crucial knowledge Flashcards
Oxygenic photosynthesis
Light stage = photosystems O2 produced
PS2 = photolysis of water produce electron
transported through chain to pS1 where it is used to reduce NADP+ to NADPH ATP is produced by atpsynthase
Light independent stage/DARK stage - calvin cycle
Use atp and nadph
Carboxylation - CO2 + rubp (rubisco) forms intermediate
Reduction - ATP and NADPH forms G3P
Regeneration of RuBP for C fixation
PQ
molar ratio of oxygen produced to carbon fixated - Photosynthesis 1 or less PQ
PQ nitrogen
if electrons are used from light dependent stage for other processes than C fixation like reduction of oxidised forms of nitrogen such as nitrate - PQ result in higher
Growth on nitrate PQ=1.4
NO4- +5.7CO2 + 5.4h2o –> C5.7H9.8O2.3N +8.25O2 + OH-
Growth on ammonia PQ=1.1
NH4+ +5.7CO2 + 3.4H2O –> C5.7H9.8O2.3N +H-
Pq shows if nitrogen species assimilated is new or regen
Biological Carbon Pump
- Production of organic material at surface by phytoplankton
- Packaging of particulate material into sinking forms
- Sinking of POC to depths
- Remineralisation of POC to CO2 in deep ocean for long term storage
Regenerated Forms of nitrogen
NH4 - bacterial deamination animal excretion
Urea - Bacterial degradation and excretion
New nitrogen forms
Nitrate - bacterial oxidation below thermocline
Nitrite - bacterial oxidation low O2 from NH4
N2 gas - N2 fixation by trichodesmium
Microbial pump
- Production of organic materials at surface by phytoplankton
- transformation of organic material into refractory dissolved organic material by bacteria allowing long term storage
Affects of oceanic systems on pumps
BCP dominates in upwelling - high nutrient availability large blooms - efficient C export
(POM) strong A-H
MCP domiantes in oligotrophic gyres - nutrient limited increase bacterial activity converts C into refractory forms (rDOM) - weak A-H
North Atlantic seasonal cycles and communities (phyto)
Winter = high nutrient low light availability (high stratification)
Spring - increased irradiance and less stratification - bloom
Nutrient levels depleted by summer high light irradiance remains
Winter = small prok + picoeuk (Prochlorococcus) = low KN
Spring = large euk (diatoms)
Summer = coccolithophores/nanoeuk
Hawaii Seasonal Cycle And Communities
Oligotrophic region - weak seasonality = low biomass
Production is greater at deep chloro max close to nitracline
Communities = small prok and picoeuk - highly adapted - loss of genes for nitrate uptake small cell = low KN
Larger euk at DCM - diatoms
Bermuda Seasonal Cycles and Community
Oligotrophic however convective overturning in winter causes blooms
Winter= convective overturning deepens mixed layer where it penetrates nitracline - influx of nutrients incr production winter/spring bloom
Spring = bloom stops nutrients depleted
Summer back to oligotrophic region
Communities = diatoms large euk during winter nanoeuk and coccolith in spring before prochloro in summer/spring
Phytoplankton dominance
Large eukaryotic phytoplankton in spring blooms –> larger cell sizes fast growth and grazer defences (frustules)
Small prokaryotic Phytoplankton in oligotrophic waters –> small cell size loss of genes required for nitrate uptake high nutrient affinity low KN
Critical depth theory
- Phytoplankton at the surface able to photosynthesise however mixed down with depth - irradiance decrease
- This means less photosynth and more resp proportionally therefore less POC/DOC production
- Assuming photo decrease w irradiance reach a depth where Resp = Photo –> Compensation Depth
- phytoplankton are consistently mixed below and above this depth above net gain below net loss
If the mixed layer was shallower than the critical depth this would cause new production - bloom
DCr = Eo/kxEc
Critical depth theory assumptions
Photosynthesis rate proportional to irradiance
Nutrient concentration is non limiting
Respiration is constant
Phytoplankton distribution constant with depth
Extinction coefficient is constant
Alternative theories to criticla depth
Disturbance recovery = balance between phyto growth and loss rates –> blooms are initiated by physical processes that disrupt the balance eg deep mixing /upwelling
Criticla turbulence = the end of net convective mixed layer deepening corresponds with net positive heat flux.
Eddy restratification = increase in average mixed layer irradiance is driven by eddie restratification rather than net buoyancy
El nino impacts
El nino - causes downwelling supresses upwelling deepning the thermocline preventing nutrients to surface –> leads to reduced phytoplankton growth less POC more rDOC
La nina - causes upwelling the thermocline shoals bringing nutrients from overlapped nitracline - increased production more POC less rDOC
Increased stratification effects
Reduction in nutrient flux to surface - decrease phyto in surface - bluer water
2nd order effects - dominance taken over by smaller eeuk and prokaryotes like Prochlorococcus - ocean colour reflects pigments
High latitude increase in light availability may lead to greening waters
Deep chlorophyll max
Forms at the density interface represented by thermacline which seperates nutrient depleted upper mixed layer and repleted sub layer
Such that phytoplankton can grow in the region by sufficient light from above and nutrients from below
Cyclonic eddies
Result in the uplift of the thermocline –> expose phytoplankton within and below thermocline adewquate nutrients and incr in light
consequently incr production - bloom increase in export prod POC
P vs E curve
Light limited region = photosynthesis rate proportional to irradiance - constant absorption from pigments to gen O2 from photolysis of water
A is the light utilization parameter - product of absorption coefficient and max quantity yield
0 = compensation irradiance P=R
The light saturation region is where photosynthesis has reached a max due to limited by enzyme rate in calvin cycle
Photoinhibition occurs damaging photosystems.
