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Article Excerpt
ABSTRACT. Sea ice is an integral part of the marine ecosystem in the Arctic and important habitat for ringed seals and polar bears. To study changes in sea ice characteristics indicative of ringed seal habitat (and linked, through predator/prey relationships, to polar bear habitat), we examined historical changes in sea ice concentration and type within M'Clintock Channel and the Gulf of Boothia, two regions of the Canadian Arctic Archipelago, during 1980-2000. Results suggest large interannual variability in winter ice conditions over the 21-year study period. In M'Clintock Channel, first-year ice types dominated consistently, while in the Gulf of Boothia, thick ice types dominated in some years. For breakup and consolidation, the regional spatial patterns differed significantly, occurring in opposite directions (N-S vs. S-N) in the two regions. The dates showed considerable interannual variability in both regions, suggesting no clear pattern of either earlier breakup or later consolidation. Analysis of satellite data confirmed the results obtained from digital ice charts. Ringed seal habitat suitability indices (HSI) indicate that both regions contained primary, secondary, and tertiary HSI classes. No trends were evident in the secondary or tertiary classes, but changes in the primary class were evident in M'Clintock Channel over the five-year period 1997-2001. Dynamic and thermodynamic sea ice processes are important to ringed seal habitat (and ultimately, polar bear habitat) at regional and hemispheric scales in the current context of climate variability and change.
Key words: sea ice, climate variability, ringed seal habitat, Phoca hispida, polar bear, Ursus maritimus, M'Clintock Channel, Gulf of Boothia
RESUME. La glace de mer fait partie integrante de l'ecosysteme marin de l'Arctique et constitue un important habitat pour le phoque annele et l'ours polaire. Au cours des annees comprises entre 1980 et 2000, afin d'etudier les changements dans les caracteristiques de glace marine denotant un habitat de phoque annele (et donc associe a un habitat d'ours polaire par l'intermediaire de la relation predateur / proie), on a examine des changements historiques dans la concentration et le type de glace de mer a l'interieur du detroit de M'Clintock et du golfe de Boothia, deux regions de l'archipel Arctique canadien. Les resultats suggerent qu'il existe une grande variabilite interannuelle dans les conditions de glace d'hiver sur cette periode de 21 ans. Dans le detroit de M'Clintock, les types de glace de l'annee predominaient de facon constante, tandis que dans le golfe de Boothia, ceux de glace epaisse predominaient certaines annees. En ce qui concerne la debacle et la consolidation, les schemas spatiaux regionaux differaient sensiblement, se produisant dans des directions opposees (N.-S. c. S.-N.) dans les deux regions. Les dates revelent une variabilite interannuelle considerable dans les deux zones, ce qui suggere qu'il n'existe pas de schemas precis de debacle precoce ou de consolidation tardive. L'analyse de donnees satellitaires a confirme les resultats obtenus a partir de cartes numeriques des glaces. Les indices de qualite des habitats du phoque annele montrent que les deux regions renferment des classes d'habitat primaire, secondaire et tertiaire. On n'a decele aucune tendance dans les classes secondaire ou tertiaire, mais des changements pour la classe primaire etaient evidents dans le detroit de M'Clintock au cours des cinq annees comprises entre 1997 et 2001. Les processus dynamiques et thermodynamiques de la glace de mer sont importants pour l'habitat du phoque annele (et, en bout de ligne, pour celui de l'ours polaire) a l'echelle regionale et hemispherique dans le contexte actuel de la variabilite et du changement climatiques.
Mots cles: glace de mer, variabilite climatique, habitat du phoque annele, Phoca hispida, ours polaire, Ursus maritimus, detroit de M'Clintock, golfe de Boothia
Traduit pour la revue Arctic par Nesida Loyer.
INTRODUCTION
In response to a C[O.sub.2]-enhanced atmosphere, polar regions of the planet will likely experience amplification in temperature (IPCC, 2001), thought to result from a variety of feedback mechanisms operating across the ocean-sea ice-atmosphere interface. Although several of these feedbacks have been identified, a significant component of the system appears to be the "sea ice-albedo" feedback mechanism (IPCC, 2001), which suggests that as the extent of sea ice is reduced (particularly in spring and fall), the ocean absorbs more energy, and a further reduction in sea ice extent occurs. This positive feedback raises the regional atmospheric temperature, thereby producing a further reduction in ice concentration (percent cover per unit area).
Recent evidence suggests that this response has in fact already begun in the Arctic. Between 1978 and 1998, there was an annual average reduction of about 34600 k[m.sup.2] in the extent of sea ice over the entire Northern Hemisphere (Parkinson et al., 1999). This reduction is spatially heterogeneous, with larger decreases in extent in particular locations (e.g., the Chukchi and Laptev Seas) and slight increases in extent in other regions (e.g., Baffin Bay). Independent evidence from other investigators confirms a reduction in both sea ice extent (Johannessen et al., 1999) and thickness (Rothrock et al., 1999).
Sea ice forms an integral part of the marine ecosystem at high latitudes. Changes in the sea ice and associated snow cover will affect light transmission and thermodynamic processes operating within the snow/sea ice system (Barber et al., 1995). These changes affect lower trophic systems. Kinematic and topographic changes in the snow/sea ice system can affect organisms at higher trophic levels through the control that sea ice exerts on the redistribution of snow (Welch and Bergmann, 1989; Iacozza and Barber, 1999) and on the spatial distribution of various sea ice types (e.g., multiyear, first-year, rubble; Stirling and Derocher, 1993).
Polar bears use both fast and marginal types of sea ice as platforms for travel and foraging. In particular, since ringed seal habitat is a primary food source for polar bears, the habitats of the polar bears are closely related to those of ringed seals. These habitats include areas immediately adjacent to pressure ridges, between multiyear and first-year floes, and at the floe edge between marginal and landfast sea ice (Stirling and Derocher, 1993; Stirling et al., 1993). We examined aspects of sea ice type from the perspective of preferred habitats for ringed seals and polar bears to determine whether sea ice conditions have changed in the two study regions. In particular, we are interested in whether the extent and distribution of ringed seal habitat (based on specific sea ice conditions) has changed in recent years. This information can then be combined with telemetry data, hunter statistics, and traditional knowledge of polar bear abundance and distribution in management of this species.
We investigated characteristics of sea ice related to ringed seal habitat in reference to two time scales: 1) 21 years (1980-2000), for general sea ice conditions within M'Clintock Channel and the Gulf of Boothia; and 2) five years (1997-2001), for ringed seal habitat identified through remote sensing in the same regions. The spatial scales of these two time frames are different because of differences in the input data; the 21-year scale is mapped at 1:10 000 and the five-year scale at 1:1000. Our five research objectives (the first three done at 1:10 000, and the last two at 1:1000) are listed below:
1) Provide a general overview of sea ice conditions (ice type concentration and floe size) in M'Clintock Channel and the Gulf of Boothia from 1980 to 2000.
2) Estimate consolidation dates and spatial pattern of consolidation (annually during 1980-2000).
3) Estimate breakup dates and spatial pattern of breakup (1980-2000).
4) Present the areal fractions and spatial patterns of multiyear, first-year, and rubble ice areas (1997-2001).
5) Compute and map a ringed seal Habitat Suitability Index (HSI) for M'Clintock Channel and the Gulf of Boothia and determine whether this HSI has changed over the period from 1997 to 2001.
These objectives cover how and where sea ice conditions have changed, how these changes relate to ringed seal habitat, and by inference, how such change may manifest itself in variability of polar bear habitat.
METHODS
Study Area
Our study focuses on two different polar bear management areas: M'Clintock Channel (MC) and the Gulf of Boothia (GB; Fig. 1). The MC management area is approximately 140 000 k[m.sup.2] (excluding land), while the GB is approximately 67 000 k[m.sup.2].
Data Description
Digital Ice Charts: The primary data sources for the first three research objectives consist of weekly regional digital ice charts for the Canadian Arctic produced by...
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