Klaus Michels

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

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Gerhard Kühn

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Bernhard Diekmann

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Hannes Grobe

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Claus‐Dieter Hillenbrand

British Antarctic Survey

H. R. Kudrass

University of Bremen

Dieter K Fütterer

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Gabriele Uenzelmann‐Neben

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Axel Suckow

CSIRO Land and Water

Monika Breitzke

University of Bremen

Michael Wiedicke

Federal Institute for Geosciences and Natural Resources

Cooperative Institutions

University of Bremen

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

International Ocean Discovery Program

Kiel University

Federal Institute for Geosciences and Natural Resources

Sam Houston State University

University of Plymouth

GEOMAR Helmholtz Centre for Ocean Research Kiel

United States Office of Personnel Management

Geological Survey of Western Australia

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The isolation of settling-velocity fractions of sand-size material; new possibilities for the settling tube technique

Journal of Sedimentary Research (1994)

Reinhard Oehmig Klaus Michels

A new method for fractionating sand-size granular material by settling velocity makes it possible to obtain up to 24 desired settling-velocity fractions as accurately and easily as obtaining settling-velocity distributions with a sedimentation balance. The complete sample is retained in the fractions. An example using typical polymodal marine sediments demonstrates the advantage of compositional analysis of settling-velocity fractions for the interpretation of sedimentation processes.

Settling

Isolation

10.1306/d4267e6f-2b26-11d7-8648000102c1865d

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Citations (6)

The southern Weddell Sea: combined contourite-turbidite sedimentation at the southeastern margin of the Weddell Gyre

Geological Society London Memoirs (2002)

Klaus Michels Gerhard Kühn Claus‐Dieter Hillenbrand Bernhard Diekmann Dieter K Fütterer

Abstract 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.

Contourite

Sedimentation

10.1144/gsl.mem.2002.022.01.22

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Citations (55)

The decomposition of polymodal settling velocity distributions for a comprehensive sedimentological description of sand‐sized samples

Sedimentology (1995)

Klaus Michels

ABSTRACT The composition of sediment samples and/or the influence of current activity on the sediment can be easily determined using the dissection of settling velocity distributions. A new dissection method for the analysis of settling velocity distributions has been developed. The initial settling velocity distribution is decomposed by means of settling velocity distributions of the main biogenic constituents, three planktic and three benthic foraminifera species. A divergence from the natural size distribution of a foraminifera species can be attributed to current influence. Thus, negative or positive skewness of current‐affected foraminifera populations indicate erosional or depositional sediment influence. The dissection of Holocene samples from the northern North Atlantic demonstrates the advantages of this method in the interpretation of sand‐size material.

Settling

Sedimentation

10.1111/j.1365-3091.1995.tb01269.x

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Citations (7)

A 5000-yr Record of Climate Change in Varved Sediments from the Oxygen Minimum Zone off Pakistan, Northeastern Arabian Sea

Quaternary Research (1999)

Ulrich von Rad Michael Schaaf Klaus Michels Hartmut Schulz Wolfgang Berger

Abstract The upper Holocene marine section from a kasten core taken from the oxygen minimum zone off Karachi (Pakistan) at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1.2 mm/yr and a unique record of monsoonal climatic variability covering the past 5000 years. Our chronostratigraphy is based on varve counts verified by conventional and AMS 14 C dating. Individual hemipelagic varve couplets are about 0.8–1.5 mm thick, with light-colored terrigenous laminae (A) deposited mainly during the winter monsoon alternating with dark-colored laminae (B) rich in marine organic matter, coccoliths, and fish debris that reflect deposition during the high-productivity season of the late summer monsoon (August–October). Precipitation and river runoff appear to control varve thickness and turbidite frequency. We infer that precipitation decreased in the river watershed (indicated by thinning varves) after 3500–4000 yr B.P. This is about the time of increasing aridification in the Near East and Middle East, as documented by decreasing Nile River runoff data and lake-level lowstands between Turkey and northwestern India. This precipitation pattern continued until today with precipitation minima about 2200–1900 yr B.P., 1000 yr B.P., and in the late Middle Ages (700–400 yr B.P.), and precipitation maxima in the intervening periods. As documented by spectral analysis, the thickness of varve couplets responds to the average length of a 250-yr cycle, a 125-yr cycle, the Gleissberg cycle of solar activity (95 yr), and a 56-yr cycle of unknown origin. Higher frequency cycles are also present at 45, 39, 29–31, and 14 yr. The sedimentary gray-value also shows strong variability in the 55-yr band plus a 31-yr cycle. Because high-frequency cyclicity in the ENSO band (ca. 3.5 and 5 yr) is only weakly expressed, our data do not support a straightforward interaction of the Pacific ENSO with the monsoon-driven climate system of the Arabian Sea.

Varve

Terrigenous sediment

10.1006/qres.1998.2016

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Citations (336)

Transfer of terrigenous material from the Ganges-Brahmaputra delta to the Bengal deep-sea fan

H. R. Kudrass V. Spieß Klaus Michels Monika Breitzke Axel Suckow

Terrigenous sediment

BENGAL

Source

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

Klaus Michels Gerhard Kühn Claus‐Dieter Hillenbrand Bernhard Diekmann Dieter K Fütterer

10.1594/pangaea.472241

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Citations (1)

Sediment transport in the shelf canyon “Swatch of No Ground” (Bay of Bengal)

Deep Sea Research Part II Topical Studies in Oceanography (2003)

Klaus Michels Axel Suckow Monika Breitzke H. R. Kudrass B. Kottke

Silt

Submarine canyon

Turbidity current

10.1016/s0967-0645(02)00617-3

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Citations (62)

Marine Geophysical Research (2001)

Klaus Michels Johannes Rogenhagen Gerhard Kühn

Contourite

Continental Margin

Turbidity current

10.1023/a:1016303817273

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Citations (47)

Inferring Maximum Geostrophic Current Velocities in the Norwegian-Greenland Sea from Settling-Velocity Measurements of Sediment Surface Samples: Methods, Application, and Results

Journal of Sedimentary Research (2000)

Klaus Michels

ABSTRACT Critical shear velocities and geostrophic current velocities were calculated from measured grain sizes and settling velocities using a Shields-type threshold curve of particle movement and assuming bedload transport for particles that were found to be transported by currents. Because this reconstruction of the current velocities is based on the coarsest transported component that could be recognized in the sediment, the resulting current velocities represent a maximum flow speed that was effective during deposition of sediment. The shape of the settling-velocity distributions identifies the dominant type of deposition that controlled the accumulation of sediment: residual, well-sorted, or low-energy depositional. The resulting pattern of reconstructed maximum geostrophic current velocities in the Norwegian-Greenland Sea reflects the known features of present-day thermohaline circulation, which is influenced by the bathymetry at many places. Reconstructed current velocities are higher in areas where the cross section of meridional flows is restricted by topographic barriers. The distribution of the depositional characters shows that residual and well-sorted sediment types are generally associated with higher current velocities in areas of strong geostrophic currents (e.g., Fram Strait and East Greenland continental slope). The low-energy depositional sediment type is widespread in the basins of the eastern Norwegian-Greenland Sea, where lower reconstructed maximum current velocities occur. The high reconstructed velocities on the Spitsbergen Bank can be attributed to the disturbance from storm waves in shallower water depths.

Settling

Norwegian

Geostrophic current

10.1306/101599701036

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Citations (17)

Smear slide analysis of sediment core GeoB6307-3

Klaus Michels

Sediment core

10.1594/pangaea.713192

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Citations (0)