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ARE CURRENT RATES OF ATMOSPHERIC NITROGEN DEPOSITION INDUCING BIOGEOCHEMICAL SHIFTS IN LAKES OF THE EASTERN CANADIAN ARCTIC?
WOLFE, ALEXANDER P University of Alberta.
Cooke, Colin A University of Alberta.
Although arctic lakes rank among the most pristine ecosystems remaining on Earth, widespread paleoecological analyses have revealed rapid recent changes in lake ecology that largely surpass Holocene natural variability, and are generally attributed to climate warming since the end of the Little Ice Age. However, the possibility that climate is only one dimension of these ecological shifts has not yet been explored, even though current warming is unlikely to exceed maximum naturally-mediated postglacial warmth. Here, we explore whether the increased availability of fixed nitrogen (N) from distant anthropogenic sources has contributed to directional changes in the biogeochemistry and ecology of two remote lakes on Baffin Island in the eastern Canadian Arctic. Paleoecological analyses, including diatom assemblages and a suite of biogeochemical proxies (organic matter, biogenic silica, organic nitrogen content and stable isotopic ratios) reveal a complex suite of progressive shifts in both lakes. Diatom assemblages began to shift as early as the mid-19th century, but major inflections in the biogeochemical proxies occurred significantly later, after 1950 A.D. Climate warming, subsequently coupled to a release from N limitation, may be acting synergistically in driving these ecosystems towards states for which no prior natural analogues exist.
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