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24 Cards in this Set
- Front
- Back
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What 2 things does photosynthesis need to function |
(1) light (2) nutrients |
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How do light levels vary? |
- latitude - season - water depth (photic zone maxes at 200 m) |
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Compensation depth |
- photosynthesis = respiration - depth of compensation light intensity - varies with light penetration - shallower with a lot of sediment or plankton in water - deeper in deep, clear water (mid-Pacific) |
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Compensation light intensity |
- light intensity at which oxygen equals that consumed in respiration |
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Surface water nutrients |
- limited unless re supplied - from deep water: turbulence and upwelling - from land: rivers and wind - recycling within euphotic zone |
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Nitrogen |
- required for protein synthesis - present in several forms in ocean and atmosphere: - N2 (gas supplied by nitrogen fixation) - ammonium (useful form) - ammonia - nitrites (useful form) - nitrates (useful form) |
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Phosphorous |
- required for synthesis of ATP and as an energy source in enzymatic activity - occurs mainly as inorganic phosphate - small amount can be transported with dust |
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Relationship between nitrogen and phosphorous |
- sea N to P ratio is 14.7:1 - regulated by uptake and decomposition of phytoplankton - N is usually limiting - P is rarely limiting - present with enough light but little PP |
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Silicon |
- can be limiting for diatoms (silica shells) |
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How nutrients are released in the photic zone |
- land runoff in coastal waters - upwelling - wind borne particles (may be significant in areas far from land) |
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What leads to patchy distribution of planktonic organisms? |
- localized reproduction - variable grazing - currents - physical conditions |
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Required conditions for a phytoplanktonic bloom |
(1) light and nutrients (2) not too much mixing: mixing depth needs to be shallower than critical depth * mixing depth < critical depth |
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Mixing depth |
- depth above which all water is thoroughly mixed due to wind |
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Critical depth |
- depth above which total O produced in water = total O consumed |
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Plankton abundance in temperate zones |
- large spring bloom followed by small fall bloom |
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Why is there low phytoplankton in the winter in temperate zones? |
- light limited - too much mixing (plankton stirred below critical depth) |
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Why do phytoplankton bloom in the spring in temperate zones? |
- surface waters are high in nutrients - high light levels from above - more stable water column (plankton not mixed below critical depth) |
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Why does phytoplankton decline after spring bloom in temperate zones? |
- nutrients are removed from the surface water - large diatoms sink to deeper water - grazing by zooplankton |
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Why does phytoplankton have a small fall bloom in temperate zones? |
- nutrients are put back in the water by all overturn and zooplankton decomposition - still enough light for photosynthesis |
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When does phytoplankton bloom in the north polar zone? |
- in may - declines in june |
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When does phytoplankton bloom in the tropical zone?
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- it stays pretty steady |
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Why is ice important in polar seas? |
- permanent fast ice - seasonal peak ice - insulates seawater from air - provides near predator free platforms - critical to high productivity - diatoms grow on underside of thin ice |
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What effect do zooplankton have on phytoplankton? |
- strong grazing effect - lower reproductive rates - peak lags behind phytoplankton |
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Harmful algal blooms |
- dinoflagellates are especially important - many start with initial input of resting stages (vegetative cells) - can produce dense blooms leading to O stress - some species have spines that disrupt gills - some produce toxins - seem to be becoming more frequent |
