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Maine Coastal Waters Conference 2009

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1 Maine Coastal Waters Conference 2009
SMS 501 Biological Oceanography 16 September 2009 Lecture 5 Mary Jane Perry Maine Coastal Waters Conference 2009 October 28 (Wednesday, 0900) Issues? Car pooling *Essay 1 due next week *Concept map 1 the following week

2 This Week – Phytoplankton II
SMS 501 Biological Oceanography 16 September 2009 Lecture 5 Mary Jane Perry This Week – Phytoplankton II Review of last week Assessing phytoplankton – as individuals or as mass Introduction to photosynthesis Pigments – photo-adaption and accessory pigments Regulation of photosynthesis Rates of primary productivity Sverdrup concept of bloom initiation

3 Review of Phytoplankton I
Phytoplankton are little factories. – transform electromagnetic energy into chemical energy. – transform dissolved nutrients & CO2 into organic particles. They are incredibly diversity, both taxonomically and functionally. – taxonomically –> 2 Super Kingdoms (Eubacteria & Eukaryotes) – size (from ~ 1 µm to 100 µm+); regional variation in size spectrum – chemical composition (fatty acids, pigments, etc.) – nutrient cycling (Si – only diatoms, N2 fixation – only cyano, etc.) Growth rate – cells increase in size (little factories) and divide. Cell number at tX = (cell number at t0 * 2kt) = (cell number at t0 * eµt) Growth rate is regulated by temperature, light, and nutrients. Satellite ocean color – reflected light; empirical relationship w/chl.

4 Phytoplankton abundance – how to assess
Two historical approaches: as individuals and as mass (average or ‘bulk’ measure) How to reconcile the two? – for example, number of cells vs. chlorophyll How are the two measures used to normalize rates? How are the two measures used in models and for prediction?

5 Measure phytoplankton as individuals with
microscope (more taxonomic information) or other technologies (less taxonomic information). microscopic identification : * microscopic identification to some taxonomic level (slow) – light microscope, if cells are large enough – SEM for small cells, not quantitative – epifluorescence (autofluorescence, stains) * image analysis, classification of types by pattern recognition other (can be fast or faster than microscope): * Coulter Counter – electronic, change in electrical impedance, but counts all particles, not just phytoplankton – size spectra * flow cytometry: light scattering and fluorescence – optical classification of particles (typically not species) * molecular probes (qualitative) – in situ hybridization & stain – couple with image analysis or flow cytometry

6 Epifluorescence microscopy
Chloroplasts (red) in colony of diatom Thalassionema ; red chl fluorescenc and blue DAPI nuclear stain. Microscopy of cells (working toward automation w/ image classification). Note morphological variation in one species, Dinophysis acuminata. Synechococcus with phycoerythrin (orange) & chl fluorescence (red)

7 Coulter Counter – electronic particle counter (counts all particles, not just phytoplankton). Particle size spectrum (~ 1 µm to about 500 µm). Sheldon et al., L&O 17: 327

8 Single cell – flow cytometry
Flow cytometry: – single cell or particle analysis – multiple optical discriminants (scatter and fluorescence) (from Sosik & Olson)

9 Phytoplankton measurement as mass (biomass)
Phytoplankton measurement as mass (biomass) (biomass is ‘state variable’ – in contrast to ‘rate’ variable) bio – biological or living; mass – grams (in MKS system - meter, kg, sec) so-called “bulk” measures of phytoplankton biomass elements – C, N, P, Si (problem: elements are not necessarily unique to phytoplankton; most elements are found in all living organisms) pigments, primary chlorophyll a – found only in photosynthetic organisms; some accessory pigments unique to specific taxon. (µg L-1 or mg m-3; mg m-2 for integrating water column) –> apply chlorophyll–to–C ratio (problem: ratio varies with light conditions of growth) unique chemicals – taxon specific (fatty acids; sterols {dino- flagellates}’ lipids {alkenones – coccolithophorids}; etc.) optics – satellite remote sensing, absorption and scattering

10 ‘Chlorophyll biomass’ – proxy for phytoplankton carbon:
extract of chlorophyll in lab & in vivo fluorescence in the water’ Chlorophyll is unique to photosynthetic organisms. One application is to use chlorophyll to obtain phytoplankton carbon. Multiply by carbon–to–chlorophyll ratio (g/g). Ratio typically (O(15 – 50 g/g)) (but can exceed 50 g/g under high light or low nutrients). Extract chlorophyll a: * filter cells * extract 90% acetone * blue light source, red light emission * concentration is proportional to red light emitted cell carbon chlorophyll a Irradiance of growth 15 50

11 Chlorophyll a is used as proxy for phytoplankton biomass because it is ONLY found in photosynthetic organisms (exception – mixotrophic species & while being digested in heterotrophs) Extracted chlorophyll a (µg/L) used in iron-fertilization experiments to assess bulk phytoplankton growth response to Fe. In vivo chlorophyll a fluorescence provides information on vertical and horizontal distribution of phytoplankton; (data collected with underwater glider in Monterey Bay)

12 Combined information from extracted chlorophyll AND flow cytometric classification (based on optical signals). ATM 13 cruise from 50ºN to 50ºS 7-m pigment (solid line) m integrated pigment (dotted) Subgroups converted to C biomass.(Note change in scales.) Note Mauritanian upwelling – 20ºN. Tarran et al DSR II 53: 1516

13 Regional biomass differences as chlorophyll a (mg chl a m-3) Oligotrophic gyres (mostly small ultra and picoplankton) Coastal upwelling (nano and larger netplankton) Coastal shelves (seasonal: spring net & nano, summer picoplankton) Equatorial Pacific upwelling (small picoplankton) (seasonality; variance high in coastal waters; eutrophication - higher) SeaWiFS chl

14 Information from phytoplankton concentration (typically chlorophyll biomass – state variable) is applied to rate measurements (rate variable) to make rates of primary productivity portable. Satellite chlorophyll concentrations

15 light CO2 + H2O -----> -(CH2O)- + O2
Photosynthesis – process of conversion of energy of electro- magnetic radiation (light) to chemical energy (ultimately, carbon). Pigments (chlorophyll a and accessory pigments are essential in this process – they absorb light. CO2 + H2O > -(CH2O)- + O2 Primary product of ‘light reactions’ are ATP & NADPH (high energy reductants). Initial product of ‘synthetic reactions’ or Calvin cycle is 3C sugar. Final products that are synthesized include proteins, lipids, nucleic acids, etc.; complex molecules require additional energy to synthesize. Photosynthetic Quotient (= ratio between O2 evolved and C fixed) varies with types of compounds synthesized; varies from ~1.0 to 1.5 light

16 P = Pmax ( 1 – e ( aE/Pmax) ) Ek = a/Pmax
Functional response of photosynthesis to light. This is P vs. E curve. Photosynthetic rates are normalized to chl a. Pmax is maximal rate; ais slope (rate/irradiance); Ek – transition from light limited photosynthesis to light saturated photosynthesis; R is phytoplankton respiration. What is gross vs. net photosynthesis? P = Pmax ( 1 – e ( aE/Pmax) ) Ek = a/Pmax

17 Light regulates photosynthesis
Light decreases exponentially with depth. irradiance (E) ln irradiance (E) E = Eo e-Kz z z Units of irradiance: mol photon m-2 s-1 or mol photon m-2 d-1 (rather than watts m-2) K, diffuse attenuation coefficient (m-1 ) z, depth (m) E, irradiance (mmoles photon m-2 s-1 ) Euphotic zone - how to define? 1% light level vs. absolute value

18 Seasonality in light equator What are implications for seasonality in photosynthesis? 1. total irradiance –> euphotic zone depth 2. day length (sp. effect) 3. solar heating –> stratification –> mixed layer depth pole

19 E = Eo e-Kz PAR (400–700 nm) vs. spectral light, E(l)
ln irradiance (E) K (l) varies for different types of water masses

20 Pigments capture energy from light
Chlorophyll a multiple pigments –> broader spectral window (chl a & b in land plants) – l of light must match l of pigment absorption Chlorophyll b or c Photosynthetic carotenoids Phycobilipigments

21 Advantage of multiple pigments – broadening of
spectral window for absorption (and growth). A mismatch between absorption and spectrum of light means no photosynthesis for that species.

22 HPLC allows resolution of individual pigments; information can be used for taxonomic classification.

23 Chem Tax (requires training) See Miller Table 2.2

24 Both rates of photosynthesis and pigment concentration per cell are regulated by irradiance
chl a/cell growth irradiance

25 Phytoplankton can photo-adapt to high or low light
1. At low light: more light-harvesting pigments At high light: fewer light-harvesting pigments but more photoprotective pigments (carotenoids). chl a/cell irradiance at which cells are grown

26 Change in pigmentation in high or low light changes photosynthetic rate as a function of irradiance.
Low-light grown cells have more light-harvesting pigments and have higher rates of photosynthesis at low light. High-light grown cells have fewer light-harvesting pigments. chl a/cell irradiance low-light grown PS rate pg C cell-1 h-1 High-light grown

27 Consequence of photo-adaptation
A cell does better at low light (synthesizes more pigments/cell) than it would without ability to change pigmentation/cell. By reducing pigments/cell at high light, a cell minimizes photo-inhibition due to photo-damage at high light. chl a/cell Down-side for oceanographers, is that the C-to-Chl ratio is not a constant but varies by factor ~3-4. irradiance growth rate hi E PS rate pg C cell-1 h-1 low E irradiance

28 Photosynthesis is a function of irradiance
Photosynthesis is a function of irradiance P = Pmax ( 1 – e ( aE/Pmax) ) Photosynthetic rate is typically normalized to chlorophyll concentration to make the measurement ‘portable’ Carbon–to–chlorophyll ratio changes with growth irradiance Light is attenuated exponentially as a function of depth; spectral attenuation varies in different water bodies. Photosynthetic accessory pigments enable phytoplankton to absorb broad spectrum of wavelengths (vs. land plants) How is photosynthetic rate measured in the ocean?

29 14CO2 + H2O ---> -(14CH2O)- + O2
Photosynthesis can be measured as oxygen evolution (often tough to make good oxygen measurement for low phytoplankton biomass) or as 14C incorporation (Steeman Nielsen, 1952) 14C added = 14C in cells on filter total alkalinity total Carbon fixed (total DIC ) Units per volume are mg C m-3 or mmol C m -3 (integrated: mg C m-2 or mmol C m-2). Make rates portable by normalizing to something (typically, chlorophyll a concentration).

30 Real data from HOTS: Pattern of photosynthetic rates as function of depth (O2 and 14C) Photosynthetic quotient O2 evolved /C fixed Why does quotient vary? DSR I 51: 1563

31 Relationship between biomass (Chl a) and productivity?
A. Thomas, UMaine Prog. Ocean. 65:159 – Arabian Sea Portability of rates: use rate information normalized to biomass PS = pigment concentration * rate per pigment (also include some type of light function)

32 Large number of models to go from satellite chlorophyll (biomass) to primary productivity (rate)

33 Use of satellite data allows one to ask questions – Does ocean productivity change with climate cycles? or Is there a secular trend in response to climate change? El Nino La Nina

34 Global annual estimates of PP:
Schroeder (1919) speculation Pg C y-1 Steemann Nielsen (1952) 14C & estimating 20 Pg C y-1 Koblentz- Mishke (1968) 14C & mapping Pg C y-1 Behrenfeld (2002) satellites & models 41 Pg C y-1

35 Regional patterns of PP, derived primarily with 14C Table from Barber and Hilting in Williams et al. (2002) (see Søndergaard for global estimates) Biomass Regional differences: (mg Chl a m-3) Oligotrophic gyres Coastal upwelling Coastal shelves Equatorial Pacific upwelling (variance is highest in coastal waters) Productivity Regional differences: (gC m-2 y-1) Oligotrophic gyres 50 Coastal shelves Upwelling (also will be seasonal and daily variability, etc.) Regional & global estimates of PP: Biomass * PP rate/biomass * area

36 Important Concepts Production is fixation of carbon; productivity is rate of production 1. gross PP: total rate of phytoplankton fixation of carbon 2. net PP: rate of phytoplankton fixation of carbon minus phytoplankton consumption* of carbon (via respiration at night) 3. net net PP or community net PP: rate of net phytoplankton fixation minus consumption (grazing by protoza and zooplankton; metabolism of DOC by bacteria). Recall dP = P(growth – loss) dt 4. new PP: exportable production to deep water column or fish (need to define boundary conditions) NB: Time period for measuring & integrating makes a difference: community net and new PP will be different if PP is integrated per hour vs. per day or per year. WHY?

37 D ARGO floats near Hawaii. Riser & Johnson. 2008. Nature 451: 323
Other ways (than 14C) to estimate primary productivity. For example, oxygen evolution and accumulation for net community PP. (longer term measurement than 14C)

38 Other ways (than 14C) to estimate primary productivity.
Lagrangian mixed-layer float, subpolar N. Atlantic spring bloom. D’Asaro et al., unpub. Other ways (than 14C) to estimate primary productivity. Mass balance – Redfield ratio for C:N O2 and nitrate from ISUS on float agree; but less POC standing stock than POC produced.

39 Draw photosynthesis vs. depth
irradiance (E) z

40 Photoinhibition – only if surface light is high
irradiance (E) z

41 Sverdrup and critical depth Relationship between gain and loss terms: dP = P (gain – loss) dt When phytoplankton gain > loss terms, bloom occurs. Could be due to more light, reduced mixing (stratification), etc. Critical depth: Depth at which integrated water column gain = integrated water column loss (photosynthesis = respiration). If mixed layer is > critical depth, no bloom. If mixed layer is < critical depth, bloom. Compensation depth: Depth at which photosynthesis = respiration.

42 Unanswered questions

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