Paleowave

Sediment Traps and Plankton Tows

A very pretty Cocodrie sunset with the R/V Pelican.

Better late than never I suppose, but I wanted to document our short research cruise aboard the R/V Point Sur that happened early last month. It was another routine sediment trap operation, but this one really stood out because we happened to see some really cool critters at sea!

As usual, the northern Gulf of Mexico sediment trap crew (Eric Tappa from the University of South Carolina, Julie Richey and Caitlin Reynolds from the USGS, myself, and another helping hand from Michael Lis, an undergraduate student from UT Austin working with me) made our way down to LUMCON at Cocodrie, Louisiana and boarded the R/V Pelican to start our transit to the sediment trap mooring site. However, things did not go as planned (as is common in the field) and our overnight transit was halted short, as we had already turned back towards port after leaving it only some hours before! It turned out that there were some serious engine problems on the ship which entailed something we could not afford - delays. Luckily, as we were sulking around LUMCON taking an in-depth look at their impressive library, the R/V Point Sur came to our rescue and their crew graciously agreed to charter our operation. 

Relief as the sediment trap comes up to the surface. Picture credit: Michael Lis.

Relief as the sediment trap comes up to the surface. Picture credit: Michael Lis.

This time, apart from sediment trap redeployment operations, we had an additional exciting task: using the plankton tow. A plankton tow is a vital tool used to sample plankton that floats freely in the surface ocean. It is, in essence, a giant net with a fine mesh that we can trawl around and look at what comes up. We intended to sample some plankton at the sediment trap site. In any case, here’s a picture collage of some of the amazing creatures we were lucky enough to catch in our plankton tow:

I'm really excited about the upcoming science from this research trip. Hopefully, we can find some interesting results! Until my next voyage, I will certainly miss being out at sea!

Another Cruise to the Northern Gulf of Mexico

The RV Point Sur, docked at Gulfport, MS. Photo credit: Natasha (processed by me)

The RV Point Sur, docked at Gulfport, MS. Photo credit: Natasha (processed by me)

As another autumn rolled by, it was time for another research cruise into the northern Gulf of Mexico for sediment trap researchAs I've blogged before, we collaborate with the USGS St. Petersburg Marine Science Center and try to help out with their long-running sediment trap program whenever we can. The sediment trap is a device placed underwater between the sea surface and seafloor that captures pelagic sedimentation (any biological/sedimentological material produced above it, that drifts into the device and gets 'trapped'). The trap has several cups where one cup is open at any time and collects material for two-to-four weeks, after which it closes and another cup is opened. Every six to ten months (depending on how it is programmed), we have to go out to where the trap is moored, retrieve it by releasing its anchor, collect all the previous samples, perform routine maintenance, and redeploy the trap with new cups.

The last sediment trap cruise I was on (March '15) proved to be quite an ill-fated mission: the trap failed to come up to the surface after the signal was sent to release its anchor (after several tries)! This not only meant that the device was lost, either tangled up at the bottom of the ocean somewhere or drifted off into some foreign land (most likely the latter), but that our last 10 months of samples were lost! Such is the mercurial nature of observational field research.

Luckily, USGS scientists Julie Richey and Caitlin Reynolds managed to procure a new sediment trap! The purpose of this mid-November trip was to deploy the new sediment trap in the same location as the last one. Our motley crew, apart from the usual suspects of myself, JulieCaitlin, and the illustrious Eric Tappa from USC, included Eric's student Chris, and graduate students Natasha and Allison from our lab. We were to sail, as usual, on the RV Pelican, out of LUMCON at Cocodrie, Louisiana. However, weather had other plans for us.

Port of Gulfport

Port of Gulfport

Gulfport Sunset.

Gulfport Sunset.

As is the case with field work, rigid plans solidified months ago, can vaporize instantly: due to weather, the RV Pelican would be severely delayed in coming back to Cocodrie such that our schedule (flights et al) couldn't be accommodated. Instead we had to go to Gulfport, MS to board the RV Point Sur - an equally capable vessel (if not more - it had just been to Antarctica some time ago!) On the way back though, to catch our flights, we would be dropped back in Cocodrie.

This being the case, we set sail around 5PM on the 18th of November from Gulfport. Coincidentally, on the flight from Austin to Dallas, I was seated (by random chance) next to chemical oceanographer Jessica Fitzsimmons, who had also sailed on the Point Sur! From Dallas, Natasha, Allison, and I took a flight to NOLA, from where we drove out to Gulfport. Though the weather in Gulfport was dreary the entire day, not really helping the city's rough look, the clouds paved way for a brilliant sunset as we made our ~22 hr journey to the trap location.

Eric Tappa with the new sediment trap. Credit: Julie Richey

Eric Tappa with the new sediment trap. Credit: Julie Richey

Caitlin, Chris, and I inspecting the sediment trap prior to deployment. Credit: Eric Tappa

Caitlin, Chris, and I inspecting the sediment trap prior to deployment. Credit: Eric Tappa

Deploying the trap is not the most tedious job out at sea. However, rough weather can complicate things, and every step you take has to be an extremely careful one. This being the case, Eric, who's had plenty of experience with these conditions and instruments, guided us (and the crew) through a safe and successful deployment. All of us watched for the two buoys to plop down beneath the sea-surface, but the 10-12 ft of swell and the intermittent rain prevented us from identifying the exact moment.

Sailing on top of a warm-core eddy, as seen by the sea-surface height map (left) and the sea-surface temperature map (right). Hot stuff!Source: CCAR 

Sailing on top of a warm-core eddy, as seen by the sea-surface height map (left) and the sea-surface temperature map (right). Hot stuff!Source: CCAR 

Generally, when we were at site, we also make measurements about the salinity, temperature, and oxygen content of the seawater with a CTD, that also collects waters at different depths. In this process, we realized that we were actually atop a warm-core eddy! This was quite exciting, as it was my first time (I study these systems) being in one, and accordingly, the water temperature was a sizzling 27ºC in November. 

The scientific party.

The scientific party.

Amidst a modest yet uncomfortable swell, we made it back to Cocodrie early Friday morning, after spending our second night on the Point Sur. The next cruise to collect all these biweekly-to-monthly cup samples that will be collected by the new sediment trap will be in May. Hopefully, we will get to do some good science with these samples!