Intro to Oceans and Marine Biomes

                                          A Brief Introduction to Oceans and Marine Biomes

              It is hard to really get a handle on exactly how large the oceans are and how much water is held in the ocean.  Oceans cover 71% of the earth’s surface: 80% of the Southern Hemisphere and 61% of the Northern Hemisphere.  The average depth of oceans is 3800 M.  Eighty four percent of water lies beneath 1825 M.

1. The Four Ocean Basins

            There are four major oceanic basins- the Atlantic, the Pacific, the Indian, and the Arctic.  Although we typically consider these oceans separately, the actually make up one large interconnected system. 

2. The Ocean Floor

The ocean floor occurs at different depths beneath the surface.  The continental shelf is an underwater extension of the continental land mass.   Although the continental shelf makes up only 8% of the seafloor, its relatively easy access makes it an important and valuable ecosystem.

The continental slope drops off at a sharp angle from the continental shelf starting at between 110 – 190 m and ending up at the abyssal plains at a depth of 2800 – 3700 m.

            Oceanic ridges consisting of undersea mountain ranges, such as the Mid Atlantic Ridge, make up 30% of ocean basin area. 

            Trenches, cut into the abyssal plains, range from 7000 m to over 11,000 m.  The deepest point in the ocean is the Marianas Trench at 11, 022 m.

3. Temperature and Light Penetration

Ocean temperatures are warmer near the equator than the poles and warmer at the surface that at depth.

Light penetration decreases with depth.  The depth of light penetration depends on turbidity, so light is able to penetrate deeper in clear tropical water.  The maximum depth for aquatic plant growth is around 190 m.

                                                                  

                                                                 Marine  Biomes

            The marine environment can be classified on the basis of three physical characteristics- light penetration, distance from shore and depth, and open water versus bottom.

            Light penetration.  The region of the ocean that receives light is known as the photic zone while the aphotic zone receives no light.

            Distance from the shore.  The intertidal zone is the region between high and low tides.  The neritic zone is the shallow region over the continental shelf (coral reefs are limited to this depth).  The oceanic zone consists of the deep water past the continental shelf.

            Estuaries

            Estuaries are found where freshwater streams or rivers merge with the ocean .  Estuaries are often bounded by mudflats or salt marshes.  Salinity can vary within an estuary both spatially and temporally (varies daily with the tides).  Nutrients added from the river makes estuaries one of the most productive ecosystems on the earth.

            Salt marshes are the dominant plant communities in estuaries in the temperate zone.  Salt marshes are dominated by grasses, but algae and phytoplankton add to the high rates of productivity. 

            In the tropics, mangroves (the mangal community) replaces salt marshes as the dominant estuary community.  Mangroves are important to coral reefs because they serve as nursery areas.

            Intertidal Zone

            The intertidal zone is found where the land meets the sea.  The intertidal zone is submerged and exposed to air.  Organisms that live in the intertidal zone are strongly influned by daily variation in water cover, temperature, nutrients, and wave action.  Intertidal communities may be found on either rocky or soft substrates.

            Soft substrate intertidal communities are found along beaches or mudflats.  The organisms that live here are mostly suspension feeders who live their lives buried in the sediments.

            The rocky intertidal community is highly vertically stratified, with organisms located in fairly distince zones.  Most intertidal organisms have adaptations that allow them to remain attached to the rocks.  Tide pools are important habitats in this community.

           

            Coral Reefs

           

            Coral reefs are found in the neritic zone in warm tropical waters (We will talk much more about them later).

            Oceanic Pelagic Ridge

            Oceanic pelagic ridge ecosystem is found far from shore.  Nutrient content is typically very low, although it can be extremely high in areas with upwellings.  Photosynthetic phytoplankton, found growing in the top 100 M, are responsible for about half of the photosynthetic activity on earth. 

            Benthos

            The benthos ecosystem is found on the ocean bottom below the neritic and pelagic zones.  Nutrients reach the sea floor through detritous.  

             Deep benthic communities found in the abyssal zone where it is constantly cold (3o C), with very high water pressure, and an absence of light can have fairly diverse invertebrate communities.

To Learn More

Ocean- http://www.eoearth.org/article/Ocean

Oceans- http://www.eoearth.org/topics/view/54325/

Water Properties: The Facts and Figures About Water- http://ga.water.usgs.gov/edu/waterproperties.html


Powerpoint Presentation

http://www.slideshare.net/MarkMcGinley/oceans-a-brief-introduction