Lecture 14: Phytoplankton (Part 2)

Nutrient?

- -Concentration which increases with increasing water depth. (blue line)

What controls primary productivity? Hint - there are 4 abiotic factors and one biotic factor?

- Light availability. (abiotic) - Nutrient supply (bottom-up controls (abiotic). -Mixing (abiotic). -Temperature (abiotic). -Grazing (biotic). ex zooplankton.

Why do certain regions of the ocean have excess nitrogen? Where is one such region?

-- East equistorial region: environment where we have nutrient limitation, more than enough sunlight. Iron limited productivity. -Low Primary productivity, North Atlantic, even down at 500m. -At Deep water forming. -Polar regions, high nutrient concentration all year.

Photic zone?

-Aka (Euphotic) zone, surface layer of ocean that has enough ight for photosynthesis to occur.

Aphotic zone?

-Part of the ocean where there is insufficient light for photosynthesis. Most of the ocean falls here.

Can you discuss the seasonal progression of the thermocline at tropical, mid-latitude, and high latitudes and discuss how that impacts the abundance of nutrients and standing stock?

-Tropics (high intensity light), low nutrients (nutrients limited, temp is high not much change, strong thermocline *stable) shallow mixed layer & deep photic zone. -Overall, low primary productivity & most is regenerated productivity. --Polar Regions, lots of light in summer (24hrs) but its intensity is low & it does not penetrate very deep. Little to no in winter. Surface water is cold, formation of seasonal thermocline in summer. Photic zone is shallow, LOTS of mixing. Overall, light availability & deep mixing limit primary productivyty (not nutrients). one large pulse of primary production. Mid-Latitudes: Intensity & duration of sunlight varies seasonally (low in winter, high in summer) Nutrients are high in winter due to a deeper mixed layer & lower productivity, low in summer for the opposite reasons. Two phytoplankton blooms when sufficient light & nutrients coincide. Surface temp follows sunlight. Strong seasonal thermocline in summer resultsin in density stratifiation, phytoplankton are not mixed below photic zone but nutrients are out of reach. Mix layer shallows in summer whiel photic zone deeps, when they cross there is a bloom.

Top-down control?

-When predator controls the abundance & dynamics of a lower trophic levels. Ex: gracing of phytoplankton by zooplankton. It will keep pop, biomass of zooplankton limited. If you don't have zooplankton around then you do not have that control

Nutricline?

-Where there is a rapid change in nutrient concentration. -depth at which there is an abrupt increase in nutrients

Critical depth?

Depth at which TOTAL photosynthesis = TOTAL respiration (ex: integrated over the entire water column)

Compensation depth?

Depth below which there is NO net production (ex: rate of photosynthesis=rate of respiration)

Turbid

Has a lot of particles.

HNLC Region?

High nutrients Low chlorophyll regions. -Micronutrient.

Why is there both a spring and fall bloom in mid-latitude locations?

Mix layer shallows in summer while photic zone deepens. When they cross there is a bloom. ---See two phytoplankton blooms when sufficient light & nutrients coincide in spring & fall.

Chlorophyll maximum?

Peaks at 30m, this is the plankton biomass. -Not peaking at surface at the ocea, about 30ish meter. This is the region where we have a combination of high nutrients and just enough light so we can have photosynthesis occur. -Peak in phytoplankton (chlorophyll maximum).

If you went out and measured the total amount of nutrients in the ocean, why would you find almost none in the surface layer?

Phytoplankton removes the nutrients from the surface waters. Once the phytoplankton die, etc, eventually the organic matter falls into the deep ocean & remineralized.

Bottom-up control?

When the energy in the system is moving from a lower trophic level to a high one. Flow of energy &

How does up-welling lead to increased phytoplankton stocks?

upwelling, from about 200 m depth, stimulating primary production. --upwellinng bring cold, nutrient-rich water from below the thermocline.