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The biological response to in situ Southern Ocean iron fertilization. Richard T. Barber and SOFeX Team SOFeX: Southern Ocean Iron Experiments, An Overview of the Biological Responses Richard Barber and the SOFeX Group
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Primary productivity, photosynthetic performance and quantum yield team on the three ships: R/V Revelle: Barber, Lance, Stuebe R/V Melville: Hilting, Hiscock, Apprill, Delizo, Tanner USCG Polar Star: Van Hilst FRRF data provided by Sasha Tozzi. PAM data provided by Jill Peloquin. POC flux data provided by Ken Buesseler.
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North Patch Temp. 7.5ºC Si(OH) 4 2.0μM NO 3 21μM +Fe 1.2nM South Patch Temp. -0.5ºC Si(OH) 4 63μM NO 3 27μM +Fe 0.7nM
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NP SP Underway nutrients and temperature figure provided by W. T. Hiscock, U. Miami.
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Surface Chl (mg Chl m -3 ) 0 1 2 3 4 Year Day 2025303540455055 SOFeX Productivity DUKE - MBARI - VIMS - SIO South Patch Fertilization Melville Revelle Polar Star
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South Patch Year Day 2025303540455055 Popt (mmolC m -3 d -1 ) 0 1 2 3 4 SOFeX Productivity DUKE - MBARI - VIMS - SIO Melville Revelle Fertilization
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Z morel (m)
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No. Patch revisit by Revelle.
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SOFeX Productivity DUKE - MBARI - VIMS - SIO North Patch Year Day 101520253035404550 Surface Chl (mg Chl m -3 ) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Melville Revelle Fertilization
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North Patch Year Day 101520253035404550 Popt (mmolC m -3 d -1 ) 0 1 2 3 4 5 6 7 SOFeX Productivity DUKE - MBARI - VIMS - SIO Melville Revelle Fertilization
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Weeks Post First Fertilization 123 Binned Int PP (mmol C m -2 d -1 ) 10 20 30 40 Out 10% In 10%
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PAM- bulk assemblage for South Patch, bars are iron additions, circled data are OUTs. Cells never reached photochemical maximum for 20 m water for PAM (0.70). Outs
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Results 10x increase in Chl in both N and S patch 10x increase in productivity (P opt ) in both N and S patch 3 to 4x increase in integrated primary productivity 3 to 4x increase in quantum yield in South patch, but no differential enhancement of quantum yield in large (> 20 μm) phytoplankton Big change in size composition in N patch despite low Si conditions, but only modest change in size composition in S patch with high Si conditions In patch POC flux about 30% of In patch PP integrated to 10% light level; Out flux about 40% of Out PP integrated to 10% light level
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Remaining Questions 1.Depth of export 2.Fate of exported organic carbon at depth 3.Cellular mechanism of “fast” photosynthetic efficiency response to Fe 4.Nature of temperature vs. photosynthetic efficiency relationship
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South Patch Year Day 2025303540455055 % Popt >20 μm 0 10 20 30 40 50 60 70 80 SOFeX Productivity DUKE - MBARI - VIMS - SIO Melville Revelle Fertilization
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Prim Prod (mmol C m -3 d -1 )
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