Publication Date:
2022-05-25
Description:
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
Description:
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.
Description:
This research was supported by ONR contract numbers N00014-82-C-0019
and N00014-85-C-0001, NSF grant numbers OCE-83-09024, OCE-84-17106, and
DPP-85-01152 and the WHO1 education office.
Keywords:
Marine sediments
;
Sediment transport
;
Knorr (Ship : 1970-) Cruise KN94
;
Columbus Iselin (Ship) Cruise CI83-13
;
Atlantis II (Ship : 1963-) Cruise AII112-23
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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