ALBERT

Description: Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional fields into a global data set. We use the S-2004 global 1-minute bathymetry as the backbone and add an improved version of the BEDMAP topography for an area that roughly coincides with the Antarctic continental shelf. Locations of the merging line have been carefully adjusted in order to get the best out of each data set. High-resolution gridded data for upper and lower ice surface topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier have been carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and again carefully merged into the existing bathymetry map. The global 1-minute dataset (RTopo-1 Version 1.0.5) has been split into two NetCDF files. The first contains digital maps for global bedrock topography, ice bottom topography, and surface elevation. The second contains the auxiliary maps for data sources and the surface type mask. A regional subset that covers all variables for the region south of 50 deg S is also available in NetCDF format. Datasets for the locations of grounding and coast lines are provided in ASCII format.

Description: A record of carbon and oxygen isotopes in benthic and planktonic foraminifers has been obtained from the interval corresponding to the last 2.4 m.y. of Site 610, Holes 610 and 610A, with a sample resolution of about 30 kyr. The record from the late Quaternary (〈0.9 Ma) shows large amplitudes and high frequencies in oxygen isotopic variation. Prior to 0.9 Ma the isotopic variability record is reduced in amplitude (but not in frequency) compared with the late Quaternary, suggesting lower ice-volume and climatic fluctuations, and higher average eustatic sea level. Left-coiling (L, polar) Neogloboquadrinapachyderma were not found in samples between 1.0 and 2.2 Ma, indicating less influence of polar front migrations in the Northeast Atlantic. Both polar planktonic faunas and larger isotope fluctuations reappear in the lowermost samples (2.3 to 2.4 Ma), pointing toward a period of larger climatic variability in the late Pliocene than in the early Quaternary. The variation in benthic d13C and hence in deep-water d13C seems to have been constant through the analyzed section, reflecting a stable variability in the production of North Atlantic Deep Water (NADW) and possibly in Norwegian-Greenland Sea Overflow. Preliminary analyses of amino-acid epimerization in N. pachyderma (L) indicate a constant rate of epimerization to approximately 0.3 Ma. Beneath this level the average epimerization rate is much reduced.

Description: The coarseness of the 10-63 µm terrigenous silt (i.e., sortable-silt) fraction tends to vary independently of sediment supply in current-sorted muds in the world's oceans, with coarser sediments representing relatively greater near-bottom flow speeds. Traditionally, the coarseness of this size fraction is described using an index called sortable-silt mean size (SS), which is an arithmetic average calculated from the differential volume or mass distribution of grains within the 10-63 µm terrigenous silt fraction, where the relative weights of the individual size bins become increasingly disproportionate, with respect to the actual number of grains within those size bins, toward the coarse end of the size range. This not only increases the absolute value of the apparent "mean size" within the 10-63 µm terrigenous silt fraction, but it may also affect the apparent pattern of relative changes in the coarseness of the sortable-silt fraction along the core. In addition, it makes SS more prone to biases due to, for example, analytical errors. Here we present a detailed analysis of grain-size distributions over three selected Holocene time intervals from two complementary sediment cores (JM97-948/2A and MD95-2011), extracted from the center of a high-accumulation area along the flow path of the main branch of the Atlantic Inflow into the Nordic Seas and show that differential-number-based statistics, which likely better describes variations in the actual coarseness of the sortable-silt fraction, may provide a more robust alternative to SS.

Description: The early to mid-Holocene thermal optimum is a well-known feature in a wide variety of paleoclimate archives from the Northern Hemisphere. Reconstructed summer temperature anomalies from across northern Europe show a clear maximum around 6000 years before present (6 ka). For the marine realm, Holocene trends in sea-surface temperature reconstructions for the North Atlantic and Norwegian Sea do not exhibit a consistent pattern of early to mid- Holocene warmth. Sea-surface temperature records based on alkenones and diatoms generally show the existence of a warm early to mid-Holocene optimum. In contrast, several foraminifer and radiolarian based temperature records from the North Atlantic and Norwegian Sea show a cool mid- Holocene anomaly and a trend towards warmer temperatures in the late Holocene. In this paper, we revisit the foraminifer record from the Vøring Plateau in the Norwegian Sea. We also compare this record with published foraminifer based temperature reconstructions from the North Atlantic and with modelled (CCSM3) upper ocean temperatures. Model results indicate that while the seasonal summer warming of the seasurface was stronger during the mid-Holocene, sub-surface depths experienced a cooling. This hydrographic setting can explain the discrepancies between the Holocene trends exhibited by phytoplankton and zooplankton based temperature proxy records.

Description: Notes from Henrik de Nie: The project started as a phenological study in cooperation with the (Dutch) meteorological institute (KNMI) to register the time of arrival of Fitis and Tjiftaf. During 1951 to 1969 he went every day to the wood (except 1966, in this year his wife died). Thereafter he went no more daily, but because he knew the wood very well and he was free to choice the day on which he did a survey, therefore he choose days with relatively good weather. He did not observe very common bird species, maybe because they are dependent on nest boxes and he did not want to be dependent on the management of the nest box-people (in fact I forgot precisely his arguments, and now I cannot ask him this): Common Starling; Eurasian Tree Sparrow (not common); Great Tit; Eurasian Blue Tit Pieter mentioned 14 species that scored many zero values or only one observation: Stock Dove; Common Cuckoo; Lesser Spotted Woodpecker; Eurasian Golden Oriole; Eurasian Nuthatch; Short-toed Treecreeper; Common Nightingale; Marsh Warbler; Lesser Whitethroat; Goldcrest; Common Firecrest (after 1970 he had difficulties in hearing these two species); Spotted Flycatcher; Eurasian Bullfinch; Black Woodpecker He also mentioned species that he found much fewer as: European Greenfinch; European Pied Flycatcher; Long-eared Owl; Red Crossbill; Sedge Warbler; Icterine Warbler; Eurasian Woodcock; Eurasian Siskin; European Green Woodpecker; Great Spotted Woodpecker; Eurasian Hobby; Western Barn Owl; Woodlark; Common Wood Pigeon; Little Owl; European Crested Tit; Hawfinch. But for these species I think that observations are strongly dependent on the number of visits to the wood. Also here, many zeros and few 1 x during the whole series of visits.

Description: Studies of ice-rafted detritus in ODP holes from the Norwegian Sea document a series of glacial episodes in the surroundings of the Norwegian - Greenland Sea from the late Miocene (5.45 Ma) through the Pliocene. These glacial events were of smaller magnitude than those of the period postdating the major onset of large scale northern hemisphere glacial cyclicity at 2.57 Ma. A further amplification of the glaciations took place after 1.2 Ma. Oxygen isotope records from benthic foraminifers indicate high-frequency global ice volume fluctuations since the late Miocene. A major glacial episode took place at 5.1 – 5 Ma, which lowered eustatic sea-level by about 80 m below the present. Similar lowerings of sea-level are also documented for some glacials in the Pliocene (3.7 – 3.1 Ma). These glacials indicate substantially larger Antarctic ice volumes than at present. The glacial episode at 5 Ma is correlated with the upper evaporite sequence of the Messinian salinity crisis in the Mediterranean. The Norwegian Sea was a net exporter of deep-water during most of the last 6 Myr. Periods of carbonate dissolution lasting several 100 kyr indicate intervals of reduced ventilation and a more stable water column in the Norwegian Sea in both the late Miocene — Pliocene and the early Quaternary. There is no clear evidence for reduced deep-water formation during the upper Messinian event. High-frequency variation in δ 13C indicates that changes in deep-water ventilation rate were coupled with orbital forcing. While the ventilation and deep-water chemistry of the Norwegian Sea has varied during the late Neogene, the δ 18O results indicate that Norwegian Sea deep-waters were denser and colder than those of the Atlantic during major portions of the last 6 Myr.