Visualizing the Data

Visualizing the BATS Data
One of the best ways to begin to understand the BATS data is to examine them visually. Scientists use three main types of plots to visualize oceanographic data: depth profiles, time-series plots, and contour plots.

Depth Profiles
A depth profile is a graph that shows how a certain water property changes with depth. For instance, a depth profile of sea water temperature shows how that property changes from the sea surface to the sea floor. Depth profiles are usually drawn with the depth along the vertical axis (y-axis). The sea surface (0 meters) is plotted at the top of the y axis, and the deepest water (e.g., 4500 meters) at the bottom. The vertical axis labels are typically on the left side of the graph. The horizontal axis (x-axis) shows the range of values of the property being graphed. The x axis is usually located on the top of the graph, with higher values to the right. In a temperature depth profile, the units on the x axis show sea water temperature in degrees Celsius. Individual points on a depth profile provide two pieces of information: the depth of the water, and the value of the property being examined.

An OceanExplorer depth profile showing sea water temperatures
measured at the BATS site during August 1989.

Time Series Plots
A time series plot is a graph that shows how the measured value of some parameter changes through time. Time series plots are used to help visualize and analyze many aspects of human endeavor, from changes in the stock market, to the profit-and-loss history of a company, or fluctuations in air temperature on a daily, monthly, or yearly basis. Analysis of time series plots is crucial to understanding the rate and patterns of global environmental change.

Oceanographic time series show how ocean-water properties change through time. For instance, the following time series of monthly sea surface temperatures from the BATS site shows how temperatures in the upper 10 meters of the Sargasso Sea fluctuated from month to month and season to season between 1988 and 1997. This time series was created using OceanExplorer.

Contour Plots
When a time series plot is combined with a depth profile, the result is a contour plot like those shown below. BATS scientists use these contour plots to help visualize how data parameters change through time throughout the water column in the Sargasso Sea.


Ocean temperature at BATS changes both with time and depth. In the winter, storms help mix deep, cold water (blues) to the surface (the white line shows the depth of winter mixing). This water is then warmed by the sun, and forms a very "stable" warm water layer (yellows and reds) at the surface. As you can see, the difference in temperature in the surface waters ranges from 18 to 29 degrees Celsius.	Nitrate and Phosphate are two essential nutrients for plant growth in the sea. At BATS, concentrations of these two nutrients are generally low. Plants take up nutrients in the surface waters, so that they are almost undetectable. However, in winter, storms mix deep, cold, nutrient-rich water into the surface waters. This can be seen well in the nitrate graph.

Primary production is the rate of plant photosynthesis. At BATS, primary production tends to be highest in the springtime when there are nutrients present in the surface waters from winter mixing, and increased day length and strength of sunlight. Just as wildflowers bloom every spring in the mountains on land, there is a spring bloom of phytoplankton in the sea! This spring bloom is also reflected in the amount of Chlorophyll a pigments in the water.	Bacteria are the primary decomposers in the sea (on land it is the fungi) and are very important in marine nutrient cycles. Many bacteria use dissolved organic material to grow. Much of this is produced by phytoplankton in the surface waters. Thus we tend to get higher numbers of bacteria where there are more plants.