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
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
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.
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.