Module 2.pdf

Greenhouse gases: Carbon Dioxide ATMO 310/ OCN 310 September 16, 2024 Distribution of Carbon on Earth The deep and surface C reservoirs are not completely separate…… Deep C reservoirs: mantle and crust Surface C reservoirs Atmosphere, oceans, land Volcanic degassing Metamorphic degassing Rock weathering Subduction or deep burial of carbonates and organic C Pre-industrial values https://www.sciencenews.org/article/where-earth-stores-its-carbon Source : Suarez et al (2019). doi: 10.2138/gselements.15.5.301. Global Carbon Cycle- anthropogenic influence Anthropogenic CO2 emissions 2010-2019 Burning fossil fuels 9.4 ± 0.5 Pg C yr-1 (~85%) Land-use change 1.6 ± 0.7 Pg C yr-1 (~15%) Total C released since 1750: 700 ± 75 Pg C Friedlingstein et al. (2020). Earth Syst. Sci. Data, 12, 3269–3340 https://doi.org/10.5194/essd-12-3269-2020 Anthropogenic CO2 emissions Total C released since 1750: 700 ± 75Pg C 46 % 31 % 23 % Friedlingstein et al. (2020) Seasonal fluctuations in atmospheric CO2 driven by land vegetation https://www.youtube.com/watch?v=x1SgmFa0r04 World’s forests net change growth loss The world’s forest area is decreasing, but the rate of loss has slowed (due to reduction in deforestation in some countries and forest expansions in others) Source: FAO. 2020. Global Forests Resources Assessment Earth’s Mean Energy Budget The Earth’s energy budget and climate change Since at least 1970, there has been a persistent imbalance in the energy flow that has led to excess energy being absorbed by different components of the climate system T/F: Incoming radiation is characterized by short wavelengths and outgoing radiation is characterized by long wavelengths. Energy balance summary Earth receives shortwave radiation from the sun, ~30% is reflected back into space (albedo), the remaining is absorbed by the atmosphere and the Earth’s surface Earth absorbs energy from the sun as well as energy re-emitted back towards the Earth by greenhouse gases Earth radiates long wave radiation to balance the energy inflow Greenhouse gases absorb and re-emit long-wave energy emitted by the Earth, warming the planet With no greenhouse gases the temperature of the planet would be -18 C or 0 F Due to the increase in greenhouse gases the planet is currently out of balance, with energy inflow exceeding outflow Composition of Earth's atmosphere Composition of Earth’s atmosphere The major constituents in our excluding water vapor atmosphere: N2, O2, and Ar are NOT greenhouse gases Greenhouse gases absorb and emit radiation within the thermal IR range Most important greenhouse gases: Water vapor (H2O) Carbon dioxide (CO2) Methane (CH4) Ozone (O3) Nitrous oxide (N2O) In addition to the gases, aerosols are also in the atmosphere and are important for Earth’s energy balance Changes in radiative forcing due to humans activities Effective radiative forcing =energy gained or lost by the Earth How long have we known about the greenhouse effect? Discovery of the greenhouse effect In 1827 French mathematician Jean-Baptiste Joseph Fourier realized that the Earth would be much colder without an atmosphere Earth’s surface temperature is the balance between two energies: light from the sun and “dark heat” (infrared radiation) Photo credits: Wikipedia Discovery of the greenhouse gases In 1859 Irish physicist John Tyndall discovered that carbon dioxide and water vapor had the ability to absorb infrared radiation He speculated that the Earth would be much colder in the absence of these gases in the atmosphere Tyndall’s invented radio spectrophotometer to measure the absorbance of infrared radiation by different gases Photo credits: Wikipedia Impacts of atmospheric CO2 on climate In 1896, Swedish scientist Svante Arrhenius followed Tyndall’s work and predicted (after one year of by-hand calculations!) the impact of CO2 on global temperature He was interested on whether changes in atmospheric CO2 could trigger ice ages He was awarded the Nobel Prize in Chemistry in Photo credit: Wiikipedia 1903 for his electrolytic theory of dissociation Arrhenius equation Doubling of atmospheric CO2 would F =  ln (C/C0) increase global temperatures by 5-6 C Trends in atmospheric CO2 In 1958 Charles David Keeling started The “Keeling Curve” monitoring the concentration of CO2 in the atmosphere He was the first to report seasonal fluctuations in atmospheric CO2 as well as the rise of atmospheric CO2 due to human activities The “Keeling Curve” has become an icon symbolizing the impact of humans on Earth https://www.youtube.com/watch?v=dXBzFNEwoj8 Trends in atmospheric CO2 Gruber&Sarmiento (2002) Mauna Loa Observatory Carbon dioxide and temperature Consistent higher and lower CO 2 concentrations during warms and cold intervals of the past, respectively In this 800k record, CO2 is never higher than ~300 ppm Parrenin et al. 2013; Snyder et al. 2016; Bereiter et al. 2015. Glacial-Interglacial CO2 records “Multiple lines of evidence show that the rate at which CO2 has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years (high confidence), and 4–5 times faster than during the last 56 million years (low confidence). How do we know that the growth in atmospheric CO2 is caused by humans ? Lines of evidence 1. Difference between the Northern and Southern hemisphere 2. Carbon isotopes of atmospheric CO2 3. Trends in atmospheric O2 “ These three lines of evidence confirm unambiguously that the atmospheric increase of CO2 is due to an oxidative process (i.e., combustion)“ 1, Differences between the Northern and Southern Hemisphere The difference between atmospheric CO2 records in the Northern (Mauna Loa) and Southern (South Pole) Hemisphere is caused primarily by the increase in emissions from fossil fuel combustion in industrialized regions, which are predominantly in the Northern Hemisphere 2. Stable isotopes of carbon in atmospheric CO2 Plants and algae prefer 12C over 13C Stable isotopes of carbon Plants and algae have lower 13C/12C relative to the atmosphere 12C → 98.9% of all carbon Fossil fuels are ancient organic material 13C → 1.1% of all carbon that used to be plants or algae, they are depleted in 13C Also deforestation returns carbon previously stored in plants (low 13C/12C) Higher 13C/12C Lower 13C/12C https://www.youtube.com/watch?v=b4QDokHJFIg 3. Trends in atmospheric O2 For every molecule of carbon burned from fossil fuels, 1.17- 1.98 molecules of O2 are consumed Declining trend in atmospheric O2 More O2 Less O2 How do we know that the growth in atmospheric CO2 is caused by humans ? 1. Difference between the Northern and Southern hemisphere 2. Carbon isotopes of atmospheric CO2 3. Trends in atmospheric O2 Summary The greenhouse effect: natural vs anthropogenic The ice core archive shows a tight coupling between temperature and carbon dioxide oscillations; natural variations in the past Both the current CO2 levels in the atmosphere and the rate of change are unprecedent for the past 800,000 years Three lines of evidence for anthropogenic change Equilibrium climate sensitivity Equilibrium climate sensitivity measures how climate models respond to a doubling of atmospheric CO2 Arrhenius The Global Carbon Cycle Sept 13, 2024 The carbon cycle is a set of processes by which carbon circulates between the different components of the biosphere and geosphere. These processes take place over different time scales Why study the carbon cycle? Tight coupling between C cycle and climate Human activities are significantly modifying Earth’s C cycle Carbon is everywhere: in rocks, oceans, soils, living creatures, atmosphere,… Carbon is the foundation of life Carbon is the source of most energy consumed by humans https://www.youtube.com/watch?v=hgFpvDNfXOk Distribution of Carbon on Earth Units: 1 Petagram (Pg) C = 1 x 1015 g C = 1 billion metric tons C= 1 Gigaton C (Gt C) Deep C reservoirs: mantle and crust (in biollion metric tons) A few metric tons….. https://www.sciencenews.org/article/where-earth-stores-its-carbon Source : Suarez et al (2019). doi: 10.2138/gselements.15.5.301. Distribution of Carbon on Earth Units: Petagram (Pg) C = 1 x 1015 g C = 1 billion metric tonnes = 1 Gigatonne (Gt) Surface C reservoirs (fast Deep C reservoirs (slow processes): processes) mantle and crust Atmosphere, oceans, land Pre-industrial values https://www.sciencenews.org/article/where-earth-stores-its-carbon Source : Suarez et al (2019). doi: 10.2138/gselements.15.5.301. Distribution of Carbon on Earth The deep and surface C reservoirs are not completely separate…… Deep C reservoirs: mantle and crust Surface C reservoirs Atmosphere, oceans, land Volcanic degassing Metamorphic degassing Subduction or deep burial of carbonates and organic C Pre-industrial values https://www.sciencenews.org/article/where-earth-stores-its-carbon Source : Suarez et al (2019). doi: 10.2138/gselements.15.5.301. The pre-industrial global carbon cycle We modify the natural C cycle 1. What drives the major/greatest fluxes of carbon on Earth’s surface? a. Rock weathering b. Volcanism c. Photosynthesis and respiration d. Air-sea exchange True or false: Prior to the industrial revolution, the oceans were a net sink of carbon. ~45% 9.5 ± 0.5 Gt C yr−1 ~29% ~26% P. Friedlingstein et al.: Global Carbon Budget 2021 What are the three sinks of anthropogenic carbon dioxide? Ocean Land Atmosphere The ocean absorbs approximately ___ of the anthropogenic CO2 released by the burning of fossil fuels. A. 50% B. 5% C. 25% D. 99% Global Carbon Cycle- anthropogenic influence T/F: The ocean has switched from a net sink to a net source of carbon. Atmospheric Carbon Dioxide Levels Mauna Loa Observatory: measured on air samples Increase rate: 2 ppm/yr Data before 1958 are from measurements of air bubbles trapped in ice cores from Antarctica https://www.youtube.com/watch?v=oHzADl-XID8 Gruber&Sarmiento (2002) Anthropogenic impacts: 2010-2019 Anthropogenic CO2 emissions 2010-2019 Burning fossil fuels 9.4 ± 0.5 Pg C yr-1 (~85%) Land-use change 1.6 ± 0.7 Pg C yr-1 (~15%) Friedlingstein et al. (2020). Earth Syst. Sci. Data, 12, 3269–3340 https://doi.org/10.5194/essd-12-3269-2020 Anthropogenic CO2 emissions Total C released since 1750: 700 ± 75Pg C 46 % 31 % 23 % Friedlingstein et al. (2020) The long-term processes Berner (2003). Nature The terrestrial biosphere Photosynthesis (plants) Respiration (plants, microbes, animals) CO2 + H2O + sunlight CH2O + O2 CH2O + O2 CO2 + H2O + energy Produces food as carbon for the ecosystem What are the squiggles? Seasonal fluctuations in atmospheric CO2 driven by land vegetation https://www.youtube.com/watch?v=x1SgmFa0r04 Seasonal fluctuations in atmospheric CO2 are driven by: a)Air-sea CO2 exchange b)Biological processes on land c) Burning of fossil fuels d)Rock weathering World’s forests net change growth loss The world’s forest area is decreasing, but the rate of loss has slowed (due to reduction in deforestation in some countries and forest expansions in others) Source: FAO. 2020. Global Forests Resources Assessment At the 2021 UN Climate Why are forests important? conference (COP26) 137 countries, containing about 85% of the world’s forested lands, committed Regulate climate by absorbing CO2 to stop and reverse from the atmosphere deforestation by 2030 Provide timber, food, fuel, and medicine for more >1/3 of the world's population Forested watersheds supply 75% of the world's accessible freshwater used in homes and to irrigate farmlands downstream Forests protect coastlines from erosion and lands from floods and other natural disasters Forests are home to 80 percent of the planet's terrestrial biodiversity Ocean carbon uptake Summary Carbon resides in various places on Earth including the atmosphere, the terrestrial biosphere and the oceans The atmosphere exchanges carbon with all other major reservoirs Exchanges between the atmosphere and the biosphere and oceans are fast Natural exchanges of carbon between the atmosphere and rocks are really slow Human activities, mainly the burning of fossil fuels and the clearing of forested land, have significantly increased atm CO2 The terrestrial biosphere takes approximately 31% of humans carbon emissions, the ocean takes 23%, and the remaining 46% stays in the atmosphere where the concentration of CO2 is increasing drastically Forests are big players among land ecosystems in taking up atmospheric CO2 and play an important role in fighting climate change Other greenhouse gases ATMO 310/OCN 310 September 18, 2024 Water vapor Methane Nitrous oxide The Earth’s energy budget and climate change Since at least 1970, there has been a persistent imbalance in the energy flow that has led to excess energy being absorbed by different components of the climate system What can you tell me about this figure? Glacial-Interglacial CO2 records “Multiple lines of evidence show that the rate at which CO2 has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years (high confidence), and 4–5 times faster than during the last 56 million years (low confidence). Lines of evidence 1. Difference between the Northern and Southern hemisphere 2. Carbon isotopes of atmospheric CO2 3. Trends in atmospheric O2 “ These three lines of evidence confirm unambiguously that the atmospheric increase of CO2 is due to an oxidative process (i.e., combustion)“ The sharp rise in atmospheric CO2 is the most important climate change driver over the last century, but not the only one… Other greenhouse gases CO2 is the major cause of human-made climate change Other GHGs are important too. They come from different sources, linger in the atmosphere for different amounts of time, and may be more or less potent at trapping heat. CO2 equivalent (CO2e): the warming effect of a certain amount of a GHG in comparison to CO2 (over 100 yrs). Ex: A metric ton of methane would warm the Earth 28 times greater than a metric ton of CO2. https://www.youtube.com/watch?v=sTvqIijqvTg https://www.youtube.com/watch?v=NzZSZForZh8 List these GHGs in order of least to greatest warming potential (CO2e). Carbon dioxide, nitrous oxide and methane Water vapor Most abundant GHG (~0.4%) Natural GHG Warmer climate holds more water vapor Important for positive feedback Very short residence time in the atmosphere (~9 days) Recent atmospheric trends in well-mixed greenhouse gases CO2 (ppm) “It is unequivocal that the increases in atmospheric carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) since the pre- industrial period are caused by human activities” -IPCC The rate of increase of CO2, CH4, and N2O in the atmosphere is unprecedented for at least the past 800,000 years Concentration increase between 1750-2019: CO2: 131.6 ± 2.9 ppm (47.3%) CH4: 1137 ± 10 ppb (156%) N2O: 62 ± 6 ppb (23.0%) The concentration and rate of increase of CO2, CH4, and N2O in the atmosphere are unprecedented for at least the past 800,000 years Methane Second most important greenhouse gas after CO2 Much more powerful greenhouse gas than CO2 but ~ 200 times less abundant (0.00017%) Responsible for ~20% of the direct radiative forcing since 1750 Short residence time in the atmosphere: ~9-12 years Main component of natural gas, used for fuel Early action on CH4 emissions might be key to limiting global warming to 1.5 or 2.0 °C https://www.youtube.com/watch?v=O3aHhhE0E54 Methane main sources and sinks 90-95% Cadena at al.(2019). doi: 10.3389/frym.2019.00133 T/F: The major natural source of methane comes from microbial processes. Methane main sources and sinks Natural Anthropogenic Sinks Wetlands (~26%) Livestock Tropospheric OH Freshwater systems Fossil fuels Stratospheric loss Geological Landfills and waste Tropospheric Cl Termites Rice cultivation Soil uptake (~5%) Ocean Biomass burning The variability in atmospheric methane is the result of the net balance between sources and sinks on the Earth’s surface and chemical losses in the atmosphere Methane emissions are difficult to constrain, primary sources are livestock, the fossil fuel industry (e.g., extraction) Recent trends in atmospheric methane Methane concentration in the atmosphere has increased by ~156% since 1750 Variable growth rate 2014-2019 9.3 ± 2.4 ppb yr-1 Units: Teragram (Tg) C = 1 x 1012 g C = 1 million metric tonnes C = 1 x 10-3 Pg C Nitrous oxide Known as the “laughing gas”, used as an anesthetic Potent greenhouse gas: 100-year warming potential 273 times higher than CO2 Long residence time in the atmosphere: ~116 years Atmospheric increase of ~20% since pre-industrial times The dominant natural source of N2O derives from microbial processes in soils, sediments and water bodies https://www.youtube.com/watch?v=ivp3XXSnwvM Microbial nitrification and denitrification Nitrification N2O → NH4 +→ NH2OH →NO2-→NO3- Denitrification NO3-→ NO2- →NO→N2O→N2 Net N2O production depends on environmental conditions such as temperature, oxygen concentrations, pH, and NH4+ and NO3- concentrations Strong temporal and spatial variability in N2O emissions Nitrous oxide main sources and sinks Natural Anthropogenic Sinks Soils Agriculture Stratospheric loss Oceans Biomass burning Atmospheric and biofuel chemistry Rivers, estuaries, Atmospheric Surface sink coast deposition Wastewater Fossil fuels and industry Changes in atmospheric N2O result largely from the balance of the net N2O sources on land and ocean, and its photochemical destruction in the stratosphere. ~43 % of N2O emissions are from anthropogenic sources, of which > 50 % is from agriculture (overuse of fertilizer) Units: Teragram (Tg) C = 1 x 1012 g C = 1 million metric tonnes C = 1 x 10-3 Pg C The greatest anthropogenic source of nitrous oxide is: A. Wastewater B. Agriculture C. Fossil fuels D. Biomass burning and biofuels Summary Water vapor is the most abundant GHG, natural, has a very short residence time (~9 days). It amplifies the warming of other greenhouse gases Methane is a short-lived (~9-year residence time) potent greenhouse gas with a 100-year global warming potential ~28 times larger than CO2 Methane has natural and anthropogenic sources, including wetlands, fossil fuels, agriculture (livestock and rice cultivation), waste management (landfills), and fires. The dominant methane sink is atmospheric oxidation, mostly to CO 2 Atmospheric methane levels have more than doubled since the industrial revolution, with variability in growth rates that are not well understood Summary Nitrous oxide is a long-lived (~116-year residence time) potent greenhouse gas with a 100-year global warming potential ~273 times larger than CO2 In natural ecosystems (both terrestrial and aquatic) nitrous oxide is produced primarily by two biogeochemical processes, nitrification and denitrification Anthropogenic nitrous oxide emissions are dominated by the addition of nitrogen fertilizer in croplands Other greenhouse gases CO2 is the major cause of human-made climate change Other GHGs are important too. They come from different sources, linger in the atmosphere for different amounts of time, and may be more or less potent at trapping heat. CO2 equivalent (CO2e): the warming effect of a certain amount of a GHG in comparison to CO2 (over 100 yrs). Ex: A metric ton of methane would warm the Earth 28 times greater than a metric ton of CO2. https://www.youtube.com/watch?v=sTvqIijqvTg https://www.youtube.com/watch?v=NzZSZForZh8 Units: Teragram (Tg) C = 1 x 1012 g C = 1 million metric tonnes C = 1 x 10-3 Pg C Units: Teragram (Tg) C = 1 x 1012 g C = 1 million metric tonnes C = 1 x 10-3 Pg C Oceans and Climate ATMO 310/ OCN 310 September 15, 2023 Why are oceans important? The global ocean covers 71% of the Earth surface ~97% of the Earth’s water is Ocean Provides the moisture to the atmosphere that feeds our rivers Large heat capacity, regulates climate Productive Large carbon reservoir https://hawaii.pbslearningmedia.org/resource /nves.sci.earth.oceancirc/global-ocean- circulation/ Distribution of heat by the ocean Ocean circulation and mixing redistribute heat and carbon over large distances and depths Lateral redistribution of heat from the tropics to the polar regions Vertical redistribution of heat and carbon through deep water formation Exchange of heat and carbon between deep water and the atmosphere in upwelling regions, which fuel biological production Lateral distribution of heat Vertical distribution of heat Image credit: NOAA Image credit: NASA Water’s heat capacity How much energy does it take to heat up 1 gram of water by 1 Kelvin? 4.184 Joules 1g 1 Kelvin 1g 0.7 J H2 O air What about a pot of tea? 1,000 grams of water at 273 K (0°C) How much energy does it take to heat it up to 373 K (100°C)? 1L 𝐽 4.184 𝑥 1,000𝑔 𝑥 100 𝐾 = 418,400 𝐽 𝑔𝐾 Ocean’s heat capacity Seawater has a heat capacity four times larger than air per unit of mass The dark blue ocean has little reflectivity → good at absorbing solar radiation Total heat capacity of the ocean is > 1,000 times larger than that of the atmosphere Oceans play a key role in moderating and regulating climate by absorbing, storing, and transporting heat supplied by the sun Source: Schmitt (2018). The oceans role in climate. Oceanography Where is global warming going? Ice Energy gain between 1971- 3% 1% Atmosphere 2018: ~435 ZJ (1021 J) 5% Land 91% Ocean The global ocean moderates Earth’s climate NASA’s Earth Observatory Ocean heat content trends Ocean warming and sea level rise Time period: 1971-2018 At the ocean surface, temperature has increased by ~0.88 °C between 1850–1900 and 2011–2020, with ~0.60 °C of this warming having occurred since 1980. The ocean drives the water cycle The oceans provide 86 % of global evaporation and receive 78 % of all rainfall. Disruption of the natural water cycle has far-reaching consequences Credit: Dennis Cain/NWS The ocean carbon pump Physical pump: air-sea exchange Air-sea exchange and mixing atmosphere The direction and magnitude of this flux CO2 depends on Partial pressure difference between the surface ocean and the atmosphere ocean (flows from high to low concentration) Gas transfer velocity, which varies CO2 mostly as a function of wind speed Carbon dioxide net air-sea fluxes To atmosphere To ocean High latitudes: Cooler water, high winds, biological drawn down of CO 2 reduces seawater CO2 Low latitudes: Warm waters, low winds, upwelling (near equator) increases seawater CO 2 Physical pump-Vertical mixing Credit: K. Cantner, AGI. As surface water travels poleward it becomes colder Colder water is able to take up more carbon dioxide Colder water is denser so it eventually sinks This vertical mixing acts as a C pump, sequestering C in the deep ocean for a long period of time, until it becomes in contact with the atmosphere in upwelling regions The biological organic carbon pump Transfer organic carbon, that is biologically produced, from surface waters to depth Mostly through sinking particles, but also physical injection pumps, and biologically mediated vertical fluxes The biological carbon pump depends on the balance between photosynthesis and respiration in the photic zone The biological carbonate pump Ca2+ + 2HCO3- CaCO3 + H2O + CO2 Microscopic shells of coccolithophore and foraminifera The White Cliffs of Dover, England The formation of CH20 (organic matter) vs CaCO3 (calcium carbonate) Shell-building organisms use carbonate ions to form CaCO3 Shells may dissolve before reaching the seafloor sediments because they are sensitive to low pH of deep ocean Shells are also sensitive to the climate change driven process, ocean acidification Can we fertilize the ocean to enhance C removal through the biological pump? https://www.youtube.com/watch?v=qkY0s_yMDe8 Long-term time series stations Ocean observations Ship-board observations: Repeated oceanographic transects Time-series stations Moorings Autonomous underwater vehicles Satellite observations https://www.youtube.com/watch?v=zMqv7p8fLWw The Argo program has deployed thousands of autonomous floats that measure/profile temperature and salinity in the world's oceans Credit: NASA Earth Observatory https://www.youtube.com/watch?v=7DTCbmyV7jA Summary The ocean is fundamental in moderating Earth’s climate, and it controls the planet’s energy, water, and carbon budgets The ocean has a large capacity to absorb, store, and distribute the heat supplied by the Sun The ocean is the main reservoir of carbon in the climate system and it absorbs a significant fraction of the fossil carbon we are putting into the atmosphere The ocean takes up carbon through the physical and biological pumps Ocean records are much shorter (and scarcer) than on land → ocean observations are critical to our understanding of its role in a complex changing climate system Distribution of heat by the ocean Ocean circulation and mixing redistribute heat and carbon over large distances and depths Lateral redistribution of heat from the tropics to the polar regions Vertical redistribution of heat and carbon through deep water formation Exchange of heat and carbon between deep water and the atmosphere in upwelling regions, which fuel biological production Lateral distribution of heat Vertical distribution of heat Image credit: NOAA Image credit: NASA Physical pump: air-sea exchange Air-sea exchange and mixing atmosphere The direction and magnitude of this flux CO2 depends on Partial pressure difference between the surface ocean and the atmosphere ocean (flows from high to low concentration) Gas transfer velocity, which varies CO2 mostly as a function of wind speed Physical pump-Vertical mixing Credit: K. Cantner, AGI. As surface water travels poleward it becomes colder Colder water is able to take up more carbon dioxide Colder water is denser so it eventually sinks This vertical mixing acts as a C pump, sequestering C in the deep ocean for a long period of time, until it becomes in contact with the atmosphere in upwelling regions The biological organic carbon pump Transfer organic carbon, that is biologically produced, from surface waters to depth Mostly through sinking particles, but also physical injection pumps, and biologically mediated vertical fluxes The biological carbon pump depends on the balance between photosynthesis and respiration in the photic zone The biological carbonate pump Ca2+ + 2HCO3- CaCO3 + H2O + CO2 Microscopic shells of coccolithophore and foraminifera The White Cliffs of Dover, England The formation of CH20 (organic matter) vs CaCO3 (calcium carbonate) Shell-building organisms use carbonate ions to form CaCO3 Shells may dissolve before reaching the seafloor sediments because they are sensitive to low pH of deep ocean Shells are also sensitive to the climate change driven process, ocean acidification Ocean acidification OCN 310 September 23, 2024 Global warming Ocean acidification Consequences of rising atmospheric CO2 Ocean acidification: the other CO2 problem! https://www.youtube.com/watch?v=fgBozLCGUHY A bit of carbonate chemistry Carbon dioxide does not simply dissolve in water like other gases, it reacts with water and forms bicarbonate and carbonate ions Dissolved inorganic carbon (DIC) forms: Atmosphere 1. Carbon dioxide (CO 2) 2. Carbonic acid (H2CO3) CO2(g) 3. Bicarbonate ion (HCO3-) CO2 + H2O HCO3- + H+ CO32- + 2H+ 4. Carbonate ion (CO 32-) Ocean -] DIC = [CO2] + [HCO3 +[CO3 2-] Total alkalinity (TA): TA = [HCO3-] + 2[CO32-] +[B(OH)4-] +[0H-] - [H+] + minor components Carbonate alkalinity (CA) Carbonate system The relative proportions of CO2, HCO3-, and CO32- control the pH (and not the other way around) The carbonate system is a natural buffer for seawater’s pH. Bjerrum plot 0.5 % CO2 86% HCO3- 13% CO32- At typical seawater conditions bicarbonate is the dominant form Source: Zeebe & Wolf-Gladrow (2001) Ocean acidification: the other CO2 problem! Bjerrum plot Changes in seawater chemistry: Increased dissolved CO2 Increased [H+] (decreased pH) Source: Zeebe & Wolf-Gladrow (2001) Increased [HCO3 -] Decreased [CO32-] The pH scale pH = -log ([H+]) pH is a measure of the [H+] [H+] can vary across many orders of magnitude, so the pH scale is logarithmic A change of one pH unit corresponds to a ten-fold change in [H+] The more [H+], the lower the pH Rising oceanic CO2 Surface water CO2 is increasing at about the same rate as in the atmosphere Decreasing oceanic pH pH distribution and trends in the ocean The saturation state of CaCO3 () Many organisms synthesize hard structures out of calcium carbonate (CaCO3) The saturation state of CaCO3 () provides a measure of the thermodynamic potential for CaCO3 to form or dissolve At  < 1, CaCO3 is undersaturated and will dissolve They are different mineral phases of CaCO3: calcite (most stable), aragonite, and magnesian calcite 𝐶𝑎 2+ 𝑆𝑊 [𝐶𝑂32− ]𝑆𝑊 = ∗ 𝐾𝑠𝑝 Ocean Acidification: Fundamental Chemistry Ca2+ + CO32- CaCO3 + Saturation State >1 CaCO3 stable W phase = [ Ca2+ ][CO32- ] =1 equilibrium K*sp,phase 

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