Phytoplankton and Productivity

1. Phytoplankton and Productivity Add critical depth

2. What affects values of PP? • Light • Nutrients • Seasonal and Global variations in PP • Add thermocline mixed layer, Eckman’s spiral

3. Water Column Structure Surface Mixed Layer (Epilimnion) Mixed Layer Depth Thermocline (Metalimnion) Depth (Hypolimnion) Temperature

4. More Aquatic Habitats (Vertical) Coastal Neritic Oceanic Euphotic zone 25m EPIpelagic 1% Light Depth 200m 100m Continental Shelf mesopelagic Permanent Thermocline 1000m Continental Slope Bathypelagic Not shown: Seasonal Thermocline (varies, 10 – 400 m, depending on season and location) Abyssopelagic Abyss … Trench

5. Aquatic Habitats (Horizontal) Polar High Latitude High Latitude Subtropical Gyre Subtropical Gyre Equatorial Equatorial Subtropical Gyre Subtropical Gyre Subtropical Gyre High Latitude Temperate Polar Not shown: Coastal, Coastal Upwelling areas

6. Global Pigment/Productivity

7. Global Pigment/Productivity

8. Ocean Phytoplankton Biomass

9. Hadley Cells, Trade Winds, Westerlies

10. Hadley Cells, Trade Winds, Westerlies

13. Northern Gyre Circulation Cyclonic Divergence High Production Subpolar Gyre Warm Currents ~ 35 N Anticyclonic Convergence Low Production Cool Currents Subtropical Gyre EQ

14. Global Pigment/Productivity Location Ann. Prim. Prod. (g C m-2 y-1) Cont. Upwelling 500-600 Cont. shelf-breaks 300-500 Subarctic Oceans 150-300 Anticyclonic gyres 50-150 Arctic Ocean 50-80 Antarctic 50-200

15. Global Pigment/Productivity- by basin Basin Productivity Percentage Pacific 19.7 Pg C y-1 42.8 Atlantic 14.5 31.5 Indian 8.0 17.3 Antarctic 2.9 6.3 Arctic 0.4 0.9 Med. 0.6 1.2 Global 46.1 100

16. Global Pigment/Productivity Behrenfeld and Falkowski model

17. Global Pigment/Productivity Howard-Yoder Model

18. Interannual changes

19. Seasonal changes Fall Winter Spring Summer

20. Global Pigment/Productivity- by season Global Annual Production 47.5 Pg C y-1 Seasonal Prod.: March-May 10.9 Seasonal Prod.: June-Aug. 13.0 Seasonal Prod.: Sept.-Nov. 12.3 Seasonal Prod.: Dec.-Feb. 11.3

21. Range of annual PP in different regions Mean annual PP (g C/m2/yr) • Continental Upwelling 500-600 • Continental shelf breaks 300-500 • Subarctic Oceans 150-300 • Anticyclonic gyres 50-150 • Arctic Ocean <50

22. Polar regions Arctic

23. North Pacific Biomass Winter Spring Summer Fall

24. North Atlantic

25. Temperate region (NW Atlantic) Winter

26. Temperate region (NW Atlantic) Onset of spring bloom- Increasing thermal stability

27. Temperate region (NW Atlantic) Decline of spring bloom Sinking 2. Grazing (lag) aggregate

28. Species succession within a bloom 1 2 3 4 Small cells High growth rates Flagellates, small diatoms Slower growing forms Dinoflagellates Auxotrophs motile Larger diatoms, high Ks Spiny forms (deter grazing) Flagellates, small diatoms Complete Nutrient depletion Cyanobacteria- N- fixers

29. Equatorial/Tropics Tropical regions (and most mid-ocean gyres) phytoplankton zooplankton Biomass Jan Dec

31. North Atlantic: Pronounced spring bloom, often a fall bloom Polar: Single pronounced bloom Standing Stock of Phytoplankton Tropical: Lack of pronounced blooms W Sp Su F

32. Phytoplankton biomass from satellites- chlorophyll a

33. Stratification/phytoplankton growth N=nutrients Pn= photosynthesis S= stratification

34. Hadley Cells, Trade Winds, Westerlies

35. Subtropical Gyre Circulation • Western boundary – intense currentsother boundaries – weaker currents • Downwelling suppresses deep mixing • Subtropical mode water separates seasonal mixed layer / thermocline from main thermocline

36. Subtropical Gyre concepts • Seasonality diminishes with decreasing latitude • Southern half of gyre – no spring bloom as nutricline / euphotic zone depth lies below deepest mixing

37. Subtropical Gyre Science Questions • Contribution to new production / CO2 flux • Factors controlling new productionPhysicalChemicalBiological (Ecological)

38. Bermuda (32 N) Time series of T&S continuously since 1954 Chemistry and biology continuously since 1988 Hawaii (21 N) T&S, chemistry and biology continuously since 1988 Sporadic, T&S, chemistry and biology since the mid-1960s Subtropical Gyre Stations

39. Productivity at Bermuda determined by maximum winter mixed layer depth Productivity nitrogen (nitrate)-limited Increasing stratification due to global warming? Historically – productivity and biomass limited by mixing / nutrient input as in Bermuda Still true? Subtropical Gyre Stations

40. Seasonal Conditions – Bermuda • Winter/Spring: mixing approaches or crosses nutricline (ca.100 m) … spring bloom occurs -- measurable nitrate at the surface -- phosphate generally absent • Summer: Nutrients absent at surface but CO2 is removed from surface waters • Fall: Mixed layer deepens toward nitricline: no fall bloom

41. Contrasting subtropical system – HawaiiNorth Pacific Subtropical Gyre (NPSG) • More southerly location means less seasonality -- more stratification • Nutricline near 200m • Peak in productivity is in the summer(light limitation / photoadaptation?) • Still significant C flux -- how? • Nitrate mostly absent -- phosphorus seasonally variable

42. Time lapse photographs of phytodetritus on the seabed at 4000m (N. Atlantic) Mound is 18cm across. Lampitt 1985