Age, pollen and spores of ODP Site 175-1082

The present-day condition of bipolar glaciation characterized by rapid and large climate fluctuations began at the end of the Pliocene with the intensification of the Northern Hemisphere continental glaciations. The global cooling steps of the late Pliocene have been documented in numerous studies of Ocean Drilling Program (ODP) sites from the Northern Hemisphere. However, the interactions between oceans and between land and ocean during these cooling steps are poorly known. In particular, data from the Southern Hemisphere are lacking. Therefore I investigated the pollen of ODP Site 1082 in the southeast Atlantic Ocean in order to obtain a high-resolution record of vegetation change in Namibia between 3.4 and 1.8 Ma. Four phases of vegetation development are inferred that are connected to global climate change. (1) Before 3 Ma, extensive, rather open grass-rich savannahs with mopane trees existed in Namibia, but the extension of desert and semidesert vegetation was still restricted. (2) Increase of winter rainfall dependent Renosterveld-like vegetation occurred between 3.1 and 2.2 Ma connected to strong advection of polar waters along the Namibian coast and a northward shift of the Polar Front Zone in the Southern Ocean. (3) Climatically induced fluctuations became stronger between 2.7 and 2.2 Ma and semiarid areas extended during glacial periods probably as the result of an increased pole-equator thermal gradient and consequently globally enhanced atmospheric circulation. (4) Aridification and climatic variability further increased after 2.2 Ma, when the Polar Front Zone migrated southward and the influence of Atlantic moisture brought by the westerlies to southern Africa declined. It is concluded that the positions of the frontal systems in the Southern Ocean which determine the locations of the high-pressure cells over the South Atlantic and the southern Indian Ocean have a strong influence on the climate of southern Africa in contrast to the climate of northwest and central Africa, which is dominated by the Saharan low-pressure cell.

The late Pliocene pollen record of ODP Site 108-658 off Cape Blanc, Atlantic Ocean

A 200 m long marine pollen record from ODP Site 658 (21°N, 19°W) reveals cyclic fluctuations in vegetation and continental climate in northwestern Africa from 3.7 to 1.7 Ma. These cycles parallel oxygen isotope stages. Prior to 3.5 Ma, the distribution of tropical forests and mangrove swamps reached Cape Blanc, 5°N of the present distribution. Between 3.5 and 2.6 Ma, forests occurred at this latitude during irregular intervals and nearly disappeared afterwards. Likewise, a Saharan paleoriver flowed continuously until isotope Stage 134 (3.35 Ma). When river discharge ceased, wind transport of pollen grains prevailed over fluvial transport. Pollen indicators of trade winds gradually increased between 3.3 and 2.5 Ma. A strong aridification of the climate of northwestern Africa occurred during isotope Stage 130 (3.26 Ma). Afterwards, humid conditions reestablised followed by another aridification around 2.7 Ma. Repetitive latitudinal shifts of vegetation zones ranging from wooded savanna to desert flora dominated for the first time between between 2.6 and 2.4 Ma as a response to the glacial stages 104, 100 and 98. Although climatic conditions, recorded in the Pliocene, were not as dry as those of the middle and Late Pleistocene, latitudinal vegetation shifts near the end of the Pliocene resembled those of the interglacial-glacial cycles of the Brunhes chron.

Miocene microflora and palaeoclimate reconstructions from three sites in Bulgaria

In this study we reconstruct quantitatively the Middle to Upper Miocene climate evolution in the southern Forecarpathian Basin (Central Paratethys area, Northwest Bulgaria) by applying the coexistence approach to 101 well-dated palynofloras isolated from three cores. The climatic evolution is compared with changes in vegetation and palaeogeography. The Middle Miocene was a period of a subtropical/warm-temperate humid climate with mean annual temperature (MAT) between 16 and 18°C and mean annual precipitation (MAP) between 1100 and 1300 mm. Thereby, during the entire Middle Miocene a trend of slightly decreasing temperatures is observed and only small climate fluctuations occur which are presumably related to palaeogeographic reorganisations. The vegetation shows a corresponding trend with a decrease in abundance of palaeotropic and thermophilous elements. The Upper Miocene is characterised by more diverse climatic conditions, probably depending on palaeogeographic and global climatic transformations. The beginning of this period is marked by a slight cooling and a significant drying of the climate, with MAT 13.3-17°C and MAP 652-759 mm. After that, fluctuations of all palaeoclimate parameters occur displaying cycles of humid/dryer and warmer/cooler conditions, which are again well reflected in the vegetation. Our study provides a first quantitative model of the Middle-Upper Miocene palaeoclimate evolution in Southeastern Europe and is characterised by a relatively high precision and resolution with respect to the climate data and stratigraphy.

Palynological and stratigraphic record from Löddigsee in Mecklenburg-Vorpommern, Germany

A Late Pleistocene and Holocene sediment core from the nowadays terrestrialised portion of the Löddigsee in Southern Mecklenburg, Germany was palynologically investigated. The lake is situated in the rarely investigated Young moraine area at the transition from the Weichselian to the Saalian glaciation. The high-resolution pollen diagram contributes to the establishment of the north-eastern German Late Pleistocene pollen stratigraphy. The vegetation distribution pattern after the end of the Weichselian is in good agreement with other studies from North-eastern Germany, but also has its own characteristics. The Holocene vegetation development reveals features from the north-eastern and north-western German lowlands. A special focus was laid on the environmental history of the two settlements on an island within the lake (Late Neolithic and Younger Slavic period), which were preserved under moist conditions. Both settlements were constructed during a period of low lake level. Although there is evidence of agriculture in the area during the respective periods, the two island settlements seem to have served other purposes.

Palaeoenvironment records of six sediment cores collected in the Gulf of Carpentaria

The Gulf of Carpentaria is an epicontinental sea (maximum depth 70 m) between Australia and New Guinea, bordered to the east by Torres Strait (currently 12 m deep) and to the west by the Arafura Sill (53 m below present sea level). Throughout the Quaternary, during times of low sea-level, the Gulf was separated from the open waters of the Indian and Pacific Oceans, forming Lake Carpentaria, an isolation basin, perched above contemporaneous sea-level with outlet channels to the Arafura Sea. A preliminary interpretation is presented of the palaeoenvironments recorded in six sediment cores collected by the IMAGES program in the Gulf of Carpentaria. The longest core (approx. 15 m) spans the past 130 ka and includes a record of sea-level/lake-level changes, with particular complexity between 80 and 40 ka when sea-level repeatedly breached and withdrew from Gulf/Lake Carpentaria. Evidence from biotic remains (foraminifers, ostracods, pollen), sedimentology and geochemistry clearly identifies a final marine transgression at about 9.7 ka (radiocarbon years). Before this transgression, Lake Carpentaria was surrounded by grassland, was near full, and may have had a surface area approaching 600 km-300 km and a depth of about 15 m. The earlier rise in sea-level which accompanied the Marine Isotopic Stage 6/5 transgression at about 130 ka is constrained by sedimentological and biotic evidence and dated by optical- and thermoluminescence and amino acid racemisation methods.

Age model and pollen analysis from site GIK16867 in the northern Angola Basin

Sporomorphs and dinoflagellate cysts from site GIK16867 in the northern Angola Basin record the vegetation history of the West African forest during the last 700 ka in relation to changes in salinity and productivity of the eastern Gulf of Guinea. During most cool and cold periods, the Afromontane forest, rather than the open grass-rich dry forest, expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the Gulf of Guinea. Except in Stage 3, when oceanic productivity was high during a period of decreased atmospheric circulation, high oceanic productivity is correlated to strong winds. The response of marine productivity in the course of a climatic cycle, however, is earlier than that of wind vigour and makes wind-stress-induced oceanic upwelling in the area less likely. Monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run-off.