The kaleidoscope ocean

Oceanic plant life is dominated by the microscopic phytoplankton. Regardless of the scale at which they are observed, they display striking heterogeneity in their distribution. At their most dramatic they paint colourful swathes across whole seas. A short history of observations of phytoplankton 'patchiness' is presented, illustrated with some of the many ideas put forward to explain it. Focus is then turned to the mesoscale, covering scales of roughly 1-500 km. It is argued that the spatial variability seen in phytoplankton at these scales gives important information on the biogeochemistry of the ocean. In particular, interplay between the physical circulation and biological processes results in constantly shifting patterns that are strongly related to changes induced in phytoplankton production. It is thought that this physical influence may play a major role in controlling the rate at which new plant material (primary production) is generated in much of the world's oceans. Major questions yet to be addressed are also discussed including the difficulty of quantifying processes on the very limit of what we can model or observe and how these processes may change in response to and exert a feedback on future climate change.