The role of different phytoplankton groups on the CO2 dynamics in the SouthWestern Atlantic Ocean

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The role of different phytoplankton groups on the
CO2 dynamics in the South-Western Atlantic Ocean

• IAA ? Irene Schloss, Gustavo Ferreyra
• UNLP ? Martha Ferrario, Gastón Almandoz, Raúl
  Codina
• SHN ? Alejandro Bianchi Carlos Balestrini
• CENPAT ?José L. Esteves Flavio Paparazzo
• LBCM ? Alain Poisson, D Ruiz Pino

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Cooperation project

• 2000 2005 Argentina DNA-IAA, National
  Hydrographic Service (Navy), France LBCM, Paris.
• From 2003 ENEA, Italy
• From 2007 DNA-IAA, LOCEAN (former LBCM, Paris,
  France), University of Perpignan (France), ENEA
  (Italy), Princeton University (USA)

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(Takahashi et al., 2002, Deep-Sea Res, II 49
1601-1622)
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Global models(Takahashi et al., 2002, Deep-Sea
Res, II 49 1601-1622)

• Estimating the effect of temperature (T) on pCO2
• (DpCO2)temp (pCO2 at Tobs)max-(pCO2 at Tobs)min
• Estimating the effect of biology (B) on pCO2
  
• (DpCO2)bio (pCO2 at Tmean)max-(pCO2 at Tmean)min
• where
• (pCO2 at Tmean) (pCO2 )obs x exp0.0423(Tmean-To
  bs)
• (pCO2 at Tobs) (Mean pCO2 ) x
  exp0.0423(Tobs-Tmean)
• T/B or T-B indicates the prevalence of
  temperature or
• Biological effects

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Biological Pump in the Ocean
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P
R
Time
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Biological processes affecting carbon dynamics in
the ocean are mainly respiration and
photosynthesis

• GPPR gt 1
• CO2_sea consumption
• Important vertical POC flux
• Fronts and interfaces
• Sporadic events
• New (NO3 based) production
• Early successional stages
• Herbivourous food web
• Uncoupling A-H

• GPPR lt 1
• CO2_sea production
• Low vertical POC flux
• Open waters.
• Most common situation in the ocean
• Regenerated (NH4 based) production
• Mid-late successional stages
• Microbial food web
• Coupling A-H

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Biological processes affecting carbon dynamics in
the ocean are mainly respiration and
photosynthesis

• GPPR gt 1
• CO2_sea consumption
• Important vertical POC flux
• Fronts and interfaces
• Sporadic events
• New (NO3 based) production
• Generally diatoms dominating phytoplankton
  assemblages
• Early successional stages
• Herbivourous food web
• Uncoupling A-H

• GPPR lt 1
• CO2_sea production
• Low vertical POC flux
• Open waters.
• Most common situation in the ocean
• Regenerated (NH4 based) production
• Generally phytoflagellates dominating
  phytoplankton assemblages
• Mid-late successional stages
• Microbial food web
• Coupling A-H

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ARGAU Cruises 2002 2004, summer and
fall (Programme de coopération entre la France et
lARGentine pour létude de locéan Atlantique
AUstral)

• Objectives
• Determine CO2 sinks and sources
• Study phytoplankton biomass and community
  metabolism
• Relate DpCO2 to plankton metabolism
• Relate the above results to (phyto)plankton
  community composition.

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Measured variables

• Meteorological variables (PAR, Wind speed,
  direction, atmospheric pressure, etc.
• CO2 atm
• CO2 sea
• SSS, SST
• Nutrients (N, P, Si)
• pH, alkalinity
• Dissolved oxygen
• Fluorescence
• Fractionated Chl.-a,
• Siliceous and calcareous phytoplankton
  composition
• Primary production, community Respiration

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ARGAU cruises (2002-2004)
Location Date Offshore waters 31/1 2/2,
2002 Coastal 23/3 26/3, 2002 Offshore
Coastal 10/4 - 13/4, 2002 Coastal 3/5 - 5/5,
2002 Coastal 7/2 - 10/2, 2003 Coastal 15/5
18/5, 2003 Offshore 27/2 1/3, 2004 Offshore
waters 13/3 16/3, 2004 Coastal 14/4-17/4, 2004
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DpCO2 pCO2 sea pCO2 atmosphere
Coastal zones CO2 source Mid shelf area CO2
sink (for summer and fall seasons, years
2000-2004 areal average -24 matm) Limit
closely follows tidal front location Bianchi et
al., 2005, JGR
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Temperature has a major role in CO2 solubility in
the sea
After removing the effect of SST in CO2
solubility, DpCO2 is still negative in most of
the area, indicating that other processes account
for the measured pCO2 sea.
pCO2 sea corrected for 4 x 5 lat long grid
boxes after Takahashi et al., 2002, DSR
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• Comparing with oxygen
• saturation
• -Areal average 108 (oversaturated).
• Undersaturated in coastal
• areas.
• Supersaturated in open
• waters.
• - Limit follows tidal (stratification) fronts

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Phytoplankton biomass distribution
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• Coccolithophores in
• satellite images
• 8 species, including E. huxleyii, with
• high abundances of Gephyrocapsa
• oceanica.
• Maximal abundances 3 x 105 cells L-1,
• in coincidence with a massive diatom bloom (one
  order of magnitude lower than in the
  North-Atlantic).
• Remote sensing sediment signal overlaps the area
  of coccolithophores presence (resuspended
  coccoliths?).
• (Resplandy et al, 2004, V Jorn. Ant.)

February, 2003
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Net community production (2002 2004, n 49)

• - Incubations in 3 x 250 ml BOD (borosilicate),
  clear and dark bottles in situ temperature 3
  initial bottles.
• 6 to 12 h exposure in 2002 and 2003 to simulated
  environmental PAR conditions results computed
  for 24 h, according to daylength
• 24 h exposure for 2004 samples under natural
  sunlight
• Winkler titration (automated Mettler DL21
  titrator)

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GPP NCP R
Respiration Net Community Production GPPR
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GPP is mostly dependent on NCP NCP is highly
correlated with phytoplankton biomass
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Biological parameter-sprocesses vs T-corrected
DpCO2
No significant relation between DpCO2 and neither
total phytoplankton biomass, NCP or the GPP R
ratio.
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Phytoplankton assemblages analyses

• - Microscopic examination, species
  identification, counting
• Measuring cell size determinig cell biovolume
• Converting cell number into phytoplankton carbon
  (PPC)
• Determining the dominant group whenever either
• diatoms, phytoflagellates or dinoflagellates
  carbon
• represented more than 50 of total PPC.
• - Relating biomass and production results, based
  on community dominance with T-corrected DpCO2 and
  O2 saturation

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R2 0.62
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R2 0.57
R2 0.40
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R2 0.37
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Biological processes affecting carbon dynamics in
the ocean are mainly respiration and
photosynthesis

• GPPR gt 1
• CO2_sea consumption
• Important vertical POC flux
• Fronts and interfaces
• Sporadic events
• New (NO3 based) production
• Generally diatoms dominating phytoplankton
  assemblages
• Early successional stages
• Herbivourous food web
• Uncoupling A-H

• GPPR lt 1
• CO2_sea production
• Low vertical POC flux
• Open waters.
• Most common situation in the ocean
• Regenerated (NH4 based) production
• Generally phytoflagellates dominating
  phytoplankton assemblages
• Mid-late successional stages
• Microbial food web
• Coupling A-H

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Present study

• GPP R gt 1 in almost all stations in the
  Argentinean shelf during summer and fall.
• There is a linear relation between DpCO2 and
  diatom-dominated biomass (chl. a) and NCP,
  regardless of biomass abundance.
• This relation is not evident in
  phytoflagellates-dominated assemblages.

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Number of stations and dominant phytoplankton
group (as PPC)
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Coastal vs oceanic summer vs fall

• In coastal areas, although GPPRgt1 DpCO2 is
  positive (potencial CO2 source) riverine input,
  organic matter remineralization and physical
  resuspension of benthic organisms could probably
  be adding to seawater pCO2.
• 22 of coastal stations presented diatom
  dominated phytoplankton assemblages (low chl.-a)
  39 open water stations were diatom dominated
  (high chl.-a)
• Significant differences were found for Chla, NCP
  and R when comparing summer and fall for all
  seasons (p lt 0.05), but not in GPPR.
• No difference in diatoms or phytoflagellates
  dominance was found between seasons.

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Conclusions

• The Argentinean shelf is a CO2 sink, which is
  consistent with O2 saturation and the
  experimental NCP and R measurements (GPPR
  generally gt1)
• Chlorophyll-a concentration is not enough as an
  indicator of pCO2 in the sea only in those
  stations dominated by diatoms a (linear) relation
  was observed between these variables.
• Half of the biomass in the areas is represented
  by phytoflagellates new insights in the
   phytoflagellates  group (NCP and R by flux
  cytometry, pigment composition, POC) are needed
  to understand their relation with pCO2

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Waters in the area of the former Larsen A barrier
X 105
Bertolin et al., 2006
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Future (some ongoing) works

• Include vertical structure of the water column in
  analysis (XBT XCTD) to estimate the impact of
  the results in the mixed layer (ENEA, Italy)
• Relation of species and pigment data with remote
  sensing information (UBA)
• Include present results in global models
• Analysis and publication of data from other
  regions studied by Irizar (Drake Passage, Weddell
  Sea, WAP)

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Thanks!

• To all the technicians from IAA, SHN and LBCM
  that participated in the cruises
• To the different crews onboard ARA  Almirante
  Irizar 
• To the funding institutions CONICET, ANPCyT,
  PROOF, IPSL