Oceanography, Essay Example

Describe the major ocean surface current patterns and discuss what produces these patterns. The major ocean surface current patters are complex, but they are driven by two main factors:  the rotation of the Earth, and the Sun.  The Sun can affect the ocean current patterns in two ways.  First of all, by heating up the atmosphere, it can create winds moving the sea’s surface by friction.  This drags the water surface along as the wind blows over.  The wind affects the ocean’s surface current patters, but it does not extend much below 100 meters, (325 feet) depth. (Schmitz 1996)

The second contributor is the effect of the Sun which alters the density of the ocean surface water by changing its temperature and or its salinity. When the water cools and or becomes saltier through evaporations it becoming denser.   This can make the water columns unstable and set up density-dependent currents call thermohaline circulation. Coriolis force affects the current as a result of the rotation of the earth. This makes the water moves right in the Northern Hemisphere, and left in the Southern.  At the equator there is a parcel of water that is moving at the same speed as the Earth.  If the current moves north without any friction, it will move faster than the Earth beneath it.  The current moves east to get farther from the equator, causing the Coriolis force increased away from the equator.

The strong small flows found in the Gulf Stream, East Australian, Agulhas, Brazil and Kuroshio currents flow at a speed of six miles per hour. These gyres are typical in the western side of the basin. The Western boundary currents are large.  The currents speed away from the western gyres is typically lower, and the eastern boundaries are much wider. The northern Indian Ocean is an exception; it has an atmospheric monsoonsystem that changes directions twice a year. There is an intense circular system that develops off of Somalia during the southwest monsoon. Doldrums are light winds that move the currents which would otherwise pile up against the western boundary of the ocean. In the thermocline, there is an eastward flowing undercurrent drive by horizontal pressure gradient.  This is found in the upper 200 meters of all three oceans.  However, their distribution may change seasonally based on the wind.

Compare and contrast the following types of waves: swells, breaking surf, and tsunamis. Be sure to include water depth, wavelength, wave speed, and causes. Swells, breaking surfs, and tsunamis are all forms of waves that take place in the ocean.  Swells are long-crested waves that symmetrically travel outside of their origin.  Swell waves with longer wavelengths travel faster, bypassing the slower shorter wavelength waves.  Storm systems from far sea approaching shore will cause swells to break.  This creates long low rolling surfs.  As the storm system gets closer to the shore, the swells are faster and higher containing crashing surfs and plunging breakers.   There are three main causes for swells, wind velocity, wind area, and duration. “During a typical open ocean winter storm, one could expect to see winds of 45-55 kts blowing over 600-1000 miles for 36 hours. In such a storm, the average highest wind waves (or ‘seas’) commonly reach 30-35 ft towards the center of the fetch area and produce a swell with a period of 17-20 seconds.” (Wave Basics)

There are three types of breaking surfs.  Spilling breakers are waves with low steepness.  This is a result of long period swell over mild slopes.  It causes rows of breakers to flow towards the beach.  Rips can move away from the beach back towards sear. They can be very strong, up to 8km/hr. The next type of breaker is plunging breakers.  These are a result of steeper waves over moderate slopes.  Some beaches are low towards low tide and steep towards high tide. This particular breaker is not swimmer friendly because of the intensity is greatly amplified by the backwash form its forerunner.    The last type of is a surging breakers.  This is where the slope of the beach exceeds the steepness of the ways.  The wave in turn does not really break it simply runs against the shore and creates larges water surges and foam. The true height of these waves is dependant on the wave length and period as well as the beach slope.  “It has been observed that a swell of 6-7m height in open sea, with a period of 21 seconds, rose to 16m height off Manihiki Atoll, Cooks Islands, on 2 June, 1967. Such swell could have arisen from a 60 knot storm.” (Anthoni 2000)

Tsunamis are a very long wave that usually is created by an earthquake or some other even that rapidly displaces a large amount of water.  This is not a normal wind-driven wave, this is an energy created by an event of water displacement.  When the wave strikes at local high tide, the land damage can be drastically more severe.  A subduction zone where geographic plates move under another plate, also known as a convergent boundary, is a scenario for generating a tsunami.  “Tsunami waves are distinguished from ordinary ocean waves by their great length between wave crests, often exceeding 100 km (60 miles ) or more in the deep ocean, and by the time between these crests, ranging from 10 minutes to an hour. As they reach the shallow waters of the coast, the waves slow down and the water can pile up into a wall of destruction tens of meters (30 ft) or more in height. Large tsunamis have been known to rise over 30 meters (100 ft).” (Great Waves)
3. Discuss how the tidal patterns vary depend on their location in the ocean? Provide specific geographic examples.

There are two main forces that cause tides, that is inertia and gravity.  These forces tied with geographic location and other factors can determine the tidal pattern.  These patterns are drastically different dependant of location.  Tidal currents are larger low wave forms of current.  These are in Open Ocean and are fairly weak; as they get closer to land they pick up speed drastically.   A tidal bore creates high wave, can be 10ft. or more with speeds of 9.3 miles per hour.  (Ross 2006)  In the Gulf of California or the Bay of Fundy in Nova Scotia the tidal patterns can reach 66ft.  This is because of the geometry of the area and their geographic position.  In other geographic locations, the tide may never reach such a magnitude or speed.

Another tidal pattern is a flood tide.  This is when the tide is rising and the water is coming in to the shore.  When the incoming water of a high-tide begins to fall or withdraw, this is called an ebb tide.  The Gulf of Mexico has a diurnal tide, which is one high tide and one low tide a day.   Most areas have two high tides and two low tides daily.  The U.S. West Coast typically has mixed tides.  The East Coast however, typically has semidiurnal tides.  An estuary tidal pattern is dependent upon its geographic location.  “With the variety of conditions across the Earth, each estuary displays a tidal pattern unique to its location.” (Niesen 1982) Other factors to consider are the ocean floor, shape of the coastline, and the depth of the water.   Local winds and any obstruction or restriction to water flow also is relevant in tidal patterns.
Discuss the differences in capabilities necessary for survival of marine organisms (larger than plankton) in the pelagic zone versus the benthic zone.

The marine organisms exist in two different zones; the pelagic zone which is the ocean water, and the benthic zone which is the seafloor.   The benthic is a very rich environment for marine organisms.  “Scientist now believe that up to 98 percent of all marine species are found in or near the ocean floor.  Most are organisms that burrow in the sand or mud, bore into or attached to rocks, live in shells, or simply move about the ocean floor.” (Science now 2011)  This includes fish that swim barely above the ocean floor.   No herbivores can survive in the deeper part of the ocean floor.

The upper part of the pelagic zone extends from the surface of the ocean to approximately 660 feet below.  This is where microscopic plants and algae live.  They use photosynthesis to provide food for themselves and then to the higher organisms. The primary consumers are the zooplankton, or microscopic animals.  They feed on phytoplankton and become food for larger animals.  Sardines, herring, tuna, other fish and swimming mammals and bonitos all survive off of zooplankton.  On top of the food chain is the toothed whale that survives off of all of the above.   The next region consists of a depth of 660 to 3000 feet below the ocean surface.  Many organisms spend daylight hours in this region, to avoid the damages of the sun, and then rise to the surface in the evening.  They can avoid predators during the day and still feed off of phytoplankton and zooplankton.  The marine organisms common in this region are squid, small fish and shellfish.   The organisms found below 3,000 feet are able to adapt to the 37 degree lightless environment.  The marine organisms that live at these levels typically feed off of each other.  They typically have large sharp teeth, expandable mouths and have a strategy for hunting their pray.
Describe at least three different threats to the marine ecosystem. For each threat, discuss its causes and potential solutions.

There are many potential threats to the marine ecosystem. In 1998 at the start of the United Nations International Year of the Ocean, more than 1,600 marine scientists and conservation biologists from 65 countries issued an unprecedented warning to the world’s governments and citizens that the sea is in trouble. The consensus is that destruction of marine biological diversity stems from five primary causes: (Panetta 2003)

1. overexploitation of species,
2. physical alteration of ecosystems,
3. pollution,
4. alien species from distant waters disrupting local food webs and

5. Global atmospheric change.

Overexploitations of species are when human usage or destruction outweighs the ability of that particular marine organism to reproduce.  Species that live in the ocean are hard to track in order to prevent overexploitation.  “This difficulty was observed in the near extinction of numerous whale species during the nineteenth and early twentieth centuries due to the unregulated harvest by multiple nations.” (B 2008)  Currently swordfish, tuna and stocks of cod are potentially at risk as well.  Potential solutions to overexploitations are to make informed decisions when purchasing seafood.  Support legislation for habitat protection and conservation of species.  And finally avoid participating in living habits that can potentially harm the marine organism.

Another marine ecosystem threat is pollution.  “Marine pollution includes a range of threats including from land-based sources, oil spills, untreated sewage, heavy siltation, eutrophication (nutrient enrichment), invasive species, persistent organic pollutants (POP’s), heavy metals from mine tailings and other sources, acidification, radioactive substances, marine litter, overfishing and destruction of coastal and marine habitats.” (McCook 1999, Nyström et al. 2000, Bellwood et al. 2004)  There are many things we can do to prevent pollution destruction to our marine ecosystem.  Personally, don’t participate.  If you can help clean up, than individuals should do what we can.  Don’t support companies or organizations that participate in any type of pollution.  And finally, support legislation to keep our marines clean in the event of a disaster like the BP oil spill.  This will allow for quick time recovery from the devastating pollution.

The final threat to the marine ecosystem is the global atmospheric change.   A major cause of this is greenhouse gases.  This will cause sea levels to rise drastically.  However the global rise in temperature that goes along with this could be devastating to many organisms.   Potential solutions include the governments involvement raise awareness as well as prevent additional damages.  There should be laws created to prevented CFC gases and to slowdown the rate of ozone depletion.  And finally we can individually reduce our energy consumption, reducing the amount of fossil fuel being burnt.

References

Anthoni, Dr J. Floor (2000) Oceanography: wave’s theory and principles of waves, how they work and what causes them.  Retrieved from: www.seafriends.org.nz/oceano/waves.htm

B, Jennifer.  (2008) Human Causes of Extinction and overexploitation. Retrieved from: http://www.brighthub.com/environment/science-environmental/articles/11285.aspx

McCook, L.J. 1999 Macroalgae, nutrients and phase shifts on coral reefs: scientific issues and management consequences for the Great Barrier Reef. Coral Reefs 18: 357-367

Niesen, T.M. 1982. The Marine Biology Coloring Book. New York: HarperCollins Publishers.

Panetta, Leon. (2003) The Pew Ocean Commission.  Retrieved from: http://www.pewtrusts.org/our_work_detail.aspx?id=130

Ross, David.  (2006)  What are Tides? Retreived from: http://www.whoi.edu/page.do?pid=11926&tid=282&cid=15406

Schmitz, William J. (1996) On the World Ocean Circulation , Vols I and II. Woods Hole Oceanographic Institution Technical Reports WHOI 96-03 and 96-08M. Woods Hole, MA.

Science Clarified. (2011) Retrieved from: http://www.scienceclarified.com/Mu-Oi/Ocean-Zones.html

The Great Waves, a brochure about tsunamis from the National Oceanic and Atmospheric Administration.  Retrieved from: http://www.prh.noaa.gov/pr/hq/itic/library/pubs/great_waves/tsunami_great_waves_1.html

Wave Basics.  Retrieved from: http://www.stormsurf.com/page2/tutorials/wavebasics.shtml