Chapter Three

Typical distributions of water characteristics

Example 4C: Vertical Distribution of Water Properties Along South-to-North Transects

DPO Text References:

DPO 4.2.5 Deep water temperature and potential temperature
DPO 4.3.3 Intermediate depth salinity
DPO 4.3.4 Deep water salinity
DPO 4.4.3 Depth distribution of potential density
DPO 4.5 Dissolved Oxygen
DPO 4.6 Nutrients and other tracers

We will now use three custom-made data files to examine the vertical distribution of water properties along south-to-north transects through the eastern Atlantic, central Pacific, and eastern Indian Oceans. The three data files needed are:

WOA09_A16.joa (Antarctic to Iceland)
WOA09_P16.joa (Antarctic to Kodiak)
WOA09_I8S_I9N.joa (Antarctica to Bangladesh)

The WOA09 in each data file name reminds you that these transects were made (are subsets taken from) the World Ocean Atlas 2009 annual one-degree data set.

The A16, P16, and I8S_I9N in the data file names indicate that the path chosen for each transect follows the track of an oceanographic section occupied during the World Ocean Circulation Experiment (WOCE) during the 1990's.


NOTE:

You can find data and information about oceanographic expeditions along these and other lines at http://cchdo.ucsd.edu



In Examples for a later DPO chapter, we will compare data from actual oceanographic expeditions along each of these WOCE lines with WOA averaged ocean data.

Here, however, the WOA versions of the WOCE transects handily provide a generally accurate depiction of:

  • The basic vertical, south-to-north configuration of global ocean seawater property distributions
  • Their basin-to-basin and equator-to-high-latitude variations


JOA's vertical section plotting tools are versatile and complex. To streamline the plot-generation interface, we have provided the ability to get a usable plot with the fewest feasible number of user-made choices:

  • Select a parameter to plot on a vertical section
  • Select a surface onto which to interpolate the data (more about this below)
  • Choose a color bar to color/contour the section data (or approve JOA's automatic color/contour choice, if presented to you)
  • Click on Plot (or OK) and, voila, you get a usable vertical section.

Now for the details.

Files that may be needed or created in this example:

  • WOA09_A16.joa
  • WOA09_P16.joa
  • WOA09_I8S_I9N.joa

Exercise 4C-01: Vertical Sections - Making a Contour Map Plot

  • Start JOA
  • File → Open…WOA09_A16.joa

    The Data Window should look approximately like this:

    target

    FIG 4c-01 Java OceanAtlas Data Window

  • PlotsContour…

    This will bring up the JOA Contour Plot dialog box:

    target

    FIG 4c-02 The Primary Contours panel of the Contour Plot dialog box

  • We show this dialog box as it appeared after we have made four choices:
    • We selected a Parameter to plot - we selected TEMP (= Temperature).
    • We selected the PRES-0-6000_srf.xml Interpolation Surface onto which to interpolate the temperature data (see below). This is a pre-chosen (by Swift) set of 64 pressure surfaces that provide an oceanographically-useful interpolated version of typical open ocean profile data.
    • We selected (actually, JOA auto-chose it for us and we accepted it) the TEMP-global_cbr.xml Colorbar to color/contour the interpolated data.
    • We selected Latitude under Offset

    All other choices in the Contour Plot dialog box shown are JOA defaults (see below for explanations of each of these). These three choices - plus the defaults - are sufficient for JOA to interpolate the data and draw a section. In fact, if you click Plot (or OK) in the Contour Plot dialog box at this point, JOA will draw this solid color contoured section:

    target

    FIG 4c-03 Contour plot


NOTE:

Recall that in the left-to-right convention used in these DPO JOA Examples, south (the Weddell Sea, off Antarctica) is on the left and the Icelandic continental slope is on the right.


The bathymetric and oceanographic features on this plot look similar to those in DPO Figure 4.10(a), as well they should, since you have just plotted multi-year averaged data along the same path as the single-cruise data used by the DPO authors. With JOA, however, it is easy to explore the data.

We suggest that users of the DPO JOA Examples now become familiar with JOA Contour Plot Options via the supplied link, before continuing to plot additional vertical sections for the DPO JOA Examples. [As always, see the JOA User Guide for in-depth discussion and details.]

At this point in your DPO JOA Examples experience, you should be ready to explore ocean-to-ocean differences in some of the most-frequently measured seawater properties.

The following data files, which we supply, will allow you to plot WOA05 time-averaged sections of temperature, salinity, dissolved oxygen, nitrate, phosphate, and silicate from the Atlantic, Pacific, and Indian Oceans, respectively:

WOA09_A16.joa (Antarctic to Iceland)
WOA09_P16.joa (Antarctic to Kodiak Island)
WOA09_I8S_I9N.joa (Antarctica to Bangladesh)

The WOA09 averaged profiles from these were chosen to follow the tracks of the WOCE A16, P16, and I8S/I9N sections shown in DPO Chapter 4.

If you have sufficient display area for your computer, you can open each of the data files at once in JOA (using JOA's Open… command under JOA's File menu three separate times), resulting in three JOA Data Windows, i.e., one for each data file.

NOTE:

To plot from a specific data set when you have multiple Data Windows open, you must have either its Data Window or any plot window made from that data set as the current (“top most”) window on your computer.

The JOA Windows menu shows every open JOA window in an easy-to-understand format. Using the Windows menu can help reduce confusion when multiple data files are open in JOA, each with its own plots.

Exercise 4C-02: Vertical Sections - Examining Contour Map Plots

  • From each of the three WOA09 data files, make contoured vertical sections to match the DPO Chapter 4 figures of:
    • temperature
    • salinity
    • sigma-0
    • sigma-4
    • silicate
    • oxygen
    • nitrate
  • Compare the South-to-North and vertical distributions of each parameter in each of the three principal ocean basins:
    • Use the x-axis scale function of the Axes scales page of the Contour Plot dialog box to set the same x-axis scale for all three sections
    • Also adjust the y-axes to be the same

    We show the three salinity sections below aligned at the Equator:

    target

    FIG 4c-07 Three salinity sections

    NOTE:

    Remember, you can click the mouse pointer on any location on any section, and the JOA browsing dot will jump to the closest data location to that spot.

    Meanwhile the JOA Data Window will show the data at that point, and the browsing spot on other JOA plots from that data set will jump to that data point on each plot. This linking of the JOA browsing mechanism is useful in exploring data.

  • Examine each of the section trios with an eye to features which are similar in each of the oceans, and features which differ.

  • Examine:

    In similar-looking features, in which ocean and/or hemisphere is each most well developed (most extreme)?

    Consider, also, that all three sections reach into the Southern Ocean, which is a circumpolar feature.

    You will find some interesting differences in water properties between the Atlantic and Pacific Oceans in particular. For example, in the salinity sections above, which are colored/contoured with the same JOA color bar, it is obvious that the North Atlantic Ocean is significantly saltier than the North Pacific Ocean.

    The DPO text will discuss this in later chapters, but this exercise provides you an opportunity to begin to familiarize yourself with typical distributions of commonly-measured seawater properties. You may find comparing the oxygen and silicate sections between the three major oceans intriguing.

Later on in the DPO JOA Examples we will plot original data from recent expeditions along the same tracks.

Copyright © 2011 Elsevier Inc. All rights reserved.
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