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Oceanography 101 POST-LAB Saunders Ocean Sediments & Bathymetry Name:___________________________ Objective: At the end of this lab, students will understand the basic features of rocks and minerals of the ocean, and the principles of magnetism and plate tectonics by: Analyzing and classifying sediments viewed under the microscope Analyzing a deep sea core sample to determine the source and formation of its sea floor sediments Using the bathymetric chart to create a transect along Hood Canal in Puget Sound in order to help explain the state of pollution there 1. Sediments (to be done in lab) (1.1) At each table should be a set of sediment slides containing various sediments from around the world. Examine the prepared sediments slides and determine their characteristics by filling out the table below. Slide A B C Description Type Sorting Oceanography 101 POST-LAB Saunders D E F G (1.2) After you have completed the table, check your results against a key provided by your instructor. Do you think Libya has much river input in its sediments? Explain.___________ ___________________________________________________________________________ ___________________________________________________________________________ (1.3) Given what we’ve learned about sediments and their sources, would you guess that the sediments of Puget Sound, which has 16 major and many minor rivers draining into it, are more terriginous, biogenous, hydrogenous, or cosmogenous? Explain.____________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ 2. Core Sample (2.1) By studying the sediments on the ocean floor, we can gather clues about what surface conditions were like at various times in the Earth's past when the sediments were deposited. Using those clues, we can try to reconstruct what might have happened during the Earth's past. As the particles pile up on the ocean floor, they begin to exert pressure on the sediments below. What do you think will happen to these sediments over time? Explain.__________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ (2.2) Below is a 6 m long core sample taken from the deep sea floor off Vancouver Island. The core sample shows fine grained mud layers alternating with sandier layers. The black layer at the bottom of the core is mainly volcanic ash (after Adams, 1990). What is the age of the oldest sediment found in this core sample?____________________ Oceanography 101 POST-LAB Saunders (2.3) How might you explain the dark layer at the bottom of the core sample? Be specific!_____ ___________________________________________________________________________ ___________________________________________________________________________ (2.4) How many alternating sand-mud layers do you count?______________________________ (2.5) How can you explain these alternating course, sandier layers with fine particle mud layers? (HINT: Note that this sample core was taken in a submarine canyon)___________________ ___________________________________________________________________________ ___________________________________________________________________________ ___________________________________________________________________________ Core sample site (2.6) Given the location of the core sample and its proximity to the Cascadia Subduction Zone, these alternating sandy-mud silt deposits are probably caused by megathrust earthquakes. A megathrust earthquake occurs where one tectonic plate is forced under (subducts) another. Oceanography 101 POST-LAB Saunders Due to the shallow dip of the plate boundary, these earthquakes are among the world's largest, with magnitudes (Mw) that can exceed 9.0. So how many megathrust earthquakes have we had in this region over the past 7770 years?______________________ (2.7) What might be the significance of the thickness of each layer?_______________________ ___________________________________________________________________________ ___________________________________________________________________________ 3. Hood Canal Bathymetry INTRODUCTION: If you haven’t heard the news lately, Hood Canal is in trouble. Large inputs of non-point and point source runoff and have lead to low oxygen environments especially in the deeper basins of Dabob Bay and Hoodsport. Let’s examine the bathymetry of Hood Canal to see if it can lend any clues as to why this particular part of Puget Sound is so impacted. (3.1) Obtain a map of Hood Canal. What is the scale on the map?_________________________ (3.2) What unit are the depth measurements?______________ (3.3) Obtain a straight edge and a pencil. Starting out near the opening of Hood Canal (near Admiralty Inlet) draw a light pencil line down the center of the canal using a straight edge, changing direction as the canal varies. Continue drawing a center line the entire length of Hood Canal all the way to Lynch Cove. How many nautical miles long was your line?_________ ______________________________________________________________________________ (3.4) If you were to divide your line into 30 increments, how many nautical miles would each increment be?__________________________________________________________________ Fathoms (3.5) Using the graph chart below, plot the bathymetry of Hood Canal along your line with a 30 increment setting (i.e. divide your line into 30 equal points and plot each point with the depth in fathoms). surface Oceanography 101 0 POST-LAB 10 Saunders 20 30 Increments Along Transect (3.6) Describe the overall shape of Hood Canal’s bathymetry.____________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ (3.7) What is the origin of the Hood Canal Basin (i.e. how did it form?)____________________ ______________________________________________________________________________ (3.8) Are there any features of Hood Canal’s bathymetry that your group can see that might influence its circulation? Explain.__________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ (3.9) Locate on your bathymetric drawing of Hood Canal a inlet named Dabob Bay. This area has been in the news recently as a place in trouble because of pollution and nutrient runoff from the surrounding farmlands and urban areas. Is there anything that you can see from its bathymetry that might indicate it has a particular susceptibility to these problems? Explain. ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________