Stable nitrogen isotope dynamics of a phytoplankton bloom: results from the SERIES experiment in the

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Stable nitrogen isotope dynamics of a
phytoplankton bloom results from the SERIES
experiment in the North Pacific Ocean.

• Joseph A. Needoba
• Mike Henry, Adrian Marchetti, Keith Johnson, Paul
  Harrison, and Tom Pedersen

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SOLAS Surface Ocean Lower Atmosphere Study
SERIES Subarctic Ecosystem Response to Iron
Enhancement Study
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Main Goal of Another Iron
Fertilization

• determining the influence of iron addition on the
  sequestration and production of climatically
  relevant gases
• CO2, DMS and organohalogens

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Overview of SERIES

• Station P
• Add Fe and SF6 tracer
• 3 ships
• J.P. Tully Create the patch, monitor the patch,
  measure atmospheric gases
• El Puma Mexico Measure biological parameters
• Kaiyo Maru Japan Extend the time series
  measurements, sediment trap deployment.

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Stable Nitrogen Isotopes

• The natural abundance ratio of 15N and 14N can be
  used as
• tracer of nitrogen and nitrogen cycle processes
  in space and time
• indicator of trophic level of an organism
• record of nitrogen cycle processes in the past

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Equatorial Pacific
Altabet and Francois, 1994
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Rayleigh Fractionation
Substrate
Product
Initial
k1
k2
Final
15N
14N
15N
14N
a k1/k2
e (1-a) 1000
d15N (15N/14Nsample - 15N/14Nstandard) 1000
15N/14Nstandard
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d15N Measurements

• Tully Collected samples for d15N measurements
  of nitrate, phytoplankton, and sediment traps
• El Puma d15N of size fractionated phytoplankton
• Kaiyo Maru d15N sediment traps

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d15N of NO3-

• Incubate sample at a high pH to remove ammonium
  and labile DON
• Reduce all NO3- to NH4, then convert to NH3 and
  trap the gas with an acid filter
• Measure the d15N of the acidified filter

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Rayleigh fractionation Single step Unidirectional
reaction Closed system
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eInstantaneous product
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Summary

• d15N follows predictable patterns during the
  course of the bloom
• Large size fraction shows a stronger response to
  iron addition
• d15N signal from the bloom was measured in the
  sediment traps at 50-125 metres

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Summary

• Isotope fractionation calculations
• between nitrate and PN 9-12 permil
• Change in d15N of nitrate 6-9 permil
• Change in d15N of PN 23 permil
• Suggests that PN is also being formed from other
  forms of nitrogen.

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Extra Thanks to
Jennifer McKay Nelson Sherry Janet
Barwell-Clarke Ming Guo David Harris Markus
Kienast