by Maxime Marin

Last year, I was asked by my supervisor Dr. Helen Phillips to participate in a voyage onboard the RV Investigator for a month during May, 2019. Having never been on a research cruise before, I realised that it was important for me to undergo such an experience and accepted the invitation.

The voyage was Australia’s main contribution to a large international effort: the second International Indian Ocean Expedition (IIOE 2). IIOE 2 is conducted from 2015-2020 by numerous countries in order to reveal new information on the Indian Ocean, especially looking at changes since the last expedition in the 1960s. Our mission onboard the RV-Investigator was to sample the 110E line from 40S to 10S and address four primary objectives:

  1. Quantification of multi-decadal, ecosystem-scale change from the 1960’s benchmark in the physical, chemical and biological properties of the water column along 110E;
  2. Characterization of the physical and biological sources of nitrogen to the region and their impacts on regional biogeochemistry and ecology (microbes and genomics);
  3. Determination of trophic relationships between nitrogen-fuelled primary production and zooplankton, including the larvae of mesopelagic fishes (food web);
  4. Relating field information on phytoplankton community composition, primary production and carbon export to bio-optical quantities derivable from satellite ocean colour radiometry.

To address those objectives, a team of 40 researchers from 18 institutions from all around the world set sail from Fremantle on May 14, 2019.

I was impressed by how big and comfortable the RV-Investigator was. It was evident that the ship was built to maximise scientific efficiency, with millions of dollar worth of equipment and machinery on the boat, meaning I was able to learn about almost every aspect of observational oceanography.

Photo: From left to right, Dr. Jessica Benthuysen (AIMS), Camille Grimaldi (UWA-AIMS), Dr. Helen Phillips (UTAS) and Maxime Marin (UTAS-CSIRO). Boarding onboard the RV Investigator in Fremantle.

I was part of the physical oceanography team, which was responsible for preparing, guiding, sampling and analysing conductivity, temperature and depth (CTD) measurements. More than 50 CTD profiles were taken during the trip, half of which were deep CTD, down to 5000m. Using a variety of other instruments attached to the CTD, we were able to collect high vertical resolution profiles over 20 stations, which gave us an idea of the vertical and horizontal structure of physical and biogeochemical conditions along the 110E line. Along with being responsible for the CTD measurements, our team also had to deploy NOAA and BoM drifters as well as Argo and deep-Argo floats. Data collected by such devices are very valuable, especially for model or satellite calibration (drifters) and measuring the ocean’s subsurface (Argo). Finally, I also got to use a unique instrument called a Vertical Microstructure Profiler (VMP), which allowed us to measure vertical mixing in the first 200m.

However, the Physical Oceanography team measurements were only a small part of sampling happening during the voyage. A multitude of nets were deployed every day, from the back deck or the side of the boat, with mesh size from millimetres to microns, sampling biodiversity from phytoplankton to fish. It was amazing to see first hand the amount of biodiversity there is in the middle of the ocean.

One of the many beautiful Indian Ocean sunsets Maxime experienced onboard the RV-Investigator

But the main part of the work onboard the vessel happened in the several labs available to scientists. Filtrations of water samples from the Niskin bottles went on 24/7 to measure the amount of nutrients, phytoplankton, bacteria etc… Once the samples were retrieved, scientists could store them in a -80°C freezer after using liquid nitrogen to instantly freeze them and conserve their properties. Data analysis onboard the RV-Investigator was trivial as the ship is equipped with satellite internet, computer rooms and its own local server where we could store and share data.

Life on the vessel was surprisingly comfortable. Although everyone must adapt to the inevitable slight rolling of the ship during the first week (some more than others; sea-sick pills helped), the weather was exceptionally good throughout the entirety of the trip. The facilities on the ship were amazing, including the very spacious sleeping quarters. Although we had to share them, roommates were usually on a opposite shift, meaning that we were alone in the room most of the time. When we were not busy doing science, we could enjoy delicious meals prepared onboard, buffet style, satisfying any different diet requirement. Once our bellies were full, we were able to rest in the three living rooms, watching movies, playing consoles, reading, or even playing darts or ping pong. For the more dedicated, the ship also has a gym.

A very valuable aspect of the trip was to meet and exchange science with other researchers from all over the world. This onboard collaboration extends after the trip, as data needs to be analysed and papers need to be written. Such a long time at sea can also forge friendships, and I was fortunate to meet incredible people without whom, undoubtedly, the voyage would not have been as easy.  However, the most memorable time of the trip happened everyday around 6pm.

Nothing beats a sunset in the middle of the ocean. Those moments made us realise how lucky we were to be oceanographers and have the opportunity to be part of such an amazing trip.