Particle Dynamics in the Sea: Processes of Production and Loss Governing the Abundance of Marine Snow
1990
Alldredge, Alice L.
Much of the suspended particulate matter in the ocean exists as aggregates of smaller particles of algae, bacteria, organic detritus and inorganic particles. The characteristics and abundances of these aggregates affect trophic interactions, chemistry and optical properties of the water column. The goal of this research was to quantify several processes governing the rates of production, breakdown and loss of marine aggregates, particularly those larger than 500 um, known as marine snow. Our results indicate that gravitational settlement is considerably more significant than disaggregation as a process of aggregate loss. Settling velocities of natural aggregates measured directly in situ increased with increasing aggregate size and ranged from 50 to 200 md for aggregates up to 75mm in length. Moreover, aggregates were very strong and resistant to disaggregation by fluid shear. High energy storm events or current shears equivalent to those in tidal channels would be required to fragment even the most fragile organic aggregates in the upper ocean. The process of aggregate formation via particle collision and subsequent attachment occurs at rates up to an order of magnitude higher than previously assumed because the attachment probabilities of colliding marine snow aggregates approaches 100%. Coagulation of diatom blooms is a significant source of marine snow in many ocean regimes.
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