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Port Susan CTD and Dissolved Oxygen Data Due: April 20th, 2010 This exercise will demonstrate a simple method for calibrating the Sea-Bird SBE 43 dissolved oxygen sensor and how to apply this to CTD data. You will plot vertical profiles of potential temperature, salinity, and dissolved oxygen from four stations in Port Susan to understand the flushing of this basin. There are three steps to the plotting exercise: 1) merging the oxygen concentration measured by shipboard titrations with the bottle data from the CTD sensors to determine a linear correction for the SBE 43 data; 2) apply this correction to the CTD data from 4 stations in Port Susan to plot temperature, salinity, and dissolved oxygen data from multiple stations on a single plot; 3) written interpretation of your data. Two CollectIt dropboxes will be open for you Excel spreadsheets and for your written assignment. Merging the titration data with the CTD data: 1. You will need to cut and paste the calculated dissolved oxygen concentrations from the Excel spreadsheet “Titration_data.xls” to the “BottleData.xls” numbers. In addition to the .CNV files you worked with last week, the Sea-Bird software generates .ROS (rosette) files with the average instrumental readings when a bottle is tripped. Someone has already cut and pasted these data into a spreadsheet for you. The key to matching the titration data to the bottle data is the unique Station and Bottle (or Niskin) pair. Triplicate samples were titrated at Station 15 - you will need to calculate a mean concentration to cut and paste. 2. Before you can plot the titration DO vs. Sbeox data, you will need to convert the units. After the units are the same, you can plot the data and fit a straight line (and find R^2). The assumption should be that the titration values are accurate and the equation of the line will permit you to correct the SBE 43 oxygen to match the titration data. Applying the linear equation to the CTD data and plotting the data: 3. The equation for this line can now be applied to the continuous profiles of CTD data in the .asc (ascii) files. There are .asc and .hdr (header) files for each station. Your next task is to plot calibrated dissolved oxygen vs depth for all 4 stations on a single figure. The naming convention for the CTD files is MMDDYYSSSCC, where M is month, D is Day, Y is Year, S is a 3-digit station number, and C is the cast number. The information on columns and station location are in the .hdr file. Note that the Sea- Bird convention is to begin numbering columns with 0 (i.e, name 0 = prDM: Pressure, Digiquartz [db] means that the first column in the .asc file is pressure measured by a Digiquartz transducer in decibars). You can create a single spreadsheet or workbook by importing these files into Excel. Apply the equation of the line from step #2 to the sbeox0Mm/Kg: Oxygen, SBE 43 [umol/Kg] column to create a new column for calibrated dissolved oxygen concentrations. Make a chart that has the calibrated dissolved oxygen concentrations plotted against depth for each station. You may use different colored lines (no symbols) to distinguish the 4 stations. 4. Prepare similar plots for salinity vs depth and potential temperature vs. depth. I would suggest using the same color for the properties at each station. Written Assignment: You should assemble the three plots into a 3-paneled plot with panel a) salinity vs depth b) potential temperature vs depth and c) calibrated dissolved oxygen vs. depth. The figure should be formatted for L&O with a well-written figure caption. There are two parts to your assignment - a results section and a discussion section. In the results section, describe the vertical and horizontal distribution of properties in Port Susan during April 2009. Station 13 is on the deep sill and the other stations are sequential to the north. Positions can be found in the .hdr files. In the discussion section, you should compare and contrast these property distributions with those reported by Cannon (1975). Cannon describes a bottom water flushing event in Port Susan. Can you see evidence of a similar event in the 2010 data? Submit your assignment via CollectIt. There will two drop boxes - one for the written assignment and one for the excel spreadsheets. They will be considered late after 1:30 PM on April 20th.
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