Earth Science Questionnaire

Earth Science Questionnaire
Module Five Notes Lesson Goals  Explain the different components of the marine and terrestrial carbon cycle.  The Terrestrial Carbon Cycle  Photosynthesis  Originated 3 billion years ago and has become one of the most important processes on Earth, helping to make our planet habitable, in stark contrast to the other known planets.  Overview, Plants capture light energy and use it to split water molecules and then combine the products with Carbon Dioxide to make Carbohydrates, which are used for fuel and construction of plants; Oxygen is merely a byproduct. o 6CO2 + 6H2O -> C6H12O6 + 6O2 o Carbon Dioxide + Water -> Sugar + Oxygen  The process takes place in the chloroplasts located in the interior of leaves. Here, chlorophyll absorbs solar energy in the red and blue parts of the spectrum. This energy is used to split a water molecule into Hydrogen and Oxygen; in the process, the plants gain chemical energy that is used in a companion process that converts Carbon Dioxide into carbohydrates represented by C6H12O6 in the above equation.  The rate of consumption of CO2 by photosynthesis is mainly a function of water availability, temperature, the concentration of CO2 in the atmosphere, and key nutrients such as Nitrogen.  As a general rule, the rates of metabolic processes increase with temperature, but there is usually an upper limit where the high temperatures begin to destroy important enzymes, or otherwise inhibit life functions. This is beneficial to plants because with the greater concentration of CO2, they do not have to open their stomata very far, since they lose water doing so, this makes them more efficient as a whole. Interestingly, the photosynthesis process does have a limit and cannot increase forever.  Plant Respiration  Photosynthesis is like “making fuel”, if the fuel was Carbohydrates, and plant respiration can be thought of as the process of burning that fuel – using it for maintenance and growth.  Litter Fall  Dead materials enter the soil in two ways, it falls onto the surface as litter, and is contributed below the service from roots. The Carbon Flow of litter fall is roughly the difference between photosynthetic uptake of Carbon and the return of Carbon through plant respiration. If this were not the case, the size of the global land biota reservoir would be growing or declining, and although some regions are growing, others are shrinking, and they nearly balance out.  The relative importance of these two pathways into the soil varies according to the plants in an ecosystem, but it appears that the two are commonly about equal.  Soil Respiration  Also sometimes referred to as decay.  Occurs within the soil as microorganisms consume the dead plant material. In terms of a chemical formula, this process is the same as described for plant respiration (the reverse of photosynthesis).  Much of the organic material added to the litter or within the root zone each year is almost completely consumed by microbes, thus there is a reservoir of carbon with a very fast turnover time – on the order of 1 to 3 years in many cases.  The byproducts of this microbial consumption are CO2 and H2O and a variety of other compounds, and are collectively known as humus.  Humus is much less palatable to microbes and is not decomposed very quickly. It is produced at shallow levels within the soil and generally moves downward and accumulates in regions of the soil with high clay content. The microbes require Oxygen to decompose humus and thus the further down it goes, the less Oxygen that is available, the slower the decomposition. That is until the soil gets worked over and humus brought back up. Eventually, the humus will get destroyed and more CO2 is released. The humus then constitutes another, longer lived, reservoir of Carbon in the soil. Both the fast and slow decomposition processes lead to an average Carbon residence time of around 20 to 30 years for most soils.  These microbes are very sensitive to the organic Carbon content of the soil, temperature, and water content, respiring faster in areas of higher Carbon concentration, temperatures, and moister conditions.  Permafrost (an unknown)  In recent years, increasing attention has been paid to permafrost   soil Carbon since the Polar Regions have been warming much faster than the rest of the Globe. As the permafrost melts, Carbon that was added to these soils, will become available for microbes to respire and release into the atmosphere. Estimates vary, but a figure of 1,000 to 1,500 GT of Carbon reflects the current thinking, this is a huge amount of Carbon and has the potential to significantly alter the future atmosphere CO2 levels. As the permafrost begins to melt, some estimates are that it will contribute something in the range of 2-5 GT C/year, which is large compared to human-related changes. Of course, some of this Carbon will be offset by new Carbon sequestered into these formerly frozen soils, but the initial shock will exist as the system will not be in equilibrium and these regions can be expected to be a net exporter of CO2 into our atmosphere.  Runoff  Most of the Carbon loss from the soil reservoir occurs through  respiration, some Carbon is transported away by water running off over the soil surface. This runoff is eventually transported to the oceans by rivers. Most recent estimates place it at 0.6 GT C/year. The Marine Carbon Cycle  Although far less obvious to us, the cycling of Carbon in the oceans is tremendously important to the global Carbon Cycle. For example, oceans absorb a large portion of the CO2 emitted through anthropogenic activities.  Ocean-Atmospheric Exchange  The exchange of a gas like CO2 between the air and seawater is governed by the differences in concentrations. It is exchanged from areas of higher to lower concentrations.  Carbonate Chemistry of Seawater o When CO2 from the atmosphere comes into contact with seawater, it can become dissolved into the water where it undergoes chemical reactions to form a series or products: 1. CO2 (dissolved gas) + H20  H2CO3 (carbonic acid) 2. H2CO3 (carbonic acid)  H+ +HCO3- (hydrogen ion + bicarbonate) 3. HCO3-  H+ +CO3-2 o The amount of CO2 as dissolved gas is what controls the concentration of CO2. This concentration depends strongly  on the temperature – it is low in cold water and high in warm water, meaning that colder parts of the ocean absorb CO2 from the atmosphere and warm parts of the ocean release CO2. o Due to these reactions, you can find all of these different forms or species of inorganic Carbon co-existing, dissolved in seawater. In reality, bicarbonate (HCO3-) is the dominant form of inorganic Carbon. Carbonate (CO32-) and dissolved CO2 are important, but secondary. o The concentration of H+ (Hydrogen ion) in seawater is what determines the pH of the water, or in other words, its acidity. o The ratio of bicarbonate (HCO3) to carbonate (CO3) is proportional to the pH.  Lower pH (acidic)= more bicarbonate  More bicarbonate = dissolved CO2 also goes up and this tends to cause CO2 gas to move from the seawater to the atmosphere. o What controls this? When more carbonate (-2 charge) than bicarbonate (-1 charge), you have a more total negative charge.  The total amount of positive charge in the oceans that has to be canceled out by the carbonate and bicarbonate – called the alkalinity.  The total amount of dissolved organic carbon in the oceans (DIC for short). o If the alkalinity is high, the more of the DIC has to take the form of carbonate (-2 charge) and the pH is higher, meaning less acidic. If the total DIC is large, then to get the charges to balance, more of the DIC has to be in the form of bicarbonate (-1 charge), which leads to a lower pH and more acidic conditions. Why does the ocean’s CO2 concentration change more slowly than the atmosphere? o The reason for this is the carbon chemistry reactions that shift some of the CO2 dissolved gas into the forms of bicarbonate and carbonate – this reduces the amount of Carbon in the form of dissolved CO2 gas, so the concentration of dissolved CO2 does not increase as much as it would if these reactions did not take place.  o As it turns out, the chemistry of Carbon in seawater is complex but also extremely important in governing the way the global Carbon cycle operates and explains why the oceans can swallow up much more atmospheric CO2 without having their own CO2 concentrations rise very much. Marine Biota Exchange – The Biologic Pump  The surface waters of the world’s oceans are home to photosynthesizing phytoplankton at the base of the food chain. These plants utilize CO2 gas dissolved in seawater and turn it into organic matter, like land plants, they respire and return CO2 to surface waters.  Many planktonic organisms also extract dissolved carbonate ions from seawater to turn them into CaCO3 (calcium carbonate) shells. When they die, their shells are quickly decomposed, before settling out into deeper waters. This decomposition thus returns Carbon, in the form of CO2, to seawater.  However, some of the organic remains and the inorganic calcium carbonate shells will sink down into Deep Ocean thus transferring Carbon from the shallow surface into the huge reservoir of the deep ocean. This transfer is often referred to as the biologic pump, and causes the concentration of CO2 gas, and also DIC in surface water to be less than that of deep water.  Why is alkalinity reduced in the surface waters? o For the same reason that DIC is depleted. o Planktonic organisms make shells of CaCO3 and when these sink to the seafloor, they carry Ca2+ ions with them, thus reducing the alkalinity. o Much of the CaCO3 is later dissolved when it reaches the deeper parts of the oceans, which explains the higher alkalinity values in the deep water. o By controlling the concentration of CO2 in the surface waters, the planktonic organisms exert a strong influence on the concentration of CO2 in the atmosphere.  What controls the strength of the biologic pump? o The photosynthesizing plankton require nutrients in addition to CO2 in order to thrive; specifically Nitrogen and Phosphorus. Most of these plants need P, N, and C in a ratio of 1:16:125, and since at present the ratio of P to N in ocean water is about 1:16, both P and N limit the growth of these phytoplankton.     o In addition to nutrients, the biological pump is sensitive to the pH of the ocean water. The oceans are adapted to a pH of 8.3 – 8.4, but if the oceans take up too much CO2 too quickly, the pH will decrease out of the optimum range for oceanic organisms. Thus lower pH will probably mean a reduction in the strength of the biological pump, which will in turn limit the oceans ability to absorb more Carbon. Downwelling Upwelling Sedimentation Volcanism and Metamorphism  Recognize that atmospheric CO2 has changed through time and how that variation has impacted climate.  You need to travel back in time 2.5 million years to find CO2 concentrations as     high as they are at present. Up and Down cycles of CO2 concentration are normal throughout Earth’s history, however the more recent past cycles have varied in only about 80 ppm. Earth’s deep past, 2.5 million years ago, shows higher but similar CO2 concentrations than present but at this time, there was very little ice on Earth and the Arctic was 15 – 20° warmer than today. Sea levels were about 20 meters higher than present. Beyond that, before 30 million years ago, CO2 concentrations were tremendously higher than they are today. Sea levels were perhaps 100 meters greater than present and there was practically no ice on Earth. The key point here is that with greater CO2 concentration comes warmer temperatures which lead to less sea ice, which means higher sea levels.  Interpret how the carbon cycle impacts Earth’s climate.  Carbon naturally moves from place-to-place, from the atmosphere into plants,   into soil, back into the atmosphere; into the oceans, the sea floor, back to the oceans and the atmosphere. The Earth naturally attempts to return to a steady-state that is similar and steady amounts of Carbon moving from “place” to “place”. Inflow = Outflow. However, as humans continue to pump GHG into the atmosphere, we through the Earth out of this “steady state” and force it to make changes in order to return to a new steady-state. Unfortunately for us, the response time of this system is many thousands of years in the making and many changes, some rather unpleasant, will be made in the search for Earth’s new steady state.  Project through modeling how the amount and rate of future carbon emissions impact climate and the chemistry of the oceans. Learning Outcomes  Why is the global carbon cycle important to climate change? o The Global Carbon Cycle is a system, a system with a traditional balancing mechanism. Throwing this system out of balance by injecting massive amounts of atmospheric CO2 amplify the natural greenhouse effect and create further disruptions down the line that build upon themselves.  How humans have perturbed the global carbon cycle. o The Human Influences on the Global Carbon Cycle  Fossil Fuel Burning  Fuels created by the slow transformation of organic materials deposited in sedimentary rocks, the fossilized remains of marine and land plants.  Primarily Carbon and Hydrogen. Methane, the main component of natural gas, has a chemical formula of CH4; petroleum is a more complex compound, but it too involves carbon and hydrogen (along with nitrogen, sulfur, and other impurities).  The combustion of fossil fuels involves the use of Oxygen and the release of Carbon Dioxide and water. o CH4 + 2O2 -> CO2 + 2H20 o This flow is currently 9 Gt C/ year. Also includes the CO2 generated in production of cement, where limestone is burned, liberating CO2.  Land-Use Changes (Forest Burning and Soil Disruption)  When deforestation occurs, most of the plant matter is either left to decompose on the ground or it is burned, the latter being the more common occurrence.  This process reduces the size (mass) of the land biota reservoir and the burning adds Carbon to the atmosphere.  Land-use changes other than deforestation can also add Carbon, agriculture, for instance, involves tilling the soil, which leads to very rapid decomposition and oxidation of soil organic matter.  This means we are talking about two separate flows – one draining the land biota reservoir and the other draining the soil reservoir, both flows transfer Carbon to the atmosphere. o Current estimates are 2 – 3 Gt C/ year, with 70% – 50% forest burning and soil disruption the rest.  Changes in values of pCO2 since (1) 1900 and (2) the late 1950’s. o The pCO2 from 1900 to present day is approximately 280 – 380 ppm (+100) o The pCO2 from the late 1950’s to present is approximately 320 – 380 ppm (+60)  What is current pCO2 value? o The current pCO2 value is approximately 380 ppm.  The significance of the annual cycle in atmospheric CO2 concentrations. o Atmospheric CO2 fluctuates throughout the year based upon vegetation growing seasons. Photosynthesis is responsible for a large portion of CO 2 being pulled from the atmosphere for the plants uses. When the weather is colder and plants are not actively growing, their demand on atmospheric CO 2 diminishes. o If land masses and vegetation were spread evenly throughout the globe, this would not make much of an annual impact on CO2 concentrations. However, presently, most land masses and vegetation exist in the Northern Hemisphere. Thus, when the Northern Hemisphere goes into its winter season, photosynthesis slows or stops, CO2 that was previously being pulled from the atmosphere is no longer disturbed by this demand on CO2. o It is a significant enough effect that it was measured on the Mauna Loa survey taken in the late 1950’s.  Correlation of CO2 concentrations with glacial cycles. o The higher CO2 concentrations Earth has, the warmer the climate, the less ice that gets created. The less ice being created, the faster the glaciers melt, this increases the amount of organic matter available for microbes to decompose and further increases the CO2 concentration of the plant. o Looking back on Earth’s deep past, it has been much warmer than it is today, with next to no ice. Earth was a far different planet under those conditions than it is today and far less hospitable to life, much less human life.  Generally speaking, the volumes of the different carbon reservoirs. o o o o o o o o Atmosphere = 750 GT Land Biota = 610 GT Surface Oceans = 970 GT Ocean Biota = 3 GT Soil = 1,580 GT Deep Oceans = 38,000 GT Mantle Sedimentary Rock = 1,000,000 GT  The role of photosynthesis and CO2 fertilization. o Photosynthesis is a process whereby plants use atmospheric CO 2 and respire Oxygen o CO2 fertilization is a process whereby plants become more efficient at photosynthesis due to increased levels of and easy access to CO 2.  The role of respiration and permafrost. o As permafrost dissipates, more previously trapped Carbon is available for surface microbes to feed upon. Their feeding and subsequent respiration serve to increase the overall atmospheric CO2 concentration.  How sea air exchange works. o The exchange of a gas like CO2 between the air and seawater is governed by the differences in concentrations. It is exchanged from areas of higher to lower concentrations.  Marine carbonate chemistry. o As CO2 dissolves into sea water, it undergoes a number of chemical reactions to form different substances.  CO2 (dissolved gas) + H20  H2CO3 (carbonic acid)  H2CO3 (carbonic acid)  H+ +HCO3- (hydrogen ion + bicarbonate)  HCO3-  H+ +CO3-2 o The ratio of HCO3- to CO32- along with the water temperature determines the CO2 concentration of seawater and also the pH. o The temperature of the water also controls how much CO2 occurs in the form of dissolved gas, thus affecting the concentration of CO2 gas in seawater. o The alkalinity of sea water represents the positively-charged ions that need to be countered by negatively-charged carbonate and bicarbonate ions. o The concentration of the total dissolved inorganic carbon (DIC), along with the alkalinity, determines the ratio of HCO3- to CO32-, and thus the CO2 concentration of seawater. If we increase DIC without changing the alkalinity, then more carbon must be in the form of HCO3-, which increases both pH and the CO2 concentration of seawater. o The CO2 concentration of seawater, relative to the atmospheric CO2, determines whether the oceans absorb or release CO2. Currently the cold parts of the oceans absorb atmospheric CO2 and the warm regions of the oceans add CO2 to the atmosphere. o The ability of carbon to switch back and forth between these three forms means that only a portion of the CO2absorbed by the oceans will remain as CO2.  The biologic pump, upwelling, downwelling, and sedimentation and their role in the marine carbon cycle. o Biological Pump  The transfer of organic remains and inorganic calcium carbonate shells from shallow surface water to the huge reservoir of the deep ocean. It causes the concentration of CO2 gas, and also DIC in the surface waters to be less than that of the deep ocean. The planktonic organisms exert a strong influence on the concentration of CO2 in the atmosphere by controlling the concentration of CO2 dissolved in the surface waters.  For instance, if the biologic pump were turned off, atmospheric CO 2 would rise to about 500 ppm (up from 380 ppm now); if the pump were operating at maximum strength (i.e. complete utilization of nutrients), atmospheric CO2 would drop to a low of 140 ppm. o Upwe…
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