Hydrobiologia (2006) 553:15–26 Ó Springer 2006 DOI 10.1007/s10750-005-1737-5 Primary Research Paper Early-20th century environmental changes inferred using subfossil diatoms from a small pond on Melville Island, N.W.T., Canadian high Arctic Bronwyn E. Keatley1,*, Marianne S.V. Douglas2 & John P. Smol1 1Department of Biology, Paleoecological Environmental Assessment and Research Laboratory, QueenÕs University, 116 Barrie St., K7L 3N6, Kingston, Ontario, Canada 2Department of Geology, Paleoenvironmental Assessment Laboratory, University of Toronto, 22 Russell St., M5S 3B1, Toronto, Ontario, Canada (*Author for correspondence: E-mail: [email protected]) Received 22 September 2004; in revised form 18 January 2005; accepted 26 January 2005 Key words: diatoms, environmental change, high arctic, paleolimnology, Melville Island Abstract Diatom-based paleolimnological studies are being increasingly used to track long-term environmental change in arctic regions. Little is known, however, about the direction and nature of such environmental changes in the western Canadian high Arctic. In this study, shifts in diatom assemblages preserved in a 210Pb-dated sediment core collected from a small pond on Melville Island, N.W.T., were interpreted to record marked environmental changes that had taken place since the early 20th century. For most of the history of the pond recorded in this core, the diatom assemblage remained relatively stable and was dominated by Fragilaria capucina. A major shift in species composition began in the early-20th century, with a sharp decline in F. capucina and a concurrent increase in Achnanthes minutissima. In the last 20 years, further changes in the diatom assemblage occurred, with a notable increase in the Nitzschia perminuta complex. The assemblage shifts recorded at this site appear to be consistent with environmental changes triggered by recent climatic warming. Introduction may provide an effective alternative method of gathering records of past environmental conditions The Arctic is well-recognized to be especially when traditional monitoring data are not available sensitive to environmental change (Serreze et al., (Smol, 2002). 2000; Houghton et al., 2001). Due to a number of Unlike many other arctic proxy records, lakes feedback mechanisms, such as snow cover-albedo, and ponds are abundant throughout the Canadian proposed temperature increases are likely to be high Arctic, and thus offer the potential of greater maximized in high-latitude regions. Thus the regional synthesis. Diatoms (class Bacillariophy- Arctic comprises a critical reference area for ceae), siliceous unicellular algae, are particularly environmental change. In the Canadian high useful paleoenvironmental indicators because they Arctic, logistical constraints and the short duration are ubiquitous, they respond rapidly to changing and poor spatial coverage of the few meteorologi- conditions, and different species often have distinct cal records makes monitoring of this vast area optima to given environmental variables (Stoermer particularly difficult. The lack of long-term & Smol, 1999). instrumental data in many ways precludes an Observational data (Serreze et al., 2000) and accurate assessment of long-term environmental proxy records (e.g., Kaufman et al., 2004) indicate change. Paleolimnological techniques, however, that the timing and nature of environmental 16 changes are not synchronous across the Arctic. century, when the diatom assemblages underwent For example, divergences in stable oxygen isotope, substantial changes that were attributed to climatic atmospheric dust, and glaciochemical records warming (Douglas et al., 1994). Since this initial between ice core records from the Devon Ice Cap study, other high arctic paleolimnological investi- (Devon Island), Penny Ice Cap (Baffin Island), and gations have shown similar changes in diatom Greenland (Camp Century and GISP2) suggest community structure since 1850 (e.g., Doubleday increasingly regional climatic influences during the et al., 1995; Gajewski et al., 1997; Wolfe, 2000; Holocene (Paterson et al., 1977; Fisher, 1979; Perren et al., 2003; Michelutti et al., 2003a; OÕBrien et al., 1995; Zdanowicz et al., 2000; Antoniades et al., 2005). These shifts have not been Grumet et al., 2001). simultaneous, but rather appear to be at least To date, most paleolimnological records from partly related to the local limnological conditions, the Canadian high Arctic are from eastern regions, such as lake size (e.g., Doubleday et al., 1995; and have illustrated differences in the timing and Michelutti et al., 2003a) and other variables. For magnitude of environmental change (e.g., Douglas example, diatom assemblages from small water et al., 1994; Doubleday et al., 1995; Perren et al., bodies near Isachsen, Ellef Ringnes Island (Fig. 1, 2003; Michelutti et al., 2003a; Antoniades et al., site b) experienced species turnover starting in the 2005). For example, diatom assemblages from mid-19th century, while those from a larger lake at shallow ponds on Cape Herschel, east-central Alert, Ellesmere Island (Fig. 1, site c), only began Ellesmere Island (Fig. 1, site g), remained relatively to shift after the mid-to late 20th century static and were interpreted to record cool temper- (Antoniades et al., 2005). Likewise, subtle diatom atures for several millennia up until the mid-19th assemblage changes at a large and deep high arctic Figure 1. Map showing location of sites discussed in this paper. The oval on the inset map shows location of Canadian High Arctic. Sites are as follows: (a) MV-AT, Melville Island; (b) Isachsen, Ellef Ringnes Island; (c) Alert, Ellesmere Island; (d) Tuborg Lake, Ellesmere Island; (e) Fosheim Peninsula, Ellesmere Island; (f) Devon Ice Cap, Devon Island; (g) Cape Hershel, Ellesmere Island; (h) Agassiz Ice Cap, Ellesmere Island; (i) Melville Island ice caps, Melville Island; (j) Meighen Ice Cap, Meighen Island; (k) Char Lake, Resolute Bay, Cornwallis Island; (l) Mould Bay, Prince Patrick Island; (m) Bathurst Island; (n) Victoria Island. 17 lake (Char Lake, Cornwallis Island, Fig. 1, site k) Table 1. Present-day physical and chemical characteristics of only began to occur in the late-1980s (Michelutti pond MV-AT were collected on July 24, 2002 et al., 2003a). These diatom community shifts were Parameter Value correlated to warmer temperatures documented by nearby instrumental meteorological records. Latitude 75° 19¢ N Warming conditions are expected to result in a Longitude 111° 25¢ W lengthening of the growing season and enhanced Maximum depth 0.40 m autochthonous production due to a reduction in Elevation 120 m asl duration of ice cover; in turn, this is expected to Specific conductivity 39 lS/cm affect limnological variables such as pH, nutrients, pH 8.1 and specific conductivity (Douglas & Smol, 1999). TP 12.7 lg/l These studies suggest that larger water bodies of TN 640 lg/l the high Arctic had a greater thermal inertia which Chl a 1.60 lg/l acted as a buffer against the early-onset of changes DOC 8.2 mg/l in diatom communities (e.g., Doubleday et al., DIC 4.8 mg/l 1995; Michelutti et al., 2003a). NH3 0.011 mg/l Paleolimnological research using abiotic prox- NO2 0.001 mg/l ies, such as varves, have also indicated relatively Cl 1.93 mg/l recent and marked environmental changes in SO4 4.8 mg/l Canadian high Arctic lakes and have similarly SiO2 0.27 mg/l been correlated to climatic warming (Smith et al., POC 0.559 mg/l 2004). Likewise, analyses of sediment cores from 5 PON 0.053 mg/l lakes on Svalbard suggested that climatic warming SRP 0.0057 mg/l was a contributing factor to changing diatom TKN 0.648 mg/l assemblages over the last 150 years (Birks et al., Al 0.02 mg/l 2004; Jones & Birks 2004). Similarly, research Ba 0.0023 mg/l programs in subarctic regions have recorded Cu 0.001 mg/l recent environmental changes consistent with Fe 0.353 mg/l warming (e.g., Sorvari et al., 2002; Ru¨hland et al., Li 0.001 mg/l 2003a). Mn 0.0052 mg/l Despite a growing body of arctic paleoenviron- Sr 0.0112 mg/l mental literature, no detailed paleolimnological inves- Ca 5.2 mg/l tigations have yet been published from the vast western Mg 2.7 mg/l Canadian high Arctic. Instrumental meteorological Na 1.5 mg/l data are from this region are sparse and of short K 0.4 mg/l duration; the nearest weather station is located at Abbreviations are as follows: TP: total phosphorus, unfiltered, Mould Bay, Prince Patrick Island (Fig. 1, site l), TN: total nitrogen, DOC: dissolved organic carbon, DIC: dis- which began collecting data in 1948. This lack of solved inorganic carbon, Chl a: chlorophyll a, POC: particulate instrumental meteorological data hampers our organic carbon, PON: particulate organic nitrogen, SRP: sol- ability to assess past climatic and associated envi- uble reactive phosphorus, TKN: total Kjeldhal nitrogen. ronmental changes from the western Canadian high Arctic. Given the sensitivity of small ponds in the eastern high Arctic (Douglas et al., 1994), a small pond on Melville Island was chosen to be the focus Study site of a high-resolution paleoenvironmental investiga- tion. The goals of this study are to assess diatom- With a surface area of 42 149 km2, Melville Island based paleolimnological changes from a small pond (Fig. 1) is the 4th largest of the Queen Elizabeth on central Melville Island, to examine whether islands, and the 7th largest of all Canadian arctic diatom assemblages changed in composition and, if islands, yet it is uninhabited. Melville Island is the so, when and why these changes occurred. only island in the western high Arctic that retains 18 small permanent ice caps. In the absence of local core from the center of the pond on July 24, 2002. meteorological records, data from Mould Bay The sediment core was sectioned into 0.5 cm (76° 13¢ N, 119° 19¢ W), Prince Patrick Island intervals from 0 to 13 cm using a Glew (1988) (Fig.