The bow of the Rubber Duck plowed through the frothy white cap of another wave and drenched us with sheets of salty water as we motored closer to the southern-most point of land in the United States; South Point on the island of Hawaii. The two 90 horse-power motors pushed us doggedly upwind toward our next survey site. With a trusty oceanographic instrument known as a CTD onboard, we were ready to collect some valuable data about the water column.
CTD — an acronym for Conductivity, Temperature, and Depth — is a tool for measuring a variety of physical properties of sea water. Although a large version of this instrument can be found on our research ship, the Hi’ialakai, we make use of a smaller version of this classic oceanographic instrument when conducting operations from our small boat, the Rubber Duck. When we arrive at a survey site in our small boat, we lower a handheld CTD over the side of the boat to collect data about the water column. The protective steal cage of the CTD houses a variety of instruments that collect data continuously as the device descends through the water column. This data includes a detailed account of water temperature, salinity, dissolved oxygen, and turbidity. This information helps us to better understand how ocean water characteristics are distributed across space and time around the islands we visit. Shallow water CTD data, coupled with results of actual water samples that are collected at CTD survey sites, helps paint a picture of major influences on reef life, such as transport of warm or cold water, nutrients, and possibly organisms from one region to another.
The view from below as a CTD is lowered over the side of the Rubber Duck by Oceanographer Oliver Vetter. NOAA Photo by N. Pomeroy
With our CTD full of detailed oceanographic data, we secured it to the console of the Rubber Duck and began our transit to the next survey site.
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