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Seamounts

Seamounts are undersea mountains. They rise steeply from the sea floor and peak below sea level. Seamounts are found in all the world's oceans. By definition, they have an elevation of more than 1000 m. They may have very steep slopes with a gradient angle of up to 60° and their summit surface area is relatively small. Seamounts are usually relatively resistant to forces of erosion because they are generally formed in volcanic processes, and therefore mainly consist of hard substrates.

  • Seamounts - unique ecosytems - Oases of the Oceans
  • "What factors are responsible for the abundance of life over seamounts?" Hubbs (1959)

The image to the right is a schematic diagram of the Great and Smalle Meteor Seamounts. (click to access a larger image)
 
While the fact that individual seamounts are generally very different in terms latitude, location with respect to ocean currents, local current patterns, proximity to other major geological features, as well as individual characteristics such as height, steepness, type of top etc., there are some common features. Paramount among these is that there seems to be more life in the oceans around seamounts. Researchers Uwe Piatkowski and Klaus von Bröckel from the Institute for Marine Research at the University of Kiel, have described seamounts as being "oases" for life in the oceans. Just why this is so, is not yet fully understood, but researchers from many nations are making some interesting discoveries.


Model showing flow between the most important links between an open ocean and a seamount ecosystem. click for larger image
Seamounts dramatically change the topography of the ocean floor. As such they induce local current patterns, which may, in turn, be responsible for increased biological production in these areas. Local upwellings bring up nutrients from the deep ocean. This enhances primary production in the area above the seamount. The seamounts also have effects on the prevailing ocean current systems, and this too may result in increasing the supply of nutrients to the waters around the seamount. The resulting increased primary production, in turn, supports more organisms at each successive level of the food chain in these waters.

Another factor that is different from "open" ocean communities is that the normal up and down, diurnal, water-column migrations, which are a common feature of ocean communities, are complicated around seamounts. Drifting and current action may move populations from beside the seamount to over it. If this happens during the upwards, night-time migration, many animals will thus be cut off from being able to "retreat" downwards to greater depths during the day. As a result bottom- and near bottom-dwelling organisms, living on the tops of seamount, will have more feeding opportunities. This will also have effects on the food chain in these areas.
 
It was hypothesised that seamount systems might form "stepping stones" for individuals from coastal populations. Early results from some genetic studies, however, are indicating that many seamounts have distinct, stable populations, which live out all of their life stages in the seamount waters. Thus each seamount could be considered as an isolated, unique ecosystem. This isolation and uniqueness has some important ramifications for plans to exploit the biological resources of any given seamount. If it is true that the populations continually "re-stock" themselves from coastal populations (the "stepping stone" hypothesis), then fisheries might be more sustainable, than if the case is otherwise. More studies are needed. (read a Russian report on seamount fisheries)

In order to learn more about the eastern Atlantic seamount system in particular (link to Atlantic map), Piatkowski and von Bröckel from the Institute for Marine Research at the University of Kiel propose the undertaking of two kinds of studies. The first would be large-scale efforts using a series of ocean research cruises, which would address the seamount system as a whole. The aim of such studies would be to develop a general model of seamount ecology. This would be combined with the second kind of study, a series of smaller, more specialised efforts that could involve mooring data-collecting probes, which would focus on individual seamounts.

The questions the researchers would like to address include:

  • physical oceanography: recording environmental parameters to identify upwelling events, Taylor columns, wave and local current patterns, and even tidal effects.
  • bio-geo-chemistry, microbiology, plankton (primary production forces): measuring parameters that will provide a picture of the nutrient fluxes and plankton communities, primary production and sedimentation processes
  • assessments of stock levels of fish and studies of colonisation, life-history, stability etc.
  • nekton and top predators assessments, occurrence and feeding behaviour of birds, migratory patterns etc.

*written with help from Uwe Piatkowski and Klaus von Bröckel from the Institute for Marine Research at the University of Kiel Research Division of Marine Ecology (see their web site - in German)

More on seamounts

Seamount online

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