02 ocean circulation S23

GEOL 305 Name: Lab 02: Ocean circulation In this lab, you will observe some experiments that were videoed and are available online and also will plot and map data to better understand ocean circulation. You will observe or plot how rotation, temperature, and salinity affect the movement and mixing of fluids. The videos are all from Dr. Mirjam Glessmer (unless otherwise stated) and are a replacement, and often times something of an improvement, from some hands on experiments that we would do if we were meeting in person. Communication: Think about ways to clearly communicate. For example, when you are reporting multiple sets of numbers in response to a question, think about ways to organize them, for example, tables. When you are answering questions, use a different color text (and then if you do corrections, use a third color ). Section 1: Surface circulation Since the dawn of human civilization, people have thrown objects into the water to see where the currents would take them (the old “note-in-a-bottle trick’). We continue to do the same thing with more sophisticated, high-tech tools like a drift current meter (Figure 1). Drift current meters are released into the ocean by ships or airplanes. They float with the currents and take measurements of the water with built-in instruments. They are tracked by satellites in orbits far above earth and transmit data several times a day. The floats on the drifter keep it at the surface of the water and hold an antenna for sending data to a satellite above. Metal vanes extend 1-meter below the surface and cause the ocean currents to move the “drifter” instead of the surface wind. 1) Data from three drift current meters (or buoys) is in Table 1. Plot that data on Figure 2 (another version is available in PowerPoint, which may be the easiest way to plot the points). Use longitude and latitude data to plot the position of each buoy location during the year; then connect the locations with lines and draw arrows to show the direction of motion. Insert your map/figure into this document (9 pts) Figure 1. A drift current meter.

GEOL 305 Env. Geology, Lab #2 – 2 Table 1: North Pacific buoy data Buoy number Position Day Latitude* Longitude** 12410 27-Feb-95 30.1 -123.7 12410 26-Mar-95 27.5 -121.8 12410 22-Apr-95 25.0 -124.6 12410 22-May-95 23.6 -128.0 12410 24-Jun-95 22.5 -133.9 12410 24-Jul-95 23.1 -138.4 12410 26-Aug-95 20.5 -145.4 12410 25-Sep-95 20.0 -147.6 12410 20-Nov-95 17.9 -155.3 12410 18-Dec-95 21.4 -159.5 15022 25-Feb-95 10.7 162.0 15022 27-Mar-95 10.5 152.1 15022 23-Apr-95 11.6 145.5 15022 20-May-95 12.4 137.6 15022 25-Jun-95 17.0 131.1 15022 22-Jul-95 21.7 127.8 15022 27-Aug-95 33.0 141.6 15022 23-Sep-95 37.0 147.8 15022 23-Oct-95 39.3 152.0 15022 25-Nov-95 40.1 154.5 15022 31-Dec-95 37.6 160.4 22217 27-Feb-95 51.2 -162.7 22217 27-Mar-95 50.4 -165.3 22217 24-Apr-95 48.7 -159.5 22217 29-May-95 50.7 -155.1 22217 26-Jun-95 50.4 -151.7 22217 24-Jul-95 51.5 -149.3 22217 28-Aug-95 51.0 -145.0 22217 25-Sep-95 53.1 -143.8 22217 23-Oct-95 55.2 -139.1 22217 27-Nov-95 57.1 -141.4 22217 18-Dec-95 56.9 -141.7 *All latitudes are in the Northern Hemisphere **Positive numbers are East Longitudes and negative numbers are West Longitudes (WAIT! Which is the eastern and which is the western hemisphere?)

GEOL 305 Env. Geology, Lab #2 – 4 c) Bonus: What is the weather phenomenon that San Francisco is most known for? How might it related to (a) and (b)? 4) Based on the year of buoy data that you plotted, estimate how long it would take for a contaminant spilled off the coast of southern California to reach the coast of Japan. (2 pts) 5) If a contaminant moves 50˚ of longitude along the equator during one year, how fast is it moving in nautical miles/hour? (Clue: at the equator, the distance between degrees of longitude is 1˚ = 60 nautical miles) (2 pts) Section 2: Temperature, salinity, density, and thermohaline circulation 6) Which is denser: cold water or warm water? Is fresh water or salt water denser? (2 pts) 7) Now watch the first 0:58 of the following video: https://vimeo.com/421491414 . What behaved as you expected? Was there you did not expect? (2 pts) 8) The density of water is a function of both salinity and temperature. The interplay between the two can have interesting effects. (3 pts) a) Make a prediction based on the following scenario. You have two cups of room-temperature water – one that is freshwater and the other is salt water – and then you add one ice cube to each cup. In which cup do you expect the ice cube will melt faster? Please briefly explain why.

GEOL 305 Env. Geology, Lab #2 – 5 b) Now watch the following video: https://vimeo.com/139232370 . The freshwater cup is on the left and the salt water cup is on the right. The ice cubes have food dye in them so that you can visualize the melting ice cube. Briefly describe what you observe and whether it matches what you predicted in 8a . c) Given your answer to #6, what do you think might have been happening? 9) Watch the short Finger of Death video: https://www.bbc.co.uk/programmes/p00l817b . Define the difference between saltwater and brine? Why is the unfrozen water sinking? (2 pts)

GEOL 305 Env. Geology, Lab #2 – 7 11) Plot the data in Table 2 (below) in Excel. Make two plots: Depth (on the y-axis with zero on top) versus temperature (x-axis) Depth (again on the y-axis) versus salinity. Label the plots with (a), (b), and (c) below and insert the labeled plots into the lab below (3 pts) a) Mixed surface layer b) Thermocline c) Deep zone of uniformly cold water Table 2: Temperature and salinity as a function of depth for a location in the Pacific Ocean Depth (m) Temp (  C) Salinity (‰) 0 24.4 36.5 250 21.2 36.3 500 6.9 35.6 750 5.1 34.7 1000 4.9 34.4 2000 4.8 34.8 3000 4.7 34.9 4000 4.6 34.8 12) Compare the two-dimensional temperature and salinity data from question #10 with your one- dimensional vertical temperature and salinity profile from question #11. Are the data in Table 2 and your plots from the low, medium, or high latitudes? Or stated another way, from the tropics, temperate, or polar latitudes? Describe why. (2 pts) 13) Look back at Figure 3 with a focus on the vertical changes in temperature and salinity at tropical, temperate, and polar latitudes. (3 pts) a) In which parts of the ocean is the water column unstable (that is, where do you think density remains the same or even decreases with depth)?

GEOL 305 Env. Geology, Lab #2 – 8 b) In which parts of the ocean is the water column stable (that is, density increases with depth)? c) Given your answers to (13a) and (13b) above, where would you expect ocean water introduced at the surface to remain at the surface? Where would you expect them to sink? 14) Now look at Berner, Chapter 1, Figure 1.13. Briefly describe and then compare and contrast that figure with Figure 3 in the lab. (3 pts) 15) Now go back and watch from ~0:58 to 2:00 in the following video: https://vimeo.com/421491414 . Briefly describe what you observe and how it might be connected to thermohaline ocean circulation. (2 pts) If you watch from ~2:00 to ~3:30, you’ll see patterns that are more reflective of atmospheric circulation. From ~3:30 to the end is what happens when solid body rotation is in effect. If you’re interested in learning more about solid body rotation, this 4-minute video is helpful and cool: https://vimeo.com/419978552 . Section 3: Synthesis questions These questions should be pretty straight forward after you completed the above but will be useful to make sure that you connect the important concepts. 16) When seawater freezes into ice in polar regions, most of the salt is left behind in the unfrozen water. How would the remaining salt affect the density of the unfrozen water? (1 pt) 17) What effect would the remaining unfrozen water have on ocean circulation? Would it have a larger effect on surface or thermohaline circulation? (1 pt) 18) Water freezes at 0˚C, yet Antarctic bottom waters may be as cold as –1.9˚C. How can this water still remain in liquid form? Give two reasons. (1 pt)