Lectures 1-12

Lecture 1: Introduction

• The ocean interacts with chemistry, physics, society, geology, and biology

• We study the ocean because of some major problems in the world

  • Climate change: coral dies

  • Acidification: ocean pH lowers

  • Deoxygenation: less or no oxygen in the water

  • Pollution: garbage accumulates in the water

• The ocean was mainly used for seaborne travel/transport and trade early

  • It became used for bad purposes

    • Extract marine resources

    • Military purposes

  • Scientific Revolution increased exploration

• Studying the ocean became the government’s responsibility

  • HMS Beagle (Darwin)

  • HMS Challenger (main one)

• New technology came about to study the ocean

  • Ocean floor topography: mountain ranges found

  • Hydrothermal vents: heated water that dissolves minerals

  • Plate tectonics: continental drift

  • Microbial life/genetics: horizontal gene transfer

• The ocean as a tool

  • Exclusives economic zones: countries have control of parts of the ocean off their coasts

  • Fisheries

  • Mining and drilling

  • Military 

  • Transportation

  • Trade: the ocean is how most materials are moved (economically best)

• Limitations to studying the ocean

  • Biological issues: can’t breathe underwater

  • Deep ocean: pressure is very high

  • Water interacts with electromagnetic radiation differently: reflects waves

  • Seawater is corrosive

  • Dynamic surface: waves move

  • It is expensive

• Bathymetry: seafloor topography can be studied using:

  • Sounders

  • Echo sounders

  • Satellites

• Seafloor sediments can be studied using:

  • Grab samplers and box corers

  • Gravity and piston corers

  • Drilling ships

  • Seismic/magnetic/gravity surveys

  • Dredges

• Ocean physics and chemistry can be studied using:

  • Water collection

  • Reversing thermometer

  • CTD: collects water samples and measures multiple things including temperature

  • Drifters/drogues/floats: measures ocean currents

  • Mechanical current meters

  • Acoustic/Doppler current meters: uses Doppler effect

• Organisms can be studied using:

  • Trawl/tow nets, traps, and water samples

  • Visual surveys

  • CTD: accidentally capture an organism

• Technological advances in fieldwork

  • Scuba and habitats

  • Piloted submersibles

  • ROVs: controlled vehicles

  • AUVs: automated vehicles

    • Argo network

  • Satellites

  • Computers and modeling

• Measuring oceanographic data

  • Graphs: can be useful but also deceiving

  • Contour plots

  • Maps

• Units

  • SI units (ex: m)

  • Derived units (ex: m^3)

  • Exceptions:

    • Sv: volumetric flow rate (1 Sv = 100 m^3/s)

    • mbar: pressure (atmosphere; 1 mbar = 100 Pa)

    • kt: speed (1 kt = ~.51 m/s)

Lecture 2: Plate Tectonics and Ocean Evolution

• We know the earth is layered because of seismic waves/earthquakes

• Body waves: pass through the interior of the earth 

  • P-waves (primary): compressional seismic waves moving through the earth

    • Extremely fast

    • Like a slinky

    • Not destructive

    • Travels through solids and liquids

    • First to be recorded on seismographs

    • Moho discontinuity: changes in P-wave velocity and angles due to boundary between the crust and mantle

  • S-waves (secondary): seismic shear waves passing through the earth

    • Moderately fast

    • Goes up and down

    • Not destructive

    • Travels through solids

      • This is how we identify that the outer core of the earth is liquid, since the S-waves stop traveling in the “Shadow Zone”

  • The velocity of waves varies and depends on the sediment through which they are passing

    • Can create curvature of waves

• Surface waves: travel along the earth’s surface

  • L-waves and R-waves

• How the earth became layered: density

  • The density of each layer of the earth increases the closer we move to the core

  • Density and temperature have an inverse relationship

    • Warmer = less density, colder = more density

  • Liquids are attempting to find areas of equal density as itself

    • Density below is higher, density above is lower

  • Gravitational separation works similar to density

    • Heavier elements go inside

    • Lighter elements go outside

  • Earth age = 4.6 billion years

  • The formation of the earth

1. Cold accretion

• Unsorted materials

• Very cold

• This homogenous mass eventually becomes layered

2. Solar winds

• The diameter of the earth was 100x larger than today

• The mass of the earth was 500x greater than today

• Gravity compacted the earth

• The solar winds boiled away lighter elements

• Heat arises from collisions 

• Radioactive decay melted much of the earth

3. Add heat

• The earth separates based on density of materials

• The earth began to heat up due to:

  • Gravitational contraction 

  • Radioactive decay of K-40 and U-235 (5x more radioactive heat production than today since these elements are becoming increasingly stable) 

    • Nuclear fission creates energy, which creates heat

  • Large meteorite impacts 

    • Energy of motion is converted into heat

• Differentiation: materials become molten due to high temperatures

  • Molten iron and nickel sink toward the center to create the core

  • The surface crust becomes composed of lighter materials (K, Na, Si)

  • The mantle becomes Mg

  • Differentiation led to the formation of a magnetic field, ocean and atmosphere, and different layers

• Outer layers

  • Lithosphere: all the crust and part of the upper mantle (rigid)

    • Thickness varies

    • Plates float on the asthenosphere

    • The interior flow is critical for the movement of plates

    • Isostasy: as density increases, height above water/other material floating in will decrease not on exam

  • Asthenosphere: part of the mantle that can flow (not liquid)

  • Continental crust: basement rocks are very old

    • Cratons: shields and platforms

    • 31% is submerged

    • Rich in aluminum silicates

  • Oceanic crust

    • Younger and thinner than continental crust

    • Rich in magnesium silicates

    • Has 3 layers: sediments, basalt/dolerite, and gabbro

  • Crust: outer shell

    • Different chemistry than the mantle

    • Consists of the oceanic and continental crust

• The earth began cooling around 4.4 Ga and is still cooling

  • Convection overturn: internal heat from the interior is transferred to the surface by convection

    • Convection dissipates the heat rapidly and the earth cooled quickly

Lecture 3: Plate Tectonics and Ocean Evolution

• The earth has plates in the lithosphere that can move as if they are puzzle pieces

• Alfred Wegener: German meteorologist/Arctic climate scientist who came up with the theory of continental drift

  • Observations he made:

    • Fit of the continents: “Pangaea” was a single land mass

    • Paleoclimate data: certain environments were different latitudes from the equator in the past

      • glacial striations in tropical climates

      • Coal is found where swamps once were

      • Coral reef existence

    • Distribution of fossils: same species fossils are found on distant continents

    • Matching geologic units: rock layers are the same on different continents

      • Mountain ranges are created at the same time, but split onto different continents

  • Theory was highly criticized as plate tectonics were not discovered yet

    • Other theory proposed: land bridges eroded away

• Observations by other scientists

• Paleomagnetism

• Seafloor spreading

• Volcano/earthquake distribution

• World War II: sonar was used to map the ocean floor; bathymetry was used to measure water depth

  • Deep sea trenches and ocean ridges were discovered

• Seafloor anatomy: along continental margins there are shelfs, slopes, and rises

• Other observations

  • Ocean sediment is thinnest at the mid ocean ridges and thickest at margins

  • The oldest ocean crust is younger than the age of the earth

  • Ocean crust (basalt) has a different chemistry than continental crust (granite)

  • More heat rises beneath the mid ocean ridges than elsewhere, causing uneven heat distribution

  • Seafloor spreading: magma rises and pushes mid ocean ridges apart

    • Testing this theory

      • Earth’s magnetic field is strongest near the poles

        • Geodynamo theory: the magnetic field is generated by the convecting, liquid metal region of the outer core

        • Geomagnetism: earth’s magnetic field polarity reverses poles periodically

      • Paleomagnetism: when magma cools, iron bearing minerals align with earth’s magnetic field

        • Basalt crystalizes and materials align with the magnetic field

      • Magnetometer: measures magnetism, which is the direction, strength, or relative change of a magnetic field at a particular location

        • Ocean crust should record earth’s magnetic reversals

    • Harry Hess proposed idea of seafloor spreading

      • Continents and ocean crust move together

      • Deep sea drilling and age of crust show how the seafloor could have spread

        • No sediment found older than 180 million years found during a deep sea drilling project

        • Thickness of sediment decreases towards ocean ridges

• Plate tectonic theory: plate movement causes continents to move and interactions at boundaries result in earthquakes, volcanoes, and mountain building

  • Ring of fire: substantial seismic activity occurs around the Pacific plate

  • Earth’s surface (lithosphere) consists of 20 plates and they move relative to each other

    • They float on the soft asthenosphere

  • Plates move around partly due to convection, but it is most likely more complex than that

  • Ridge push force: force that drives plates away from a mid ocean ridge

  • Slab pull force: force down-going plates/slabs apply to oceanic lithosphere at a convergent margin

Lecture 4: Plate Tectonics and Ocean Evolution

• Plate boundaries: where the action occurs

  • Divergent: plates move apart

    • Found in oceans and mid-ocean ridges

      • Atlantic Mid-Ocean Ridge

    • New crust is formed

    • Earthquakes occur and there are small volcanic eruptions

    • Seafloor spreading with oceanic ridges: seafloor is elevated, which forms oceanic ridges

      • Along the axis of some ridge segments is a deep rift valley

    • Continental rifting: divergent plate boundaries that develop within a continent

  • Convergent: plates move together

    • More dense plate sinks under less dense plate and one plate is consumed

    • Earthquakes occur and there are large volcanic eruptions

    • Types of collisions

      • Oceanic-continental: forms continental volcanic arc and felsic rocks

        • Chile is extremely earthquake and tsunami prone

      • Oceanic-oceanic: forms oceanic island arc and felsic rocks

        • The Aleutian island arc has many volcanoes

      • Continental-continental: forms mountain range and metamorphic rocks

        • The Himalayan mountains were created by this

  • Transform: plates move along each other

    • No new crust forms

    • No plate is consumed

    • No volcanic eruptions occur but earthquakes do

    • The San Andreas Fault doesn’t form any rock

    • Transform fault boundary: two plates grind against each other without the production or destruction of lithosphere

      • Fracture zones: active transform faults and their inactive extensions into the plate interior

    • Seafloor spreading can cause plates to run into each other

• Continental margins

  • Passive: not on a plate boundary

    • Wide shelf

    • Shallow slope

    • No earthquakes

    • No volcanoes

  • Active: on a plate boundary

    • Narrow shelf: subduction of crust causes no buildup of crust

    • Steep slope

    • Earthquakes

    • Volcanoes

• Hot spot: location at the base of the lithosphere/top of a mantle plume where temperatures can cause melting

  • Hot spot under oceanic crust stays in the same place with the lithosphere moves across the hot spot

    • Hawaii was created from this, and plate movement directions can be determined by looking at the island chain

  • Yellowstone hot spot is in continental crust

• Atolls: forms around a hotspot and the island moves off the hotspot and begins eroding away; coral reef forms around island

  • Lagoon built off coral reef is left

• Triple junction: meeting point between 3 plates

• Ocean basins are formed from continental rifting

  • Rift valley will hold water

• Water exists between 273-373 K

• Meteorites can be used for testing in place of the mantle to see how much water is in the mantle

• Cometary ice hypothesis: ocean water is theorized to have come from comets instead of inside the earth

• Hydrogen in ocean water is more like meteors than comets

• Water sources: outgassing of the earth (80-90%) and cometary ice (10-20%)

Lecture 5 & 6: Properties of Water and Seawater

• Water is vital for:

  • Life

  • Climate regulation

  • Transport (biogeochemistry)

    • Water cycle: biogeochemical cycle

  • Economies, industries, and cultures

• Oceans first formed during Archean Eon

• Amount of water: 2.0*10^9 km^3

• Where the water is: 96.5% in ocean, 3.5% is freshwater

  • In freshwater:

    • Ice caps/glaciers: 1.78%

    • Surface waters: .013%

    • Air/soil: .002%

    • Groundwater: 1.69%

• Amount of potable/drinkable water: comparable to a drop of water in a 5 gallon bucket

• Water makes earth unique as other planets do not have liquid, solid, and gas water all at once on the surface

• Bonds in water

  • Van der Waals force: weakest

  • Hydrogen bond: electrostatic, hydrogen (+), donor (-), acceptor (-), important structural role

  • Ionic bond: electrostatic polarity, soluble in water, great electric conductor in solution

  • Covalent bond: strongest, electron sharing

• Unique properties of water

  • Heat capacity: amount of heat needed to change an object’s temperature; high for water

  • Latent heat: what you need for a phase change

    • Sensible heat: what you feel

    • Types of latent heat: fusion and vaporization

      • Vaporization is higher than that of any other substance

      • High amount of energy needed for a phase change

  • Thermal expansion: solid is normally denser than liquid which is denser than gas, but this is not true for water

    • Water has its max density at 4 degrees C

    • Seawater freezes below 0 degrees C

      • Temperature and salinity affect at what point ocean water freezes

  • Solvent: water is a universal solvent

    • Solute dissolves in solvent

    • Solution is the combination of solute and solvent

    • Helps with extracting minerals and having chemical reactions and biogeochemical cycles

      • Reservoirs hold water naturally and residence time is how long the water stays there

      • Biogeochemical cycle examples: water cycle, carbon cycle, marine nitrogen cycle

    • Major dissolved elements in ocean water (constituents): mainly chlorine and sodium (salt)

      • Created from erosion

      • Also calcium: makes parts of marine lifes’ habitats

      • [ ] = concentration

      • Precipitation/evaporation can remove these constituents from the ocean

      • Salinity does not vary drastically

    • Minor constituents: mainly bromine and carbon

      • Precipitation is not a main way to take them from the ocean

      • Short residence times due to variability

    • All constituents: 99.6% of dissolved solids

    • Trace elements: .4% of dissolved solids

      • Lots of variability

      • Mainly zinc

    • Radionuclides: natural and anthropogenic isotopes

      • Helps measure ocean circulation and food webs

    • Organic compounds: wide array exists but less than 1% have been identified

      • Can be natural or synthetic

      • Some are essential and some are highly toxic

      • Helpful to bacteria and archaea

    • Dissolved gases: move between the atmosphere and the ocean

      • Measured by saturation solubility and their concentration in seawater

      • Gases are more soluble in colder temperatures

      • Air-sea interactions drive the movement of gases in and out of solutions

        • Photosynthesis and respiration help

      • Ocean is a major carbon dioxide sink (similar to a reservoir)

        • Critical for pH buffering

  • Surface tension: molecules pulled together by van der Waals force

    • Hydrogen bonds make this possible

    • Distance between molecules is shorter in liquids than air

• Electromagnetic radiation and water interactions

  • Limited transmission of wavelengths

  • Infrared and UV wavelengths are absorbed rapidly

  • On the visible spectrum, red is the shallowest and blue/green is the deepest

    • Depends on what is in the water

• Sound in the ocean: dependent on salinity, temperature, and pressure

  • 4 times faster in water than in air

  • Acoustic thermometry: precisely measures temperature

    • Heard Island experiment used this

  • The bloop: loudest sound underwater

  • Krakatoa eruption: loudest sound above water

Lecture 7: Ocean-Atmosphere Interactions

• Ocean drives climate/weather

  • Affects temperature distribution, wind/circulation, precipitation, and storms

• Layers of the atmosphere (highest to lowest)

  • Exosphere

  • Thermosphere

  • Mesosphere

  • Stratosphere

  • Troposphere

• Layers of the atmosphere

  • There are pauses between the layers

  • They have differences in density which varies due to pressure, temperature, and water vapor

  • Ozone layer blocks UV radiation, but hole is problematic

  • Ionosphere, homosphere, heterosphere

  • Planetary boundary layer

• Composition of the atmosphere

  • Early atmosphere: H/H- compounds

  • Prebiotic atmosphere: N2, CO2, and inert gases

  • Biotic atmosphere: mainly N2 and O2 with inert gases

  • Composition of gases vary through time

• Water vapor: varies across temperature

  • Temperature increases concentration of water vapor and decreases density

  • Clausius-Clapeyron relationship increases temperature and decreases concentration of water vapor

  • When air is decreased and rises, pressure decreases

  • Transferring heat uses water vapor (hurricanes)

Lecture 8: Ocean-Atmosphere Interactions

• Water budget: the input of water into a reservoir and output of water that is regulated

• Heat budget: the balance between incoming and outgoing radiation

  • Shortwaves are incoming and longwaves are outgoing

    • If they are not equal, water can be gained and temperatures drop, or water can be lost and temperatures rise

      • We are currently in a period of warming of the earth

  • Heat is transferred by conduction (sensible heat), vaporization (latent heat), and radiation

• There is a relationship between latitude and radiation

  • Insolation becomes diffuse as the sun’s rays do not hit the earth flat at higher latitudes, causing the concentration of the ray to be smaller per square meter

  • There is an equator and pole difference between absorption rate (large) and radiation rate (small)

  • Milankovitch cycles over a long period of time

    • The changes in earth’s orbit; long term climate change

• Heat is transferred to the poles through ocean currents and atmospheric circulation

  • Ocean currents take warmer temperatures to the poles, and the earth’s atmospheric circulation is set up in a 3-cell model

    • Cells: polar, mid-latitude, and hadley

• Coriolis force and effect: force on an object due to earth’s rotation; dependent on latitude and direction is dependent on hemisphere

• If the planet was not rotating, temperature and pressure would drive single-cell circulation

• Intertropical convergence zone: a band of storms (tropical cyclones) that migrates seasonally

• The earth’s axis tilt leads to seasonal variability

  • Landmass distribution complicates this

  • Lag in the timing of the max and min of temperatures in the ocean and land

    • Land heats up before the ocean

  • Water properties influence the seasons

  • A monsoon is a seasonal reversal of winds driven by pressure changes

Lecture 8: Ocean-Atmosphere Interactions

• Surface salinity: amount of salt in the ocean

  • Tends to be low around the equator

  • Controlled by evaporation/precipitation rates, runoff (freshwater input from rivers and glaciers), and upwelling/downwelling

    • Adding water (precipitation) decreases salinity and taking water (evaporation) increases salinity

• Dissolved salts are staying in the solution

• Runoff: freshwater input from land from rivers/estuaries

• Upwelling: driven by winds; Ekman transport/spiral

  • Salinity increases with depth

• Salinity is typically highest in marginal seas

  • Mediterranean Sea: ~38% surface salinity; 100 year residence time

    • Sills (pieces of land that come up in water) block water moving around; there could be more exchange of water between bodies of water without them

    • Messinian salinity crisis: drying of the Mediterranean Sea

      • Millions of years ago

      • Sea level drop and evaporite formation (salt deposits)

      • Zanclean floods: flooding from the Strait of Gibraltar of 10 or more meters per day

• El Niño (ocean) Southern Oscillation (atmosphere): affects ocean and atmosphere conditions

  • Teleconnection: has a widespread effect on climate

  • Southern Oscillation: pressure difference between Darwin and Tahiti

  • Warm phase/high sea surface temperatures

    • La Niña: cold phase/low sea surface temperatures

  • Winds weaken to allow for warm water to move east

    • La Niña: winds strengthen

  • Thermocline: a layer in the ocean where the temperature rapidly changes with depth

    • El Niño: farther from the surface; warm water layer is prominent

    • La Niña: closer to the surface; cold water layer is prominent

  • Internal climate variability: influences the climate system, but not influenced by the climate system

    • The sun influences our climate, but we do not influence the sun

  • Influences tornadoes and hurricanes

Lecture 9: Ocean-Atmosphere Interactions

• Oceans follow latitudinal temperature gradient to determine their climate zones

  • More complicated on land because more climate zones exist on land, unlike on the ocean

• Seasonal temperature lags: there are differences in thermal properties between water, air, and land, even among different places at the same latitude

  • Reason for hurricane season peaking in September

• Island and mountain effect: air is forced to rise by topographic highs

  • Produces a distinct gradient in precipitation

• Pressure gradient: drives wind

  • High pressure: cloud free, sunny, crisp weather

    • Diverges at the water’s surface, converges aloft

    • Rotates counterclockwise/right in the southern hemisphere

  • Low pressure: unstable, precipitation, stormy, humid weather

    • Converges at the water’s surface, diverges aloft

    • Rotates clockwise/left in the southern hemisphere

• Tropical cyclones: not around the equator because the coriolis force does not exist there (warm core)

  • Extratropical cyclone: forms via cyclogenesis and creates a wide range of weather conditions (cold core)

    • Warm/cold fronts are separations of air masses along frontal boundaries

      • Stationary fronts move parallel along each other and do not collide

      • Causes a wave to form around the boundary, and air begins to circulate

        • Low pressure forms as the circulation increases; this is amplified over water

        • Occluded front: sectors form and the cold front catches up with the warm front

          • Eventually the system runs out of energy and dissipates

  • Nor’easters: form over warm waters

    • Winds come from the northeast

    • Type A: forms in the Gulf of Mexico/North Atlantic Bight

    • Type B: forms in the Midwest and catches onto the Gulf Stream

• Land and sea breezes: thermal differences between the land and sea

  • Land heats up to max temperature first during the day, and the ocean is typically warmer than land at night

  • Essential for reducing temperature variability

• Coastal fog: coastal upwelling causes cool waters to be nearshore and warm waters to be offshore

  • Moisture is transported via sea breezes, then it condenses and creates fog

Lecture 10: Ocean Circulation

• Currents: important for movement of water masses, heat, chemical constituents, sediment, and organisms

  • Heat is transported from the tropics to the poles

  • Drives convection

• Water can be moved by wind and density (temperature, salinity, or pressure gradient)

• Wind currents: winds move across the ocean surface

  • Friction and kinetic energy causes movement

  • Current velocity is substantially less than wind velocity because water is more viscous than air

  • Energy is transferred downward (max depth is 100-200 m)

  • Currents continue after wind stops due to momentum and the sloping sea surface

    • Convergence, divergence, and the horizontal pressure gradient creates the slope

  • Direction and speed are controlled by friction, the horizontal pressure gradient, the coriolis effect, and coasts

    • Competing components balance currents using the coriolis force

      • Geostrophic current: the balance between the pressure gradient force and coriolis force drives what direction the geostrophic current moves

• Energy is moving down between layers of water

  • As energy is moving down, each layer is being pushed or pulled, and energy is being lost

    • Friction is created between layers

    • Velocity decreases as energy hits each new layer as it moves down

• Ekman spiral: the coriolis force deflects water; deflection continues with depth

  • Max depth: 100-200 m

  • Deflection stops below the wind-driven layer

  • Needed for a full Ekman spiral: uniform density, depth, and constant wind for 1+ days

  • Net water transport includes the entire spiral

  • Pycnocline: vertical density gradient

    • Can be a thermocline, halocline, or both

    • Uniform density is needed for a full Ekman spiral

      • Upper layer needs to be well mixed

    • Water masses don/t impart any friction on each other

    • Controls Ekman spiral’s depth

  • Thermocline: vertical temperature gradient

  • Halocline: vertical salinity gradient

  • Pycnocline, thermocline, and haloclines differ spatially and seasonally

  • Ekman transport: movement of water 90 degrees to the right of the wind in the northern hemisphere (left of the wind in the southern hemisphere)

    • On the sea surface, convergence is seen in the northern hemisphere and divergence is seen in the southern hemisphere

• Open ocean surface currents: Ekman transport on a global scale

  • Atmospheric circulation affects the direction of surface currents

  • Pressure gradients in the atmosphere and the ocean form from Ekman transport and coriolis deflection

  • Gyres represent the average wind energy input

    • Subtropical gyres form clockwise in the northern hemisphere and counterclockwise in the southern hemisphere

    • Polar gyres are less established and rotate in the opposite direction

      • Does not occur in the southern hemisphere

  • Eastern and western boundary currents highlight additional factors that come into play outside of gyres

    • Eastern: in the eastern part of the ocean

      • Nutrient poor and upwelling does not often occur

    • Western: in the western part of the ocean

      • Narrower and faster than eastern currents

      • Upwelling occurs and phytoplankton blooms can occur

    • Coriolis and continents influence them

    • Eastern and western boundary currents have differences in depth, width, volume, velocity, boundaries, temperatures, etc.

    • Westward intensification

  • Equatorial surface currents: flow east to west/west to east without being deflected since coriolis is at its minimum at the equator and maximum at the poles

    • Displacement of ITCZ influences Ekman transport and shifts the surface sea slope

    • A pressure gradient also develops

  • Polar surface currents: more variability in polar gyres than subtropical gyres

    • Winds are more variable and there is complex basin geometry

    • They differ between the hemispheres because of continent concentration and connections between oceans

      • Southern hemisphere: Antarctic coastal current and antarctic circumpolar current

• Upwelling and downwelling: wind moving water

  • Types: open ocean (wind) and coastal (wind and coastlines)

  • Influences pycnocline depth

  • Biologically and ecologically important for nutrient transport for organisms

    • Increases in photosynthesis and biomass

Lecture 11: Ocean Circulation

• Upwelling increases primary productivity, causing nutrients to be brought to the photic zone

  • Concentration of nutrients goes up, phytoplankton and zooplankton biomass increases, and catch yield goes up

  • Seasonal variability plays a role in this as summer conditions are more stable than winter conditions

  • Upwelling of nutrients allows for growth

    • Need carbon dioxide, oxygen, water, and sunlight for photosynthesis in the ocean, similar to on land

      • Trace elements promote growth

  • Chlorophyll is more concentrated around the equator and coasts

    • El Niño has less primary productivity compared to La Niña based off of chlorophyll concentration

• Coastal currents are not a part of larger gyre circulation due to pressure gradients in the atmosphere

  • Size varies due to differences in continental shelf width

    • West coast: shelf is narrower

    • East coast: shelf is wider

  • These are also influenced by coastal winds/storms, tides, freshwater input/rivers, bathymetry, and coastal geomorphology

  • Seasonal changes in winds can cause seasonal changes in coastal currents

    • Winter: the prevailing wind direction is inward toward the coast

    • Summer: the prevailing wind direction is downward parallel to the coast

  • Coastal currents are strongest due to changes in bathymetry and coastal geomorphology

• Eddies: hurricanes, tornadoes, midlatitude cyclones, and whirlpools

  • They have cultural significance

  • More wind velocity is needed to create an ocean eddie than an atmospheric eddie

  • Atmospheric eddies and ocean eddies differ in spatial and temporal scales

    • Ocean: takes longer to form and more strength of winds

    • Atmospheric: takes shorter time to form and are not as strong as ocean eddies

  • Eddies are a transport mechanism along ocean fronts (boundaries between differ water masses)

    • Meanders in currents: there is a boundary dividing cold and warm waters -> currents form in each separately -> warm eddies break off into cold waters and cold eddies break off into warm waters

      • This is due to momentum

      • Warm and cold core eddies exist due to rotation being different depending on if they are warm or cold and divergence

        • Warm core: downwelling

        • Cold core: upwelling

    • Transport between and within basins: heat, nutrients, dissolved materials, and marine organisms are transported

  • Langmuir circulation: streaks of white on the water

    • Wind driven: width and depth are a function of wind speed

    • Zones of convergence and divergence

Lecture 12: Ocean Circulation

• Thermohaline circulation: driven by density

  • Density is controlled by temperature and salinity

    • Density and temperature have an inverse relationship

    • Density and salinity have a direct relationship

  • Water moves along a density gradient until it has reached a point of equilibrium

• Pycnocline: made of the thermocline and halocline

  • Mixed layer that has seasonal patterns

  • Summer thermocline is the largest, winter thermocline does not exist

• Temperature decreases with depth and warmer waters are deeper with higher latitudes (insulation)

• Bottom water formation: when isotherms restrict/cut off warm water areas at the surface from cold water areas

• Temperature distribution at surface waters is mostly uniform, but salinity distribution at surface waters is not

  • Temperature ranges are large whereas salinity ranges are not

• Water from different sources helps create different water masses

  • Ex: Mediterranean Sea and Atlantic Ocean: Mediterranean salinity and temperature > Atlantic salinity and temperature, and the Mediterranean is denser

  • Density can allow for tracking of water masses

• Water masses in the Atlantic: when convergence occurs, pressure goes up and water wants to sink, and new underwater masses are created

  • Density differences hinder vertical mixing (water masses stay separate)

    • Can be offset by currents, internal waves, and tides, but not significantly

  • Horizontal flow requires less energy opposed to vertical flow

    • Water masses can spread out

• Bottom water formation: changes in density causing water masses to move vertically on a large scale

  • Water density is increased by lowering temperature and rising salinity

  • Only occurs at specific locations: North Atlantic and Antarctic

  • Meridional overturning circulation: the return flow of water that once was warm, began sinking and got cold, then returned to its original place

  • Mixing can occur due to turbulence from currents, internal waves, and tides

  • Bottom water formation and meridional overturning circulation are important in the climate system as oceans are major sinks for carbon dioxide

    • These processes allow for dissolved gases like oxygen to get to the deep ocean

      • Another source of oxygen in the deep ocean is dark oxygen

    • They are essential for transport in the global climate system which takes around 1000 years to complete

      • New water is created at deep water formation sits

      • Oldest water is located in the North Pacific

      • Important for heat transport

  • Atlantic meridional overturning circulation has weakened and is slowing

    • This is a response to warming and meltwater

    • Widespread effects are seen through positive/negative feedback

      • Positive: allows a cycle to continue; negative: cuts off a cycle

      • Circulation gets stronger/weaker at one point, so all circulation must get stronger/weaker

        • Explained by paleoclimatology and paleoceanography

• Last glacial maximum: late Pleistocene epoch

  • Ice sheets were at largest extent with dry conditions and lowering sea levels

  • AMOC was weaker and more variable

• Late glacial interstadial: warm period in between glacial periods

  • Changing circulation and glaciovolcanism

  • Glacial retreat causes meltwater pulses

  • People expand across land

• Younger dryas: glacial outburst flood leading to rapid cooling in Europe

  • Massive inflow of freshwater in the Atlantic ocean

  • Changes differ between regions

    • Southeast US: warmer and wetter

    • Appalachian Mountain boreal forest: expansion

    • East Asia: increased aridity

  • Named after mountain avens