Pollen and organic-walled dinoflagellate cyst assemblages of sediment core GeoB9503-5

Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB 9503-5 retrieved from the mud-belt ( 50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term palaeoceanographic and palaeoenvironmental changes in subtropical NW Africa during the time interval from ca. 4200 to 1200 cal yr BP. Our study emphasizes significant coeval changes in continental and oceanic environments in and off Senegal and shows that initial dry conditions were followed by a strong and rapid increase in humidity between ca. 2900 and 2500 cal yr BP. After ca. 2500 cal yr BP, the environment slowly became drier again as indicated by slight increases in Sahelian savannah and desert elements in the pollen record. Around ca. 2200 cal yr BP, this relatively dry period ended with periodic pulses of high terrigenous contributions and strong fluctuations in fern spore and river plume dinoflagellate cyst percentages as well as in the fluxes of pollen, dinoflagellate cysts, fresh-water algae and plant cuticles, suggesting "episodic flash flood" events of the Senegal River. The driest phase developed after about 2100 cal yr BP.

Dinoflagellate cyst of sediment core M35003-4 southeast of Grenada

High-resolution, well-dated calcareous dinoflagellate cyst and organic carbon records from a 58 kyr sediment core (M35003-4) located southeast of the island of Grenada show that rapid and pronounced changes in cyst association and accumulation and organic carbon deposition occurred, controlled by (1) a significant southward shift in the position of the North Equatorial Current during the last glacial period and the Younger Dryas cold interval and (2) rapid changes in local productivity in marine isotopic stage 3 that are associated with variations in Orinoco River nutrient discharge and coastal upwelling strength. Prominent cyst accumulation peaks representing extremely oligotrophic and stratified thermocline conditions mimic the Greenland ice core and northern Atlantic Dansgaard/Oeschger stadials and Heinrich events. We provide new evidence for a coupled tropical/high-latitude Atlantic climate system during the last glacial period and suggest that changes in the zonality of the low-latitude winds may play an important role in modulating rapid interhemispheric climate variability.

Late Pliocene dinoflagellate cyst and diatom analysis from a high resolution sequence in DSDP Site 594, Chatham Rise, south west Pacific

A high resolution mixed carbonate and siliciclastic sequence from DSDP Site 594 contains a detailed record of climate change in the late Pliocene. The sequence can be accurately dated by the LAD of Nitzschia weaveri, the LAD of Thalassiosira insigna, the LAD of T. vulnifica and the LAD of T. kolbei diatom datums. Carbonate content and delta18O signatures provide added resolution and place the sequence between isotope stage 100 and 92. The sequence contains well-preserved and diverse dinoflagellate cyst floras. Use of principal component (PCA) and canonical correspondence analyses (CCA) identifies changes in the assemblages that principally reflect warming and cooling trends. Species association with warmer climates included Impagidinium patulum, I. paradoxum and I. sp. cf. paradoxum while those from cooler climates include Invertecysta tabulata and I. velorum. CCA is shown to be a valuable method of determining the past environmental preferences of extinct species such as I. tabulata.