5/2/13. Zooplankton! Phytoplankton! Nutrients!

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1 Phytoplankton! Zooplankton! Nutrients! 1

2 Phytoplankton! Zooplankton! Critical Depth Recycled Nutrients! Oxidized Nutrients! Detritus! Rest of Ocean Biological and Solubility Pumps 2

3 New (Export) vs. Regenerated Production Redfield (1958) Dugdale & Goering (1967) Eppley & Peterson (1979) Shuter (1979) Fisheries CO 2 Sequestration Nitrate Ammonium Adapted from Chisholm 2000 Assumptions: We have chosen a box large enough to balance out advection and diffusion Everything, on average, is in steady-state Because it is in steady state, we can assume Redfield- Ratios There must be mass balance (nothing appears or disappears) 3

4 Estimating New Production In Vitro 14C Assimilation hours-->day O2 evolution hours-->day 15N measurements hours-->day 18O2 evolution hours-->day Physical Transport Sediment traps days-->months Bulk Property NO3 flux to photic zone hours-->days OUR below photic zone seasonal-->annual 238U/234Th days Other Remote Sensing days-->weighted annual Optimal energy conversion instantaneous Reconciling Time-Space Scales! Steady State? Mass Balance Sediment Traps Incubations FRRF PvsE Source: 4

5 Eppley & Peterson, 1979 Defined the f-ratio Determined that there are worldwide patterns in export production Can estimate export from total productivity IP = P B opt Chl opt z eu t irr I o I o [mg C m-2 d -1 ] P B opt - maximum C fixation rate per unit chlorophyll Chl opt - chlorophyll concentration at the depth of P B opt z eu - euphotic depth t irr - photoperiod I o - surface irradiance Behrenfeld and Falkowski L+O 42:1-20 5

6 Hypothesis: A large body of evidence leads to the conclusion that light limits the growth of phytoplankton. The distribution of phytoplankton should reflect the distribution of light. Photosynthesis mgc (mg Chl) -1 h High Light Cells Low Light Cells Irradiance (µmol quanta m -2 s -1 ) But it looks like light kills phytoplankton. Hypothesis rejected 6

7 Hypothesis: There is also evidence leads to the conclusion that higher temperatures enhance the growth of phytoplankton. The distribution of phytoplankton should reflect the distribution of surface temperature. Temperature ( o C) SST Looks like phytoplankton have a low boiling point. Hypothesis rejected. 7

8 Well, its not light, not temperature, what could it be? Mar. Aug. Mixed Layer Depths A simple calculation, but a complex interaction. Annual average surface nitrate concentration. Vigorous fluid mixing introduces a net flux of nitrate (read nutrients) into the surface, well-lit layer leading to patterns of biomass (chlorophyll in this case) 8

9 5/2/13 VGPM-derived Carbon Export! Laws et al., 2000 Surface Nutrients Export Note that the highest export is NOT where there are lots of excess nutrients Laws et al.,

10 Large Scale Patterns! Kudela et al., 2005, Oceanography 18: Seasonal Patterns! We will return to this, but globally, we start to see both spatial and seasonal patterns driven by the combination of physics (nutrients, mixing), light, and temperature Kudela et al., 2005, Oceanography 18:

11 New (Export) vs. Regenerated Production Redfield (1958) Dugdale & Goering (1967) Eppley & Peterson (1979) Shuter (1979) Fisheries CO 2 Sequestration Nitrate Ammonium Adapted from Chisholm 2000 New (Export) vs. Regenerated Production Redfield (1958): to first order, all plankton have similar ratios of elements, meaning we can track any element and convert to any other (remember that this also means that ON AVERAGE, phytoplankton are growing optimally, because we deviate from Redfield when nutrient (growth) limited). Dugdale & Goering, 1967: Because of Redfield ratios, we can track one element (N) and take advantage of the fact that nitrate is generally new (exogenous) while ammonium/urea is generally regenerated (endogenous) to a system. At the time, we thought N2 fixation and other sources were negligible. 11

12 New (Export) vs. Regenerated Production Eppley & Peterson (1979): If we integrate over large space and time scales, New Production has to equal Export Production. So we have a simple way of estimating how stable an ecosystem is, how much energy is available for fisheries, etc. Shuter (1979): States that Redfield Ratios for BIOMASS must mean that organisms are taking up elements at the same proportions. In other words, you can track ANY ONE ELEMENT and assume it is representative of GROWTH. Phytoplankton! Zooplankton! Nutrients! Taken together, these concepts allow us to simplify biology. We can track any nutrient (the N box), assume that ON AVERAGE growth and composition are the same (the P box) and relate new/regenerated production to export (the Z box). But we know that is not always how the ocean works. 12

13 Zehr & Kudela, 2011, Annu. Rev. Mar. Sci, 3: Summary Points:! The conceptual N cycle (and therefore new/regenerated production) is in a state of flux, with new organisms and processes being discovered (and unknown global implications) Although there are hypotheses about the global N balance, and how the N cycle may be affected by global climate change, there are too many unconstrained uncertainties and we therefore can only predict the most obvious responses to past or future climate change Zehr & Kudela, 2011, Annu. Rev. Mar. Sci, 3:

14 5/2/13 Sediment Traps! Stokes Law! Q: How long does it take for a particle to sink in the ocean? A: We need to know 3 things: 1) density of the particle 2) radius of the particle 3) density of seawater Then we use Stokes Law: radius Density Viscosity V = 2 / 9 g r2 (ρ -ρ) /ρ v Velocity gravity Particle density - water 14

15 Applications of Stoke s Law! V = 2 / 9 g r 2 (ρ -ρ) /ρ v V = r 2 r = 3 to 40 microns r = 3 to 40 x10-4 cm Simplification for spherical particles with densities near that of rock V = (3 to 40 x10-4 ) 2 V = cm/s 11 to 2300 days to sink! Martin s Equation (VERTEX)! Biomass decreases essentially exponentially with depth. Martin Equation: F=Fz(Z0/Z)^b (b= for Monterey) 15

16 Thorium Fluxes (U238/Th234)! 16

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18 Conservative vs. Non-Conservative Conservative properties follow linear mixing laws Temperature Gases Non-Conservative properties are non-linear in space and time Biology Salinity Non-reactive elements Some properties fall in-between Nutrients Apparent Oxygen Utilization Oxygen Utilization Rate! O2 Organic carbon inorganic nutrients 18

19 Nitrate Mass Balance Equals New (Export) Production Turk et al., 2001 Reconciling Time-Space Scales! Steady State? Mass Balance Sediment Traps Incubations FRRF PvsE Source: 19

20 Large Cells = High Biomass From Chisholm, 1992 Figure 3, 8 Wilkerson et al. 2000, DSR 47:

21 Adding it all up. There are limiting elements to both the rate of growth and biomass of phytoplankton On average, biomass is in Redfield-proportions for C:N:P:O (:Si) Large cells are capable of faster uptake due to internal pools and surge kinetics Only cells growing near µmax are Redfield Export production mass decreases logarithmically with depth Therefore, diatoms and other large, heavy cells are extremely important! 21