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Fe-Stimulated Changes in Phytoplankton Biomarker Distributions and Carbon Isotopic Compositions During SOFeX R. Bidigare, S. Christensen, S. Brown, K.

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Presentation on theme: "Fe-Stimulated Changes in Phytoplankton Biomarker Distributions and Carbon Isotopic Compositions During SOFeX R. Bidigare, S. Christensen, S. Brown, K."— Presentation transcript:

1 Fe-Stimulated Changes in Phytoplankton Biomarker Distributions and Carbon Isotopic Compositions During SOFeX R. Bidigare, S. Christensen, S. Brown, K. Selph, C. Sheridan, N. Cassar & M. Landry Department of Oceanography University of Hawai‘i

2 Research Objectives Investigate phytoplankton community responses to four sequential iron enrichments (0.7 nM each) at 66°S, 172°W (“Southern Patch”) Monitor pigment biomarker distributions and  13 C ratios in the “Southern Patch” and at outside stations to infer Fe-stimulated changes in algal biomass, composition and growth physiology

3 HPLC TChl a  Turner Chl HPLC TChl a (ng L -1 ) Turner Chloropigment (ng L -1 ) SOFeX Southern Patch (R/VMelville) We hypothesize that the variable positive bias observed in the Fl Chl measurements result from the accumulation of fluorescent zooplankton grazing products (Steryl Chlorin Esters???) TChl a = Chl a + Chlorophyllide a

4 Total Chlorophyll a (ng L -1 ) Depth (m) SOFeX Southern Patch d d d d d d 9.27 d 9.18 d 9.08 d 8.99 d 6.66 d 4.74 d Pre

5 Total Chlorophyll a (ng L -1 ) Time Since Initial Fe Addition (days) SOFeX Southern Patch (0-30 m) In Out Pre

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7 Fucoxanthin (ng L -1 ) Time Since Initial Fe Addition (days) SOFeX Southern Patch (0-30 m) In Out Pre

8 Photoadaptation Index

9 Daily PAR (Ein m -2 ) Time Since Initial Fe Infusion (days) SOFeX Southern Patch

10 Ln (Biomass) Time Since Initial Fe Addition (days) y = 0.058x r 2 = 0.83 y = 0.095x r 2 = 0.84 SOFeX Southern Patch (0-30 m) C Chl Phytoplankton Net Growth Rate

11 Apparent Phytoplankton Net Growth Rates During SOFeX (Southern Patch)

12  13 C IN -  13 C OUT ( ‰) Time Since Initial Fe Infusion (days) SOFeX Southern Patch Bulk POC (mixed layer)

13 Summary Fe enrichment produced an 10-fold increase in [TChl a] in the SOFeX Southern Patch (0.2  2.0 mg/m 3 ) Only small changes in phytoplankton size structure were observed following Fe enrichment (  >20  m size fx) Variations in xanthophyll cycle pigment ratios indicate that light limitation may have restricted the magnitude of the phytoplankton response to Fe addition A differential response to Fe enrichment was observed for the Southern Patch phytoplankton community with diatoms > pelagophytes > dinoflagellates > haptophytes A ~1‰ enrichment in 13 C was measured in the POC pool in the Southern Patch relative to the outside stations

14 Future Directions Identify fluorescent grazing products  13 C biomarker analyses –Lipids (irmGC/MS) –Pigments (irmLC/MS) –SOFeX large-volume pump samples –Phytoplankton “soup” samples –AESOPS sediment core samples

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