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Koopmann, B (1981): Age models, accumulation rates, and grain size distributions of sediment cores from the northern subtropical Atlantic [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.548484, Supplement to: Koopmann, B (1981): Sedimentation von Saharastaub im subtropischen Nordatlantik während der letzten 25.000 Jahre. Meteor Forschungsergebnisse, Deutsche Forschungsgemeinschaft, Reihe C Geologie und Geophysik, Gebrüder Bornträger, Berlin, Stuttgart, C35, 23-59, hdl:10013/epic.33257.d001

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Abstract:
The terrigenous sediment proportion of the deep sea sediments from off Northwest Africa has been studied in order to distinguish between the aeolian and the fluvial sediment supply. The present and fossil Saharan dust trajectories were recognized from the distribution patterns of the aeolian sediment. The following timeslices have been investigated: Present, 6,000, 12,000 and 18,000 y. B. P. Furthermore, the quantity of dust deposited off the Saharan coast has been estimated. For this purpose, 80 surface sediment samples and 34 sediment cores have been analysed. The stratigraphy of the cores has been achieved from oxygen isotopic curves, 14C-dating, foraminiferal transfer temperatures, and carbonate contents.
Silt sized biogenic opal generally accounts for less than 2 % of the total insoluble sediment proportion. Only under productive upwelling waters and off river mouths, the opal proportion exceeds 2 % significantly.
The modern terrigenous sediment from off the Saharan coast is generally characterized by intensely stained quartz grains. They indicate an origin from southern Saharan and Sahelian laterites, and a zonal aeolian transport in midtropospheric levels, between 1.5 an 5.5 km, by 'Harmattan' Winds. The dust particles follow large outbreaks of Saharan air across the African coast between 15° and 21° N. Their trajectories are centered at about 18° N and continue further into a clockwise gyre situated south of the Canary Islands. This course is indicated by a sickle-shaped tongue of coarser grain sizes in the deep-sea sediment. Such loess-sized terrigenous particles only settle within a zone extending to 700 km offshore. Fine silt and clay sized particles, with grain sizes smaller than 10- 15 µm, drift still further west and can be traced up to more than 4,000 km distance from their source areas.
Additional terrigenous silt which is poor in stained quartz occurs within a narrow zone off the western Sahara between 20° and 27° N only. It depicts the present dust supply by the trade winds close to the surface.
The dust load originates from the northwestern Sahara, the Atlas Mountains and coastal areas, which contain a particularly low amount of stained quartz. The distribution pattern of these pale quartz sediments reveals a SSW-dispersal of dust being consistent with the present trade wind direction from the NNE.
In comparison to the sediments from off the Sahara and the deeper subtropical Atlantic, the sediments off river mouths, in particular off the Senegal river, are characterized by an additional input of fine grained terrigenous particles (< 6 µm). This is due to fluvial suspension load. The fluvial discharge leads to a relative excess of fine grained particles and is observed in a correlation diagram of the modal grain sizes of terrigenous silt with the proportion of fine fraction (< 6 µm).
The aeolian sediment contribution by the Harmattan Winds strongly decreased during the Climatic Optimum at 6,000 y. B. P. The dust discharge of the trade winds is hardly detectable in the deep-sea sediments. This probably indicates a weakened atmospheric circulation. In contrast, the fluvial sediment supply reached a maximum, and can be traced to beyond Cape Blanc. Thus, the Saharan climate was more humid at 6,000 y B. P. A latitudinal shift of the Harmattan driven dust outbreaks cannot be observed.
Also during the Glacial, 18,000 y. B. P., Harmattan dust transport crossed the African coast at latitudes of 15°-20° N. Its sediment load increased intensively, and markedly coarser grains spread further into the Atlantic Ocean. An expanded zone of pale-quart sediments indicates an enhanced dust supply by the trade winds blowing from the NE. No synglacial fluvial sediment contribution can be recognized between 12° and 30° N. This indicates a dry glacial climate and a strengthened stmospheric circulation over the Sahelian and Saharan region.
The climatic transition pahes, at 12, 000 y. B. P., between the last Glacial and the Intergalcial, which is compareable to the Alerod in Europe, is characterized by an intermediate supply of terrigenous particles. The Harmattan dust transport wa weaker than during the Glacial. The northeasterly trade winds were still intensive. River supply reached a first postglacial maximum seaward of the Senegal river mouth. This indicates increasing humidity over the southern Sahara and a weaker atmospheric circulation as compared to the glacial.
The accumulation rates of the terrigenous silt proportion (> 6 µm) decrcase exponentially with increasing distance from the Saharan coast. Those of the terrigenous fine fraction (< 6 µm) follow the same trend and show almost similar gradients. Accordingly, also the terrigenous fine fraction is believed to result predominantly from aeolian transport.
In the Atlantic deep-sea sediments, the annual terrigenous sediment accumulation has fluctuated, from about 60 million tons p. a. during the Late Glacial (13,500-18,000 y. B. P, aeolian supply only) to about 33 million tons p. a. during the Holocene Climatic Optimum (6,000-9,000 y. B. P, mainly fluvial supply), when the river supply has reached a maximum, and to about 45 million tons p. a. during the last 4,000 years B. P. (fluvial supply only south of 18° N).
Coverage:
Median Latitude: 19.538334 * Median Longitude: -22.183269 * South-bound Latitude: 0.166667 * West-bound Longitude: -50.350000 * North-bound Latitude: 33.850000 * East-bound Longitude: -9.408000
Date/Time Start: 1956-09-10T00:00:00 * Date/Time End: 1979-01-01T00:00:00
Event(s):
A180-73 * Latitude: 0.166667 * Longitude: -23.000000 * Elevation: -3749.0 m * Recovery: 4.9 m * Campaign: A150/180 * Method/Device: Piston corer (PC)
GIK12309-2 * Latitude: 26.838330 * Longitude: -15.110000 * Date/Time: 1971-10-31T00:00:00 * Elevation: -2820.0 m * Recovery: 3.5 m * Location: East Atlantic * Campaign: M25 * Basis: Meteor (1964) * Method/Device: Kasten corer (KAL) * Comment: core was frozen
GIK12310-4 * Latitude: 23.498333 * Longitude: -18.716667 * Date/Time: 1971-11-02T00:00:00 * Elevation: -3080.0 m * Recovery: 5.57 m * Location: East Atlantic * Campaign: M25 * Basis: Meteor (1964) * Method/Device: Kasten corer (KAL)
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
53 datasets

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Datasets listed in this publication series

  1. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core A180-73 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536291
  2. Koopmann, B (1981): Age model of sediment core A180-073 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536317
  3. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12309-2 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536292
  4. Koopmann, B (1981): Age model of sediment core GIK12309-2 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536318
  5. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12310-4 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536293
  6. Koopmann, B (1981): Age model of sediment core GIK12310-4 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536319
  7. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12328-5 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536294
  8. Koopmann, B (1981): Age model of sediment core GIK12328-5 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536320
  9. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12329-6 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536295
  10. Koopmann, B (1981): Age model of sediment core GIK12329-6 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536321
  11. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12331-4 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536296
  12. Koopmann, B (1981): Age model of sediment core GIK12331-4 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536322
  13. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12345-5 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536297
  14. Koopmann, B (1981): Age model of sediment core GIK12345-5 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536323
  15. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12347-2 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536298
  16. Koopmann, B (1981): Age model of sediment core GIK12347-2 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536324
  17. Koopmann, B (1981): Age model of sediment core GIK12379-3 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536325
  18. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK12392-1 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536299
  19. Koopmann, B (1981): Age model of sediment core GIK12392-1 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536326
  20. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK13207-3 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536300
  21. Koopmann, B (1981): Age model of sediment core GIK13207-3 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536327
  22. Koopmann, B (1981): Age model of sediment core GIK13209-2 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536328
  23. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core GIK13289-2 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536301
  24. Koopmann, B (1981): Age model of sediment core M8_017-1 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536329
  25. Koopmann, B (1981): Age model of sediment core SP8-4 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536330
  26. Koopmann, B (1981): Age model of sediment core V10-83 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536331
  27. Koopmann, B (1981): Age model of sediment core V16-20 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536332
  28. Koopmann, B (1981): Age model of sediment core V19-303 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536333
  29. Koopmann, B (1981): Age model of sediment core V20-241 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536334
  30. Koopmann, B (1981): Age model of sediment core V22-194 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536335
  31. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V22-196 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536302
  32. Koopmann, B (1981): Age model of sediment core V22-196 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536336
  33. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V22-197 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536303
  34. Koopmann, B (1981): Age model of sediment core V22-197 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536337
  35. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V23-91 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536304
  36. Koopmann, B (1981): Age model of sediment core V23-91 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536338
  37. Koopmann, B (1981): Age model of sediment core V23-93 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536339
  38. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V23-100 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536305
  39. Koopmann, B (1981): Age model of sediment core V23-100 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536340
  40. Koopmann, B (1981): Age model of sediment core V25-44 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536341
  41. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V26-41 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536306
  42. Koopmann, B (1981): Age model of sediment core V26-41 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536342
  43. Koopmann, B (1981): Age model of sediment core V27-178 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536343
  44. Koopmann, B (1981): Age model of sediment core V31-2 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536344
  45. Koopmann, B (1981): Grain size distribution of carbonate free sediment for the time slice 12000 years B.P. of sediment cores of the northern subtropical Atlantic (App. 3). https://doi.org/10.1594/PANGAEA.536353
  46. Koopmann, B (1981): Accumalion rate of carbonte free sediment for sediment core V32-31 northern subtropical Atlantic (App. 4). https://doi.org/10.1594/PANGAEA.536307
  47. Koopmann, B (1981): Age model of sediment core V32-31 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536345
  48. Koopmann, B (1981): Age model of sediment core V32-32 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536346
  49. Koopmann, B (1981): Grain size distribution of carbonate free sediment for the time slice 6000 years B.P. of sediment cores of the northern subtropical Atlantic (App. 3). https://doi.org/10.1594/PANGAEA.536350
  50. Koopmann, B (1981): Grain size distribution of carbonate free sediment for the time slice 18000 years B.P. of sediment cores of the northern subtropical Atlantic (App. 3). https://doi.org/10.1594/PANGAEA.536354
  51. Koopmann, B (1981): Age model of sediment core GIK13289-1/2 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536348
  52. Koopmann, B (1981): Age model of sediment core V32-33 northern subtropical Atlantic (Table 3). https://doi.org/10.1594/PANGAEA.536347
  53. Koopmann, B (1981): Grain size distribution of terrigenous, carbonate free sediments in surface samples of the northern subtropical Atlantic (App. 2). https://doi.org/10.1594/PANGAEA.536289