Thursday, November 20, 2014

It's winter! Marine snow?

Six feet in 24 hours: that was the unfortunate high rate of snowfall in Buffalo, New York, on the shore of Lake Erie on Tuesday, 11/18/2014. Even for a region used to very snowy winters, that was excessive and paralyzing.

Six meters in a million years. That is the accumulation rate for "marine snow". Marine snow, according to the National Oceanic and Atmospheric Administration (NOAA) informational webpage on the subject (, is the shower of organic matter falling from upper marine waters to the ocean bottom. The "snow" consists of fluffy agglomerations of generally structureless decaying organic matter, the microbes feasting on it, clay particles, dust, tiny plankton shell pieces. The "flakes" may get to several centimeters. The organic matter may be consumed or depleted before it settles on the bottom, or may accumulate and be a food source at the seafloor. The NOAA page says that 3/4 of the seafloor may be covered with an accumulated organic ooze from marine snow deposition.
One-centimeter aquatic snow aggregate, Lake Constance, Germany.
Microbes consume organic matter in marine snow and release carbon dioxide, so the velocity of settling affects exposure time and has a direct impact on the amount of CO2 released back to the ocean. The amount and type of particulates in the snow affect the density of a clump and its settling rate. In Proceedings of the National Academy of Sciences in 2010, Kindler and others ( conclude that the highly porous marine snow (~95% water) may stall during their journey to the bottom when increasing water density halts settling. When diffusion eventually replaces the less dense water from shallower depths within the flakes with denser water, the agglomerations resume their journey to the bottom.
Besides its importance in the ocean carbon cycle, the amorphous organic matter (AOM) in marine snow is a great petroleum precursor. If preserved, due to low or zero oxygen in ocean floor sediments or overlying waters, and buried to a few km or more, the AOM will start producing liquid hydrocarbons. A good description of amorphous organic matter and various formation pathways, modern and ancient, is found in the 1995 text "Sedimentary Organic Matter" by R. V. Tyson. Pacton and others (2011; describe the structures and process of formation of amorphous organic matter at the sediment/water interface.

No comments:

Post a Comment