Description: Benthic fauna constantly modifies their physical, chemical and biological environment. The permanent biological reworking of surface sediments mediates biogeochemical processes at the seafloor and is, therefore, of global importance. There are numerous studies measuring the rate and extent of bioturbation worldwide, however, information on mixing rates in the deep ocean and especially in the Polar Regions are extremely scarce; to our knowledge there is, by now, only a single study providing bioturbation rates from the deep Arctic Ocean. The present study presents mixing rates and mixed layer depths for the deep seafloor at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. Two stations at similar water depths (2400 m and 2500 m water depth, respectively) but approx. 55 km apart from each other were chosen to carry out long-term (2 and 4 years, respectively) in situ bioturbation experiments using luminophores as a tracer. Biodiffusion-like mixing rates Db at the experimental sites were rather similar (0.26 cm2 a-1 at HG-IV; 0.28 cm2 a-1 at S3); slightly (non-significantly) higher Db values at the southern HAUSGARTEN site S3 could be explained by more favorable environmental conditions and related differences in the faunal composition. Indications for a non-local transport of sediment particles from the surface to deeper parts of the sediment, resulting in higher values for the Non-Local Index (NLI), could only be found for the central HAUSGARTEN site HG-IV. Elevated densities of burrowing megafauna at HG-IV, compared to S3, might be responsible for the subsurface maxima in luminophore distribution and comparably higher NLI values at the central HAUSGARTEN site (5.37 at HG-IV; 3.26 at S3). Mixed layer depths L at the two sites were almost identical; considerable mixing of surface sediments occurred down to max. 6-7 cm sediment depth.

Description: In this paper the concept of resilience is discussed on the base of 13 case studies from the German branch of the International Long-Term Ecological Research Program. In the introduction the resilience approach is presented as one possibility to describe ecosystem dynamics. The relations with the concepts of adaptability and ecological integrity are discussed and the research questions are formulated. The focal research objectives are related to the conditions of resilient behaviour of ecosystems, the role of spatio-temporal scales, the differences between short- or long-term dynamics, the basic methodological requirements to exactly define resilience, the role of the reference state and indicators and the suitability of resilience as a management concept. The main part of the paper consists of 13 small case study descriptions, which demonstrate phase transitions and resilient dynamics of several terrestrial and aquatic ecosystems at different time scales. In the discussion, some problems arising from the interpretation of the time series are highlighted and discussed. The topics of discussion are the conceptual challenges of the resilience approach, methodological problems, the role of indicator selection, the complex interactions between different disturbances, the significance of time scales and a comparison of the case studies. The article ends with a conclusion which focuses on the demand to link resilience with adaptability, in order to support the long-term dynamics of ecosystem development.

Description: Time-series studies of arctic marine ecosystems are rare. This is not surprising since polar regions are largely only accessible by means of expensive modern infrastructure and instrumentation. In 1999, the Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) established the LTER (Long-Term Ecological Research) observatory HAUSGARTEN crossing the Fram Strait at about 79°N. Multidisciplinary investigations covering all parts of the open-ocean ecosystem are carried out at a total of 21 permanent sampling sites in water depths ranging between 250 and 5,500 m. From the outset, repeated sampling in the water column and at the deep seafloor during regular expeditions in summer months was complemented by continuous year-round sampling and sensing using autonomous instruments in anchored devices (i.e., moorings and free-falling systems). The central HAUSGARTEN station at 2,500 m water depth in the eastern Fram Strait serves as an experimental area for unique biological in situ experiments at the seafloor, simulating various scenarios in changing environmental settings. Long-term ecological research at the HAUSGARTEN observatory revealed a number of interesting temporal trends in numerous biological variables from the pelagic system to the deep seafloor. Contrary to common intuition, the entire ecosystem responded exceptionally fast to environmental changes in the upper water column. Major variations were associated with a warm water anomaly evident in surface waters in eastern parts of the Fram Strait between 2005 and 2008. However, even after 15 years of intense time-series work at HAUSGARTEN, we cannot yet predict with complete certainty whether these trends indicate lasting alterations due to anthropologically-induced global environmental changes of the system, or whether they reflect natural variability on multiyear time-scales, for example, in relation to decadal oscillatory atmospheric processes.

Description: Some of the highest microplastic concentrations in marine environments have been reported from the Fram Strait in the Arctic. This region supports a diverse ecosystem dependent on high concentrations of zooplankton at the base of the food web. Zooplankton samples were collected during research cruises using Bongo and MOCNESS nets in the boreal summers of 2018 and 2019. Using FTIR scanning spectroscopy in combination with an automated polymer identification approach, we show that all five species of Arctic zooplankton investigated had ingested microplastics. Amphipod species, found in surface waters or closely associated with sea ice, had ingested significantly more microplastic per individual (Themisto libellula: 1.8, Themisto abyssorrum: 1, Apherusa glacialis: 1) than copepod species (Calanus hyperboreus: 0.21, Calanus glacialis/finmarchicus: 0.01). The majority of microplastics ingested were below 50 μm in size, all were fragments and several different polymer types were present. We quantified microplastics in water samples collected at six of the same stations as the Calanus using an underway sampling system (inlet at 6.5 m water depth). Fragments of several polymer types and anthropogenic cellulosic fibres were present, with an average concentration of 7 microplastic particles (MP) L−1 (0–18.5 MP L−1). In comparison to the water samples, those microplastics found ingested by zooplankton were significantly smaller, highlighting that the smaller-sized microplastics were being selected for by the zooplankton. High levels of microplastic ingestion in zooplankton have been associated with negative effects on growth, development, and fecundity. As Arctic zooplankton only have a short window of biological productivity, any negative effect could have broad consequences. As global plastic consumption continues to increase and climate change continues to reduce sea ice cover, releasing ice-bound microplastics and leaving ice free areas open to exploitation, the Arctic could be exposed to further plastic pollution which could place additional strain on this fragile ecosystem.