IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

Lecture 7 Ocean Color and Phytoplankton Growth IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

This lecture includes the following topics: 1. Chlorophyll and photosynthesis 2. Vertical distribution of phytoplankton in the ocean 3. Estimation of phytoplankton biomass from satellite ocean color observations 4. Estimation of chlorophyll fluorescence from MODIS ocean color observations 5. Estimation of coccolithophores concentration and harmful algal blooms 6. Seasonal cycles of phytoplankton biomass 7. Global phytoplankton biomass and primary production IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

1. Chlorophyll and photosynthesis Green color of plants, including phytoplankton, is a result of plant pigments, primarily chlorophyll a. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

1. Chlorophyll and photosynthesis Chlorophyll absorbs light energy and stores it in the form of chemical agent ATP. This energy is used for the synthesis of organic matter. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

1. Chlorophyll and photosynthesis The synthesis of organic matter by plants (primary production) is a basic source of food for all living organisms. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean Photosynthesis cannot proceed without light; so, in the deep layer phytoplankton growth is “light limited” Another requirement for photosynthesis is a sufficient concentration of nutrients (nitrates, phosphates, iron, etc.). In stratified water nutrients in the upper mixed layer are consumed by phytoplankton; so, phytoplankton growth there is “nutrient limited”. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean The growth of phytoplankton occurs in the layer where both light and nutrient concentration are sufficient. With increase of the upwelling nutrient flux the conditions of phytoplankton growth become better and the maximum of its vertical distribution moves to more shallow layer. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean When nutrient flux is very intensive and phytoplankton biomass is high, the maximum of vertical distribution of phytoplankton is located at the surface. The result is a direct correlation between total phytoplankton (or chlorophyll) concentration in water column (or within the euphotic layer) and in the thin surface layer. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean Hence, both the surface chlorophyll concentration and the chlorophyll concentration above the penetration depth can be used as a measure of water productivity, i. e., phytoplankton biomass. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean Vertical distribution of ecosystem characteristics at a typical station in the oligotrophic waters shows deep phytoplankton maximum and nutricline. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean Vertical distribution of ecosystem characteristics at a typical station in the eutrophic boreal waters shows shallow phytoplankton maximum and nutricline. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean What layer contributes to the color of ocean surface? 0 Vertical attenuation of sun light (I) with depth (Z) can be described by exponential equation Iz = I0*exp(-k*Z) Deeper from the surface - less light is reflected or scattered by phytoplankton cells and contributes to the color of ocean surface. L i g h t 10 ) 20 m ( h t p e D 30 40 50 IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean What layer contributes to the color of ocean surface? Iz = I0*exp(-k*Z) Coefficient K is called “attenuation coefficient”; it is measured in 1/m. The value 1/K is called “attenuation length”, and the layer of this length is called “penetration depth” (Zpd). Another depth used in ocean optic is “euphotic depth” (Ze); it is defined as the depth where the downwelling PAR (Photosynthetically Active Radiation) is reduced to 1% of its value at the surface. These two values are related by empirical equation Zpd Ze / 4.6 IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

2. Vertical distribution of phytoplankton in the ocean What layer contributes to the color of ocean surface? The Csat(averaged concentration "seen" by a remote sensor) is computed as follows: Csat is correlated with phytoplankton biomass in water column. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

3. Estimation of phytoplankton biomass from satellite ocean color observations Empirical models are based on direct correlations between normalized water-leaving radiation and chlorophyll concentration. Semi-analytic models are based on the Inherited Optical Properties (IOPs) of water column, i.e., absorption and backscattering of different water constituents (phytoplankton, suspended sediments, CDOM, etc.). It is assumed that chlorophyll concentration in phytoplankton is a constant. In practice, chlorophyll content varies within a wide range. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. Recent studies of the College of Oceanic and Atmospheric Sciences at Oregon State University. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. Light energy not used for photosynthesis is lost as heat and fluorescence. Fp + Ff + Fh = 1 IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

Light absorption by algal pigments Light emitted by chlorophyll 4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. Regular method to calculate Chl fluorescence : use Fluorescence Line Height IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. • Fluorescence can be used as another measure of chlorophyll, but only in chlorophyll-rich water, because the optical signal produced by chlorophyll absorption substantially exceeds the signal of fluorescence. • ADVANTAGE: Absorption-based algorithms fail in waters where there are other materials that absorb and scatter and are not correlated with chlorophyll • Sediment • Dissolved organic matter • Chlorophyll fluorescence is specific to chlorophyll • LIMITATION: it also depends on physiology IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. MODIS successfully estimates FLH from space even in low chlorophyll case 1 waters IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. • ΦP + ΦF + Φh = 1 • P – photosynthesis; F – fluorescence; H – heat. • Φh (heat) is assumed a constant; • Estimation of chlorophyll concentration • assumes ΦF  constant • Estimation of primary production • assumes a predictable relationship • between ΦF and ΦP IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. Physiological parameters (APR and CFE) vary spatially. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

4. Estimation of chlorophyll fluorescence from MODIS ocean color observations. The patterns of variability of phytoplankton physiology estimated from fluorescence can be used in for evaluation of photosynthesis and primary production. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

5. Estimation of coccolithophores concentration and harmful algal blooms. Coccolithophores are small algae containing coccoliths – inorganic carbon structures. The blooms of coccolithophores result in very intensive water surface backscattering and hinder remote-sensed estimation of phytoplankton biomass. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

5. Estimation of coccolithophores concentration and harmful algal blooms. From typical to coccolithophores backscattering spectra we can now estimate the biomass of these algae. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

5. Estimation of coccolithophores concentration and harmful algal blooms. Optical measurements of MODIS enable estimation of not only chlorophyll a concentration, but also concentrations of pheopigments, which are produced by zooplankton during grazing. Decreased concentration of pheopigments indicates absence of grazing typical to harmful algal bloom. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

5. Estimation of coccolithophores concentration and harmful algal blooms. This image shows the area of harmful algal bloom near the Pacific coast of Central America. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass One of the main goals of remote-sensing observations is the study of seasonal cycles of phytoplankton biomass in different regions of the World Ocean. In many regions these cycles repeat every year including minor details. This pattern is a result of seasonal oscillations of physical environment. In high latitudes these oscillations are more pronounced, and the response of phytoplankton is more evident. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Typical pattern of seasonal variations of phytoplankton in temperate latitudes is known since the beginning of 20th century. The main feature is a short-period (1-2 weeks) "vernal bloom" called in parallel with seasonal cycle of terrestrial plants. The cycle contains the period of exponential growth and then abrupt decrease resulting from grazing of phytoplankton by zooplankton. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass The hydrological conditions of start of the spring bloom of phytoplankton were described and explained by Harold Sverdrup in 1953. He attributed the beginning of spring bloom to the formation of seasonal thermocline, when the upper mixed layer is separated from deeper water column and phytoplankton Is retained in illuminated (euphotic) layer. The strengthening of seasonal thermocline in summer results in nutrient limitation of phytoplankton growth. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Stratification within the euphotic layer is a primary factor controlling phytoplankton growth. We consider two main factors limiting phytoplankton growth: illumination and nutrients. Light limitation is crucial under low stratification (e. g., winter convection), because algae cells are dispersed by turbulent mixing within deep dark layers. Nutrient limitation is crucial under enhanced stratification (e. g., seasonal thermocline in summer), because nutrients do not penetrate into the euphotic (i. e., well illuminated) upper mixed layer. The hydrometeorological factors (heat flux, wind, freshwater load with precipitation and river discharge) either increase or decrease the stratification within the euphotic layer. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Typical seasonal cycles of phytoplankton result from the combined effect of seasonal cycles of hydrometeorological factors influencing water stratification within the euphotic layer. The most illustrative is the phytoplankton seasonal cycle in mid-latitudes with two maxima in spring and autumn: IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass In high latitudes (cold and windy) winter minimum is more pronounced and summer minimum is less pronounced. In low latitudes (warm and less windy) winter minimum is less pronounced or absent and summer minimum is more pronounced. Deviations from typical seasonal pattern of hydrometeorological factors result in local peculiarities of phytoplankton cycle. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Typical seasonal cycles of phytoplankton described by Alan Longharst are given below. He distinguishes eight types of cycle. The figures illustrate pigment concentration (Chl), primary production (P), mixed layer depth (Zm), and the period when the picnocline is illuminated (■■). IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Near Newfoundland two different water masses (cold Labrador Current and warm Gulf Stream) are separated by frontal zone. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Four small regions were selected in the zones of influence of the Labrador Current, the Gulf Stream, and over shallow and deep parts of the Newfoundland Bank. Seasonal patterns were typical to Arctic, coastal, mid-latitude, and subtropical regions. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Seasonal patterns were typical to Arctic, coastal, mid-latitude, and subtropical regions. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass In April 1999 unusual wind pattern (weak wind in northern part and strong wind in southern part) resulted in stronger bloom of phytoplankton. Weak wind in northern (light-limited) zone enhanced stratification; strong wind in southern (nutrient-limited) zone eroded thermocline; both favored phytoplankton growth. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass These images show seasonal variations of plant pigment concentration in in the Ligurian Sea. January 1998, March 1998, and August 1998 Subtropical seasonal cycle with summer minimum and higher chlorophyll concentration during winter-spring is evident. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass These images show seasonal variations of plant pigment concentration in in the Ligurian Sea. March 1999, April 1999, and May 1999 In 1999 typical to mid-latitudes spring bloom was observed. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

3 ) 3 m / 81/82 2 g m ( l l y 98/99 h p o r o l h 1 c 80/81 0.9 S 82/83 C 0.8 Z 85/86 C 0.7 y l 97/98 0.6 h t n o 0.5 m m 0.4 u 83/84 m 84/85 79/80 i 78/79 x 0.3 a M 0.2 8 9 10 11 12 13 14 15 D i f f e r e n c e i n a i r t e m p e r a t u r e b e t w e e n A u g u s t a n d N o v e m b e r ( C ) o 6. Seasonal cycles of phytoplankton biomass Significant correlation was revealed between air temperature contrast in autumn and the magnitude of spring bloom next spring (CZCS and SeaWiFS data). IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass Cold and windy autumn of 1998 preceded vigorous spring bloom in spring 1999. Explanation: 1. Deeper winter convection and enrichment of the upper layer with nutrients. 2. Cold winter and warm spring favors formation of seasonal thermocline. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

6. Seasonal cycles of phytoplankton biomass These SeaWiFS monthly composite images averaged over 1997-2001 and NCEP wind data illustrate seasonal variations of California upwelling. Stronger wind and increased phytoplankton biomass are observed in summer. IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth

IoE 184 - The Basics of Satellite Oceanography. 7. Ocean Color and Phytoplankton Growth