Marine Microbial Processes at Interfaces: Cellular to Global Scales and Processes

The interface between regions of distinct characteristics are frequent sites of enhanced biological, biochemical, biophysical and phytochemical activities. The most commonly considered boundaries are between the ocean and atmosphere, ice and ocean, land and ocean, sediment and water, two water masses of different densities (i.e. pycnocline) or chemical properties (chemocline). Indeed physical, chemical, and biological processes at interfaces play important roles regulating material and energy flows in the Earth-Ocean System. For the World Ocean, a neglected yet potentially important interface is between free-living unicells and the environment. For example, heterotrophic bacteria, are ubiquitous and abundant (~1.2 x 10²⁹ cells) throughout the ocean, especially in the upper 200m (~3.6 x 10²⁸ cells). For cells with an average diameter of 0.8 µm, their surface area interface with the seawater environment is ~1.3 x 10¹⁷ m² for the global ocean and the is ~7.2 x 10¹⁶ m² for the upper 200m. Compared with the ocean-atmosphere interface of ~5.1 x 10¹⁴ m², this biological interface is over two orders of magnitude larger. The chemical, nutrient and gas exchanges that occur at the interface between unicells and the environment may be among the dominant interface process in the ocean and they need to be quantified and considered in order to understand the fluxes of gasses, material and energy in the World Ocean.