Reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate 32 change. This review summarizes available information from diverse Holocene paleoenvironmental records across eastern Beringia (Alaska, westernmost Canada and adjacent 34 seas), and it quantifies the primary trends of temperature-and moisture-sensitive records based in part on midges, pollen, and biogeochemical indicators (compiled in the recently published Arctic 36Holocene database, and updated here to v2.1). The composite time series from these proxy records are compared with new summaries of mountain-glacier and lake-level fluctuations, 38 terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies to clarify multi-centennial-to millennial-scale trends in 40Holocene climate change. To focus the synthesis, the paleo data are used to frame specific questions that can be addressed with simulations by Earth system models to investigate the 42 causes and dynamics of past and future climate change. This systematic review shows that, during the early Holocene (11.7-8.2 ka), rather than a prominent thermal maximum as suggested 44 previously, temperatures were highly variable, at times both higher and lower than present (approximate mid-20 th -century average), with no clear spatial pattern. Composited pollen, midge 46 and other proxy records average out the variability and show the overall lowest summer and mean-annual temperatures across the study region during the earliest Holocene, followed by 48 warming over the early Holocene. The sparse data available on early Holocene glaciation show that glaciers in southern Alaska were as extensive then as they were during the late Holocene. 50Early Holocene lake levels were low in interior Alaska, but moisture indicators show pronounced differences across the region. The highest frequency of both peatland and thaw-lake initiation 52 ages also occurred during the early Holocene. During the middle Holocene (8.2-4.2 ka), glaciers 3 retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as 54 reflected in most proxy types. Following the middle Holocene thermal maximum, temperatures decreased starting between 4 and 3 ka, signaling the onset of Neoglacial cooling. Glaciers in the 56 Brooks and Alaska Ranges advanced to their maximum Holocene extent as lakes generally rose to modern levels. Temperature differences for averaged 500-year time steps typically ranged by 58 1-2°C for individual records in the Arctic Holocene database, with a transition to a cooler late Holocene that was neither abrupt nor spatially coherent. The longest and highest-resolution 60 terrestrial water isotope records previously interpreted to represent changes in the Aleutian lowpressure system around this time are here shown to be largely contradictory. Furthermore, there 62 are too few records with sufficient resolution to ...

Late Holocene (Neoglacial) moraines occurring within 1 or 2 km of present glacier margins are prominent features in the forefields of Spitsbergen glaciers. 'Little Ice Age' moraines are typically the most extensive and best preserved; moraines of older Holocene advances are much less common. Where observed, older moraines occur as moraine remnants and provide irrefutable evidence of earlier Neoglacial advances. The fragmentary moraine record indicates two 'Little Ice Age' advances and two older Neoglacial advances. Lichenometry provides calibrated ages for periods of moraine stabilization. The oldest moraines stabilized by ca. 1500 years ago, and a second group of moraines stabilized by ca. 1000 years ago. 'Little Ice Age' moraines were deposited during two periods: an early group of moraines stabilized ca. 650 years ago and a later group during the last several centuries. The proposed moraine chronology compares well with other proxy climate records on Spitsbergen and with moraine records from areas bordering the Norwegian-Greenland Sea.

The Arctic region is subject to a great amplitude of climate variability and is currently undergoing large-scale changes due in part to anthropogenic global warming. Accurate projections of future change depend on anticipating the response of the Arctic climate system to forcing, and understanding how the response to human forcing will interact with natural climate variations. The Svalbard Archipelago occupies an important location for studying patterns and causes of Arctic climate variability; however, available paleoclimate records from Svalbard are of restricted use due to limitations of existing climate proxies. Here we present a sub-decadal-to multidecadal-scale record of summer temperature for the past 1800 yr from lake sediments of Kongressvatnet on West Spitsbergen, Svalbard, based on the fi rst instrumental calibration of the alkenone paleothermometer. The age model for the High Arctic lake sediments is based on 210 Pb, plutonium activity, and the fi rst application of tephrochronology to lake sediments in this region. We fi nd that the summer warmth of the past 50 yr recorded in both the instrumental and alkenone records was unmatched in West Spitsbergen in the course of the past 1800 yr, including during the Medieval Climate Anomaly, and that summers during the Little Ice Age (LIA) of the 18 th and 19 th centuries on Svalbard were not particularly cold, even though glaciers occupied their maximum Holocene extent. Our results suggest that increased wintertime precipitation, rather than cold temperatures, was responsible for LIA glaciations on Svalbard and that increased heat transport into the Arctic via the West Spitsbergen Current began ca. A.D. 1600.

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