Tab. 1: Rates of advance of the frontal push-moraines of 19 lobes in front of an approx. 4.5 km long margin of the Kötlujökull

In the last years masses of ice, about 5 km long, have been protruding from the lowest part of an advancing glacier margin of the Kötlujökull in Southern Iceland. In the summer of 1983, they appeared as sediment-covered lobes, 10-60 m long, bordering the glacier rnargin like agarland. 1 to 3 push-rnoraines without ice core, rnostly sickle-shaped, occured first in the frontal parts of the lobes: behind thern came several ice-cored moraines with heights of up to several metres. The active ice in front of the precipice of the glacier is called the "glacier-foot" in this paper. The digging out of 9 lobes and the measuring of the advance of 19 lobes showed that in most cases this glacierfoot had split up at its distal end into several plate- or stem-shaped pieces of ice which were situated one upon the other, separated by moraine deposits and proceeding irregularly into the foreland at the rate of several mm/h, The sometimes different rate of advance in the same lobe and different rates of advanee in adjoining lobes (some being entirely inactive) point to a type of rnovement which is independent of the general advance of the glacier. Research in the winter of 1983/84 showed less activity in 3 examined lobes, but the activity had not ceased. The advancement of the lower parts of the glacier-foot into and across the sands of the foreland implies the following genesis of pushmoraines: Shoving off a plate of sand, folding it and pushing it over the foreland at average rates of up to 7,2 mm/h, according to the investigations in thc summer of 1983. At a certain stage of the folding process, new folds begin to develop in front of the old, and the old folds are shifted onto the backslope of thc folds in front of them until they are completely unired. In this way, "püe-moraines" arise, which become higher and higher. They include two or more folds declining towards the glacier. Systems of small moraines presumably of the same genesis occur on old moraine areas in front of the Kötlujökull. The possible cause of formation of a glacier-foot is discussed, and the moraines of the Kötlujökull are compared with certain pleistocene push-moraines.

Radionuclides in the water column at stations near the Antarctic Polar Front in the South Atlantic

Vertical profiles of dissolved and particulate 230Th and 231Pa were obtained across the Antarctic Circumpolar Current (ACC) in the southern Atlantic. North of the Polar Front, dissolved and total 230Th increase with depth in conformity with published scavenging models. There is no depletion of 230Th or 231Pa in the water column south of the Polar Front, thought to be an area of enhanced biological productivity. 230Th concentrations increase three-fold to the Weddell Sea across the ACC. Dissolved and total 231Pa concentrations are relatively constant below 500 m depth at about 0.3 dpm m**-3, and change little with depth or latitude. The results from the Weddell Gyre are explained by a mixing-scavenging model that takes into account the input of lower Circumpolar Deep Water through upwelling, which is the main source of water in the Weddell Gyre and is enriched in 230Th but not in 231Pa. 230Th accumulates in the Weddell Gyre as a result of a reduction in the scavenging rate and by ingrowth from 234U. Ingrowth is more significant for 230Th than for 231Pa because the residence time of water in the gyre (about 35 years) is similar to the scavenging residence time of Th in the south Atlantic (29 years) but shorter than that of Pa (120 years). It is argued that changes in 230Th accumulation in the past may reflect changes in water residence time and in the formation rate of Weddell Sea Deep Water.

In situ pore water oxygen microprofiles from the Polar Front, Southern South Atlantic Ocean

Without doubt, global climate change is directly linked to the anthropogenic release of greenhouse gases such as carbon dioxide (CO2) and methane (UN IPCC-Report 2007). Therefore, research efforts to comprehend the global carbon cycle have increased during the last years. In the context of the observed changes, it is of particular interest to decipher the role of the hydro-, bio- and atmospheres and how the different compartments of the earth system are affected by the increase of atmospheric CO2. Due to its huge carbon inventory, the marine carbon cycle represents the most important component in this respect. Numerous findings suggest that the Southern Ocean plays a key role in terms of oceanic CO2 uptake. However, an exact quantification of such fluxes of material is hard to achieve for large areas, not least on account of the inaccessibility of this remote region. In particular, there exist so far only few accurate data for benthic carbon fluxes. The latter can be derived from high resolution pore water oxygen profiles, as one possible method. However the ex situ flux determinations carried out on sediment cores, tend to suffer from temperature and pressure artefacts. Alternatively, oxygen microprofiles can be measured in situ, i.e. at the seafloor. Until now, no such data have been published for the Southern Ocean. During the Antarctic Expedition ANT-XXI/4, within the framework of this thesis, in situ and ex situ oxygen profiles were measured and used to derive benthic organic carbon fluxes. Having both types of measurements from the same locations, it was possible to establish a depth-related correction function which was applied subsequently to revise published and additional unpublished carbon fluxes to the seafloor. This resulted in a consistent data base of benthic carbon inputs covering many important sub-regions of the Southern Ocean including the Amundsen and Bellingshausen Seas (southern Pacific), Scotia and Weddell Seas (southern South Atlantic) as well as the Crozet Basin (southern Indian Ocean). Including additional locations on the Antarctic Shelf, there are now 134 new and revised measurement locations, covering almost 180° of the Southern Ocean, for which benthic organic carbon fluxes and sedimentary oxygen penetration depth values are available. Further, benthic carbon fluxes were empirically related to dominant diatom distributions in surface sediments as well as to long-term remotely sensed chlorophyll-a estimates. The comparison of these results with benthic carbon fluxes of the entire Atlantic Ocean reveals significantly higher export efficiencies for the Southern Ocean than have previously been assumed, especially for the area of the opal belt.

Chemistry and boron isotope ratios of Izu arc front volcanic rocks

The process of fluid release from the subducting slab beneath the Izu arc volcanic front (Izu VF) was examined by measuring B concentrations and B isotope ratios in the Neogene fallout tephra (ODP Site 782A). Both were measured by secondary ion mass spectrometry, in a subset of matrix glasses and glassy plagioclase-hosted melt inclusions selected from material previously analyzed for major and trace elements (glasses) and radiogenic isotopes (Sr, Nd, Pb; bulk tephra). These tephra glasses have high B abundances (~10-60 ppm) and heavy delta11B values (+4.5? to +12.0?), extending the previously reported range for Izu VF rocks (delta11B, +7.0? to +7.3?). The glasses show striking negative correlations of delta11B with large ion lithophile element (LILE)/Nb ratios. These correlations cannot be explained by mixing two separate slab fluids, originating from the subducting sediment and the subducting basaltic crust, respectively (model A). Two alternative models (models B and C) are proposed. Model B proposes that the inverse correlations are inherited from altered oceanic crust (AOC), which shows a systematic decrease of B and LILE with increasing depth (from basaltic layer 2A to layer 3), paralleled by an increase in delta11B (from ~ +1? to +10? to +24?). In this model, the contribution of sedimentary B is insignificant (<4% of B in the Izu VF rocks). Model C explains the correlation as a mixture of a low-delta11B (~ +1?) 'composite' slab fluid (a mixture of metasediment- and metabasalt-derived fluids) with a metasomatized mantle wedge containing elevated B (~1-2 ppm) and heavy delta11B (~ +14?). The mantle wedge was likely metasomatized by 11B-rich fluids beneath the outer forearc, and subsequently down dragged to arc front depths by the descending slab. Pb-B isotope systematics indicate that, at arc front depths, ~ 53% of the B in the Izu VF is derived from the wedge. This implies that the heavy delta11B values of Izu VF rocks are largely a result of fluid fractionation, and do not reflect variations in slab source provenance (i.e. subducting sediment vs. basaltic crust). Since the B content of the peridotite at the outer forearc (7-58 ppm B, mean 24 +/- 16 ppm) is much higher than beneath the arc front (~1-2 ppm B), the hydrated mantle wedge must have released a B-rich fluid on its downward path. This 'wedge flux' can explain (1) the across-arc decrease in B and delta11B (e.g. Izu, Kuriles), without requiring a progressive decrease in fluid flux from the subducting slab, and (2) the thermal structure of volcanic arcs, as reflected in the B and delta11B variations of volcanic arc rocks.

Abundance and biomass of mesozooplankton collected in front of the Danube Delta in May and October 1978

The Gurile Dunarii 1978 dataset contains zooplankton data collected in May and October 1978 in 14 station allong 3 transect in front of the Danube Delta (45°05' - 44°45'N, 30°02'- 29°27'E). Zooplankton sampling was undertaken at 14 stations where samples were collected using a Juday closing net in the 0-10, 10-20, 20-30, 30-40 and 40-50m layer (depending also on the water masses). The dataset includes samples analysed for mesozooplankton species composition and abundance. Sampling volume was estimated by multiplying the mouth area with the wire length. Taxon-specific mesozooplankton abundance was count under microscope. Total abundance is the sum of the counted individuals. Total biomass Fodder, Rotifera , Ctenophora and Noctiluca was estimated using a tabel with wet weight for each species an stage.

Planktic foraminiferal and sea surface temperature record during the last 1 Myr across the Subtropical Front, Southwest Pacific

Planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature (SST) for the last 1 million years (Myr) are compared between core sites to the north (ODP 1125, 178 faunas) and south (DSDP 594, 374 faunas) of the present location of the Subtropical Front (STF), east of New Zealand. Faunas beneath cool subtropical water (STW) north of the STF are dominated by dextral Neogloboquadrina pachyderma, Globorotalia inflata, and Globigerina bulloides, whereas faunas to the south are strongly dominated by sinistral N. pachyderma (80-95% in glacials), with increased G. bulloides (20-50%) and dextral N. pachyderma (15-50%) in interglacials (beneath Subantarctic Water, or SAW). Canonical correspondence analysis indicates that at both sites, SST and related factors were the most important environmental influences on faunal composition. Greater climate-related faunal fluctuations occur in the south. Significant faunal changes occur through time at both sites, particularly towards the end of the mid-Pleistocene climate transition, MIS18-15 (e.g., decline of Globorotalia crassula in STW, disappearance of Globorotalia puncticulata in SAW), and during MIS8-5. Interglacial SST estimates in the north are similar to the present day throughout the last 1 Myr. To the south, interglacial SSTs are more variable with peaks 4-7 °C cooler than present through much of the early and middle Pleistocene, but in MIS11, MIS5.5, and early MIS1, peaks are estimated to have been 2-4 °C warmer than present. These high temperatures are attributed to southward spread of the STF across the submarine Chatham Rise, along which the STF appears to have been dynamically positioned throughout most of the last 1 Myr. For much of the last 1 Myr, glacial SST estimates in the north were only 1-2 °C cooler than the present interglacial, except in MIS16, MIS8, MIS6, and MIS4-2 when estimates are 4-7 °C cooler. These cooler temperatures are attributed to jetting of SAW through the Mernoo Saddle (across the Chatham Rise) and/or waning of the STW current. To the south, glacial SST estimates were consistently 10-11 °C cooler than present, similar to temperatures and faunas currently found in the vicinity of the Polar Front. One interpretation is that these cold temperatures reflect thermocline changes and increased Circumpolar Surface Water spinning off the Subantarctic Front as an enhanced Bounty Gyre along the south side of the Chatham Rise. For most of the last 1 Myr, the temperature gradient across the STF has been considerably greater than the present 4 °C. During glacial episodes, the STF in this region did not migrate northwards, but instead there was an intensification of the temperature gradient across it (interglacials 4-11 °C; glacials 8-14 °C).