From the depths of the Southern Ocean

Back in early February I was lucky enough to be on board the R.V Marion Dufresne sediment coring mission ACCLIMATE2. We sailed down to 53’S collecting sediment cores which will be used for palaeo-climate reconstruction.

Why is this important?

Around the Antarctic region, a powerful current known as the Antarctic Circumpolar Current (ACC) flows clockwise and achieves speeds of 100-150 Sv (hm3/s). In the surface waters, sharp temperature and salinity changes are present as we sail further south in the current, these are ‘Fronts’.

Onboard this Marion Dufresne mission we were able to cross over these ACC fronts.

Implications on climate

Sea Surface Temperatures consistently decreased as we left Durban between 27-20ºC until entering the ACC system where we experienced a sharp ~10ºC drop in the surface temperature in just 500 km. Once sailing within the ACC itself, the temperature changes were less pronounced but perfectly noticeable between fronts.

Through analysing the sediment cores we collected, we will be able to reconstruct ocean circulation changes and see rapid climate variations! These sediment cores really are key archives to the past!

For my study, I will be linking humid periods (which we can see clearly in the sediment core after we analyse it) with early modern human behaviour evolution! Our sediment core site is located near to some of the Southern Africa archaeological caves, which show evidence of our ancestors' rapid cultural changes and innovation within the past records.

I was lucky enough to go to Blombos Cave Archaeological Site in South Africa after the cruise where we were taken into the cave to see some evidence firsthand of our ancestors' cultural innovation skills

The Journey

Whilst landing in Durban, South Africa, we were able to appreciate South Africa and its diverse landscapes: green hills, covered with fields and forests, plateaus cut by different rivers over which towns and villages stretch as far as the eye can see. I think of how I'm finally in the Southern Hemisphere for the first time in my life!

The first things that strike you: the temperature (+/- 30 ° C) and humidity.

The journey through South Africa was short-lived as no sooner had we left the airport, we joined the Durban port customs service for an official exit from the country. We were then dropped off at the Marion Dufresne, the largest ship in the French oceanographic fleet. we were spoilt with all her amenities: sports equipment, comfortable cabins, a library, a bar, a dining room and excellent meals (table service included!).

Setting Sail

"It is 2 pm, and we are off! The Marion Dufresne sets sail, the swell comes to lift the ship as soon as it leaves the port. Already the sea is choppy and we need to find our sea legs!

We turned one last time to wave goodbye to Durban, where we return in 3 weeks. Now we head south to the first core drilling site!"

At 39°S we were cruising towards Site 3, situated near to another drill site. We were unable to core Site 1 or 2 so are all hopeful for Site 3 and have our fingers crossed! Sites 1 and 2 are situated under the influence of the strongest Western Boundary Current in the world- the Agulhas Current.

Marine sediments are valuable archives for reconstructing past climate and ocean variability, therefore it is important to select the appropriate site for coring. Before coring we carry out a Pre-Site Survey which helps generate images of the sea floor using Bathymetric surveys and Multi-beam Sonars and allows us to select the best location for collecting a sediment core. These surveys are necessary in order to find the safest location for the coring as we do not want to drill into hard rock and break the instruments. Also finding an area with a high sedimentation rate is advantageous for studying sediment cores extending further back in time, therefore avoiding gulleys and canyons which have likely been infilled with newer sediments rapidly is key. However, there are some limitations with multi beam bathymetry such as interference which is noise from unwanted sources. We also saw artefacts and multiples in the images from refractions, both of which make interpretation difficult and add to the struggle of finding the perfect site.

At 40°32.39 S, the Piston corer made contact with the seafloor sediment! However, what an eventful night we had! We arrived at our new station late last night and were all set to deploy the sediment corer. The crew were ready out on deck, the scientists were ready in the science room, but the machine however was not. It turns out there was a fault with the winch and the remote control so whilst that was getting fixed, we could not core. And yet, the crew worked super hard and have already managed to fix the fault!

Our current location is 49°15.53 S, 6°E, the waves have noticeably increased in size as we crossed the polar front and we head to station 5 which is situated at 52°S, 5°E. We have been working in shifts to get the samples scanned, photographed and stored. But enough of the science, let’s get down and muddy with what we have been up to in our spare time.

Throughout the day when not on shift, most of us work in the science room. We also keep on lookout for wildlife, we saw a baby Macaroni Penguin yesterday and lots of sea birds from albatross to petrels. However, as soon as the clock strikes 18:45 we head to the bar for a well-deserved beverage. The bar tender Bruno serves a variety of very well priced drinks. For dinner, we usually have a starter, main course, cheese board and fruit selection.

Once we are comfortably full (sometimes slightly uncomfortable) we begin the evening entertainment. This is usually a good old card game. We split up testing our luck in different games, some of us teaching and others learning how to play. Most importantly, it is our down time so time to chill, have a good laugh and usually share a few bottles of vin. The most popular game by far is ‘Wie is de Ezel?’ translated as Where is the Donkey? A card game we have invested a lot of evenings in, laughing, keeping track of scores and mainly shouting Donkey at the top of our lungs!

Success! Despite the powerful Agulhas Current, the last two core samples were collected. The journey back to Durban was a great opportunity to rest and enjoy the last days and last hours at sea.

Jean-Paul Vandelrinden gave us an interesting lecture on his research work concerning isolated communities and their reactions to climate change. It was also an opportunity for us to discuss the popular culture surrounding science, a subject much more complex than what one might think at first glance. It is of utmost importance for us to promote climate science but it is also one of the major challenges of this century. The fight against global warming skeptics will only halt if the transmission of scientific knowledge to the general public improves.

A birthday like no other

I was lucky enough to celebrate my 23rd birthday onboard, whilst we were sailing back to Durban! It was actually a big occasion to celebrate that day as we had finished drilling and it was the end of the research campaign so we had a BBQ on deck, with the warm winds blowing and the Agulhas Current travelling against us. What an amazing experience, and one I will not forget!