Sedimentological and Grain Size Characteristics of Two Lake Cores from Himachal Pradesh, India

Two lake cores from Khajjiar (length 746 cm) and Rewalsar lakes (length 647 cm) in Himachal Pradesh (India) were retrieved to understand the sedimentological characteristics and variation in grain size distribution. Both the lake cores are Upper Holocene in age. The Rewalsar lake sediments are composed predominantly of silt with small amounts of clay, whereas the Khajjiar sediments contain sand, silt and clay and both cores have high carbonaceous matter. The standard deviation ranges from 0.88 ϕ to 2.56 ϕ for Khajjiar lake and from 0.957 ϕ to 2.264 ϕ for Rewalsar lake, indicating poorly to very poorly sorted core sediments. The values of the Kurtosis vary between 0.678 ϕ and 1.205 ϕ for Khajjiar lake and from 0.8 ϕ to 1.2.4 ϕ for Rewalsar lake, viewing platykurtic to leptokurtic nature. Further, the skewness value ranges from -0.097 ϕ to 0.240 ϕ for Khajjiar lake and 0.079 ϕ to 0.25 ϕ for Rewalsar lake revealing fine to symmetrical skewness model. The bivariate plots by using the grain-size parameters were also interpreted. The Total Organic Carbon (TOC) is higher in the Khajjiar lake sediments (0.9 to 31.2%; av. 10.6%), compared to that in the Rewalsar lake sediments (1.0 to 9.0; av. 2.6%). The sedimentological characteristics indicate that the energy conditions were linked to the climatic conditions prevailing in the area. In general, the Khajjiar lake core is composed of relatively coarser sediments and more affected by arid conditions while the fine fraction of the Rewalsar shows the consequence of lower energy conditions. The Khajjiar lake shows the transition from fluctuating conditions (zone 1) to humid (zone 2) to arid (zone 3), while the Rewalsar shows the change from fluctuating (zone 1) to humid conditions (zones 2 and 3). The similarity between zone 1 and 2 of both the lake profiles shows that both lakes have experienced similar climatic conditions during the deposition, revealing domination of fluctuating and arid conditions.

Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

The timing of human colonization of East Polynesia, a vast area lying between Hawai‘i, Rapa Nui, and New Zealand, is much debated and the underlying causes of this great migration have been enigmatic. Our study generates evidence for human dispersal into eastern Polynesia from islands to the west from around AD 900 and contemporaneous paleoclimate data from the likely source region. Lake cores from Atiu, Southern Cook Islands (SCIs) register evidence of pig and/or human occupation on a virgin landscape at this time, followed by changes in lake carbon around AD 1000 and significant anthropogenic disturbance from c. AD 1100. The broader paleoclimate context of these early voyages of exploration are derived from the Atiu lake core and complemented by additional lake cores from Samoa (directly west) and Vanuatu (southwest) and published hydroclimate proxies from the Society Islands (northeast) and Kiribati (north). Algal lipid and leaf wax biomarkers allow for comparisons of changing hydroclimate conditions across the region before, during, and after human arrival in the SCIs. The evidence indicates a prolonged drought in the likely western source region for these colonists, lasting c. 200 to 400 y, contemporaneous with the phasing of human dispersal into the Pacific. We propose that drying climate, coupled with documented social pressures and societal developments, instigated initial eastward exploration, resulting in SCI landfall(s) and return voyaging, with colonization a century or two later. This incremental settlement process likely involved the accumulation of critical maritime knowledge over several generations.

Holocene reconstruction of plant and mammal communities in the Austrian and Italian Alps

<p>The Eastern Alps in Europe have a rich alpine biodiversity and a long archaeological history. However, the palaeoecological record of this region has been relatively understudied, which has limited our understanding of the formation of the contemporary vegetation since the end of the last Ice Age, including the likely impacts of changes in climate and human pressures through pasturing and agriculture. To fill this knowledge gap, we are using plant and mammal sedaDNA taken from five sub-alpine to alpine Holocene lake cores in the Austrian and Italian Eastern Alps: Grosser Winterleitensee, Krummschnabelsee, Mittlerer Kaltenbachsee and Sulzkarsee (Austria), and Laghetti Colbricon (Italy). We will outline our first results on full plant community reconstructions from some lakes and on the mammal presence. Findings from the plant record will allow us for uncovering the Holocene dynamics of plant communities, and for identifying key intervals where biodiversity may have been strongly affected by anthropogenic factors and climate change. The mammal sedaDNA data will also be used to track the presence of domestic livestock through time and therefore provide insight into past human pastoral practices in the region.</p>

Land Use and the Human Impact on the Environment in Medieval Italy

Modern narratives about changes in the Italian landscape during the early Middle Ages have often been based on assumptions about changing demography; the loss and replacement of complex Roman economic, political and agricultural systems; and broader changes in climate. Using fossil pollen taken from lake cores in the Rieti basin to reconstruct local ecological conditions, close examinations of two discreet periods offer new insights into the changes from small-scale agriculture to silvo-pastoralism that began during the late sixth and early seventh centuries. The deforestation of the ninth century, accompanied by an increase in cultivation, was the result of a long-term accumulation of territory under monastic control. The fact that these changes in the landscape run counter to the prevailing climatic conditions underscores the success of human management of the environment.

New age controls on the tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

The chronology of over 50 tephra layers preserved in a lake sediment core from Laguna La Trapananda (LLT) in the southern portion of the Andean Southern Volcanic Zone (SSVZ), Chile, is constrained by new radiocarbon age determinations, which span the period from late Pleistocene glacial retreat to the late Holocene. The tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the SSVZ volcanoes Mentolat, Hudson, Macá, and potentially Cay. The new age determinations are used to estimate the ages of the >50 tephra in the LLT core, as well as those from the other previously described lake cores in the area, by a Bayesian statistical method. The results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost SSVZ. They indicate that there was essentially no increase in the rate of eruptions from late-glacial to recent times due to deglaciation. They also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic, paleoecologic, archaeologic and tephrochronologic studies in central Patagonia.

Severe Drought May Have Helped Hasten Ancient Maya’s Collapse

Chemical signatures from sediments in lake cores reveal that the centuries-long drought during the fall of Classic Maya civilization was worse than researchers had imagined.

Re-evaluating black carbon in the Himalayas and the Tibetan Plateau: concentrations and deposition

Black carbon (BC) is the second most important warming component in the atmosphere after CO2. The BC in the Himalayas and the Tibetan Plateau (HTP) has influenced the Indian monsoon and accelerated the retreat of glaciers, resulting in serious consequences for billions of Asian residents. Although a number of related studies have been conducted in this region, the BC concentrations and deposition rates remain poorly constrained. Because of the presence of arid environments and the potential influence of carbonates in mineral dust (MD), the reported BC concentrations in the HTP are overestimated. In addition, large discrepancies have been reported among the BC deposition derived from lake cores, ice cores, snow pits and models. Therefore, the actual BC concentration and deposition values in this sensitive region must be determined. A comparison between the BC concentrations in acid (HCl)-treated and untreated total suspected particle samples from the HTP showed that the BC concentrations previously reported for the Nam Co station (central part of the HTP) and the Everest station (northern slope of the central Himalayas) were overestimated by approximately 52 ± 35 and 39 ± 24 %, respectively, because of the influence of carbonates in MD. Additionally, the organic carbon (OC) levels were overestimated by approximately 22 ± 10 and 22 ± 12 % for the same reason. Based on previously reported values from the study region, we propose that the actual BC concentrations at the Nam Co and Everest stations are 61 and 154 ng m−3, respectively. Furthermore, a comprehensive comparison of the BC deposition rates obtained via different methods indicated that the deposition of BC in HTP lake cores was mainly related to river sediment transport from the lake basin as a result of climate change (e.g., increases in temperature and precipitation) and that relatively little BC deposition occurred via atmospheric deposition. Therefore, previously reported BC deposition rates from lake cores overestimated the atmospheric deposition of BC in the HTP. Correspondingly, BC deposition derived from snow pits and ice cores agreed well with that derived from models, implying that the BC depositions of these two methods reflect the actual values in the HTP. Therefore, based on reported values from snow pits and ice cores, we propose that the BC deposition in the HTP is 17. 9 ± 5. 3 mg m−2 a−1, with higher and lower values appearing along the fringes and central areas of the HTP, respectively. These adjusted BC concentrations and deposition values in the HTP are critical for performing accurate evaluations of other BC factors, such as atmospheric distribution, radiative forcing and chemical transport in the HTP.

Reevaluating the black carbon in the Himalayan and Tibetan Plateau: concentration and deposition

Black carbon (BC) is the second most important warming component in the atmosphere after CO2. The BC in the Himalayan and Tibetan Plateau (HTP) has shaped the evolution of the Indian Monsoon and accelerated the retreat of glaciers, thereby resulting in serious consequences for billions of Asian residents. Although a number of related studies of this region have been conducted, the BC concentration and deposition indexes remain poorly understood. Because of the presence of arid environments and the potential influence of carbonates from mineral dust (MD), the reported concentrations of BC from the HTP are overestimated. In addition, large discrepancies in the deposition of BC have been reported from lake cores, ice cores, snowpits and models. Therefore, the actual BC concentration and deposition values in this sensitive region must be determined. A comparison between the BC values of acid (HCl) fumigated and original aerosol samples from the HTP showed that the BC concentrations previously reported for the Namco station (central part of the HTP) and the Everest station (northern slope of the central Himalayas) were overestimated by approximately 47 ± 37 % and 35 ± 26 %, respectively, because of the influence of carbonates from MD. Additionally, the organic carbon (OC) levels were overestimated by roughly 22 ± 10 % and 22 ± 12 % for the same reason. Based on previously reported values from these two areas, we propose that the actual BC concentrations at the Namco and Everest stations are 44 ng m−3 and 164 ng m−3, respectively. Second, a comprehensive comparison of the BC deposition levels obtained via different methods indicated that the BC deposits derived from lake cores of the HTP were mainly caused by river sediments transported from the lake basin as a result of climate change (e.g., increases in temperature and precipitation), and fewer BC deposits were related to atmospheric deposition. Therefore, previously reported BC deposition levels from lake cores overestimated the atmospheric deposition of BC in the HTP. Correspondingly, BC deposition derived from snowpit, ice core and model from the HTP were not only agree very well with each other, but also were close to those of other remote areas (e.g., Arctic), implying that the BC deposits calculated from these three methods reflect the actual values. Therefore, based on reported values of snowpits and ice cores, we propose that the BC deposits of the HTP range from 10 mg m−2 a−1 to 25 mg m−2 a−1, with high and low values appearing along the fringes and central areas of the HTP, respectively. The adjusted BC concentration and deposition values in the HTP observed here are critical for performing accurate evaluations of other indexes of BC such as atmospheric distribution, radiative forcing and chemical transport in the HTP.