need to couple the TCN data with additional soils analyses, biological studies and quantitative geomorphology to provide a more robust test of the nunatak hypothesis.

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