EEMB 142B Midterm II study sheet

EEMB 142B Midterm II study sheet - EEMB 142B Midterm II...

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EEMB 142B Midterm II study sheet Lecture 11 Turbulence in Upper Mixed Layer o Circulates phytoplankton cells • May reduce photoinhibition leading to higher overall rates of photosynthesis • May facilitate or reduce success of feeding by zooplankton and fish larvae. • May entrain nutrients from thermocline o Effects rates of photobleaching of dissolved organic carbon (and thus changes in labile organic matter) • Entrainment of deeper water and nutrient supply • Rate of loss of green house gases • Calculation of lake metabolism Reynolds # R e = (ul)/v u= velocity l= depth of mixed layer v= kinematic viscosity (10 -6 m 2 /s) HIGH VALUES = TURBULENT Richardson # Ri = g/ρ (dρ/dz)/(du/dz) 2 g = gravity (9.81 m s -2 ) ρ = density (kg m -3 ) z = depth u = velocity Instability if R i <0.25 Kelvin Helmholtz Billows -Form due to shear in stratified water - Instability if Ri <0.25 Lecture 12 Lecture 13
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Buoyancy Frequency A measure of the stability of density structure in lakes and oceans N2 = g / ρ (d ρ /dz) g = gravity 9.8 m s-2 ρ = density d ρ /dz is density gradient, that is, the change in density with depth Units of N are s-1 or, by recalling that there are 2 pi radians in a cycle, we convert to cycles per hour (cph). What are the impacts of raising the deep water? • Potential to destabilize the lake. – What mechanisms would cause the destabilization? • Increased flux of CO2 and CH4 to the atmosphere • Increased loading of nutrients to surface waters. • Less risk of a catastrophic eruption Density Structure and Internal Waves • Internal waves occur in stratified waters. • They look like waves we see on the sea surface. • They are initiated when a disturbance causes a pycnocline to tilt. • For Lake Kivu, the disturbance could be wind, an earthquake, or a volcano.
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EEMB 142B Midterm II study sheet - EEMB 142B Midterm II...

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