NutrientsNutrients are generally considered to be elements or compounds (e.g. N is anutrient, NO3 and NH4 are types of N compound that are also nutrients) that areneeded for biological growth.Classification of Elements or Nutrients (Wally Broecker):Bio-unlimiting—their distribution is determined solely by physics• generally show no vertical structure in the ocean• or they covary with sodium, etc.• may be necessary for biology, but so abundant that they never run out…forexample, sodium and potassium are used by cells, but the distribution hasnothing to do with biologyBio-intermediate—they are needed for biological processes, but they aren’tentirely controlled by biology• typically covary with Phosphorous with depth, to some point• this may be because they are actually biologically used in small quantities(e.g. carbon, nickel, calcium, selenium) or because they mimic bio-activeelements (e.g. germanium)Bio-limiting—essentially zero in the surface waters, increase with depth-subdivided into Macronutrients and Micronutrients• macronutrients make up the gross composition of organisms:• P, C, N, Si, O, H• Generally used to make up the skeleton, major pools, etc.• micronutrients are needed in trace quantities, and are often found in tracequantitities-Zn, Fe, Se, Mn, Co -often used in enzyme reactionsNon-Cyclic—so reactive, they are immediately “scavenged” or removed byattachment to particles• Th, Pb, Fe• Can use this principal to look at sedimentation rates-Th234 equilibrium valuesUNITS: we usually refer to nutrient values in terms of their molar quantities. Thisis typically expressed as µg-at or mg-at per unit volume, or as µM or mM. Theseare typically interchangeable but if there’s more than one atom per molecule, thisis NOT true! Carbon is unusual in that we sometimes refer to it in terms of grams.1 Mol = 6.02 E 23 atoms of substance1 Molar = 1 Mol/LitermM =1/1000 (Total carbon)µM =1E-6 (most macronutrients)nM=1E-9 (micronutrients such as iron)pM=1E-12 (micronutrients, trace organics such as pesticides)1 µg-at L-1 equals 1 mg-at m-3, so when we integrate, µg-at L-1 becomesmg m-2Biolimiting NutrientsWe are interested in these because they control production and biomass.Liebig Limitation: the nutrient that controls the absolute accumulation of biomass.Blackman Limitation: we need to consider not only the nutrient that limitsabsolute accumulation, but how fast we get there (rate-limiting factors)Distribution:Vertically: obviously more in the deep water than in the surface watersBIOLOGICAL PUMP—Phytoplankton take up C, Nutrients, die, sink out (about90% stays in euphotic zone and is recycled)….pumps C and nuts towards thebottomGlobally:PO4 is low in the Atlantic, high in the Indian and Pacific (1.2, 2.5, 3)NO3 is low in Atlantic, higher in Indian and highest in Pacific (20, 35, 40)Si shows strong gradient between Atlantic, Indian, Pacific (30, 120,160)A.C.Redfield – 1930’s at WHOI, noticed a relationship between NO3:PO4, thenlater between NO3:PO4:O. This has since then been extended to include allbiolimiting nutrients. In general, inorganic nutrients are found at a constant ratio,throughout the world’s oceans.Shuter (1979) Formally extended this by stating that phytoplankton take upnutrients in constant proportions…e.g. organisms also have a Redfield Ratio foruptake ratesIs this true? More or less….phytoplankton generally have Redfield proportions.Exceptions: Dinoflagellates often have 9:1 C:NBacteria typically have C:N of about 2-4:1Soft tissue: 105:15:1Hard Parts (shells): 26:0:0 (26:50 Ca:Si)Deep Water: 1000:15:1, 5000:50(C=CO2+HCO3+H2CO3)Shallow Water: 869:0:0 (974:0)BIOLOGICAL UTILIZATION:• Biology is generally considered to be controlled by N, P, or Si (now also Fe)• Fresh water, P is almost always limiting…this is because P is extremelyparticle-reactive, and freshwater has a high surface area to volume ratio• In the oceans, we generally assume that N is limitingPhosphorous Cycle:• Only place it can come from is outside the oceans, or from internal recycling• Turns over very quickly…• Primary type is PO4, but DOP is also important• Used in DNA, RNA, phospholipid bilayer, ATP, ADP, etc.Silica Cycle• most abundant element in continental crust• also has to come from outside the oceans• very abundant in the older ocean basins, also high in freshwater runoff• used as silicic acid (SiOH4)• primarily used by diatoms (and silicoflagellates) as skeletal structure• used to think it had an extremely slow dissolution rate, because diatomscover the skeleton with a membrane, and essentially a chemical reaction thatdissolves it, so slows down at cold temperaturesIron Cycle• extremely reactive, also extremely bio-reactive• most of it comes from 3 sources: biological turnover, upwelling (fromcontinental crusts), and aeolian deposition• bacteria make compounds called siderophores that react with Fe, make itavailable…appears that diatoms can also access that form of ironNitrogen Cycle• Much more complicated than P or Si• About 70% of the atmosphere is N2 gas, but this gas is inert• There are many forms of N available to oceanic phytoplankton:• Inorganic (NO3, NO2, N2)• Organic (NH4, urea, DFAA, other DON compounds)• Nitrifying Bacteria: oxidize NH4NO2NO3• Denitrifying Bacteria: reverse process (mostly occurs in anoxicsediments…they are using NO3 and NO2 as electron donors)• Nitrogen Fixation: can directly utilize N2 gas by “fixing” it into organiccompounds….this is extremely energy inefficient, and can’t occur in thepresence of oxygenUPTAKE MEASUREMENTSWe can measure nutrient uptake in 3 ways:1) Nutrient depletion…this is cheap and easy, but only as sensitive asthe method you use, and can’t account for transformation to differentcompounds (e.g uptake of NO3, release of NH4)2) Radio-isotopes…these are extremely sensitive, but they areradioactive, and not all compounds have them (e.g. Nitrogen)3) Stable-Isotopes…primarily N, C, and SiWhen we use isotopes, we measure two different things:V: the velocity of uptake, time dependentRho: the absolute uptake rate (volume or biomass dependent)Radioisotopes measure Rho, need to measure biomass to get VStable Isotopes measure V, need biomass to get RhoNote that we can increase uptake rates by either having a low V and highbiomass (so high Rho), or having low biomass but high V.Kinetics of