2 July 2013
72 ° 32 North and 44 ° 06 East.
This is the spot where the scientists on the Tara Oceans Polar Circle expedition decided to shut down the engines, and begin the first long sampling station of the Murmansk-Dudinka leg. Here water masses coming from the Atlantic enter the Barents Sea from the south, and meet masses of polar water. In this area defined as a ‘polar front’, scientists and sailors plan to perform 22 samplings in 2 consecutive days. A scientific marathon which will be repeated 3 more times during the month of navigation between the two Russian ports.
7:30 Monday morning on Tara’s deck – the crew is ready to begin the first long station since leaving Murmansk.The sun is shining as if to encourage the troops, and a stowaway – a Guillemot – cousin of the small Arctic penguin, has joined the group. As usual, the rosette equipped with its CTD, is the first to take the plunge. Its 10 Niskin bottles descend into the 7.5° C water to bring back the first samples that will define the profile of the water column.
“We found a DCM, a Deep Chlorophyll Max -– the depth where there’s the most chlorophyll, therefore phytoplankton, about 40 meters below the surface. We expected to find a deeper, less-pronounced DCM because of the Atlantic water masses and the late summer season, but I think we’re still seeing the influence of coastal waters,” says Stéphane Pesant, co-chief scientist on this leg.
“The samples quickly reveal that the environment is not very productive here, at least at this time of year. “There aren’t many diatoms*, but I saw a lot of dinoflagellates** and they’re really beautiful!” says Joannie, emerging from the dry lab. Dinoflagellates are mixotrophic microorganisms that can survive with or without light. Diatoms, in contrast, can not live without light or nitrates.
Maneuvers continue on deck. The rosette, several nets including the manta (a special net for collecting plastic) and also the high-flow pump, all take turns exploring the ocean depths, providing constant work for the scientific team. Each sample must be filtered and put into a vial labeled with a bar code, then stored in the refrigerator or freezer.
The scientific marathon continues. The advantage of sampling in the Arctic at this time of year is that we don’t have to do night watch! The sun constantly illuminates the sea, and plankton doesn’t make daily vertical migrations. It’s 7:30 p.m. Monday night on Tara’s deck, and sampling is still in full swing. This long station will be followed by daily short stations. By comparing the different sampling stations, the scientists can determine to what degree the first long station was representative of Atlantic waters.
The objective of this leg between Murmansk and Dudinka is to collect samples in the different water masses characteristic of the Barents Sea and the Kara Sea. Having sampled the water masses from the Atlantic, south of the polar front, the scientists will conduct a second long station, north of the polar front, plunging their instruments in the Arctic waters free of ice.
“This second station will allow us to compare the planktonic ecosystems to the south and north of the polar front,” says Stéphane Pesant. Then Tara will reach the edge of the ice pack, hoping to arrive before the ice retreats. In these high latitudes, the scientists want to study the ecosystems associated with sea ice. The fourth and final station before arriving at Dudinka will be influenced by the fresh waters of the Enisej, nearly 12 nautical miles from the coast.
A vast program awaits us, with increasingly difficult conditions. For now only the presence of the Guillemot tells the Tara team that we’re really in the Arctic.
Anna Deniaud Garcia & Stéphane Pesant
* Unicellular micro-algae surrounded by a single shell made of silicon.
** Unicellular micro-algae with 2 flagella, a cellulose casing, and chloroplasts enabling them to carry out photosynthesis.