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The present study examines the effects of experimentally generated disturbance on bathyal nematode communities at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN, situated in the Fram Strait, between Greenland and Svalbard. In order to understand the complex interactions between the biota and environmental perturbations we deployed a free-falling device (bottom lander) equipped with three rotating fork-like disturber units, able to perturbate the upper sediment layers with different disturbance frequencies at chosen time intervals. During a one-year deployment at 2493 m water depth, disturber unit DI was programmed to rotate every 14 days, DII every 28 days, and DIII every 72 days, resulting in 28, 14, and 7 perturbations, respectively. Sediment sampling following this experimental period was conducted with push-coring devices deployed by the Remotely Operated Vehicle “QUEST 4000” (MARUM, Bremen). These sediment cores were sub-sampled to determine the effect of the sediment perturbations on various sediment parameters (i.e., grain size distribution, chloroplastic pigment concentrations) as well as on benthic nematode communities. A total of 4773 nematodes from 27 families and 81 genera were identified. Nematode densities in the disturbed areas ranged from 617 ind. / 10 cm2 to 1566 ind. / 10 cm2, with a mean density of 1193 ind. / 10 cm2 observed overall in the disturbed sediments. Control sediments contained on average 20% more nematode specimens than were found within the disturbed sediments, with an average density of 1477 ind. / 10 cm2 observed. Nematode evenness (J'), genera richness (EG(51)) and heterogeneity (H′) were not significantly different between the treatments and controls (undisturbed vs disturbance). We found a significant effect of the interaction of disturbance frequency and sediment depth (interaction term Fr x De) on heterogeneity and genera richness, while evenness significantly differed between different sediment depths (De) and within the disturbed sediments between different disturbance frequencies (Fr). Although surface sediments in the three disturbed areas were effectively perturbated, sediment depth still has the most pronounced influence on nematode community attributes, while the experimentally induced disturbance had only a limited impact on nematode diversity and community structure. Although we found the density of some nematode genera was negatively affected by the disturbances, the deep-sea nematode community at HAUSGARTEN was generally characterized by a relatively high diversity and seemed to be largely resilient to the experimental disturbances.

Towed camera systems are commonly used to collect photo and video images of the deep seafloor for a wide variety of purposes, from pure exploratory research to the development of management plans. Ongoing technological developments are increasing the quantity and quality of data collected from the deep seafloor. Despite these improvements, the area of seafloor, which towed systems can survey, optically remains limited by the rapid attenuation of visible wavelengths within water. We present an overview of a new towed camera platform integrating additional acoustical devices: the ocean floor observation and bathymetry system (OFOBS). The towed system maintains continuous direct communication via fiber optic cable with a support vessel, operational at depths up to 6000 m. In addition to collecting seafloor photo and video data, OFOBS gathers sidescan data over a 100-m swath width. OFOBS functionality is further augmented by a forward looking sonar, used to aid in hazard avoidance and real-time course correction. Data collected during the first field deployments of OFOBS, at a range of seamounts on the Langseth Ridge/Gakkel Ridge intersection (86 degrees N, 61 degrees E) in the high Arctic in September 2016, are presented to demonstrate the functionality of the system. Collected from a location with near continuous ice cover, this explanatory data set highlights the advantages of the system for deep-sea survey work in environments currently difficult to access for the majority of subsurface research platforms.

An Integrated Sediment Disturber (ISD) was developed to study the effects of repeated physical disturbances on sediment geochemistry and associated benthic fauna. The ISD is capable to generate a strong, more or less uniform mixing of surface sediments by three rotating fork-like disturber units of approximately 1 m in diameter. Perturbations can be set at different intensities and frequencies, e.g., on times scales of hours, days, or weeks, depending on the experimental design. The ISD carries an Autonomous Positioning Drive (APD) module, which allows the three-dimensional positioning of sensors by a programmable controller. The three circular disturbed zones and an undisturbed control area in-between can be monitored at specified frequencies using a microprofiler with microelectrodes for measuring various parameters (e.g., oxygen, pH, hydrogen sulphide). All operations are supervised by a digital stills camera. Sediment sampling at the start and end point using coring devices handled by divers (and potentially undertaken using a Remotely Operated Vehicle) provides material to study shifts in biodiversity of the small sedimentinhabiting biota and alterations in ecosystem functioning in response to perturbations and the changing geochemical characteristics of surface sediments.

The marine Arctic has played an essential role in the history of our planet over the past 130 million years and contributes considerably to the present functioning of Earth and its life. The global cycles of a variety of materials fundamental to atmospheric conditions and thus to life depend to a signifi cant extent on Arctic marine processes (Aargaard et al., 1999). The past decades have seen remarkable changes in key Arctic variables. The decrease of sea-ice extent and sea-ice thickness in the past decade is statistically signifi - cant (Cavalieri et al., 1997; Parkinson et al., 1999; Walsh and Chapman, 2001; Partington et al., 2003; Johannessen et al., 2004). There have also been large changes in the upper and intermediate layers of the ocean, which have environmental implications. For instance, the deep Greenland Sea has continued its decadal trend towards warmer and saltier conditions, with a corresponding decrease in oxygen content, refl ecting the lack of effective local convection and ventilation (Dickson et al., 1996; Boenisch et al., 1997). Changes in temperature and salinity and associated shifts in nutrient distributions will directly affect the marine biota on multiple scales from communities and populations to individuals, consequently altering food-web structures and ecosystem functioning (Benson and Trites, 2002; Moore, 2003; Schumacher et al., 2003; Wiltshire and Manly, 2004; Perry et al., 2005). Today, we do not know whether the severe alterations in abiotic parameters represent perturbations due to human impacts, natural long-term trends, or new equilibriums (Bengtson et al., 2004). Because Arctic organisms are highly adapted to extreme environmental conditions with strong seasonal forcing, the accelerating rate of recent climate change challenges the resilience of Arctic life (Hassol, 2004). The entire system is likely to be severely affected by changing ice and water conditions, varying primary production and food availability to faunal communities, an increase in contaminants, and possibly increased UV irradiance. The stability of a number of Arctic populations and ecosystems is probably not strong enough to withstand the sum of these factors, which might lead to a collapse of subsystems. To detect and track the impact of large-scale environmental changes in the transition zone between the northern North Atlantic and the central Arctic Ocean, and to determine experimentally the factors controlling deep-sea biodiversity, the German Alfred Wegener Institute for Polar and Marine Research (AWI) established the deepsea, long-term observatory HAUSGARTEN, representing the fi rst, and by now only, open-ocean, long-term station in a polar region.