Accelerated settling of particulate matter by ’marine snow’ aggregates
Asper, Vernon L.
MetadataShow full item record
KeywordMarine sediments; Sediment transport; Knorr (Ship : 1970-) Cruise KN94; Columbus Iselin (Ship) Cruise CI83-13; Atlantis II (Ship : 1963-) Cruise AII112-23
Samples from time-series sediment traps deployed in three distinct oceanographic settings (North Pacific, Panama Basin, and Black Sea) provide strong evidence for rapid settling of marine particles by aggregates. Particle water column residence times were determined by measuring the time lag between the interception of a flux event in a shallow trap and the interception of the same event in a deeper trap at the same site. Effective sinking speeds were determined by dividing the vertical offset of the traps (meters) by the interception lag time (days). At station Papa in the North Pacific, all particles settle at 175 m day-1, regardless of their composition, indicating that all types of material may be settling in common packages. Evidence from the other two sites (Panama Basin and Black Sea) shows that particle transport may be vertical, lateral, or a combination of directions, with much of the Black Sea flux signal being dominated by lateral input. In order to ascertain whether marine snow aggregates represent viable transport packages, surveys were conducted of the abundance of these aggregates at several stations in the eastern North Atlantic and Panama Basin using a photographic technique. Marine snow aggregates were found in concentrations ranging from ~1 mm3 liter-1 to more than 500 mm3 liter-1. In open ocean environments, abundances are higher near the surface (production) and decline with depth (decomposition). However, in areas near sources of deep input of resuspended material, concentrations reach mid-water maxima, reflecting lateral transport. A model is proposed to relate the observed aggregate abundances, time series sediment flux and inferred circulation. In this model, depthwise variations in sediment flux and aggregate abundance result from suspension from the sea floor and lateral transport of suspended aggregates which were produced or modified on the sea floor. Temporal changes in sediment flux result from variations in the input of fast-sinking material which falls from the surface, intercepts the suspended aggregates, and transports them to the sea floor. A new combination sediment trap and camera system was built and deployed in the Panama Basin with the intent of measuring the flux of marine snow aggregates. This device consists of a cylindrical tube which is open at the top and sealed at the bottom by a clear plate. Material lying on the bottom plate is illuminated by strobe lights mounted in the wall of the cylinder and photographed by a camera which is positioned below the bottom plate. Flux is determined as the number of aggregates arriving during the time interval between photographic frames (# area-1 time-1). Results show that essentially all material arrives in the form of aggregates with minor contributions of fecal pellets and solitary particles. Sinking speeds (m day-1), calculated by dividing the flux of aggregates (# m-2 day-1) by their abundance (# m-3), indicate that the larger (4-5mm) aggregates are flocculent and sink slowly (~1m day-1) while the smaller aggregates (1-2.5mm) are more compact and sink more quickly (~36m day-1). These large, slow-sinking aggregates may have been re-suspended from the sediment water interface at nearby basin margins.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1985
Suggested CitationThesis: Asper, Vernon L., "Accelerated settling of particulate matter by ’marine snow’ aggregates", 1985-12, DOI:10.1575/1912/3367, https://hdl.handle.net/1912/3367
Showing items related by title, author, creator and subject.
Temporal and spatial variability in sedimentation in the Black Sea : cruise report R/V Knorr 134-8, Black Sea Leg 1, April 16-May 7, 1988 Honjo, Susumu; Hay, Bernward J.; Members of the Scientific Shipboard Party (Woods Hole Oceanographic Institution, 1988-10)This document represents the cruise report of the highly successful Leg 1 of the R/V Knorr cruise to the Black Sea (Cruise 134-8) as a joint Turkish-American Oceanographic Expedition (Izmir to Istanbul, April 16 to May ...
Bathymetry and sediment thickness survey of the Hawaii-2 cable : cruise report for Kiwi expedition leg 2 on the R/V Roger Revelle Stephen, Ralph A.; Swift, Stephen A.; Greaves, Robert J. (Woods Hole Oceanographic Institution, 1997)The primary purpose of this cruise was to identify at least two potential observatory sites along the Hawaii-2 cable that would be suitable for drilling a hole to basement. There is a funded program, the Hawaii-2 Observatory ...
Fatty acids and fatty acid esters of particulate matter collected in sediment traps in the Peru upwelling area R/V Knorr Cruise 73, February/March 1978 Wakeham, Stuart G.; Livramento, Joaquim B.; Farrington, John W. (Woods Hole Oceanographic Institution, 1983-09)Particulate matter samples were collected using free-drifting sediment traps in the Peru upwelling area in 1978 to assess the vertical flux and organic composition of lipids associated with particles sinking out of ...