1. Phytoplankton and nutrient dynamics in a vortex off Western Australia Paterson, H. L. 1, Waite, A. M. 1, Thompson, P. 2 1 The University of Western Australia, 2 CSIRO Marine Research

2. Introduction Understand the role of meso- scale eddies in transporting material offshore and modifying productivity. In May 2007 we investigated an eddy during its formation. –Physical and chemical properties of the eddy –Picoplankton distribution (Flow- cytometry, SYBR Green 1) Offshore, >90% of the phytoplankton in the <5µm fraction (Koslow et al. 2007) Picture

3. 113.4 Transect May 20 2006 MODIS SST MODIS chlorophyll image

4. Salinity and Temperature 113.4 Salinity maximum Central Indian Ocean Water North side High current speed Leeuwin Current (Low salinity Warm) South side Dissociation between high current speed and Leeuwin Current???? Dilution of the Leeuwin Current? Centre Gradient across body of eddy Isohaline Contour Line Salinity = 35.65

5. Water-mass - T/S? Salinity maximum – Central Indian Ocean water T/S plot does not clearly separate water-masses

6. Potential eddy water T/S plot. Data 0 – 150 m four casts per region

7. Surface silicate Surface nitrate

8. Isohaline Contour Line Salinity = 35.65 Silicate and nitrate 113.4

9. Eddies 2003 Anya’s chapter from the text book

10. Warm Core Eddy: Anomalous Large Diatom Population Key Features: 1. Atypical of open ocean 2. V. Deep mixed layer (275 m) 3. Low-light, low nutrient Calculations estimate that >1 μM L -1 of nitrate was required during eddy formation to establish diatom population >20  m fraction on GF/F

11. Synechococcus sp. Prochlorococcus sp. Synechococcus sp.Prochlorococcus sp.

12. Synechococcus sp. Prochlorococcus sp. Y=1.22X+2.0*10 12

14. Transect 113.4 Synechococcus sp. Prochlorococcus sp.

15. Prochloroccocus sp. 0.4 µM L -1

16. Transect 113.4 Pico-eukaryotes Heterotrophic Bacteria

17. Transect 113.4 Fluorescence

18. Eddy formation, propagation and detachment SST Blue Link Images (CSIRO)

19. Conceptual model of warm-core eddy

20. Cell cycle Growth of phytoplankton using cell cycle analysis Can be done using flow cytometry

22. Flow data

23. Gaussian 4 parameter curve Synechococcus P<0.0001 R 2 = 0.59 Prochlorococcus P<0.0001 R 2 = 0.40

24. Conclusion or questions and acknowledgments Eddy water shelf origin. Eddy - shelf water modified by Leeuwin Current entrainment. –Modification of Leeuwin Current as it circles the eddy. Nitrate and silicate concentrated by different mechanisms? Leeuwin Current is a source of Prochlorococcus sp. Abundance of Prochlorococcus sp. related to nitrate availability. Synechococcus sp. Shelf/coastal origin. Asymmetry of the eddy – Salinity, Nitrate, Prochlorococcus sp. Leeuwin Current modification enhances productivity? Is the salinity maximum a physical barrier, what is its contribution to the biology of the eddy?

25. Acknowledgments Waite et al., ARC discovery grant 2006 - 2008 Waite, Thompson and Twomey, SRFME Collaborative Grant Waite, Thompson and Beckley, Marine National Facility Ship Time Southern Surveyor MNF staff and crew Ming Feng, CSIRO Adele Pile Kathy Heel-Miller and the Biomedical Imagine Centre (UWA)