ABSTRACT: Sunshine - an important bioclimatic control on Holocene and last interglacial vegetational development in Eastern Baffin Island, Arctic Canada.

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

The past can play a tremendously important role in helping us understand future climate change and associated tundra ecosystem response. Feedbacks in Arctic climate system associated with clouds (or inversely, sunshine conditions) is still a major source of uncertainty in model projections of global warming. At polar latitudes, the availability of light and the atmospheric moisture are interrelated with cloud cover, which should indeed play an important role in plant physiology. This study presents Last Interglacial (ca. 125,000 years ago) and Holocene (last 11,500 years) vegetation and climate changes at Fog Lake (67°11’N, 63°15’W) on eastern Baffin Island, Arctic Canada. The vegetation cover is reported as structural vegetation types, or biomes. July air temperature and sunshine during the growing season (June-July-August- September) were reconstructed from pollen assemblageswith the modern analogue technique. The vegetation of the Last Interglacial period evolved from a prostrate dwarfshrub tundra to a low- and high-shrub tundra vegetation. The succession of four arctic biomes was distinguishedfrom the Last Interglacial sediments, whereas only one arctic biome was recorded in the Holocene sediments. From ca. 8300 cal. year BP to present, hemiprostrate dwarf-shrub tundra occupied the soils around Fog Lake. During the Last Interglacial, growing season sunshine was higher than during the Holocene and July air temperature was 4 to 5°C warmer than present. A Principal Component Analysis helped in assessing relationship between floristic gradients and climate. Major changes in vegetation cover through the Last Interglacial and Holocene are clearly shown in the July air temperature reconstruction curve, whereas minor changes seem to be better depicted in the growing season sunshine reconstruction curve. We thus suggest that Julyair temperature is the climate parameter that has driven the major vegetation changes through the Last Interglacial and the Holocene at Fog Lake, and that these vegetation changes might have been induced by changes in growing season sunshine which affected the length of the vegetation period available to tundra species, especially during September. During the Last Interglacial, summer warming and lengthening of the growing season helped the development of a shrub tundra vegetation on eastern Baffin Island. Increasing deciduous shrub abundance (e.g., Betula) during the Last Interglacial is an important result, as it suggests that the directional changes that occurred on eastern Baffin Island are consistent with experimental tundra warming. A shift from herbaceous to woody tundra would have important implications for processes and interactions within tundra ecosystems and between tundra and the atmosphere, notably through a decrease in albedo. An increased cloudiness (or decreased sunshine) is expected to accompany a climate warming. It is thus important that we improve our understanding of how a change in shrub cover and sunshine likely influence the behaviour of the climate system. This study demonstrates that growing season sunshine conditions can be reconstructed from arctic pollen assemblages, thus providing information on feedbacks associated with cloud cover and summer temperatures, and therefore growing season length.

Bibliography of Canadian Geomorphology