Recent summer warming in northwestern Canada exceeds the Holocene thermal maximum

Abstract

Eastern Beringia is one of the few Western Arctic regions where full Holocene climate reconstructions are possible. However, most full Holocene reconstructions in Eastern Beringia are based either on pollen or midges, which show conflicting early Holocene summer temperature histories. This discrepancy precludes understanding the factors that drove past (and potentially future) climate change and calls for independent proxies to advance the debate. We present a ~13.6 ka summer temperature reconstruction in central Yukon, part of Eastern Beringia, using precipitation isotopes in syngenetic permafrost. The reconstruction shows that early Holocene summers were consistently warmer than the Holocene mean, as supported by midges, and a thermal maximum at ~7.6–6.6 ka BP. This maximum was followed by a ~6 ka cooling, and later abruptly reversed by industrial-era warming leading to a modern climate that is unprecedented in the Holocene context and exceeds the Holocene thermal maximum by +1.7 ± 0.7 °C.

Global Isotope Hydrogeology―Review

“…Over 100 studies have discussed paleoclimate shifts on the basis of stable oxygen or hydrogen isotope compositions of older groundwaters (Table ). ∆δ 18 O late‐Pleistocene values have been interpreted in many ways, some of which include (i) deglacial changes to sea surface δ 18 O or physiochemical conditions that influence isotope effects (e.g., humidity influences kinetic isotope effects; sea surface temperatures influence equilibrium isotope effects; e.g., Wood, ); (ii) deglacial changes to moisture sources and atmospheric circulation patterns (e.g., Pausata et al, ); (iii) deglacial changes to atmospheric temperatures (e.g., Bahir et al, ; Porter et al, ), which influence air mass rainout; (iv) deglacial changes to regional precipitation rates (e.g., Wang, Edwards, et al, ); (v) deglacial changes in the seasonal distribution of precipitation (e.g., J. Li, et al, ); and/or (vi) deglacial changes in the seasonality of groundwater recharge ratios (e.g., Huneau et al, ; see Table ; Figure ).…”

“…The availability of deuterium excess values in fossil groundwater records provides an advantage over most other late‐Pleistocene isotopic records, which usually enable measurement of only one of O or H isotope systematics (e.g., solely δ 2 H data for leaf wax—e.g., Konecky et al, ; solely δ 18 O for lake sediment carbonate minerals—e.g., Mandl et al, ; solely δ 18 O for pedogenic carbonates—e.g., Oerter et al, ; and solely δ 18 O for most speleothems—e.g., Wang et al, ; cf. Porter et al, ). Fossil versus modern‐era groundwater deuterium excess values have been compared in several aquifer systems, with some studies demonstrating different late‐Pleistocene and late‐Holocene deuterium excess values (Weyhenmeyer et al, ) and others showing deuterium excess values to have been similar‐to‐present during the last ice age (e.g., Huneau et al, ).…”

Long‐term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

“…Peatland formation in this region began 8,000-9,000 years ago following deglaciation (Halsey et al, 1998). A cooling of the climate~6,000 years ago following the Holocene thermal maximum (Porter et al, 2019) led to the earliest permafrost aggradation in the area, but this became more widespread following further cooling~1,200 years ago (Loisel et al, 2014;Pelletier et al, 2017). Permafrost peatlands make up >25% of land cover and peat deposits vary in thickness from 2 to 6 m throughout the sporadic-discontinuous permafrost zone of boreal western Canada (Bauer et al, 2003;Beilman et al, 2008;Hugelius et al, 2014;Vitt et al, 2000).…”

Inferring responses to climate warming from latitudinal pattern of clonal hybridization

“…In conclusion, the present study provides an empirical framework to assess how historical climate warming influenced hybridization between sympatric sister species. However, detection of contemporary hybridization close to the northern limit of historical hybridization suggests that the current warming episode is going beyond the limits of the Holocene Optimum, a conclusion recently reached by Porter et al (2019) on warming in northwestern Canada.…”

“…12,000 years BP was marked by a strong increase in temperature, while the following Kyears were punctuated by cooling and warming episodes (Marcott, Shakun, Clark, & Mix, 2013). For instance, the Holocene Climate Optimum was a period characterized by the warmest temperatures since the end of the Pleistocene, with conditions warmer than now (but see Porter et al, 2019). The time of Holocene Climate Optimum varied widely across the planet (Kaufman et al, 2016;Marcott et al, 2013).…”