COSPAR SRSSO Taipei Taiwan

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and the S2O2 A path to understanding
basin-scale variability recorded in Cariaco Basin
sediments? F. E. Muller-Karger, R. Varela, R.
Thunell, M. Scranton, G. Taylor, and R.
Weisberg

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• PROJECT OBJECTIVES
• Understand how contemporary sedimentation
  patterns reflect climatic and oceanographic
  variability in the tropical western Atlantic Ocean

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• Hypotheses
• Hypothesis 1 Sediments and sinking flux of
  particulate matter reflect upper ocean
  variability.
• Hypothesis 2 Sediments in anoxic waters exhibit
  similar organic carbon preservation to those in
  Cariaco oxic environments.
• Hypothesis 3 Hydrography is directly related to
  regional wind variability, with modulation by
  larger scale changes.

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• Hypotheses (cont.)
• Hypothesis 4 Chemoautotrophic bacteria at the
  oxic-anoxic interface alter the chemical
  characteristics of the vertical particulate
  organic flux, and, at least seasonally, are a
  major contributor to the total carbon flux in the
  basin.
• Hypothesis 5 Chemoautotrophy and carbon
  respiration in the depth range of the oxic-anoxic
  interface are controlled by lateral transport of
  dissolved oxygen at mid-depth (ventilation
  events).

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• SITE SELECTION RATIONALE
• Exceptional archive of past global climate
  changes
• Quiescent at depth / Anoxic
• Varved sediments (annual light/dark layer
  couplet)
• Light (phytoplankton)
• Dark (terrestrial)
• Upper 150 m openly connected with the Atlantic
  Ocean
• Key link to Atlantic Ocean and tropics
  variability

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• STATUS
• Monthly time series started November 1995
• 63 monthly cruises through February 2001
• Data and program description on web page
• http//paria.marine.usf.edu
• Data submitted regularly to NODC and SeaBASS

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POC fluxes observed in the 455 m trap subtracted
from POC fluxes to 265 m. Positive values can be
interpreted as 1) analytical uncertainty, 2)
horizontal transport or 3) in situ production
(chemoautotrophy).
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Carbon isotopic composition of POC at four depths
in the Cariaco Basin.
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S2O2

• Issue (political reality) Community support
• Recommendation Community needs to support time
  series like CARIACO at time of agency review, and
  not just verbally outside the review process.

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S2O2

• Issue (scientific reality) Basin-scale physical
  and chemical oceanographic variability
• What are cross-basin transport mechanisms?
• Energy, water, chemical properties
• What is variation in NEC?
• What is variation in flow within gyre?
• What is variation in cross-equatorial flow?
• What is mesoscale eddy variability?

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Age of Cariaco sediment varves compared to age of
tree-rings (from Hughen et al., 1998 Nature)
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CARIACO ADCP data (north-south component, v).
Contours indicate -10 cm/s (continuous contours)
and 10 cm/s (broken contours) regions. Blue
shows negative (southward) velocities and red
shows positive (northward) velocities. Vertical
broken lines show dates of CARIACO cruises.
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CARIACO ADCP data (east-west component, u).
Contours indicate -15 cm/s (continuous contour)
and 15 cm/s (broken contour) regions. Blue shows
negative (westward) velocities and red shows
positive (eastward) velocities. Vertical broken
lines show dates of CARIACO cruises.
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Cariaco varve chronology compared with GISP2 ice
core (from Hughen et al., 1998 Nature)
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1996
1997
1999
1998
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1996
1997
1999
1998
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1996
1997
1999
1998
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1996
1997
1999
1998
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1996
1997
1999
1998
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125 m
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Vertical profiles of bacterial net production,
dark carbon fixation, nitrate and hydrogen
sulfide concentration in the Cariaco Basin in
May, 1997. Bacterial net production estimated
measuring 3H-leucine incorporation into
precipitated protein
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CONCLUSIONS (1)

• Cariaco is not at all the quiescent, steady state
  environment, or even the gradually changing
  environment, envisioned by previous workers
• Seasonal cycle punctuated by strong events
• This is reason for historical underestimates of
  production
• Production typically exceeds 500 gC m-2 y-1

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CONCLUSIONS (2)

• Organic carbon flux directly related to surface
  production
• Approximately 2 of surface production reaches
  bottom
• Chemosynthesis demonstrated and shown to be
  considerable
• What is the role of chemosynthesis at oxic-anoxic
  interface?

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CONCLUSIONS (3)

• Ventilation of mid-water plays an important role
• Do varying redox conditions alter composition of
  sinking material?
• Vertical particle flux is a sink of carbon, but
  Cariaco is a CO2 source to the atmosphere
  year-round
• Is this a significant sink of carbon absorbed at
  mid-latitudes?
• What is implication for upwelling along margins?

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CONCLUSIONS (4)

• 1997-1998 El Niño seems to have affected Cariaco
• Large decrease in primary production
• Less persistent upwelling (but not weaker trades)
• What is the teleconnection mechanism?
• Cariaco reflects variation in the Atlantic Ocean
• What is relative importance of
• Eddies
• Cross-equatorial flow
• N Equatorial Current?