Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉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.〈/p〉

Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

Description: Federal Ministry of Education and Research (BMBF)

Description: Helmholtz‐Gemeinschaft

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.

Description: The collection of zooplankton swimmers and sinkers in time-series sediment traps provides a unique insight into year-round and inter-annual trends in zooplankton population dynamics. Such samples are particularly valuable in remote and difficult to access areas such as the Arctic Ocean, where samples from the ice-covered seasons 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 m, 800-1320 m, and 2320-2550 m, over a period of 16 years (2000-2016) at the central station of the LTER (Long-Term Ecological Research) HAUSGARTEN observatory in the Fram Strait. The time-series data include the abundance of copepoda, foraminifera, ostracoda, amphipoda, pteropoda, and chaetognatha that were collected in the sediment trap time-series.

Description: Pelagic amphipods represent a large fraction of organisms entering sediment traps as so-called “swimmers.” These swimmers were sampled with sediment traps (∼200– 300 m water depth) with two mooring arrays deployed at two different positions in the Long-Term Ecological Research observatory HAUSGARTEN in the northeastern Fram Strait. This sampling allowed us to investigate amphipod year-round abundances and inter-annual trends from 2000 onward. In this study, newly analyzed data from a 3-years period (August 2011–June 2014) are presented, extending this long-term investigation. In our results, the species Themisto abyssorum, T. libellula, and T. compressa dominated the swimmer biomass, corroborating previous studies. The observed increase of amphipod abundances persisted in all three species, additionally implying that Themisto compressa maintained its population off Svalbard, which appeared for the first time here after a warm anomaly in 2004–2007. This study provides evidence for changes in amphipod community patterns that can mainly be attributed to growing abundances of T. compressa. Similarly, another hyperiid, Lanceola clausii, also increased in abundance over the investigated period. For T. libellula, almost no juvenile individuals were recorded in the sampling period 2013/14, even though juveniles of this species were common in earlier records. The three more years of observations clearly suggest that recently documented environmental shifts persist in the eastern Fram Strait. They also highlight the merit of using sediment trap time series to obtain year-round data sets needed to reveal processes and range shift dynamics in the pelagic system on a long-term basis.

Description: Summary: During the last twenty years, the Arctic is under rapid environmental change also affecting the marine fauna. In this context, samples from sediment traps (200m water depth) of the Long-Term Ecological Research (LTER) observatory HAUSGARTEN in the northeastern Fram Strait (79°N, 4°E) have been used to obtain year-round abundances and inter-annual trends of zooplankton swimmers in time-series from the year 2000 until 2014. Those time-series sediment trap samples offer a unique insight into Arctic zooplankton population dynamics and changes therein. Dominating swimmer biomass, Arctic pelagic amphipods represent a valuable data source to reveal environmental changes. Amphipods are key species in the Arctic pelagic system linking primary consumers such as copepods with higher trophic levels like marine mammals and sea birds. This investigation is mainly based on amphipod sampling data of three consecutive years (2011-2014) obtained at two locations within the LTER HAUSGARTEN. In total, seven amphipod species of four taxonomic families could be observed (Hyperiidae, Lanceolidae, Eusiridae, and Gammaridae). Amphipods of the genus Themisto could be shown to dominate the epipelagic amphipod community by 〉97%. The latest abundance development of the native Themisto species – the boreal T. abyssorum and the Arctic T. libellula – and the intruding T. compressa is described and related to environmental data such as sea ice extend, North Atlantic Oscillation index, marine current velocity, current direction, ocean temperature, and water salinity. Between 2000 and 2014, increasing amphipod abundances could be observed, presumably due to changed trophic interactions and the warming system. Abundances analyzed at the central HAUSGARTEN site were considerably larger than at the northern location, which was likely provoked by hydrographic features and differences in sea ice cover. Further, range shifts in amphipods are evident: abundances of the North Atlantic species T. compressa continued to increase compared to mid-2000s, which may be attributed to warmer Atlantic water inflow causing slightly higher ocean temperatures in eastern Fram Strait. This trend is also supported by elevated abundances of the temperate species Lanceola clausi observed in the HAUSGARTEN sediment traps time-series. In addition, hardly any immature individual of the Arctic T. libellula was recorded in the sampling period 2013/14, even though juveniles of this species were common previously. These findings suggest environmental shifts taking place in the seasonally ice-covered eastern Fram Strait. The three dominating pelagic Themisto-species showed significant seasonal variability, with high abundances in summer and lower quantities in winter. Overall, Themisto abyssorum dominated the amphipod community by 〉50%. However, in 2012/13, T. abyssorum and T. libellula were present in nearly equal proportions (~40%) at both HAUSGARTEN sites. That sampling period was characterized by ambivalent ocean temperatures with a first warm winter and a pronounced temperature drop after which cold water prevailed all summer 2013 long. Whereas the two native species were present throughout the year, T. compressa was absent over long periods in winter (November to February). T. libellula featured erratic occurrences in late summers between July and September. A seasonal pattern was also evident in the gender analysis, which revealed similar patterns for the native species with elevated male proportions in winter only (up to 32%), which was reversed for T. compressa (40% in summers). Overall, high male proportions in T. compressa could be observed irrespective of the HAUSGARTEN site. Maturity studies rendered noteworthy proportions of juveniles for T. abyssorum only, which were further seasonally well distributed at the northern HAUSGARTEN site. No juveniles of T. compressa were detected in winters. Hence, this study also strongly highlights the advantages of sediment trap swimmer investigations in pelagic zooplankton studies complementing yet established research approaches. The present master thesis highly supports the use of sediment trap time-series to obtain year-round data sets which on a long-term basis enlarge our knowledge on pelagic 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: Amphipods are key species linking primary consumers such as copepods with higher trophic levels like marine mammals and sea birds. Studying Arctic pelagic amphipods in the Fram Strait region over a period of 15 years represents an outstanding opportunity in determining range shifts since only three species of the genus Themisto dominate the upper pelagic system of Fram Strait. Samples from sediment traps of the Long-Term-Ecological Research (LTER) observatory HAUSGARTEN in the northeastern Fram Strait (79°N, 4°C) have been used to obtain year-round abundance time series from the year 2000 until 2014. For this period range shifts in amphipods are evident:, the North-Atlantic species T. compressa was first observed in the samples in the eastern Fram Strait in 2004. It is further shown for recent years (2004 -2014) that this southern intruder got established in the Fram Strait. Also, the latest abundance development of the native species – the boreal T. abyssorum and the Arctic T. libellula – is described and related to environmental data such as marine current velocity, current direction, water temperature, and sea ice extend. Grouping patterns of yearly averaged amphipod abundances per mooring using multivariate statistics varied indicating a highly diverse system. Whether or not these dynamics are due to climate change or natural variability cannot yet be stated. A shift in the abundance pattern of Arctic amphipods will heavily impact marine food webs with implications up and down the food chain.