Paleontological and sedimentological investigations of a sediment profile from northeast Greenland

The Kap Mackenzie area on the outer coast of northeast Greenland was glaciated during the last glacial stage, and pre-Holocene shell material was brought to the area. Dating of marine shells indicates that deglaciation occurred in the earliest Holocene, before 10 800 cal. a BP. The marine limit is around 53 m a.s.l. In the wake of the deglaciation, a glaciomarine fauna characterized the area, but after c. one millennium a more species-rich marine fauna took over. This fauna included Mytilus edulis and Mysella sovaliki, which do not live in the region at present; the latter is new to the Holocene fauna of northeast Greenland. The oldest M. edulis sample is dated to c. 9500 cal. a BP, which is the earliest date for the species from the region and indicates that the Holocene thermal maximum began earlier in the region than previously documented. This is supported by driftwood dated to c. 9650 cal. a BP, which is the earliest driftwood date so far from northeastern Greenland and implies that the coastal area was at least partly free of sea ice in summer. As indicated by former studies, the Storegga tsunami hit the Kap Mackenzie area at c. 8100 cal. a BP. Loon Lake, at 18 m a.s.l., was isolated from the sea at c. 6200 cal. a BP, which is distinctly later than expected from existing relative sea-level curves for the region.

Plant species, biomass and environmental characteristics of relevés along the North America Arctic bioclimate gradient

Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small patterned-ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonalpatterned-ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-ground complexes with the largest thermal differential between the patterned-ground features and the surrounding vegetation exhibited the clearest patterned-ground morphologies.

Pollen analysis of surface sediments from the Gulf of Guinea and offshore NW-Africa

The areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes, whereas wind transport is much more important than river transport. Pollen distribution patterns of Pinus, Artemisia, Chenopodiaceae-Amaranthaceae, and Asteraceae Tubuliflorae trace atmospheric transport by the northeast trades. Pollen transport by the African Easterly Jet is reflected in the pollen distribution patterns of Chenopodiaceae-Amaranthaceae, Asteraceae Tubuliflorae, and Mitracarpus. Grass pollen distribution registers the latitudinal extension of Sahel, savannas and dry open forests. Marine pollen distribution patterns of Combretaceae-Melastomataceae, Alchornea, and Elaeis reflect the extension of wooded grasslands and transitional forests. Pollen from the Guinean-Congolian/Zambezian forest and from the Sudanian/Guinean vegetation zones mark the northernmost extension of the tropical rain forest. Rhizophora pollen in marine sediments traces the distribution of mangrove swamps. Only near the continent, pollen of Rhizophora, Mitracarpus, Chenopodiaceae-Amaranthaceae, and pollen from the Sudanian and Guinean vegetation zones are transported by the Upwelling Under Current and the Equatorial Under Current, where those currents act as bottom currents. The distribution of pollen in marine sediments, reflecting the position of major climatic zones (desert, dry tropics, humid tropics), can be used in tracing climatic changes in the past.

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.

Pollen and spores of sites GeoB8331 and GeoB8323, Namaqualand Mudbelt, Holocene South Africa

To better understand Holocene vegetation and hydrological changes in South Africa, we analyzed pollen and microcharcoal records of two marine sites GeoB8331 and GeoB8323 from the Namaqualand mudbelt offshore the west coast of South Africa covering the last 9900 and 2200 years, respectively. Our data corroborate findings from literature that climate developments apparently contrast between the summer rainfall zone (SRZ) and winter rainfall zone (WRZ) over the last 9900 years, especially during the early and middle Holocene. During the early Holocene (9900-7800 cal.yr BP), a minimum of grass pollen suggests low summer rainfall in the SRZ, and the initial presence of Renosterveld vegetation indicates relatively wet conditions in the WRZ. Towards the middle Holocene (7800-2400 cal. yr BP), a rather moist savanna/grassland rich in grasses suggests higher summer rainfall in the SRZ resulting from increased austral summer insolation and a decline of fynbos vegetation accompanied by an increasing Succulent Karoo vegetation in the WRZ possibly suggests a southward shift of the Southern Hemisphere westerlies. During the last 2200 years, a trend towards higher aridity was observed for the SRZ, while the climate in the WRZ remained relatively stable. The Little Ice Age (ca. 700-200 cal. yr BP) was rather cool in both rainfall zones and drier in the SRZ while wetter in the WRZ.