Earth System Cycles - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Earth System Cycles

Any treatment of the Earth System needs to recognize the importance of water in developing and maintaining life. Refer to the diagram at the top of page 14-1 for a reminder of how water is partitioned among its environments in the oceans and on land.

On the rest of this page, we show several schematic or flow diagrams that give some indication of the intricately convolved chemical and biochemical components and areas (topics) of import to the major Earth Systems - singly or combined - as they persistently modify the processes acting within them. First to look at is the vital Water Cycle.

Water Cycle diagram.

This deceptively simple diagram is similar to those found in nearly all textbooks on Environmental Science, Physical Geology, and Meteorology. It shows the pattern of water leaving and returning to the Earth's surface. The process is cyclic in that, eventually, a water molecule leaving the ocean to enter the atmosphere ultimately returns to that source. The rates of movement and the quantities involved (often shown in more detailed diagrams) vary among the specific processes (and within a process this variation changes in place and time of year). But, in the long run, the cycle continues, such that the various amounts maintain an overall mass balance, neglecting losses to outer space and gains from meteorites.

One of the classic diagrams supporting Earth System Science relates fluid and biological Earth processes that operate between the Physical Climate system and the Biogeochemical system, receiving external energy inputs from the Sun and Earth's internal heat and being affected by human activities. We present a simplified version, known as the Bretherton Diagram, below.

Bretherton Diagram showing the processes operating between the physical climate system and the biogeochemical system.

We invite you to peruse this diagram to gain a feel for how these processes, driven by energy, climate, biogeochemistry, and human activities, interrelate.

The ultimate driver is solar energy (orders of magnitude greater than volcanic energy or the standard heat flow from the interior [mantle and crust; radioactive decay is the prime source). Estimates of energy in calories from the Sun during a full year (averaged daily over the rotational cycle) are around 13 x 1023 cal. per annum (or at any given second, 40 million billion calories/sec). Much of this energy is partioned into heating of the atmosphere, the oceans, and the land surface; most of the remainder is involved in plant photosynthesis.

Below, we summarize biogeochemical cycles, which depict the flow of important elements and compounds within the ecosystem as conveyed by biological and (geo)physical processes:

Biogeochemical Cycle diagram.

One of the key cycles is that of the migrating and locating of carbon. Other geochemical element-based cycles include oxygen, nitrogen, phosphorus, sulphur, and iron. The next diagram outlines the main constituents (carbon and its compounds), and where they reside at any time within the four spheres. We find carbon in the solid Earth mainly in limestones and in petroleum and gas deposits.

Carbon Cycle diagram.

Information on the mass balances within the carbon cycle has been obtained with fair reliability. We depict here the exchange of carbon, in units of 1015 g C yr-1, among the major reservoirs.

Schematic diagram indicating the flow or exchange of carbon among various reservoirs in the ocean and on the land

Carbon dioxide is a critical component in this cycle, being free in the atmosphere, dissolved in the oceans, integral in plant cells, and locked into sediments (limestones).

Because of the importance of this cycle, we recommend you visit this Carbon cycle site which reviews the fundamentals that affect this cyclical process.

Almost every important element within the Earth's spheres, and some of the more significant compounds (e.g., CO2, NO3, SO2) have been traced as they move through the systems. There are many geochemical cycles besides those just examined. Those of iron, calcium, phosphorus, sulphur and silicon are well-known. We show one more example: Oxygen.

The oxygen geochemical cycle.

Cycles, such as those shown above, have interconnected links and passages which influence their components. The process is called feedback. A positive feedback increases or enhances the process or activity. A negative feedback reduces or reverses the process. A good review of the feedback concept is found on this Wikipedia website.

Here is an example of feedback that is pertinent to global climate change. In Canada, parts of Europe, and Siberia, and elsewhere, there are large areas that contain peat bogs. These result from partial or inhibited decomposition of accumulations of vegetation, mainly in lakes and swamps. In the geologic past, complete vegetation decay could result in coal deposits. Peat bogs represent incomplete decay, usually under conditions in which colder temperatures are the norm. Peat bogs formed during glacial periods over the last few million years. But now, with the rapid increase in CO2 owing to human-related activities, such as auto exhaust or smoke from coal-burning plants, the average temperatures and temperature maxima are rising in part because of the greenhouse effect described on page 16-2. This is producing a positive feedback that affects the peat bogs by causing them to warm up and accelerate their decay. As a consequence, this will add signficant amounts of CO2 into the atmosphere, further exacerbating the rise in temperatures. One negative feedback from this will be the decrease in ice accumulation that means reduction or disappearance of glaciers and ice caps.

From the above, we sense that Earth System Science deals primarily with matters of climatology and atmospheric physics/chemistry, as influenced by essential interactions with the ocean reservoir, water partitioning on the land, biological intakes and effluents, and particles and gases released from volcanoes. Unlike Landsat and similar programs, the emphasis of Earth System Science and its supporting EOS programs has shifted from solid Earth and land use to the environment.

Accelerated global change is, by definition, a global problem. In addition, as we already noted with the example of the SO2 aerosol generated by Mount Pinatubo, what happens in any region of our planet may affect many other regions. How, then, do we address and keep checking on these global concerns?

As we shall see later in this Section, the entire field of Earth Systems Science is at the heart of a huge, multinational effort to use space platforms to monitor the Earth's atmosphere, oceans, biosphere, and active geosystems on the land. As part of that complex program, NASA has inaugurated a series of low cost, quick development satellite-based missions that go under the name Earth System Science Pathfinder (ESSP). Beginning in 2002, the hoped-for one to two launches per year will each be highly focused on a single problem. Each mission will be run by the organization that "wins" in the semi-annual Announcement of Opportunity. That organization (be it public or private) will be funded to design, manage, and interpret the mission program, with help from NASA. The first three missions selected are code-named GRACE, Calypso, and Cloudsat. These are described as part of the ESSP website.