Ocean Primary Productivity (Week 6)
Ocean Primary Productivity (Week 6) BIOEE 1540
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This 6 page Class Notes was uploaded by Erica on Wednesday October 21, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 37 views.
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Date Created: 10/21/15
Ocean Primary Production 1 Why Study Primary Production Forms the base of the food web Carbon cycle 9 closely related to global warming issue Photosynthesis consumes C02 to form carbon of algae Respiration produces C02 The difference between photosynthesis and respiration by all organisms is what sinks to the oor of the ocean 2 Requirements for Growth Primary Production consumes C02 and forms organic carbon that sinks into the deep ocean amp makes oxygen 0 Plankton Small organisms that drift with ocean currents Phytoplankton Small cells that contain chlorophyll and drift with ocean currents Photosynthesis 6C02 6H20 Light Energy 9 C6H1206 02 Carbon dioxide water sunlight energy 9 glucose oxygen Primary Production requires light amp plant nutrients N P Si etc Net Primary Production NPP is the difference between the amount of C02 consumed by photosynthesis and the amount that is produced by respiration NPP Photosynthesis Respiration Net gain loss of carbon Major Phytoplankton Groups the vast majority of primary production is carried out through phytoplankton Diatoms Require Silica Flagellates Motile so they don t sink Photosynthetic Bacteria able to grow at low nutrient concentrations Pattern of Light and Nutrient uptake by Phytoplankton Light dependency NPP phytoplankton cells don t have enough light to photosynthesize fast enough to meet metabolic needs Cell respiration gt Photosynthesis Growth Rate Low light levels 9 light limited Optimal light levels 9 light saturated Very high light levels 9 photoinhibited Compensation Depth where ambient light intensity compensation light intensity Nutrient dependency NPP Nutrient needed proportional to phytoplankton cell mass volume Amount of nutrient that can be transported into a cell proportional to cell s surface area Small cells 9 larger surface area volume ratio than larger cells 0 Smaller cells grow better at lower nutrient concentrations 4 Phytoplankton Nutrients of interest Nitrogen Phosphorus Silica Iron I Main source of N P amp Si is by vertical mixing upwelling of nutrientrich deepwater to the surface Main source of Fe input is from dust blowing off of continents 0 Fe limited regions southern ocean subpolar north pacific eastern equatorial pacific Large Phytoplankton Small Phytoplankton gt HIGH Nutrient Concentration Summary Light is plentiful nutrients are limiting Deep ocean nutrients plentiful light limiting Surface amp deep waters separated by thermocline Primary Production is enhanced when there s high light amp high nutrients 3 Spatial Variations of Primary Production Subtr0pical Gyre Regions Convergence of Ekman Layer forms a moundlens of warm low nutrient water and associated downward surface layer velocity into deep oceans Therefore it is difficult for nutrients to move upward to the surface ocean 9 PP is exceptionally low with very little seasonal variation Equat0rial Pacific and Atlantic Regions Easterly trade winds cause surface waters to pile up in the west Thermocline is deep in west and shallow in east Proximity of thermocline in the east enhances upwelling nutrient rich water to the lighted region of the surface ocean 9 enhanced biological productivity Equatorial Very little seasonal variation Atlantic Modest seasonal variation due to trade wind bursts in spring Costal Regions Tidal Mixing occurs in shallow continental shelf regions tide wave motion accelerates horizontally when squeezed onto the shallow continental shelf high speed tidal currents 9 turbulence that causes mixing from top to bottom 0 Seasonally steady o Mixes water column bottom to top amp brings nutrientrich water to surface Costal Upwelling results from Wind Ekman Transport 0 Seasonally variable 0 Greatly enhances upward movement of nutrientrich deep water 0 5 major upwelling regions in the world Summary 0 Dramatic increases in primary production occur wherever and whenever deep nutrient rich water is brought up to the ocean surface 0 Subtropical Gyre Primary Production I Low primary production yearround because of persistent lens of warm water 0 Equatorial Primary Production Modest seasonality in the Atlantic I Strong interannual variation in the Pacific because of El Nino more on this in later lectures 0 Coastal Primary Production I High year round exceptionally high during upwelling periods in certain regions I California Chile Portugal Northwest Africa South Africa and Arabian Peninsula 4 Temporal Variations of Primary Production Westerly Wind Belt Region 3060 degree latitude Strong seasonal variation in seasurface temperature in both Pacific and Atlantic Strong seasonal change in the depth of the seasonal thermocline in the Atlantic not Pacific b c it s not salty enough Temperature 0C Temperature 0C 0 5 10 15 20 25 0 5 10 15 20 25 0 O Mixing Depth 100 100 E 200 200 3 3 8 D 300 300 400 400 500 500 Winter Light Intensity Net Primary Production 0 25 50 75 100 1 0 1 2 3 4 5 0 0 Photoiuhibited Light Saturated 50 50 Light Limited g I Compensation 5 Depth 0 100 100 a I Q I I 150 150 I I I I 200 200 39 The Critical Depth Cells below the compensation depth lose carbon because light is too low for NPP The average light level that phytoplankton experience in 1 day becomes dimmer as mixing depth increases Cells that mix below the critical depth they have lost too much carbon because of spending too much of the day below the compensation depth Spring Shoaling of Thermocline above Critical Depth brings positive NPP Changes in mixing depth relative to critical depth determines of NPP is or 9 will phytoplankton blooms occur Winter mixing is below critical depth NPP negative Spring mixing is above critical depth NPP positive Large seasonal increase in RF in the North Atlantic due to deep winter mixing amp strong springtime stratification Westerly Wind Region Deep vertical mixing in winter brings high levels of nutrients to surface Formation of shallow thermocline in spring 9 nutrients a re still plentiful from winter spring bloom forms Continued stratification in summer 9 mixing remains shallow nutrient limited Polar Ocean Regions Same as temperate ocean but melting of ice shelf enhances stratification 5 Total Global Ocean Primary Production Global NPP is about 104 Gt C yr 1 Terrestrial NPP is about 54 of Global NPP Oceanic NPP is about 46 of Global NPP Total Global Ocean 50 Gt Carbon per year Open ocean exhibits small low intensities of PP but they make up most of the global ocean total NPP 71 6 Evolving Concepts Iron Limitation Main source of Iron input to surface ocean is dust blowing off from continents High nitrate low chlorophyll regions 0 Southern Ocean 0 Equatorial Pacific 0 Subarctic Pacific Phosphorus Limitation Station Aloha in the North Pacific Subtropical Gyre Conclusions N and sometimes Fe amp P often limits phytoplankton growth Global ocean primary production is of the same order of magnitude as the global terrestrial system The rate of primary productivity per square meter in the open ocean is low but because this region is so vast it dominates the total global ocean PP