Abstract

Stable carbon ({delta}13C) and nitrogen ({delta}15N) isotope analysis was conducted on modern and archaeological polar bear bone collagen from the Canadian Arctic Archipelago to investigate potential changes in polar bear foraging ecology over four-millennia. Polar bear{delta} 13C values showed a significant decline in the modern samples relative to all archaeological time-bins, indicating a disruption in the sources of production that support the food web, occurring after the Industrial Revolution. The trophic structure, indicated through{delta} 15N, remained unaltered throughout all time periods. The lower{delta} 13C observed in the modern samples indicates a change in the relative importance of pelagic (supported by open-water phytoplankton) over sympagic (supported by sea ice-associated algae) primary production. The consistency in polar bear{delta} 13C through the late Holocene includes climatic shifts such as the Medieval Warm Period (MWP, A.D. 950-1250) and the early stages of the Little Ice Age (LIA, A.D. 1300-1850). These findings suggest that polar bears inhabit a food web that is more pelagic and less sympagic today than it was through the Late Holocene. We suggest that modern, anthropogenic warming has already affected food web structure in the Canadian Arctic Archipelago when modern data are contextualized with a deep time perspective. Research HighlightsO_LIModern polar bear bone collagen{delta} 13C suggests recent decline in ice associated prey. C_LIO_LIArchaeological polar bear bone collagen suggests food web stability for millennia. C_LIO_LINo change in sea-ice association through the Medieval Warm Period and Little Ice Age. C_LIO_LIRecent isotopic shifts are unusual relative to the stability of ancient samples. C_LIO_LIModern Arctic warming has isotopically observable impacts that past events did not. C_LI OR Significance StatementThe lack of behavioral plasticity of both polar bears and their principal prey, ringed seals, make these species particularly vulnerable to declining sea ice. While the Lancaster Sound food web has demonstrated stability through past climate fluctuations, the speed and magnitude of ongoing changes in the Arctic has had an observable effect on the source of primary production. Given that past climate fluctuations are referenced as an argument to minimize the importance of modern anthropogenic warming, it is important to take opportunities to position contemporary climate change relative to the archaeological record. Here we present a unique illustration of the effects of past and present warming on polar bear diet and the marine food web in the Canadian Arctic Archipelago.