A 10400-year-old bowhead whale (Balaena mysticetus) skull from Ellef Ringnes Island, Nunavut: implications for sea-ice conditions in high Arctic Canada at the end of the last glaciation.(Report)

ABSTRACT. Variations in the distribution and radiocarbon ages of postglacial bowhead whale (Balaena mysticetus) remains throughout the Canadian Arctic Archipelago indicate that the range of this whale expanded and contracted several times during the Holocene. Since the annual bowhead migration reflects the preference of this species for an ice-edge habitat, fossil bowheads have been used to infer that significant variations in summer sea-ice extent occurred throughout the archipelago during the last 10.5 thousand years. Previous studies have demonstrated that climatic amelioration, concomitant with enhanced meltwater flux from the retreating Laurentide Ice Sheet, cleared sea ice from the inter-island channels of the central archipelago, enabling early Holocene bowhead whales to extend beyond the range of contemporary populations. A 10.4 ka BP bowhead whale skull was discovered on Ellef Ringnes Island in the northern Canadian Arctic Archipelago, 700 km north of its previously reported early Holocene range. Consequently, sea ice along the polar margin of the Canadian Arctic Archipelago is inferred to have been less extensive than previously recognized. Both biological evidence and glaciological evidence suggest that this reduction in sea-ice extent was the result of climate forcing, amplified by meltwater-driven outflows from the rapidly retreating marine-based sector of the Innuitian Ice Sheet. Following a reduction of these outflows at ~9 ka BP, sea-ice conditions worsened, despite ongoing climatic amelioration, preventing additional bowhead whale incursions until ~4 ka BP.

Key words: bowhead whale, sea ice, deglaciation, ocean currents, paleoclimate

RESUME. Des variations en matiere de repartitions et d'ages determines par la methods du carbone 14 relativement aux restes de baleines boreales (Balaena mysticetus) postglaeiaires trouves dans I'archipel arctique canadien laissent croire que le parcours de cette baleine s'est agrandi et s'est retreci a maintes reprises pendant la periodc de I'Holocene. Puisque la migration annuelle de la baleine boreale tient compte de la preference de cette espece pour un habitat de lisieres de glace, les fossiles de baleines boreales ont permis de deduire qu'il y a eu d'importantes variations en matiere d'etendue de la glace de mer a la grandeur de l'archipel en ete au cours des derniers 10,5 milliers d'annees. Des etudes anterieures ont permis de demontrer que 1'amelioration climatique, alliee au plus grand debit de l'eau de fusion provenant de la calotte glaciaire reculante des Laurentides, ont eu pour effet d'enlever la glace des canaux interinsulaires de l'archipel central, ce qui a permis aux baleines boreales de l'Holocene inferieur de se rendre au-dela du parcours des populations contemporaines. Le crane d'une baleine boreale de 10,4 ka avant le present qui a ete decouvert sur l'ile Ellef Ringnes dans le nord de l'archipel arctique canadien se trouvait a 700 km au nord du parcours de l'Holocene inferieur signale auparavant. Par consequent, on en deduit que la glace de mer le long de la marge polaire de l'archipel arctique canadien aurait ete moins etendue qu'on ne le croyait avant. Les preuves biologiques et les preuves glaciologiques laissent croire que cette reduction de 1'etendue de glace de mer decoulait du forcage climatique, ce qui etait amplifie par les ecoulements d'eau de fusion provenant du secteur marin de la calotte glaciaire inukienne reculant rapidement. Suivant la reduction de ces ecoulements a ~9 ka avant le present, les conditions entouranl la glace de mer se sont empirees malgre l'amelioration climatique constante, ce qui a empeche d'autres incursions de la part des baleines boreales et ce, jusque vers ~4 ka avant le present.

Mots cles: baleine boreale, glace de mer, deglaciation, courants oceaniques, paleoclimat

Traduit pour la revue Arctic par Nicole Giguere.

INTRODUCTION

A variety of environmental proxies document a significant amelioration in Arctic climate at the end of the last glaciation, culminating in a peak in postglacial warming associated with increased summer insolation between 12000 and 10000 calendar years BP (Berger, 1988; Berger and Loutre, 1991; Kaufman et al., 2004). The Holocene thermal maximum was followed by climatic deterioration that began in the mid-Holocene, and persisted to the 19th century (Bradley, 1990; Fisher et al., 2006). However, spatial variations in the timing and magnitude of the response of proxy records to early Holocene warming demonstrate that significant local-scale factors modulated or amplified the effects of radative forcing across the western Arctic (Kaufman et al., 2004).