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Does Biological Community Structure Influence Biogeochemical Fluxes? JGOFS Says Yes! Anthony F. Michaels University of Southern California Wrigley Institute for Environmental Studies. Roadmap. What do we mean by community structure? - PowerPoint PPT Presentation
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Does Biological Community Structure Influence Biogeochemical Fluxes?
JGOFS Says Yes!
Anthony F. MichaelsAnthony F. MichaelsUniversity of Southern CaliforniaUniversity of Southern California
Wrigley Institute for Environmental StudiesWrigley Institute for Environmental Studies
RoadmapRoadmap
• What do we mean by community structure?
• Selected survey of community impacts on global carbon cycle– HNLC– Particulate Inorganic Carbon– Nitrogen Fixation– Remineralization length-scales
Tension and BalanceTension and Balance
• Biologist’s love of the details of life
• Biogeochemist’s need to simplify in order to model global dynamics
What do we need to What do we need to get a food web?get a food web?
Phytoplankton
Zooplankton
NutrientsSinking
Particles
SinksStays Suspended
What do we need to What do we need to get a food web?get a food web?
Phytoplankton
Zooplankton
NutrientsSinking
Particles
SinksStays Suspended
Bacteria
(Fasham et al., 1990)
Time
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Nitrate
PhytoZoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
So, what are we really asking?
Nitrate
Phyto
Zoop
P-Z-N Dynamics: Populations Change through TimeP-Z-N Dynamics: Populations Change through Time
Phyto
Does it matter what biology is hidden within each box?Does it matter what biology is hidden within each box?
Phyto
DiatomsPrasinophytesPrymnesiophytes
ProchlorococcusSynechococcus
Is this level of details necessary Is this level of details necessary to understand the carbon cycle?to understand the carbon cycle?
Rephrase the QuestionRephrase the Question
Do we need more structure thanP-Z-N-B to capture the important
carbon dynamics for global scales?
(e.g., more phytoplankton, more zooplankton, viruses, marine snow, etc.)
Pico-Phyto
Nano-Phyto
Micro-Phyto
Community Structure and Flux: Community Structure and Flux: Circa 1988Circa 1988
Start with big size range of plantsStart with big size range of plants
<2 µm 2-20 µm 20-200 µm
Nutrients
Pico-Phyto
Nano-Phyto
Micro-Phyto
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Meso-Meso-ZooZoo
Nutrients
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Meso-Meso-ZooZoo
Nutrients
Bacteria & Nutrients
Sinking Paricles
Stays Suspended
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Meso-Meso-ZooZoo
Bacteria & Nutrients
Sinking Particle
s
Stays Suspended
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Meso-Meso-ZooZoo
Foodwebs and Flux - 1988Foodwebs and Flux - 1988
• Focus on f-ratio and the amount of export from surface waters
• “Ryther-esque” outcome (# trophic steps, transfer efficiency)
• Imply that removal of carbon from surface is directly related to exchange with atmosphere
Ocean biology maintains a vertical DIC gradient:Ocean biology maintains a vertical DIC gradient:Balance of biology and physicsBalance of biology and physics
Nitrate+Nitrite
Dissolved Inorganic Carbon
What Processes Have Significant What Processes Have Significant Affects on Air-Sea Partitioning of Affects on Air-Sea Partitioning of
Carbon Dioxide?Carbon Dioxide?
1. Incomplete Nutrient Utilization (HNLC)
2. Particulate Inorganic Carbon:Organic Carbon Ratio
3. Changes in Nitrogen fixation:Denitrification balance (LNLC)
4. Changes in Remineralization Length-scales
Do food webs matter for any of these?
1.1. Incomplete Nutrient Utilization in Incomplete Nutrient Utilization in the Surface Waters (HNLC)the Surface Waters (HNLC)
Century residence times
Decadal residence times
Millenial residence times Dissolved Inorganic Carbon
Nitrate+Nitrite
Most of the ocean shows Most of the ocean shows near-complete nutrient utilizationnear-complete nutrient utilization
Surface Nitrate (µmoles/kg)
Low Nutrient AreasLow Nutrient Areas
If nutrient levels stay near detection and if C:N:P stoichiometry is constant,
then P-Z-N might be enough for the global carbon models
– Those are some big “ifs”
– There is more of interest on this planet than just global carbon
HNLC RegionsHNLC Regions
Changes in net utilization of surface nutrients Changes in net utilization of surface nutrients changes DIC gradient and air-sea partitioning changes DIC gradient and air-sea partitioning
(within limits)(within limits)
• High-nutrient, low chlorophyll areas (HNLC) in Southern Ocean, Equatorial Pacific, North Pacific and some coastal zones
• Trace nutrient limitation (Fe), Diatom blooms (Si)
• Reduce HNLC area - 15-100 ppm reduction in atm CO2
• Amenable to direct manipulation (political hot potato)
Nutrient Cycling in the Modern Southern OceanNutrient Cycling in the Modern Southern Ocean
(Anderson et al., 2002)
(Anderson et al., 2002)
Nutrient Cycling in the Glacial Southern OceanNutrient Cycling in the Glacial Southern Ocean
Nutrient Cycling in the Glacial Southern OceanNutrient Cycling in the Glacial Southern Ocean
(Anderson et al., 2002)
Nutrient Cycling in the Glacial Southern OceanNutrient Cycling in the Glacial Southern Ocean
(Anderson et al., 2002)
1.1. Incomplete Nutrient Utilization in Incomplete Nutrient Utilization in the Surface Waters (HNLC)the Surface Waters (HNLC)
Influence of Community Structure?Influence of Community Structure?
• Taxa-specific responses to Fe• Si+N requirements in diatoms, N
requirements in other phytoplankton• Taxa-specific grazing responses• Ballasting issues
2. Changes in2. Changes inParticulate Inorganic Carbon FluxParticulate Inorganic Carbon Flux
• Archer and Maier-Reimer, 1994
• Skeletons of coccolithophorids, foraminifera and pteropods
• Alkalinity change! Increase in PIC flux -> increase in pCO2
• Net effect on atmosphere depends on PIC:POC ratio
• Community structure effects analogous to remineralization length scale
(Sarmiento et al., 2002)
Carbonate Flux Linked toCarbonate Flux Linked to
Organic Carbon Flux via BallastingOrganic Carbon Flux via Ballasting (a la Armstrong et al, 2002)(a la Armstrong et al, 2002)
(Klaas and Archer, 2002)
2.2. Changes inChanges inParticulate Inorganic Carbon FluxParticulate Inorganic Carbon Flux
Influence of Community Structure?Influence of Community Structure?
• Carbonate skeletons found in a subset of taxa: coccolithophorids, foraminifera and pteropods
• Ecosystem dynamics will determine relative contributions of these taxa
• Mix of autotrophs and heterotrophs - must be mix of top-down and bottom-up controls
• Some of these taxa susceptible to creating blooms
• Ballasting link to organic carbon fluxes, stronger for carbonate fluxes than opal (correlation - causation?)
3. Changes in Nitrogen Fixation - Denitrification Balance
Century residence times
Decadal residence times
Millenial residence times
Lower DIC
Nitrate+Nitrite
Dissolved Inorganic Carbon
Higher DIC
Extra Nitrogen Fixation
3. Changes in Nitrogen Fixation - Denitrification Balance
Century residence times
Decadal residence times
Millenial residence times
Lower DIC
Nitrate+Nitrite
Dissolved Inorganic Carbon
Higher DICExtraDenitrification
Trichodesmium spp.Trichodesmium spp.Best Known Planktonic DiazotrophBest Known Planktonic Diazotroph
Excess Nitrate (µmoles/kg)
Dep
th (
m)
1 Year
4 Years7 Years
7.5 Years
7.3 Years
9 Years
8 Years
11 Years
39 Years
29 Years
19 Years
15 Years
12 Years
0 4 50
200
400
600
800
1000
1200
Excess Nitrate = NO3 - 16*PO4
Data from BATS
(Gruber and Sarmiento, 1997)
N* in the Atlantic Ocean
(Deutsch et al., 2001)
N* in the Pacific Ocean
(Husar et al., 1997)
Key Assumptions and Dynamics:Key Assumptions and Dynamics:
• Iron from dust limits nitrogen fixation
• Reasonable flexibility in N:P ratios and nutrient controls on N-fixation
• Carbon Modeling
– NCAR Ocean GCM (Doney)
– Multi-compartment box model (Sigman)
– Add adequate N fixation for 1 Gt/y C fixation
– Restrict N fixation to 10-40° (N and S)
– C:N=6.6, Assume flexible N:P within N* range
– 100-300 year runs
(Doney, Moore in prep)
(Doney, Moore in prep)
Nitrogen Fixation Feedback Cycle Hypothesis(as an example)
Two Additional Biological Two Additional Biological Characteristics:Characteristics:
• Diazotrophs form large surface blooms
Two Additional Biological Two Additional Biological Characteristics:Characteristics:
• Diazotrophs form large surface blooms
• Nitrogen fixation dynamics seem to change on decadal time-scales (at least in the Pacific Ocean)
Dave Karl and co-workers
Dave Karl and co-workers
3.Changes inNitrogen Fixation - Denitrification Balance
Influence of Community Structure?Influence of Community Structure?
• Diazotrophy found in a distinct subset of all prokaryotic taxa
• Chemical defenses against grazing in some• Some taxa symbiotic in eukaryotes (esp.
diatoms, creates silica requirement)• Denitrification - special environmental
conditions, specific prokaryotes
4. Changes in remineralization length-4. Changes in remineralization length-scales and C-N-P stoichiometryscales and C-N-P stoichiometry
Century residence times
Decadal residence times
Millenial residence times Dissolved Inorganic Carbon
Nitrate+Nitrite
Changes in remineralization length-scalesChanges in remineralization length-scales
• Depends on the depth horizon and ventilation time-scale:
– Annual: 10-20 Gt C/y – Multi-annual (>200 m): 5-10 Gt C/y– Multi-Decadal: 2-4 Gt C/y– > Centennial: ~1-2 Gt C/y
0
200
400
600
800
1000
1200
1400
0 2 4 6 8 10 12 14
b=1.5b=1b=0.7
De
pth
(m
)
POC Rain (mmolC/m2d)
1-3 GtC/yr
Export ~5-15 GtC/yr
Global PP~50 GtC/yr
Larger b value, more POC is recycled in upper oceanSmaller b value, more POC gets to deep ocean
Small b
Large b
Fz = F100 *(z/100)-b
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15 20 25
NABEEQPACASSO
Exp
on
ent,
b
POC Export at 100 m (mmolC m-2 d-1)
US-JGOFS Open-Ocean SitesUS-JGOFS Open-Ocean Sites
(Berelson, 2001)
(Martin et al., 1987)
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15 20 25
JGOFSMartin OceanMarginMartin Margin
Exp
onen
t, b
POC Export at 100 m (mmolC m-2 d-1)Berelson (in prep)
Slope’s always positive---
best explanation-
Reactivity POC > Reactivity bSi
0
1000
2000
3000
4000
50000 0.5 1 1.5 2 2.5 3
Arabian SeaEqPac Central Cal.NABEUSJGOFS SO (NACC)Guinea BasinWalvis RidgeOS Papa
Wat
er D
epth
(m
)
bSi/Corg ratio (molar)Berelson (in prep)
Can bSi content slow net particle settling rates?(Hypothesis: Yes)
Higher bSi Content
SteeperSlope
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2 2.5
Sediment Trap Data
Slo
pe
(1/m
) x1
0^5
Si/Corg
at 3000 m
Berelson (in prep)
0
50
100
150
200
Eq. (880-2284) Eq. (2284-3618)) 5°N (1191-2091)
El Nino Non-El Nino
Set
tlin
g V
eloc
ity
(m/d
ay)
Location (depth, m)
US-JGOFS EqPac—1992US-JGOFS EqPac—1992
Low Opal
Hi Opal
Berelson (2001)
1 mm
salp
euphausiid
copepod
Fecal Pellets
Bacteria & Nutrients
Sinking Particle
s
Stays Suspended
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Meso-Meso-ZooZoo
Bacteria & Nutrients
Pico-Phyto
Nano-Phyto
Micro-Phyto
Nano-Nano-ZooZoo
Micro-Micro-ZooZoo
Sinking Particles
SALPSSALPS
Twice in a decade!Twice in a decade!
Enormous Blooms!
Asexual reproduction by budding
The Outer LimitsThe Outer Limits
~ 0.5 Gt C
~ 1 Gt C
Ecosystems and Ecosystems and Plankton BloomsPlankton Blooms
• Ecosystems are complex-dynamical systems
• Bloom dynamics are poorly understood and hard to study
• Top-down vs bottom-up, a debate that is sorely lacking in ocean science
• Blooms created and controlled by internal dynamics of ecosystem, rarely bounded by external controls like nutrients
4.4. Changes in remineralization length-Changes in remineralization length-scales and C-N-P stoichiometryscales and C-N-P stoichiometry
Influence of Community Structure?Influence of Community Structure?
• Mix of biological and physical sources to different types of sinking particles
• Ballasting signals (mechanisms?)
• Diatom blooms may have non-intuitive impact on remineralization length-scale
• Bloom forming organisms create unique time-space scale issues for remineralization and for science.
ConclusionsConclusions
• Community structure matters for the partitioning of carbon between ocean and atmosphere.
• JGOFS has clarified some simple issues that now allow us to ask much more sophisticated questions.
• We still lack tools to study these processes on the time, space and taxonomic levels that are required.
• When community structure is important, the outcome is often emergent from internal dynamics.
Future DirectionsFuture Directions
• Community structure where it matters (HNLC, nitrogen fixation, etc.)
• The “twilight zone” and below
• Bloom dynamics (when they occur and when they matter)
• Complex systems approaches
• Be ready for surprises (viruses, archea, who knows what else).
Thank you!Thank you!
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