A Note on the Holocene History of a Portion of Northernmost Ellesmere Island

Abstract

Three points raised in Lyons and Mielke's paper on the "Holocene history of a portion of northernmost Ellesmere Island" warrant further discussion. ... The points to be discussed deal with: 1) the Holocene chronology, 2) the interpretation of postglacial uplift, and 3) the form of the postglacial uplift curve on northern Ellesmere Island. ... Lyons and Mielke place the Pleistocene/Holocene boundary on northern Ellesmere Island at 10,000-13,000 BP. This boundary is based on inference from the Greenland ice core, since the authors state that "there is no reliable information on northernmost Ellesmere Island which closely fixes the transition from the Pleistocene to the Holocene". ... It seems clear that the estimated time profile through the Greenland ice core is particularly subject to question and should not be assumed to be free of error or without the need of being clarified by the radiocarbon-dated terrestrial record (not vice versa). ... Terasmae has described the time-transgressive nature of the late glacial/postglacial boundary in southeastern Canada (ca. 10,000 BP), and hence, similar time-transgressive problems might be expected in the arctic events. ... The terrestrial record from northern Ellesmere Island, therefore, should be accepted on its own merit .... The present writer suggests, therefore, that the local Pleistocene/Holocene boundary on northern Ellesmere Island occurred between 7500-8100 BP rather than 10,000-13,000 BP. This is also the case indicated by the majority of radiocarbon dates from raised marine deposits in Archer Fiord/Lady Franklin Bay. ... Lyons and Mielke also infer that the observed postglacial uplift on Ward Hunt Island is a product of the maximum Pleistocene ice thicknesses in this area. ... There is, however, no stratigraphic evidence that the maximum Pleistocene ice thickness in this area caused this Holocene uplift (7755 ±150 BP ...). It is equally possible that this postglacial emergence on Ward Hunt Island (only 38 m. a.s.l.) could have been produced beyond a restricted inland ice margin entirely independent of this most extensive ice advance. The present author has modelled the postglacial uplift over northeastern Ellesmere Island and northwestern Greenland using relatively small ice advances during the last glaciation, and the resulting uplift is consistent with the observed isobases over this area. ... Hence, there is no apparent need for the maximum Pleistocene ice load in this area to produce this moderate amount of postglacial uplift - in fact, these are very possibly two discrete events separated by an unknown amount of time. Evidence from northwestern Greenland and from eastern Baffin Island suggests that the maximum Pleistocene glaciations in these areas are much older than the last glaciation. ... The postglacial uplift curve constructed by Lyons and Mielkel is quite steep showing >70 per cent of the postglacial uplift occurring in the first two thousand years following deglaciation. ... On the curve of Lyons and Mielke postglacial uplift has almost completely flattened-off by ca. 5000 BP. Whether this is an accurate representation of the postglacial uplift process in this area or whether it is a problem of stratigraphy is not clear. ... Before such steep curves are assumed to accurately represent post-glacial uplift on northern Ellesmere Island, many more stratigraphically-controlled shell and driftwood samples must be obtained and dated. Also it needs to be determined whether the north coast of the island is undergoing a renewed submergence which could distort the real form of the uplift curve, particularly in its lower elevations. It is clear that Lyons and Mielke have made a valuable contribution to the Holocene history of northern Ellesmere Island, particularly around the evolution of the Ward Hunt Ice Shelf. However, the local data on the Pleistocene/Holocene boundary must be evaluated on their own merit, and caution should be exercised in making correlations with such data as the Greenland ice core which must, in return, be clarified by the land record provided by glacial geology.