Oceanographers use a variety of tools to sample the water column. Each has its own benefits and limitations, from sample size, to depth rating and length of deployment, so if multiple instruments are used in conjunction with one other, the data can be looked at simultaneously for a more comprehensive understanding than any single system on its own. We are combining biological sampling, such as nets, with chemistry sampling, such as water samples, to piece together our best guess about what organisms are here, where in the water column they spend their time, and what the water chemistry is like at those depths.
Last night we reached our first real station at 2000 (8pm). Everything was planned out ahead of time to keep us on schedule!
|Schedule for our first station on our handy white board. It lasted 18 hours!|
Sometimes we use acronyms and nicknames to talk about the equipment. Below is a breakdown of what everything is and what the different instruments allow us to do:
CTD Rosette – Contains equipment for testing the biological, chemical, and physical properties of the water column. Holds 24 Niskin bottles that can collect water samples at different depths for ship-board chemical analysis. The bottles can be triggered from a computer in the lab. We have a VPR attached to the bottom of the rosette. VPR stands for Video Plankton Recorder. It takes photos at 20 frames per second and can give us an idea of what critters are living where in water column.
|CTD Rosette. The grey bottles are the Niskin bottles. The VPR is attached below the bottles and is bolted to the yellow frame.|
MOCNESS - Multiple Opening and Closing Net and Environmental Sensing System, a net system with 9 separate nets to allow sampling at discrete depths for zooplankton. Similar to the CTD, the nets can be triggered to close from a computer on the vessel.
|Deploying the MOCNESS, with its nine nets streaming behind it.|
HammarHead – Broadband Echosounder – This is a towed body (named after the WHOI engineer who designed it, Terry Hammar) that we send down to as much as 500 m in depth, carrying a broadband sonar system manufactured by Edgetech Inc. Broadband means that instead of a tone (single frequency) this system transmits a chirp with an increasing frequency pattern, which gives us more information about backscattering and the returns we get at different frequencies help us distinguish among the different sources of backscattering present (e.g., zooplankton from fish). The hammerhead has 6 transducers, each covering a different frequency band. The HammarHead is a towed body that we are deploying of the stern using an A frame winch system. Stability is important for acoustics, so it has fins on the sides and on the tail. The angles of these fins are adjustable. It picks up organisms like fish and zooplankton aggregations and also can detect physical characteristics like internal waves.
|Recovering the HammarHead towed body|
We also have an echosounder system attached to the ship that is constantly running:
Hull mounted split-beam multi-frequency echosounder – Attached to the bottom of our ship are 4 transducers manufactured by Hydroacoustic Technology Inc that we keep running continuously. This system functions similarly to the HammerHead but instead of spanning a continuous range of frequencies, it operates at 4 discrete frequencies. The advantage to mounting the transducers to the hull is that we can operate them while the vessel transits between our study stations at full speed (about 10 knots)