Episodic Productivity Flashcards
Deep Chlorophyll maximum
Peak in chlorophyll below the mix layer
What causes a deep chlorophyll maximum
Hypothesis 1:
Chl maximum develops at the shallowest point where nutrients are present
The highest light levels they can get while still having nutrients
Hypothesis 2:
Chl maximum at low light levels (base of euphotic) as a photo-acclimatization strategy
Produce more chl a when light levels are low
Where do we see the classic bloom mechanics?
In the Atlantic and southern ocean
Why do we see a later bloom in the arctic?
The light is not intense enough until far later into the year – irradiance doesn’t peak until much later
Sea ice covers the arctic ocean in winter, and some ice persists into winter
The ice blocks light, and allows snow buildup
Need enough light and heat to melt the ice before bloom can occur, bloom follows melting sea ice
Bloom often occurs after peak sunlight, because it requires the melting of the sea ice
Coastal Upwelling Zone Nutrient Dynamics
Episodic nutrient input to the surface ocean drives episodic productivity and blooms
How does upwelling work?
Water moves 90° to the wind blowing on the surface due to the Coriolis force (upper 50m) of water)
In the Northern Hemisphere, water moves 90° to the right and to the left in Southern Hemisphere
When winds blow along shore, they cause water to move offshore, thus pulling deeper denser water to the surface to replace it
This brings nutrients with it to the surface waters
Why is chlorophyll sometimes a poor measure of phytoplankton biomass?
Species differ in the amounts of chlorophyll they produce
Chl a production is dependent on ambient light levels experienced
Why do polar oceans show one large bloom near the summer solstice?
There is when there is finally enough light, and the ice and snow has melted to allow light penetration for a bloom
If winds are blowing N to S off Vancouver Island, which way will the surface water move?
The surface water will move offshore East to West
Coastal Upwelling
Bring cold nutrient-rich water to the surface from below
Stimulates phytoplankton productivity
Winds need to move surface waters away from shore to cause upwelling
Sporadic productivity in upwelling zones
The productivity occurs in pulses
Varaiable winds change direction
Frequent shifts between upwelling favourable, and downwelling or neutral winds
Species dominance in coastal upwelling
Diatoms make up 50-80% of upwelling production
Totally dominate upwelling blooms
Mesocosm upwelling experiment
Bring deep water and expose it to surface light
Upwelling stimulates productivity of all phytoplankton
Large phytoplankton increase most rapidly
Large chaetoceros deblis do the best (centric diatom)
Upwelling Zone Species Succession
The initial population before the nutrient pulse is small phytoplankton
Large diatoms then dominate after nutrients
Then small phytoplankton again once the nutrients run out
Small cells have high SA/V so efficient nutrient uptake at low nutrients
Large cells have higher growth rate, more volume for photosynthesis and growth (high kN and Gmax)
Equatorial Water movement
Winds blow parallel to equator causing diverging water movement away from equator
Causing upwelling
