Zusammenfassung

Summary Introduction to Physical Oceanography

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Kurs
Introduction to Physical Oceanography (GEO41453)

Hochschule
Universiteit Utrecht (UU)

This file includes all 14 lectures given in the course in . The course supervisor was Roderik van der Wal. It includes all the information from the PowerPoints and a lot of information that was only told during the lectures (I made very elaborate notes). It also includes additions that were importa...

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Typ Zusammenfassung

physical oceanography
ocean dynamics
el nino
amoc
ocean observations
geostrophy
baroclinic and barotropic
sea level rise
ice sheet dynamics
ipcc
climate change
eddies
ekman transport
ocean variability

Hochschule
Universiteit Utrecht (UU)
Studium
Marine Sciences
Kurs
Introduction to Physical Oceanography (GEO41453)

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Introduction to Physical Oceanography –
Summary
Lecture 1 – Introduction to our oceans
Different scales of circulation in the ocean, transport in many directions. There is chaos!
Physical oceanography = field of study that deals with the physical properties and dynamics of the
ocean and its influence on climate and atmosphere.
Using : Observations, Numerical model output, Theoretical studies, Process-based numerical model
experiments
Ocean properties and dynamics → play a key role. Many feedbacks between:
Economy:
- Transport → transport of water but also of boats etc
o Thermohaline, gyres (localized circulation in a bigger system)
o Driven by temperature differences, wind circulation and topography
Energy transition → wind farms, tidal systems, osmosis
- Tourism → Ocean plays a role in distributing plastic
Ecosystems:
- Habitat → Largest habitat on earth!
- Food security → fisheries and aquaculture (e.g. seaweeds)
- Natural defence → mangroves and coral reefs pose protection
Climate:
- Heat uptake and transport → Surplus of radiation in equatorial regions is transported away
- Carbon, nutrient and hydrological cycle
- Forcing for ice sheets
- Atmospheric composition & circulation
Ocean and climate change

Energy take up, (not carbon dioxide → ENERGY) → 95%
- Total energy added to the climate system is 250 ZJ = 250.000.000.000.000.000.000.000 Joule
- Between 1970 and 2010 this is 104 million atomic bombs added into the ocean (like
Hiroshima), 3.3 bombs s-1
Ocean’s role in taking up CO2
- 25% of emitted CO2 goes into the ocean (25% on land, 50% in atmosphere)
- Inter-annual variability between land and atmosphere due to seasonality of the biosphere
- To stay below 1.5 degree warming we need CO2 removal
Past and projected changes in the ocean
- Temperature (Arctic sea ice is directly related), marine heatwaves, decrease of pH, oxygen
decrease, increase heat content
- Sea level rise: expansion of sea water and melting of land ice.
Ocean dynamics → ocean releases energy into the atmosphere causing storms (cyclones, hurricanes)

, - Forces: e.g. salinity and wind
- Properties
- Domain: set by continents, in this course set as constant.
Ocean topography

- Only 23% of the ocean is mapped (large uncertainty)
- 71% of earth surface
- Sea surface slope measurement from satellites can be transformed to seafloor bathymetry
Topographic details matter!
- Impacts strength, pathway & stability of ocean currents → bottom roughness affects mixing
- Mapping of seafloor important for plate tectonics → may reveal important areas for
generation of earthquakes and tsunamis.
Ocean basins
Using clustering techniques to find regions that are characterised by distinct flow properties

Properties of sea water
Temperature
- Reflects amount of heat held and transported by ocean, plays role in circulation via density
- -2°C at poles to >28°C at equator
- Primarily influenced by heating at air-sea interface
Horizontal distribution: surface heat flux, circulation, mixing and upwelling
Vertical distribution: thermocline. Heat flow from high to low (in or out of the ocean)
- Surface ocean T: reflected by heat influx (e.g. in summer) or heat outflux
o Constant T at the surface due to mixing by surface (wind) waves and/or instability of
the water column due to cooling/evaporation

, - Deep ocean T: quite consistent (even at equator!)
- Global warming → warming will eventually also warm deeper ocean
Difference between temperature and heat
- The heat content of seawater is its thermodynamic energy, related to T but not the same
o Units are Joule = kg m2/s2
- Heat content
o is specific heat (~ 4000 J/kg/K) is mass (kg) is temperature (K)
o Heat is zero at absolute zero temperature (on Kelvin scale)
- Heat change per unit time = is in Watt (W) → 1 W = 1 J/s
- Heat flux = is amount of heat entering a system per unit time per unit area → W/m2

o Order of magnitude important in understanding what is important and what is less
o Ocean: 50 W/m2
o On average negative fluxes: looses heat to atmosphere
Potential temperature = θ

Pressure increases with depth, water is compressible → when water is moved down pressure
increases and water is heated up (reverse from rising and cooling/expanding air) → T increases even
if no extra heat is added, no measure for heat content → use potential temperature!
- = T of sea water if it is moved to the surface (p=0) without exchange of heat salt, or
dissipation of kinetic energy
o Removes effect of adiabatic (without changes in amount of heat) warming
- Potential temperature < Temperature
o Larger difference with depth
- Conservative Temperature = Θ = embeds sea water heat capacity with p, θ, and S
o Differences small but important
- THUS because of the compressibility of sea water we use conservative or potential T
Salinity

, - Atlantic most saline. Poles more fresh water input. Gyres more saline. Fresh at river outlets
- Climate change: fresh gets fresher, saltier gets saltier
- Plays important role in circulation via density
- At depth less saline because at surface there is evaporation
- High salinity at subtropics → more evaporation than precipitation → output of fresh water
→ salt more concentrated
- Lower salinity at tropics → more P than E → input fresh water → salt more diluted
Absolute salinity = fraction of non-H2O in water (all dissolved material, mainly sodium chloride)
- Often expressed in g/kg or psu
- Sea water on average 35 g/kg
Practical Salinity = unitless measure of sea salt using conductivity
Density = ρ → mainly influenced by pressure → linear increase of density with depth
- Mass of 1m3 of sea water ranges 1020-1039 kg/m3 → slightly higher than pure water
- Often expressed with 1000 removed
- A (very!) complicated function of temperature, salinity and depth (pressure)

- Ocean is mostly in the grey bar
- Fresh water → T of max density is 4°C → water of 4 degrees at bottom of fresh water lake
- Ocean water → T of max density is below freezing point → thus at bottom is coldest water
Important because:
- Determines what sinks or floats → plastic, sediment, plankton/biomass (carbon)
- Determines how water circulates → against density costs energy
- Important for dynamical feature like mixing, convection and internal waves
Pressure = p
- Pressure differences main drivers of ocean circulation
- P = ocean pressure = the weight of seawater per square meter – force F per unit area A
o (g = gravitational acceleration = 9.81 m/s2)
- Almost linearly related to depth and density
- P increases with 1 atm (1 bar = 105 N/m2) per 10 m water → 1dbar per 1 m water
o Increases so rapidly because density of water is a factor of 103 larger than that of
atmosphere

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