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: The collection of zooplankton swimmers and sinkers in time-series sediment traps provides unique insight into year-round and interannual trends in zooplankton population dynamics. These samples are particularly valuable in remote and difficult to access areas such as the Arctic Ocean, where samples from the ice-covered season are rare. In the present study, we investigated zooplankton composition based on swimmers and sinkers collected by sediment traps at water depths of 180–280, 800–1320, and 2320–2550 m, over a period of 16 yr (2000–2016) at the Long-Term Ecological Research observatory HAUSGARTEN located in the eastern Fram Strait (79°N, 4°E). The time-series data showed seasonal and interannual trends within the dominant zooplankton groups including copepoda, foraminifera, ostracoda, amphipoda, pteropoda, and chaetognatha. Amphipoda and copepoda dominated the abundance of swimmers while pteropoda and foraminifera were the most important sinkers. Although the seasonal occurrence of these groups was relatively consistent between years, there were notable interannual variations in abundance, suggesting the influence of various environmental conditions such as sea-ice dynamic and lateral advection of water masses, for example, meltwater and Atlantic water. Statistical analyses revealed a correlation between the Arctic dipole climatic index and sea-ice dynamics (i.e., ice coverage and concentration), as well as the importance of the distance from the ice edge on swimmer composition patterns and carbon export.