Proxy-Derived Reconstructions of Holocene Paleoclimate for the Hudson Bay Lowlands, an Extensive Peatland in Northern Canada

The Hudson Bay Lowlands (HBL) is an extensive peatland in northern Canada where an estimated 31 Pg of carbon have accumulated during the Holocene. Given the large size of this carbon pool and the rapid rate of climate warming at high latitudes, quantifying the responses of this peatland to climate change is a critical research priority. Comparing Holocene paleoclimate reconstructions and paleo-vegetation and carbon dynamics in HBL peatlands through analyses of sediment cores is an effective approach to understanding the sensitivity of the carbon pool to climate. Robust paleoclimate reconstructions for the Holocene are needed for such comparisons. Until recently, there have been few paleoclimate reconstructions available for the HBL. Owing to the unique geographic setting of this low lying region to the west of Hudson Bay, reconstructions from adjacent subarctic regions are not directly applicable. We synthesize in this paper a series of paleoenvironmental records derived from biological proxies preserved in lake and wetland sediment cores collected from within the HBL with the goal of improving available paleoclimate information for the region. Our available pollen records document a series of vegetation changes during the Holocene, beginning with the establishment of coastal or salt marsh communities after emergence of the HBL from the Tyrrell Sea, followed by establishment of vegetation typical of poor fens or bogs. These local vegetation changes are apparently primarily related to hydrological changes driven by isostatic rebound and autogenic processes. Regional assemblages composed of tree pollen, which may be more directly tied to climate, show less variability during the Holocene. Reconstructions using modern analogs suggest minimal variation in temperature during the period of record, although these reconstructions show a moderate increase in precipitation following 3000 yrs BP, corresponding to Neoglacial climates reported at other northern high latitude sites. These findings are also supported by a diatom record from a lake situated in an ice-marginal landform; this paleolimnological record suggests a primary effect of hydrological change on proxy assemblages, with climate as a secondary driver. Testate amoeba derived reconstructions of depth to the water table at a bog site also support a wetter Neoglacial climate in the region. Finally diatom and pollen records show marked recent changes over the past century, including increases in minerotrophic plant taxa and planktonic diatoms, suggesting effects of recent warming on HBL peatland environments.