Evidence for a warmer period during the 12th and 13th centuries AD from chironomid assemblages in Southampton Island, Nunavut, Canada

This study presents the Late-Holocene evolution of a northern Southampton Island (Nunavut, Canada) lake, using fossil chironomids supported by sedimentological evidences (XRF, grain size and CNS). All proxies revealed a relatively stable environment during the last millennium with short-lived events driving changes in the entire lake ecosystem. The chironomid-based paleotemperatures revealed variations of significant amplitude coincident with changes in the sediment density and chemical composition of the core. Higher temperature intervals were generally correlated to lower sediment density with higher chironomid concentration and diversity. Higher temperatures were recorded from cal yr AD 1160 to AD 1360, which may correspond to the Medieval Warm Period. Between cal yr AD 1360 and AD 1700, lower temperatures were probably related to a Little Ice Age event. This study presents new information on the timing of known climatic events which will refine our knowledge of the paleoclimate and climatic models of the Foxe Basin region. It also provides a new framework for the evolution of such freshwater ecosystems under the “Anthropocene” and underlines the importance of including sedimentological proxies when interpreting chironomid remains as this combined approach provides an extended overview of the past hydrological and geochemical changes and their impacts on lake biota.     

A pre-Ipswichian cold stage mammalian fauna from the Balderton Sand and Gravel,Lincolnshire, England

The Balderton Sand and Gravel has yielded one of very few mammalian faunas dated to the penultimate Cold Stage in Britain. The assemblage is dominated by mammoth and woolly rhinoceros, with subordinate horse, red deer, bison, straight-tusked elephant, musk ox, reindeer, wolf, lion, brown bear and cf. narrow-nosed rhinoceros. This fauna indicates cold stage conditions, probably including one or more interstadial episodes. The presence of straight-tusked elephant and cf. narrow-nosed rhinoceros supports its pre-Devensian age, and provides corroboration for the occurrence of these taxa in the British Wolstonian. An attempt is made to analyse the fossil collection by preservation type and adhering sediment: the occurrence of individual species appears to be largely uncorrelated with lithology. The Balderton assemblage corresponds well to other British mammal faunas assigned to a cold interval between the Hoxnian and Ipswichian Interglacials.     

Post‐glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut,Canada

Climate models suggest that the global warming during the early to mid‐Holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo. We investigated the Holocene vegetation history of low arctic continental Nunavut, Canada, from a radiocarbon‐dated sediment core from TK‐2 Lake, a small‐lake ca. 200 km north of the limit of the forest‐tundra. The pollen and loss‐on‐ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca. 9000 cal. yr BP with dominance of Betula, especially since 8700 cal. yr BP. At 8100–7900 cal. yr BP the dominance of the shrub tundra was punctuated by a transient decline of Betula and coincident increases of Ericaceae undiff., Vaccinium‐type, and Gramineae. This suggests an abrupt disturbance of the Betula glandulosa population, approximately simultaneously with the sudden 8200 cal. yr BP event in the North Atlantic. However, in the absence of other sites studied in the area, linkage to the 8200 cal. yr BP event remains tentative. The lack of any evidence of forest‐tundra in the region constrains the northern limit of the mid‐Holocene advance of the forest‐tundra boundary in central northern Canada. Consequently, our results show that the climate models imposing a mid‐Holocene advance of the limit of the forest‐tundra to the arctic coast of Canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest. Copyright © 2003 John Wiley & Sons, Ltd.     

Autumn snowfall and hydroclimatic variability during the past millennium inferred from the varved sediments of meromictic Lake A, northern Ellesmere Island, Canada

We examined the hydroclimatic signal in a record of annual lamina (varve) thickness from High Arctic Lake A, Ellesmere Island (83°00.00′N, 75°30.00′W). In this unglacierized catchment, nival melt is the dominant source for meltwater and transport of sediment to the lake, and autumn snowfall is highly influential on varve thickness through the amount of snow available for melt in the following year. For the period during which climatic data are available, varve thickness in Lake A was significantly correlated (r = 0.50, p < 0.01) with the cumulative snowfall from August to October (ASO) during the previous year and, to a lesser extent, ASO mean daily temperature (r = 0.39, p < 0.01) at Alert, Nunavut (175 km east). The varve thickness record, interpreted as a proxy record of ASO snowfall and, by extension, ASO temperature, indicated above-mean conditions during five periods of the past millennium, including most of the 20th century. These results corresponded well to other available high-resolution proxy climate records from the region, with some discrepancies prior to AD 1500 and during the period AD 1700-1900.