Age deterimation of sediment cores from the Atlantic Ocean

High resolution benthic oxygen isotope records combined with radiocarbon datings, from cores retrieved in the North, Equatorial, and South Atlantic are used to establish a reliable cronostratigraphy for the last 60 ky. This common temporal framework enables us to study the timing of the sub-Milankovitch climate variability in the entire surface Atlantic during this period, as reflected in planktonic oxygen isotope records. Variations in sea surface temperatures in the Equatorial and South Atlantic reveal two warm periods during the mid-stage 3 which are correlated to the warming observed in the North Atlantic after Heinrich events (HL) 5 and 4. However, the records show that the warming started about 1500 y earlier in the South Atlantic. A zonally averaged ocean circulation model simulates a similar north-south thermal antiphasing between the latitudes of our coring sites, when pertubated by a freshwater flux anomaly. We infer that the observed phase relationship between the northern and the southern Atlantic is related to periods of reduced NADW production in the North Atlantic, such as during HL5 and HL4.

Sedimentologic and magnetic data of sediment cores on the western slope of the Mid-Atlantic Ridge

The relative paleointensity (RPI) method assumes that the intensity of post depositional remanent magnetization (PDRM) depends exclusively on the magnetic field strength and the concentration of the magnetic carriers. Sedimentary remanence is regarded as an equilibrium state between aligning geomagnetic and randomizing interparticle forces. Just how strong these mechanical and electrostatic forces are, depends on many petrophysical factors related to mineralogy, particle size and shape of the matrix constituents. We therefore test the hypothesis that variations in sediment lithology modulate RPI records. For 90 selected Late Quaternary sediment samples from the subtropical and subantarctic South Atlantic Ocean a combined paleomagnetic and sedimentological dataset was established. Misleading alterations of the magnetic mineral fraction were detected by a routine Fe/kappa test (Funk, J., von Dobeneck, T., Reitz, A., 2004. Integrated rock magnetic and geochemical quantification of redoxomorphic iron mineral diagenesis in Late Quaternary sediments from the Equatorial Atlantic. In: Wefer, G., Mulitza, S., Ratmeyer, V. (Eds.), The South Atlantic in the Late Quaternary: reconstruction of material budgets and current systems. Springer-Verlag, Berlin/Heidelberg/New York/Tokyo, pp. 239-262). Samples with any indication of suboxic magnetite dissolution were excluded from the dataset. The parameters under study include carbonate, opal and terrigenous content, grain size distribution and clay mineral composition. Their bi- and multivariate correlations with the RPI signal were statistically investigated using standard techniques and criteria. While several of the parameters did not yield significant results, clay grain size and chlorite correlate weakly and opal, illite and kaolinite correlate moderately to the NRM/ARM signal used here as a RPI measure. The most influential single sedimentological factor is the kaolinite/illite ratio with a Pearson's coefficient of 0.51 and 99.9% significance. A three-member regression model suggests that matrix effects can make up over 50% of the observed RPI dynamics.

Grain size composition of sediment cores from the Weddell Sea, Antarctica

Sedimentary processes in the southeastern Weddell Sea are influenced by glacial-interglacial ice-shelf dynamics and the cyclonic circulation of the Weddell Gyre, which affects all water masses down to the sea floor. Significantly increased sedimentation rates occur during glacial stages, when ice sheets advance to the shelf edge and trigger gravitational sediment transport to the deep sea. Downslope transport on the Crary Fan and off Dronning Maud and Coats Land is channelized into three huge channel systems, which originate on the eastern-, the central and the western Crary Fan. They gradually turn from a northerly direction eastward until they follow a course parallel to the continental slope. All channels show strongly asymmetric cross sections with well-developed levees on their northwestern sides, forming wedge-shaped sediment bodies. They level off very gently. Levees on the southeastern sides are small, if present at all. This characteristic morphology likely results from the process of combined turbidite-contourite deposition. Strong thermohaline currents of the Weddell Gyre entrain particles from turbidity-current suspensions, which flow down the channels, and carry them westward out of the channel where they settle on a surface gently dipping away from the channel. These sediments are intercalated with overbank deposits of high-energy and high-volume turbidity currents, which preferentially flood the left of the channels (looking downchannel) as a result of Coriolis force. In the distal setting of the easternmost channel-levee complex, where thermohaline currents are directed northeastward as a result of a recirculation of water masses from the Enderby Basin, the setting and the internal structures of a wedge-shaped sediment body indicate a contourite drift rather than a channel levee. Dating of the sediments reveals that the levees in their present form started to develop with a late Miocene cooling event, which caused an expansion of the East Antarctic Ice Sheet and an invigoration of thermohaline current activity.

Clay mineralogy of sediment cores from the Arctic Ocean

This study focuses on sedimentological investigations of sediment cores recovered during the international Arctic'91, expeditions with the German research ice breaker RV "Polarstern" to the European sector of the Arctic Ocean. Here, we deduce the last glacial/interglacial changes in transport mechanism and sedimentation from the clay mineral group smectite. We choose the smectites as an example of how sediment mineralogy can be linked with particular source regions (the Kara and Laptev seas), distinct transport mechanism (sea ice and surface currents) and sedimentation processes. Smectite contents in Arctic sediments discussed for two time slices, including the Last Glacial Maximum (LGM), and the last deglaciation (Termination I), reveal the highest variability subsequent to the retreat of the Eurasian ice sheets. Our results show that smectite anomalies in the Eurasian Basin are associated with distinct meltwater pulses and occurred around 13.5-13.0 14C ka B.P. Compelling evidence is provided that these anomalies are deduced from sea-ice entrained sediments from the eastern Kara Sea that entered the Arctic Ocean after ice-sheet break-up and eventually flooding of the Kara Sea. We propose that smectite anomalies in sediments of the eastern Arctic Ocean can be utilized to identify deglacial events and to help decipher configurations of the Eurasian ice sheets. The identification of smectite maxima along the modern sea-ice edge in the Eurasian Basin further indicates biologically enhanced sedimentation from melting sea ice allowing the reconstruction of seasonally open water in the region. Hence, considering the poor preservation conditions of primary paleoceanographic proxies in the Arctic Ocean, the clay mineral contents, particularly the smectite group, may be one alternative tool for paleoclimatic reconstruction in the Eurasian Basin.

Age determination and stable isotope composition of sediment cores from the Arctic Ocean

On the basis of 52 sediment cores, analyzed and dated at high resolution, the paleoceanography and climate of the Last Glacial Maximum (LGM) were reconstructed in detail for the Fram Strait and the eastern and central Arctic Ocean. Sediment composition and stable isotope data suggest three distinct paleoenvironments: (1) a productive region in the eastern to central Fram Strait and along the northern Barents Sea continental margin characterized by Atlantic Water advection, frequent open water conditions, and occasional local meltwater supply and iceberg calving from the Barents Sea Ice Sheet; (2) an intermediate region in the southwestern Eurasian Basin (up to 84-85°N) and the western Fram Strait characterized by subsurface Atlantic Water advection and recirculation, a moderately high planktic productivity, and a perennial ice cover that breaks up only occasionally; and (3) a central Arctic region (north of 85°N in the Eurasian Basin) characterized by a low-salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates. Although the total inflow of Atlantic Water into the Arctic Ocean may have been reduced during the LGM, its impact on ice coverage and halocline structure in the Fram Strait and southwestern Eurasian Basin was strong.

(Table 1) Age determination of sediment cores south of the Faeroe Islands

A study was made of three cores from the Faeroe-Shetland gateway, based on planktonic foraminifera, oxygen isotopes, accelerator mass spectrometry 14C dates, magnetic susceptibility, and counts of ice rafted debris (IRD). The data, covering the period 30-10 ka, show that during the Last Glacial Maximum the Arctic Front occupied a position close to the Faeroes, allowing a persisting inflow of Atlantic surface water into the Faeroe-Shetland Channel. The oceanographic environment during deposition of two IRD layers is influenced by Atlantic surface water masses during the lower IRD layer, with transport of icebergs from N-NW. Polar surface water conditions prevailed only during deposition of the upper IRD layer. There is no indication of surface meltwater influence in the region during the deglaciation, but there is a persistent influence of Atlantic surface water masses in the region. Thus we conclude that during almost the entire period (30-10 ka) the Faeroe-Shetland Channel was a gateway for transport of Atlantic surface water toward the Norwegian Sea.

(Table 1) Age determination of sediment cores of the Labrador Sea

A close look at the sedimentology of Heinrich event 4 from the northwest Labrador Sea indicates that an extended ice margin, perhaps greater than before Heinrich events 1 or 2 (H-1 and H-2), existed in the Hudson Strait region pre-Heinrich event 4 (H-4) and, that on the basis of characteristics of the sediment unit, Heinrich event-4 was different than Heinrich events 1 or 2 (i.e., larger ice sheet collapse(?), longer duration(?), "dirtier" icebergs(?)). Other data from across the southern and eastern margin of the Laurentide Ice Sheet, as well as Greenland and the North Atlantic, support this interpretation, possibly indicating a relative mid-Wisconsin glacial maximum pre-Heinrich event 4. Many of these data also indicate that Heinrich event 4 (35 ka) resulted in serious climatic and oceanographic reorganizations. We suggest that Heinrich event 4 gutted the Hudson Strait, leaving it devoid of ice for Heinrich event 3. We further hypothesize that Heinrich event 3 did not originate from axial ice transport along the Hudson Strait; thus Heinrich event 3 may be more analogous to the proposed northward advancing ice from Ungava Bay during Heinrich event 0 than to the more typical down-the-strait flow during H-1, H-2, and H-4. Consequently, the climatic and oceanographic impacts resulting from Heinrich events are highly susceptible to the type, origin, and magnitude of ice sheet collapse, something which varied per Heinrich event during the last glacial period.

(Table 1) Radiocarbon and OSL ages of sediment cores C1-C5 drilled during the COAST expedition to Cape Mamontov Klyk in April 2005

The palaeoenvironmental development of the western Laptev Sea is understood primarily from investigations of exposed cliffs and surface sediment cores from the shelf. In 2005, a core transect was drilled between the Taymyr Peninsula and the Lena Delta, an area that was part of the westernmost region of the non-glaciated Beringian landmass during the late Quaternary. The transect of five cores, one terrestrial and four marine, taken near Cape Mamontov Klyk reached 12 km offshore and 77 m below sea level. A multiproxy approach combined cryolithological, sedimentological, geochronological (14C-AMS, OSL on quartz, IR-OSL on feldspars) and palaeoecological (pollen, diatoms) methods. Our interpretation of the proxies focuses on landscape history and the transition of terrestrial into subsea permafrost. Marine interglacial deposits overlain by relict terrestrial permafrost within the same offshore core were encountered in the western Laptev Sea. Moreover, the marine interglacial deposits lay unexpectedly deep at 64 m below modern sea level 12 km from the current coastline, while no marine deposits were encountered onshore. This implies that the position of the Eemian coastline presumably was similar to today's. The landscape reconstruction suggests Eemian coastal lagoons and thermokarst lakes, followed by Early to Middle Weichselian fluvially dominated terrestrial deposition. During the Late Weichselian, this fluvial landscape was transformed into a poorly drained accumulation plain, characterized by widespread and broad ice-wedge polygons. Finally, the shelf plain was flooded by the sea during the Holocene, resulting in the inundation and degradation of terrestrial permafrost and its transformation into subsea permafrost.

Age model and stable isotopes of sediment cores from north-central Chile and south-central Chile

Terrigenous sediment supply, marine transport, and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings. Sequence stratigraphic models predict coarse-grained sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves. To decipher the controls on Holocene highstand turbidite deposition, we analyzed 12 sediment cores from spatially discrete, coeval turbidite systems along the Chile margin (29° - 40°S) with changing climatic and geomorphic characteristics but uniform changes in sea level. Sediment cores from intraslope basins in north-central Chile (29° - 33°S) offshore a narrow to absent shelf record a shut-off of turbidite deposition during the Holocene due to postglacial aridification. In contrast, core sites in south-central Chile (36° - 40°S) offshore a wide shelf record frequent turbidite deposition during highstand conditions. Two core sites are linked to the Biobío river-canyon system and receive sediment directly from the river mouth. However, intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies. High sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control Holocene turbidite sedimentation and distribution. Shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment-mass balances.

""Captive Column" crash tests - crash testing of a light standard luminaire [sic] pole. Final report.

Federal Highway Administration, Washington, D.C.

Development and testing of INTRAS, a microscopic freeway simulation model. Volume 4: program documentation. Final report.

Federal Highway Administration, Office of Research and Development, Washington, D.C.

Optimization and testing of highway materials to mitigate ice adhesion : interim report.

Mode of access: Internet.

Performance testing of the Tetradyne high speed air jet skimmer /

Mode of access: Internet.

Performance testing of an improved driver restraint system for subcompact cars. Volume II - final report.

National Highway Traffic Safety Administration, Washington, D.C.

Feasibility of carrier-based fitness-for-duty testing of commercial drivers. Final report.

National Highway Traffic Safety Administration, Office of Crash Avoidance, Washington, D.C.