Inheritance from prior exposure often complicates the interpretation of terrestrial cosmogenic nuclide (TCN) inventories in glaciated terrain. Lochnagar, a mountain in eastern Scotland, holds a clear geomorphological record of corrie glaciation and the thinning of the last Scottish ice sheet over the last ~15 ka. Yet attempts to date the main stages in deglaciation after sampling of 21 granite boulders for 10Be, 26Al and 14C from corrie moraines, an ice sheet lateral moraine and boulder spreads revealed widespread, but variable, TCN inheritance. Only the youngest boulder ages fit within the range of expected deglaciation ages. To identify the sources of geological uncertainty, we provide simple models of ice cover duration and erosion histories for plateau, corrie and strath landscape domains, identify the variable nuclide inheritance that derives from different sources for boulders in these domains, and outline the effects of rotation, splitting and erosion of boulders during glacial transport. The combined effects increase clustering around arbitrary mean TCN values that exceed deglaciation ages. A further implication is that boulders have survived beneath overriding ice sheets. Such boulder trapping at Lochnagar may have resulted from topographic controls on katabatic winds and surface ablation acting on a thinning, cold-based ice sheet.
The response of aquatic ecosystems in the Sierra Nevada (California, USA) to late Quaternary hydroclimate changes remains mostly unknown. Mono Lake, a large endorheic lake just east of the Sierra Nevada, contains an expanded archive of laminated sediments that can be used to examine the response of benthos to environmental changes. Fossil ostracodes from a radiocarbon-dated core were used to examine paleoecologic changes from ~16.6 to 4.3k cal a bp. Seven species were identified, with the co-occurrence of Limnocythere ceriotuberosa and Limnocythere staplini indicating a large SO42−-rich lake in the Pleistocene. The Younger Dryas was complex, with Fabaeformiscandona caudata reflecting a cold and deep lake ~13.0–12.2k cal a bp, followed by an interval of extensive littoral habitat from ~12.2–11.6k cal a bp. Ostracode diversity, valves g–1 and the ratio of adult:juvenile valves declined after ~10.7k cal a bp due to regression, altered hydrochemistry and seasonal anoxia. Strong seasonality during the Early Holocene is suggested by the presence of reworked ostracodes and macrocharcoal, delivered to Mono Lake by erosion of ancient lake beds in the basin. A depauperate ostracode fauna in the Middle Holocene suggests a strong sensitivity to drought in this ecosystem, which has implications for biodiversity in the future.
The bay barnacle Amphibalanus improvisus (Darwin, 1854) has been found in Northern Germany in brackish marine sediments of the Holsteinian interglacial. Whereas the cause of the contemporary distribution of this species is anthropogenic and there is evidence that it has resulted mainly from shipping, the fossil findings demonstrate that A. improvisus had also already reached Europe naturally during the Pleistocene in Europe, probably via the Gulf Stream system of the Atlantic. Today, A. improvisus is considered one of the most successful aquatic invasive species worldwide and it is characterized by a high environmental tolerance. The ingression of the Holsteinian Sea, during the Pleistocene, took place during the climate optimum from the North Sea into the ‘Elbe Estuary’ through the Hamburg region and far to the south-east into Brandenburg. It has been possible to reconstruct the palaeo-ecological conditions based in particular on molluscs. Accordingly, environmental conditions ranged from normal marine in the north, via brackish in the transitional area to limnic–fluviatile in the Berlin region. The morphological features of the bay barnacles and their ecological parameters are described here in detail. In addition, we provide a general review of the known Pleistocene Balanidae in northern central Europe.
While humic lakes are common in northern Europe, in central Europe they are rare and our understanding of their ontogeny is insufficient. Here, we present the reconstruction of the development of a humic lake in the Tatra Mountains (Slovakia) over the last 8000 years using chironomids along with diatoms, pollen and non-pollen palynomorphs. The compositional changes in aquatic proxies suggest three developmental stages. Since its formation the lake has been oligotrophic (phase 1), and its chemistry was controlled by subsurface waters rich in base cations buffering the effect of acid humic substances from forest and peat that were already present in the catchment. The beginning of the transition to phase 2 (~4400 cal a bp) is marked by simultaneous alterations in all proxies. Climate change combined with the local geochemistry was able to alter the limnological conditions supporting unique chironomid assemblages that have no analogues in recent Carpathian lakes. At ~3400 cal a bp the lake shifted to a phase when acidophilic/acidotolerant taxa indicate characteristic humic lake conditions (phase 3). Some chironomid taxa appearing ~2000 years ago for the first time indicate a dystrophic state in which the lake has remained until now. Human activities have been detected in the area since the Aeneolithic but had no direct influence on the lake.
The Last Glacial Maximum (LGM; 26,000–19,000 years before the present) altered the distribution of species worldwide. Its effect is poorly known in tropical regions because the cooling and drought reached during that period are uncertain. Here, I generated hypotheses regarding the possible responses of cloud forest mammals in the Oaxacan Highlands (OH) of Mexico, a region with one of the most extensive cloud forests in the Neotropics. First, I used three General Circulation Models (GCMs: CCSM3, MIROC-ESM and MPI) to characterize probable climates during the LGM. Then, I used ecological niche models to estimate the current and LGM potential distributions of four cloud forest species. As in other locations, the results show that GCMs are consistent with cooler conditions relative to today; however, the three GCMs estimate precipitation regimes with notable variations in the region. MPI indicates that the LGM could have been even wetter than present. Consequently, the MPI scenario allowed more widespread potential distributions of mammals. The paleodistributions show how mid- and lowlands were essential for the long-term survival of these ‘high-mountain mammals’ throughout the last glacial–interglacial cycle. The paleodistributions presented here are precise hypotheses that can be tested based on paleoecological and genetic evidence.
Periods of acute climate stress – the convergence of low subsistence yields due to poor climate conditions and ineffective buffering strategies due to climate variability – critically reduces peoples’ ability to subsist and mitigate food shortages, thereby creating conditions that could result in profound social change. Here, paleoclimate reconstructions are used to identify periods of acute stress at three large Ancestral Pueblo villages in the US Southwest. These periods are examined in relation to occupation histories at each village showing that in certain instances, acute climate stress played a primary role in people's decisions to leave communities. However, not all of the communities reacted to stress in the same way indicating that distinct patterns of climate and social context played an important role in influencing how acute climate stress was experienced by different groups. Results from this study highlight the importance of community-specific histories when considering the impact of climate stress on past people.
Overflow events are important embodiments of the evolutionary characteristics of the lower Yellow River. Lakes in the lower reaches of the Yellow River have the capacity to record these events. Due to the complex provenance and transport pathways of sediments in local lakes, it is difficult to extract reliable information on sediments delivered by the Yellow River based on conventional methods and proxies. Here, we show results from a genetically meaningful end-member (EM) decomposition of sediment grain-size data from Huangdun ancient lake. The grain-size of the sediments can be decomposed into three end-members. Comprehensive analysis combining environmental magnetism and geochemical indicators clarifies the significance of each end-member. EM1 represents mixed signals of various proximal fluvial sediments and the Yellow River materials. EM2 is similar to terrestrial fine-grained debris in conjunction with local pedogenic materials, aeolian inputs and some Yi River materials. EM3 represents a component that is mainly derived from long-distance transport by the lower Yellow River. End-member analysis successfully identified overflow events of the lower Yellow River on a southward-flowing path during the Holocene. This study provides a meaningful attempt to reconstruct the evolutionary history of the lower Yellow River from sedimentary records.
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