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 0 1000 2000 3000 4000 HPLC TChl a (ng L -1 ) 01000200030004000 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. 050010001500200025003000 Total Chlorophyll a (ng L -1 ) -150 -120 -90 -60 -30 0 Depth (m) SOFeX Southern Patch 20.75 d 20.14 d 17.68 d 14.65 d 14.11 d 10.80 d 9.27 d 9.18 d 9.08 d 8.99 d 6.66 d 4.74 d Pre

5. 0 500 1000 1500 2000 2500 3000 Total Chlorophyll a (ng L -1 ) -23813182328 Time Since Initial Fe Addition (days) SOFeX Southern Patch (0-30 m) In Out Pre

7. 0 300 600 900 1200 1500 Fucoxanthin (ng L -1 ) -23813182328 Time Since Initial Fe Addition (days) SOFeX Southern Patch (0-30 m) In Out Pre

8. Photoadaptation Index

9. 0 10 20 30 40 50 Daily PAR (Ein m -2 ) 456789101112131415161718192021 Time Since Initial Fe Infusion (days) SOFeX Southern Patch

10. 3 4 5 6 7 8 Ln (Biomass) 0510152025 Time Since Initial Fe Addition (days) y = 0.058x + 3.778 r 2 = 0.83 y = 0.095x + 5.608 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. -0.4 0 0.4 0.8 1.2  13 C IN -  13 C OUT ( ‰) 471011151821 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