Most of what we know from ocean life derives from extractive sampling using nets, bottles, grabs, cores or trawls. While providing valuable material, e.g. for biodiversity or experimental studies, these destructive methods fail to preserve the spatial structure and function characterizing living communities, where bottom trawls reduce underwater seascapes to piles of unsorted creatures on deck. Over the last decades, technological advancements have begun to shed a new and fascinating light on marine biology. Cabled instruments and observatories now allow to explore living communities in their natural environment in a non-destructive manner:
- Remotely operated vehicles (ROVs) equipped with cameras and sensor packages provide high-resolution images from the plankton and seabed communities in their dynamic surroundings,
- Eddy Covariance measurements allow the continuous and non-invasive determination of benthic fluxes of oxygen, particles and heat in the benthic boundary layer,
- sampling the seabed and the water column above with Multi Corers and Carousel Water Samplers is essential for the scientific work of the BPP section,
- Microsensor measurements offer insights into instantaneous physiological processes and help to understand possible mechanisms to cope with future climate conditions,
- Biologging units and satellite transmitters allow to study the marine environment from the perspective of marine mammels.
These tools are used and refined by BPP scientists engineers and technicians to understand the factors governing Antarctic communities in an era of climate change and to assess the role of Antarctic communities in geochemical cycling.
Remotely Operated Vehicle (ROV)
Investigations with Remotely Operated Vehicles (ROVs) in coastal areas and along the high Antarctic continental shelves and slopes show rich benthic communities, such as coral reefs or sponge beds.
Except for its surface skin the ocean has long defied human observation. Remotely Operated Vehicles (ROV) now offer the opportunity to extend the vertical range of human exploration far beyond the reaches of conventional SCUBA-diving. Equipped with high-resolution cameras and sensor packages, these unmanned submersibles transmit their data via umbillical cable to the surface, allowing researchers and engineers to collect stunning seafloor images and environmental information in real-time. While the collection of samples has so far been the privilege of large multi-million dollar ROVs operated by teams of engineers, the cleft between these so-called working class ROVs and the much smaller inspection class ROVs is narrowing: engineers and scientists from BPP and industry have now managed to mate a small inspection class ROV with a 7 degrees-of-freedom hydraulic arm, creating the likely smallest working class ROV to date. With a vertical range of 500 m permitting access to the Antarctic continental shelf, this system was deployed during the Polarstern cruise PS96 to explore the hanging benthos below the 150m thick shelf ice in the Drescher Inlet. Polarstern cruise PS111 offered the first time a chance to explore the grounding line where the antarctic shelf ice meets the sea-floor. Various missions operated from Polarstern, the antarctic sea-ice, or from small boats show the enormous potential of such hybrid-technology. Because of it 360 degrees of freedom, the ROV is able to operate upside down and therefore capable investigating struktures underneath rocky slopes, caves or beneath the sea ans shelf ice respectively.
The Eddy Covariance technique is a method to determine the flux of solutes and particles across the bentho-pelagic interface. It allows assessing the flux non-invasively over long time periods, even for benthic habitats that are not accessible with common methods.
The Eddy Covariance (EC) technique measures the flux in the benthic boundary layer at 10-50 cm above the seabed. The EC technique combines the measurements of flow velocity and concentration of substances at high frequencies from which the flux can be calculated. To date, concentration measurements at high frequency are possible only for oxygen, temperature, particles, and recently for H+ (pH). Most commonly, the benthic oxygen uptake is targeted, because it is a reliable proxy for benthic carbon turnover. In shallow euphotic waters, benthic oxygen respiration and production from benthic algae can be measured over day-night cycles to determine the net oxygen flux and thus the autotrophic–heterotrophic balance of the benthic ecosystem. The basis for EC measurements is the turbulent mass transport in benthic boundary layers. It is therefore an ideal tool to study also the impact of hydrodynamic conditions on benthic fluxes and understand how the fauna adapts and benthic habitats are formed.
Benthic and pelagic sampling
The sampling of the seabed - the benthic - and the water column above - the pelagic - is obligatory for the scientific work of the BPP section in order to obtain essential data.
We take water and sediment samples in the Weddell Sea (Antarctica) and Patagonian fjords (Chile), supported by well-equipped large research vessels such as the icebreaker POLARSTERN as well as but also by small, open working boats. Water samples: Niskin bottles, named after their inventor, take a defined amount of water at desired depth by closing the end caps of this tube-like bottle. As a rule, several bottles are always lowered together at depth. Each bottle „catches“ water from different depths. The bottles are locked at depth and taken on board the ship for analyses. In-situ measurements of physical water properties are carried out by CTD (Conductivity Temperature Depth) units, that is lowered together with the bottles. Seabed samples: in order to analyse the sediment of the seabed under laboratory conditions, cylindrical sediment samples of ca. 30 cm length are punched by Multicorer (MUC) and taken on board.
Microsensor measurements on the cold-water coral Desmophyllum dianthus offer insight into instantaneous physiological processes and help to understand possible mechanisms to cope with future climate conditions.
Microsensors are very thin sensors with tip diameters of less than 10 μm. They allow to measure on the micro-scale diffusion processes and fluxes directly at the surface of organisms, within their surrounding boundary layer or even within their tissues. In close cooperation with the Microsensor group of the Max-Planck-Institute (MPI) in Bremen we use microsensors for oxygen, pH and calcium to study and describe the respiration and calcification of cold water corals from Patagonian fjords in Chile under different environmental conditions. Of special interest is the scleractinian cold-water coral Desmophyllum dianthus which grows in the strongly stratified Comau Fjord under water chemical conditions which resemble conditions predicted for future climate scenarios. D. dianthus thus offers insight into possible adaptation and regulation mechanisms needed to cope with our prospective climate.
Satellite tracking and Biologging
The instrumentation of seals with satellite transmitters and bio-logging technologies elucidates bentho-pelagic processes in the Antarctic sea ice zone.
Satellite-relayed dive-loggers record water temperature and salinity profiles along the seals’ foraging dives and transmit these data to polar orbiting satellites when the seals are surfacing. The reconciliation of seal borne data with oceanographic features provides new insights into intermediate and upper trophic level interactions. Seal-mounted cameras spot prey objects from the seals’ perspective in coastal sea ice habitats even underneath Antarctic ice shelves. Seals as autonomous samplers and remotely operated vehicles facilitate novel approaches in observational ecology to improve our understanding of distribution patterns of Antarctic top predators and underlying bentho-pelagic processes in difficult-to-study areas and seasons in the high Antarctic sea ice zone. All data are accessible via PANGAEA’s Marine Mammal Tracking project.