Russell sprays mud off the bottom of the Sea Bird after a successful profile has been completed.

As soon as it is up, the shroud is replaced on the delicate light sensor and the power switch is flipped to "off." After rinsing, it is brought on deck, connected to the computer, and the date is downloaded.

Examples of temperature profiles are presented here. Temperature is the primary controller of density in freshwaters like Lake Michigan. In winter, even coastal water is very cold. At left a March profile has temperature less than 2ºC (red line) from top to bottom. Note that the profile starts at a little deeper than 1m. This is because the instrument itself (pictured above) is more than a meter long. When the top is just in the water, the bottom, with several of the sensors, is close to 1 1/2m below the surface. Likewise, dissolved oxygen (blue line) is uniform with depth at nearly 14mg/L. The absence of vertical structure is evidence of complete mixing of the water column, and is especially common in shallow waters such as Green Can Reef.

As water warms, the solubility of gases like oxygen decreases. In May (left), the water at Green Can has warmed to 8ºC while dissolved oxygen has decreased to 12mg/L. Because this station is shallow (about 17m), little wind is required to mix it up during the late spring and early summer, keeping profiles uniform despite rising temperatures.

Even shallow stations can become strongly stratified, when surface water is much warmer than bottom water and density keeps the two physically separate. In September, we see an excellent example of this for Green Can Reef. Surface water (0-10m) had reached 21ºC while dissolved oxygen had decreased to about 8mg/L. At the depth of the temperature gradient, or thermocline, the temperature rapidly dropped to 12ºC with oxygen increasing in a mirror fashion to almost 11mg/L. Bottom water (13m and deeper) was again constant.

Deeper stations, like the 100m Fox Point station in offshore, open Lake Michigan demonstrate even more defined profiles of temperature and dissolved oxygen.

Related web links:
Sea-Bird Electronics SBE 25