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“Only those that intend the absurd, achieve the impossible” Escher Dissolved gases in water Take a break, Grab a soda… soda… Let’s assume we have a clear bottle of soda… You pop the lid ! gas escapes! (pressure) You shake it ! more gas escapes! (mixing) You warm it up ! even more gas escapes! (temperature) Does it stop? !When final gas content of soda is at equilibrium with temperature and pressure Oceanography Lecture 16 a. Dissolved gases b. The chemistry of Life and Biogeochemical Cycles c. Nutrient cycles d. The carbonate system and the Carbon cycle e. Coastal hypoxia Dissolved gases in water Take a break, Grab a soda… soda… The total amount of gas that can be dissolved eventually reaches an equilibrium concentration which is proportional to: - Atmospheric concentration of gas in atmosphere - Temperature, - Pressure, - Salinity of water. The amount of gas usually " as: P" T# S# Density structure of the Ocean Oxygen in the Ocean CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas) Photosynthesis possible only in photic zone (0-200 m) Oxygen minimum (utilization) at pycnocline – O2 Minimum Dissolved gases in the Ocean Dissolved gases in the Ocean Temperature is the most important controlling factor! The most abundant gases in the atmosphere: - N2 (78%) - O2 (21%) - Argon (0.9%) - CO2 (0.03%) The most abundant gases in the Oceans: - CO2 (94.3%). Much more soluble! - N2 (3.4%) - O2 (2%) - Argon (0.3%) Difference due to the reactivity of CO2 is seawater leading to the various carbonate and bicarbonate equilibria CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas) Photosynthesis only in possible in photic zone (0-200 m) Oxygen limitation (utilization) at pycnocline – O2 Minimum CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- Dissolved gases in the Ocean Dissolved gases in the Ocean Argon and the other noble gases (He, Ne, Kr, and Ra) and Nitrogen are essentially unreactive in the Oceans: Conservative gases In contrast, CO2 and O2 concentrations are altered by many biological and chemical processes in the sea. Non-conservative gases Photosynthesis/Respiration: CO2(gas) + H2O + Energy % H12C6O6 (sugar) + O2 (gas) H12C6O6 (sugar) + O2 (gas) % CO2(gas) + H2O + Energy Defining the Ecosystem Biology is not the sole subject of ecosystem studies ! The flow of energy and materials (i.e. water, chemicals) into and out of biological communities defines the main theme of ecosystem studies CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas) Photosynthesis only possible in photic zone (0-200 m) Oxygen limitation (utilization) at pycnocline – O2 Minimum Defining the Ocean Ecosystem There exists an inseparable relationship between the flow of energy and the flow of nutrient elements (i.e. N, P, K, Ca, etc) Biogeochemical Cycles Chemical Elements (the Periodic Table) and those essential for life " Of the 103 elements in the Periodic Table, only 24 are required by organisms " Macronutrients: Required in large amount (“Big Six” Six”: C, N, P, S, O, H) " Micronutrients: small or moderate amount Required elt A simple thing, really… Chemical Elements - Essential for life Carbon " Carbon forms three-dimensional molecules of large size and complexity in organic (carbon-containing) compounds that form large molecules (amino acids, sugars, enzymes, DNA), and other chemicals vital to life on Earth. Required for some life forms Toxic elt Chemistry of Life… Element Major Components Carbon Oxygen Hydrogen Nitrogen Macronutrients Phosphorus Sulfur Calcium Silicon Sodium Magnesium Chlorine Potassium Iodine Micronutrients Iron Copper Zinc Symbol C O H N P S Ca Si Na Mg Cl K I Fe Cu Zn Representative Use >100,000 of every M atoms All organic molecules Almost all organic molecules All organic molecules Proteins, Nucleic acids 1,000 < per M atoms <100,000 Nucleic acids, teeth/bones/shell Proteins, cell division Shell, bone, coral, teeth Hard parts Body fluids, osmotic regulation Osmotic regulation, chlorophyll ATP formation, nerve discharge Nerve discharge, osmotic balance Thyroid hormone < 1,000 of every M atoms Electron transport, N assimilation Electron transport Nucleic acid replication Chemical Elements - Essential for life Nitrogen " Nitrogen (along with carbon) is the essential element that allows formation of amino acids (! proteins) and DNA. Proteins contain up to 16% N Chemical Elements - Essential for life Carbon:Nitrogen:Phosphorus Ratios " Organisms actively concentrate certain elements essential for life: ! Algae concentrate Iron (Fe) 100,000 times vs. its concentration in the Ocean • Most organisms keep a rather constant chemical composition ! Algae and plankton C:N:P ratio of 106:16:1 (Redfield Ratio) ! Soil microbes maintain a relatively constant proportion of nutrients in their biomass (and at higher levels than the OM they decompose) Chemical Elements - Essential for life Phosphorus " Phosphorus is the “energy element” element” occurring in compounds called ATP and ADP important for energy transfer processes and DNA. Chemical Elements - Essential for life • Availability of some elements (particularly N & P) is often limited and the supply of these elements may control the rate (or type) of primary production in ocean ecosystems. • External sources of nutrients are varied and depend of nutrient ! Annual circulation dominates most inputs of limiting elements (N, P, K) Biogeochemical cycles in the Ocean The carbonate system and the Carbon cycle CO2(gas) dissolves readily in water and forms carbonic acid (H2CO3). However, at pH of natural waters, carbonic acid equilibrates as bicarbonate (HCO3-: 80%) CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas) The carbonate system and the Carbon cycle The carbonate system and the Carbon cycle Ca+ + CO32- $ CaCO3 (solid) Formation of CaCO3 skeleton parts by micro-organisms as hard part: ! foraminifers, coccolithophorids, pteropods to precipitate CaCO3. CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- + Ca2+$ CaCO3 The carbonate system and the Carbon cycle Ca+ + CO32- $ CaCO3 (solid) Ocean surface waters are nearly everywhere supersaturated with respect to calcium carbonate. However, no spontaneous precipitation occurs! (inhibition from Mg2+ in solution) !Intervention of marine organisms (foraminifers, coccolithophorids, pteropods) to precipitate CaCO3. - CaCO3 dissolves readily with decreasing temperature and increasing pressure. Also, - Calcite and Aragonite have the same formula but different crystalline structure. Aragonite is less stable. The carbonate system and the Carbon cycle Where should you find carbonate sedimentation? Where should you not find it? The carbonate system and the Carbon cycle As organic matter (OM) “rains” to the sea floor, it is mostly degraded (>90% regeneration!) ! production of CO2 ! increased formation of acid ! increased dissolution of carbonates! CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3 Where should you find carbonate sedimentation? Where should you not find it? The carbonate system and the Carbon cycle Carbonate Compensation Depth (CCD): the depth at which all carbonates have dissolved ! The CCD is shallower for Aragonite that for calcite CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3 CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3 The Carbon cycle •Different timescales •Most C in carbonate rocks (85%) •Second largest reservoir in soil and sediment OM (15%) •Dissolved C in Oceans (0.08%) •Fossil fuels (0.02%) •Additional less significant reservoirs (Atmosphere, Biosphere, etc) • General equilibrium: 75%! Dissolved (trace) nutrients in the Ocean Phosphorus Nitrogen Biogeochemical cycles in the Ocean CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas) The silicon cycle Silicon behaves like a nutrient ! Minor element ! essential for formation of frustules ! undersaturated in the Oceans ! Micro-organisms (diatoms, radiolaria) can still use it! ! More soluble in cold waters. ! No Compensation Depth: Slow dissolution despite undersaturation! ! General equilibrium: 10%! CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas) Where should you find silicate sedimentation? Where should you not find it? Hardness and detergents Distribution of Ocean Sediments The hard and soft appellation of waters reflect the fact that doubly charged Ca2+ and Mg2+ ions can precipitate detergents (molecules with long hydrocarbon chains and polar head groups) Detergents are excellent cleanser because of their ability to act as emulsifying agents (an emulsifier is capable of dispersing one liquid into another immiscible liquid). Disadvantages: As salts of weak acids, they are converted by mineral acids into free fatty acids: CH3(CH2)16CO2-Na+ + HCl ! CH3(CH2)16CO2H + Na+ + Cl- Soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron: 2 CH3(CH2)16CO2-Na+ + Mg2+ ! [CH3(CH2)16CO2]2Mg2+ + 2 Na+ Where should you find silicate sedimentation? Where should you not find it? Hardness and detergents Phosphorus Control Measures A U.S. Case Study Addition of chelating agents (builder) can bind with cations through multiple bonds. Particularly effective chelating agents: The first is a limiting nutrient, the other two biodegrade slowly (T dependent) and mobilize toxic chemical! Sodium Tripolyphosphate (STP) Nitrilotriactetic acid (NTA) EDTA Source: USGS 1999 • • As more States passed detergent-bans legislation, the industry was faced with maintaining duplicate inventories of detergent around the Nation and ultimately decided (cost effective) to phase out phosphorus use in domestic detergents Phosphates are still permitted in dishwashing detergents and industrial cleaning agents. Phosphorus Control Measures A U.S. Case Study Phosphorus Control Measures A U.S. Case Study Source: USGS 1999 Source: USGS 1999 • • As more States passed detergent-bans legislation, the industry was faced with maintaining duplicate inventories of detergent around the Nation and ultimately decided (cost effective) to phase out phosphorus use in domestic detergents Phosphates are still permitted in dishwashing detergents and industrial cleaning agents. Phosphorus Control Measures: A U.S. Case Study • • Only about 15% of municipal waste-water treatment plants (~40% of total municipal waste-water discharge) were required to monitor phosphorus Only 7% have phosphorus limitations (0.5-1.5 mg/L) through tertiary treatment! Non-Point Sources of Phosphorus Phosphorus from manure and commercial fertilizers • • Phosphate ban reduced annual loads to Lake Erie (&86%) and Chesapeake Bay (& (& 55%) Temporal trend in declining phosphorus levels in surface waters (except Southeast). However, at least one third of all hydrological units studied showed more than 1/2 of total phosphorus concentrations exceeding the EPA recommended limit in flowing waters (0.1 mg/L) Coastal Hypoxia Nutrient over-enrichment from anthropogenic sources is one of the major stresses impacting coastal ecosystems. Generally, excess nutrients lead to eutrophic conditions and increased algal production which in turn increases the availability of organic carbon within the aquatic ecosystem. Gulf Coast Hypoxia Nitrogen is the most significant nutrient controlling algal growth in coastal waters, while phosphorus is the most significant nutrient in fresh water Both the near-coastal hydrodynamics that generate water column stratification and the nutrients that fuel primary productivity contribute to the formation of hypoxic zones. Human activities on land can add excess nutrients to coastal areas or compromise the ability of ecosystems to remove nutrients either from the landscape or from the waterways themselves. (source: USGC) Coastal Hypoxia Coastal Hypoxia Gulf of Mexico: a large area of the Louisiana continental shelf with seasonallydepleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low oxygen levels. The oxygen depletion (hypoxia) begins in late spring, reaches a maximum in midsummer, and disappears in the fall. After the Mississippi River flood of 1993, the spatial extent of this zone more than doubled in size, to over 18,000 km2, and has remained about that size each year through midsummer 1997. The hypoxic zone forms in the middle of the most important commercial and recreational fisheries in the coterminous United States and could threaten the economy of this region of the Gulf. Estimated areal extent of bottom water hypoxia from mid-summer cruise in the period 1985-1999 20 103 km2 15 10 5 0 (source: Louisiana Universities marine Consortium) Gulf Coast Hypoxia Gulf Coast Hypoxia Long-term record of drainage basin changes: Nitrogen yields from the Mississippi River Drainage Basin About 56% of the nitrate transported to the Gulf enters the Mississippi River above the Ohio River. The Ohio basin subsequently adds another 34% of the nitrate load. 106 metric tons/year a) annual amount of fertilizer application 106 of acres b) area artificially drained 1900 1920 1940 1960 1980 2000 Gulf Coast Hypoxia On average, 61% of the nitrogen load is nitrate; 24% is dissolved organic nitrogen. The most significant nutrient trend has been nitrate loads, which have almost tripled from 0.33 million metric tons per year during 1955-70 to 0.95 million metric tons per year during 1980-96 2.5 30 Streamflow 25 2.0 Organic N 1.5 20 1.0 15 Nitrate 10 0.5 1950 1960 1970 1980 2000 That’s it folks…