Only those that intend the absurd achieve the impossible Escher Biogeochemical Cycles A simple thing really OCNG 251 Oceanography Tuesday Dec 04th 2008 a The chemistry of Life and Biogeochemical Cycles c Nutrient cycles d The carbonate system and the Carbon cycle e Ocean Acidification f Coastal hypoxia 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 The flow of energy and materials i e water chemicals into and out of biological communities defines ecosystem studies Chemical Elements the Periodic Table and those essential for life Chemistry of 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 Required for some life forms Toxic elt 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 acids sugars enzymes DNA and other chemicals vital to life on Earth 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 Phosphorus Chemical Elements Essential for life Carbon Nitrogen Phosphorus Ratios Phosphorus is the energy element element occurring in compounds called ATP and ADP important for energy transfer processes and DNA 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 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 Recycling dominates most inputs of limiting elements N P K Biogeochemical cycles in the Ocean CO2 gas H2O Nutrients N P Energy OM O2 gas The carbonate system and the Carbon cycle CO2 gas dissolves readily in water and forms carbonic acid H2CO3 However at pH of natural waters waters carbonic acid equilibrates as bicarbonate HCO3 80 The carbonate system and the Carbon cycle Ca CO32 CaCO3 solid Formation of CaCO3 skeleton parts by micro organisms as hard part foraminifers 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 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 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 CO2 gas H2O H2CO3 H HCO3 H CO32 CaCO3 The carbonate system and the Carbon cycle CO2 gas H2O H2CO3 H HCO3 H CO32 CaCO3 Where should you find carbonate sedimentation 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 Ocean Acidification Ocean Acidification Incorporation of anthropogenic CO2 to the ocean Incorporation of anthropogenic CO2 to the ocean CO2 gas H2O H2CO3 H HCO3 H CO32 CaCO3 CO2 gas H2O H2CO3 H HCO3 H CO32 CaCO3 Biogeochemical cycles in the Ocean Dissolved trace nutrients in the Ocean Phosphorus Nitrogen CO2 gas H2O Nutrients N P Energy OM O2 gas 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 organisms diatoms radiolaria can still use it More soluble in cold waters No Compensation Depth Slow dissolution despite undersaturation Where should you find silicate sedimentation Where should you not find it Distribution of Ocean Sediments 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 Estimated areal extent of bottom water hypoxia from mid summer cruise in the period 1985 1999 20 15 103 km2 Gulf of Mexico a large area of the Louisiana continental shelf with seasonally depleted 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 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 10 5 0 source Louisiana Universities marine Consortium Gulf Coast Hypoxia Gulf Coast Hypoxia Nitrogen yields from the Mississippi River Drainage