Download 2009, final Lecture 9 Marine Snow

The Biological Pump
Transfer of Energy and Material to the Deep Sea
Formation and Fate of Marine Snow
The ‘Missing’ Carbon
Atmospheric Increases are ~3.2 Gt y-1
Anthropogenic inputs are ~5.4 Gt y-1
~2.2 Gt of anthropogenic Carbon input is not
accounted for in the atmosphere, and is therefore
missing.
The Biological Pump
Marine Snow
Marine Snow Particles
Marine Snow Particles
Discarded feeding houses
Marine Snow Particles
‘Comets’
Contribution of Marine Snow to Vertical Flux
Narrow window of particle sizes which are large
enough to sink but numerous enough to be widely
distributed.
Cells
Snow
Bodies
2
200
20,000 (um)
cell
chain
plankton
poop
aggregates
Willie
X
1-10 m
50 m
Available to
water column
processes
100 m
2000 m
Reduction in Vertical Flux over Depth
1
The Martin Curve
50% losses by 300 m
75% losses by 500 m
90% losses by 1500 m
Martin and Knauer 1981
2
3
Explanations for the Shape of the Martin Curve
• Bacterial decomposition = remineralization of Carbon
• Cryptic swimmer distribution
• Smaller, slower sinking particles at depth
Extreme Deposition: Food Falls
• Rare events (not recorded in traps)
• Deposit large amounts of high quality organic
materials to sea floor (low C:N)
• Rapid sinking, reach 1000s of meters in few days
• Large bodies that remain intact (whales, fish,
macroalgae, etc)
Aggregates
Composition of Marine Snow
Once living material (detrital) that is large enough to
be seen by the unaided eye.
Described first by Suzuki and Kato (1955)
High C:N makes for poor food quality.
• Senescent phytoplankton
• Feeding webs (e.g., pteropods,
larvaceans)
• Fecal pellets
• Zooplankton moults
Formation of Marine Snow
Type A: Mucous feeding webs are discarded
individually.
Type B: Smaller particles aggregate into larger,
faster sinking particles.
Aggregates
How does Type B Snow Form?
Coagulation Theory: Particle Collision Rates
Differential settling velocities
Turbulent motions
How does Type B Snow Form?
Coagulation Theory: Particle Stickiness
Transparent Exopolymeric Particles
TEPs
Related to bloom conditions of phytoplankton:
• High phyto concentration
• Nutrient depletion
• Self-sedimenting strategy?
Properties of Type B Marine Snow
• High porosity (99% water)
• Carbon source for bacteria and protozoan grazers
(gases often produced)
• Some snow >90% bacteria
• Pore water exchanges dictate chemical gradients
Marine Snow Dynamics
Where will Snow Contribute to Missing Carbon?
Only ~1% of annual new
production reaches sea floor