The ocean is central to the global carbon cycle and helps mitigate the greenhouse effect. Quantifying the processes that alter the form and abundance of carbon in the ocean are important for understanding and predicting global climate change. Most of the organic carbon which becomes sequestered in deep sea sediments, thus removing it for long periods from the global carbon cycle, sinks as large aggregates of detritus, algae and fecal matter > 0.5 mm in diameter, known as marine snow because of their resemblance to a snow storm.

Dr. Alice Alldredge and her graduate student, Lisa Dilling, recently discovered a new process that may be very important in governing the quantity of sinking carbon that can reach the ocean floor. They discovered that krill, shrimp like animals that migrate from deep water in the day time up to the surface every night to feed, actually fragmented break up marine snow as they swim near these sinking aggregates.

Fragmentation of marine snow occurs primarily at night in surface waters, producing very low abundances of big particles at night. In the daytime big aggregates reform and marine snow is much more abundant.

This diurnal pattern in the abundance of marine snow results in reduced sinking of carbon at night and a pulsed delivery of food to the animals on the seafloor.

Disaggregation of marine snow by swimming and migrating animals may alter the sizes of particles available to grazers and bacteria and reduce the amount of sedimenting particulate carbon by generating smaller particles that potentially sink more slowly and reside longer in the water column. This newly discovered process reduces carbon sedimentation and provides a previously unconsidered link between animal behavior and the biogeochemistry of the sea. It may help explain the exponential reduction in particle flux with depth observed in parts of the ocean and help balance oceanic carbon models.