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Methodology

Science at Sea

The posts on oceanbites.org focus mostly on recently published scientific papers, and sometimes we don’t mention how the researchers got their data (it is often not the most entertaining part of the story). Sometimes it can seem like scientists just wave a wand and collect all their data! Unfortunately, real life is not like the world of Harry Potter- so how do scientists actually get to the end product of their research? First, they need to acquire their samples. For oceanographic research, many samples must come from (surprise, surprise) the ocean! This means researchers must collect water, rocks, or organisms they are interested in from the location in the ocean they are studying.

I just returned from a cruise aboard the R/V Endeavor , which is one of the National Science Foundation-owned vessels used for conducting scientific research. Scientists go on cruises to conduct all sorts of research (analyzing water chemistry, collecting different types of fishes, taking cores of ocean sediment, etc.) and those varied goals of research require different instruments. On this cruise, I had firsthand experience with a few common oceanographic instruments (as well as one brand new one!) that scientists use for conducting their research. Let’s take a look at how science is typically done on board a ship:

First things first – the days are long. Operating a ship is expensive and money doesn’t grow on trees, so every hour of ship time counts. Scientists must carefully plan which instruments can be deployed at specific times and make sure that samples are collected as efficiently as possible. For many scientists, this equates to working very long days (18+ in some cases!). So, guess you could say that one of the most important research instruments on a ship is the coffee pot!

The instrumentation: Scientists use a variety of tools to sample and collect data based on the needs of their research. My cruise focused on teaching us to use some of the basic instruments, which are summarized below.

Nets – Nets come in all sorts of shapes and sizes, and are made for with all sorts of different purposes (Figure 1). Nets can have varying mesh sizes, which are used to capture different organisms (think: you want to catch a bunch of big cod? Need a big mesh size. Want some plankton? Better use a much smaller mesh size).

Figure 1: Some of the different types of nets used for collecting samples. A) Large plankton net being deployed off the back of a research vessel (image from earthobservatory.nasa.gov). B) MOCNESS with multiple nets on a single frame (image from (www.gma.org). C) Isaacs-Kid Midwater trawl (image from www.hydrobios.de) and D) Bongo net- with two nets towed side by side (image from www.hydrobios.de).

Figure 1: Some of the different types of nets used for collecting samples. A) Large plankton net being deployed off the back of a research vessel (image from earthobservatory.nasa.gov). B) MOCNESS with multiple nets on a single frame (image from www.gma.org). C) Isaacs-Kid Midwater trawl (image from www.hydrobios.de) and D) Bongo net- with two nets towed side by side (image from www.hydrobios.de).

Some nets are controlled by onboard computers to close at a certain depth because in some cases, scientists only want to collect animals at a certain depth so they can be confident their samples are from the depth they care about. – Some nets are even fancier and include instruments to measure certain environmental conditions in the water (i.e. temperature) or have multiple nets all linked together on one frame to sample at multiple depths (MOCNESS, or multiple opening and closing net with environmental sensing system; Figure 1b). Scientists have to determine what type of organisms they want to collect and at what depths they need to sample in order to choose a proper net.

Figure 2: A) CTD package being deployed off the side of a research vessel (image from oceanexplorer.noaa.gov) B) scientist collecting water samples out of a Niskin bottle on the CTD (Image from www.schmidtocean.org).

Figure 2: A) CTD package being deployed off the side of a research vessel (image from oceanexplorer.noaa.gov) B) Scientist collecting water samples out of a Niskin bottle on the CTD (Image from www.schmidtocean.org).

CTD – (or Conductivity, Temperature, Depth Sensors; Figure 2). As the name suggests, this instrument senses salinity (measured via conductivity), temperature, and depth of the water. The CTD is attached to a large frame (called a rosette) which holds a bunch of water sampling bottles (called Niskin bottles). Occasionally, other probes are also attached to the rosette, such as oxygen or fluorescence meters. The instrument is deployed using one of the boat’s winches and is then lowered to the desired depth. As the instrument descends, CTD probes gather information about the physical and chemical properties of the water. Scientists can use these physical and chemical properties to determine where they would like to collect water samples. To do this, someone on board the ship tells the CTD to close one of the Niskin bottles, trapping water from that depth. The scientists can now move to a new depth, close another Niskin bottle, and continue until all samples have been taken. Once the instrument is pulled back onto the ship, scientists can collect the water samples from the different depths to use for their analyses.

Figure 3: The Wire Flyer developed by scientists at the University of Rhode Island’s Graduate School of Oceanography (image from gregory-designs.com).

Figure 3: The Wire Flyer developed by scientists at the University of Rhode Island’s Graduate School of Oceanography (image from gregory-designs.com).

The Wire Flyer – This is a relatively new instrument for oceanographic sampling (Figure 3). It was developed by scientists at the University of Rhode Island’s Graduate School of Oceanography. Dr. Chris Roman and some of his colleagues were on board testing out their device and making sure it was ready to take out for future data collection. See Chris Roman explain the concept behind his device in this video.

This device measures similar properties to the CTD. The difference is that, instead of descending to a depth once and sampling within that same horizontal profile like a CTD, the wire flyer is towed behind the boat, “flying” up and down on a wire- increasing the area sampled within the water column.

Figure 4: a yummy tie dye cake (image from http://birdonacake.blogspot.com/2012/02/rainbow-tie-dye-cake.html)

Figure 4: a yummy tie dye cake (image from http://birdonacake.blogspot.com/2012/02/rainbow-tie-dye-cake.html)

To give you an idea of why the wire flyer is different from other instruments, let’s take a more manageable example: You get one of these cool tie dye cakes for your birthday (Figure 4). You want to know which colors are where in the cake. To do this, you are given a single slice of the cake. You can see that the colors are stacked: red, yellow, green, blue, purple from top to bottom. But you have no idea if the colors are layered that way throughout the cake. To get a better idea you take another slice and find the layers are now red, orange, green, yellow, blue, purple – different from before. The more and more slices of cake you take, the clearer the picture you get about the composition of the whole cake.

Same with oceanographic testing – the CTD essentially takes a single piece of cake (one profile of the ocean), while the Wire Flyer is able to keep going back and grabbing more pieces to get a better picture of the actual composition of the ocean.

Conclusion:

A lot of hard work goes into gathering the samples needed to conduct research. Scientists use instruments like those explained here to collect the samples for their specific research project. The data collected from experiments at sea can be taken back to the lab, analyzed, and published in articles like the ones we share with you on oceanbites.org.

This cruise was sponsored by Rhode Island Teachers at Sea to teach Rhode Island grade school teachers about this scientific process. To see more about the cruise and to get the perspective from the teachers involved visit: http://www.gso.uri.edu/rieducatorscruise/ or watch this video the teachers put together, documenting their experience on board the R/V Endeavor.

Ashley Marranzino
I recently graduated with my MS from the University of Rhode Island. I specialize in studying fish biology/ecology, and deep-sea biology but love all things to do with marine biology.

Discussion

One Response to “Science at Sea”

  1. I was lucky enough to accompany some grad students aboard the RV Cap’n Bert recently, as they surveyed the bottom of Narragansett Bay. The story is on my blog, “Science and Nature for a Pie.”

    http://scienceandnatureforapie.com/what-lies-beneath-uri-surveys-rhode-island-waters/

    Posted by Hugh Markey | August 28, 2015, 8:02 pm

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