Tom Browning & Heather Bouman (Oxford) Mark Moore (NOCS)

1. JC068 Phytoplankton:Concentrations, Species, and Physiological StatusUK-GEOTRACES: Ocean Micronutrient Cycles WP5: Biological responses and cycling of micronutrients Tom Browning & Heather Bouman (Oxford) Mark Moore (NOCS)

2. IntroductionChlorophyll Cell Size Phytoplankton Types Fe Limitation Summary Sea Surface Temperature NASA MODIS January 2012 SST 45 30 15 0 30°S 40 °S 50°S Temperature (°C) 50°W 30 °W 10°W 10°E JC068 CTD Temperature Depth (m) Temperature (°C)

3. IntroductionChlorophyll Cell Size Phytoplankton Types Fe Limitation Summary Macronutrients Nitrate (µM) Depth (m) Phosphate (µM) Depth (m)

4. Introduction ChlorophyllCell Size Phytoplankton Types Fe Limitation Summary Phytoplankton Biomass NASA MODIS January 2012 Chlorophyll 10 1 0.1 0 30°S 40 °S 50°S Chlorophyll Concentration (mg/m3) 50°W 30 °W 10°W 10°E JC068 Bottle Data: Chlorophyll Concentration Chlorophyll Concentration (mg/m3) Depth (m)

5. Introduction ChlorophyllCell Size Phytoplankton Types Fe Limitation Summary Phytoplankton Biomass - Climatology NASA MODIS Chlorophyll, 9 km2 resolution Month averaged JC068 D357 Chlorophyll Concentration (mg/m3)

6. Introduction Chlorophyll Cell SizePhytoplankton Types Fe Limitation Summary Phytoplankton Absorption Chlorophyll a-specific absorption at 440 nm: indicator of phytoplankton size Larger aph(440)* = smaller cells Depth (m) aph(440)* (m2 mg-1) Samples run by Christian Utschig

7. Introduction Chlorophyll Cell Size Phytoplankton TypesFe Limitation Summary Nanophytoplankton (2-20 µm) Picophytoplankton (0.2-2 µm) Depth (m) Synechococcus Prochlorococcus Depth (m) Total Bacteria Analytical Flow Cytometry Cell counts (cells/µL) Depth (m)

8. Introduction Chlorophyll Cell Size Phytoplankton Types Fe LimitationSummary Phytoplankton Photophysiology Fv/Fm Depth (m) Fv/Fm: Thought to be influenced by phytoplankton species, light climate, micronutrients and macronutrients. Fv/Fm in JC068 transect, a signature of Fe limitation

9. Introduction Chlorophyll Cell Size Phytoplankton Types Fe LimitationSummary Fe incubation experiments Initial Control Fe addition (2 nM) Immediate analysis 24 hour incubation 24 hour incubation ΔFv/Fm = Fv/Fm Fe amended bottle – Fv/Fm Control bottle

10. Introduction Chlorophyll Cell Size Phytoplankton Types Fe LimitationSummary • Two dominant regimes: • 1) Subtropical Gyre type waters • Low macronutrients • Fe replete • High irradiance (near surface) • 2) AAC source waters • High macronutrients • Fe limited • Possible light limitation Gough Island =

11. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary A B A Chlorophyll Concentration (mg/m3) Depth (m) Samples to be run: HPLC; microscopy; N-Fixers; DNA

12. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary D357 Pre-bloom (leg 1) and bloom (leg 2) conditions Cause: shallowing of mixed layer = increased light Depressed mixed layer Fv/Fm = Fe limitation October – January: shift from Fe limited to macronutrient limited environment as bloom consumes macronutrients. 1st LEG 2nd LEG