Environmental Change in Marine Systems
Introduction
1. Key features of the marine environment
Module 1 introduced the physical environment, particularly as it relates to the terrestrial environment. Most terrestrial organisms – animals, plants and others – are, obviously, surrounded by air for much of the time. In contrast, by definition, aquatic organisms are surrounded by water for much of the time. As "environments", air and water differ in some important ways; ways which can affect the biology of the organisms inhabiting them. Some organisms experience both kinds of environments at different times during their life, over short or long time-scales: for instance, frogs are aquatic as larvae but may be largely terrestrial as adults; organisms on the sea-shore are submerged and exposed as the tide rises and falls.
In the first part of the introduction, we examine key physical features of the marine environment.
The physical framework
F. P. Shepard – referred to by some as the "father of marine geology " – once famously wrote: "Man’s perpetual curiosity regarding the unknown has opened many frontiers. Among the last to yield to the advance of scientific exploration has been the ocean floor. Until recent years much more was known about the surface of the moon than about the vast areas that lie beneath three-fourths of the surface of our own planet.” (Submarine Geology, 1948, by F. P. Shepard. p. 1.) The readings below provide some general introductory information about the oceans and their biota.
Read some basic statistics on the oceans:
http://www.physicalgeography.net/fundamentals/8o.html.
Note: Approximately 71% of the world's surface is covered by oceans and these contain about 97% of the planet's water.
Examine the physiography of the ocean basins:
http://www.physicalgeography.net/fundamentals/10p.html.
Note: Most human activity in the oceans occurs in the shallow continental shelf surrounding the coast and this is the region which we will focus on in this unit.
In Australia, as in many other countries, most humans live near the coast. Read about how coasts are formed and their features.
The biota – animals, plants and others – inhabiting marine ecosystems can be classified on the basis of the physical features of the environment they inhabit. Read how the biota is classified on the basis of depth and other physical features: http://en.wikipedia.org/wiki/Ocean#Regions.
Note: In this module we will examine, as examples of marine ecosystems, mangrove forests, which are intertidal, and coral reefs, which are largely subtidal but are often partly intertidal.
Properties of water
Water is an unusual substance with unique properties. It is, of course, essential for life as we know it.
Read about some of the important properties of water:
http://www.physicalgeography.net/fundamentals/8a.html.
Note: Of particular importance are that it has high specific heat, high heat conductance and is a universal solvent. There is more information about its properties here: read the section on "Chemical and physical properties".
Read about salinity, and how it is defined and measured:
https://www.nature.com/scitable/knowledge/library/key-physical-variables-in-the-ocean-temperature-102805293/.
Note: The "obvious" idea that salinity is the amount of salt in the water is not incorrect but the situation is more complex than it may at first appear. Also, see here, where different terms referring to the salinity of a body of water are defined.
Read about how temperature in the oceans is defined and measured.
Note: information on sea temperature is now based on measurements with instruments (ship, buoy) and from satellites.
Read about how temperature and salinity vary around the oceans:
https://svs.gsfc.nasa.gov/3652.
Read about how the penetration of light through seawater varies with depth and location:
https://manoa.hawaii.edu/exploringourfluidearth/physical/ocean-depths/light-ocean.
Note: temperature (and salinity and water density) also varies with depth but the variation in light has important consequences for photosynthesis and marine food chains.
These physical and chemical properties affect marine organisms and biological and ecological processes. In the next section of this introduction to Module 4, Environmental Change in Marine Systems, we look at important differences between marine and terrestrial (and, to some extent, aquatic) environments.
References
The key sources for this first section are listed below.
Pidwirny, M. (2008) Fundamentals of Physical Geography (2nd Edition). Available on-line at http://www.physicalgeography.net/fundamentals/contents.html in HTML format.
Note: you can use the search engine with key words like ‘marine’, ‘marine and coastal’ etc. Some other search results may come up first but look for search results that include ‘www.physicalgeography.net › …’