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
PPT, evap, runoff, and I vary greatly with latitude. Continuous heating at the equator causes air to rise. The rising air cools with increasign distance from the warm earth, cooling air is able to hold less moisture and the resulting seasonal rainfall is generally high in eq. regions. P. 60.

3. Water Column Structure
Surface
Mixed Layer
(Epilimnion)
Mixed Layer
Depth
Thermocline
(Metalimnion)
Depth
Why is the thermocline so important is our discussion of PP? Thermocline = water layer in which temp changes most rapidly with depth. How deep is the mixed layer?
Anticyclonic circulation pattern results in convergence of surface water toward the central area of the gyre and deepening of the thermocline. Consequently, nutrient levels in the euphotic zone are comparatively low and PP is nutrient limited.
Turbulent mixing by winds and waves transfers heat downward from the surface. In low and mid-latitudes, this creates a surface mixed layer of water of uniform temperature (few meters to seveeral hundred meters deep). There is a seasonal vs. a permanent thermocline. The water layer where the temp gradient is the steepest is the permanent thermocline. Water desity changes – warmer low density on top and colder denser water below. In temperate climates, seasonal thermoclines are established in the surface layer during the summer. These result from increased solar radiation that elevates surface temp at a time when winds are not strong. In the fall, water is cooled (less solar radiation) and increased winds cause sufficient turbulence to mix upper layers and break down the thermocline. Show a spring thermocline on the left side and a summer one on the right. Biological productivity on a global scale and temporal scale are affected by the changing thermoclines.
(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
Along eastern boundary currents get upwelling
Wind driven circulation regions are isolated central gyres with low productivity
Subtropical Gyre
High Latitude Temperate
Polar
Not shown: Coastal, Coastal Upwelling areas

6. Global Pigment/Productivity
Global satellite production maps
Only using remote sensing can you get a synoptic view of the earth’s surface and estimate
productivity; how accurate this is cannot be determined, but it is likely close to ± 50%
Production estimated from using pigment data (irradience sensed from space) and
developing an algorithm to calculate production
Annual composite of production (from Paul Falkowski’s web site), and SeaWifs annual PP
• Coastal upwelling and equatorial upwelling- the most productive zones. Productivity
appears to follow dust input of iron; generally higher is shallow, coastal regions than
in deep-water areas (consistent with iron/nutrient inputs)
• Monsoonal upwelling in Indian Ocean
• N. subarctic Pacific- highly productive
• N. Atlantic- extremely productive, but boom or bust
• Subtropical gyres- low
• So. Ocean- satellites don’t cover it very well (lots of cloud cover), but can be very
productive in summer. But covered half the year with ice (not productive the rest of
the year)
• Arctic- lowest productivity on annual basis of anywhere on earth
In general, high productivity areas dominated by diatoms,
Coccolithophorids occur in high concentrations in gyres, sometimes in higher latitudes too
Dinoflagellates, cyanobacteria- oligotrophic, also low light levels.

7. Global Pigment/Productivity

8. Ocean Phytoplankton Biomass

9. Hadley Cells, Trade Winds, Westerlies

10. Hadley Cells, Trade Winds, Westerlies

11. The world's oceans travel in well-defined circular patterns called currents which flow like rivers. When the atmosphere pushes over the surface of the ocean some of the energy goes to forming waves while the rest goes to pushing the water in the direction of the wind. North of the equator currents bend to the right, south of the equator they bend to the left. This is called the Coriolis effect. Winds, continents and the Coriolis effect make currents flow around the oceans in huge loops called gyres.
Energy from the sun also causes currents to flow. Water near the equator is heated more than water at middle latitudes causing a surface flow toward the poles. Where two currents meet, the colder water sinks pushing warmer water up to the surface.

12. Cyclonic counter clockwise upwelling divergent
Anticyclonic clockwise downwelling convergent

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
Cont. shelf-breaks
Subarctic Oceans
Anticyclonic gyres
Arctic Ocean
Antarctic

15. Global Pigment/Productivity- by basin
Basin Productivity Percentage
Pacific Pg C y
Atlantic
Indian
Antarctic
Arctic
Med
Global
Oceanic Production: by basin
Pacific- largest ocean basin
Antarctic and Artic unproductive on an annual basis (ice cover, low light)
Models- e.g., Behrenfield and Falkowski, Howard-Yoder models
Models use irradience, pigment field. Come up with algorithm to estimate production
Different models have different predictions, variability in estimates is due to the uncertainty
in the physiological parameters in the models
Can change on interannual basis
Changes on seasonal basis- note N.A. bloom

16. Global Pigment/Productivity
Behrenfeld and Falkowski model

17. Global Pigment/Productivity
Howard-Yoder Model

18. Interannual
changes

19. Winter
Fall
Seasonal changes
Spring
Summer

20. Global Pigment/Productivity- by season
Global Annual Production 47.5 Pg C y-1
Seasonal Prod.: March-May
Seasonal Prod.: June-Aug
Seasonal Prod.: Sept.-Nov
Seasonal Prod.: Dec.-Feb 1
Changes on seasonal basis- note N.A. bloom
Oceanic production: seasonal (taken from
Maximum forced in large part by North Atlantic bloom
II. Seasonal cycles of production/ biogeochemistry:
To model system, need to know light, nutrients, mixed layer depth, grazers, temp.
Biomass

21. Range of annual PP in different regions Mean annual PP (g C/m2/yr)
Continental Upwelling
Continental shelf breaks
Subarctic Oceans
Anticyclonic gyres
Arctic Ocean <50
p. 68 book

22. Polar regions
Arctic

23. North Pacific Biomass Winter Spring Summer Fall
One bump in Oct/Nov. for phytoplankton biomass. Outside coastal influences there is virtually no change in the
Winter Spring Summer Fall

24. North Atlantic 2 bumps bimodal temperature peak
Seasonal cycles of production/ biogeochemistry
In winter:
a light limited system:
1. solar radiation low, short day lengths
2. cold water temperature, little vertical stability
3. low phytoplankton biomass
4. zooplankton low, because not much food around
5. storms- deep mixing
**mixing is below the critical depth—so net loss

25. Temperate region (NW Atlantic)
Winter

26. Temperate region (NW Atlantic) Onset of spring bloom-
Increasing thermal stability
Onset of spring bloom:
1. increasing thermal stability- **mixed layer above critical depth
2. increasing solar radiation
3. decreasing storms
4. nutrients high- (from previous mixing)
bloom conditions- usually larger- net plankton like diatoms, dinosbetter adapted to respond to high nutrients than pico/ nannoplankton 3
Fall bloom
Zooplankton feces-recycled nutrients- PO4, NH4
Release from grazing pressure (copepods consumed, zooplankton starved)
fall storms inject nutrients, partial breakdown of H2O stratification
Modification for upwelling systems:
(upwelling on CA coast, june-sept.; in Peru, almost continual)
1. bloom prolonged
2. biomass transported offshore
3. nutrient depletion, sinking- high C/N ratio in slope sediments, much of production sinks
ungrazed
4. system intermittent- episodic, wind spins up system, then relaxation
6. some phytoplankton may use circulation cells for life stage transport

27. Temperate region (NW Atlantic)
Decline of spring bloom
Sinking
2. Grazing (lag)
aggregate
Decline of spring bloom (summer)
1. growth limited by total nutrients
2. losses to sinking- perhaps bulk of cells sink out
-sinking rate related to physiological state
-most typical phytoplankton of spring bloom are diatoms (non - motile, so sink)
-some form resting spores
2. losses to grazers-grazing control
reason for lag:
e.g. copepod
Cv adults eggs nauplii copepodites
function of temperature, but may take days before significant
number of feeding copepods

28. Species succession within a bloom
Small cells
High growth rates
Flagellates, small diatoms
species succession: Raymond Margalef- spanish ecologist (and others)
1. small cells with high growth rates
not a lot of diversity, tend to be non-motile
some that form gelatinous colonies
(leakage- conditions the water)
e.g. small flagellates, diatoms
Sleletonema (small diatom)-[[check]]
2. Larger diatoms (S/V decreases)
-spiny forms (increased adaptations to deter grazing)
-auxotrophs (require vitamens)
-resting spore formers
-moderate growht rates with high Ks
e.g. Chaetoceros
3. Increase in slower growing forms- Dinoflagellates
Auxotrophs- vitamine requiring forms
large diatoms with endosymnbionts
cells often motile (goes along with nutrient depletion)
red tides
e.g. Rhizoselenia, Dinoflagellates
4. complete N depletion
get N fixers- cyanos- tricho
other pico plankton and nanoplankton
succession phase can be interrupted or restarted by mixing events (sequence can repeat
itself during upwelling)
only quasi-predictable, some order to sequence, but unpredictable
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
Biomass
zooplankton
Unpredictable muted change
Jan
Dec

30. Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water. There are at least five types of upwelling: coastal upwelling, large-scale wind-driven upwelling in the ocean interior, upwelling associated with eddies, topographically-associated upwelling, and broad-diffusive upwelling in the ocean interior. However, in the tropical pacific area upwelling is not common, and very rare.

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 currents other 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
The spring bloom is a sudden and strong bloom of phytoplankton in the spring in temperate and sub-polar oceans. In the winter, the ocean waters are mixed, i.e., the water is circulated from the bottom to the top of the ocean because the water is relatively cold (and thereby have the same density) throughout the water column. In the early spring, the upper water layers therefore have enough nutrients (circulated up from bottom waters) but phytoplankton are unable to thrive because they are circulated down to depths where there is not enough light for them to survive. However, as the ocean becomes warmer in the spring, the warm water will tend to stay at the top, stabilizing the water. At this time, the phytoplankton are kept in waters with enough lights and with abundant nutrients, and their population numbers explode. However, the phytoplankton use up the available nutrients during a relatively short time (a few weeks to a few months), and their numbers dwindle in summer.

37. Subtropical Gyre Science Questions
Contribution to new production / CO2 flux
Factors controlling new production Physical Chemical Biological (Ecological)

38. Subtropical Gyre Stations
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

39. Subtropical Gyre Stations
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?

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 – Hawaii North 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