Production and Life OCEA 101

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1 Production and Life OCEA 101

2 Overview Photosynthesis Primary production Phytoplankton biomass Controls on primary production and biomass Food webs

3 Photosynthesis Photosynthesis requires: (i) sunlight (ii) inorganic nutrients (iii) carbon dioxide Photosynthesis in the ocean can be limited by: (a) light availability (b) nutrient availablility (c) temperature Rarely is CO 2 availability a limiting factor.

4 Pigments Phytoplankton use pigments to absorb sunlight. The most common pigment is chlorophyll a absorbs blue and red light best. There are other important pigments that absorb at other wavelengths and extend the range of depths at which phytoplankton can grow.

5 Carbon Fixation Photosynthesis generates organic carbon from inorganic carbon (CO 2 ) a.k.a carbon fixation 6CO H 2 O * Solar energy Chlorophyll a C 6 H 12 O 6 + 6O 2* + 6H 2 O Catalyst Sugar (O * - oxygen derived from water not carbon dioxide)

6 Carbon Fixation Photosynthesis generates organic carbon from inorganic carbon (CO 2 ) a.k.a carbon fixation 6CO H 2 O * Solar energy Chlorophyll a Catalyst C 6 H 12 O 6 + 6O 2* + 6H 2 O Sugar Phytoplankton produce more than half the oxygen we breathe!

7 Light and Dark Reactions Light Reactions: - Light energy=>chemical energy -O2 released as by product -Occurs in the grana of the chloroplast Dark Reactions (light independent): - Uses energy from light reactions - Carbon fixation takes place -CO2 is combined with hydrogen to form carbohydrates -Occurs in the stroma of the chloroplast

8 Fluorescence Photosynthesis is not 100% efficient: - some of the absorbed solar energy is lost as heat during chemical reactions - some is lost via fluorescence Fluorescence in dinoflagellates

9 Diatom in white light Diatom in blue light, flurorescing as red light

10 Primary Production: = the production of organic matter from inorganic nutrients using light energy Gross Vs Net Gross Production: The total amount of carbon fixed, or oxygen generated Net Production: Gross minus the cost of respiration Net =(Gross - Respiration) amount available for heterotroph consumption Usually expressed in units of carbon per unit area per unit time: coastal net PP ~10 gc m -2 day -1 open ocean PP ~1 gc m -2 day -1

11 Measuring Primary Productivity Recall general photosynthesis reaction: nco 2 + 2nH 2 O * Solar energy Chlorophyll a (CH 2 O) n + no 2* + nh 2 O Amount of C fixed is proportional to amount CO 2 consumed Primary productivity can be determined by uptake of CO 2 using uptake of carbon-14, a radioactive isotope of carbon

12 Water samples taken from different depths and placed in light and dark bottles. Carbon-14 added to all bottles. (Initial concentration of C-14 is known.) Water bottles returned to depth collected for 24hrs. (or can be simulated on deck) Samples are filtered out onto filters that capture phytoplankton which contain the fixed C-14 C-14 fixed is measured in lab. The dark bottles act as a control Total (net)pp=light -Dark In the example shown, max primary productivity is at 30m. The compensation depth is where net primary productivity is zero (NPP=0, therefore, GPP=Respiration)

13 Redfield Ratios When abundant nutrients are present and phytoplankton growth is optimal, then we find that the molar weights of C, N and P are in balance according to: C : N : P = 106 : 16 : 1 Organisms decompose/die and release nutrients back into the water column in this ratio This is called the Redfield Ratio.

14 Phytoplankton Biomass Total phytoplankton (P) biomass at any time a.k.a. phytoplankton standing stock Standing stock depends on: (i) growth of P (ii) reproduction of P (iii) natural mortality of P (iv) grazing of P by zooplankton (Z) } Production } Losses Standing Stock = Production - Losses

15 Measuring Phytoplankton Standing Stock (Biomass) All phytoplankton contain Chl a, therefore use this as a marker to measure phytoplankton Phytoplankton biomass can be estimated by counting phytoplankton using a fluorometer Satellites also provide measures of biomass by measuring ocean colour.

16 Phytoplankton Blooms Blooms of P occur when P biomass increases MORE rapidly than it is consumed by grazers. Two hypothetical ocean sites: Site A (e.g. subpolar N. Atlantic in spring) Net Primary production is the same at oth sites Site B (e.g. subtropical N. Pacific) Site A: Grazers low Standing crop increases rapidly Bloom conditions! Site B: Grazers abundant Standing crop low Most of what is produced is consumed immediately

17 Controls on Primary Production and Biomass Phytoplankton primary productivity (PP) is controlled by: (a) temperature (b) light level (c) nutrient availability Biomass is also reduced by grazing

18 Temperature & Phytoplankton Eppley (1972) plotted species growth vs. temp. Empirically determined that all phytoplankton fit under a curve Different types of phytoplankton have different optimal temperatures for growth Growth Rate Temperature (deg C)

19 Light Level & Phytoplankton Diatom Dinoflagellate Primary Productivity (y-axis) vs irradiance (light level) (x-axis) for (a) diatoms and (b) dinoflagellates. Note how the diatoms are photoinhibited at high light levels, while the dinoflagellates are apparently not.

20 Nutrient Availability & Phytoplankton Growth rate of a diatom as a function of available nitrate

21 Primary Production New Production

22 Polar Oceans: Seasonality in P Biomass Winter Spring Summer Autumn

23 Polar Oceans Winter no light; sea-ice; nutrient rich waters under ice Summer abundant light; ice-melt leads to exposed surface and increased nutrients Summer bloom in phytoplankton with zooplankton lagging ~ a month

24 Subtropical Oceans Abundant sunlight year round Low nutrient and highly stratified water column Phytoplankton confined to near surface Grazing of phytoplankton by zooplankton leads to low biomass

25 Subtropical Oceans

26 Temperate Latitude Oceans Winter low light level; deep mixed layer (ML); high nutrient (N); low P; low Z Spring increase in light and stratification; shallower ML; low Z; ideal conditions for P - BLOOM! Summer high light level; reduced N due to low supply rate and consumption by P; reduction in P due to grazing by Z. Fall sufficient light; deepening ML/breakdown in stratification replenishes N; fall (secondary) bloom in P.

27 July 1998 Ocean Colour

28 Oct 1998 Ocean Colour

29 Jan 1999 Ocean Colour Phytoplankton + grazers mixed down Nutrients mixed up

30 April 1998 Ocean Colour

31 Sverdrup s Critical Depth The CRITICAL DEPTH (described by Sverdrup) is the depth to which phytoplankton can be mixed, and still have net photosynthesis, because on average, they spend more than half the day above the COMPENSATION DEPTH. Data from 1949 (66N, 2E) showing the relationship between approximate critical depth (shading for values of attenuation coeff k= ) and mixed layer depth (MLD). Phytoplankton (and zooplankton) Counts increase in April-May When critical depth > MLD.

32 Global Primary Productivity

33 Mean primary productivity of coastal systems is 6x that in the open oceans HOWEVER, if we multiply this by the area of each of these systems, we see that the open ocean has more than two times the Total Primary Productivity Total PP in open ocean > that of upwelling + coastal systems combined!

34 Eastern Boundary Current Systems Upwelling=Productive Waters Daily average primary production and annual fish catch for the four eastern boundary current large marine ecosystem regimes (global average daily production is provided for reference). These four LMEs account for only 1.9% of the world s oceans, but represent 3.7% of global production and greater than 23% of global fish catch. Figure based on data from the FAO fisheries database.

35 Foodwebs

36 Ecosystems and Energy Transfer Trophic Levels: each level of organism Trophic Transfer: percentage of energy lost

37 Food Chains: short, direct transfer of energy from phytoplankton to apex predators

38 Illustration by S. Cook, Scripps Institution of Oceanography

39 The Microbial Web Viruses can account for a major source of phytoplankton mortality Bacteria can provide 50% of phytoplankton nutrients Some ecosystems can be net heterotrophic

40 Recall the solubility and biological pumps

41 98% of ocean s biomass! Food Pyramids

42 Benefits of Microbes used to clean up environmental pollutants (bioremediation of 89 Exxon Valdez oil spill) yield benefits to medicine and technology used to make products like toothpaste, wine and beer ancient microbes buried deep in the earth is responsible for the oil and natural gas we use to heat our homes and run our cars Removes half the CO2 we pump out into the environment each year HOWEVER - also responsible for HAB s (e.g., red tides) 42