Presentation on theme: "The Carbon Cycle The carbon cycle: exchange of carbon between various reservoirs within the earth system. The carbon cycle is a bio-geochemical cycle and."— Presentation transcript:
The Carbon Cycle The carbon cycle: exchange of carbon between various reservoirs within the earth system. The carbon cycle is a bio-geochemical cycle and since it involves the biosphere
stalactitestalactite cavecave CO 2 + H 2 O --> H 2 CO 3 CO2 + OH- --> CO3- Ca 2+ + 2 HCO 3 - --> Ca(HCO 3 ) 2 H 2 CO 3 + [CaCO 3 ] krist --> [Ca(HCO3) 2 ] solv Ca(HCO 3 ) 2 -> CaCO 3 + CO 2 + H 2 O
Photosynthetic carbon fixation and the flux of organic matter to depth, termed organic carbon pump, generates a CO 2 sink in the ocean. In contrast, calcium carbonate production and its transport to depth, referred to as the carbonate pump, releases CO 2 in the surface layer.
The marine biosphere operates like a 'biological pump'. In the sunlit uppermost 100 meters of the ocean, photosynthesis serves as a source of oxygen and a sink for carbon dioxide and nutrients like phosphorous. DIC and [H+] decrease, net consumption of CO2 in the upper layers, has to be balanced by inorganic carbon by transport Sink of CO2, pH decrease Organic carbon cycle pump
The marine biosphere is active only in those limited regions of the ocean where upwelling is bringing up nutrients from below. Once nutrients reach the sunlit upper layer of the ocean they are used up in a matter of days by explosive plankton blooms.
UPWELLINGS BRING NUTRIENTS TO THE SURFACE Like any other life form, phytoplankton requires nutrients to grow. In the ocean, those nutrients are often found in cold, deep water. Large phytoplankton blooms tend to coincide with natural phenomena that drive that nutrient rich water to the surface. The process is called upwelling, and it happens in a couple of different ways. The principle mechanism by which deep, cold, and nutrient rich water rises up through the water column can be found along the western coasts of the continents. Or, said more specifically, upwellings often take place along the eastern margins of oceanic basins. Here � s what � s happening: winds coming off principal land masses push surface layers of water away from the shore. Into the resulting wind-driven void deeper water underneath the surface layers rushes in toward the coast, bringing with it nutrients for life to bloom. Exceptions: Indian Ocean, monsoon related weather patterns, the ocean currents create coastal upwelling patterns. On the equator, water currents on either side of the hemispheric dividing line are generally moving in opposite directions again due to planetary rotation and the Coriolis effect. As those currents rush past each other they ostensibly "peel back" the surface of the ocean, creating a void for deeper water to rush in and take its place.
Dissolution of mineral calcite (and aragonite): Mineral calcium carbonate shells Shells sink and eventually dissolve, either in the water column or in the sediments
Calcification: Some marine organisms combine calcium with bicarbonate ions to make calcareous shells or skeletons CO 2 balance of calcification: Calcification produces CO 2 ! Ca 2+ + 2 HCO 3- = CaCO 3 + H 2 O + CO 2 Oceanic blooms of coccolithophorids and production of coral reefs DO NOT help decreasing the atmospheric increase in CO 2
Biological Pump(s) The ocean plays a major role in the global carbon cycle, exchanging CO 2 with the overlying atmosphere. Uptake of atmospheric CO 2 by the oceans is driven by physicochemical processes as well as biological fixation of inorganic carbon species. The biogenic production of organic material and carbonate minerals in the surface ocean and their subsequent transport to depth are termed the "biological carbon pumps".
Dissolution of calcium carbonate Dissolution of calcium carbonate in seawater is influenced by three major factors: temperature, pressure and partial pressure of carbon dioxide (CO2). The easiest way to understand calcium carbonate (CaCO3) dissolution is to recognize that it is controlled, in large part, by the solubility of CO2: CaCO3 + H20 + CO2 Ca++ + 2HCO3- The more CO2 that can be held in solution, the more CaCO3 that will dissolve. Since more CO2 can be held in solution at higher pressures and cooler temperatures, CaCO3 is more soluble in the deep ocean than in surface waters. Finally, as CO2 is added to the water, more CaCO3 can dissolve. The result is that, as more CO2 is added to deep ocean water by the respiration of organisms, the more corrosive the bottom water becomes to calcareous shells.
The depth at which surface production of CaCO3 equals dissolution is called the calcium carbonate compensation depth (CCD). Above this depth, carbonate oozes can accumulate, below the CCD only terrigenous sediments, oceanic clays, or siliceous oozes can accumulate.calcium carbonate compensation depth The calcium carbonate compensation depth beneath the temperate and tropical Atlantic is approximately 5,000 m deep, while in the Pacific, it is shallower, about 4,200-4,500 m, except beneath the equatorial upwelling zone, where the CCD is about 5,000 m. The CCD in the Indian Ocean is intermediate between the Atlantic and the Pacific. The CCD is relatively shallow in high latitudes. Ooze=Schlamm
The long term organic carbon cycle Only a tiny fraction of the organic material that is generated by photosynthesis each year escapes the decay process by being buried and ultimately incorporated into fossil fuel deposits or sediments containing more dilute fragments of organic material. Through this slow process, carbon from both terrestrial and marine biosphere reservoirs enters into the long term organic carbon cycle. Weathering releases carbon back into the other reservoirs.
Carbonates (H20, CO2 and Rocks) Carbonates are chemical weathering products of volcanic rocks Carbonate form in aqueous environments Carbonates decompose at high temperatures Urey Reaction: MgCaSi 2 O 6 + 2CO 2 + 2H 2 O = MgCO 3 + CaCO 3 + 2SiO 2 + 2H 2 O Pyroxene (basalt) Carbonic Acid Carbonates Quartz Hot Cold (reconstitution) (weathering) Ideas: 1.Early climate of Mars was warm and wet, net carbonate formation decreased atmospheric CO2 over time, resulting in today’s cold climate 2.Present ~6.1 mbar atmospheric pressure is no coincidence, regulated by formation of carbonates in ephemeral liquid water environments Spectroscopic evidence for carbonates on surface, and some Mars meteorites: ~1% carbonate
New satellite sensors provide new ways of looking at Earth. In addition to measuring vegetation density, MODIS can also measure photosynthetic activity. An accurate estimate of the amount of carbon absorbed by plants. The image above shows photosynthetic activity during December 2000. (courtesy Peter Votava, Montana) High carbon consumption
The fist global image of the Earth’s biosphere was created by NASA scientists using ocean data from the Coastal Zone Color Scanner (CZCS) and land data from the Advanced Very High Resolution Radiometer (AVHRR). Altogether, the data took almost 8 years to compile. Current satellite instruments like the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) and can produce images like this roughly once a week. (Image courtesy NASA GSFC)