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 Institute, Helmholtz-Centre for Polar and Marine Research (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 5500 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 2500 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: The by-collection of zooplankton swimmers in time-series sediment traps offers a unique insight into year-round and inter-annual trends in zooplankton population dynamics. These samples are especially valuable in remote and difficult to access areas such as the Arctic, where samples from the ice-covered winter season are rare. In the present study we investigate the year-round swimmer composition of sediment trap samples collected at water depths of 200-300 m over a period of 12 years (2000-2012) at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN located in the northeastern Fram Strait (79? N, 4? E). Here we describe seasonal and inter-annual appearances within the dominant zooplankton groups including amphipods, chaetognaths, copepods, ostracods and pteropods. Amphipods and copepods made up the largest amount of the swimmer fraction. Although the seasonal occurrence of these groups was relatively consistent between years there were notable inter-annual variations in abundance that suggested the influence of different environmental conditions. In addition to these general patterns, specific changes were also detected. Notably, concerning pelagic amphipods, the occurrence of a southern invader Themisto compressa could be observed from 2004 onwards. Concurrent to this observation a reversal in dominance of the arctic pteropod species Limacina helicina towards the subarctic-boreal L. retroversa was noticed. In addition to a long-term trend in warming in eastern Fram Strait since 1997, a warm anomaly event was also observed during late 2004 to 2007. Whether these trends indicate lasting alterations due to global environmental change, or simply reflect natural variability on multiyear time-scales is presently unclear.

Description: Time-series sediment traps were deployed at 4 depths in the eastern Fram Strait from July 2007 to June 2008 to investigate variations in the magnitude and composition of the sinking particulate matter from upper waters to the seafloor. Sediment traps were deployed at 196 m in the Atlantic Water layer, at 1296 and 2364 m in the intermediate and deep waters, and at 2430 m on a benthic lander in the near-bottom layer. Fluxes of total particulate matter, particulate organic carbon, particulate organic nitrogen, biogenic matter, lithogenic matter, biogenic particulate silica, calcium carbonate, dominant phytoplankton cells, and zooplankton fecal pellets increased with depth, indicating the importance of lateral advection on fluxes in the deep Fram Strait. The lateral supply of particulate matter was further supported by the constant fluxes of biomarkers such as brassicasterol, alkenones, campesterol, beta-sitosterol, and IP25 at all depths sampled. However, enhanced fluxes of diatoms and appendicularian fecal pellets from the upper waters to the seafloor in the presence of ice during spring indicated the rapid export (15-35 days) of locally-produced large particles that likely contributed most of the food supply to the benthic communities. These results show that lateral supply and downward fluxes are both important processes influencing the transport of particulate matter to the seafloor in the deep eastern Fram Strait, and that particulate matter size dictates the prevailing sinking process.

Description: The by-collection of zooplankton swimmers in time-series sediment traps offers a unique insight into year-round and inter-annual trends in zooplankton population dynamics. These samples are especially valuable in remote and difficult to access areas such as the Arctic, where samples from the ice-covered winter season are rare. In the present study we investigate the year-round swimmer composition of sediment trap samples collected at water depths of 200-300 m over a period of 12 years (2000-2012) at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN located in the northeastern Fram Strait (79° N, 4° E). Here we describe seasonal and inter-annual appearances within the dominant zooplankton groups including amphipods, chaetognaths, copepods, ostracods and pteropods. Amphipods and copepods made up the largest amount of the swimmer fraction. Although the seasonal occurrence of these groups was relatively consistent between years there were notable inter-annual variations in abundance that suggested the influence of different environmental conditions. In addition to these general patterns, specific changes were also detected. Notably, concerning pelagic amphipods, the occurrence of a southern invader Themisto compressa could be observed from 2004 onwards. Concurrent to this observation a reversal in dominance of the arctic pteropod species Limacina helicina towards the subarctic-boreal L. retroversa was noticed. In addition to a long-term trend in warming in eastern Fram Strait since 1997, a warm anomaly event was also observed during late 2004 to 2007. Whether these trends indicate lasting alterations due to global environmental change, or simply reflect natural variability on multiyear time-scales is presently unclear.

Description: Time-series sediment traps were deployed at 4 depths in the eastern Fram Strait from July 2007 to June 2008 to investigate variations in the magnitude and composition of the sinking particulate matter from upper waters to the seafloor. Sediment traps were deployed at 196 m in the Atlantic Water layer, at 1296 and 2364 m in the intermediate and deep waters, and at 2430 m on a benthic lander in the near-bottom layer. Fluxes of total particulate matter, particulate organic carbon, particulate organic nitrogen, biogenic matter, lithogenic matter, biogenic particulate silica, calcium carbonate, dominant phytoplankton cells, and zooplankton fecal pellets increased with depth, indicating the importance of lateral advection on fluxes in the deep Fram Strait. The lateral supply of particulate matter was further supported by the constant fluxes of biomarkers such as brassicasterol, alkenones, campesterol, β-sitosterol, and IP25 at all depths sampled. However, enhanced fluxes of diatoms and appendicularian fecal pellets from the upper waters to the seafloor in the presence of ice during spring indicated the rapid export (15–35 days) of locally-produced large particles that likely contributed most of the food supply to the benthic communities. These results show that lateral supply and downward fluxes are both important processes influencing the transport of particulate matter to the seafloor in the deep eastern Fram Strait, and that particulate matter size dictates the prevailing sinking process.