|
Article Excerpt
(Received 10 September 2008; accepted in revised form 15 December 2008)
ABSTRACT. Seven species of freshwater ostracodes were identified from the sediments of 43 lakes on eight islands across the Canadian Arctic Archipelago. No ostracodes were encountered in the sediments of almost half of the lakes, and most were found at sites that had higher alkalinity. Several taxa endemic to Arctic regions are found across the Arctic Archipelago, including Candona rectangulata Alm, Limnocythere liporeticulata Delorme, and Tonnacypris glacialis Sars. The distributions of Cytherissa lacustris Sars, Cyclocypris globosa Sars, Limnocythere sappaensis Staplin, and Limnocythere (Limnocytherina) camera Delorme are more limited; this fact is attributed to differences in ion composition and concentrations.
Key words: ostracodes, distributions, biogeography, limnology, paleolimnology, Canadian Arctic
RESUME. Sept especes d'ostracodes d'eau douce ont ete identifiees a partir des sediments de 43 lacs repartis dans huit iles de l'archipel Arctique canadien. Aucun ostracode n'a ete decele dans les sediments de pres de la moitie des lacs, et la plupart ont ete trouves dans des lieux ayant un taux d'alcalinite plus eleve. Plusieurs taxons endemiques aux regions de l'Arctique se retrouvent a la grandeur de l'archipel Arctique, dont le Candona rectangulata Alm, le Limnocythere liporeticidata Delorme et le Tonnacypris glacialis Sars. Les repartitions de Cytherissa lacustris Sars, de Cyclocypris globosa Sars, de Limnocythere sappaensis Staplin et de Limnocythere (Limnocytherina) camera Delorme sont plus restreintes, ce qui est attribuable aux differences sur le plan de la composition et des concentrations en ions.
Mots cles: ostracodes, repartitions, biogeographie, limnologie, paleolimnologie, Arctique canadien
Traduit pour la revue Arctic par Nicole Giguere.
INTRODUCTION
Ostracodes are small, bivalved crustaceans that occur in all aquatic habitats. They typically live at the sediment-water interface and consume organic detritus. Previous work has shown that certain taxa are often associated with specific habitats (Delorme, 1990) and water chemistry (Forester, 1983; Smith, 1993). As with other aquatic organisms, species distributions are determined by ecological factors such as depth, temperature, and ionic composition and concentrations (De Deckker and Forester, 1988; Holmes, 1992; Smith and Home, 2002). The body of an ostracode is contained within a carapace made of low-magnesium calcite, and although the body generally decomposes after the ostracode dies, the shells preserve well in lake sediments. They are therefore potentially useful organisms for reconstructing past environments (Griffiths and Holmes, 2000). However, their fossils have not been used to their full potential in studies of freshwater systems, partly because understanding of their biogeography is limited.
The biodiversity of freshwater ostracodes in the circumpolar Arctic has been documented from Russia (e.g., Bronshtein, 1988), the Siberian Arctic (e.g., Neale, 1969; Wetterich et al., 2005), Scandinavia (e.g., Alm, 1914 in Delorme, 1968), and Greenland (e.g., Roen, 1962, 1981). In North America, the ostracode fauna has been documented from Alaska (Swain, 1963), the Northwest Territories (Tressler, 1957; Delorme and Zoltai, 1984), and the Yukon (Bunbury and Gajewski, 2005). However, most of the work in Canada has been limited to regions south of 60[degrees] N (Delorme, 1970a, b, c, d, 1971, 1978), and as a result, little is known about the ostracode fauna in the Canadian Arctic.
To use a group of organisms as paleoenvironmental indicators, it is necessary first to understand the ecological tolerances of the different species before attempting to infer past environments on the basis of fossils extracted from sediments. These tolerances are typically determined by sampling a geographical array of lakes and establishing which variables best explain the distribution and abundance of the organism in question. Several studies have explored the modern distribution of ostracodes and related environmental variables, including Smith (1993), Bunbury and Gajewski (2005), and Viehberg (2006); however, these data sets are limited in spatial extent and therefore provide an incomplete picture of the ecology of these organisms. More data from across the entire geographic and environmental domain of the constituent species would enhance our understanding of their modern ecology and enable their use as quantitative paleoenvironmental indicators. These types of studies are particularly useful from northern regions, as the taxa that exist there today are adapted to the cold climate and have the potential to provide modern analogues for late-Pleistocene and early-Holocene sequences elsewhere. For example, Delorme and Zoltai (1984) identified sites in the Canadian North as potential modern analogues for Holocene and Pleistocene ostracode assemblages.
This study documents the freshwater ostracode taxa present across the Canadian Arctic Archipelago. We determine the environmental variables that affect their distribution and abundance in the Canadian North and provide additional data on the ecology of different species. This work will improve our ability to attempt paleoenvironmental reconstructions, as well as to document further the biodiversity of the Arctic.
STUDY AREA
Lake sediments and water chemistry data for this study were available from 43 sites across a broad area of the central and northern Canadian Arctic Archipelago (Fig. 1a). The region is divided into six geologic provinces (Fig. Id). For example, sites on Devon Island are located on Paleozoic sedimentary rocks that are carbonate-rich (Wheeler et al., 1997), whereas most sites on Somerset Island are underlain by Precambrian sedimentary and volcanic bedrock. Sites on Victoria Island (KR06, KR08; unofficial site codes) are underlain by evaporitic rocks, or mafic intrusive rocks (diorite and gabbro; WB01) and those in the Fosheim region of Ellesmere Island are in an area with considerable Tertiary deposits.
Climate patterns in the Archipelago do not follow a latitudinal line, as the coldest temperatures occur in the northwest and on northern Ellesmere Island (Fig. 1c; Edlund and Alt, 1989). Warmer temperatures occur in the low Arctic and on the Fosheim Peninsula on Ellesmere Island and nearby Axel Heiberg Island. The...
|
