Oceanography L6-10
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Oceanography L6-10 - Marcador
Oceanography L6-10 - Detalles
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| Methods of study the oceans. | 1. Ships - research vessels are sophisticated and expensive. CTD measurements : Conductivity (related to salinity)-a wire with a conductive core is lowered through the water, Temperature and Depth. 2. Mathematical models 3. Satellites (SeaWiFS) 4. Mesocosms 5. Laboratory studies |
| Types of phytoplankton - Diatoms | -Possess a hard external inorganic frustule silicate. -Generally unicellular, fast growing and some form aggregates. -Dominate the Spring bloom. -"Pill-box" description. -Asexual reproduction, but sexual reproduction makes auxospore: larger cell, produce a frustule and have normal size and shape. -Pennate diatoms: elongate and usually benthic. -Centric diatoms: valves are arranged radially or concentrically around a point-common in the plankton. Mechanisms which retard sinking & allow diatoms to remain in lit surface waters |
| Types of phytoplankton - Dinoflagellates | -Unicellular and some form chains. -Have 2 flagella. Some are autotrophic, 50% are heterotrophs and eat phytoplankton/zooplankton. Some are mixotrophic. -Separate into: Thecate (cellulose) and Naked (without). Have 2 taxonomic groups: Desmophycae (flagella arise from anterior, Cell wall has two valves that separate during division) and Dinophycae (The majority, most are thecate, posterior flagella and form a girdle). -Form blooms named "red-tides": they may contain neurotoxins (saxitoxin), shellfish filtrate the toxin and it can cause paralysis to us. |
| Types of phytoplankton - Coccolithophores | -Belong to prymnesiophytes. -Unicellular and are important in the biogeiochemical cycle of C,S. -Have hard outer layer called cocoliths. -Increase of coccolithophorids, increase in CO2, positive feedback of CO2 in the atmosphere. -Widespread distribution: Emiliana Haxleyi is most common and cause albedo on surface from reflective of light by large blooms, It also synthesises DMSP as an omsolyte, the precursor of DMS |
| DMS importance | When released in the atm it forms SO2 an H2SO4 and acidic aerosols. They absorb and reflect solar radiation back to space, act as cloud condensation nuclei. |
| Types of Phytoplankton - Microflagellates | -very fast growing. -one of the most abundant phytoplankton groups present in winter in temperate seas. -numerous other species of small, naked, flagellated organisms exist, but are poorly known because of difficulties in isolation |
| Types of Phytoplankton - marine cyanobacteria | Play important roles in marine nitrogen fixation and primary production in the sea e.g. Synechococcus, Prochlorococcus and Trichodesmium. |
| Zooplankton | By definition all are heterotrophic : require organic substrates as sources of chemical energy. Obtain these by ingestion. There are herbivores, carnivores, detritovores (consume dead organic material) and omnivores. Holoplankton: life spent in the water column. Meroplankton: temporary residents. |
| Why we need to understand carbon flux pathways | I) in order to predict whether the oceans will respond to increasing atmospheric CO2 by acting as a net CO2 sink. ii) biodiversity & fisheries management also requires predicting spatial-temporal patterns of carbon fluxes into various biomass & species pools. |
| Organic matter synthesized by phytoplankton can enter 3 main pathways | I) it can be eaten by protozoa & metazoa (zooplankton). ii) it can be utilised by bacteria. iii) it can aggregate & sediment. |
| Classical Food Web | Phytoplankton → zooplankton → fish. Microbial Loop: Bacterial biomass roughly= phytoplankton biomass. Bacterial C demand is often equivalent to about half of the primary production. Thus major fluxes of organic matter occur via the route: phytoplankton → DOC → bacteria → protozoa. |
| The Microbial Loop is fuelled by dissolved organic matter | I) excretion of DOC by phytoplankton & cell lysi. ii) ‘sloppy feeding’ by zooplankton which can’t feed efficiently on small particles, and release DOC. |
| Primary Production | Fixation of CO2 to produce biomass. Greatest part is photosynthetic by phytoplankton. Chemoautotrophic bacteria can support animal communities at hydrothermal vents. Phytoplankton restricted to the surface mixed layer - the euphotic zone. Primary production includes DOC excreted by phytoplankton which is available to, & utilised by, bacteria |
| Methods of measuring phytoplankton biomass | Pigments: chl a is easily measured by fluorometry in which the sample is illuminated with blue light, chl a emits red light as fluorescence. Microscopy. Electronic particle counter. Flow cytometry & image analysis |
| Methods of measuring phytoplankton production | A) 14C incorporation (incubations following incorporation into biomass). b) oxygen production in photosynthesis (need to account for respiration). |
| Limits to phytoplankton production | I) Physical processes: Light, Temperature, Vertical Mixing, Advection, Stratification. ii) Chemical processes. iii) Grazing by microzooplankton, copepods, jellyfish etc. iv) Infection e.g. by viruses. |
| Light in the sea | This infrared radiation is quickly absorbed and converted to heat in the upper few metres. Ultraviolet radiation (<380 nm) forms only a small fraction of the total radiation & is rapidly scattered and absorbed, except in very clear ocean waters. Remaining 50% of the radiation comprises the visible spectrum. In oceanic regions blue-green light penetrates the deepest. In coastal regions green light penetrates the deepest. |
| Phytoplankton seasonal cycle | Winter: Low production, deep mixing and mixed out of euphotic zone. Spring: Thermocline is stronger, high biomass, diatoms stop growing. Zooplankton have longer generation times and leads to lag phase and the increase of grazers. Increase ammonia excretion. Si recycling is slow so diatoms are being replaced by microflagellates. Late summer: Increased grazing activity results in more re-generation of nutrients & there can be a late summer bloom. Dinoflagellates may sometimes dominate giving rise to ‘red tides’. Late Autumn: More heat is lost, thermocline is eroded, phyt. are mixing below the euphotic zone. |
| Summary of physiological features of picoplankton | Unicellular, Ovoid, Small size (ca 1.0 µm in diameter), Photoautotrophic (mostly obligate), Orange fluorescence, Widespread, Non-motile, Possess distinct pigment complement. |
| Phycobilisomes | The light harvesting complex for photosystem II (PSII) in cyanobacteria >95% of the light they absorb is passed to PSII. PBS core: composed of 2 or more commonly 3 cylinders. These core cylinders are composed of a stack of 4 discs. The cylinders form a triangular prism. Radiating from 2 sides of this core are 6 peripheral rod substructures : each rod is composed of a stack of discs. The number of discs per rod can range from 2-6 and is dependent on the source of the organism and the nutrient conditions employed. PBS are composed of 2 types of protein : phycobiliproteins and linker polypepetides. |
| 3 major classes of phycobiliproteins | Phycoerythrins, phycocyanins, allophycocyanins |
| Phycobiliprotein pigments | All phycobiliproteins carry at least one linear tetrapyrrole chromophore. The chromophores impart to the proteins their characteristic visible absorption properties. 4 chemically distinct chromophores are known to occur among cyanobacterial biliproteins :- phycocyanobilin, phycoerythrobilin, phycourobilin and a bilividin-type chromophore. 2 distinct sub-populations distinguished on the basis of the predominant chromophore associated with phycoerythrin a) phycourobilin-rich strains - characteristic of the open ocean b) low phycourobilin-containing strains associated with shelf waters |
| Vertical distribution | In the marine environment there are essentially two types of vertical water columns: vertically mixed & stratified; hence organisms will adapt to the presence or absence of a light & nutrient gradient. Depends on: i) depth to which photosynthetically active light penetrates the water column to 1% transmittance. ii) Synechococcus numbers below the 1% light level probably due to mixing. |
| Horizontal distribution of marine Synechococcus | May be affected by seasonal heating of the water and nutrient availability e.g. Fig. 4. shows where a change in water mass (& subsequently temperature) had a dramatic effect on Synechococcus numbers. |
| Diurnal patterns | In culture: light - Production and cell number increase. Dark - Stops. In lab: Light - cell number increase. Dark - decrease by gazers. |
| Flow cytometry I | - a flow cell which consists of a capillary containing a flowing sheath fluid. - a laser beam is focussed on the capillary & each particle is illuminated as it passes through the beam. -light emitted as autofluorescence or induced fluorescence from fluorescent dyes can be collected quantitatively from each particle. |
| Flow cytometry II: uses | Sort cells, detection of specific types of cell in situ using the unique fluorescent pigments of phytoplankton, immunofluorescence analysis, DNA content & cell cycle analysis. Sensitivity: alter the beam shape, reduce sample velocity and intensity will increase. |
| Prochlorococcus | Unicellular, coccoid, Small size, obligately photoautotrophic, red fluorescence, generally restricted to waters > 15°C, Non-motile, Possess distinct pigment complement. Proliferates in oligotrophic areas of the world oceans and seas, the most abundant photosynthetic organism known to date on Earth, is able to sustain growth and photosynthesis under a very wide range of irradiance from the surface, can also grow in waters with low levels of inorganic nutrients |
| Identification of Prochlorococcus | Free-living single celled organisms <1 µm in diameter. Possess appressed photosynthetic thylakoids adjacent to their gram -ve cell walls. Characteristic pigment composition: divinyl chlorophyll a and b; The ratios of dvchl a and b differ between strains and light intensities; dvchl a and b absorb efficiently at wavelengths available in the blue-light dominated deep euphotic zone of the open ocean. |
| Principles of biological cycles | Largely mediated by microbes & especially bacteria. Energy & mass are conserved. Biochemical transformations require energy. There are three energy states - light, heat & chemical biological. Processes result in ecosystem chemistry deviating from the thermodynamic equilibrium. Biology in the sea is involved in the flux of energy & the associated cycling of elements |
| Stable & non-stable states | Major elements of biological importance have differing oxidation states. Energy is required for a biological system to convert an element to its ‘unstable state’; the major process is photosynthesis. Energy is liberated in biological systems by converting from the ‘unstable’ to the ‘stable’ state; this is respiration. |
| Mineralisation | Takes place throughout the water column & at the sea floor. Decomposition of organic material takes place via oxidative degradation through the action of heterotrophic bacteria. In anoxic conditions, bacterial degradation is anaerobic using oxygen found in sulphate and nitrate radicals to produce highly reduced compounds such as methane, hydrogen sulphide & ammonia. The ability to utilise sulphate as an electron acceptor for energy-generating processes is restricted to the obligately anaerobic sulphate-reducing bacteria. Chemoautotrophs, use compounds high in chemical energy. |
| The marine nitrogen cycle | Complex cycle. Dominant form is the Nitrate ion, which is what phyt. eat. Some phytoplankton species can utilise organic nitrogen forms such as urea & amino acids. The oxidation of ammonia to nitrite and then nitrate is known as nitrification; the bacteria that carry out this process are nitrifying bacteria. The reverse process of forming reduced nitrogen compounds from nitrate is known as denitrification carried out by denitrifying bacteria. |
| Nitrogen cycle (Pt.2) | Nitrogen fixation involves the conversion of dissolved nitrogen gas to organic nitrogen compound carried out mainly by cyanobacteria. Dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) both serve as nutrients for bacterial growth. Bacteria break down proteins to amino acids & ammonia, & the ammonia is then oxidised during nitrification. The eventual release of dissolved inorganic nitrogen (DIN) makes these forms available again for uptake by the phyt. |
| New and regenerated N | I) one fraction is derived from nitrogen recycled from organic matter within the euphotic zone. Primarily in the form of ammonia and urea this form is regenerated nitrogen. ii) another fraction is derived from new nitrogen which comes from sources outside the euphotic zone. |
| The f-ratio | In oligotrophic areas of the oceans there is little upward movement of water from below the euphotic zone and thus the amount of new nitrogen is relatively small. In upwelling regions, however, the amount of new nitrogen is very large. The ratio of new production to total (new + regenerated) production is referred to as the f-ratio. This number is probably 0.1 or less in oligotrophic waters, but as high as 0.8 in upwelling zones. Annual average for the whole ocean is between 0.3-0.5. |
| Global phosphorous cycle | No gaseous components. Phosphate is produced in extremely anoxic conditions. Come from weathering or calcium phosphate. No mediated by microbes. P-flux is from rivers. Organic phosphate can easily be hydrolysed and taken up by phyt. Large reservoir of Phosphate in the sea. The conc. deposited in the ocean sediments is small. |
| Microbes and Sulphur | Sulphur is abundant in the oceans - present as SO42+. marine biota re not limited by the availability of sulphur. microbial activity in the surface ocean can have a significant effect as a source of DMS to the atmosphere. |
| DMS and climate | DMS accounts for ca 50% of the natural emissions of sulphur to the atmosphere. DMS increases cloud condensation nuclei in the atmosphere leading to greater cloudiness. DMS has the potential to act as a negative feedback of global warming. Controversial hypothesis - industrial sources of atmospheric sulphur have also increased, whilst there is no evidence of increased cloudiness or cooler temperatures. |
| Biology and CO2 | Primary production air-sea exchange CO2. Photosynthesis fixes CO2 into organic cells. Changing dissolved inorganic C to organic biomass decreases pCO2, which promotes the drawdown of CO2 from the atmosphere. Phytoplankton utilise nitrate and increase alkaline which decrease pCO2. Biological pump: phyt. sink below seasonal thermocline and zooplankton feed and migrate dropping faeces. |
| Ways to increase CO2 drawdown | Ocean is not C limited. PP is limited by nutrient conc. There is no potential to increase the flux of nutrients unless the Greenhouse effect causes major changes in ocean circulation. Fe is an essential microelement for phytoplankton, required e.g. for chlorophyll synthesis & nitrate reduction. The source of iron in seawater is dust from the land brought by winds |
| Two experiments : IronEx I & II | IronEx I: on addition of Fe there was a rapid increase in primary production - although only sustained for a few days - possibly due to the fact that Fe is rapidly converted into a form that is biologically unavailable. IronEx II - multiple additions of Fe, over several days, were used to simulate a natural Fe input event. A massive phytoplankton bloom was triggered which was not significantly checked by either grazing or secondary nutrient limitation. This bloom significantly reduced CO2 concentrations in the surface layer. |
| Nitrogen fixation in the sea | N cycle includes a gaseous phase (N2) which is fixed into biologically available ammonium by nitrogen fixation. The atmosphere provides a large potential reservoir of N. Generally N2 fixation rates are low and there are few N2 fixing organisms. In cyanobacteria nitrogenase is usually found in heterocysts (specialised cells, lacking PSII activity & hence anaerobic); or temporal separation of N2-fixation & photosynthesis. N2 -fixation genes are dispersed throughout the prokaryotic kingdom. Factors that might limit the genetic potential & expression of N2-fixation in the marine environment : i) the large energy & reductant requirement, ii) sensitivity of nitrogenase to inactivation by O2, iii) repression of nitrogenase activity by fixed nitrogen e.g nitrate, ammonia iv) the requirement for micronutrients such as molybdenum, vanadium & iron |
| Trichodesmium | Trichodesmium is the dominant N2 fixing organism. BUT Less abundant N2 fixing organisms are found in certain regions. It is a cyanobacterium of the order Oscillatoriales, produces only vegetative cells, Trichodesmium means a bundle of threads, a number of species have been described, surface aggregations can be detected from space. Trichodesmium only fixes N2 during the day! – and in fact N2 -fixation is light dependent (very odd). |
| Diel cycle of nitrogen fixation | Possible that the cycle of nitrogen fixation is due to a circadian rhythm. Day-advantage: Use energy/reductants from photosynthesis. Night: present as high molecular mass form (inactive) and is determined by how much fixation occurs. Light: cause initiation of synthesis and return of the Fe protein to the active low molecular mass. Modification in inactive from occurs in O2 presence. Fe protein could play a role in protection of nitrogenase from inactivation by O2 but not simultaneous photosynthesis/fixation. |
| Characteristics of Trichodesmium that may be relevant to its planktonic existence. | I) forms colonies which may: allow self-shading, provide a habitat for O2 consume symbionts, facilitate the creation of reduced O2 zones. ii) produces gas vacuoles which: allow modification of sinking, allow active migration and enhance the availability of dilute nutrients such as P. iii) extensive methylation of Trichodesmium DNA: modification of adenine residues, may inhibit infection, conferring stability against high UV. |
| Deep Sea Microbiology | Considerable biological activity is found in the photic zone (down to ca 300m) and at depths down to 1000m. Depths > 1000m (deep sea) are in comparison ‘deserts’ and biologically inactive. Exceptions do exist though e.g hydrothermal vents. 3 major environmental extremes: low temperature, high pressure and low nutrient levels. |
| Hydrothermal vents | Hot vents ‘black smokers’ - hot hydrothermal fluid containing abundant metal sulphides reaches the sea floor directly & precipitates on emerging into cold seawater forming a tower or chimney. Warm vents - where hot hydrothermal fluid is cooled by seawater permeating the sediment. ‘White smokers’ emit lighter-hued minerals, such as those containing barium, calcium, and silicon. These vents also tend to have lower temperature plumes. These are alkaline hydrothermal vents. |
| Around hydrothermal vents thriving invertebrate communities exist, supported by the activity of microorganisms: | Tubeworms over 2m in length, & large numbers of clams & mussels. Vents do not discharge organic matter. Rather, reduced inorganic material. Animal communities are dependent on lithotrophic bacteria which grow at the expense of inorganic energy sources. We can find: Sulphur-oxidising lithotrophs, Nitrifying bacteria, Hydrogen-oxidising bacteria, Iron & manganese oxidising bacteria, Methylotrophic bacteria, microbes thus use inorganic material to gain energy |
| Direct symbiotic relationships of bacteria & animals | 2 m long tubeworms (Family Pogonophora). These lack a mouth, gut or anus but contain a modified gastrointestinal tract consisiting of spongy tissue called the trophosome. Trophosome tissue contains S granules, but with large numbers ~ 109 cells/g tissue of the S-oxidising bacterium. Tubeworms are organotrophs - living off the excretory products & dead cells of the lithotrophic symbiont. S-oxidising bacterial communities have also been found in the gill tissues of giant clams & mussels. It’s possible methane-oxidising bacteria also play a role as symbionts in hydrothermal vent animals. |