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

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

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

4. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary Chlorophyll Concentration (mg/m 3 ) NASA MODIS January 2012 Chlorophyll Phytoplankton Biomass JC068 Bottle Data: Chlorophyll Concentration Depth (m) 10 1 0.1 0 Chlorophyll Concentration (mg/m 3 ) 30°S 40 °S 50°S 50°W 30 °W 10°W 10°E

5. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary JC068 D357 Chlorophyll Concentration (mg/m 3 ) Phytoplankton Biomass - Climatology NASA MODIS Chlorophyll, 9 km 2 resolution Month averaged

6. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary a ph (440)* (m 2 mg -1 ) Chlorophyll a-specific absorption at 440 nm: indicator of phytoplankton size Larger a ph (440)* = smaller cells Phytoplankton Absorption Samples run by Christian Utschig Depth (m)

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

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

9. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary ΔF v /F m = F v /F m Fe amended bottle – F v /F m Control bottle ControlFe addition (2 nM)Initial Immediate analysis24 hour incubation Fe incubation experiments

10. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary = Gough Island 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

11. Introduction Chlorophyll Cell Size Phytoplankton Types Fe Limitation Summary Chlorophyll Concentration (mg/m 3 ) Depth (m) A: Warmer, low macronutrients, stratified B: Colder, high macronutrients, deeper mixed layer Low surface chlorophyllHigher surface chlorophyll Dominated by smaller cellsDominated by large cells Fe repleteFe limited ABA 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 F v /F m = Fe limitation October – January: shift from Fe limited to macronutrient limited environment as bloom consumes macronutrients. 1 st LEG 2 nd LEG