Oligocene and Neogene radiolarians from the Labrador Sea

Two sites in the Labrador Sea and one site in Baffin Bay were drilled during Leg 105. Radiolarians were recovered at all three sites, although at Site 645 (Baffin Bay), radiolarians were present in useful numbers only in the mudline sample. Radiolarians of late Neogene age were recovered at Site 646 south of Greenland, while early Oligocene and early Miocene radiolarians were recovered from the Labrador Sea at Site 647. In Site 646, radiolarian and other coarse-fraction abundances vary dramatically from sample to sample and may reflect deep-water depositional processes as well as changes in surface-water conditions. Site 647 siliceous microfossils reach their peak abundance and preservation in Core 105-647A-25R and decline gradually upward into the lower Miocene (Cores 105-647A-13R and -14R). Siliceous microfossil abundances in counts of the > 38-µm Carbonate-free coarse fraction from the siliceous interval are correlated to each other, but not to the abundance of nonbiogenic coarse-fraction components. Radiolarian abundances in specimens per gram (but not diatom abundances) are correlated to bulk opal concentration and to the organic carbon content of the sediment. The abundance of radiolarians and other siliceous microfossils within the lower Oligocene to lower Miocene is interpreted as reflecting changes in surface-water productivity. With only a few exceptions, no stratigraphic indicator species were seen in samples from either Site 646 or Site 647. The absence of both tropical/subtropical and Norwegian-Greenland Sea stratigraphic forms is due to the dominance of subarctic North Atlantic taxa in Leg 105 assemblages. The early Oligocene and early Miocene assemblages recovered at Site 647 are of particular interest, as very little material of these ages has previously been recovered from the subarctic North Atlantic region, and virtually no descriptive work has been conducted on the more endemic components of the radiolarian assemblages from these time intervals. Thus, this report concentrates on providing, at least in part, the first comprehensive documentation of early Oligocene and early Miocene radiolarians from the subarctic North Atlantic, with emphasis on basic descriptions, measurements, and photographic documentation. However, synonymic work and formal designation of new species names has been deferred until additional material from other regions can be examined. The sole exception is the emendation of Theocalyptra tetracantha Bjorklund and Kellogg 1972 to Cycladophora tetracantha n. comb.

Tab.1: Tabulation of pinguin population within the Antarctic Peninsula region

Six species of penguins breed on the Antarctic continent, the Antarctic Peninsula, the South Shetland and South Orkney Islands. Their breeding populations within the Antarctic Peninsula, and the South Orkney and South Shetland Is., and estimates of global populations are given. Typical breeding seasons are also presented, but it must be noted that these will vary inter-annually and intra-annually under the influence of factors such as sea-ice extent and ENSO (interannual) and the location of each breeding colony (southerly localities will be later than northerly localities, as their breeding season is "compressed" within the shorter summer). Their foraging strategies (categorized as near-shore or offshore) and typical durations of foraging trips are also tabulated. As with breeding season events, foraging behaviour will vary intra-seasonally and inter-seasonally (in terms of dive duration, dive depth, foraging location, etc). The distribution of known penguin breeding colonies is circum-continental, with Emperor and Adelie penguins predominant on approximately 75 % of the coast, with two major concentrations in the Ross Sea and in Prydz Bay. The third concentration is in the Antarctic Peninsula region, where some of the largest penguin colonies are present. All six species breed within the area (predominantly Chinstrap Penguins), and the Peninsula region has a greater diversity than the remainder ofthe Antarctic with respect to penguins. The distribution at sea of nonbreeding penguins is less cIear. Non-breeding individuals of all six species move throughout the Southern Ocean, and in many cases, to areas well north of the winter pack-ice zone. However, it is not possible to estimate densities of penguins at sea as there are no estimates of non-breeding penguin populations the extent of their travels.

Biostratigraphy of selected taxa and radiolarian events in ODP Hole 183-1138A sediments

Well-preserved radiolarian assemblages of late middle Miocene to early Pliocene age are found in Ocean Drilling Program (ODP) Hole 1138A (Cores 183-1138A-12R to 20R), which was rotary drilled into the Central Kerguelen Plateau. The faunas are typical for Antarctic assemblages of this time interval, and the site appears to have been south of the Polar Front during the time period studied. Despite only moderate drilling recovery of the section, most late middle to early Pliocene radiolarian zones are present, although at the sample resolution used, subzones could not be identified. A significant discontinuity in the section is present at the boundary between lithologic Units I and II (between Cores 183-1138A-12R and 13R), corresponding to an interval from at least 4.6 to 6.1 Ma. Mixed late Miocene-early Pliocene assemblages are seen in the base of Core 183-1138A-12R (Sample 183-1138A-12R-3, 20 cm), and the overlying basal Pliocene Tau Zone appears to be absent. It cannot be determined if the discontinuity is due to incomplete recovery of the section and drilling disturbance or if it reflects a primary sedimentary structure - a hiatus or interval of condensed sedimentation.

Diatom abundances in sediment core CESAR_83-006

The modern Arctic Ocean is regarded as a barometer of global change and amplifier of global warming (Graversen et al., 2008, doi:10.1038/nature06502) and therefore records of past Arctic change are critical for palaeoclimate reconstruction. Little is known of the state of the Arctic Ocean in the greenhouse period of the Late Cretaceous epoch (65-99 million years ago), yet records from such times may yield important clues to Arctic Ocean behaviour in near-future warmer climates. Here we present a seasonally resolved Cretaceous sedimentary record from the Alpha ridge of the Arctic Ocean. This palaeo-sediment trap provides new insight into the workings of the Cretaceous marine biological carbon pump. Seasonal primary production was dominated by diatom algae but was not related to upwelling as was previously hypothesized (Kitchell and Clark, 1982, doi:10.1016/0031-0182(82)90087-6). Rather, production occurred within a stratified water column, involving specially adapted species in blooms resembling those of the modern North Pacific subtropical gyre (Dore et al., 2008, doi:10.1016/j.pocean.2007.10.002), or those indicated for the Mediterranean sapropels (Kemp et al., 1999, doi:10.1038/18001). With increased CO2 levels and warming currently driving increased stratification in the global ocean (Sarmiento et al., 1998, doi:10.1038/30455), this style of production that is adapted to stratification may become more widespread. Our evidence for seasonal diatom production and flux testify to an ice-free summer, but thin accumulations of terrigenous sediment within the diatom ooze are consistent with the presence of intermittent sea ice in the winter, supporting a wide body of evidence for low temperatures in the Late Cretaceous Arctic Ocean (Falcon-Lang et al., 2004, doi:10.1016/j.palaeo.2004.05.016; Amiot et al., 2004, doi:10.1016/j.epsl.2004.07.015; Otto-Bliesner et al., 2002, doi:10.1029/2001JD000821), rather than recent suggestions of a 15 °C mean annual temperature at this time (Jenkyns et al., 2004, doi:10.1038/nature03143).

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.

Oxygen consumption in Arctic sediments

Total sediment oxygen consumption rates (TSOC or Jtot), measured during sediment-water incubations, and sediment oxygen microdistributions were studied at 16 stations in the Arctic Ocean (Svalbard area). The oxygen consumption rates ranged between 1.85 and 11.2 mmol m**-2 d**-1, and oxygen penetrated from 5.0 to >59 mm into the investigated sediments. Measured TSOC exceeded the calculated diffusive oxygen fluxes (Jdiff) by 1.1-4.8 times. Diffusive fluxes across the sediment-water interface were calculated using the whole measured microprofiles, rather than the linear oxygen gradient in the top sediment layer. The lack of a significant correlation between found abundances of bioirrigating meiofauna and high Jtot/Jdiff ratios as well as minor discrepancies in measured TSOC between replicate sediment cores, suggest molecular diffusion, not bioirrigation, to be the most important transport mechanism for oxygen across the sediment-water interface and within these sediments. The high ratios of Jtot/Jdiff obtained for some stations were therefore suggested to be caused by topographic factors, i.e. underestimation of the actual sediment surface area when one-dimensional diffusive fluxes were calculated, or sampling artifacts during core recovery from great water depths. Measured TSOC correlated to water depth raised to the -0.4 to -0.5 power (TSOC = water depth**-0.4 to -0.5) for all investigated stations, but they could be divided into two groups representing different geographical areas with different sediment oxygen consumption characteristics. The differences in TSOC between the two areas were suggested to reflect hydrographic factors (such as ice coverage and import/production of reactive particulate organic material) related to the dominating water mass (Atlantic or polar) in each of the two areas. The good correlation between TSOC and water depth**-0.4 to -0.5 rules out any of the stations investigated to be topographic depressions with pronounced enhanced sediment oxygen consumption.