My name is Austin Todd, and I am a first-year M.S. student in physical oceanography at FSU. This is actually my fifth year at FSU, where I completed a B.S. in meteorology and mathematics, and I am currently working under Dr. Eric Chassignet in ocean modeling in the Gulf of Mexico.
On this I6S cruise, I am part of the CTD (conductivity, temperature, and depth) operations group. We basically run most of the operations of the CTD, including preparation, deployment, monitoring, and recovery of the CTD sampling apparatus. Our group is responsible for obtaining water samples from all depths of the ocean selected for sampling at each station.
The sampling scheme varies slightly depending on the depth at each station, especially if we have to go deeper. Investigators usually cover areas near the surface with a higher density of samples, as that’s where conductivity and temperature gradients are sharpest.
Our CTD sampling process will deviate from usual scheme
Thorsten informed me that our particular sampling mode is set up a bit differently from most CLIVAR cruises; we are sampling in a bit higher density near the bottom. The main reason for this is that Thorsten (Professor Thorsten Dittmar teaching us a class aboard this cruise) and Kevin (Professor Kevin Speer, our Chief Scientist) are both interested in Antarctic Bottom Water (AABW). Soon you'll see individual profiles of our FSU faculty leaders during our cruise.
There can be differences in the AABW resulting from differing modes of formation. 1) The less salty bottom water forms from very cold, therefore very dense, fresh water left by melting sea ice. 2) The saltier bottom water forms as a product of the freezing process of sea ice. The freezing of seawater produces ice that is nearly fresh, as its salts or brines are ejected into underlying waters. That salt-enriched water is then denser than surrounding waters.
Waters reaching a critical density, either by extreme cooling or by salt enrichment via injected brines, will sink as a result to form AABW. Kevin and Thorsten would like to see the formation-derived differences in these two AABW masses if the existing sea ice situation will let us go far enough up onto the Antarctic continental shelf.
Gearing up to sample
To prepare the CTD, we make sure that all of the bottles on the rosette are cocked open, and that the other instruments on the housing are ready to go. There is also a Lowered Acoustic Doppler Current Profiler (LADCP) on the CTD housing that measures ocean currents at depths as the CTD is lowered. We are responsible for turning on and downloading collected data with this instrument.
When the CTD is in the water, we sit at a desk looking at about 12 different screens with all sorts of information from imagery of the estimated bottom depth, to live video feeds of the deck, to ship position, ADCP plots, the CTD raw data output, and information from the winch control---the really long cable that connects the CTD to the electronics on board. We take a planned scheme of depths for which water samples are required, and we make sure that a bottle at each of these water depths is filled.
This is a very important job, because it is our duty to make sure bottles are filled with water from each different depth. Because different water masses reside at different depths in the ocean, it is essential that we do our job to collect data at the right levels. The chemists can then collect well-distributed samples from each water column.
Furthermore, with the raw data from the CTD, we can determine what the temperature, salinity, and oxygen levels are at different depths. From this data, we can determine where these various water masses are. In this section of the world, knowing the location of water masses is particularly important because the Southern Ocean is where water from all over the world meets.
FSU COAPS graduate student Austin Todd is very excited for his chance to sample dissolved inorganic carbon off the main Rosette. He is wearinf gloves to help lessen contamination potential.
Lastly, I wanted to add a bit about my other responsibilities. Aside from the direct CTD operations, I am also responsible for taking several water samples from the Niskin bottles on the rosette. Many different research groups compose CLIVAR, but not every group can send representatives to collect samples on every cruise. Therefore, the sampling is left to available members onboard, which happens to be our CTD operations group for I6S.
In total, we are responsible for taking samples for dissolved organic carbon (DOC), silicon isotopes, H2O18, salts, and nutrients. We do not actually analyze these samples, but simply take the water samples from the rosette. The salts and nutrients are analyzed onboard by the Oceanographic Data Facility (ODF) group from Scripps. The DOC, Si isotopes, and H2O18 samples are all saved and analyzed onshore.
Personal impressions of ship-board life
Being on a cruise is a very different experience from anything I've ever done. It is really fascinating that everyone here is focused on science 24 hours a day. It makes for a very productive environment. My bunk is in the bow of the ship, and being rocked to sleep every night is also completely different. I haven't gotten seasick yet, so that's definitely good.
The weather was really nice for the first week, but yesterday some weather came our way, bringing the clouds, winds and waves with it. I am working on a 12 midnight - 12 noon shift, and that is very different from my normal routine as well. I am happy as can be, though. I get to work outside, and see the sun rise every morning. Plus, the people onboard are really a pleasure to work with and to be around every day.