Research Corner
View a complete listing of Scientific Equipment on board Sailing School Vessels Corwith
Cramer and Robert
C. Seamans.
Download
Scientific Equipment Brochure PDF (1.4 MG)
Students Collect CTD Data for Themselves and Oceanographic Community
With today’s availability of satellite-based seamless global sea-surface temperature measurements, it can be hard to appreciate the much less glamorous tools in the oceanographer’s toolbox. Yet our understanding of the oceans improved radically during the pre-satellite days of the last century.
- Students of S-191 deploying the rosette water sampler. On the job are first assistant scientist Sarah Piwinski and students Ben Schellenpfeffer and Claudette Baisden.
At the center of this improvement was a class of instruments that gave researchers access to vertical profiles of the temperature and salinity characteristics of the oceans. These tools remain just as necessary today, and onboard any research ship today you’ll find a collection of conductivity-temperature-depth profilers, or CTDs. What’s at stake? Well, the global climate, for example. Ocean circulation and global climate are closely linked, with many deep-ocean features playing a key role in shaping climate fluctuations. Repeated measurements of water temperatures deep below the ocean surface are necessary to understand how, for example, the deep ocean conveyor works. The conveyor is a heat exchange mechanism between the equator and polar regions, incorporating both surface currents and deep-sea flow. Other research applications of CTD’s with a lot of current interest include the El Ninõ/Southern Oscillation in the Pacific, and the North Atlantic Oscillation in the North Atlantic.
- On station, deploying a CTD in the Caribbean during C-184. Scientist Meg Estapa helps student Stephen Kerrigan.
In the fall of 1988, SEA added two Seabird Electronics’ Seacat 19 CTD profilers to the suites of sampling equipment carried aboard the SSV Westward and the SSV Corwith Cramer. These instruments were cutting-edge technology at the time, and are now ubiquitous in oceanographic research. Sixteen years and five instruments later, undergraduate researchers aboard the Cramer still sample the waters off Cape Cod, in the Sargasso Sea, and throughout the Caribbean using Seabird’s CTD profilers. Cramer’s three-year-old sister ship, the SSV Robert C. Seamans, works along the North American west coast, across the equatorial Pacific to French Polynesia, and northeast to Hawaii and the Pacific Northwest. On average, one SEA class will collect 23 CTD casts during its sea component. With two vessels sailing ten semesters a year, this has resulted in the accumulation of a huge (and growing) CTD dataset, consisting of 2,560 casts to date. Furthermore, cruise tracks remain the same year after year. This has allowed SEA’s students to collect CTD data from the same Atlantic regions over 15 years; the Pacific dataset is now three years long and growing rapidly. In the last two years, in-situ fluorometers have further enhanced the sampling capabilities of the CTDs on the Cramer and Seamans, allowing measurements of primary productivity with every cast.
- The geographical coverage of SEA's CTD sampling.
While these CTD cast files have been stored on SEA’s data servers for well over a decade, recent years have seen a leap in the quality and amount of electronic data coming in from the vessels’ shipboard ADCP, flow-through, and sub-bottom sonar systems. The need for an organizational framework for the new data has spurred a concurrent effort to index and publish SEA’s older data, which is unique in that it comes from often-undersampled areas, and consists of repeated measurements made over many years. A major part of this objective was achieved in the fall of 2004 with the compilation, indexing, and quality control of SEA’s past CTD data.
- Temperature profiles across equatorial Pacific during March 2003 (top) and April 2004 (bottom). Notice how the depth at which the most abrupt temperature change occurs has shifted deeper by up to 50 meters in 2004. These are changes that occur between non-El Ninõ years, and may help explain how severe a subsequent ENSO event might become.
Ocean Data View (ODV) was the software environment chosen for this CTD database. ODV is a data management and graphing program that is tailored for use with oceanographic data. Datasets created in ODV are platform-independent, and its flexible sorting and plotting tools have led to its increasingly widespread use in the larger oceanographic community. For several years now, students on SEA’s vessels have also used ODV as a way to visualize physical and chemical oceanographic data. Therefore, it is an efficient way to share the data with outside researchers as well as to incorporate the archive into undergraduate research projects at SEA. The built-in quality-control tools in ODV also made it an easy software environment in which to build and standardize a new collection.
So what have we been seeing? Some recent student research projects at SEA have used time-series data from the CTD archive to take a closer look at the effects of ENSO (El Ninõ/Southern Oscillation) in the Pacific and the NAO (North Atlantic Oscillation) in the Atlantic. Specific examples include interannual comparisons of the equatorial Pacific, right in the thick of the waters most affected by El Ninõ. It turns out that even during quiet, non-ENSO years, there are substantial changes in the temperature and salinity of these waters. All of this information contributes to a better understanding of the role of these waters in the global climate during non-Enso years.
External links:
- Sea-Bird Electronics, Inc - Precision Oceanographic Instruments
- "A Chilling Possibility"
Science@NASA article - "Ocean "Conveyor Belt" Sustains Sea Life, Study Says"
National Geographic Article - eWOCE - Electronic Atlas of WOCE Data
- What is an El Niņo?
National Oceanic and Atmospheric Administration (NOAA)
