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Biogeography of freshwater ostracodes in the Canadian Arctic Archipelago.

(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 growing season is short, occurring between late June and August, and continuous permafrost is widespread, limiting groundwater inputs to lakes (Woo, 1991).

METHODS

Water chemistry and sediment samples were collected from 43 lakes, either using a small inflatable raft or directly from the ice surface, between 1992 and 2004. Water sample collection and analysis followed Environment Canada (1994) protocols, the details of which are discussed in Hamilton et al. (2001), Bouchard et al. (2004), and Gajewski et al. (2005). Sediment was sampled using either an Ekman dredge or a piston corer with a five-inch diameter plastic tube, and in both cases the uppermost 1-2 cm of sediment was subsampled for ostracode valves.

Between 8 and 57.5 [cm.sup.3] of sediment was subsampled and processed using standard methods for the extraction of ostracodes from lake sediments (Holmes, 2001). Sediment disaggregation depended on the nature of the sediment at each site; organic sediment samples were soaked overnight in 10% potassium hydroxide, whereas carbonate sediments were soaked for 48 hours in 5% sodium hexameta-phosphate. Disaggregated sediments were sieved through 125 [micro]m stainless steel sieve or Nitex[C] mesh. Valves were hand-picked using a 0/5 brush under 10x magnification and mounted on micropaleontological slides using gum traga-canth. None of the specimens appeared to contain soft parts (e.g., appendages); however, many of the samples included well-preserved adult and juvenile valves or carapaces, suggesting that ostracodes were living in the lake at the time of sample collection (Forester, 1983). Adult valves (including carapaces) were enumerated. All specimens are stored at the Laboratory for Paleoclimatology and Climatology, Department of Geography, University of Ottawa.

Of the 43 lakes evaluated, only 24 had identifiable adult ostracodes (min = 1; max = 102, mean = 36). In most samples, ostracode valve concentrations were very low. Ten [cm.sup.3] was initially subsampled and evaluated for adult specimens. If several individuals (i.e., more than 1 valve per [cm.sup.3]) were encountered, then subsampling was continued until the total number of valves was 50 or greater (Bunbury and Gajewski, 2005). If very few or no specimens were encountered, then subsampling for that site was suspended; however, ostracode presence at such sites was still recorded. In one case (Lake HW02), only one juvenile ostracode valve was encountered, and this information was included in the total concentration computation for that site. At four sites where ostracodes were present, the amount of sediment was depleted; therefore, counts did not reach 50 (CI07, CI16, KR06, and KR08). Identifications were achieved using 20x to 40x magnification and taxonomy followed Delorme (1968, 1970a, b, c, 1971).

A Geographic Information System was used to assign mean July air temperature (40-year means; Atkinson and Gajewski, 2002), vegetation (CAVM Team, 2003), and bedrock geology (Wheeler et al., 1997) to each site. The total concentration of ostracode valves that occurred in the 43 lakes was mapped, as were the concentrations of individual ostracode species found in the 24 lakes. Maps assist in understanding the spatial distribution of the taxa in relation to mean July temperature, vegetation, and bedrock geology.

Environmental variables considered here are those that influence ostracode distribution: temperature and lake depth, pH, alkalinity, conductance, and ionic composition of the lake water (Griffiths and Holmes, 2000). Water temperature data were missing for lake CI03; therefore, the mean of the data set (3.5[degrees]C) was substituted in that one instance. With the exception of air temperature (AirTemp), water temperature ([H.sub.2]OTemp), pH, magnesium-calcium ratio (Mg/Ca), and the alkalinity-calcium ratio (Alk/Ca), all environmental variables were transformed prior to data analysis. Depth, calcium ([Ca.sup.2+]), magnesium ([Mg.sup.2+]), sulphate ([SO.sub.4.sup.2-]), chloride ([Cl.sup.-]), and alkalinity were square root-transformed, and conductance (Cond), sodium ([Na.sup.+]), and potassium ([K.sup.+]) were log-transformed. Geologic provinces (GeolProv) and vegetation types (Veg) indicated on the maps were also included as explanatory variables.

A principal components analysis (PCA) was used to investigate the relations between the species and the environmental variables. This analysis combines variables together into separate linear components: the first component explains the main variation in the data, and the second component explains more of the variation, but is orthogonal to the first component (Davis, 1973). Percentage species data were log-transformed prior to analysis, and a correlation matrix was used to summarize the variation in the species data set (CANOCO 4.5; ter Braak and Smilauer, 2002).

RESULTS

Seven taxa were encountered from 24 lakes on eight islands in the Canadian Arctic Archipelago (Table 1; Fig. 1c-f). Taxa with the greatest number of occurrences are Candona rectangulata Alm, 1914 (present in 16 lakes), Cytherissa lacustris (Sars, 1863) (13 lakes), and Limno-cythere liporeticulata Delorme, 1968 (12), whereas less abundant taxa are Tonnacypris glacialis (Sars, 1890) (4), Cyclocypris globosa (Sars, 1863) (2), Limnocythere sappaensis Staplin, 1963 (1), and Limnocythere (Limnocythe-rind) camera Delorme, 1967 (1; Fig. 2).

[FIGURE 2 OMITTED]
TABLE 1. Ostracode taxa found in 43 lakes in the Canadian Arctic
Archipelago, showing total valves and concentrations (valves per
[cm.sup.3]) for each lake.

Lake         Lat          Long        Island    Cytherissa    Candona
        ([degrees]N)  ([degrees]W)               lacustris  rectangulata

Allen       73.62         98.47     Prince of
                                    Wales

BC01        75.18        111.93     Melville

CI01        73.88         94.87     Somerset        10           1

CI03        73.21         94.32     Somerset

CI04        73.03         94.93     Somerset

CI05        72.73         95.99     Somerset

CI06        72.67         95.05     Somerset

CI07        72.59         95.06     Somerset

CI08        72.49         95.09     Somerset        30          15

CI09        72.27         95.09     Somerset         4

CI10        72.01         94.87     Somerset

CI13        72.31         94.13     Somerset

CI16        76.50         98.16     Somerset                    24

CI17        76.60         98.87     Bathurst        54

CI19        76.51         99.11     Bathurst                    50

CI22        75.90         99.22     Bathurst

CI23        75.53         98.21     Bathurst        63           6

CI28        75.29         99.80     Bathurst                     1

CI29        75.02        100.20     Bathurst

DV01        74.99         90.36     Devon

DV02        74.93         88.68     Devon           28          29

DV05        75.52         92.05     Devon           42           4

DV06        75.51         91.99     Devon            2           4

DV07        75.53         91.97     Devon           16          33

DV08        75.37         89.49     Devon                       45

DV09        75.58         89.32     Devon            1

DV10        75.54         89.75     Devon

E505        79.98         82.97     Ellesmere

E506        80.57         84.47     Ellesmere

EU01        79.90         84.88     Ellesmere                   23

Gemini      79.99         84.13     Ellesmere                    1

HW01        80.02         83.39     Ellesmere                   44

HW02        79.73         83.47     Ellesmere

HW03        79.73         85.81     Ellesmere

HW05        80.18         87.69     Axel
                                    Heiberg

HW06        80.26         87.77     Axel
                                    Heiberg

HW07        79.72         83.52     Ellesmere

HW08        79.72         83.50     Ellesmere

KR06        71.32        113.97     Victoria        16

KR08        71.31        113.67     Victoria        14           4

Ridge       79.94         84.62     Ellesmere                   32

WB01        72.29        109.99     Victoria

Wolf        73.58         98.48     Prince of        2
                                    Wales

Lake        Lat        Long       Island   Cyclocypris  Limnocythere
        ([degrees]  ([degrees]               globosa     sappaensis
             N)         W)

Allen      73.62       98.47    Prince of
                                Wales

BC01       75.18      111.93    Melville

CI01       73.88       94.87    Somerset

CI03       73.21       94.32    Somerset

CI04       73.03       94.93    Somerset

CI05       72.73       95.99    Somerset

CI06       72.67       95.05    Somerset

CI07       72.59       95.06    Somerset       32

CI08       72.49       95.09    Somerset

CI09       72.27       95.09    Somerset

CI10       72.01       94.87    Somerset

CI13       72.31       94.13    Somerset

CI16       76.50       98.16    Somerset

CI17       76.60       98.87    Bathurst

CI19       76.51       99.11    Bathurst

CI22       75.90       99.22    Bathurst

CI23       75.53       98.21    Bathurst

CI28       75.29       99.80    Bathurst

CI29       75.02      100.20    Bathurst

DV01       74.99       90.36    Devon

DV02       74.93       88.68    Devon

DV05       75.52       92.05    Devon

DV06       75.51       91.99    Devon

DV07       75.53       91.97    Devon

DV08       75.37       89.49    Devon

DV09       75.58       89.32    Devon

DV10       75.54       89.75    Devon

E505       79.98       82.97    Ellesmere

E506       80.57       84.47    Ellesmere

EU01       79.90       84.88    Ellesmere                    21

Gemini     79.99       84.13    Ellesmere

HW01       80.02       83.39    Ellesmere

HW02       79.73       83.47    Ellesmere

HW03       79.73       85.81    Ellesmere

HW05       80.18       87.69    Axel
                                Heiberg

HW06       80.26       87.77    Axel
                                Heiberg

HW07       79.72       83.52    Ellesmere

HW08       79.72       83.50    Ellesmere

KR06       71.32      113.97    Victoria

KR08       71.31      113.67    Victoria

Ridge      79.94       84.62    Ellesmere

WB01       72.29      109.99    Victoria        2

Wolf       73.58       98.48    Prince of
                                Wales

Lake        Lat        Long      Island     Limnocythere   Limnocythere
        ([degrees]  ([degrees]             liporeticulata     camera
             N)         W)

Allen      73.62       98.47    Prince of
                                Wales

BC01       75.18      111.93    Melville

CI01       73.88       94.87    Somerset         39

CI03       73.21       94.32    Somerset          6

CI04       73.03       94.93    Somerset

CI05       72.73       95.99    Somerset

CI06       72.67       95.05    Somerset

CI07       72.59       95.06    Somerset

CI08       72.49       95.09    Somerset         10

CI09       72.27       95.09    Somerset

CI10       72.01       94.87    Somerset

CI13       72.31       94.13    Somerset

CI16       76.50       98.16    Somerset

CI17       76.60       98.87    Bathurst

CI19       76.51       99.11    Bathurst

CI22       75.90       99.22    Bathurst

CI23       75.53       98.21    Bathurst         33

CI28       75.29       99.80    Bathurst

CI29       75.02      100.20    Bathurst

DV01       74.99       90.36    Devon

DV02       74.93       88.68    Devon

DV05       75.52       92.05    Devon            14

DV06       75.51       91.99    Devon

DV07       75.53       91.97    Devon             4

DV08       75.37       89.49    Devon

DV09       75.58       89.32    Devon

DV10       75.54       89.75    Devon

E505       79.98       82.97    Ellesmere

E506       80.57       84.47    Ellesmere

EU01       79.90       84.88    Ellesmere         7

Gemini     79.99       84.13    Ellesmere         1              1

HW01       80.02       83.39    Ellesmere        47

HW02       79.73       83.47    Ellesmere

HW03       79.73       85.81    Ellesmere

HW05       80.18       87.69    Axel
                                Heiberg

HW06       80.26       87.77    Axel
                                Heiberg

HW07       79.72       83.52    Ellesmere

HW08       79.72       83.50    Ellesmere

KR06       71.32      113.97    Victoria          2

KR08       71.31      113.67    Victoria          2

Ridge      79.94       84.62    Ellesmere        64

WB01       72.29      109.99    Victoria

Wolf       73.58       98.48    Prince of
                                Wales

Lake        Lat        Long          Island      Tonnacypris  Total
        ([degrees]  ([degrees]                    glacialis   valves
             N)         W)

Allen   73.62         98.47     Prince of Wales

BC01    75.18        111.93     Melville

CI01    73.88         94.87     Somerset                        50

CI03    73.21         94.32     Somerset                         6

CI04    73.03         94.93     Somerset

CI05    72.73         95.99     Somerset

CI06    72.67         95.05     Somerset

CI07    72.59         95.06     Somerset                        32

CI08    72.49         95.09     Somerset              2         57

CI09    72.27         95.09     Somerset                         4

CI10    72.01         94.87     Somerset

CI13    72.31         94.13     Somerset

CI16    76.50         98.16     Somerset                        24

CI17    76.60         98.87     Bathurst                        54

CI19    76.51         99.11     Bathurst              5         55

CI22    75.90         99.22     Bathurst

CI23    75.53         98.21     Bathurst                       102

CI28    75.29         99.80     Bathurst                         1

CI29    75.02        100.20     Bathurst

DV01    74.99         90.36     Devon

DV02    74.93         88.68     Devon                           57

DV05    75.52         92.05     Devon                           60

DV06    75.51         91.99     Devon                            6

DV07    75.53         91.97     Devon                           53

DV08    75.37         89.49     Devon                 5         50

DV09    75.58         89.32     Devon                            1

DV10    75.54         89.75     Devon

E505    79.98         82.97     Ellesmere

E506    80.57         84.47     Ellesmere

EU01    79.90         84.88     Ellesmere                       51

Gemini  79.99         84.13     Ellesmere                        3

HW01    80.02         83.39     Ellesmere             7         98

HW02    79.73         83.47     Ellesmere                        1 (1)

HW03    79.73         85.81     Ellesmere

HW05    80.18         87.69     Axel Heiberg

HW06    80.26         87.77     Axel Heiberg

HW07    79.72         83.52     Ellesmere

HW08    79.72         83.50     Ellesmere

KR06    71.32        113.97     Victoria                        18

KR08    71.31        113.67     Victoria                        20

Ridge   79.94         84.62     Ellesmere                       96

WB01    72.29        109.99     Victoria                         2

Wolf    73.58         98.48     Prince of Wales                  2

Lake    Lat ([degrees]  Long ([degrees]  Island           Concentration
              N)              W)                           (valves per
                                                           [cm.sup.3])

Allen       73.62            98.47       Prince of Wales

BC01        75.18           111.93       Melville

CI01        73.88            94.87       Somerset             4.17

CI03        73.21            94.32       Somerset             0.20

CI04        73.03            94.93       Somerset

CI05        72.73            95.99       Somerset

CI06        72.67            95.05       Somerset

CI07        72.59            95.06       Somerset             1.45

CI08        72.49            95.09       Somerset             0.99

CI09        72.27            95.09       Somerset             0.13

CI10        72.01            94.87       Somerset

CI13        72.31            94.13       Somerset

CI16        76.50            98.16       Somerset             0.61

CI17        76.60            98.87       Bathurst             1.80

CI19        76.51            99.11       Bathurst             1.83

CI22        75.90            99.22       Bathurst

CI23        75.53            98.21       Bathurst             3.40

CI28        75.29            99.80       Bathurst             0.10

CI29        75.02           100.20       Bathurst

DV01        74.99            90.36       Devon

DV02        74.93            88.68       Devon                2.85

DV05        75.52            92.05       Devon                1.33

DV06        75.51            91.99       Devon                0.60

DV07        75.53            91.97       Devon                1.06

DV08        75.37            89.49       Devon                0.91

DV09        75.58            89.32       Devon                0.05

DV10        75.54            89.75       Devon

E505        79.98            82.97       Ellesmere

E506        80.57            84.47       Ellesmere

EU01        79.90            84.88       Ellesmere            2.22

Gemini      79.99            84.13       Ellesmere            0.10

HW01        80.02            83.39       Ellesmere            9.80

HW02        79.73            83.47       Ellesmere            0.10

HW03        79.73            85.81       Ellesmere

HW05        80.18            87.69       Axel Heiberg

HW06        80.26            87.77       Axel Heiberg

HW07        79.72            83.52       Ellesmere

HW08        79.72            83.50       Ellesmere

KR06        71.32           113.97       Victoria             2.25

KR08        71.31           113.67       Victoria             2.50

Ridge       79.94            84.62       Ellesmere            4.80

WB01        72.29           109.99       Victoria             0.20

Wolf        73.58            98.48       Prince of Wales      0.07

(1) Juvenile ostracode.


C. lacustris is present in lakes at lower latitudes and absent from lakes in the High Arctic (Fig. 1c), whereas C. rectangulata, L. liporeticulata, and T. glacialis are present in lakes found across the entire area (Fig. 1d-f). C. globosa is limited to the more southerly sites, and L. camera and L. sappaensis occur only on the Fosheim Peninsula on Elles-mere Island (Fig. 1e).

Ostracode concentrations vary between 0.1 and 9.8 valves per [cm.sup.3] of sediment, with the highest concentrations (> 4 valves per [cm.sup.3]) occurring in the Fosheim region (Fig. 1b; Table 1). Concentrations of C. rectangulata are greater in the middle and High Arctic, whereas L. liporeticulata has both high and low concentrations across the entire region.

A large amount of the total variance (44%) is explained by the first two axes of the principal components analysis (PCA; Fig. 3). The first axis explains 26.8% of the variance in the data and includes variables related to ion concentrations, as well as the physical variables [H.sub.2]OTemp and Depth. The second and third axes explain 17.2% and 16.2% of the variation, respectively; GeolProv is correlated with axis two, and AirTemp and K are correlated with axis three (not shown). C. rectangulata, L. liporeticulata, and T. glacialis are taxa correlated with axis one, whereas C. lacustris is negatively correlated and T. glacialis is positively correlated with axis two. L. camera and L. sappaensis are positively correlated with axis three, whereas T. glacialis is negatively correlated. Lakes where ostracodes are present have higher ion concentrations, pH, and alkalinity and are located on the right side of the tri-plot, whereas sites without ostracodes have low ion concentrations, low pH, and low alkalinity values and are located on the left of the tri-plot (Fig. 3).

[FIGURE 3 OMITTED]

A majority of the lakes have a log alkalinity/calcium ratio (Log Alk/Ca) greater than 1, particularly those that contain ostracodes; however, there are exceptions (Fig. 4). Bicarbonate ([HCO.sub.3.sup.-])-depleted sites (three lakes) are those with Log (Alk/Ca) less than 0 and log conductance (Log Cond) greater than 6, whereas bicarbonate-enriched sites (four lakes) have Log (Alk/Ca) greater than 0 and Log Cond greater than 6 (Curry, 1997, 1999). In these Arctic lakes, the bicarbonate-depleted sites are dominated by sulphate ([SO.sub.4.sup.2-]), and the bicarbonate-enriched lakes are dominated or enriched by sodium ([Na.sup.+]) or chloride ([CI.sup.-]) or both (Table 2). All other lakes have lower conductance, and most are dominated by calcium ([Ca.sup.2+]), which is more characteristic of freshwater lakes (Kalff, 2002).

[FIGURE 4 OMITTED]
TABLE 2. Environmental data from 43 lakes in the Canadian Arctic
Archipelago.

Lake         Air      Depth        Conductance         Water      pH
        temperature    (m)   ([mu]S * [cm.sup.-1])  temperature
        ([degrees]C)                                ([degrees]C)

Allen        4.8        4.0             68               9.0      7.7

BC01         4.0       10.9              7              -0.4      8.0

CI01         4.5        2.0            150               1.9      7.6

CI03         4.0        0.5             40               3.5      7.5

CI04         4.0        1.0             20               0.7      7.7

CI05         5.0        1.0             70               5.8      7.6

CI06         5.0        1.0             50               1.4      7.8

CI07         5.4        5.5             80               1.1      7.8

CI08         5.2        4.0            170               7.9      8.1

CI09         5.4        4.0             30               0.1      8.2

CI10         5.6       19.0             30               1.5      7.9

CI13         5.0        0.5             80               2.6      7.9

CI16         4.0        1.0             70               3.1      8.0

CI17         2.0        3.5             80               3.1      8.0

CI19         4.0        1.0             80               4.1      8.2

CI22         4.6        8.0             90               6.9      8.1

CI23         4.5        9.5             70               1.2      8.0

CI28         4.0        0.5             40               6.7      7.9

CI29         4.8        6.5             30               2.3      7.8

DV01         4.3        4.5             91               2.0      8.4

DV02         4.8        7.5            445               2.6      7.9

DV05         4.5       11.0            153               5.1      8.6

DV06         4.4        4.0            158               8.5      8.4

DV07         4.4        5.0            148               8.0      8.4

DV08         4.7        3.0            175              10.5      8.4

DV09         4.9       15.0            167               4.2      8.4

DV10         4.7       11.0             92               7.9      8.3

E505         6.0        2.5             56               0.1      7.1

E506         4.8       14.0             19               1.1      7.0

EU01         6.7        6.5           2000              10.0      8.6

Gemini       7.6        0.1            388               0.9      8.2

HW01         6.7        3.7            366               0.7      8.2

HW02         5.4        4.5            126               4.2      7.7

HW03         3.9       13.0            524               1.9      7.8

HW05         6.8        3.7            998               2.5      8.0

HW06         6.7        3.5            293               2.5      8.0

HW07         5.8        6.0             79               0.9      7.3

HW08         5.8        8.5             98               3.0      7.5

KR06         6.8        4.5             19               0.0      7.6

KR08         6.4        3.3            420               0.1      8.1

Ridge        6.5        5.0            506               6.5      8.3

WB01         6.3       20.0            139               2.3      8.0

Wolf         4.9        6.0             65               1.5      8.4

Mean         5.1        5.8            204               3.5      8.0

Median       4.9        4.5             90               2.5      8.0

             Ca           Mg           Cl           Na           K
Lake       (mg *        (mg *        (mg *        (mg *       (mg *
        [1.sup.-1])  [1.sup.-1])  [1.sup.-1])  [1.sup.-1])  [1.sup.-1)

Allen      11.60        4.40         1.68         0.80         0.20

BC01        0.17        0.18         0.40         0.36         0.09

CI01       22.00        3.90         1.27         0.67         0.22

CI03        6.60        3.90         1.28         0.56         0.16

CI04        3.80        1.56         0.82         0.52         0.26

CI05        9.50        5.90         5.91         2.00         0.52

CI06        9.50        3.70         0.90         0.65         0.24

CI07       16.00        5.90         4.50         1.60         0.29

CI08       28.00       13.20         3.87         2.20         0.66

CI09        6.30        2.10         0.88         0.55         0.15

CI10        5.80        1.97         1.06         0.53         0.12

CI13       13.80        5.10         1.99         0.89         0.28

CI16       16.30        2.10         1.74         1.18         0.15

CI17       17.50        2.50         1.90         1.78         0.51

CI19       19.30        2.80         1.23         1.26         0.36

CI22       23.00        2.90         0.39         0.49         0.69

CI23       18.90        0.46         0.83         0.65         0.11

CI28        5.00        0.76         4.46         2.00         0.23

CI29        1.09        1.11         8.54         4.00         0.37

DV01       29.20        4.80         1.64         0.70       < 0.2 (1)

DV02      140.00       17.20         4.22         2.30         0.40

DV05       24.20        4.30         2.28         0.90       < 0.2

DV06       25.80        4.40         2.05         0.90         0.20

DV07       24.70        4.30         2.32         0.90         0.40

DV08       27.30        6.40         2.06         1.00         0.20

DV09       26.80        5.20         2.93         1.90         0.20

DV10       11.80        5.20         1.78         0.90       < 0.2

E505        5.20        1.10         0.60         0.50         0.30

E506        2.50        0.60         1.30         0.60       < 0.2

EU01       57.40       38.70       217.00       281.00        13.80

Gemini     31.00       16.40        32.70        20.30         3.40

HW01       45.10       11.40        31.80        8.22          1.62

HW02       13.50        2.49         1.94         4.55         1.46

HW03       37.70       15.20        48.30        24.60         3.86

HW05       38.90       17.50       202.00       101.00         4.17

HW06       24.10        9.86        16.30        11.40         1.10

HW07        9.90        1.52         1.40         1.71         0.59

HW08       12.10        2.10         1.28         4.21         0.52

KR06        5.70        2.80         0.80         0.25         0.15

KR08       78.00       18.80         1.70         1.53         1.76

Ridge      37.10       18.10        57.90        38.20         3.70

WB01       23.00        5.10         1.80         0.53         1.40

Wolf       14.60        5.30         1.58         0.80         0.30

Mean       22.79        6.59        15.84        12.36         1.16

Median     17.50        4.30         1.80         1.00         0.36

            [SO.sub.4]         Alkalinity
Lake    (mg * [l.sup.-1])  (mg * [l.sup.-1] as  Mg/Ca  Alk/Ca
                              Ca[CO.sub.3])

Allen           2.30               57            0.38   4.89

BC01            0.50               2             1.02  11.56

CI01            2.22               72            0.18   3.26

CI03            0.40               30            0.59   4.55

CI04            3.71               11            0.41   2.89

CI05            0.11               41            0.62   4.32

CI06            2.15               34            0.39   3.58

CI07            1.61               57            0.37   3.55

CI08           25.05               92            0.47   3.27

CI09            1.62               20            0.33   3.16

CI10            1.11               20            0.34   3.43

CI13            1.69               50            0.37   3.62

CI16            0.75               50            0.13   3.07

CI17            3.70               48            0.14   2.73

CI19            6.56               53            0.15   2.75

CI22            7.54               59            0.13   2.56

CI23            0.36               50            0.02   2.64

CI28            0.12               18            0.15   3.60

CI29            1.17                3            1.02   2.74

DV01            1.10              101            0.16   3.45

DV02          395.00               68            0.12   0.48

DV05            1.30               87            0.18   3.58

DV06            0.60               91            0.17   3.51

DV07            0.90               88            0.17   3.56

DV08            8.70               94            0.23   3.45

DV09            5.90               91            0.19   3.38

DV10            0.80               57            0.44   4.85

E505            2.80               19            0.21   3.70

E506            2.10               11            0.24   4.45

EU01          101.00              253            0.67   4.41

Gemini         17.30              171            0.53   5.52

HW01            3.40              180            0.25   3.99

HW02           24.40               25            0.18   1.84

HW03           89.40               44            0.40   1.15

HW05            2.10              127            0.45   3.25

HW06           17.50              100            0.41   4.14

HW07            4.90               29            0.15   2.96

HW08            5.00               45            0.17   3.72

KR06            2.20               19            0.49   3.32

KR08          128.00              106            0.24   1.35

Ridge           7.40              220            0.49   5.93

WB01            3.30               42            0.22   1.82

Wolf            4.10               69            0.36   4.71

Mean           20.74               67            0.33   3.60

Median          2.30               53            0.25   3.45

(1) Concentration was below the detection limit.


Convex hulls indicating species distributions as a function of conductance and the alkalinity/calcium ratio reveal the broad ranges of C. lacustris, C. rectangulata, and L. liporeticulata, and the narrow range of T. glacialis. C. lacustris can tolerate bicarbonate-depleted lake water dominated by sulphate; however, it is excluded from sites that are bicarbonate-enriched with high concentrations of sodium and chloride. In comparison, L. liporeticulata is found in lakes with high sodium and chloride concentrations. There are several sites throughout these ranges where no ostracodes were encountered. T. glacialis is limited to sites with Log Alk/Ca greater than 1, and Log Cond between 4 and 6; however, this result is based on only four occurrences.

DISCUSSION

The distribution of freshwater ostracodes in the Canadian Arctic Archipelago is primarily dependent upon the alkalinity of the lake water. This is a measure of calcium carbonate in the lake water. To live and grow in a particular site, ostracodes require an available source of calcium carbonate from which to construct their shells (Delorme, 1991). Water temperature and lake depth also affect ostracode presence within a lake, but to a lesser extent. C. rectangulata, L. liporeticulata, and T. glacialis are found across the entire region because their requirements for shell creation and preservation are met and each species can tolerate the cold temperatures associated with Arctic environments. All three of these taxa are endemic to the Arctic, with C. rectangulata and T. glacialis known throughout the circumpolar region (Roen, 1962; Bronshtein, 1988; Delorme, 1991; Little and Hebert, 1997; Griffiths et al., 1998; Wetterich et al., 2008; Wojtasik, 2008), and L. liporeticulata from the Canadian Arctic (Delorme, 1991).

Sites on Victoria and Somerset islands are warmer than sites located in the middle Arctic; however, we suggest that the low concentrations of C. rectangulata in this area are related to lower alkalinity values (Fig. 1d; Table 2). In comparison, C. globosa is restricted to lakes in the southern portion of the study area, suggesting that the species is unable to tolerate the cooler temperatures and higher alkalinity found in our more northern sites (Fig. 1e). C. lacustris can withstand the colder mean July temperatures located in the middle Arctic, but it is absent from lakes at high latitudes, where mean July temperatures are warmer and alkalinity is higher (Fig. 1c).

Two taxa were found only once in two separate lakes on Ellesmere Island. L. sappaensis occurs at the site (EU01) that has the highest values in the data set for alkalinity, sodium, and chloride (Fig. 1e; Table 2). This taxon typically occurs in sodium-bicarbonate waters (Forester, 1983), is common in lakes on the Canadian Prairies (Delorme, 1971), and inhabits alkaline lakes in the Midwest of the United States (Smith, 1993). Several of the lakes in the Fosheim region of Ellesmere Island have emerged from the sea, and they retain high values of sodium and chloride as a legacy of submergence (Hamilton et al., 2000). Other taxa in the assemblage at Lake EU01 are C. rectangulata and L. liporeticulata, indicating the ability of these two taxa to tolerate high values of sodium and chloride. Delorme (1991) also found C. rectangulata in sites that were subject to sea spray, indicating the species' tolerance for saline conditions.

L. camera is the second taxon found only once in this study and is one of three individuals encountered at Gemini Lake. This site has high alkalinity and conductance values (Table 2), which are attributed to elevated sodium and chloride levels (although these levels are not as high as those at Lake EU01). This taxon is rare, but it has been encountered on the Canadian Prairies (Delorme, 1971), which suggests an association with saline conditions. The presence of L. sappaensis and L. camera appears limited to sites in the Fosheim region; however, this is the only area where lakes with higher salinities were sampled. If more saline lakes from across the Canadian Arctic were to be sampled, we might be better able to determine the spatial distribution of these taxa. In addition, the identification of these rare species suggests that expanding the data set to include more lakes may identify other taxa in the region.

Ostracodes are found at sites in the Canadian Arctic that have higher alkalinity, and the widespread species C. rectangulata, L. liporeticulata, and T. glacialis are present across the Arctic because they can withstand the cold temperatures. The distribution of individual species appears influenced by the composition of the lake water. C. rectangulata has a broad tolerance for different ions (i.e., sulphate, sodium, and chloride); however, it is absent from sites with low ion concentrations (Fig. 3; Table 2). L. liporeticulata occurs in lakes with a wide range of alkalinity values and those dominated by sodium and chloride, but it is absent from waters with a high sulphate content. C. lacustris can tolerate elevated sulphate values, but prefers sites with low ion concentrations. In comparison, T. glacialis and C. globosa appear to have a much narrower tolerance with respect to ion content and are found at sites with lower conductance values. L. sappaensis and L. camera occupy lakes dominated by sodium and chloride, with L. sappaensis present only in a saline lake.

Ostracodes are neither abundant nor diverse in the Canadian Arctic Archipelago; nevertheless, several taxa are found across the region, and some taxa are found in a restricted group of lakes. As is the case in southern regions, those taxa that can tolerate the cold temperatures are influenced by the ion concentration of the lake waters. The results presented in this study further our knowledge of the distribution of ostracode taxa and provide data that can be used in paleoenvironmental studies in the region.

ACKNOWLEDGEMENTS

We would like to thank all of the people who assisted in the fieldwork component of this study over the years. Funding sources include an NSERC Discovery Grant, Northern Supplement, and logistic support by the Polar Continental Shelf Project (PCSP, Contribution Number 04608). We appreciate the comments from Finn Viehberg, Jonathan Holmes, and an anonymous reviewer, which improved the quality of this manuscript.

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JOAN BUNBURY (1), (2) and KONRAD GAJEWSKI (1)

(1) Laboratory for Paleoclimatology and Climatology, Department of Geography, University of Ottawa, Ottawa, Ontario KlN 6N5, Canada

(2) Corresponding author: jbunbury@uottawa.ca

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