Evidence for a sedimentary fingerprint of an asymmetric flow field surrounding a short seamount

• Published in: Earth and Planetary Science Letters
• Main Authors: Turnewitsch, Robert, Reyss, Jean-Louis, Chapman, David C, Thomson, J, Lampitt, Richard S
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2004
• Subjects: FLUXES; Geochemistry & Geophysics; DYNAMICS; TH-230; WATER COLUMN; OCEANS; SEA-FLOOR; 20-DEGREES-W; PB-210; TEMPORAL VARIABILITY; NORTH-ATLANTIC; North Atlantic; Northeast Atlantic
• Online Access: https://pure.uhi.ac.uk/en/publications/10e51236-974b-4802-a265-a4fbd6340baf; https://doi.org/10.1016/j.epsl.2004.03.042

Physical oceanographic modeling and field studies have shown that kilometer-scale seafloor elevations of comparable breadth and width (abyssal hills, knolls, seamounts) are surrounded by complex flow fields. Asymmetric flow fields, reversed flow and closed streamlines around the topographic feature (Taylor caps), and resonantly amplified tidal currents around the seamount rim potentially control near-bottom particle dynamics, particle deposition at the seafloor and, consequently, the formation of the sedimentary record. We combine numerical modeling and field data to study how such topographically controlled flow-field features are reflected in the sedimentary record. Sediment deposition on a topographically isolated abyssal knoll (height: 900 m) on the Porcupine Abyssal Plain in the Northeast Atlantic (water depth above the abyssal plain: 4850 m) was studied, (1) by comparing the spatial distribution of Pb-210 fluxes, calculated from inventories of sedimentary excess Pb-210, with Pb-210 input from the water column as recorded by sediment traps; and (2) by comparing sedimentary grain-size distributions and Zr/Al ratios (an indicator for contents of the heavy mineral zircon) at slope, summit and far-field sites. Given Rossby numbers greater than or equal to 0.23, a fractional seamount height of similar to 0.2, and the absence of diurnal tides it is concluded that an asymmetric flow field without Taylor cap and without amplified tidal currents around the seamount rim is the principal flow-field feature at this knoll. The results and conclusions are as follows: (1) Geochemical and grain-size patterns in the sedimentary record largely agree with the predicted pattern of flow intensity around the topographic elevation: with increasing current strength (erosiveness) there is evidence for a growing discrepancy between water column-derived and sediment-derived Pb-210-fluxes, and for increasing contents of larger and heavier particles. The topographically controlled flow field distorts a homogeneous particle-flux input ...