Frank Preusser

Regional insolation forcing of late Quaternary climate change in the Southern Hemisphere

In agreement with the Milankovitch orbital forcing hypothesis it is often assumed that glacial–interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth. It is difficult to test this assumption, because of the paucity of long, continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals. Here we present an independently dated terrestrial pollen record from a peat bog on South Island, New Zealand, to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial–interglacial cycles. Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences: in particular, an earlier onset and longer duration of the Last Glacial Maximum. Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing. Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change.

Humid periods in southern Arabia: Windows of opportunity for modern human dispersal

Arabia is a key area for the dispersal of anatomically modern humans (AMH, Homo sapiens) out of Africa. Given its modern hostile environment, the question of the timing of dispersal is also a question of climatic conditions. Fresh water and food were crucial factors facilitating AMH expansions into Arabia. By dating relict lake deposits, four periods of lake formation were identified: one during the early Holocene and three during the late Pleistocene centered ca. 80, ca. 100, and ca. 125 ka. Favorable environmental conditions during these periods allowed AMH to migrate across southern Arabia. Between ca. 75 and 10.5 ka, arid conditions prevailed and turned southern Arabia into a natural barrier for human dispersal. Thus, expansion of AMH through the southern corridor into Asia must have taken place before 75 ka, possibly in multiple dispersals.

Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka

We present a high-resolution and independently dated multiproxy lake sediment record from the paleolake at Les Echets in southeastern France that displays synchronous changes in independent limnic and terrestrial ecosystem proxies, in concert with millennial-scale climate oscillations during the last glacial period. Distinct lake-level fluctuations, low lake organic productivity, and open, treeless vegetation indicate cold and dry conditions in response to Heinrich events. Alternating phases of higher and low lake organic productivity, stratified surface waters and long-lasting lake ice cover, decreased or increased catchment erosion, and tree-dominated or herb-dominated vegetation resemble Dansgaard-Oeschger interstadialstadial variability. Transitions between different ecological states occurred in as little as 40–230 yr and seem to have been controlled by the position of the Polar Front. Ecosystem response after 30 ka suggests that local climate conditions became more important. Our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with Dansgaard-Oeschger and Heinrich events, and that regional factors modulated ecosystem response.

Periglacial landscape evolution and environmental changes of Arctic lowland areas for the last 60 000 years (western Laptev Sea coast, Cape Mamontov Klyk)

Non-glaciated Arctic lowlands in north-east Siberia were subjected to extensive landscape and environmental changes during the Late Quaternary. Coastal cliffs along the Arctic shelf seas expose terrestrial archives containing numerous palaeoenvironmental indicators (e.g., pollen, plant macro-fossils and mammal fossils) preserved in the permafrost. The presented sedimentological (grain size, magnetic susceptibility and biogeochemical parameters), cryolithological, geochronological (radiocarbon, accelerator mass spectrometry and infrared-stimulated luminescence), heavy mineral and palaeoecological records from Cape Mamontov Klyk record the environmental dynamics of an Arctic shelf lowland east of the Taymyr Peninsula, and thus, near the eastern edge of the Eurasian ice sheet, over the last 60 Ky. This region is also considered to be the westernmost part of Beringia, the non-glaciated landmass that lay between the Eurasian and the Laurentian ice caps during the Late Pleistocene. Several units and subunits of sand deposits, peat–sand alternations, ice-rich palaeocryosol sequences (Ice Complex) and peaty fillings of thermokarst depressions and valleys were presented. The recorded proxy data sets reflect cold stadial climate conditions between 60 and 50 Kya, moderate inderstadial conditions between 50 and 25 Kya and cold stadial conditions from 25 to 15 Kya. The Late Pleistocene to Holocene transition, including the Allerød warm period, the early to middle Holocene thermal optimum and the late Holocene cooling, are also recorded. Three phases of landscape dynamic (fluvial/alluvial, irregular slope run-off and thermokarst) were presented in a schematic model, and were subsequently correlated with the supraregional environmental history between the Early Weichselian and the Holocene.

Drainage basin response to climate change in the Pisco valley, Peru

The Quaternary development of the Pisco valley in central Peru has been characterized by multiple phases of sediment accumulation and erosion that formed distinct levels of cut-and-fill terraces and alluvial fans. Luminescence dating shows that they formed in response to at least two different stages of sediment accumulation and erosion during the past 60 ka, the main phase of sediment aggradation occurring between ca. 54 and 38 ka ago. The ages show that sediment accumulation was contemporaneous with the time intervals of the Minchin (47.8–36 ka ago, with enhanced precipitation beginning ca. 54.8 ka ago) and Tauca (26–14.9 ka ago) paleolakes on the Altiplano, where the headwaters of the Pisco River are located. We conclude that sediment accumulation was triggered by shifts toward a more humid climate, whereas erosion is the response of the fluvial system to the depletion of the hillslope sediment reservoirs.

LUMINESCENCE DATING OF FLUVIAL SEDIMENTS AND OVERBANK DEPOSITS FROM GOSSAU, SWITZERLAND : FINE GRAIN DATING

Abstract Last glacial fluvial sediments and overbank deposits from Gossau, Switzerland, have been investigated applying infrared stimulated luminescence (IRSL) and thermoluminescence (TL) to polymineral fine grains. Age estimates have been determined using IRSL and TL broad band, blue, yellow and UV emissions. The IRSL dates are mainly consistent with independent dating results while most of the TL measurements result in age overestimations caused by insufficient bleaching before deposition.

Potential of Autoradiography to Detect Spatially Resolved Radiation Patterns in the Context of Trapped Charge Dating

Potential of Autoradiography to Detect Spatially Resolved Radiation Patterns in the Context of Trapped Charge Dating Recent developments in optically stimulated luminescence (OSL) dating allow the determination of signals in increasingly smaller sample amounts. This has led to microdosimetry having a larger impact on equivalent dose (DE) distributions and therefore, detection and assessment of spatial distribution of radionuclides has become more important. This study demonstrates the application of autoradiography using imaging plates to determine spatially resolved radiation inhomogeneities in different types of samples. Qualitative evaluations of radiation inhomogeneity are carried out on unconsolidated sediments as well as on hard rock samples. While indicating some limitations of applicability, the results demonstrate that the method is an efficient tool to detect and document spatial variations in a samples radiation field. It therefore provides a possibility to rapidly screen samples to check whether microdosimetry might affect the DE data. Furthermore, an approach to calibrate autoradiographic images for quantitative use is suggested. Using pressed powder pellets of reference materials, a series of calibration images were exposed, from which a functional relation between specific sample activity and greyscale value in the autoradiographic image has been deduced. Testing the calibration on a set of 16 geological samples, of which their radionuclide content is known, shows a good correlation between specific activities calculated from the nuclide content and specific activities deduced from the autoradiographic images. These findings illustrate the potential of autoradiography with imaging plates to detect spatial distributions of radionuclides and to tackle certain aspects of the problem of microdosimetry in modern trapped charge dating.

Characterisation and evolution of the River Rhine system

The River Rhine and its tributaries represent one of the largest drainage systems in Europe. Its prominence among other fluvial systems is due to the location of its headwaters within the central Swiss Alps, which were repeatedly glaciated during the Quaternary, and the concurrence of major parts of the River Rhine course with the European Cenozoic Rift System. Sediments of the Rhine have thus recorded both changes in climate and tectonic activity as well as sea level change in the lower part of the river course. The River Rhine is composed of different subdivisions characterised by distinct geographical and geological settings. Vorder-and Hinterrhein in the headwaters are inner-alpine rivers frequently influenced in their course by tectonic lines and the blockage of valley floors by the deposits of mass movements. The Alpenrhein is located in a main Alpine valley that drains into a large foreland basin, the Bodensee (Lake Constance). The Hochrhein flows out of the lake following the Jura Mountains in a western direction. All these areas display a series of geological features such as moraine ridges and outwash plains, which directly reflect Quaternary glaciations of the Alps. The Oberrhein (Upper Rhine) Valley, as a graben structure, is part of the rifting system that started to develop during the middle Tertiary. The northern end of the graben is represented by the triple junction of the Mainz Basin, which is mainly characterised by the remains of marine transgressions that occurred during the initial rifting phase. The Rhine continues following the western branch of the tectonic system by passing through the Rhenish Massif. Uplift in this so-called Mittelrhein (Middle Rhine) area is well documented by a flight of late Tertiary to Quaternary river terraces. This region is also characterised by young volcanic activity as found, for example, in the Eifel volcanic field. The Niederheinische Bucht (Lower Rhine Embayment), especially the Roer Valley Rift System, represents the northern continuation of the rifting system. This area is characterised by differential uplift in the southern and subsidence in the northern part of the basin, which continues into the Netherlands. Here, the main stream of the River Rhine is separated into different branches developing an active delta at the coast of the North Sea. When the North Sea Basin was covered by ice during the Elsterian, Saalian and probably also the Weichselian glaciation and global sea level was low, the Rhine continued its course through the English Channel and flowed into the North Atlantic off Brittany.

ESR dating of raised coral reefs from Kish Island, Persian Gulf

Electron spin resonance (ESR) dating of raised coral reefs from Kish Island, Persian Gulf, Iran, was used for the calculation of uplift rates. From the methodological point of view, it has been demonstrated that concentrations of uranium, as needed for the calculation of dose rates, determined by instrumental neutron activation analyses were significantly lower than the results of inductively coupled plasma—mass spectrometry and are probably systematically underestimated. The ESR ages for the corals show no increase with elevation as was expected due to field observations. This apparent discrepancy is explained by the dicyclic nature of the palaeo-reef. Average uplift rates for Kish Island are between ∼0.13 and ∼0.24 mm a−1. This is consistent with previous estimates based on 230Th/234U dating of raised marine deposits from the nearby Iranian mainland and Qeshm Island, Strait of Hormuz, but contrary to results based on 14C dating that predicted uplift rates as high as 3 mm a−1 in that area. It is once more demonstrated that 14C dates >20 ka from this context often have to be interpreted as minimum ages.

Radiocarbon and luminescence dating of overbank deposits in outwash sediments of the Last Glacial Maximum in North Westland, New Zealand

Abstract In the Grey River valley, North Westland, New Zealand, extensive terraces of outwash sediments assigned to the Otira glaciation form outstanding geomorphologic features. Four layers of organic sediments subdivide stratified outwash gravels of the major terrace. The age of the fine‐grained sediments is constrained by 55 radiocarbon (14C) ages and 8 optically stimulated luminescence (OSL) ages. The calibrated radiocarbon ages cover the age range between 21 350 and 23 890 cal yr BP. The ages for each different layer are consistent and are in stratigraphic order with mean ages of 22 350 cal yr BP (layer A), 22 470 cal yr BP (layer B), 22 930 cal yr BP (layer C), and 22 960 cal yr BP (layer D). OSL dating of the silty overbank deposits alternating with the organic beds imply a deposition at 21 700 ± 2600 yr. The use of different organic compounds for radiocarbon dating (separated organic residues, humic acids, terrestrial seeds) and the consistency with the luminescence dating support the reliability of the results. We use the informal name Raupo complex for the overbank deposits and consider it to reflect a moderate climate oscillation between two glacial advances during Oxygen Isotope Stage 2.