Wes Struble: Analysis of Water Samples, March 4, 2012

NOAA Teacher at Sea
Wes Struble
Aboard NOAA Ship Ronald H. Brown
February 15 – March 5, 2012

Mission: Western Boundary Time Series
Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas
Date: March 4, 2012

Weather Data from the Bridge

Position:30 deg 37 min North Latitude & 79 deg 29 min West Longitude
Windspeed: 30 knots
Wind Direction: North
Air Temperature: 14.1 deg C / 57.4 deg F
Water Temperature: 25.6 deg C / 78.4 deg F
Atm Pressure: 1007.2 mb
Water Depth:740 meters / 2428 feet
Cloud Cover: 85%
Cloud Type: Cumulonimbus and Stratus

Science/Technology Log:

In the previous log I described a CTD cast in detail from start to finish. Now that the CTD platform is on the deck of the Ron Brown the actual sampling process can begin. The CTD has a number of Niskin bottles holding a little more than 10 liters of water each. Water samples from each bottle must be collected and analyzed for various parameters which could include: Salinity, Oxygen content, Inorganic carbon, and others. On this cruise most of the CTD casts were sampled for both salinity and dissolved oxygen.

The first step in measuring salinity involves a careful rinsing of the sample bottles. After a standard three rinses, the bottle is filled and the depth from which the water was sampled is recorded for each bottle.

As a beautiful western Atlantic sunset falls on the Ron Brown another night of CTD's begins

I prepare a water sample for dissolved oxygen analysis after a CTD Cast at 2:00 am

The dissolved oxygen analysis lab station in one of the science labs on the Ron Brown

The full sample bottles are then either taken to the dissolved oxygen lab station or the Salinity lab station for analysis.

A close-up of the amperometric titration apparatus for analysis of dissolved oxygen in one of the science labs on the Ron Brown. A solution of Manganese Chloride and a combination of Sodium Hydroxide/Sodium Iodide is added to the water sample to sequester the oxygen and then when the temperature is stable the solution is amperometrically titrated with thiosulfate.

The Ron Brown off the starboard stern from the workboat

The "climate airlock" leading to the salinity analysis lab. The airlock helps keep the water samples under constant temperature and humidity conditions.

The two Autosals in the Salinity lab. These are precision instruments for measuring the salinity of seawater

A east-west cross-section across the eastern Atlantic Ocean. The eastern US coast is at left. The diagram illustrates north (reds)-south (blues) movement of the Antilles and Deep Western Boundary Current. Vertical scale in meters horizontal scale in 100,000 meter units (100 kilometers)