Small Things Considered

Though seawater looks uniform to our eyes, it is actually highly heterogeneous, containing vast amounts of microscopic particles, fluctuating chemical and nutri-ent gradients, and 1 billion or so diverse microbial organisms per liter. Turbu-lence, diffusion, thermal mixing, and currents add to the patchiness of ocean water, churning and stirring molecular-sized resources. Near the coastal oceans and in estuaries, especially at higher lati-tudes that have distinct seasons, varying sources of dissolved organic compounds make microgradients even more pro-nounced: during times of high river discharge, a coastal environment can become inundated with resources from washed-out terrestrial matter, often leading to phytoplankton blooms.