Shelf Sea Processes

Shelf seas are arguably the most valuable biome on earth

Supporting rich biodiversity, capacity for carbon cycling & storage, ability to cycle and eliminate waste, as a recreation space, and potential for renewable energy

Take a deep dive into shelf seas…

  • Nutrients and organic matter enter the marine system through riverine inputs, direct run-off from land and atmospheric deposition.
  • Photosynthesis by phytoplankton (primary production) combines CO2 with inorganic nutrients (nitrate, phosphate, silicate, iron) to create organic compounds.
  • Coupling between the water column and seabed. Nutrients, carbon and contaminants are deposited from the overlying water column and either stored or recycled in marine sediments on the seafloor. The release of nutrients and iron from the seabed can stimulate water column productivity.
  • At the sea-surface, gases such as CO2 and O2 diffuse in and out, with exchanges controlled by concentration gradients, temperature and mixing processes. Water exchange occurs between shelf seas and the open ocean across the shelf-edge.
  • Nutrients, iron and carbon compounds are also transferred, both dissolved in the water column and through suspended sediment, including being transported off the shelf to the deep ocean.
  • The water column can be mixed or stratified, driven by tides, winds, and seasonal variations in temperature and freshwater inputs. These circulation processes in the water column interact with local geology and seafloor morphology to determine whether the seafloor is muddy, sandy or rocky, and whether sediments are eroding or accumulating, resulting in very different biological communities.
  • The seafloor is a mosaic of different habitats, from fine muds to coarse sands or boulders and rocks, with associated diverse biological communities. Heterogeneity exists from a micro-to macro scale across time and space.
  • Shelf sea sediments vary greatly with physical conditions, such as tidal currents and bed shear stress.
    • Muddy and sandy sediments support different faunal communities and differ in their biogeochemical processes, controls and rates – e.g. oxygen levels, nutrient cycling, acidity.
    • Seasonal cycles introduce patterns, modified by interannual differences.
    • Winds and tides introduce mixing events.

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