Examples of the lithosphere contributing to the biogeochemical cycles would include continental drift and vulcanism. Continental drift can be seen in: divergence; such as sea floor spreading (where the continental plates are spreading and new mantle is being built) or rifting (as seen on land margins); subduction (where the heavier oceanic plate is sinking beneath the lighter lithospheric plate); and transformation (where two plates move in opposite directions past each other.) Divergence and subduction are significant for the biogeochemical cycle as they make and destroy mantle thus changing the materials accessible for other processes.
The most spectacular instance of the lithosphere contributing to the biogeochemical cycle would be vulcanism. Volcanoes differ in their size, impact and composition. They can eject massive amounts of ash, gas and vapour into the atmosphere. The gases in and of themselves can be deadly, there can be localised rain events and even acid rain, lahars or jokulhlaups, as illustrated in Figure 2, and if the volcanic plume carries significant amounts of material into the stratosphere the jets stream can carry material around the globe (Kemp 1994: 105-106), reflecting the incoming solar radiation, resulting in ‘global dimming’, (Sturman and Tapper 2006: 474, 512) where the diminished levels of sunlight are such as to cause noticeable cooling at the ground level (Kemp 1994: 108).
Fig. 2: Volcanic Impact on the Global Environment (Wikipedia contributors 2006c)
As one example, Mt Pinatubo erupted in June 1991, killing hundreds and causing US$260 million worth of damage locally (Smith 2001: 114). Globally, the volcanic plume went more than 30 km into the atmosphere (Smith 2001: 158) and contributed to the very cool summer in New Zealand in 1992-1993 (Sturman and Tapper 2006: 415).
The atmosphere
The atmosphere is the mixture of gases, called air, enveloping our planet (Marshak and Prothero 2001: 611). The chemical components in air are “78% nitrogen (N2) and 21% oxygen (O2), with minor amounts (1% total) of argon, carbon dioxide (CO2), neon, methane, ozone, carbon monoxide, and sulphur dixode” (Marshak and Prothero 2001: 37). It provides a breathable atmosphere for the biosphere; plants, both aquatic and terrestrial, breath carbon dioxide and expel oxygen which is breathed by fauna who exhale carbon dioxide. Wind can move soils and erode rocks and form tornadoes. In conjunction with solar radiation and water, the atmosphere creates clouds, precipitation such as rain, snow and hail, and storm events such as cyclones or hurricanes.
A significant atmospheric process is the ozone cycle. Ozone (O3) is “a gas that absorbs harmful (short-wave length) radiation from the sun” (Marshak and Prothero 2001: 612) and is “essential component of the earth/atmosphere system because of its ability to protect the biosphere” (Kemp 2004: 361). Most ozone (80%) is found at an altitude of around 25km (Sturman and Tapper 2006: 465), as illustrated in Figure 3.
Fig. 3: Ozone concentrations by altitude (Newman and NASA 2005b)
Ozone in the troposheric zone is considered to be a pollutant, which can irritate the eyes, harm the repiratory system and be harmful to plants (Kemp 2004: 361). Ozone is a naturally occurring compound, formed by a two-step reaction:
(1) O2 + energy (from the sun) -> 2O (2 oxygen atoms that are not bonded together);
(2) O2 + O -> O3
(Marshak and Prothero 2001: 612)
Ozone is also created by lightning in the troposphere, and is destroyed by naturally occuring chemical compounds (Kemp 2004: 363).
The biosphere
The biosphere, or ecosphere, is the band “a few kilometres above and a few kilometres below [the surface of Earth]” (Marshak and Prothero 2001: 711) which contains all terrestrial life, and is “an interactive layer incorporating life on the Earth’s land and water surfaces plus organisms in the lowest part of the atmosphere and the upper part of the soil and water layers” (Kemp 2004: 408). It took photosynthetic organisms (cyanobacteria) millions of years to break down volcanic gases and release oxygen, making possible the evolution of more complex, multicellular life-forms (Marshak and Prothero 2001: 612). Plants utilise nutrients in soil and rocks to grow, and when they die or are eaten these nutrients become available for the use of other organisms. Dead material which is deposited under select conditions (buried in an anaerobic environment) could over time become fossil fuel, such coal, oil or natural gas (Kemp 2004: 412). All life needs water to exist: “water is the most fundamental substance making life possible on our planet” (Clarke 1993: i), and humans have dammed rivers, altered their flows, and used water for industry and irrigation (Postel 1993: 22-23). At the moment there is a lot of discussion that the world should sustain biodiversity such as the World Commission on Environment and Development (since 1983) and the Rio Earth Summit (1992) (Kemp 2004: 143), at the same time as human interaction has caused the extinction of plant and animal species too numerous to list, possibly as many as 250,000 species a year (Kemp 2004: 248).
The hydrosphere
The hydrosphere is “that part of the Earth’s crust covered by water, both salt and fresh” (Kemp 2004: 413) including clouds, rivers, streams, springs, swamps, lakes and oceans. There are about 1360 million cubic kilometres of water on Earth (Clarke 1993: 8; Marshak and Prothero 2001: 479). If all the water in the world was liquid, the sea level would rise three kilometres (Clarke 1993: 8). More than 97% of all water is in the oceans, (Clarke 1993: 8) and most of the remaining three percent is locked up in ice caps and glaciers. The ‘cryosphere’ is the term given to this frozen water (Kemp 2004: 509), as illustrated in Figure 4, and which is where the freeze/ thaw cycle of water can break rock.
Fig 4: A Snapshot of the Cryosphere: Near Real-Time Daily Representation of Global Ice Concentration and Snow Extent (NSIDC 2006)
Roughly 126–127 thousand cubic kilometres is contained in lakes, rivers and streams (Clarke 1993: 8; Marshak and Prothero 2001: 479). Water inter-reacts with the three other spheres and can erode rock using onshore wave action or flood movement, transporting material as with moraines or lahars (Gomez et al. 2002: 217-222), warm or cool the atmosphere, and is essential to life.
The hydrological cycle
The hydrological cycle is “the movement of water from reservoir to reservoir… passing through both nonliving and living entities” (Marshak and Prothero 2001: 713). The hydrological cycle is significant because:
Water is present in the atmosphere in only miniscule amounts, but it plays an important role in the aquatic environment by providing the precipitation to replenish the groundwater and surface water reservoirs (Kemp 2004: 57).
Fig. 5: The Water Cycle (Wikipedia contributors 2006b)
The hydrological cycle is complex, with many possible paths, Figure 5 illustrates this showing various mechanisms for moving water between bodies, such as evaporation from the ocean, run-off into the ocean, transpiration into the atmosphere, subsurface flow and infiltration.
Global environmental change
Global environmental change is “the transformation or modification of both physical and biological components of the Earth system through time” (Marshak and Prothero 2001: 708). It is an ever-present and complex process (Kemp 2004: 465), it is not a human creation. It has taken 3.8 billion years for the global environment to change enough to support life on land. Global environmental change is a long-term process, although short term events may be noted in ones lifetime (Kemp 1994: 181), such as when wells in Canterbury that have never been dry before are drying up, or rivers running dry (Kent 2006: A17; Rodgers 2006: A17). Over time the polar ice caps and tropical rain forest have expanded and contracted (Marshak and Prothero 2001: 694), and the flora and fauna of the planet has changed accordingly (Kemp 2004: 76).
There have been numerous human impacts on global environmental change through the ages including ‘firestick farming,’ which saw the deforestation of large tracts as humans came into contact with pristine habitats (Flannery 2002: 222-223). Since the beginning of the industrial era, circa 1800, large volumes of sink materials have been released into the atmosphere and hydrosphere as by-products of mechanisation and urbanisation, as illustrated in Figure 6, exacerbated by the population growth which they have enabled (Kemp 2004: 125-128).
Fig 6. The Present Carbon Cycle, showing the annual 5.5 gigatons of fossil fuel emissions (UNEP 1996b)
Industrially produced aerosols have caused global dimming (Sturman and Tapper 2006: 474) and in many regions acid rain from sulphur dioxide and photochemical smog from nitrogen oxides or volatile organic compounds (Kemp 2004: 321). Currently the anthropogenic impacts of most concern are global warming and ozone depletion.
Global warming
Carbon dioxide in the atmosphere, along with water vapour, methane, and twenty other gases are responsible for the ‘greenhouse effect’ which is the term given to the capture of outgoing terrestrial radiation, and the subsequent retention of heat by the atmosphere, as illustrated in Figure 7. (Kemp 1994: 16).
Fig. 7: The Greenhouse Effect (UNEP 1996a)
The level of carbon dioxide in the atmosphere is increasing, as illustrated in Figure 8, as result of burning fossil fuels and tropical deforestation (Sturman and Tapper 2006: 20).
Fig. 8: The increasing global atmospheric concentrations of CO2 (UNEP 1999)
This has disrupted the equilibrium of the carbon cycle (Kemp 1994: 145) and global means surfaces temperatures have risen 0.6 +/-0.2 °C during the twentieth century (Sturman and Tapper 2006: 462-463), although significant temperature fluctuations have occurred in the past ten thousand years:
Before the human impact on the climatic environment was globally significant, and were caused by natural variability in the earth/atmosphere system. In contrast, modern global warming appears to have been initiated by human activities that have caused what at first sight seem to be relatively minor changes in the composition of the atmosphere. (Kemp 2004: 374).
The effects of global warming in the ocean and atmosphere are evidenced in more intense tropical storm activity (which is generated by the intense heat gathered from the ocean), melting of the polar caps and glaciers, (with a significant rise in sea level and associated decrease in salinity), and increased water scarcity, as in Africa (where 80 per cent of dry land now suffers from desertification (Smith 2001: 300) and water allocation is becoming more contested. (Sichingabula and Sikazwe 1999: 297)). One of the problems in predicting global warming is the limited data available (Sturman and Tapper 2006: 430).
The ozone hole
As mentioned earlier ozone keeps out ultraviolet radiation, and is necessary for life. The ‘ozone hole’ is a naturally occurring feature in the stratosphere over Antarctica which coincides with the Southern spring. As a result of the production of chlorofluorocarbons (CFCs) by human industrial processes, ozone is being destroyed at an accelerated rate, and the ozone hole has grown, as illustrated in Figure 9. Once scientists were aware of the existence of the ozone hole CFC production was curtailed, although there has not been sufficient time to observe if this is of benefit (Kemp 2004: 366-374).
Fig. 9: The Ozone Hole as at 4 October 2004 (Newman and NASA 2005a)
Conclusion
In this essay the Earth’s biogeochemical cycle has been assessed as a closed system that exists with finite resources. The parts of the biogeochemical cycle have been identified as the atmosphere, lithosphere, hydrosphere and biosphere; with these all these four parts inter-reacting, and the elements within them circulating in an ongoing, dynamic series of complex exchanges. Natural processes identified inside the biogeochemical cycle include vulcanism, the ozone cycle, the production of oxygen by biospheric organism, and the necessity of maintaining the water cycle due to the critical importance of fresh drinkable water, which is relatively scarce, for terrestrial life.
Global environmental change is the ongoing transformation over time of the worlds land surfaces; water, both in form and availability; the atmosphere, in terms of its chemical makeup, temperature fluctuations and climate change; and the responding flora and fauna adaptations. Changes in the biogeochemical cycle directly affect global environmental change, as illustrated in the increase in atmospheric carbon dioxide levels and subsequent warming, and ozone depletion. In the last two hundred year there has been a massive increase in the human impact on the global environment as a result of industrialisation and deforestation, disrupting the biogeochemical cycles, and on the basis of current trends human impact upon the process needs to be brought into check. It would seem that unless humans can become more bio-friendly global environmental change will accelerate. There will not be a biogeochemical cycle equilibrium conducive to habitation: there will not be sustainable growth for everyone, food for everyone and water for everyone as the biosphere could be devoid of life.
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