Post-Midterm 3 Content

Question 1

define Upwelling (Ekman Divergence)

Answer 1

As water at the surface diverges, the surface height will decrease slightly, and water will come up from below to replace the water that is moving away from each other.
- drawing up of water from the deep to supply it to the surface is called upwelling.

Question 2

define Downwelling (Ekman Convergence)

Answer 2

As water at the surface gets pushed towards itself, surface height will increase slightly, and cause water to “pile up” and be forced downwards. This is called downwelling.

Question 3

what areas of the ocean will be more productive at the surface?

Answer 3

Areas where there is upwelling occurring, because nutrients will be brought up from the deep.
Around 60 deg Latitude

Question 4

What is occurring in a Sub-Polar region in the N hemisphere?

Answer 4

• low atmospheric pressure
• counter-clockwise winds (Cyclonic)
• Ekman Divergence
• upwelling w/ high productivity
• thin mixed layer

Question 5

What is occurring in a Sub-Tropical region in the N hemisphere?

Answer 5

• high atmospheric pressure
• clockwise winds
• Ekman Convergence
• downwelling
• nutrient poor region (oligotrophic) w/ low productivity
• thick mixed layer

Question 6

what is the Aleutian Low

Answer 6

region in the north pacific ocean where there is cyclonic (counter-clockwise) winds and low atmospheric pressure
- dominates the wind pattern in the winter

Question 7

what is the Pacific high

Answer 7

region in the mid-pacific ocean where there is anti-cyclonic (clockwise) winds that create a region of high atmospheric pressure
- dominates the wind pattern in the summer

Question 8

In winter, Ekman flux off our coast is directed where?

Answer 8

TOWARDS our coast (90 degrees right of the winds moving from the southwest)

Question 9

In summer, Ekman flux off our coast is directed where?

Answer 9

AWAY from our coast (90 degrees right of the winds coming from northwest)

Question 10

Model of coastal upwelling in summer

Answer 10

• summer winds are moving South
• Ekman flux is moving offshore
• divergence near the land
• surface height goes down slightly
• UPWELLING of deep water to fill in space where water is diverging away from land
• Nutrient Rich area

Question 11

Model of coastal downwelling in winter

Answer 11

• winter winds are moving North
• Ekman flux is moving towards shore
• convergence at the shore
• surface height goes up
• DOWNWELLING occurs due to pile up of water
• nutrient deplete area

Question 12

define Pycnoline

Answer 12

change in density with depth

Question 13

define Thermocline

Answer 13

change in temperature with depth
- usually found below the mixed layer, because the mixed layer is fairly even temperature

Question 14

how does Ekman convergence affect stratification?

Answer 14

Ekman convergence deepens the thermocline because it pushes the mixed layer deeper, making a thicker surface layer
- reduces nutrients in the surface by bringing them to the deep through downwelling

Question 15

how does Ekman divergence affect stratification?

Answer 15

Ekman divergence raises the pycnocline, because it lowers pressure and causes upwelling.
- this raises the pycnocline to be shallower compared to regions away from the upwelling region
- can cause RELATIVE high pressure under the uplifted deep layer

Question 16

Geostrophic current caused by Ekman divergence in N Hemisphere ?

Answer 16

Geostrophic current around a region of low pressure moves counter-clockwise around the divergence (keeps High pressure on its RIGHT i.e. coriolis force directed to the right)

Question 17

Gyre circulation in N hemisphere – winds around surface divergence?

Answer 17

winds will move counter-clockwise around the region of low pressure, with geostrophic flow also moving under the wind.
- Coriolis force pointed outwards

Question 18

Gyre circulation in N hemisphere – winds around surface convergence?

Answer 18

winds move clockwise around region of high pressure.
- Ekman flux is directed inward, caused high pressure in the surface.
- geostrophic flow moves clockwise under the winds.

Question 19

directions of gyre circulation in the North Pacific?

Answer 19

• in the sub-polar N Pacific, there is counter-clockwise flow
• in the sub-tropical N pacific, there is clockwise flow

Question 20

Currents off the coast: Surface Jet

Answer 20

This is a surface current that is driven by the winds moving down or up the coast, located above the continental shelf break

Question 21

Currents off the coast: California Current

Answer 21

current that is part of the subtropical gyre (farther offshore than the surface jet) moving south along the coast

Question 22

Currents off the coast: Poleward undercurrent

Answer 22

an current under the surface layer that moves toward the poles (opposite direction to the California current)

Question 23

How does f (coriolis force) change with latitude?

Answer 23

in N and S hemisphere, f increases with latitude
- more + in N
- more - in S

Question 24

what is f (coriolis force) at the equator?

Answer 24

right at the equator, f (and coriolis force) is zero

Question 25

at the equator, what direction is the surface flux?

Answer 25

near surface flux right along the equator moves in the direction of the wind.

Question 26

what is the Intertropical Convergence Zone (ITCZ)?

Answer 26

region where the two Hadley cells converge - rising air here causes wet, unstable air and frequent/violent thunderstorms - it is NEAR the equator (not exactly at it) due to the unequal distributions of land in the N and S hemisphere and seasonal changes.

Question 27

latitude of the ITCZ

Answer 27

in January, ITCZ is at 7 deg N in July, ITCZ is at 10 deg N

Question 28

Direction of Ekman flux near the ITCZ

Answer 28

North of ITCZ = Ekman flux to the northwest (winds coming from the northeast) 7 deg N = low wind, little Ekman flux 3 deg N = Ekman flux to the northeast (winds from the southeast at Equator = winds from the east, flux to the west 5 deg S = winds from the east, Ekman flux to the south

Question 29

Ekman convergences near the equator?

Answer 29

surface convergence happens between the ITCZ and the equator (High pressure region)

Question 30

Ekman divergence near the equator?

Answer 30

surface divergence happens north and south of the equator (Low pressure region)

Question 31

what is the Equatorial Counter-Current

Answer 31

in upper layer, wind drives surface flow to the west along the equator in lower layer, the wind effect is not strong, but the pressure gradient that is built up from west-east causes a gradient of High to Low pressure. - this causes a very FAST undercurrent flow from west to east (driven by pressure gradient)

Question 32

productivity around the equator?

Answer 32

there is higher productivity in small bands on either side of the equator due to low pressure/upwelling that occurs, bringing nutrients up from the deep. - right along the equator, however, is a region of high pressure where there is low nutrient availability

Question 33

North Pacific regions of high and low productivity (chlorophyll)

Answer 33

High = sub-polar, coastal regions, along the equator Low = sub-tropical N pacific

Question 34

characteristics of downwelling gyres in the Atlantic subtropics?

Answer 34

- surface convergence - warm surface temperatures - nutrient poor due to downwelling

Question 35

pressures in sub-polar vs sub-tropical gyres

Answer 35

sub-polar = low pressure centre sub-tropical = high pressure centre - in both north and south hemispheres

Question 36

characteristics of upwelling gyres in the Atlantic subpolars?

Answer 36

- surface divergence - cool temperatures - nutrient-rich waters brought up from the deep (upwelling)

Question 37

Productivity levels: Continental shelf

Answer 37

year-round bloom OR seasonal blooms due to river-runoff and/or tidal mixing

Question 38

Productivity levels: Coastal upwelling

Answer 38

eastern side of ocean basins, blooms for extended periods (driven by wind/geostrophic flow causing upwelling)

Question 39

Productivity levels: Equatorial Upwelling

Answer 39

narrow band along the equator, driven by plentiful light, divergent upwelling causing blooms for extended periods of time

Question 40

Productivity levels: subtropical convergences/downwelling gyres

Answer 40

warm, stratified waters with low productivity year rounds.

Question 41

Productivity levels: Temperate regions

Answer 41

1. winter mixing, spring bloom and/or fall bloom 2. divergent gyres

Question 42

Productivity levels: Polar regions

Answer 42

light limited 3/4 of the year, summer bloom only when winds decrease and surface temperature increases

Question 43

how is phytoplankton growth limited by P (phosphorus) concentration?

Answer 43

low [P] in seawater results in low intracellular P. As P limitation increases, C:P increases. Eventually this inhibits cell division.

Question 44

How are most nutrients uptaken by phytoplankton?

Answer 44

Phytoplankton uptake most nutrients via Active transport. - active transport uses energy to transport nutrient into the cell against an electrochemical gradient - follows Michaelis-Menten (MM) Kinetics

Question 45

Michaelis-Menten (MM) Kinetics

Answer 45

uptake rate is a function of external nutrient concentration. - uptake rate depends on number of nutrient transporters, time it takes to handle the nutrients, and nutrient concentration

Question 46

define Nutrient uptake rate v (MM kinetics)

Answer 46

v = Vmax (S/(S+Ks) v = uptake rate Vmax = max rate of nutrient uptake S = nutrient concentration Ks = half-saturation constant for uptake where v=1/2Vmax

Question 47

what is the trade-off between Ks and Vmax

Answer 47

low Ks results in a slower/lower Vmax, while high Ks results in faster Vmax

Question 48

when will Vmax be high versus low?

Answer 48

Vmax will be high in a high nutrient region, and low in a low nutrient region.

Question 49

paradox of phytoplankton

Answer 49

phytoplankton need basically all the same nutrients, but they don't outcompete each other because nutrient concentrations and conditions change rapidly, favouring different species at given times.

Question 50

phytoplankton characteristics in oligotrophic regions?

Answer 50

- small cell size (high SA:V ratio) - high affinity transporters to limiting substrate (low Ks) ex. coccolithophorids, small dinoflagellates, Prochlorococcus, Synechococcus

Question 51

phytoplankton characteristics in upwelling regions?

Answer 51

- large cell size - large vacuoles to store nutrients - high Vmax & Ks - fast growth rate ex. diatoms, large dinoflagellates

Question 52

high productivity food webs include...

Answer 52

- large phytoplankton - few upper trophic levels - efficient transfer of organic C up the food web - efficient sinking of organic C from surface to deep

Question 53

low productivity food webs include...

Answer 53

- small phytoplankton - lots of upper trophic levels - inefficient transfer of organic C up the food web - inefficient sinking of organic C from the surface to deep ocean

Question 54

what controls primary productivity in High Nitrate Low Chlorophyll regions (HNLC)?

Answer 54

- there is observed excess nutrients (nitrate) in the southern ocean and subarctic pacific. - hypothesized that iron is the primary limiting nutrient in these regions.

Question 55

the Iron Hypothesis

Answer 55

1. higher iron (Fe) supply is correlated with lower CO2 concentrations. 2. the concentration of Iron in seawater is very low, but still follows a distribution like any other nutrient (with small increase at surface due to dust input)

Question 56

why would Iron be a limiting/important nutrient?

Answer 56

- Fe is in high demand by phytoplankton because it is used in many physiological systems and biological reactions --including photosynthesis - it has an extremely short residence time (days-weeks in the surface, 10-100 years in deep ocean)

Question 57

how is iron added to the ocean in soluble forms?

Answer 57

primarily from ocean bottom (sediments and hydrothermal vents), where biogenic material is degrading & released soluble iron back into the seawater--can be brought up to the surface by mixing and upwelling Atmospheric dust (most important main source) carries iron from land over the ocean and deposits it in tiny amounts, able to dissolve.

Question 58

what would the impacts be of massive Iron fertilization of the ocean?

Answer 58

- massive phytoplankton bloom - large decay of phytoplankton results in high CO2 and low O2 in the deep - other decomposing bacteria become present and produce higher amounts of potent GHG like methane and Nitrous Oxide)

Question 59

where are diatoms the dominant phytoplankton taxa?

Answer 59

nutrient rich, sub-polar regions Southern Ocean!

Question 60

where are large phytoplankton the dominant taxa (not diatoms)

Answer 60

nutrient rich, coastal regions of the sub-polar areas

Question 61

where are small eukaryotic phyplankton the dominant taxa (Synechococcus, small coccolithophorids and dinoflagellates) ?

Answer 61

nutrient poor, temperate and sub tropical regions - where there is upwelling

Question 62

where are Synechococcus and Prochlorococcus the most dominant phytoplankton taxa?

Answer 62

moderately nutrient rich along the equatorial region.

Question 63

what is the "Biological Pump" in the ocean?

Answer 63

this is the transfer of CO2 from the atmosphere to the deep ocean mediated by phytoplankton C fixation in surface waters - it is inefficient in 30% of the global ocean due to low Fe concentrations/inputs

Question 64

how can iron limitation be identified on a graph?

Answer 64

iron limitation is identified by high N:Fe ratios found below the mixed layer.

Question 65

the first phytoplankton to bloom after winter mixing ends is...

Answer 65

Diatoms - use NO3- (rich waters from the winter mixing), will likely run out of this first which will cause the bloom to die - large cell size with fast growth rates - low-light adapted (high alpha, low Pmax, large # of photosynthetic units)

Question 66

most likely phytoplankton that will grow after diatom spring bloom has decayed are...

Answer 66

Dinoflagellates - smaller size (higher SA:V ratio for optimum nutrient uptake) - use recycled N at surface (NH4+) and some NO3- at depth (can use their flagella to move up and down the water column) - slower growth rates and adapted to lower nutrients -

Question 67

phytoplankton blooming in summer will be..

Answer 67

Diatoms - high light adapted (low alpha, high Pmax) - fast growth rates - large vacuoles to store NO3- - adapted to high nutrients

Question 68

why is there N-limitation in coastal waters off Vancouver island?

Answer 68

because in summer the Ekman flux is moving offshore, resulting in coastal upwelling. - the northward undercurrent brings water from an OMZ where there's denitrification and anammox, resulting in upwelling of this water. - makes N* negative resulting in N-limitation

Question 69

Is there iron limitation off coast of Vancouver island?

Answer 69

close to shore, Fe is not limited because the continental shelf sediments supplies Fe to the surface waters far off shore, Fe is limited due to lack of dust input and sedimentary sources being too deep to be sources of Fe to the surface.