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This 8 page Class Notes was uploaded by Sidnee Notetaker on Monday October 19, 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 17 views.
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Date Created: 10/19/15
Ocean Primary Production Wednesday September 3D 2 15 1136 AM I Why Study Primary Production A Base of the Food Web 1 Primary production forms the base of marine food webs so understanding the variability of primary production in the ocean allows for a better understanding of the variability of all marine organisms Ecosystem Function B Essential Element of the Global Carbon Cycle 1 Another major goal of biological oceanography is to understand how life in the ocean affects global elemental cycles gt Biogeochemistry a The global carbon cycle is a big topic because it is closely related to our global warming problem b Photosynthesis consumes carbon dioxide gas to form the particulate carbon of algae c Respiration by all organisms produces carbon dioxide gas d The difference between photosynthesis and respiration by all of the organisms is what sinks to the ocean floor plaI 39M ll39md laud uc phmulluIi nIpirdion IkeI uf luunl raidtn Magnitude of C02 flux between Land and Ocean Reservoirs Part requirements for growth A Definitions 1 Plankton Small organisms that drift with the ocean currents 2 Phytoplankton Small cells often single cells but sometimes chains or colonies of many cells that contain chlorophyll and drift with ocean currents 3 Photosynthesis refers to the chemical reaction that uses water and carbon dioxide gas and the energy of sun light to form glucose and oxygen Glucose then serves as the energy source for all subsequent biochemical reactions The overall photosynthetic reaction is given by III 6C02 6H20 Light Energy gt C6H1206 602 B Light and Nutrient Requirements 1 Strictly speaking photosynthesis only depends on the availability of water carbon dioxide and sunlight Primary production however involves the synthesis of complex organic compounds and therefore requires the uptake of plant nutrients for the construction of complex molecules that are needed to form new cellular components 2 Consequently the magnitude of primary production depends not only on sunlight but also on the availability of essential plant nutrients C Net Primary Production 1 Reactions needed to construct new complex molecules and to provide basal metabolic needs consume oxygen and generate C02 which is exactly the opposite of what happens during photosynthesis Collectively the generation of C02 by this process is referred to as respiration a Net Primary Production NPP is the difference between the amount of C02 consumed by photosynthesis and the amount of C02 produced by respiration b Equivalently it is the Net Gain or Net Loss of carbon within the cell 2 The Big Picture About Primary Production a Primary Production Effectively Consumes Carbon Dioxide Gas and forms particulate organic carbon that can sink into the deep ocean b Primary Production Makes Oxygen c Primary Production Requires Light and Essential Plant Nutrients eg N P Si Fe and a bunch of others d Net Primary Production is Photosynthesis Respiration Net Gain or Net Loss of Carbon in the Cell D Major Phytoplankton Groups 1 The vast majority of primary production in the ocean is carried out by chlorophyll containing singlecelled Ocean primary Production Page 1 organisms referred to collectively as Phytoplankton There are three main groups of phytoplankton a Diatoms Require Silica b Flagellates Motile so they are able to avoid sinking in calm waters c Photosynthetic Bacteria Able to grow at very low nutrient concentrations Pattern of Light and Nutrient Uptake by Phytoplankton A LightDependency of Net Primary Production 1 At light levels below the compensation light level phytoplankton cells do not have sufficient light to photosynthesize fast enough to meet their basal metabolic needs and so cell respiration exceeds photosynthesis and this then leads to negative values of net primary production At low light levels phytoplankton are light limited At optimal light levels phytoplankton are light saturated At very high light levels phytoplankton are photoinhibited The depth at which the ambient light intensity is equal to the compensation light intensity is called the compensation depth WPWP Net Primary Production quot 39 to r39 I uw Innmu Light Intensity B NutrientDependency of Primary Production 1 The amount of nutrient needed for growth by an individual phytoplankton cell is proportional to the cell s mass or equivalently to the cell s volume 2 The amount of nutrient that can be transported into a cell is proportional to the cell s surface area 3 Small cells have a larger surface area to volume ratio than do larger cells so smaller cells can grow better at lower nutrient concentrations smaller cells can more efficiently supply their needs at low nutrient concentration than can large cells Growth Flare Large Phth pla nk t o I1 Erna II P h ytopllan kton 1 HIGH Nutrient Concentration Dominant Cell Diameters of Phytoplankton Assemblage 0 g 0 1000 pm LOW HKJH Nutrient Concentration C The 4 Phytoplankton Nutrients of Interest to Oceanographers 1 Phytoplankton cells need a wide range of different chemical elements nutrients for growth eg Cu Zn etc but there are four nutrients that are of most interest to oceanographers a Nitrogen b Phosphorous c Silica for diatoms d Iron 2 The interest is due to the fact that at any given place or time in the ocean it is one of these four nutrients that can be in short supply and can limit the growth of phytoplankton IV The Main Source of Nitrogen Phosphorous and Silica to the Surface Ocean A The main source of nitrogen phosphorous and silica to the surface layer of the ocean is by vertically mixing or upwelling of nutrientrich deepwater to the surface B The example data given at the right is for nitrate but the same general pattern holds for phosphate and silicate Ocean primary Production Page 2 V Depth melersl North South Equator O 6 I 18 24 30 36 42 48 Nitrate micromolar C Questions 1 Most nutrients except for iron as you soon will see sit in the deeper part of the ocean and are occasionally brought to the surface ocean to quotfeed the phytoplankton 2 One of the main mechanisms for getting deep nutrients into the surface sunlit layer of the ocean is mixing across the thermoclinepcynocline El Then What do you expect might happen to ocean primary production under a global warming scenario that enhances only temperatures of the surface layer of the ocean and leaves the deep layer cold ie strengthens the thermoclinepcynocline Decrease pkg quotspitlb Jun 0 laidn omitfuel huntg land ow photo3 Ithnk l lf39atc In Nthago or an uplalv Itll pIric 1 The thermocline acts to hold phytoplankton near the sunlit surface ocean 2 The thermocline also acts as a significant barrier to upward mixing of nutrient rich deep water The stronger the thermal stratification the strong the inhibition of nutrient mixing Iron Limitation A Surface Nitrate Concentration l Sew surlncc mlrmc mmnl N In U 5 ll l5 2 25 30 B The main source of Iron input to the surface ocean is from dust blowing off of continents 1 Iron Limited Regions ka Southern Ocean b Subpolar North Pacific c Eastern Equatorial Pacific Monmv din C LL AHLIV r m39 you Ocean primary Production Page 3 V Spatial Patterns of Primary Production A Surface convergence of the Ekman Layer in the subtropics forced by the Trade and Westerly Winds forms a moundlens of warm lownutrient water and associated gyre rotation and an associated downward surface layer velocity into the deeper ocean Taken together this makes it difficult for nutrients to move upward to the the surface ocean and so primary production of exceptionally low yearround in the subtropical gyres Subtropical Gyres Exhibit Low Primary Production on a per meter square basis and Very Little Seasonal Variation Winter Spring an 394quot ms was no 45 u urn quot u uquot In I 5 u I 1 III u on on an In Summer Fall 7 quotI II I 39 t O Iquot U iquot III V I 39 ID I I II 39 l in us uu an I u Seasonal Net Primary Production 9 C m 2 season39 239 25 55 75 107 125 56 Equatorial Upwelling of Cold NutrientRich Deep Water in the Eastern Equatorial Pacific and Atlantic a Easterly Trade Winds Cause Surface Waters to Pile Up in the West b Themocline is Deep in the West and Shallow in the East c Proximity of Thermocline Near the Surface in the East Enhances Upwelling of Cold and NutrientRich DeepWater to the Lighted Region of the Surface Ocean and Thus Enhances Biological Productivity in this Area The Equatorial Pacific Exhibits Very Little Seasonal Variability in Primary Production Atlantic Exhibits Modest Seasonal Variability Because of Sudden Seasonal Trade Wind Bursts in Spring Coastal Regions 1 Tidal Mixing occurs in shallow continental shelf regions a Seasonally Steady b Mixes the water column from bottom to top and brings bottom water rich in nutrients to the ocean surface 2 Coastal Upwelling results from WindEkman Offshore Transport a Seasonally Variable b Greatly enhances upward movement of deep water that is rich in nutrients Abyssal mus Guyot island Corvtoenl S39xel Shedbreak Sim Rise Depth km 1 Tidal mixing occurs as the tide wave motion accelerates horizontally when it is squeezed onto the shallow continental shelf 2 The high speed tidal currents break into vigorous turbulence that causes mixing from top to bottom of the continental shelf water column Ocean primary Production Page 4 G Vertical Distribution of Chlorophyll and Temperature Over the Continental Shelf vertically uniform green region Shelf Tidal Mixing Offshore Region Front Deep Ocean E 6 5 3 2 Sir 3 2 24 26 28 3O 32 34 40 log 3 mm Lines temperature 0 C Colour phytoplankton biomass mg chi m 3 l 1 Notice the abrupt change in chlorophyll distribution into fully mixed from top to bottom left side of figure on the shelf side of the tidal mixing front H Coastal Upwelling Along the Washington Oregon Coast 1 Wind blowing out ofthe north drives the Ekman layer to the right northern hemisphere which is offshore 2 The offshore transport of the Ekman surface layer is replaced by upwelling of deeper cold nutrientrich water along the coast 3 Wind blowing out ofthe south drives the Ekman Layer again to the right because northern hemisphere which is onshore 4 The onshore transport of the Ekman surface layer is driven downward a process called downwelling 5 Major Upwelling Regions in the World Seasonal J Change in the 39 Prevailing Wind Direction 0 1601150 150 W HO39W w 30w 60w 0 w leanuary VII Primary Production Temporal Variations A Seasonal Changes in Coastal Primary Production 1 Tidal Mixing brings nutrients to the surface yearround Coastal Upwelling seasonally superimposes additional nutrients B Large Seasonal Increase in Primary Production Occurs in the North Atlantic During the Spring Season C Westerly Wind Belt Region ca 3060 degree latitude 1 Strong Seasonal Variation in SeaSurface Temperature in Both the Pacific and Atlantic 2 Strong Seasonal Change in the Depth of the Seasonal Thermocline in the Atlantic but not the Pacific the Pacific is not salty enough Ocean primary Production Page 5 D Summer and Winter Differences in Mixing Depth Due to Changes in the Depth of the Seasonal Thermocline in Westerly Wind Region iemperature 3C lemperature Cl 0 5 10 15 20 25 0 5 10 395 20 25 A 0 quot Mixing Depth 100 200 Depth ml 300 400 500 Winter E Light Limitation Laboratory Measurements Low Light Intensity o High 26 DE 5 a 4 UghtlJmlud Light Saturated PhotolnMNtod m I E 39 e 3 S I I 2 q I 5 I c l 39 gt I 8 I 639 0 I C O O C I I EI c 39 o 390 Compensation 3 i r I Ugtnlmmny Z V Direct Water Column Measurements Light Intensity Net Primary Production 02550751004012345 i 0 Phoioanhibmd J Ilight Saturated Light Limited 50 100 ISO 200 F The Critical Depth 1 When cells are below the Compensation Depth they lose carbon because light is too dim to allow for positive net primary production NPP 2 The average light level that phytoplankton experience over the course of a day becomes dimmer as mixing depth increases because cells spend an increasing proportion of the day below the compensation depth in the dark 3 When cells mix below to the Critical Depth they have spent too much of the day below the compensation depth losing carbon a net losses of carbon experienced while below the compensation depth exceed the net gains of carbon experienced while above the compensation depth Net Primary Production Photosynthesis Respiration 1 O 1 2 3 O 5 O odniidoob po IdoouiIioou o39oooiioi Compensation Depth 100 Ocean primary Production Page 6 Net Primary Production Photosynthesis Respiration 1 O I 2 3 O 50 l Si bi b i39 viii 6 Compensation Depth Critical Depth 200 G Spring Shoaling of the Thermocline above the Critical Depth Brings about Positive Net Primary Production NPP 1 Changes in the mixing depth relative to the critical depth determines if NPP is positive or negative and thereby determines if phytoplankton blooms will occur ie ifwhen there is positive NPP 2 In winter mixing is below the critical depth due to cold winter storms and NPP is negative 3 In spring mixing is above the critical depth due to shallow thermocline and NPP is positive Photosynthesis Basal Respiration 1 0 1 2 3 j I39llIII IIIII WIN 090 1 I if I Irratnd 1 lm Abundant 1 l m Muir1m Nutrient Abundant 2 Nutrient Abundant J Hunkn I Imucd 7 Nutrient Widest Winter Spring Summer I 7 quot I Large Seasonal Increase in Primary Production Occurs in the North Atlantic Due To 1 Deep Winter Mixing 2 Strong Springtime Stratification J Westerly Wind Region 1 Deep vertical mixing in winter a brings high levels of nutrients to the surface b causes phytoplankton to mix below the critical depth and so even though nutrients are plentiful cells spend too much time in the dark and NPP is light limited 2 Formation of shallow thermocline in spring a depth of mixing confined above the shallow thermocline and above the critical depth so phytoplankton Ocean primary Production Page 7 spend much of the day high in the water column where there is lots of sunlight b Nutrients are still plentiful from winter mixing so cells have lots of nutrients and lots of sunlight and spring bloom forms 3 Continued stratification in summer a Mixing remains shallow and above the critical depth but nutrients are depleted and NPP is nutrient limited K Polar Ocean Regions 1 same as temperate ocean but melting of ice shelf enhances stratification VIII Magnitude of Global Primary Production in Different Oceanic Provinces A Global Distribution of Annual Net Primary Production NPP 1 Global NPP is about 104 Gt C yr1 2 Terrestrial NPP is about 54 of Global NPP 3 Oceanic NPP is about 46 of Global NPP World Ocean Net Primary Production Annual Regional Regional 03in Primary Regional Percentage of segrfgrrlc Area Production Primary Annual Global 9 10quot Km mg C m 39 d 39 Production Ocean Primary Gt C y1 Production iesie39y Wind 129 9 345 163 32 3 Trade mpg 139 9 255 13 o 26139n Polar 208 853 64 13 Coastal 37 4 1 055 144 29 Total Global Ocean 50 Gt carbon per Year Note 6 Gigaion 10quot metric tones 10quot grams Longhurs at al 1995i Journal of Plankton Research 17 i6 12451271 1 While the Open Ocean Trade Winds Westerly Wind and Polar regions exhibit relatively low intensities of primary production NPP per square meter relative to coastal regions they contribute most 71 as a whole to the global ocean total NPP because of the vast areas comprising these regions IX Evolving Concepts in Ocean Primary Production A Iron Limitation 1 High Nitrate Low Chlorophyll Regions 1 Southern Ocean 2Equatorial Pacific and 3 Subarctic Pacific 2 The main source of Iron input to the surface ocean is from dust blowing off of continents B Phosphate Limitation 1 Station Aloha in the North Pacific Subtropical Gyre Ocean primary Production Page 8
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