Phytoplankton and Productivity Add critical depth

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.

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

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

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

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.

Global Pigment/Productivity

Ocean Phytoplankton Biomass

Hadley Cells, Trade Winds, Westerlies

Hadley Cells, Trade Winds, Westerlies

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.

Cyclonic counter clockwise upwelling divergent Anticyclonic clockwise downwelling convergent

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

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

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 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

Global Pigment/Productivity Behrenfeld and Falkowski model

Global Pigment/Productivity Howard-Yoder Model

Interannual changes

Winter Fall Seasonal changes Spring Summer

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 1 Changes on seasonal basis- note N.A. bloom Oceanic production: seasonal (taken from http://marine.rutgers.edu/opp/) 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

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 p. 68 book

Polar regions Arctic

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

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

Temperate region (NW Atlantic) Winter

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

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 30-60 days before significant number of feeding copepods

Species succession within a bloom 1 2 3 4 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

Equatorial/Tropics Tropical regions (and most mid-ocean gyres) phytoplankton Biomass zooplankton Unpredictable muted change Jan Dec

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.

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

Phytoplankton biomass from satellites- chlorophyll a

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

Hadley Cells, Trade Winds, Westerlies

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

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.

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

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

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?

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

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

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