Calcareous nannofossils of ODP Leg 101 holes

Leg 101 of the Ocean Drilling Program drilled 19 holes at 11 sites to investigate the geology of the Straits of Florida and the northern Bahamas. Drilling at Site 626 indicated that the Gulf Stream has had significant flow through the Straits of Florida for at least the last 24 million years. Winnowed, foraminiferal grainstones and packstones with sparse nannofossil assemblages and the reworking of older nannofossils suggest strong bottom-current activity throughout this interval. Drilling north of Little Bahama Bank and in Exuma Sound documents the growth of platform slopes during the late Cenozoic. Nannofossil biostratigraphy of the upper Cenozoic sediments from the Little Bahama Bank and Exuma Sound slope transects indicates relatively continuous deposition, with only short breaks in the periplatform ooze and/or calciturbidite accumulation during the late Pliocene. These unconformities may be linked to sea-level lowstands. Nannofossil assemblages are generally poorly preserved owing to accelerated diagenesis caused by high aragonite and high magnesium calcite contents of bank-derived material. High rates of influx of bank-derived materials appear to coincide with highstands of sea level. Periplatform sediments are largely limited to the upper Cenozoic at Little Bahama Bank. Pelagic and/or hemipelagic conditions existed during the Late Cretaceous and Paleogene. A relatively complete, continuous section of Oligocene is present in the Little Bahama Bank area, although the rest of the Paleogene is thin. Paleogene material is also present in Northeast Providence Channel, although its thickness is uncertain. A thick upper Campanian chalk sequence with abundant, moderately to well-preserved nannofossils occurs in the Little Bahama Bank area. Hemipelagic nannofossil marls and marly chalks at Little Bahama Bank contain an excellent nannofossil record, which indicates a continuous lowermost to middle Cenomanian sequence overlying the upper Albian drowned platform. These hemipelagic sediments are significantly younger than the organic-rich, middle Albian limestones in Northeast Providence Channel. The latter indicate that a deep-water channel was already well established by the middle Albian.

Pollen and spore deposition in different areas of the Lena Delta

Studies of the annual pollen and spore deposition in different areas of the Lena Delta were undertaken for the first time in the Asian sector of the Arctic during the Russian-German ''LENA 98'' and ''LENA 99'' expeditions in the framework of the International ''Laptev Sea System-2000'' Project. To achieve this objective, three spore-pollen traps were set up along the meridional delta profile in accordance with the European Pollen Monitoring Programme for the period July 1998 to August 1999. A comparison between the results of spore-pollen analysis of the contents of traps and the surrounding vegetation was performed. The results confirmed the current spore-pollen spectra are comprised both of pollen and spores of the local plants and of long-distance pollen and spores. The dependence of the long-distance pollen deposition on the character of the wind regime of the region was established. The prevailing southerly and southeasterly wind direction determines the main pollen influx of tree species from the areas of their growth south of the delta. The features of the morphological structure and fossilization of pollen and the features of the productive capability and plant growing conditions are of large significance in the pollen transfer and deposition.

Maastrichtian calcareous nannofossils of Kronsmoor-Section

The latest Campanian-earliest Maastrichtian interval is well known as a period of intense climate cooling. This cooling caused a distinctive bipolar biogeographic distribution of calcareous nannofossil assemblages: High latitude settings were dominated by newly evolving endemic taxa, former cosmopolitan species disappeared at the same time and equatorial communities experienced an invasion of cool water taxa. The impact of this cooling on northern mid-latitude assemblages is, however, less well known. In order to overcome this gap we studied the Kronsmoor section (northwest Germany). This section provides a continuous upper Campanian - lower Maastrichtian succession with moderately to well preserved nannofossils. Uppermost Campanian assemblages are dominated by Prediscosphaera cretacea; other common taxa include Prediscosphaera stoveri, Watznaueria barnesiae and Micula staurophora. The lower Maastrichtian is characterized by lower numbers of P. cretacea and frequent Kamptnerius magnificus, Arkhangelskiella cymbiformis and Cribrosphaerella ehrenbergii. These changes reflect, in part, the Campanian-Maastrichtian boundary cooling since some successful taxa (e.g. K. magnificus) are related to cool surface waters. Other shifts in the nannofossil communities were perhaps the result of a changing nutrient regime. Stronger latitudinal gradients may have increased wind velocities and thus the eolian input of ferruginous dust required by N-fixing bacteria. The enhanced high latitude deep-water formation probably changed the bottom-water environment in disfavor of denitrificating organisms. A decline of chemical weathering and fluviatile transport may have reduced the amount of bioavailable phosphate. These processes led to an increased nitrate and a decreased phosphate content shifting the nutrient regime from nitrate towards phosphate limitation.

Diatom, ice rafted debris and Neogloboquadrina pachyderma (sinistral) abundance in sediment core OCE326-GGC14

A high-resolution diatom census coupled with other proxy data from Laurentian Fan (LF) provides a detailed description of the last deglaciation, bringing new insight to that period by revealing directly the timing of sea-ice formation and melting. Cold events Heinrich Event 1 (H1) and the Younger Dryas (YD) were multiphase events. H1 (~16.8-15.7 cal kyr BP) was defined by a two-pulse release of icebergs promoting sea-ice formation. Melting of sea-ice after H1 corresponds to a cold and fresh anomaly that may have kept the Bølling colder than the Allerød. At ~13.6 cal kyr BP, a cooling trend culminated with sea-ice formation, marking the YD onset (~12.8 cal kyr BP). The decrease in sea-ice (~12.2 cal kyr BP) led to a YD second phase characterized by very cold winters. However, the contribution of warm water diatoms tends to increase at the same time and the YD gradual end (~11.6 cal kyr BP) contrasts with its abrupt end in Greenland ice cores. The YD cannot be regarded as an event triggered by a fresh water input through the Laurentian Channel since only one weak brief input nearly 1000 yrs after its onset is recorded. Very cold and cool conditions without ice mark the following Preboreal. A northward heat flux between 10.8 and 10.2 cal kyr BP was interrupted by the increased influence of coastal waters likely fed by inland melting. There was no further development of sea-ice or ice-drift then.