CdCa as a watermass tracer

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Cd/Ca as a watermass tracer

• Paleoproxy seminar, 4/9/08
• Louisa Bradtmiller

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Principles

• Cd distribution is very similar to PO4-

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Principles

• Depleted at surface
• Regenerated into deeper (older) water
• PO4- depends on original concentration, transit
  time

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Principles

• Benthic forams record Cd content of overlying
  waters reconstruct PO4-
• WHY? No one really knows
• Linked to at least one algal metalloenzyme
• Could be actively taken up as a nutrient, or just
  adsorbed onto particles

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Calibration

• Curve, or just 2 line segments

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Calibration

• Calibration is global
• Scatter around any given PO4- value is relatively
  large given modern ocean Cd gradients

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Species effects

• Cdw(Cd/Ca)foram/DpCawater
• BUT, Dp varies with water depth in calcitic
  species
• So, you have to use aragonitic species
• No T dependence
• No species offset w/in calcitic species

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Carbonate saturation

• DCd reduced in low CO32- water
• Less variability than Zn or Ba, but CO32- could
  still control Cd over glacial/interglacial
  timescales
• Some regions (ie. S Atl.) worse than others

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Other

• Picked samples show large scatter, much greater
  than crushed, homogenized
• Equivalent to 16 of Atl. gradient
• No inter-lab standards w/r/t
• Cleaning (3 different procedures)
• Measurement (AAS vs. ICPMS vs. TIMS)

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