THE ATTACHMENT PROBABILITIES OF MARINE SNOW AND THEIR IMPLICATIONS FOR PARTICLE COAGULATION IN THE OCEAN

The rate at which suspended particles in the ocean coagulate to form larger, more rapidly sinking aggregates is directly related to the frequency with which the particles stick together once they have collided. The attachment probabilities of marine macroscopic detrital aggregates, known as marine snow, were determined by video recording and analysing individual particle-particle interactions between 660 pairs of aggregates colliding together via gravitational settlement. Attachment probabilities of natural marine aggregates in the size range from 0.2 to 7.6 mm are the highest yet reported for natural particles, ranging from 0.60 (60% of collisions result in attachment) for amorphous detrital aggregates to 0.88 for flocculated diatoms. Attachment probabilities increase with increasing particle volume, surface area of contact and collision velocity. Large size and surface complexity resulting in multi-point contact between colliding particles and the abundance of sticky, microbially-produced exopolymers on the aggregate surfaces probably contribute to high aggregation efficiencies. The high attachment probabilities of suspended macroaggregates suggest that the rate of aggregation of organic particles by physical coagulation in the ocean may be many times higher than previously predicted.