Roland Mäusbacher

Climate change on the Tibetan Plateau in response to shifting atmospheric circulation since the LGM

The Tibetan Plateau (TP) is primarily influenced by the northern hemispheric middle latitude Westerlies and the Indian summer monsoon (ISM). The extent, long-distance effects and potential long-term changes of these two atmospheric circulations are not yet fully understood. Here, we analyse modern airborne pollen in a transition zone of seasonally alternating dominance of the Westerlies and the ISM to develop a pollen discrimination index (PDI) that allows us to distinguish between the intensities of the two circulation systems. This index is applied to interpret a continuous lacustrine sedimentary record from Lake Nam Co covering the past 24 cal kyr BP to investigate long-term variations in the atmospheric circulation systems. Climatic variations on the central TP widely correspond to those of the North Atlantic (NA) realm, but are controlled through different mechanisms resulting from the changing climatic conditions since the Last Glacial Maximum (LGM). During the LGM, until 16.5 cal kyr BP, the TP was dominated by the Westerlies. After 16.5 cal kyr BP, the climatic conditions were mainly controlled by the ISM. From 11.6 to 9 cal kyr BP, the TP was exposed to enhanced solar radiation at the low latitudes, resulting in greater water availability.

A 700‐year record on the effects of climate and human impact on the southern cape coast inferred from lake sediments of eilandvlei, wilderness embayment, south africa

Abstract The southern Cape coast, outh frica, is sensitive to climate fluctuations as it is influenced by different atmospheric and oceanic circulation systems. Palaeoecological evidence of Holocene climate variations in this region is presently limited. Here, we present a lake sediment record spanning approximately the last 670 years from ilandvlei, a brackish coastal lake situated mid‐way between Cape Town and Port lizabeth. The results from geochemical and sedimentological analyses point to an increase in minerogenic sediment input from the catchment starting around ad 1400. Changes in the seasonal distribution of rainfall during the Little Ice Age may have altered river discharge and increased erosion rates and fluvial sediment transport in pre‐colonial times. A rising mean lake level, possibly associated with an altered water balance or relative sea‐level rise, may offer an explanation for the deposition of finer sediments. After ad 1450, reduced burial flux of elements associated with autochthonous sediment formation may have resulted from ecological changes in ilandvlei. Enhanced sedimentation rates, increasing carbon, nitrogen, phosphorous and biogenic silica concentrations, as well as high concentrations of proxies for allochthonous sediment input (e.g. aluminium, titanium, zirconium) point to increasing sediment and nutrient flux into ilandvlei from the late nineteenth century onwards. The most likely factor involved in these recent changes is land‐use change and other forms of human impact.

Reconstruction of the Depositional History of the Former Coastal Lagoon of Vilamoura (Algarve, Portugal): A Sedimentological, Microfaunal and Geophysical Approach

Abstract The late Holocene evolution of the former coastal lagoon of Vilamoura was reconstructed according to sediment cores and geophysical profiles. According to sedimentological analyses of the cores, five palaeoenvironmental stages were defined. (1) The pretransgression stage is represented by an erosive surface formed during incision of the river into the basement because of a lower sea level. This palaeosurface was retraced by refraction seismic profiles, showing that the marine transgression took place on a wide plain with several incised channels. (2) The development of an estuary started by transgression into the river valley corresponding to the postglacial sea level rise. Radiocarbon dating indicates a sea level not lower than −4 m at a minimum age of 4716 ± 72 Cal BP. After the transgressive maximum, infilling of the estuary started, beginning with (3) subtidal infilling related to the formation of a sandy barrier followed by (4) supratidal infilling with further accretion of the barrier, changing the previous open bay into a coastal lagoon. (5) Finally, the lagoon was fluvially filled with terrestrial sediments, changing the marine to a fluvial milieu with floodplain deposition. Analysis of benthic foraminiferal and ostracod assemblages revealed additional information about the environmental conditions during evolution of the estuary, which led to a further subdivision of the marine facies into stages with mainly estuarine, lagoonal, or marine influence. The end of the marine stage was dated at 2895 ± 48 Cal BP, indicating a pre-Roman onset of human-induced soil erosion.

Sediment dynamics and hydrologic events affecting small lacustrine systems on the southern-central Tibetan Plateau – the example of TT Lake

A sedimentological, geochemical, micropaleontological, and palynological study of a lacustrine sediment record from the small TT Lake (southern-central Tibetan Plateau) shows that the background sedimentation was frequently interrupted by event-related deposits. These event-related deposits are interpreted as the result of hydrologic events that are triggered by above-average precipitation events. In total, 11 events were recorded in the TT Lake sequence. Two types can be differentiated: fluvial runoff events caused by precipitation that carried sediment in suspension into the lake and a sediment mass transport caused by torrential precipitation. The hydrologic events appear to be decoupled from long-term climate and environmental variations, but there is evidence that anthropogenic impact, in terms of pastoralism, might have favored the runoff events. The multi-proxy approach proved to be valuable and allowed for a detailed study of sedimentary processes within the lake and its watershed in order to assess their triggering processes and dynamics. The findings show the complexity of these sedimentary processes and their controlling factors, and the study aims to improve their understanding. This study is the first effort to investigate event-related deposits and sedimentary processes on the Tibetan Plateau and its triggering processes and dynamics by utilizing lacustrine sediment records.

Holocene lake level history of the Tangra Yumco lake system, southern-central Tibetan Plateau

Massive carbonate banks representing ancient lacustrine deposits are exposed in the catchment of the lake Tangra Yumco (southern-central Tibetan Plateau) and nearby lake Xuru Co. Nine sediment samples were taken below and above these lacustrine deposits to determine periods of changing lake level using optically stimulated luminescence (OSL) applying a multiple-aliquot regeneration (MAR) protocol. According to facies and stratigraphy, samples below the carbonate banks indicate a rising and samples from above a falling lake level. The results indicate that the rising lake level of Tangra Yumco passed the sampling location at 10.5 and 2.1 ka while a falling lake level passed the sampling location at 0.9 ka. The rising lake level of Xuru Co passed the sampling location at 7.9 and 1.7 ka and a falling lake level at 0.5 ka showing a similar trend as at Tangra Yumco. Combining these results with recalculated cosmogenic nuclide ages and previously published feldspar luminescence data allows the establishment of a Holocene lake level reconstruction for Tangra Yumco, which is unique for the southern-central Tibetan Plateau. The lake level of Tangra Yumco crested a lake level highstand of 181–183 m above the recent lake level prior to 8.5 ka and has generally fallen after 8.5 ka, with a minor lake level rise at 2.1 ka. Lake level variations at Tangra Yumco occur simultaneously with other lakes on the Tibetan Plateau indicating that variations were controlled by monsoonal dynamics with a moist early Holocene and a successive reduction of available moisture thereafter. The average rate of the lake level rise between 10.5 and 8.5 ka is at least 0.05 m a−1 (compared with a modern value of 0.38 m a−1), providing valuable insights in the monsoonal impact on lake level change on the southern-central Tibetan Plateau.

High‐resolution paleomagnetic and sedimentological investigations on the Tibetan Plateau for the past 16 ka cal B.P.—The Tangra Yumco record

The spatial distribution of paleomagnetic secular variation (PSV) records on the Tibetan Plateau and adjacent areas covering the Holocene and Late Glacial is sparse. In order to reconstruct PSV in this area, a piston core covering the past 17.5 ka cal B.P. retrieved from Lake Tangra Yumco, southern‐central Tibetan Plateau, was analyzed. In the laminated sediments, several event layers are intercalated. Those were identified by sedimentological analysis and excluded for age‐depth modeling and interpretation. Paleomagnetic measurements on u‐channels reveal two contrasting core sections. The lower section (dated to 17.5–15.9 ka cal B.P.) is very coarse grained (up to 220 µm) and characterized by low intensities (0.8 mA m−1) and high maximum angular deviation values (mean 25°), making it unsuitable for PSV reconstruction. In contrast, the upper unit (dated to <15.9 ka cal B.P.) yields ideal properties with a well‐defined magnetization carried by low‐coercivity minerals in the pseudo single domain state making those younger sediments a proper record for PSV studies. The robustness of the PSV reconstruction for the past 3000 years is highlighted by a comparable inclination and declination pattern of three short sediment cores (2 m) from Tangra Yumco. On a regional scale, the obtained inclination signal for the past 15.9 ka cal B.P. is in good agreement with the Lake Baikal record (3000 km to the North), PSV stack for East Asia, as well as with predictions of geomagnetic field models. This study is a step forward in constructing a PSV reference curve for central Asia. -- Keywords : paleomagnetic secular variations (PSV) ; magnetostratigraphy ; Tibetan Plateau ; lake sediments ; Tangra Yumco ; inclination.

Towards an integration of process measurements, archive analysis and modelling in geomorphology — the Kärkevagge experimental site, Abisko area, northern Sweden

The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change.

ENSO and monsoon variability during the past 1.5 kyr as reflected in sediments from Lake Kalimpaa, Central Sulawesi (Indonesia):

The climate of Sulawesi is driven by the monsoon system as well as the El Niño-Southern Oscillation (ENSO). Until now, mechanisms and long-term variations of these complex interacting climate processes have been poorly understood. This paper uses a sediment record from Lake Kalimpaa to investigate long-term rainfall trends of the past ~1500 years. Granulometric and geochemical data provide indications for an increasingly wetter climate (higher rainfall intensities and/or mean rainfall) on centennial to millennial time scales from approximately ad 560 to the 20th century. Highest rainfall intensities probably occurred at the end of the ‘Little Ice Age’ (LIA). The trend towards wetter conditions during this time could also be detected in other palaeoclimatic studies from the region. A plausible explanation for these observations is the southward displacement of the Intertropical Convergence Zone (ITCZ) associated with changes in monsoon dynamics. However, comparison of the results with other proxy and model data indicates that the long-term rainfall variability in Central Sulawesi is also determined by variations in ENSO. During the 20th century, the climate signal in the Kalimpaa record is superimposed by human impact. Moreover, the data suggest that two periods of disturbance occurred within the lake catchment between about ad 1090–1190 and ad 1450–1620. Comparison with fire frequency derived from macro-charcoal analysis indicates that these events were caused by forest fires which likely took place during periods of drought. Broadly simultaneous drought periods have been detected in records from East Java suggesting a regional drought occurrence affecting at least East Java and Sulawesi.

Landslides and Deserted Places in the Semi-Arid Environment of the Inner Himalaya

Among other geomorphologic hazards, landslides are a common feature in high mountain areas like the Himalayan Range (cf. Shroder 1989). On the southern flanks of the Himalayas, specially the Low and Middle Himalaya, landslides, representing the dominant hillslope process (Whitehouse 1990), are of special concern as they cause permanent loss of agricultural land (Ives & Messerli 1981), block important roads and even destroy housing (cf. Schelling 1988). The dominance of landslides in this region can be attributed to lithology, the tectonic stress applied to the rocks and steep relief In addition the climatic conditions promote deep weathering and provide landslide triggering rainfall events, generally mainly during the monsoon (cf. Kienholz et al. 1982, Bartaiya & Valdiya 1989).

Hochwasserdynamik und Sedimenttransport

Jede Messung in der Natur ist ein Eingriff in ein naturliches oder quasinaturliches System; das Ziel jeder dieser Messungen ist es, Daten zu erheben, mit deren Hilfe das untersuchte System ganz oder in bestimmten Aspekten beschrieben und erforscht werden kann. Dabei sind drei Dinge sicherzustellen: 1. Der Eingriff darf das System nicht so storen, das die Meswerte im besten Fall zwar reproduzierbar, zur Zustandserfassung aber unbrauchbar sind. 2. Die Messungen mussen sinnvoll im Hinblick auf die Fragestellung, d. h. auf die zu prufende Hypothese sein.; 3. Die Messungen durfen einen im Hinblick auf den Untersuchungsmasstab und das Ergebnis sinnvollen Aufwand nicht uberschreiten.