1.5: Chapter Summary

Introduction

The oceans influence our daily lives in many different ways. Understanding how they affect us requires an interdisciplinary approach that includes knowledge of the geology, physics, chemistry, and biology of the oceans and how these aspects interact.

Most of the world’s population lives near the oceans or a river that connects to the oceans. The oceans provide many resources, especially food and transportation corridors, but they are also susceptible to pollution, habitat damage, and other impacts of human activities. Recreational uses of the oceans and awareness of the unique nature of marine ecosystems and species have grown explosively in the past several decades.

The Oceans and Earth’s Environment

Humans have altered Earth’s environment in a number of ways. The most important of these has almost certainly been deforestation and use of fossil fuels that has raised the atmospheric concentration of carbon dioxide from about 280 ppm prior to the industrial revolution (ca. 1750) to nearly 430 ppm in 2025. The rate at which this concentration has risen has accelerated and is now about 2.6 ppm per year. The rise in atmospheric carbon dioxide, climate change, ocean acidification, and ocean deoxygenation, which together are the most serious long-term threats to Earth’s environment resulting from human activities. Each of these threatens to disrupt global ecosystems, and, when combined, they pose the risk of a mass extinction of species. Climate change also threatens to adversely impact humans directly in a number of ways, including increasing the severity and probably the rate of occurrence of extreme weather events, rising sea level, and increased coastal erosion. Climate is controlled by the atmosphere and oceans working together in complex ways, which will be explored in this text. Understanding these complex interactions is the key to understanding the oceans and the future of climate change, acidification, and deoxygenation.

Oceans and the Origins of Life.

Many organic compounds probably were formed in the early oceans, but it is not known how these simple compounds were combined into more complex molecules that formed the basis for the creation of the first life form. However, it is thought that early life was found predominantly in the oceans. The first life for which we have evidence was bacteria-like, existed about 4.2 billion years ago, and must have been chemosynthetic, as there was no oxygen in the early atmosphere. Eventually, microorganisms developed that used photosynthesis, which splits water into hydrogen (which is utilized by the organism in its metabolism) and oxygen (which is released). Between about 1 and 2 billion years ago, photosynthetic organisms added oxygen to the atmosphere until it reached its current concentration of about 20%. Chemosynthetic organisms either died out or were restricted to limited oxygen-free environments, and species developed that depended on respiration using oxygen from their environment. Today, all species of animals and most other species respire and need oxygen in their environment. The first primitive higher animals, invertebrates such as sponges, appeared about 700 million years ago. Fishes developed about 510 million years ago. The first land plants and mammals developed about 500 and 200 million years ago, respectively.

How to Study Ocean Data.

Maps and charts are used extensively to display ocean science data. Each graph, map, or chart may represent data in a different way using different distortions of the real world. Graphs may have axes that do not start at zero or are nonlinear. The choice of axis can substantially change how the same set of data is perceived at first glance.

Contour plots are used extensively to represent the distribution of properties on a two-dimensional surface, such as the Earth’s surface. If the intervals between contours on the contour plot are all the same, the relative distance between two contours is a measure of the gradient of the plotted property. However, on some maps, the contour interval changes from one area of the plot to another (usually to avoid crowding of contours), so the values of each contour must be examined to interpret gradients on the plot properly. Most contour plots in this text are color-shaded between the contours. Red always represents the highest value of the parameter plotted, grading through the spectrum to blue as the lowest value.

Maps and charts are used to represent horizontal distributions. Profiles are vertical cross sections through the Earth or the oceans and generally display contours to show the vertical distribution of properties. Most profile plots in this text are greatly vertically exaggerated. This exaggeration is necessary because the depth of the oceans, and the thickness of the Earth’s crust, are extremely small compared to the width of the oceans or land masses.

The Earth is spherical, and a system of latitude and longitude has been developed to identify specific locations on this sphere. Latitude is referenced to the equator, a circle around the Earth halfway between the poles, which is designated as 0° latitude. Other latitudes are expressed by the angle between a line from the Earth’s center to the location in question and a line from the Earth’s center to the equator. There are 90° of latitude; the North Pole is at 90°N and the South Pole at 90°S. Longitude is referenced to the prime meridian, a line designated as 0° that is drawn through the North and South Poles and that passes through Greenwich, England. Locations on the continuation of that same circle connecting the poles on the side of the Earth away from Greenwich are designated as both longitude 180°W and 180°E. Other longitudes lie between 0° and either 180°W or 180°E, and they are determined by the angle and direction between a line drawn between the Earth’s center and the prime meridian and a line between the Earth’s center and the specific location. One degree of latitude is the same distance regardless of its location on Earth. The distance represented by 1° of longitude varies from a maximum at the equator to zero at the poles.

Maps and charts must represent the spherical surface of the Earth or oceans in only two dimensions. No two-dimensional projection can correctly maintain relative distances, compass directions, relative areas, and the proper shape of features on a sphere. Therefore, all maps and charts distort one or more of these characteristics. The Mercator projection, which is the most widely used projection in atlases, depicts the distance between degrees of longitude as the same regardless of latitude. Thus, this projection preserves the relative directions between locations, but it distorts all three of the other relationships. The distortion is not important in regional maps of low latitudes, but it becomes greater at high latitudes and for global maps. Ocean scientists and this text use a variety of other projections for specific purposes. For example, Goode’s interrupted projection is often used because it generally preserves relative areas and distances, and it can be drawn to represent all the major oceans without having to split them at the edge of the map.

To represent very large or very small numbers, scientists use scientific notation based on powers of 10. A standard system of scientific units (SI) is now in place and is becoming more widely used, but it is not yet universal. Both scientific notation and SI units are used extensively in this text.

Key Terms

You should recognize and understand the meaning of all terms that are in boldface type in the text. All those terms are defined in the Glossary. The following are some less familiar key scientific terms that are used in this chapter and that are essential to know and be able to use in classroom discussions or exam answers.

acidification	isobar
bathymetric	isopycnal
chart	isotherm
chronometer	latitude
chemosynthetic	longitude
contour	photosynthetic
crust	phototroph
deoxygenation	phototrophic
detritus	pycnocline
fossil fuel	respiration
greenhouse effect	steady state
invertebrates	topographic

 

Study Questions

1. What causes the greenhouse effect?
2. Why weren’t the first living organisms capable of photosynthesis?
3. What are the essential things to look at the first time you study a graph?
4. What information can we get from studying a contour plot?
5. What is vertical exaggeration in a profile?
6. Are lines of longitude parallel to each other?
7. What are the four characteristics we would like a map projection to preserve?
8. On a Mercator projection map of the world, which countries or areas appear larger than they really are compared to other areas on the map?

Critical Thinking Questions

1. We are concerned that the Earth’s climate may change because of the increase in atmospheric carbon dioxide concentration that has resulted from human activities over the past century or more. It has been suggested that, since trees absorb carbon dioxide and release oxygen, we can solve the problem by replanting forests and planting many more trees in our urban areas. If we were to plant trees wherever they would grow on the entire planet, would this be enough to reverse the trend of increasing carbon dioxide concentration in the atmosphere? Explain the reasons for your answer. If you are not able to answer this question, what information would you need to do so?
2. A number of developing nations, especially those in Africa and South America, have suggested that world maps used in all textbooks and atlases should use a projection other than the Mercator projection. What do you think is their reason for this suggestion?