MSCI3001 Physical Oceanography MSCI5004 Oceanographic Processes

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1 MSCI3001 Physical Oceanography MSCI5004 Oceanographic Processes Katrin Meissner Alex Sen Gupta Laura Ciasto Climate Change Research Centre (CCRC) Dr. Katrin Meissner Room: 472 CCRC Contact hours: Mon 1-4pm Dr. Alex Sen Gupta Room: 454 CCRC Contact hours: Tue 1-3pm Course Information Dr. Laura Ciasto tutorials & computer labs Room: 451 CCRC Contact hours: Thu 1-5pm Lecture Monday 10am 12. CCRC Seminar Room, Mathews level 4 Lab Wednesday 3 5pm. Red Centre, Room RC-G012A (weeks 2,4,6,8,10,12) Tute Wednesday 2 4pm. BioSc, Room 456 (weeks 3,5,7,9,11,13) Assessment The final mark for MSCI3001 will be calculated as follows: 3 Comp Labs 4+5+5% each (14% in total) Assignment 1 12% Assignment 2 16% Research Project/presentation 13%/ 5% Final examination 40% The final mark for MSCI5004 will be calculated as follows: 3 Comp Labs 5+5+6% each (16% in total) Assignment 1 13% Assignment 2 17% Research Project/presentation 13%/ 5% Final examination 35% **If not otherwise stated, all pieces of assessment are due by Friday noon of the week indicated.** They should be put into submission box or handed in to Simone Purdue or Stephen Grey, CCRC reception, Mathews level 4 **To pass this course satisfactory performance across all components of the course is required** Course Webpage All the information for the course will be available at Course Outline Course notes Matlab tutorial notes Matlab tutorial data Lecture slides (will be put up a few days prior to class) Please check this site once a week for important information If you want reminders please Laura with MSCI3001 or MSCI5004 in the subject (a.sengupta@unsw.edu.au)! 1

2 Textbooks Introductory oceanography, H.V. Thurman An introduction to the world s oceans, A.C. Duxbury and A. Duxbury Descriptive physical oceanography, G.L. Pickard and W.J. Emery Introductory dynamical oceanography, Pond and G.L. Pickard Regional oceanography: an introduction, M. Tomczak and J.S. Godfrey Ocean Circulation (Open University) Waves, tides, and shallow-water processes (Open University) Introduction to Physical Oceanography, J.A. Knauss (Prentice Hall) Computer Labs For the computer labs you will need a lab password. You can set these passwords before you come to class at: You will need your unipass / zpass to authenticate. If you have not done this by the time you come to class you can log into a 'Linux' machine with: user: newuser pass: newuser This will take you to the same page. Research Project/Presentation!Top 3 choices, by the end of this week to a.sengupta@unsw.edu.au!planning stage. A half one page outline by Friday week 6 (27 th August). bullet points at least 3 journal articles!written report. Maximum of 3 typed pages + figures!presentation. 6 minute talk (+ 2 minutes of Q&A) using powerpoint (or equivalent).!workshop Environment (if possible)!possible oceanography on Europa, could this mean life on another planet?!accelerated warming of the Tasman Sea, physical reasons and biological consequences.!enso and tuna!enso and sardines!global warming changes to the physical and biological pumps what does it mean for carbon capture.!pros and cons of iron fertilisation!the Southern Annular mode effects on the ocean and its biology!daisyworld how biology modulates our climate over billions of years.!marine life s influence on the evolution of the atmosphere!can salps counter Global Warming!Is there any observational evidence for Global Warming affecting marine life?!ocean eddies and biological productivity!how productivity is enhanced along ocean fronts!life and sea-ice!the physical and biological oceanography of lake Vostock!Ocean acidification and coral reefs!ocean acidification and high-latitude ecosystems!npz modelling combining ocean physics and ecosystems!seasonality of the Californian upwelling system!can satellites provide us with accurate measures of ocean productivity!challenges of hydrothermal vent ecosystems!what limits ocean productivity how do different regions get their nutrients!hurricanes and primary productivity!ocean circulation and reproductive biology/life cycles!ocean circulation and biogeography / species distribution / invasive species (modelling)!aeolian dust input into the ocean across different timescales!rubber ducks, sport shoes & ocean circulation early/historic oceanographic discoveries!how has remote sensing revolutionised oceanography!how have ARGO floats revolutionised oceanography!thermohaline circulation changes due to Global Warming and implications for the marine ecosystem!changes in the Southern Annular Mode and the biology of the Southern Ocean 2

3 bcpid ? bclid= &bctid=

4 !!!! Weather Prediction Climate Prediction Climate Change ENSO Dispersion of jellyfish larvae (Dawson et al. 2005) 4

5 For a 0.5m rise in sea level - in Sydney at 1 in a 100 year flooding event will likely occur every year Courtesy of John Hunter UTAS Barrier to withstand 1:10 yr event Map of Ocean CO2 Uptake (IPCC) For a 0.5m rise in sea level - in Sydney at 1 in a 100 year flooding event will likely occur every year Courtesy of John Hunter UTAS Barrier to withstand 1:10 yr event 5

6 Oceanic time scales & length scales Time Scale 100 y 2 yrs Deep water formation Climate Change N. Atlantic Oscillation El Nino Month days mins Boundary Fronts currents Eddies Upwelling Weather Diurnal cycle Turbulence Hail storm Molecular Waves cms 10 m 1 km 100 km km Spatial Scale Oceanic and Atmospheric Phenomena Oceanic and Atmospheric Phenomena 6

7 Properties of the oceans Water covers ~71% of world surface Average depth 3800m Pacific Ocean 46% Atlantic Ocean 23% Indian Ocean 20% Others 11% Q. What is the volume of the ocean? Q. What is the aspect ratio of a piece of paper? (a 500 sheet ream of paper has a width of ~5cm)? Q, What is the aspect ratio of the ocean (i.e. a typical depth H divided by a typical length, L)? The aspect ratio turns out to have important consequences for the magnitude of typical velocities in the horizontal compared to vertical directions Properties of the oceans Measuring the Ocean Echo sounders (time taken to bounce a sound wave) Gravity measurements the slope of the surface is affected by the gravitational attraction of underlying bathymetry features (see Giod) Properties of the Ocean Temperature (T)!Temperature is important because it reflects the amount of heat held and transported by the ocean.!plays important role in circulation via density!the temperature range in the ocean varies from -2 C ( at the poles to >28 C at the equator.!the temperature of the ocean is primarily influenced by the heating at the air-sea interface. 7

8 surface Potential Temperature (!)! The temperature a water parcel would have at the surface, if it were raised to the surface adiabatically.! Adiabatically: No heat is transferred to or from the fluid.! From chemistry, VT = constant.! Thus, as pressure increases, (volume decreases) and temp increases. 8

9 Why Potential Temperature?!! removes the effect of pressure on temperature Atlantic Potential Temp Properties of the Ocean Salinity! Total dissolved solids (mainly sodium chloride, or table salt )! About 3.5% by weight (i.e 35kg of salt in 1000kg of pure water on average)! Usually expressed as 35psu (practical salinity units, psu, or ppt) What sets the salinity in the ocean? 9

10 Properties of the Ocean Surface Salinity Salinity! Total dissolved solids (mainly sodium chloride, or table salt )! About 3.5% by weight (i.e 35kg of salt in 1000kg of pure water on average)! Usually expressed as 35psu (practical salinity units, or ppt parts per thousand they are the same)! Varies geographically according to Evaporation, precipitation, rivers, ice formation and ice melt.! Plays an important part in ocean circulation, through influence on density E - P Polar Temperate Tropical! Surface salinity determined by surface Freshwater Flux 10

11 ! Density is the mass of sea water per unit volume. Kg / m 3! Density depends on salinity, temperature and pressure. - Density increases with increasing salinity - Density increases with decreasing temperature! Seawater density ranges from kg/m!, the average density is 1025 kg/m!! Density increases with pressure, as the pressure force squashes water into a smaller volume.! Lighter water is - warmer - fresher! Denser water is - colder - more saline! Generally for stability, less dense water overlies more dense water otherwise convection The Equation of State For regions where T and S vary little, we may assume a linear equation of state. At T=30, S=40, P=0 (e.g. Dead Sea), "= ! What is the density if we increase the temp by 2 C (sun)? 2.! What is the density if we decreasing the salinity 1psu (rain)? 3.! What is the density if we decrease the temp 2 C (night)? 4.! What is the density if we increase the salinity 0.5psu (wind/ evaporation)? Where alpha and beta are nearly constant expansion coefficients for T and S. 11

12 Types of Density For most applications we can use a simplified linear Equation of State:!~ =! o [1-#(T-T o )+$(S-S o )] Where! o is a reference density, and # & $ are nearly constant expansion coefficients.! o = 1028 kg/m 3 # = 1.7 x 10 4 K -1 $ = 7.6 x 10 4 T = 10 C S = 35 psu! In-situ " =! s,t,p 1000! Sigma t " t =! s,t,0 1000! Is density parcel would have if raised to the surface! Removes pressure s HUGE effect on compressibility! Potential " # =! s,#,0 1000! Is density parcel would have if raised to the surface adiabatically! Removes Pressure s HUGE effect on compressibility! Removes Pressure s much smaller effect on temperature Changes with depth Atlantic Potential Density 12

13 !!!!! Ocean pressure is the weight of seawater per unit area (force per unit area). P=F/A It is mainly a function of depth (also depends on density). P=F/A = mg/a =!gh Pressure in the ocean increases at a rate of about 1 atmosphere OR bar per 10 m of water. Or pressure increases by 1 dbar per 1 m of water. Differences in pressure one of major drivers of ocean circulation Stiletto vs Elephant Other Properties watermass formation Oxygen Stopped here! Can use other properties as tracers showing source of water.! Dissolved phosphate, silicate, nitrate, and nitrites, indicative of e.g. upwelling, biological activity etc.! Dissolved Oxygen (ml/l) tells us when water was last in contact with the atmosphere.! Radioactive elements such as tritium and radiocarbon and CFCs were introduced to the atmosphere by humans. We can use them as tracers in the ocean. 51 Cross-section of oxygen content along 135 W in Pacific Ocean (WOCE). 13

14 Anthropogenic compounds and chemicals can act as tracers in the ocean. e.g. CFCs Recently overturned waters carry a higher signature of CFC than older water. Carbon-14 = measure of age of the water Rapid increase in CFCs since introduction in 1930s 53 Cross-section of carbon-14 ( 14 C) content along 150 W in Pacific Ocean (WOCE). He comes from the earth s mantle and is emitted at plate boundaries, i.e. at mid ocean ridges.!used to track water plumes from hydrothermal vents 14

15 Light in the Ocean The vertical penetration of light decreases with depth: - Scattering of molecules and absorption by molecules and particulate matter - Light intensity (I) decreases as a function of depth Where I o is the surface intensity, and k is the attenuation coefficient - The length scale z = k -1 is the e-folding scale of penetration Light (cont d)! For seawater the coefficient k varies with wavelength.! For clear ocean, k is a minimum at 0.45 %m i.e blue light is attenuated best.! At both shorter and longer wavelengths the attenuation is greater (hence penetration of light is less) Light intensity with depth Light intensity with depth and light required for biological processes (Sarmiento & Gruber 2006) Light absorption with depth (Mann & Lazier 1996)! Nearly all the energy is absorbed in the surface waters 15

16 Coordinate systems and Notation Thermocline Sharp temperature gradient Halocline Sharp salinity gradient Pycnocline Sharp density gradient Oceans What can you say about the gradient? What can you say about the gradient? 16

17 What can you say about the gradient? A Gradient is a measure of how a quantity (pressure, salt, temperature, density) changes with direction: e.g # 2 # 1 "# x 2 x = 1 "x In most applications in oceanography, the gradient term in an equation, such as: Can be approximated as "#, "#, "# "x "y "z dt dx, d" dy, etc Change Where is the temperature gradient bigger? 100m 1000m Where is the temperature gradient bigger? dt/dx ~ 2 o C/ 100m = 0.02 o Cm m dt/dx ~ 2 o C/1000m = o C m m 17

18 Units Force N (Newtons) 1 bar = 100 Pa Pa = Nm -2! Next week: Thermohaline Circulation! Wednesday: Computer Lab: Make sure you set your password! Send me an so I can put you on the mailing list! me your research project title by the end of the week Questions Questions B A What is dt/dz in region A, B and C? What you think the corresponding density profile would look like? If the light intensity, I, at depth z is given by: I(z) = I o e "0.5(z) At what depth will intensity drop of by 50%? You will need to use the ln function on you calculator. No calculator write down how you would do it. C Name 2 processes that might give rise to the homogeneous temperature at A? If the density of water is 1027kgm -3 calculate the weight of water above a 1m 2 horizontal area at 100m depth. Now calculate what the pressure exerted on that area is. Remember density =mass / volume weight (or force) = mass x g Pressure = force / area 18