Bottom-current speed in the Vema Channel recorded by particle size of sediment fine-fraction

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Ledbetter, M. T. (1984). Bottom-current speed in the Vema Channel recorded by particle size of sediment fine-fraction. Marine Geology, 58(1), 137-149.
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TitleBottom-current speed in the Vema Channel recorded by particle size of sediment fine-fraction
AuthorsM. Ledbetter
AbstractThe particle-size distribution of the carbonate-free silt fraction was determined in forty-two core-top samples from the east flank of the Vema Channel in order to allow comparison of the mean particle size with near-bottom current speed based on nearby CTD and current-meter observations. The silt mean particle size fluctuates insignificantly between 1450-3950 m but coarsens markedly below 4000 m under Antarctic-source bottom currents. The top of the zone of coarse sizes approximates the top of Lower Circumpolar Water (LCPW) at ∼4000 m; the steep gradient to coarsest sizes in the axis of the channel marks the transition to Antarctic Bottom Water (AABW). The vertical profile of mean particle size on the east flank correlates in general respects with the vertical velocity gradient in the channel axis although the core sites on the east flank are as far as ∼200 miles from the current-meter arrays. Nevertheless, this relationship is used to infer that the non-carbonate particle sizes deposited on the east flank of the channel may be an indication of bottom-current speed and, therefore, the mean size is used to reconstruct profiles of mean current speed for three time slices (18, 120 and 140 ka B.P.). During glacial isotopic stages 2 and 6 the particle sizes deposited on the east flank of the channel are characterized by finer sizes at nearly all depths and the zone of coarse sizes corresponding to LCPW and AABW deepens. During interglacial isotopic stage 5e, the particlesize profile is very similar to the modern profile; however, LCPW and AABW appear to be deeper than at present. The finer particle sizes deposited at nearly all depths during glacial periods indicates that the velocity of deep circulation in the Atlantic was reduced in response to the ice ages. Deep circulation during isotopic stage 5e closely resembled modern circulation; however, AABW production rates may have been less that at present. © 1984.
JournalMarine Geology
Date1984
Volume58
Issue1-2
Start page137
End page149
ISSN0025-3227
SubjectsGEOLOGY - Subaqueous, PARTICLE SIZE ANALYSIS, SEDIMENTATION, OCEANOGRAPHY
NoteCited By (since 1996):16, Rocks and Cores, CODEN: MAGEA

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