primary production & seasonality

Question 1

summarise photosynthesis in terms of the photosystems

Answer 1

Light into PSII -> energy transferred across membrane -> provides energy to PSI

Question 2

what happens to energy as wavelength decreases

Answer 2

energy also decreases
explain why plants don’t utilise radio waves (low energy) and prioritise visible wavelengths instead

Question 3

what happens to absorption in water as wavelength increases

Answer 3

absorption also increases

Question 4

what wavelengths get absorbed

Answer 4

• ~50% infra red >780 nm
• ~50% visible spectrum ~400-~700 nm
• <1% ultraviolet <380 nm

Question 5

why are only blues and blacks visible in deep waters

Answer 5

rest has been fully absorbed by water

Question 6

what wavelengths have Things like phytoplankton have to evolve to make use of

Answer 6

the more blue/green parts of the visible spectrum
- also contain additional pigments to increase the amount of energy they are able to make use of e.g. photosynthetic carrotenoids

Question 7

what happens to photosynthesis as light intensity increases

Answer 7

also increases - up to a certain point…..

Question 8

what happens when phytoplankton receives too much light

Answer 8

sterilisation of the plankton will occur

Question 9

how do plankton cope with sterilisation due to too much light

Answer 9

photoprotectant carrotenoids -> absorb the same light as the photosynthetic carrotenoids but do not pass it on to chlorophyll a (dissapate it as heat instead to get rid of it)

Question 10

what allows us to identify groups of phytoplankton

Answer 10

The different proportions and types of accessory pigments

Question 11

formula to calculate the diffuse attenuation coefficient (m-1) -> how mercy the water is

Answer 11

Iz = I0 e-kz (make K the subject)
big k = mercy water
Use k to calculate I (light) at any depth in the water column

Question 12

what’s a thermocline

Answer 12

zone of sharply changing temperature

Question 13

what’s a Halocline

Answer 13

zone of sharply changing salinity

Question 14

what’s a Pycnocline

Answer 14

zone of sharply changing density

Question 15

what’s a Ergocline

Answer 15

energy gradient (amount of energy needed to mix water down to that depth)

Question 16

where does the most production occur

Answer 16

the mixed layer

Question 17

what’s planktons movement controlled by

Answer 17

the surface mixed layer (SML) -> depth varies depending on wind speed and heating

Question 18

how to calculate average irradiance (I) in the SML

Answer 18

k (attenuation) x h (depth of SML)
- Phytoplankton experience fluctuating light in this SML

Question 19

Surface mixed layers in winter vs summer

Answer 19

• winter it is deep + less light (but more nutrients)
• summer its more shallow + more light (but less nutrients)

Question 20

formula to calculate gross primary production (Pg)

Answer 20

Ke + (I)
- Pmax = max rate of photosynthesis
- Ke = half-saturation constant
- (I) = ambient PAR
- Pmax and Ke varies between species, leading to succession of different phytoplankton species

Question 21

formula to calculate net primary production (Pn)

Answer 21

Ke + (I - Ic)
- takes respiration into consideration
- Ic = amount of light needed to balance respiration of the plankton at that depth

Question 22

formula to calculate compensation depth (Zc)

Answer 22

k
- depth at which photosynthetic production = respiratory losses i.e. Depth at which = I = Ic
- Compensation depth = bottom of euphotic zone
- Describes plankton when they are still (problem – they always move with the water)

Question 23

what’s critical depth (Zcrit)

Answer 23

depth of a SML in which respiration = photo over 24 h
- aka the depth at which the amount of light available for photosynthesis is just enough to support the metabolic needs of phytoplankton

Question 24

what happens when the critical depth is smaller and bigger than the depth of SML

Answer 24

• If depth of SML > Zcrit -> no growth
• If depth of SML < Zcrit -> growth (spring bloom) - getting enough energy from the sun to support increase in population

Question 25

what determines whether a community is able to survive

Answer 25

balance of total energy used for respiration in 24hr + total energy used for photo in 24hr

Question 26

what kind of community do we have when enery used for respiration is more and less than that used for photosynthesis

Answer 26

• If total energy used for resp in 24hr > total energy used for photo in 24hr, community = heterotrophic – no growth of phytoplankton
• If total energy used for resp in 24hr < total energy used for photo in 24hr, community = autotrophic – P > R = growth

Question 27

is phytoplankton conc higher in winter or summer

Answer 27

summer

Question 28

what does Phyto productivity, biomass & composition rely on

Answer 28

light, nutrients, mixing & grazing
- usually follows a seasonal pattern

Question 29

describe the thermocline in summer

Answer 29

quite steep - less energy, more light

Question 30

describe the thermocline in fall/autumn

Answer 30

Much smaller thermocline – less light, more energy (wind etc - more mixing)

Question 31

describe the thermocline in winter

Answer 31

very deep - Entire seabed = mixes waters - Loads of energy (more turnover), dark

Question 32

describe the thermocline in spring

Answer 32

Build-up of thermocline again - Less energy, more light

Question 33

is the winter SML more or less than Zcrit (critical depth)

Answer 33

SML > Zcrit = no phyto growth

Question 34

is the spring SML more or less than Zcrit (critical depth)

Answer 34

SML < Zcrit = phyto growth

Question 35

is the summer SML more or less than Zcrit (critical depth)

Answer 35

SML < Zcrit = phyto growth

Question 36

is the autumn SML more or less than Zcrit (critical depth)

Answer 36

SML > Zcrit = no phyto growth

Question 37

winter water characteristics

Answer 37

• A lot of energy in system - Water column well mixed
• Heterotrophic system
• [Nutrient] (N, P, Si) high: decomposition of OM - no phyto to eat it
• Low PAR: cloud, short days, sun low in sky
• Sea: turbid, stirred sediment
• Low ambient irradiance & high suspended particulate loading = shallow Zcrit
• Mean resp > mean photo = no phyto growth
• [Chl a] uniformly low

Question 38

spring water characteristics

Answer 38

• Day length increases, wind speeds decrease
• Sea-surface absorbs heat faster than turbulence can redistributed it
• Thermocline forms: resists vertical mixing
• Sediment settles – water gets clearer
• High nutrients & light = high growth rate
• Diatoms dominate – high growth rate
• Result: high [chl a] = spring bloom
• 1-2 weeks: diatoms exhaust NO3- in SML
• Bloom ends quite quickly – not enough nutrients for diatom
• Mesozooplankton: slow to respond
• Most phyto OM exported to benthos
• Heterotrophic dinoflagellates can respond more rapidly to feed on diatoms

Question 39

summer water characteristics

Answer 39

• Big change in temp
• Water column: highly stratified
• SML:👇nutrients, ^ chl a
• Small phyto: take up nutrients, maintain position
• Prey & predator growth = well matched: little export

Question 40

autumn water characteristics

Answer 40

• Reverse of spring
• Increased turbulence: storms, lower temps
• SML deepens: nutrients entrained into SML
• Short lived diatom bloom
• Stratification breaks down completely

Question 41

why does shallow water prevent phyto growth

Answer 41

mixed all year, high suspended sediment load

Question 42

what is temperate productivity

Answer 42

Summer = plenty of light, not enough nutrients – between the two is where we get plenty of light and nutrients for the phytoplankton
- Zooplankton will follow this phytoplankton trend