Pollen and non-pollen palynomorph records of the Holocene part of the composite sediment core TMD from lake Tso Moriri (NW India) and of modern surface samples from the Tso Moriri region

The high-altitude lake Tso Moriri (32°55'46'' N, 78°19'24'' E; 4522 m a.s.l.) is situated at the margin of the ISM and westerly influences in the Trans-Himalayan region of Ladakh. Human settlements are rare and domestic and wild animals are concentrating at the alpine meadows. A set of modern surface samples and fossil pollen from deep-water TMD core was evaluated with a focus on indicator types revealing human impact, grazing activities and lake system development during the last ca. 12 cal ka BP. Furthermore, the non-pollen palynomorph (NPP) record, comprising remains of limnic algae and invertebrates as well as fungal spores and charred plant tissue fragments, were examined in order to attest palaeolimnic phases and human impact, respectively. Changes in the early and middle Holocene limnic environment are mainly influenced by regional climatic conditions and glacier-fed meltwater flow in the catchment area. The NPP record indicates low lake productivity with high influx of freshwater between ca. 11.5 and 4.5 cal ka BP which is in agreement with the regional monsoon dynamics and published climate reconstructions. Geomorphologic observations suggest that during this period of enhanced precipitation the lake had a regular outflow and contributed large amounts of water to the Sutlej River, the lower reaches of which were integral part of the Indus Civilization area. The inferred minimum fresh water input and maximum lake productivity between ca. 4.5-1.8 cal ka BP coincides with the reconstruction of greatest aridity and glaciation in the Korzong valley resulting in significantly reduced or even ceased outflow. We suggest that lowered lake levels and river discharge on a larger regional scale may have caused irrigation problems and harvest losses in the Indus valley and lowlands occupied by sedentary agricultural communities. This scenario, in turn, supports the theory that, Mature Harappan urbanism (ca. 4.5-3.9 cal ka BP) emerged in order to facilitate storage, protection, administration, and redistribution of crop yields and secondly, the eventual collapse of the Harappan Culture (ca. 3.5-3 cal ka BP) was promoted by prolonged aridity. There is no clear evidence for human impact around Tso Moriri prior to ca. 3.7 cal ka BP, with a more distinct record since ca. 2.7 cal ka BP. This suggests that the sedimentary record from Tso Moriri primarily archives the regional climate history.

Neogene floras and palaeoclimatic estimates from various sites of South-West China

Neogene climates and vegetation history of western Yunnan are reconstructed on the basis of known fossil plants using the Coexistence Approach (CA) and Leaf Margin Analysis (LMA). Four Neogene leaf floras from Tengchong, Jianchuan and Eryuan in southwestern China are analyzed by the CA, and the paleoclimatic data of one Miocene carpoflora from Longling and three Pliocene palynofloras from Longling, Yangyi and Eryuan are used for comparison. The Miocene vegetation of the whole of West Yunnan is subtropical evergreen broad-leaved forest, and a similar mean annual precipitation is inferred for Tengchong, Longling and Jianchuan. However, by the Late Pliocene a large difference in vegetation occurred between the two slopes of Gaoligong Mountain, western Yunnan. The region of Tengchong retained a subtropical evergreen broad-leaved forest vegetation, whereas in Yangyi and Eryuan a vertical vegetation zonation had developed, which consists, in ascending order, of humid evergreen broad-leaved, needle and broad-leaved mixed evergreen, and coniferous forests. Distinctively, the Late Pliocene vegetational patterns of West Yunnan were already very similar to those of the present, and the Pliocene mean annual precipitation in Tengchong was markedly higher than that of Yangyi and Eryuan. Considering that the overall vegetation of West Yunnan and the precipitation at Yangyi and Eryuan have undergone no distinct change since the Late Pliocene, we conclude that the Hengduan Mountains on the northern boundary of West Yunnan must have arisen after the Miocene and approached their highest elevation before the Late Pliocene. Furthermore, the fact of the eastern portion of the Tibetan Plateau underwent a slight uplift after the Late Pliocene is also supported.

Palynology of ODP Site 108-658

Ocean Drilling Program Site 658 at 21°N off northwest Africa has a high sedimentation rate and a high concentration of pollen grains and is thus very suitable for detailed pollen analysis. The time scale for the upper 100 m (the last 670 k.y.) of Site 658 is based on biostratigraphic data and isotope stratigraphy. The pollen record has been divided into 34 zones. These are classified into 7 zone types covering a range from very arid to rather humid conditions. The sequence shows a long-term climatic decline: strong glacial stages were found only after 480 k.y. and strong interglacial stages only before 280 k.y. The Site 658 record correlates well with a terrestrial sequence from northern Greece, although both records differ in their response to global climatic change. Spectral analysis shows a 100- and a 42-k.y. period in the curves of pollen brought in by the northwest trade winds and only a 42-k.y. period in the curves of pollen mostly transported by the African Easterly Jet. A 31-k.y. period is found in the curves for Ephedra and Chenopodiaceae-Amaranthaceae. In addition, Ephedra shows a 54-k.y. period.

Pollen distribution in marine sediment samples along the south-western African coast

The distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents. The wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories. Isobaric, 4-day backward trajectories are calculated using the modelled wind-field of ECHAM3, and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south-eastern Atlantic. Trajectories and clusters based on the modelled wind-field of the Last Glacial Maximum hardly differ from those of the present-day. Trajectory clusters show three regional, and two seasonal patterns, determining the pathways of aeolian pollen transport into the south-eastern Atlantic ocean. Mainly, transport out of the continent occurs during austral fall and winter, when easterly and south-easterly winds prevail. South of 25°S, winds blow mostly from the west and southwest, and aeolian terrestrial input is very low. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent. The northern Angola Basin receives pollen and spores from the Congolian and Zambezian forests mainly through river discharge. The Zambezian vegetation zone is the main source area for wind-blown pollen in sediments of the Angola Basin, while the semi-desert and desert areas are the main sources for pollen in sediments of the Walvis Basin and on the Walvis Ridge. A transect of six marine pollen records along the south-western African coast indicates considerable changes in the vegetation of southern Africa between glacial and interglacial periods. Important changes in the vegetation are the decline of forests in equatorial Africa and the north of southern Africa and a northward shift of winter rain vegetation along the western escarpment.

Pollen analysis of sediment cores from the mouth of the river Congo to Walvis Bay and Lüderitz

The distribution of pollen in marine sediments is used to record vegetation changes over the past 30,000 years on the adjacent continent. A transect of marine pollen sequences from the mouth of the river Congo (~5°S) to Walvis Bay and Lüderitz (~25°S) shows vegetation changes in Congo, Angola and Namibia from the last glacial period into the Holocene. The comparison of pollen records from different latitudes provides information about the latitudinal shift of open forest and savannahs (Poaceae pollen), the extension of lowland forest (rain forest pollen) and Afromontane forest (Podocarpus pollen), and the position of the desert fringe (pollen of Caryophyllaceae, Chenopodiaceae and Amaranthaceae). High Cyperaceae pollen percentages in sediments from the last glacial period off the mouth of the river Congo suggest the presence of open swamps rather than savannah vegetation in the Congo Basin. Pollen from Restionaceae in combination with Stoebe-type pollen (probably from Elytropappus) indicates a possible northwards extension of winter rain vegetation during the last glacial period. The record of Rhizophora (mangrove) pollen is linked to erosion of the continental shelf and sea-level rise. Pollen influx is highest off river mouths (10-2000 grains year**-1 cm**-2), close to the coast (300-6000 grains year**-1 cm**-2), but is an order of magnitude lower at sites situated far from the continent (<10 grains year**-1 cm**-2).

Pollen analysis and age model of sediment core GIK-15856-2

Pollen and spores from a deep-sea core located west of the Niger Delta record an uninterrupted area of lowland rain forest in West Africa from Guinea to Cameroon during the last Interglacial and the early Holocene. During other periods of the last 150 ka, a savanna corridor between the western - Guinean - and the eastern - Congolian - part of the African lowland rain forest existed. This so-called Dahomey Gap had its largest extension during Glacial Stages 6, 4, 3, and 2. Reduced surface salinity in the eastern Gulf of Guinea as recorded by dinoflagellate cysts indicates sufficient precipitation for extensive forest growth during Stages 5 and 1. The large modern extension of dry forest and savanna in West Africa cannot be solely explained by climatic factors. Mangrove expansion in and west of the Niger Delta was largest during the phases of sea-level rise of Stages 5 and 1. During Stages 6, 4, 3, and 2, shelf areas were exposed and the area of the mangrove swamps was minimal.

Pollen record and dating of sediment core GIK16776-1 off Liberia

Based on pollen analysis of a sediment core from the Atlantic Ocean off Liberia the West African vegetation history for the last 400 ka is reconstructed. During the cold oxygen isotope stages 12, 10, 8, 6, 4, 3 and 2 an arid climate is indicated, resulting in a southward shifting of the southern border of the savanna. Late Pleistocene glacial stages were more arid than during the Middle Pleistocene. A persistence of the rain forest in the area, even during the glacial stages, is recorded. This suggests a glacial refuge of rain forest situated in the Guinean mountains. Afromontane forests with Podocarpus occurred in the Guinean mountains from the stages 12 to 2 and disappeared after. The tree expanded from higher to lower elevations twice in the warm oxygen isotope stage 11 (pollen subzones 11d, 11b) and at least twice during the warm stage 5 (pollen subzones 5d, 5a), indicating a relative cool but humid climate for these periods.

Pollen analysis of surface sediment off northwest Africa

Over 100 samples of recent surface sediments from the bottomn of the Atlantic Ocean offshore NW Africa between 34° and 6° N have been analysed palynologically. The objective of this study was to reveal the relation between source areas, transport systems, and resulting distribution patterns of pollen and spores in marine sediments off NW Africa, in order to lay a sound foundation for the interpretation of pollen records of marine cores from this area. The clear zonation of the NW-African vegetation (due to the distinct climatic gradient) is helpful in determining main source areas, and the presence of some major wind belts facilitates the registration of the average course of wind trajectories. The present circulation pattern is driven by the intertropical front (ITCZ) which shifts over the continent between c. 22° N (summer position) and c. 4° N (winter position) in the course of the year. Determination of the period of main pollen release and the average atmospheric circulation pattern effective at that time of the years is of prime importance. The distribution patterns in recent marine sediments of pollen of a series of genera and families appear to record climatological/ecological variables, such as the trajectory of the NE trade, January trades, African Easterly Jet (Saharan Air Layer), the northernmost and southernmost position of the intertropical convergence zone, and the extent and latitudinal situation of the NW-African vegetation belt. Pollen analysis of a series of dated deep-sea cores taken between c. 35° and the equator off NW African enable the construction of paleo-distribution maps for time slices of the past, forming a register of paleoclimatological/paleoecological information.