The timing and extent of the last glaciation in the Altai Mountains are key to understanding climate change in this critical region. However, robust glacial chronologies are sparse across the Altai Mountains, especially in the Chinese Altai, impeding the correlation of glacial events and examination of the possible climate forcing mechanisms. Here, we report twenty new Be-10 exposure-ages obtained from two moraines in the headwater area of the Xiaokelanhe River, Chinese Altai. The inner latero-frontal moraine yields exposure-ages ranging from 16.60 +/- 1.00 to 20.41 +/- 1.15 ka (n = 5), reflecting a limited advance during the global Last Glacial Maximum (LGM). The morpho-stratigraphically older moraine remnants have exposure-ages of 14.36 +/- 0.94-38.98 +/- 2.23 ka (n = 15). The tentatively determined moraine age of 34.10 +/- 4.99 ka suggests that the local LGM in the Xiaokelanhe River likely occurred during Marine Isotope Stage (MIS) 3 or earlier. From a compilation of the 20 new, and 79 previously published exposure-ages, we observe at least three distinct glacial events during the last glacial, with the local LGM occurring prior to MIS 2. A comparison between the timing of glacial activities and climate proxies suggests a potential combination of summer solar insolation, North Atlantic climate oscillations, and atmospheric CO2 levels, as triggers for glacial movements during the last glacial cycle. Precipitation delivered by the mid-latitude westerlies may have also contributed to glacial advances during MIS 3. These correlations remain tentative however, due to limited chronological control.

Absolute-age dating horizons play a pillar role in the reconstruction of an ice core chronology. In the modern era, these have included the global fallout from massive volcanic eruptions, atmospheric and marine thermonuclear weapons testing and nuclear accidents. After the occurrence of the Fukushima Daiichi nuclear accident (FDNA) on March 11 2011, the simulation of the radioactivity from the FDNA by a dispersion model (HYSPLIT) shows that the nuclides reached the study area in late March, consistent with the ground measurements in Xi'an, Lanzhou and Urumqi. To investigate the deposition of radioactivity resulting from the FDNA, we collected snowpack samples from four glaciers (i.e. Glacier No. 1, Glacier No. 72, Qiyi and Shiyi glaciers, respectively) in northwestern China and analysed them for total beta activity (TBA). The measured TBA in the FDNA layers were increased by two to four times, compared with the averages in the non-FDNA layers. We revisited Glacier No. 1 in 2018 and studied a much deeper snow-pit profile for the TBA, seven years after the first-time investigation into a relatively shallow snow pit in 2011. The TBA concentrated in a dust layer and became more significant in 2018 compared to that in 2011. We compared the TBA in Glacier No. 1 with that in the Muztagata glacier from the Chernobyl accident in 1986, and the depositions of radioactivity in the two High-Asian glaciers were comparable. We conclude that the FDNA formed a distinctly new lasting reference in the snow, which could help date the snow and ice in the Northern Hemisphere.

Thicker snowpacks and their insulation effects cause winter-warming and invoke thaw of permafrost ecosystems. Temperature-dependent decomposition of previously frozen carbon (C) is currently considered one of the strongest feedbacks between the Arctic and the climate system, but the direction and magnitude of the net C balance remains uncertain. This is because winter effects are rarely integrated with C fluxes during the snow-free season and because predicting the net C balance from both surface processes and thawing deep layers remains challenging. In this study, we quantified changes in the long-term net C balance (net ecosystem production) in a subarctic peat plateau subjected to 10 years of experimental winter-warming. By combining(210)Pb and(14)Cdating of peat cores with peat growth models, we investigated thawing effects on year-round primary production and C losses through respiration and leaching from both shallow and deep peat layers. Winter-warming and permafrost thaw had no effect on the net C balance, but strongly affected gross C fluxes. Carbon losses through decomposition from the upper peat were reduced as thawing of permafrost induced surface subsidence and subsequent waterlogging. However, primary production was also reduced likely due to a strong decline in bryophytes cover while losses from the old C pool almost tripled, caused by the deepened active layer. Our findings highlight the need to estimate long-term responses of whole-year production and decomposition processes to thawing, both in shallow and deep soil layers, as they may contrast and lead to unexpected net effects on permafrost C storage.

The timing of neoglacial advances in the Antarctic Peninsula (AP) is not yet well constrained. Accurate temporal reconstruction of Neoglaciation in the AP is needed to better understand past glacial responses and regional and global teleconnections during the Holocene. Here, we examine all available information about neoglacial advances in the South Shetland Islands (SSI) as well as in the broader geographical context of the AP region and Antarctic continent. In order to shed light on the contrasting chronologies existing for neoglacial advances in these regions, we focused on a case study where a detailed picture of the Holocene deglaciation was already available. Lake sediments revealed that Byers Peninsula, west of Livingston Island (SSI), was fully deglaciated during the Holocene Thermal Maximum. To complement this approach, we identified glacially polished bedrock surfaces, erratic boulders and a moraine ridge near the present front of the glacier in the SE corner. We applied cosmogenic ray exposure (CRE) dating using in situ Cl-36 for basalt rocks and Be-10 for granitic rocks in: (i) 8 samples from glacial erratic and ice-rafted boulders, (ii) 2 samples from moraine boulders, (iii) 2 samples from polished bedrock surfaces, and (iv) 1 sample from an erratic boulder deposited on one of these surfaces. The CRE dates indicate that the onset of deglaciation started around 9.9 +/- 1.2 ka, with two phases of glacier expansion during the Mid-Late Holocene forming moraines at similar to 4.1 +/- 0.5 and similar to 1.0 +/- 0.2 ka, respectively. The main neoglacial advances in the AP and the SSI were mostly synchronous and coincided with cold periods, as shown by other records (e.g. glacio-isostatic marine terraces, marine and lake sediments). In addition, these periods of glacial expansion show a similar timing to those recorded in the Arctic. These results suggest that Neoglaciation was driven by global climate forcing in both polar areas despite temporal variations at regional and local scale. (C) 2020 Elsevier Ltd. All rights reserved.

Cryosols contain roughly 1700 Gt of Soil organic carbon (SOC) roughly double the carbon content of the atmosphere. As global temperature rises and permafrost thaws, this carbon reservoir becomes vulnerable to microbial decomposition, resulting in greenhouse gas emissions that will amplify anthropogenic warming. Improving our understanding of carbon dynamics in thawing permafrost requires more data on carbon and nitrogen content, soil physical and chemical properties and substrate quality in cryosols. We analyzed five permafrost cores obtained from the North Slope of Alaska during the summer of 2009. The relationship between SOC and soil bulk density can be adequately represented by a logarithmic function. Gas fluxes at -5 degrees C and -5 degrees C were measured to calculate the temperature response quotient (Q(10)). Q(10) and the respiration per unit soil C were higher in permafrost-affected soils than that in the active layer, suggesting that decomposition and heterotrophic respiration in ciyosols may contribute more to global warming. (C) 2014 Published by Elsevier B.V.