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The Habitable Planet: A Systems Approach to Environmental Science 


Oceans cover three-quarters of the Earth's surface, but many parts of the deep oceans have yet to be explored. Learn about the large-scale ocean circulation patterns that help to regulate temperatures and weather patterns on land, and the microscopic marine organisms that form the base of marine food webs.

Interactive Labs

Carbon Lab (Units 1-3, 13)

Throughout this course, the carbon cycle is featured as one of the most important planetary systems. This lab uses a robust model of the carbon cycle to give you an intuitive sense for how the system works.  It also allows you to experiment with how human inputs to the cycle might change global outcomes to the year 2100 and beyond. One especially relevant human impact is the increase in atmospheric CO2 levels. Between 1850 and today, atmospheric concentrations have risen from 287 ppm (parts per million) to over 380 ppm a level higher than any known on Earth in more than 30 million years (see Unit 12 to find out how scientists measure ancient atmospheric carbon levels). You will experiment with the human factors that contribute to this rise, and see how different inputs to the carbon cycle might affect concentrations of the greenhouse gas CO2.   launch lab


Unit 3: Oceans // Glossary

biological pump
The sum of a suite of biologically-mediated processes that transport carbon from the surface euphotic zone (the depth of the water that is exposed to sufficient sunlight for photosynthesis to occur) to the ocean’s interior.

A relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. Algal blooms may occur in freshwater or marine environments.

The upward force on an object produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object.

compensation depth
Depth at which light intensity reaches a level at which oxygen evolved from a photosynthesizing organism equals that consumed by its respiration.

compensation zone
The point at which there is just enough light for a plant to survive. At this point all the food produced by photosynthesis is used up by respiration. For aquatic plants, the compensation point is the depth of water at which there is just enough light to sustain life (deeper water = less light = less photosynthesis).

Coriolis force
The apparent force, resulting from the rotation of the Earth, that deflects air or water movement.

Ekman transport
The change in wind direction with altitude caused by the varying effect of surface friction.

El Niño Southern Oscillation (ENSO)
A global event arising from large-scale interactions between the ocean and the atmosphere, usually an oscillation in the surface pressure (atmospheric mass) between the southeastern tropical Pacific and the Australian-Indonesian regions.

A large group of amoeboid protists with reticulating pseudopods—fine strands of cytoplasm that branch and merge to form a dynamic net. They typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure.

A circular or spiral motion, especially a circular ocean current.

Hadley circulation
A general circulation pattern in which air rises near the equator, flows north and south away from the equator at high altitudes, sinks near the poles, and flows back along the surface from both poles to the equator.

marine snow
The tiny leftovers of animals, plants, and non-living matter in the ocean’s sun-suffused upper zones. Among these particles are chains of single-celled plants called diatoms, shreds of zooplankters’ mucous food traps, soot, fecal pellets, dust motes, radioactive fallout, sand grains, pollen, and pollutants. Microorganisms also live inside and on top of these odd-shaped flakes.

North Atlantic Oscillation (NAO)
A major disturbance of the atmospheric circulation and climate of the North Atlantic-European region, linked to a waxing and waning of the dominant middle-latitude westerly wind flow during winter.The NAO Index is based on the pressure difference between various stations to the north (Iceland) and south (Azores) of the middle latitude westerly flow. It is, therefore, a measure of the strength of these winds.

Pacific Decadal Oscillation (PDO)
A pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of lat. 20° N. During a “warm” or “positive” phase, the west Pacific becomes cool and part of the eastern ocean warms; during a “cool” or “negative” phase, the opposite pattern occurs.

Microscopic plants that live in the water column of oceans, seas, and bodies of fresh water and are the foundation of the marine food chain.

specific heat capacity
The amount of heat, measured in calories, required to raise the temperature of one gram of a substance by one Celsius degree.

A layer within a body of water or air where the temperature changes rapidly with depth.The thermocline varies with latitude and season: it is permanent in the tropics, variable in the temperate climates (strongest during the summer), and weak to nonexistent in the polar regions, where the water column is cold from the surface to the bottom.

thermohaline circulation
The global density-driven circulation of the oceans.

An oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water.

Walker circulation
An atmospheric circulation of air at the equatorial Pacific Ocean, responsible for creating ocean upwelling off the coasts of Peru and Ecuador. This brings nutrient-rich cold water to the surface, increasing fishing stocks.

Microscopic animals that live in the water column of oceans, seas, and bodies of fresh water. The smallest zooplankton can be characterized as recyclers of water-column nutrients and often are closely tied to measures of nutrient enrichment. Larger zooplankton are important food for forage fish species and larval stages of all fish.

Series Directory

The Habitable Planet: A Systems Approach to Environmental Science 


Harvard Smithsonian Center for Astrophysics in association with the Harvard University Center for the Environment. 2007.
  • ISBN: 1-57680-883-1