Relative importance of hydrological and climatic controls on Holocene paleoenvironments inferred using diatom and pollen records from a lake in the central Hudson Bay Lowlands, Canada

Abstract

Postglacial paleoenvironmental changes and landscape development in the Hudson Bay Lowlands in subarctic Canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice-marginal landform. Coarsegrained, inorganic sediments at the base of the Lake AT01 core suggest a high-energy periglacial environment, following isostatic emergence from Hudson Bay around 6840 cal. BP. Initial diatom assemblages dominated by Fragilaria spp., and pollen of Shepherdia canadensis, indicate early successional conditions in a recently deglaciated environment. Around 6200 cal. BP, tychoplanktonic Fragilarioid diatoms are replaced by large benthics. Coincident increases in Equisetum spores, Cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte-rich shallow lake. While the Holocene Thermal Maximum and subsequent Neoglacial may have contributed to these shifts, pollen and diatom records suggest only subtle responses to Holocene climatic changes. A core chronology inferred from radioisotopes suggests a hiatus in sediment accumulation between 3650 and 200 cal. BP. Peaks in carbonate inferred from loss-on-ignition and increases in bulk density in that section of the core suggest some effect of erosional or thermokarst processes, or the breaching of a sandbar, now a remnant island in the lake, in the drainage of the lake and ensuing hiatus. Sediment accumulation resumed within the past two centuries; diatom assemblages in the uppermost section are characterized initially by benthic diatoms of smaller valve size compared with the pre-hiatus assemblages. More recently, increases in the planktonic diatom Cyclotella stelligera are recorded, signaling significant environmental changes.

An 11,000‐yr record of diatom assemblage responses to climate and terrestrial vegetation changes, southwestern Québec

“…, Friel et al. ). However, abrupt centennial‐scale changes in the Lac Noir diatom assemblages at 3.6 ka suggest that the lake responded quickly to deteriorating climate conditions.…”

“…Inputs of mineral‐rich sediments to lakes were recorded as elevated magnetic susceptibility values in lake sediments from southern Québec and Ontario (Fuller , Friel et al. ) and at the base of the Lac Noir core (Fig. ).…”

“…) was linked to subtle changes in pollen and diatom records across eastern North America (Gajewski , , Fuller , Friel et al. , Beck et al. ).…”

“…In response to Neoglaciation beginning at 3000 cal. yr. BP, studies generally revealed subtle, less-pronounced changes in aquatic biota to cooling and wetter conditions (Magnuson et al 1997, Viau et al 2006, Friel et al 2014). However, abrupt centennial-scale changes in the Lac Noir diatom assemblages at 3.6 ka suggest that the lake responded quickly to deteriorating climate conditions.…”

“…The vegetation consisted of herbaceous or shrub tundra along with trees such as Picea glauca and Thuja-Juniperus (Fuller 1997), as they were able to establish in minerogenic sediments following ice retreat from the region (Perren et al 2012). Inputs of mineral-rich sediments to lakes were recorded as elevated magnetic susceptibility values in lake sediments from southern Qu ebec and Ontario (Fuller 1997, Friel et al 2014) and at the base of the Lac Noir core (Fig. 5).…”