Just another day at the office - Sail along with our researchers on the Atlantic

Curious about the daily activities of a scientist during fieldwork? In this blog, we follow two of our scientists during their BEYΩND expedition on the research vessel Pelagia. Olivier Sulpis and Anne Kruijt do research on so called ‘marine snow’. Sail with them, learn about their research and get an insight into their life on board.

Read the blog by Anne Kruijt.

Blog Olivier Sulpis – March 2nd, 2023

It has been two weeks and a half since we have left Cape Town, and we are now a few days away from Cape Verde. In all that time, we have sailed across 50 degrees of latitude, visited many biomes, spotted crowds of dolphins, flying fish and whales. We have sailed over many underwater valleys and mountains, trenches, and seamounts, yet we could see none of them, as all around us was nothing but flat, blue water. The sky and weather evolution has been hard to miss though. The first week, in the summer of the southern hemisphere, was characterized by bright blue skies and warm weather. As we got closer to low latitudes, the air became more humid and the heat harder to bear. Hours after we crossed the equator, we encountered pouring rain, and the next few days were spent covered by gigantic cumulonimbus clouds. We are now back to the northern hemisphere, back to winter.

Sky over the equatorial Atlantic

During all that time, besides the water, plankton, and sediment sampling operations that regularly took place, some unusual science activities took place in one of the Pelagia’s lab. We have been setting up a new kind of experiment meant to simulate the fall of marine snow, which can be thought of as the shower of biogenic material free-falling from the ocean surface to the seafloor.

I am grateful to the captain and all the crew for giving me the opportunity to be part of this expedition, for their curiosity and interest, and for always being so helpful when we needed it

Dr. Olivier Sulpis
Biologist Robin van Dijk from Groningen University picking the perfect candidate for the marine snow experiments, from all the plankton caught in the nets

Most of the marine snow is composed of carcasses, seashells, algae, that sink to the seafloor after the death of organisms living at the ocean surface. There are even some living animals that can be part of marine snow. For instance, there are species of sea snails that cannot swim and spend their whole life attached to air bubbles at the very surface of the ocean. In a moment of inattention, they eventually let go of these bubble rafts and inevitably start sinking to the seafloor. In the ocean, pressure increases about one atmosphere for every 10 meters of water depth. Most human beings would not survive a few tens of meters below the ocean surface. Yet, even at the deep seafloor, most of which is located at depths where pressure is about 500 times that of the atmosphere, life is abundant. The deep ocean is home to a myriad of unknown microbes adapted to those high pressures that feed on marine snow. Only a small fraction of organic marine snow escapes decomposition and becomes up buried in sediments of the seafloor. High pressures of the deep ocean are also causing the dissolution of hard marine snow particles such as seashells.

The high-pressure reactor, containing seawater and marine snow particles under a pressure of 500 atmospheres

It is extremely complicated to collect marine snow from the sea because these deep sea environments are hard to reach, because existing devices to sample marine snow are subject to well-known collection bias, and because retrieved organisms would burst upon depressurization. Instead, we have chosen an alternative approach: simulating the free fall of marine snow particles in the laboratory, using a new reactor in which seawater and marine snow particles collected from a plankton net can be placed and monitored under pressures of up to 500 atmospheres. This allows microbes living in marine snow to do their thing, at the high pressures to which they are acclimated. Pressure within the reactor filled with seawater and marine snow is gradually increased, at a pace that reproduces the marine snow sinking rates of the particles we put in, and we stand there observing what is going on.  

Interpreting all the data we gathered will have to wait, as now is the time for cleaning up the labs, packing up our nets, high-pressure reactors, and other devices, to prepare the ship for the next science expedition. I am grateful to the captain and all the crew for giving me the opportunity to be part of this expedition, for their curiosity and interest, and for always being so helpful when we needed it. 

A piece of the seafloor, taken with a monocorer at more than 4 km below the sea surface