| Autor: |
Mirzaloo, M., Nürnberg, D., Kienast, M., Lubbe, H. J. L. |
| Předmět: |
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| Zdroj: |
Geochemistry, Geophysics, Geosystems: G3; Aug2019, Vol. 20 Issue 8, p4184-4201, 18p |
| Abstrakt: |
Unique marine sediment cores retrieved from the southwestern slope of the Iceland‐Faroe Ridge (IFR), close to the main axis of the Iceland‐Scotland Overflow Water (ISOW), revealed prominent sedimentary cycles reflecting near‐bottom current dynamics, sediment transport, and deposition, coincident with Dansgaard‐Oeschger cycles and deglacial perturbations of the Atlantic Meridional Overturning Circulation. The transition between Greenland Stadials (GSs) and Greenland Interstadials (GIs) follows a distinct, recurring sedimentation pattern. Basaltic (Ti‐rich) silts were transported from local volcanic sources by strong bottom currents and deposited during GIs comparable to modern ocean circulation. Finer‐grained felsic (K‐rich) sediments were deposited during GSs, when Iceland‐Scotland Overflow was weak. Possible felsic source areas include British‐Ireland and/or Fennoscandian shelf areas. A cyclic sawtooth pattern of bottom current strength is characterized by gradual intensification during GIs followed by a sharp decline toward GSs as is documented at core sites along the flank of Reykjanes Ridge. The cores north of the Faroe Channel instead document the opposite pattern. This suggests that the near‐bottom currents along the Reykjanes Ridge are strongly controlled by the flow cascading over the IFR. Heinrich‐(like) HS‐1 and HS‐2, are characterized by the deposition of very fine felsic sediments pointing to weakened bottom currents. Distinct coarse‐grained intervals of ice‐rafted debris are absent from the sediment records, although pebble‐ and gravel‐sized ice‐rafted debris is irregularly distributed throughout the fine sediment matrix. Near‐bottom currents are considered to have a major control on the lithogenic sediment deposition southwest of the IFR and further downstream. Plain Language Summary: The northward flow of warm North Atlantic water into the Nordic Seas and the southward return of cold and dense overflow water toward the Atlantic basin drive the Atlantic Meridional Overturning Circulation, which is a significant component in the Earth's climate system. Reconstructions of past Atlantic Meridional Overturning Circulation variations are pivotal to our knowledge of the climate response to rapid warming both in the past and the future. The Iceland‐Scotland Ridge is an important gateway for southward‐directed Iceland‐Scotland Overflow Water. Unique marine sedimentary archives from the southwestern slope of the Iceland‐Faroe Ridge close to the main axis of Iceland‐Scotland Overflow Water were systematically studied for their grain size distributions and chemical composition in order to reconstruct near‐bottom circulation dynamics during rapid cooling and warming phases in the northern Atlantic basin. The records reveal marked changes in particle size and provenance, which are clearly related to near‐bottom current speed and hence overflow over the Iceland‐Scotland Ridge coincident with major abrupt climate change events. Key Points: Marine sediment cores from the southwest Iceland‐Faroe Ridge reveal prominent sedimentary cycles due to Iceland‐Scotland Overflow dynamicsVariations in grain‐size distributions and provenance are tightly coupled following Dansgaard‐Oeschger cycles over the last 55‐6 ka BPCurrent‐controlled sediment deposition reflects the cumulative effect of overflow cascading over the ridge and through the Faroe Channels [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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