Student Connection

October 14, 1999  The TOWNSEND CROMWELL got underway from Honolulu on October 6 to begin a month long reef restoration cruise within the Northwest Hawaiian Islands National Wildlife Refuge. The objective of the cruise is to survey the fringing reefs around Lisianski Atoll and Pearl and Hermes Reef to quantify, and remove fishing net debris. Fishing net from areas north of the islands gets transported by wind and currents to the reefs were it tangles on shallow coral. The net then becomes an entrapment hazard to the endangered Hawaiian Monk seal which lives and breeds on the small islands throughout the northwest Hawaiian Island chain. Scientists monitoring the seal populations on the islands have observed seals tangled in net debris. This cruise will be a cooperative venture between the NOAA Ship TOWNSEND CROMWELL, the National Marine Fisheries Service Honolulu Laboratory, and the U.S. Coast Guard Cutter WALNUT. During the TOWNSEND CROMWELL's five day transit from Honolulu to Lisianski Island we conducted seven CTD casts along the major island banks. A CTD cast is an instrument that is lowered over the side of the ship which measures (C)onductivity, (T)emperature and (D)epth. Conductivity is related to salinity - so two basic properties of seawater can be measured with a CTD: salinity and temperature. Additional instruments can be added to the CTD package including flourometers and dissolved oxygen sensors. The CTD provides the physical oceanographer with the basic tools to understand currents and nutrient transport. This information is then used to understand biological properties of ocean waters such as primary productivity and larval transport.

A simpler instrument called an XBT (which stands for Expendable Bathythermograph), is also deployed off the TOWNSEND CROMWELL. This instrument consists of a lead weighted thermister attached to a thin copper wire. The lead thermister is dropped out of a launcher which contains a spool of wire and is connected to a computer. The thermister drops through the water column and constantly measures temperature. Depth is calculated by knowing the descent rate of the lead weight. When the weight reaches 760 meters the wire is parted and the measurement complete. The result is a temperature depth profile. The TOWNSEND CROMWELL routinely deploys an XBT every 20 miles while transiting along the Hawaiian Island chain.

Lieutenant Brian Parker has left the ship for a new assignment at a NOAA National Marine Fisheries Service laboratory. All of us here on the ship wish him the best of luck and thank him for doing an outstanding job with the website. The ship's new Operations Officer is Lieutenant Nathan Hill who will be working closely with the scientists in carrying out the TOWNSEND CROMWELL's missions.

Other cruise write-ups for TC-99-10

• October 14
• October 26
• November 01

Last modified October 15, 1999