What lives in the deep sea and how do topographical features and ocean current systems affect the distribution of these marine organisms? The two-month cruise by MAR-ECO researchers aboard the new Norwegian research vessel, G.O. Sars, during the summer of 2004 hopes to find some answers to these questions.
By Elinor Bartle
Extreme conditions have made deep-sea exploration nearly as challenging as space exploration, and nearly as infrequent. The deep waters of the ocean, surprisingly, do not provide a uniform environment where marine organisms are uniformly distributed. They are affected by a number of topographical features that are much more dramatic than any found on land.
Among these, the mid-ocean ridges are some of the most impressive. These ridges have a complex topography involving submarine rises and seamounts, some of which actually rise above the ocean surface, as well as perpendicular-running canyons or fracture zones. These large-scale topographical features influence local and regional water circulation patterns. The surface circulation in the ocean is strongly influenced by winds and the Corioli’s forces of the spinning earth, whereas density effects due to temperature and salinity are more important for watermass movements at deeper levels.
The G.O. Sars sets sail from Bergen, Norway, 5 June, 2004. July 3-4, the ship will dock in Horta in the Azores. While the crew changes, there will be an open ship opportunity for interested members of the public. An exciting two-months will end in Bergen, 4 August, 2004. Details of the cruise and day-to-day highlights will be available on MAR-ECO’s ship-to-shore web site.
RV G.O. Sars
The cruise is divided into two one-month “legs”; the first travelling south along the mid-Atlantic Ridge from south of Iceland to the Azores, the second travelling north along the same route, but particularly concentrating in two subareas, one just north of the Azores (approx 43°N), the second near the Charlie-Gibbs Fracture Zone (approx 52°N).
South along the ridge to the Azores
Olav Rune Godø, research leader in Observational Methods at the Norwegian Institute of Marine Research, is the cruise leader for the first leg. The goal for this first leg is to obtain an overall quantitative assessment of the marine organisms present so as to generate an overview of this ecosystem that then can be studied in greater detail in a few strategic locations during the second leg. Researchers will focus on the marine communities in the water column within the top 3000m.
Olav Rune Godø
During the first leg the ship will conduct extensive acoustic survey activities. Acoustic information will be logged continuously from equipment mounted on the ship’s hull or on the specially designed drop keel. This keel helps reduce near-surface noise and damping effects during poor weather conditions. Data will also be collected from instrumentation on a towed array. Ship mounted acoustic data collecting only covers waters to depths of about 1000m. The towed array provides complementary data to depths of at least 2500m.
Acoustic data will be collected at five different frequencies (18, 38, 120, 200, and 400 kHz). These acoustic data can be resolved to provide biomass information at a species or population level. The scientific crew, consisting of 30 technology and marine biology specialists, will collaborate to interpret the information.
Currently eleven long stations and seven short stations are planned along the route. Their locations are based on previously gathered bathymetric and fishery information. The stations are defined as being long (20 hours) or short (16 hours) depending on the activities undertaken. Activities will include vertical profiling of salinity, temperature, video images of plankton, bioluminescence, and depth-stratified plankton sampling (multinets and macrozooplankton trawls), as well as a fishing with mid-water fish trawls.
The planned track of the RV G.O.Sars on Leg 1 of the 2004 MAR-ECO cruise
The stations criss-cross the ridge, the Charlie-Gibbs Fracture Zone and the sub-polar front waters, in order to generate as much data as possible about any potentially different environments and ecosystems. It will also be possible to undertake some opportunistic sampling along the way, should the acoustic data reveal unusual changes, or should the concentrations of marine mammals and birds reveal an interesting ecological location.
During the first leg, the ship will launch three independent, bottom-moored, monitoring instrument packages, including echosounders donated to MAR-ECO by the Norwegian marine technology company, KONGSBERG Simrad. A free-fall lander recording images of fish and other animals attracted to bait will also be deployed by the MAR-ECO partners from the University of Aberdeen (see feature article in this issue). This equipment will be picked up during the second leg. Godø wishes that it was possible to leave them out longer so that it was data could be recorded year-round in order to observe seasonal differences and trends. However, he concedes, that even a few weeks window of data is better than the short snap-shot a ship can take when it is on station.
Another unique dimension to the first leg is the presence of a Norwegian Broadcasting Corporation (NRK) film-crew and an artist, Ørnulf Opdahl. Opdahl is a well-known Norwegian artist with a special love of marine themes. According to Godø, it is important in science to ask the right questions, and he sees the addition of these “non-scientists” as an enrichment to the cruise with their potentially different viewpoints and ideas.
Detailed investigations in strategic locations
Odd Aksel Bergstad, the MAR-ECO project leader, is the cruise leader for the second leg. This leg’s goal is to undertake more in-depth studies of deep-water organisms in two particular areas. Eight days will be spent to cover five stations in an area north of the Azores (approx 43°N). Here the work will focus on potential animal community differences east and west of the mid-Atlantic Ridge. Stations will be positioned at approximately 2000 and 3000m on the east and west sides of the ridge, respectively, as well as one at 1000m at the top of the ridge.
Odd Aksel Bergstad
The ship will then spend twelve days and cover 10-12 stations near the Charlie-Gibbs Fracture Zone, where the work will focus on potential differences north and south of the zone (five stations each). These stations will also hopefully be north and south of the sub-polar front, which is generally located near this fracture zone. The remaining two stations will be taken in the deep waters of the Fracture Zone.
A station during the second leg will involve about 30 hours of continuous activity. After some preliminary bathymetry work to determine optimal trawl locations, the activity will begin with the deployment of a lander. The lander will descend to the bottom where it will attract and film organisms, and will be recovered at the end of the station activities. In addition to oceanographic and plankton vertical profiling activities, a major part of the station activity will involve ROV (Remotely Operated Vehicle) deployment. The G.O. Sars will carry two ROVs, the Aglantha, which can descend to 2000m and a new ROV that will be able to descend to 5000m. Researchers must plan station activities carefully. Deep water sampling can be difficult and time consuming. The deployment of a fish trawl giving one hour bottom time at 3000m would take at least six hours of valuable station time. ROV-deployment may be even longer, requiring seven to eight hours for a similar observation period.
ROVs give researchers freedom of movement in deep, otherwise inaccessible locations using video and still cameras to record observations. This work is critical for gaining a comprehensive view of the deep sea environment, because many organisms can either avoid trawl nets, or they have fragile bodies that are irreparably damaged by the nets. This problem is particularly true for gelatinous zooplankton organisms (jellyfish), which scientists believe may be major players in the deep sea food chain. The use of high quality digital video material ensures that the images collected are of a sufficient quality for scientific record keeping.
During leg 2, a Norwegian longliner will operate passive fishing gear (longline, traps), in areas nearby the G.O. Sars. This activity will supplement efforts to collect large, highly mobile organisms by bottom trawls operated by the research vessel.