The Arctic Ocean is changing, rapidly. Sea ice concentrations and ice extent are decreasing, the ocean and atmosphere are warming, fresh water discharges are increasing and stratification, mixing and circulation regimes are altering. All these changes impact the Arctic Oceans ecosystem, from the sea surface to the sea floor.
Longer and more expansive open water periods influence the timing of phytoplankton blooms which are important for sustaining life, from the tiny zooplankton throughout the water column to the sediment dwellers at the seafloor, right up to the whales and seals at the top of the food chain. Changes in the light and nutrient regimes have consequences for the amount and quality of particulate and dissolved organic matter, the cycling of nutrients in the water and sediments, and consequently the biodiversity of life that can be supported. The migration and grazing of zooplankton, behaviors that transfer huge quantities of carbon into the ocean interior, will also be affected.
I was lucky enough to head north this summer to the Barents Sea (the bit between Svalbard and Norway) with a team of 29 scientists, all of us funded by NERC’s Changing Arctic Ocean Programme (www.changing-arctic-ocean.ac.uk), to start collecting data that will help us understand the impact of climate change on Arctic ecosystems. This will ultimately inform our conservation and management strategies of polar regions.
We loaded the RRS James Clark Ross in Southampton with an impressive array of kit and instrumentation ready to collect, preserve, filter, sieve, incubate and analyse huge quantities of water, sediment and fauna. A keen subset of the team stayed onboard while we made our way north to Tromso. We spent our time setting up the labs, preparing our equipment, finding our sea legs and adjusting ourselves to eating a cooked breakfast, a two-course lunch and a three-course dinner every day (not that anyone complained). We crossed the Arctic Circle (66° 33′ N) on a sunny summer evening standing on the back deck in shorts and t-shirts. Not necessarily what you’d expect from an ‘Arctic’ cruise.
We collected the rest of the science team by boat transfer in a beautiful fjord just outside Tromso and within a few hours were at our first station and ready for science. We had 32 days to collect all our samples and to push as far north into the ice as we could.
The main means of collecting water was by lowering a frame of instrumentation (measuring temperature, salinity, oxygen concentration, light….) and twenty-four 20 L bottles that can be closed remotely at any depth from a computer on the ship. The deepest bottle we fired was at 3.5 km below the sea surface where the water temperature was below 0°C. The high pressure and high salt content of the water keeps it from freezing. During the expedition we collected over 20,000 L of water in this way. Most of it was taken into the ship’s laboratories where it was analysed for its nutrient and oxygen content, the amount of organic material present and its composition, the numbers and types of phytoplankton (marine algae) living in it, and for the isotopic signatures of different chemical compounds. This not only tells you something about the water masses present but can also indicate changes at the base of the food chain, changes that could resonate through the trophic levels to the top predators. The water, and more importantly the phytoplankton in it, was also used in primary production incubation experiments where the rates of carbon fixation were calculated, a process that is central to the marine biological carbon pump.
For one particular experiment, we could not collect enough water from the bottles alone. Instead we lowered a set of high volume pumps, fitted with special filter paper to collect particulate organic material from the surface water. In total over 29,000 L of water and all the particles within it (plus a few jelly fish that got too close) was filtered. That’s about the same amount of water you would use if you had a bath every day for a year.
Each day at noon and midnight we went fishing for zooplankton – tiny animals that feed on phytoplankton. A net was lowered down to 200 m and anything caught in it flushed into a container at the bottom. Once back onboard thousands of individual animals were picked out under a microscope (by hand) and they will be used to help us understand what factors, such as nutrient variability, shape the base of the food chain, and what the zooplankton community structure is across the Arctic.
In much the same way as we needed large volumes of water, we also needed vast quantities of sediment to investigate the fauna living within it and the geochemical processes sustaining this life. We took with us a selection of different coring and trawling equipment: box corers to bring onboard 0.5 m2 x 40 cm deep slices of sediment; a multi-corer comprising up to 12 tubes that would penetrate 40 cm into the seafloor and recover intact cores of sediment and the water above it; and an Agassiz trawl, a sledge towed along the bottom collecting animals living on or just beneath the seafloor.
Before blindly attempting to drive almost 1 ton of steel box corer into the seafloor, we sent down an underwater video camera to make sure we were above soft sediment and not hard rock. This also provided stunning live imagery of the larger animals living at the bottom. Arctic cod, brittle stars and basket stars were particular crowd pleasers. In total 600 photographs of the Arctic seabed were taken in depths of up to 1000 m.
Once we were satisfied that our coring equipment would not be damaged we launched into an intensive period of coring and trawling. For an oceanographer that had not been exposed to much seafloor work this was a real eye opener. Never would I have listed a shovel and supersized piece of plywood with rope handles as essential pieces of science kit, but when you need to drag large quantities of mud across the deck and pass it through a series of sieves being enthusiastically shaken and hosed down in freezing cold water, you can’t do without them. All this sieving helped sort out the various sizes of animals living in the sediment, from those larger than 1 cm across, to organisms that were only 63µm. The smallest of these tiny worms and crustaceans live within the spaces between individual grains of sand and mud and can only be seen under a microscope.
In addition to all the ship based sampling, we deployed a marine glider. These autonomous underwater vehicles carry scientific sensors and are capable of surviving at sea for several months and travelling many hundreds of kilometers. After some rigorous ballast and satellite communications testing we deployed a glider carrying temperature, salinity, pressure, chlorophyll, oxygen and light sensors. It spent two weeks making its way north towards the ice edge continually diving between the surface and 200 m depth. It revealed in a level of detail not possible with traditional ship based measurements how the properties of the water change as you move further into the Arctic.
We entered the ice to the east of Svalbard 12 days into the cruise. We were instantly greeted by a family of three polar bears that wandered past us on the search for food. Over the next two weeks we saw a total of 6 bears, including a few brave individuals who came within a few meters of the ship. Day or night, everyone stopped working and rushed to the foredeck to enjoy the experience.
Wildlife away from the ice zone was not in short supply either. A lucky few had a close encounter with breaching hump-backs, and there were plenty of Fin whales, Killer whales and Pilot whales to be spotted. We caught sight of a shy walrus, but he preferred to avoid the cameras and kept himself hidden behind the pack ice.
Working in the ice presented new challenges. Driven by the wind and ocean currents the ice pack was continually moving and the ship had to push its way slowly and carefully through it. Open water leads where the ship was able to deploy instrumentation opened and closed up again within hours. Predicting when the ice pack will loosen and samples can be collected isn’t an exact science. We used satellite images sent daily to the ship to help improve our chances of finding stable leads and the ships crew navigated locally using the ships radar. Thankfully perseverance and patience won through and everyone collected valuable data from the ice zone.
All four projects (ARISE, DIAPOD, ChAOS and Arctic PRIZE) are going back to the Arctic in 2018 to continue exploring this beautiful but rapidly changing environment. You can find out more about each project from their webpages and by following their Twitter feeds.
ARISE at https://arcticarise.wordpress.com and @project_ARISE
ChAOS at https://www.changing-arctic-ocean.ac.uk/project/chaos/ and @Arctic_Seafloor
Arctic PRIZE at www.changing-arctic-ocean.ac.uk/project/arctic-prize/
Written by Dr Jo Hopkins, a physical oceanographer at the National Oceanography Centre, Liverpool.