Arctic summer temperatures mostly cooled over the last~7 kyr, owing to decreasing summer insolation. However, knowledge of the winter season is limited in the Arctic paleoclimate literature. Here we develop a composite record of δ 18 O from ice wedges-a winter precipitation archive-to reconstruct changes in winter climate in the northwestern Canadian Arctic since~7.4 kyr b2k. Our record shows a long-term δ 18 O enrichment (+(0.14 ± 0.10)‰ kyr −1), suggesting winter temperatures increased since the mid-Holocene, a finding that is corroborated by reconstructions from the Siberian Arctic. Winter warming over the last~7 kyr is consistent with increasing winter insolation and greenhouse gas forcing. This study provides some of the first insights on the sensitivity of winter temperatures in the Canadian Arctic to past, and potentially future, climate forcings, and contributes to a more seasonally holistic understanding of the Arctic system. Plain Language Summary The history of climate change during the last 11,700 years, a period known as the Holocene Epoch, has been traditionally studied using natural climate proxies such as tree rings or pollen in the sedimentary record. Such records allow us to better understand past climate variability in response to changing greenhouse gas concentrations, solar radiation, and other boundary conditions. However, most traditional climate proxies are biological and sensitive mainly to growing-season conditions, whereas changes in cold-season conditions are not well described in the literature. This is especially true in the Arctic where recent climate warming has been most pronounced in the winter season, but few cold-season-specific proxy records are available. In this study, we develop a~7,400-year record of the δ 18 O isotope composition of relict ice wedges in the northwestern Canadian Arctic, a proxy type that is specifically sensitive to cold-season conditions. We observe a long-term increase in ice-wedge δ 18 O over the past 7,400 years, indicating warming winter temperatures since the mid-Holocene. This warming corresponds to increasing winter solar radiation and greenhouse gas concentrations and is in agreement with recent reports from ice wedges in the Siberian Arctic.

Ice wedges are a characteristic ground ice feature in permafrost regions that form primarily from the meltwater of the seasonal snowpack. Ice‐wedge oxygen and hydrogen stable isotopes have been used in winter paleotemperature reconstructions; however, until recently, the ion geochemistry of ice wedges has rarely been analyzed as a potential paleoclimate proxy. This potential is greatest for ice wedges located in coastal regions, where marine aerosols are the dominant contributor to snowpack impurities. Here, we evaluate the source and integrity of ionic concentrations of a coastal ice wedge in the northwestern Canadian Arctic (Beaufort Sea coast) to evaluate the use of ice wedges as a marine aerosol archive. Comparison to a regionally comparable snowpack reveals remarkably similar ionic concentrations for Cl−, Na+, Br−, SO42−, Ca2+, and Mg2+, with a Cl−/Na+ ratio similar to bulk seawater (1.80 vs. 1.79 in seawater), suggesting that marine aerosols, probably from sea salt aerosol production during blowing snow events over sea ice as indicated by depleted SO42− values relative to Na+, are probably the dominant contributor to ion concentrations. A previously established linear age model for the ice wedge is used to develop a continuous ion record spanning ~4,600 to ~700 yr b2k. Cl− and Na+ concentrations reveal a strong and continuous increase in concentrations over the late Holocene, thought to be driven by reduced distance‐to‐coast of up to 1 km as a result of coastal erosion. This study presents a novel interpretation of ice‐wedge geochemical data and represents the first Holocene ice‐wedge ion record.

<p>Rapid and sustained warming of the northern high latitudes has led to increased permafrost thaw and retrogressive thaw slump (RTS) activity in some areas of the Arctic. Thaw slumps are common in the Tuktoyaktuk Coastlands (Northwest Territories, Canada) and expose relict ice wedge polygon networks that contain a long-term record of winter precipitation isotopes. Notably, the stable isotope geochemistry of ice wedges can be used as a paleotemperature proxy for the winter season, a seasonality that is largely missing from current understandings of Holocene paleoclimate change in the Arctic.</p><p> </p><p>In this study, we sampled lateral cross-sections of four relict ice wedges from RTS exposures at coastal sites on Hooper Island, Pelly Island, Richards Island and near Tuktoyaktuk. Ice blocks capturing the entire growth sequences of the ice wedges (i.e., ice wedge center to ice-sediment contact) were collected by chainsaw and kept frozen in field coolers, and later sub-sampled at high-resolution in a cold lab. The ice wedges were sub-sampled at 1-1.5 cm horizontal resolution, integrating ~1-3 ice veins per sample on average. We analysed the stable hydrogen- and oxygen-isotope ratios (δ<sup>2</sup>H and δ<sup>18</sup>O) of each sample (N = 803). The age of the ice was estimated by AMS-DO<sup>14</sup>C dating of 6 to 10 samples per ice wedge, evenly distributed across each wedge to capture the full range of ages. A composite δ<sup>18</sup>O record spanning the period 7,400-600 cal yr BP was also constructed using the dated samples only (N = 36). The all-sample co-isotope (δ<sup>2</sup>H-δ<sup>18</sup>O) data are defined by regression line that is remarkably similar to the Local Meteoric Water Line, suggesting the ice wedges reliably preserve the isotopic composition of local precipitation, which is strongly influenced by mean air temperatures. The composite record shows an increase in δ<sup>18</sup>O over the last 7,400 years which we interpret as a long-term warming trend of the mean winter climate. This warming trend is largely explained by increasing November-April insolation at 69°N, a result that is corroborated by two independent high-resolution ice wedge records from the Siberian Arctic and is also in agreement with model-based simulations of the winter climate. This record, the first of its kind in the North American Arctic, provides a more seasonally holistic perspective on Holocene climate change and highlights the potential to use permafrost isotope records to fill paleoclimate knowledge gaps in Arctic regions were more traditional precipitation isotope archives (e.g., ice cores) do not exist.</p>