Bottom currents and abyssal sedimentation processes south of Iceland

Financial support for shipboard operations and most of the post-cruisedata analysis was provided by NSF Grant OCE76-Sl49l to Dr. Charles Hollister.Sediment trap and hydrocast operations received partial supportunder ONR Contract N00014-74-C-0262.

An investigation was carried out to observe the geologic effects ofsteady bottom currents on sediments of East Katla Ridge on the southerninsular rise of Iceland. Near-bottom southwest to west-flowing currentsexceeded 20 cm sec-1 for two weeks over a 25-kilometer wide section ofthe ridge flank between approximately 1400 and 1800 meters water depth;maximum density and minimum temperature were observed at 1800 meters.Total transport of Iceland-Scotland Overflow Water was calculated to be5.0 x 106 m3 sec-1; suspended sediment transport is approximately0.4 x 106 grams sec-1, with a net deposition of 10 to 15 cm/1000years estimated from the flux difference in and out of the station array.Sediment distribution patterns indicate that the current axis, whereflow exceeds approximately 15 cm sec-1, is a site of erosion and winnowing(sand layer formation) while the current margin is a site of rapidaccumulation (from observed Holocene rates of 25 to 35 cm per 1000 yr toestimated rates of greater than 100 cm/1000 yr based on 3.5 kHz echo-sounderrecords). Holocene silty turbidites are locally thick in a sub-marinechannel; sandy turbidites and current-winnowed 'sandy contourites'are present in the axis of the major submarine canyon.‘ Sandy contourite' deposits beneath the axis of the Iceland-ScotlandOverflow Current are very poorly sorted muddy sands lacking primary sedimentarystructures. Bioturbation is inferred to cause the unique characteristicsof these deposits, as well as the absence of fine silt laminaein 'muddy contourites' at the current margin.

Submitted in partial fulfillment of the requirements for theDegree of Doctor of Philosophy at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology October 1979