Abstract
This study presents a diatom-based analysis of the post-glacial Holocene environmental history at Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post-glacial diatom assemblages (10 200–10 000 cal yr BP) consisted mainly of small, benthic fragilarioid taxa. Poor diatom preservation in the early Holocene (~10 000–6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediment records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid-Holocene. During this time period, cooling causing changes in lake ice phenology was likely a major driver of the reconstructed mid-Holocene pH decline. Watershed processes, including reduced fluxes of base cations as the rate of sediment accumulation slowed, may also be contributors to long-term shifts in lake water pH and associated changes in diatom assemblages. The uppermost sediments in the Lake RS29 record were characterized by abrupt declines in Aulacoseira alpigena and increases in benthic diatom taxa Cyclotella sensu lato, suggesting an increase in lake water pH and longer ice-free seasons.
Highlights
Understanding long-term climate impacts on the aquatic communities of Arctic lakes requires separating the effects of climate variations from changes within the lake and in the watershed, as well as from the processes associated with lake ontogeny over the long time span of the Holocene (Fritz and Anderson 2013; Rühland et al 2015)
Bedrock lithology is the strongest predictor of lake water pH in Arctic systems; lakes with lower pH and poor buffering capacity are found on crystalline rocks whereas the large parts of the Canadian Arctic underlain by carbonate rocks support more alkaline lakes with significant buffering capacity (Fortin and Gajewski 2009)
Core chronology The RS29 core measured 150 cm; its chronology is based on a total of 8 radiocarbon dates (2 on mosses, 2 on macrofossil fragments and 4 bulk sediment dates; Table 1), as well as the interface assigned as modern (1991 AD)(Gajewski 1995)
Summary
Understanding long-term climate impacts on the aquatic communities of Arctic lakes requires separating the effects of climate variations from changes within the lake and in the watershed, as well as from the processes associated with lake ontogeny over the long time span of the Holocene (Fritz and Anderson 2013; Rühland et al 2015). Numerous non-climate factors have been shown to influence diatom assemblages and production including limnological variables, bedrock geology and other watershed characteristics (e.g., Lim et al 2001; Bouchard et al 2004; Fortin and Gajewski 2009; Finkelstein et al 2014). Comparative analyses have shown that diatom communities differ greatly between nearby sites due to factors of lake morphometry, dispersal and watershed characteristics (Smith 2002; Finkelstein and Gajewski 2007, 2008; Rühland et al 2015). Superimposed on the primary control imposed by bedrock, variability in lake water pH over time may be in part influenced by climate, via fluctuations in https://mc06.manuscriptcentral.com/asopen-pubs
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