A comparison of glacier melt on debris-covered glaciers in the northern and southern Caucasus

The glacier coverage in the Caucasus Mountains underwent considerable changes during the last decades. In some regions, the observed reduction in glacier area is comparable to those in the European Alps and the extent of supra-glacial debris increased on many glaciers. Only a few glaciers in the Caucasus are monitored on a regular basis, while for most areas no continuous field measurements are available. In this study, regional differences of the conditions for glacier melt with a special focus on debris covered glacier tongues in the well-studied Adyl-su basin on the northern slope of the Caucasus Mountains (Russia) is compared with the Zopkhito basin which has similar characteristics but is located on the southern slope in Georgia. The paper focuses on the effect of supra-glacial debris cover on glacier summer melt. There are systematic differences in the distribution and increase of the debris cover on the glaciers of the two basins. In the Adyl-su basin an extensive debris cover on the glacier tongues is common, however, only those glacier tongues that are positioned at the lowest elevations in the Zopkhito basin show a considerable extent of supra-glacial debris. The observed increase in debris cover is considerably stronger in the north. Field experiments show that thermal resistance of the debris cover in both basins is somewhat higher than in other glaciated regions of the world, but there is also a significant difference between the two regions. A simple ablation model accounting for the effect of debris cover on ice melt shows that melt rates are considerably higher in the northern basin despite a wider debris distribution. This difference between the two regions can be attributed to different meteorological conditions which are characterised by more frequent cloud cover and precipitation in the south. Furthermore ablation is strongly influenced by the occurrence of supra-glacial debris cover in both basins, reducing the total amount of melt on the studied glaciers by about 25 %. This effect mitigates glacier retreat in the lower sectors of the ablation zones considerably. The sensitivity to moderate changes in the debris cover, however, is rather small which implies only gradual changes of the melt regime due to debris cover dynamics during the near future

О влиянии поверхностной морены на состояние ледника Джанкуат (Центральный Кавказ) к 2025 г.

Current glaciation of the Central Caucasus is in the regressive stage of evolution. Observed long rising of the air temperature in the ablation seasons (almost 1 °C since 1968 on the Djankuat Glacier) together with insignificant growth of winter precipitation caused a long period of the glacier degradation: since 1871 the mass balance of the glacier, with rare exceptions, remained negative. During this time, the glacier has lost about 60 m w.e. mainly by areas of the smallest ice thickness, i.e. the steep slopes of the rocky framing of the fi n basin which become exposing from ice due to conditions of extreme instability. In parallel with the processes of freezing and thawing in cracks, this leads to a signifi ant increase in the frequency of rockfalls. In 2001–2003, huge rockfalls occurred on the glacier from the slopes, which had recently undergone deglaciation. The last one covered 4% of the glacier surface with about 70 000 m3 of clastic products. The marine cover differs significantly from the open ice surface in its thermal characteristics, which affect the structure of the thermal balance and the absolute values of ablation. The temperature inside the moraine is positive throughout the ablation season, even at a depth of 60 cm, but the absolute values of daily maximum melting are five times lower than those on open ice. The influence of the moraine material layer on the ablation is determined not only by its thickness, but also by the structure. The fi ld experiment conducted in 2011 demonstrated that melting under a layer of coarse-grained material (particle diameter 16–17 cm) is four times faster than under a layer of fi e-grained (7–8 cm) material equal in thickness. The study of the influence of the surface moraine and the account of its further growth in thickness and area made it possible to predict changes in the surface of the glacier by 2025. The climatic forecast was made using the HadCM3 model (A2 climate change scenario). Data on air temperature and precipitation were used to construct a predictive fi ld of the mass balance of the Djankuat Glacier for each year until 2025. Th s became possible by the use of a quantitative parameterized relationship between the mass balance of the entire glacier and each of its points, identifi d in the study of the total mass transfer of the glacier, as well as parameterized linear regression equations. The forecast of hypsometry of the Djankuat Glacier made it possible to determine that by 2025 the depression of the tongue areas covered by the moraine will be 7–15 m (or 42–45%) smaller than areas of the open ice. Th s means that at the present stage of the glaciation development the surface moraine plays a role in the evolution of the glacier, commensurable with the climate factor.Преобладание отрицательных значений баланса массы ледника Джанкуат за минувшие полтора столетия привело к значительному накоплению моренного материала на его поверхности. Поверхностная морена искажает структуру теплового баланса и влияет на изменение баланса массы ледника. В настоящее время поверхностная морена перекрывает 13% площади ледника и на 93% этой площади оказывает бронирующее воздействие. На основании климатической модели HadCM3 установлено, что к 2025 г. забронированные мореной участки языка будут понижаться на 7–15 м (или на 42–45%) медленнее, чем участки открытого льда. Ныне поверхностная морена играет в эволюции ледника роль, соизмеримую с климатическим фактором

Influence of the surface moraine on the state of Djankuat Glacier (Central Caucasus) by 2025

Current glaciation of the Central Caucasus is in the regressive stage of evolution. Observed long rising of the air temperature in the ablation seasons (almost 1 °C since 1968 on the Djankuat Glacier) together with insignificant growth of winter precipitation caused a long period of the glacier degradation: since 1871 the mass balance of the glacier, with rare exceptions, remained negative. During this time, the glacier has lost about 60 m w.e. mainly by areas of the smallest ice thickness, i.e. the steep slopes of the rocky framing of the fi n basin which become exposing from ice due to conditions of extreme instability. In parallel with the processes of freezing and thawing in cracks, this leads to a signifi ant increase in the frequency of rockfalls. In 2001–2003, huge rockfalls occurred on the glacier from the slopes, which had recently undergone deglaciation. The last one covered 4% of the glacier surface with about 70 000 m3 of clastic products. The marine cover differs significantly from the open ice surface in its thermal characteristics, which affect the structure of the thermal balance and the absolute values of ablation. The temperature inside the moraine is positive throughout the ablation season, even at a depth of 60 cm, but the absolute values of daily maximum melting are five times lower than those on open ice. The influence of the moraine material layer on the ablation is determined not only by its thickness, but also by the structure. The fi ld experiment conducted in 2011 demonstrated that melting under a layer of coarse-grained material (particle diameter 16–17 cm) is four times faster than under a layer of fi e-grained (7–8 cm) material equal in thickness. The study of the influence of the surface moraine and the account of its further growth in thickness and area made it possible to predict changes in the surface of the glacier by 2025. The climatic forecast was made using the HadCM3 model (A2 climate change scenario). Data on air temperature and precipitation were used to construct a predictive fi ld of the mass balance of the Djankuat Glacier for each year until 2025. Th s became possible by the use of a quantitative parameterized relationship between the mass balance of the entire glacier and each of its points, identifi d in the study of the total mass transfer of the glacier, as well as parameterized linear regression equations. The forecast of hypsometry of the Djankuat Glacier made it possible to determine that by 2025 the depression of the tongue areas covered by the moraine will be 7–15 m (or 42–45%) smaller than areas of the open ice. Th s means that at the present stage of the glaciation development the surface moraine plays a role in the evolution of the glacier, commensurable with the climate factor

The genetic prehistory of the Greater Caucasus

Archaeogenetic studies have described the formation of Eurasian ’}steppe ancestry{’ as a mixture of Eastern and Caucasus hunter-gatherers. However, it remains unclear when and where this ancestry arose and whether it was related to a horizon of cultural innovations in the 4th millennium BCE that subsequently facilitated the advance of pastoral societies likely linked to the dispersal of Indo-European languages. To address this, we generated genome-wide SNP data from 45 prehistoric individuals along a 3000-year temporal transect in the North Caucasus. We observe a genetic separation between the groups of the Caucasus and those of the adjacent steppe. The Caucasus groups are genetically similar to contemporaneous populations south of it, suggesting that - unlike today - the Caucasus acted as a bridge rather than an insurmountable barrier to human movement. The steppe groups from Yamnaya and subsequent pastoralist cultures show evidence for previously undetected Anatolian farmer-related ancestry from different contact zones, while Steppe Maykop individuals harbour additional Upper Palaeolithic Siberian and Native American related ancestry

Ancient human genome-wide data from a 3000-year interval in the Caucasus corresponds with eco-geographic regions

Archaeogenetic studies have described the formation of Eurasian ‘steppe ancestry’ as a mixture of Eastern and Caucasus hunter-gatherers. However, it remains unclear when and where this ancestry arose and whether it was related to a horizon of cultural innovations in the 4th millennium BCE that subsequently facilitated the advance of pastoral societies in Eurasia. Here we generated genome-wide SNP data from 45 prehistoric individuals along a 3000-year temporal transect in the North Caucasus. We observe a genetic separation between the groups of the Caucasus and those of the adjacent steppe. The northern Caucasus groups are genetically similar to contemporaneous populations south of it, suggesting human movement across the mountain range during the Bronze Age. The steppe groups from Yamnaya and subsequent pastoralist cultures show evidence for previously undetected farmer-related ancestry from different contact zones, while Steppe Maykop individuals harbour additional Upper Palaeolithic Siberian and Native American related ancestry

Archaeometallurgical Investigations in Nakhchivan, Azerbaijan: What Does the Evidence from Late Chalcolithic Ovçular Tepesi Tell Us about the Beginning of Extractive Metallurgy?

International audienceThe Late Chalcolithic (4400–3950 b.c.) occupation levels from Ovçular Tepesi have yielded a significant assemblage of copper objects and remains of copper production. Together with ore finds, two fragments of nozzle, crucible remains, and a number of small metal artifacts, this assemblage includes the unexpected discovery of three copper axes in an infant burial jar. These axes are the earliest examples of large copper tools known to date in southwestern Asia, whether it is in the Caucasus, Iran, or the Anatolian highlands. More importantly, the fact that these objects were locally produced suggests that significant metallurgical activities were being carried out at Ovçular as early as the second half of the 5th millennium b.c. After presenting the evidence from Ovçular Tepesi, this paper will proceed to a reassessment of the available archaeological and geochemical data concerning the emergence of extractive metallurgy in the southern Caucasus. © 2017, © Trustees of Boston University 2017