Presentation on theme: "Lecture 11: Ocean Primary Production and Biogeochemical Controls Oceanic ecosystem largely depends on the biochemical process of phytoplankton."— Presentation transcript:
Lecture 11: Ocean Primary Production and Biogeochemical Controls Oceanic ecosystem largely depends on the biochemical process of phytoplankton
1.Understand the trophic dynamics in the ocean 2.Know the marine productivity and its global distribution 3.Biological productivity in the upwelling water Learning Objectives
ENERGY Autotrophs: organisms capable of self-nourishment by synthesizing food from inorganic nutrients heterotrophs: organisms not belonging to autotrophs; all animals are heterotrophs c.f. Fig.10-1 in text
Difference between Mass (i.e. chemicals) Transfer and energy path
Difference between Mass Transfer and energy path
Difference between Mass Transfer and energy path Energy is replenished all the time Physiologic processes
Trophic levels and dynamics Trophic dynamics: study the interrelationships among organisms by means of the nutrition flow in the ecosystem The first trophic level is the autotroph, i.e. the plant producer, providing the matter and energy to the higher trophic levels, i.e. consumers Although simple, it reminds us that all of the energy that a species expends relies on the photosynthesis of plants Simple food chain
Food Web: a network of interlaced and interdependent food chains Omnivore: both plant and animal eater grazing food chain phytoplankton → zooplankton → nekton detritus food chain detritus → deposit feeder → nekton
Energy pyramid Energy amount increases Higher order trophic levels depend on the lower order trophic levels Where does the energy go? biomass increases Size increases
simple rule Typically, a positive correlation exists between body size of aqua animals and their trophic level Exceptions? Energy transfer between trophic levels is not efficient
Five basic consuming types of aqua animals (Fig.10-3 in text) Grazer − herbivores (e.g. sea urchin) Predator − carnivores (e.g. shark) Scavenger − benthic invertebrates (e.g. crab) Filter feeder − animals living in burrows Deposit feeder − animals living in sediments Dynamical time lag exists between the food abundance and animal population
Trophic levels and dynamics Food Web Energy Sunlight and nutrition supplies are two principal factors that limit the primary production in the ocean. In addition to forming carbohydrates (via photosynthesis), plants also manufacture other organic compounds, including proteins, lipids, and nucleic acids such as DNA and RNA.
Plankton blooms Cell division causes diatom populations to increase dramatically and rapidly (within several days) under preferable growth conditions Red tide
Plankton Blooms Bands of the dionflagellate Lingulodinium polyedrum moving onshore over the troughs of a series of internal waves
Nonlinear Internal Waves and Phytoplankton Isopycnals Have you noted how fast the time lapse is !
Why do we care about the Carbon Export Production? The total amount of carbon in the ocean is about 50 times greater than the amount in the atmosphere, and is exchanged with the atmosphere on a time-scale of several hundred years. At least 50% of the oxygen we breathe comes from the photosynthesis of marine plants. Currently, 48% of the carbon emitted to the atmosphere by fossil fuel burning is sequestered into the ocean. But the future fate of this important carbon sink is largely uncertain (therefore anxious) because of potential climate change impacts on ocean circulation, biogeochemical cycling, and ecosystem dynamics => Definition of primary productivity in the ocean
Roles of bacterial in the ecosystem 1.Bacterial decompose dead tissue and release essential inorganic nutrients into the water for recycling by plants. *NH 3 + 2O 2 → H + + NO 3 - +H 2 O (aerobic bacterial) *SO 4 2- → 2O 2 + S 2- (anaerobic bacterial) 2.Plays both the starting point (providing nutrients for plant photosynthesis) and the ending point (proceeding the decay of organic matter) of the food cycle that provides the linkage between nonliving and living matter. 3.Also serve as food for some species of zooplankton
Cyanobacteria (blue-green algae) are predominantly photosynthetic prokaryotic ( 初核質 ) organisms containing a blue pigment in addition to chlorophyll. They use sunlight directly to manufacture food from dissolved nutrients.
Hydrothermal vents and Chemosynthetic bacteria The base of vent community is occupied by microbes rather than by plants, because there is no light in the deep sea. Chemical energy released by the oxidation of inorganic compounds is used to produce food.
Global Carbon Cycle Marine Biota Export Production inside the ocean
(1) Nutrient Sources for Primary Production and (2) limitations of CO 2 fluxes The fluxed of organic carbon must be sustained by an adequate flux of macro nutrients (P, N, Si) If macro nutrients are unavailable then the CO 2 flux is reduced! What are the controllers on Export Production? Macronutrients vs. micronutrients (p339 in text)
1) Ocean nutrient inventory 2) Utilization of nutrients in HNLC condition 3) Change of Redfield Ratio ( A. C. Redfield 1958;1963 ) What are the controllers on Export Production?
Nitrogen appears to be the most important controlling factor that limit the primary productivity of ecosystems. 1) Ocean nutrient inventory What are the controllers on Export Production? Why ? (important; p339 in text) N is an essential nutrient for all living organisms (nucleic acids and amino acids) N has many oxidation states, which makes speciation and redox chemistry very interesting NH4 + is the preferred N nutrient
NO 3 Chlorophyll Large detritus Organic matter N2N2 NH 4 NO 3 Water column Sediment Phytoplankton NH 4 Mineralization Uptake Nitrification Grazing Mortality Zooplankton Susp. particles Aerobic mineralization De-nitrification N2N2 Fixation Mix Layer depth De-nitrification − the removal of fixed N, mostly NO3 -, resulting in the formation of nonbiologically available N, primarily N 2 gas Continental shelf sediments are responsible for up to 67% of marine N denitrification estimates
2) Utilization of nutrients in HNLC What are the controllers on Export Production?
HNLC − High-Nutrient, Low-Chlorophyll It describe areas of the ocean where the number of phytoplankton are low in spite of high macronutrient concentrations (nitrate, phosphate, silica acid). HNLC is thought to be caused by the scarcity of iron (a micronutrient which phytoplankton require for photosynthesis) and high grazing rates of micro-zooplankton that feed on the phytoplankton. The HNLC condition has been observed in the equatorial and sub-arctic Pacific Ocean, the Southern Ocean, and in strong upwelling regimes, such as off central and northern California and off Peru.
Nitrate and phosphate concentrations are high year round but standing stocks of phytoplankton are always low (0.2-0.4 µg/L; normal yield is 1 µg /L) Iron concentrations in these waters are sub- nanomolar: the same as those that are known to limit growth of phytoplankton, particularly large species such as diatoms. Addition of low levels of Fe promotes growth of large phytoplankton. -bottle experiments -in situ fertilization experiments
One of the possible solutions to global warming is to fertilize HNLC ocean areas lacking iron with iron to increase CO 2 absorption from phytoplankton.
Redfield ratio (stoichiometry) − the molecular ratio of carbon, nitrogen and phosphorus in phytoplankton. Redfield (1963) described the remarkable congruence between the chemistry of the deep ocean and the chemistry of living things in the surface ocean (i.e. phytoplankton). Both have N:P ratios of about 16. When nutrients are not limiting, the molar element ratio C:N:P in most phytoplankton is 116:16:1. Redfield thought it wasn't purely coincidental that the vast oceans would have a chemistry perfectly suited to the requirements of living organisms. He considered how the cycles of not just N and P but also C and O could interact to result in this match.
N* = N – 16 P N = 25790 N 2 fixation De-nitrification Modern Time
Biologically Mediated Exchange of CO 2 Between the Ocean and Atmosphere
Regions with upwelling represent the productivity Equatorial upwelling Coastal upwelling Water turbidity
oceanterrestrial area Open oceandeserts continental shelvesforest; grassland upwelling regionsrain forests shallow estuariesfarmlands