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1Chapter 10: Biolimiting Elements James W. Murray- vertical and horizontal segregation Univ. Washington- case studies (Fe and N)(10/29/01)By definition, biolimiting elements are those:necessary to sustain lifeandexist in low concentrationsFor the most part the prototypical macro biolimiting elements are:Pas PO4Soft PartsNas NO3 "Si as H4SiO4Hard PartsSeveral trace elements can be limiting, most notably iron.I. Vertical distributionsBox models can be used to determine the rates of transfer between reservoirs andtransformations within a reservoir.Fig 10-1 Schematic of 2-box modelAdvantages- Easy to conceptualize- Provide an overview of fluxes, reservoir sizes and turnover or residence times- Provide the basis for more detailed modelsDisadvantages- the analysis is superficial- little insight is gained into processes (e.g. transport)- we usually assume homogeneous distributions within reservoirs2Broecker (1971) Two-Box Model (Fig 10-2)Surface Box Vup = V down = Vmix = Annual water transport = 300 cm y-1Deep BoxVmix/Vriver = 30B = Vriver Criver + Vmix Cdeep - Vmix Csurff B = Vriver Criver(1-f) B = Vmix Cdeep - Vmix CsurfAssumptions:2 boxes - each well mixedrivers the only sourcesediments the only sinkremoval is by biogenic particlessteady stateVriver CriverVriver x 0Vmix CdeepVmixf x BB(1-f) x B3Mass Balance - Surface BoxInputs OutputsVriver Criver + Vmix Cdeep = Vmix Csurf + BMass Balance - Deep BoxVmix Csurf + (1-f) B = Vmix CdeepMass Balance - Whole OceanVriver Criver = f BTwo important properties1. g = efficiency of bioremoval from the surface as particles. = bioremoval/inputs = B / (VrCr + Vmix Cdeep)Element gN, P 0.95Si 1.00C 0.20Ca 0.012. f = fraction of particles that don't dissolve. This is the efficiency of ultimate removal.f B = Vriver Criverf = Vriver Criver / B = Vriver Criver / (Vriver Criver + Vmix Cdeep - Vmix Csurf) = 1 / (1 + Vmix/Vriver (Cdeep/Criver - Csurf/Criver))Element fN,P,Si 0.01C 0.02Ca 0.124The fraction of an element removed to the sediments for each visit to the surface boxis given by the product of f x g.For PO4f x g = 0.01 x 0.95 = 0.0095Particle flux total particle particle fluxto sediments flux to sediments =Total particle Total input to total input toFlux surface box surface boxSo f x g = 0.01 which means that 1% of the PO4 introduced to the surface ocean isremoved during each mixing cycle.If the mixing time of the ocean is 1000 y, then PO4 goes through 1 / f x g = 105cycles of 1000 y / 105 cycles = 9.5 years / cycleOr 1 / f x g = the average number of cycles (through the thermocline) that an elementcycles through the ocean before being removed permanently to the sediments.Fig 10-35Table 10-1Table 10-26II. Perturbation analysis1. The simple model can be used to evaluate the outcome of different physical andbiological perturbations. In this case we ask how the concentration of PO4 in the deepocean will change when we double the rate of physical exchange (e.g. Vm) once thecontrolling process (P burial) is known.Fig 10-47Fig 10-58III. Horizontal distributionsThe superposition of the vertical flux of biologically produced particles on the horizontalcirculation of the ocean results in:a) Low surface nutrient concentrationsb) High nutrient concentrations in the deep oceanc) Higher nutrient concentrations in the deep Pacific than the deep Atlanticd) a shallower calcium carbonate compensation depth in the Pacific than the AtlanticFig 10-6 Conveyor Belt9Fig 10-710Trace elements in seawaterDefinition: Those elements that do not contribute to the salinityAll elements less than 1 mg kg-1.Why:1. many are micronutrients (e.g. Fe, Cu)2. others are toxic (e.g. Cu, Hg)3. can be tracers for redox conditions (Cr, I, Mn, Re, Mo, V, U)4. can be enriched in economic deposits such as manganese nodules (e.g. Cu, Co, Ni,Cd)5. some are tracers of pollution (e.g. Pb, Pu, Ag)Difficult to collect samples for without contamination and to analyze.Most data available since 1975.Oceanographic consistency(Boyle and Edmond (1975) Nature, 253, 107-109)Acceptance of data must satisfy two criteria:1. Verticle profiles should be smooth2. Correlations should exist with other elements that share the same controllingmechanisms. See examples in Fig 10-8.Summary of concentrations:See Table 1 in Lecture 1 of notes which gives the composition of seawaterFig 10-9: The "state of play" diagram showing the range of concentrations for differentelements. Concentrations are as low as 10-21 M. How many atoms is this?11Fig 10-812Fig 10-9 Concentration range of trace elements in seawater13Examples:Conservative - Cesium (Cs)Molybdenum (Mo) - under oxic conditionsMetal Limiting and Toxicity - Copper (Fig 10-10, 10-11) Role of Free Metal IonNutrient Like - Shallow and Deep RegenerationBarium (Fig 10-12)Zinc (Fig 10-8)GermaniumCadmium (Fig 10-8; 10-13; 10-14)IodateNickel (Fig 10-8)Copper (Fig 10-8; see also paper by Boyle)Surface EnrichmentLead (Fig 10-8; 10-15)Manganese (Fig 10-17)MercuryMid-depth MaximumManganese (Fig 10-17)IronNear Bottom EnrichmentNorth Sea Metals (Cd, Cu, Mn) (Fig 10-19)Deep DepletionLead-210 (Fig 10-8; 10-18)Aluminum (Fig 10-16)Manganese (Fig 10-8; 10-17)14Fig 10-10 Dependency of plankton growth rate on the activity of Cu2+.Fig 10-11 Activity of the free Cu2+ ion (pCu) from various sites.15Fig 10-12 Barium data from the Atlantic and the Ba-Si relationship (Chan et al, 1977)16Fig 10-13 Cadmium profiles and the Cd-PO4 relationship (Bruland, 1980)17Fig 10-14 Cadmium as a tracer for paleophosphate.a) Cd-PO4 from the world's ocean (Hester and Boyle, 1982)b) Cd/Ca in benthic forams versus bottom water PO4.18Fig 10-15 a)Lead in Greenland Ice cores (Murozumi et al, 1969).b) Lead profiles in seawater and new atmospheric input fluxes (Shen and Boyle, 1987).19Fig 10-16 a) Aluminum profiles from the Pacificb)comparison on Atlantic and Pacific.c)20Fig 10-1721Fig 10-18 Lead scavenged from the deep sea - seen in 210Pb data, relative to its parent226Ra..22d) Fig 10-19 Sediments are a source of metals on the continental shelves.e)23f) Biolimiting Elements - Case Studies (4/28/99)The tradtional paradigm has been that nitrogen is the limiting nutrient in theocean. This has been inferred in many ways, one of which are property-property plotssuch as NO3 versus PO4. An example is shown in Fig 10-20 which shows NO3 versusPO4 for all the GEOSECS data from the Pacific. There is a linear relationship which has


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