Gulf of Mexico expedition blog: Understanding the role of delta systems on carbon cycling

The mighty Mississippi river and its Atchafalaya branch bring in vast amounts of sediment material and dissolved nutrients into the northern Gulf of Mexico. By doing so, these rivers have an enormous impact on the chemistry and biology in the water and on the seafloor in this region. The GoM2020 cruise, a close collaboration between Utrecht University, NESSC and NIOZ, aims to improve our understanding of the role of such large delta systems on cycling of carbon and important nutrients as nitrogen and phosphorus. Join expedition leader Dr Francien Peterse, Dr Francesca Sangiorgi, Yord Yedema, and Wesley Plugge from Utrecht University and the other scientific crew on their journey on RV Pelagia from 1-21 February by following this blog!

1 February: Transit to Texas

Scientific crew in front of RV Pelagia. Credit: Rick Hennekam

We’re on the move. Yesterday we left from the Bahamas towards the southeastern coast of Texas, starting our adventure to study the water column and sediment archive in the northern Gulf of Mexico (GoM). From the Texas coast, we will gradually move in eastern direction along the coast of Louisiana to visit study sites with depths ranging from 20 meters to 3200 meters. Onboard are nine scientists, who heavily rely on the support provided by eleven dedicated crew members and two technical engineers on Research Vessel (R/V) Pelagia. Everyone is very eager to start, yet, as the ship moves with a speed of about 9 to 10 knots (around 17 km/h) it will take four more days before we arrive at the first station. We have to be patient…

Scientific crew. Credit: Rick Hennekam

The Mississippi/Atchafalaya delta, and thus this expedition, has a lot to offer from a scientific point of view. Not only will we study the burial of organic carbon in delta sediments  – a potential sink for the greenhouse gas CO2 – we will also study the microbial community and the impact and extent of pollution instigated by the blowout of BP’s Deepwater Horizon, the largest marine oil spill in history. Last but not least, our research will focus on the processes that lead to oxygen concentrations less than 2 mg per liter water (or hypoxia); concentrations that cause large-scale mortality in animals like shrimps and fish. Since the 1970s, the area of hypoxia has increased at alarming rates in this delta, reaching maximum values of about 20.000 km2, which isclose to half of the surface area of The Netherlands. The massive increase in nutrients introduced in the Mississippi watershed by humans is a key player to cause this expansion of oxygen deficiency. The GoM2020 cruise will focus on extending our knowledge on the cycling of nutrients within the water and the sediments and its association to deoxygenation.

Cruise plan meeting. Credit: Rick Hennekam

Our current pace with the ship should bring us at our first station on the 5 February – somewhat later than scheduled – where we will start our scientific sampling frenzy. Some setbacks were encountered before embarking on this expedition. Yet, from a ‘glass-half-full’ perspective, it is good that we encountered these before actually setting sail. Unfortunately, we had to exchange cooks, as some more important family matters occurred for our initial cook. Also, one of our fellow scientists (Yord) found out that a hand infection was worsening. After some minor surgery (all is well!), he needed to stay behind in Nassau in the Bahamas. The rumour is going around that Yord will still write the next blog from the hospital.

While waiting for arrival at our first station, the rest of the scientists are using their time by setting up the lab spaces, presenting scientific backgrounds and goals, discussing and updating the sampling plan (done!), and just existing. We have to be patient…

Rick Hennekam – Paleoceanographer at NIOZ

5 February: Before the mud - the diary of a long transit

Taking off on the RV Pelagia. Credit: Francien Peterse

We left Nassau in the Bahamas on January, 31st at 11 am. A brief and not too difficult calculation made us realize we had just started a very long transit: 1200 miles, 10 knots speed (10 miles per hour), 120 hours, exactly 5 days… 5 days? What can 9 scientists do on a boat during 5 days transit?

Each day on the R/V Pelagia is paced by breakfast at 7 am, lunch at 12.30 am, and dinner at 6 pm. Eating rituals are quick and efficient, eating is not quite seen as a pleasure when you are on a ship, although the food prepared by our cook HendrikJan is delicious. Eating is rather seen as a way of surviving. Each meal takes about 20 minutes, and the days (on transit) are very long.

But scientists are full of great ideas… so here is how we spent our time.

Day 1: the day went by quite quickly, sharing some ideas, getting acquainted to the ship and the life on board. The evenings after dinner are a great opportunity to share scientific background, projects, science plans, goals to be achieved with this expedition and beyond. Torbjörn, Geology professor at Tulane University, and Wesley, MSc-student Marine Sciences at Utrecht University, were the first on stage. Torbjörn talked about the Mississippi fluvial deltaic sediments and their high potential for carbon storage. Wesley introduced his project, a combination of palynology and lipid biomarker analyses to trace terrestrial organic molecules to the marine environment. The project uses surface sediment samples collected 2 years ago along a transect offshore the Atchafalaya river (branch of the Mississippi) during the NICO (Netherlands Initiative Changing Oceans) Leg 7 expedition.

Francien and Francesca sharing their office. Credit: Francien Peterse

Day 2: activity kept going. Reading papers, discussing sampling strategies, catching up with work left behind. A great opportunity to exchange ideas and talk about past, present and future science. Francien, organic geochemist at Utrecht University and I, palynologist at Utrecht University are happily sharing the office.

In the evening, Laura, a NESSC-researcher working at NIOZ, presented her PhD project on calcification of benthic foraminifers and her ultimate target to find a proxy for CO2 and pH. Zeynep, postdoc in organic geochemistry at NIOZ and sea-going expeditions expert, shared with us some results of the NICO Leg 7 expedition.

Day 3: the day was “easily” filled: seasickness kept us busy. Someone (me) slept 22 hours, someone provided repeatedly fresh food for fish, all of us looking like zombies the day after. No pictures available of this day.

Day 4: as the sea calmed down, activity picked up. The day started with a coffee or a tea on the deck waiting for the sunrise. While Rick Hennekam, postdoc in paleoceanography at NIOZ, was trying to find a highly organic geochemistry-oriented paper interesting, Kristin, PhD at NIOZ, decided it was time to prepare the material for sampling, label bags and vials.

In the evening’s presentation round, Rick talked about the power of XRF scanning marine sediments and Kristin explained her research project on dynamics of hypoxic and anoxic environments and the complex incubation experiments she is setting up on board.

Day 5: Alena and Laura decided to take action and start prepping material for their sampling: endless writing codes on plastic bags, and bottles, while drinking Coca Cola to stay awake.

In the evening it was my turn to talk about primary production, eutrophication in coastal areas, Harmful Algal Blooms (HABs). I made a wish: reconstruct past HABs of Karenia brevis (the nasty dinoflagellates causing toxic blooms each year in the Gulf of Mexico). We shall see. Francien explained her goals and related challenges of tracing the terrestrial organic molecules into the marine sediments. To conclude the round of presentations, Alena, PhD candidate at NIOZ, presented her project on the characterization of microbial communities in marine sediments with a focus on Woeseiales.

We missed Yord, the youngest NESSC PhD candidate, who started his PhD at Utrecht University, as his project is tightly related to the expedition.

The bell rings, time for lunch!

Francesca Sangiorgi - palynologist at Utrecht University

6 February: First day of sampling - A muddy experience

The CTD and multicorer are waiting. Credit: Francien Peterse

Before I begin, let me establish 3 things:

1. I’m a microbiologist by training.

2. I have two things I really need to be clean: my kitchen and the lab I work in, everything else comes second.

3. I’m the only microbiologist on board.

The day starts with anticipation. Finally we will have something do to other than sit around and write blog entries or play card games, though the PIs did get proper work done. So after a quick breakfast we all rush outside at 7:45 am to find that the nice temperature of 20  ͦC that we had the first week, has overnight changed to 7  ͦC. So we all rush back inside to get more layers on top the existing ones. The station where we now are is the first on the transect along the plum of the Atchafalaya river along the coast of Louisiana. The depth at this point is around 20 metres, so sampling should be quick. The CTD starts going down and within 5 minutes it’s back up with the first water samples. While the crew was working, all the scientists were standing in the way - a common start as I was told. Now we go on to the truly exciting part: the multicore!

We enthusiastically have 12 tubes loaded, and the preset weight on top. We let it go down, it does what it’s designed for, we get it up… and we see a bunch of basically empty tubes. All the excitement from earlier is gone. So we have the crew load on more weight and drop it again. This time we have cores of 5-10 cm, not good enough. We put on maximum weight and decrease the number of tubes to 8 – down and up again: We finally have acceptable samples! The excitement is back.

Francien playing with mud. Credit: Alena di Primio

My excitement is quickly turned into something else (confusion) as Kristin, Zeynep, and Francien start mashing the sediment which dropped out from the cores between their fingers and smell it. As I was later told Torbjӧrn even tasted it! Then they start analyzing the grain size and color with the others and I’m standing there not quite able to grasp how they suddenly went from sophisticated scientists to people playing with mud. But the work continues and we start getting into it. I help with operating the hydraulic core slicer and together with Laura, Francesca, and Wesley we get everything neatly packed. The second smaller shock comes when in order to clean spatulas and rings, they use water instead of ethanol! My world is at this point being turned upside down. I was taught that ethanol is your best friend when it comes to cleaning material, and here they go and use water. At one point it’s also clearly not clean anymore as the sediments turn it muddy, and they still keep on using it! How is this supposed to result in good clean samples? Everything has got to be contaminated at this point, right?

During lunch we arrive at the second station and it starts all over again. 8 tubes, 20 metres, full weight, CTD down and up, multicore down and up, scientists are playing with mud again, I’m still confounded. We start slicing and proceed with a minor interruption of Zeynep purposefully putting a mud smudge on my cheek which I did not appreciate tremendously, if I’m being honest. After cleaning my face we still finish with some spare time before dinner.

At this point the wet lab is a mess in my eyes, so I do what I must and clean up. This state of dirt would never be acceptable in a microbiology lab. Never! I wipe the tools and working space with ethanol, put everything where it belongs and make sure that I have everything prepared for the next station. Things are somewhat sterile again and I’m happy. My happiness isn’t allowed to last for too long though, as the third station approaches and the muddy mess ensues once more. Once more the routine, once more playing with mud, once more I clean up after, and finally somewhere around 9 in the evening we call it a day.

The next morning I wake up, accept my fate, and start playing with mud with the others (though with smaller quantities and less enthusiasm).

Alena di Primio - PhD candidate at NIOZ

8 February: (Almost) coming home

Sunrise over calm waters with an offshore drilling rig in the background. Credit: Torbjörn Törnqvist

Our sampling campaign started for real on a chilly Thursday morning off Galveston, Texas, and then took us eastward along the Louisiana coast. This region is not only home to me; over the past few decades I have spent numerous field campaigns in the expansive wetlands right across the shoreline. Naturally, I am eagerly looking for land, especially after the fresh blast of Canadian air eventually brought us chilly but calm winter weather, including generous sunshine. We enjoy some of the clearest views of the horizon that one can get in this part of the world. But all I see is ocean, peppered with oil & gas platforms.

When we get closer to the mouth of the Atchafalaya River, one of the target areas of the expedition, I go up to the bridge to borrow binoculars. I try to take advantage of the height to spot the most striking topographic features that are out there along this part of the coast: a line of salt domes known as “The Five Islands.” They are like small mountains in this otherwise nearly flat terrain. One of them is Avery Island, where Tabasco comes from. But no matter how hard I peek, there is nothing in sight. Granted, we are tens of kilometers from the shoreline so it’s quite a distance, but still… This is when I’m reminded that we are tracking one of the lowest-lying coastal zones in the world, with most of the land just a few decimeters above sea level. As a result, this coast is also among the most vulnerable: it loses wetlands at a rate of about one football field every 100 minutes.

When I was asked a few months ago if I wanted to join this cruise, I didn’t need much time to think about it. It was clear that this expedition contained a lot of elements that intersected with and complemented my interests. My initial response was whether it would be possible to join for just one week (perhaps I imagined some sort of spectacular drop-off and pick-up by helicopter?). Thankfully, that was not an option – you either participate for real or you don’t.

Over time, my research interests have slowly crept more and more toward the ocean. One of my most recent papers came out in Ocean Science, so perhaps getting out on an oceanographic cruise was inevitable. Over the past few years, the work within my group at Tulane University in New Orleans has started to consider organic carbon fluxes and burial, in and around the Mississippi Delta. All of this work has focused on areas that are currently land, while we know that a large portion of the carbon that flows down the river ends up in the ocean.

As a result, it wasn’t hard for me to get excited about this cruise, since studying the sources, pathways, and burial of organic carbon in Gulf of Mexico sediments is one of its main objectives. Along the lengthy transport path that is the Mississippi River, some of the carbon may be returned to the atmosphere as carbon dioxide and contribute to further global warming and sea-level rise. These are potentially life or death issues for areas like coastal Louisiana that we need to better understand.

One of the great things about expeditions like this one is the amount of time available to talk science and kick around new ideas, in ways that are just different from the rushed skype meetings and hectic mega-conferences that seem to dominate the lives of scientists these days. There is no better way for new collaborations to take root. We are a multidisciplinary science team, strikingly young in age (not counting myself!), but with nine of us we are also easily outnumbered by a crew of 13. The Pelagia crew is a phenomenal group of people, many of them with intriguing life stories filled with adventure

Chef Hendrik (middle) surrounded by some very happy customers. Credit: Torbjörn Törnqvist

Our masterful cook Hendrikjan Lokhorst, who flew in last minute from his home base in Athens to join this expedition, is treating us to new culinary surprises every day – greatly surpassing my expectations that looked more like “scheepsbeschuit” and dried meat. For example, it didn’t occur to me that I would enjoy an appetizer of Dutch shrimp (topped off with a particularly delicious sauce) while sailing among Louisiana’s Gulf shrimp. So one lesson learned: if you want to lose weight, these research cruises are dangerous!

Between all the busy work, there are still enough moments to take in spectacular sunsets, watch pelicans sailing by, and follow dolphin families jumping and playing around our ship. It’s an odd feeling that while I write this and enjoy the peaceful scenery, Mardi Gras is ramping up back home in New Orleans, with the legendary Krewe de Vieux parade about to roll – only a few hours away.

Torbjörn Törnqvist - Quaternary scientist/Geology professor at Tulane University

19 February: Looking back

Back in Nassau. Credit: Francien Peterse

When I learned last November that I had the chance to take the RV Pelagia to the Gulf of Mexico, I had no idea that everything would work out as well as it did. Normally, it takes a lot of time to plan and prepare for a research expedition – permit requests need to be submitted 6 months in advance, for example. But here we prove: if really you want something to happen, you can make it happen.

Our cruise plan was based on the program that we initially made for the NICO expedition in 2018. At that time, we could not carry out most of the program due to endless waiting for the arrival of a container with equipment, a really long transit to the Gulf, and bad weather once we finally started sampling.

This time around I was determined to visit all the sites on the program and collect as much material as we could store on the ship. I even had the marine facilities at NIOZ send extra freezers and fridges over for more storage space. In the meantime we also had obtained funding for a PhD project on ‘The fate of terrestrial organic carbon in the marine realm’, designed for the samples that we would collect during this expedition, from NESSC. The pressure was on!

Sure enough, we encountered the first hiccups in Nassau, with a last minute crew change and the hospitalization of Yord (the (un)lucky PhD student on this project) for a bad infection in his hand for which he had to fly home, followed by a day of sea sickness of practically all scientific participants once we finally left port.

Shaking the bottles of rose Bengal water. Credit: Francien Peterse

But as soon as we fully entered the Gulf, the sea calmed down, the sun came out, and luck was on our side again. This appeared to be one of those magical expeditions where everything seems to work out: we visited all stations according to the plan, collected all samples on our wish lists, piston cores came up full, and even managed to squeeze in two additional sites that came up during our scientific discussions while slicing the multicores. In total, we have visited 21 stations, deployed the multicorer 37 times, retrieved a total of 45.91 metres of piston core, collected about 4000 sediment samples, filled over 250 bottles with rose Bengal to stain living benthic foraminifera, and labeled over 4500 vials for porewater collection. Clearly enough material to write a PhD thesis or two!

Our success was first of all made possible by the crew of the Pelagia, who were always ready to deploy whatever instrument we desired, or to sail the extra mile(s) for a new sample location. The smooth operation of the scientific sampling machine was the second ingredient of our success: Zeynep and Alena took care of the multicorer as soon as it got on deck, Francesca, Torbjörn, Laura, Wesley, and Alena formed the core slicing team (with cries of victory when the hydraulic slicer with 0.1 mm scale was stopped at the exact sampling depth), Rick and Zeynep managed the piston cores, Laura shook each of the bottles filled with rose Bengal for at least 1 minute, and Kristin was hidden away in her container on the back deck to fill all the nicely labeled vials with pore water under the anoxic conditions in the glove bag.

Barry, the winner of the GoM2020 Salinity Award. Credit: Fancien Peterse

In between sampling we had fun with our spontaneous ‘guess-the-salinity-at-the-next-station’ competition. The close vicinity of our sample sites to the Atchafalaya and Mississippi Rivers ensured that the salinity of the surface water was different at every station. The crew also participated, and became more and more competitive at each station. In the end, the competition was between Barry, representing the deck crew, and scientists Francesca and Rick. After (almost correctly) estimating the salinity of a salt water mixture (24 psu) that we had prepared in the kitchen, Barry turned out to be the well-deserved winner of the one and only GoM2020 Salinity Award.

I have very much enjoyed this cruise, and I hope that the data will turn out as nice as collecting the samples was.

Francien Peterse - chief scientist and Organic Geochemist at Utrecht University

Cleaning the multicorer after the last station. Credit: Francien Peterse