Ecology: the Biology of Interactions. 2.05. Energy Sources for BGC Cycles

Ukrainian language (latest version) / Russian language (updates discontinued)

2.04. Biogeochemical Cycles

D. Shabanov, M. Kravchenko. Ecology: the Biology of Interactions Chapter 2. Biospherology

2.06. The Biogeochemical Cycle of Carbon

2.05. Energy Sources for BGC Cycles We find no vestige of a beginning, and no prospect of an end. James Hutton The movement of elements in the biosphere is sustained by three main energy sources (“drive belts” for BGC cycles): — the energy of the Sun, transformed by the hydrosphere and atmosphere in the hydrological cycle (Fig. 2.5.1); — the energy of the Sun, stored in organic substances during photosynthesis (Fig. 2.5.2); — chthonic energy, that is, the maternal energy of the Earth; thanks to it, the movement of tectonic plates and volcanism sustain the cycle of rock transformation and lift material from the Earth’s interior to where it becomes accessible to water, wind, and biological erosion (Fig. 2.5.3). Let us consider these “drive belts” in more detail. The hydrological cycle. Solar rays heat the Earth’s surface (Fig. 2.5.1). Part of their energy is spent on evaporation of water, and another part on heating the air. Uneven heating of air masses causes their circulation. Air masses formed above the oceans and rich in water vapor are carried by winds over the continents. Falling as precipitation, water returns to the oceans through rivers and groundwater. This movement of water fluxes ensures the destruction of rocks (water erosion) and the transport of significant amounts of matter to the oceans. [IMG_1] Fig. 2.5.1. The global hydrological cycle (water cycle in nature). Numbers are geograms (10^20 g); for pools, average values; for fluxes, per year The hydrological cycle transforms far more energy than is stored during photosynthesis. In fact, the diagram shown is designed for an equilibrium situation and does not correspond to the current state of affairs, because at present humans withdraw water from underground reservoirs substantially faster than those reservoirs are replenished by natural processes. The biogenic cycle. The most important process that accumulates energy in the biosphere in a form available to living organisms is photosynthesis. Thanks to it, inorganic nutrients available to plants are assimilated into primary production (plant biomass, Fig. 2.5.2). In a number of ecosystems, a similar role is played by bacterial and archaeal chemosynthesis. The energy stored in the organic substances of producers is transferred to heterotrophic organisms, sustaining their vital activity. Chemical reactions in living organisms and their transport of diverse substances, proceeding at the expense of the energy accumulated during photosynthesis, are one of the “drive belts” of BGC cycles. [IMG_2] Fig. 2.5.2. The main biological processes driving BGC cycles We use the term “chthonic energy” to denote the energy of the Earth’s interior, the maternal energy of the Earth. The word itself derives from one of Gaia’s epithets, Chthonia. In mythology, chthonic deities (and, more broadly, chthonic beings) are forces personifying the natural power of the Earth. Chthonic energy drives the cycle of rock transformation, which is a consequence of plate tectonics (more broadly, lithospheric activity). The pioneer in the study of lithospheric plate tectonics (Greek tektonike, the art of building) was the German meteorologist Alfred Wegener, who proposed the hypothesis of continental drift in 1915. His contemporaries ridiculed the idea, but new data obtained in the mid-twentieth century unexpectedly forced scientists to return to it. It is now known that, contrary to Wegener’s original view, what move are not the continents but lithospheric plates on which the continents are located. Data from studies of the ocean floor showed that new crust is formed at mid-ocean ridges and spreads away from them in both directions, carrying the continents upon it. About a dozen major plates and a larger number of smaller ones are distinguished; their rate of movement is from 1 to 20 cm per year. Where plates collide, one begins to descend beneath the other, lifting it upward. Rocks can be divided into sedimentary, metamorphosed, and igneous. Sedimentary rocks form at the bottoms of water bodies. Because of plate tectonics, water-rich sedimentary rocks sink to depth, into zones of high pressure and temperature. There they become metamorphosed rocks. The presence of water lowers the melting point of rocks, and active volcanism is observed in such places. Stresses arising in rocks are released by earthquakes. Volcanism lifts molten rocks in the form of magma; as a result, igneous rocks are formed. In addition, plate tectonics brings metamorphosed rocks to the surface. The uplift of rocks through mountain building and volcanism leads to their weathering; the elements they contain become available again to organisms living at the planet’s surface (Fig. 2.5.3). [IMG_3] Fig. 2.5.3. The rock transformation cycle. Numbers are geograms (10^20 g) per million years. Continents are granite blocks overlain by sediments and resting above a basalt layer. Continental crust is thicker than oceanic crust and floats in the viscous mantle. Rock uplift occurs through volcanic activity and mountain building during continental collision Thus, the sedimentary cycle is the movement of biogens from living matter into sedimentary rocks formed on the ocean floor, followed by their uplift above sea level owing to plate tectonics and volcanism, and then by the weathering of biogens and their re-entry into living matter. Additional materials: Educational model: The hydrological cycle Educational model: Plate tectonics Educational model: Energy sources for BGC cycles, using the phosphorus cycle as an example Column: A Diet Without Phosphorus? Ukrainian / Russian 2.04. Biogeochemical Cycles

D. Shabanov, M. Kravchenko. Ecology: the Biology of Interactions Chapter 2. Biospherology

2.06. The Biogeochemical Cycle of Carbon

2.06. Biogeochemical Cycle of Carbon