ALBERT

Description: Freshwater ostracods (Crustacea, Ostracoda) are of interest in modern biological studies, while fossil records of ostracod valves enable us to reconstruct past lacustrine environments. The about 1mm long crustaceans carry a calcite carapace that is biomineralized from dissolved components in the ambient water, and completely envelopes their body. Ostracods inhabit almost all aquatic environments, even shallow freshwater ponds in the vast circumartic permafrost areas. In high-latitude areas, ostracod species diversity, their modern ecological demands, and instrumental records of environmental parameters are only scarcely documented. Such reference information is the key to quantitatively reconstruct past environments from fossil ostracod assemblages. This gap in ostracod data limits their use as biological indicators in the Arctic, where the effects of future climate warming are expected to be strongest. The objective of the study presented here was to extend the data set on arctic freshwater ostracods and environmental records by characterizing presentday habitat conditions, abundance and diversity of ostracod assemblages in periglacial freshwaters on Svalbard. The aims of this project were 1. to conduct an inventory of the abundance, diversity and ecological ranges of the freshwater ostracods living in polygon ponds in Adventdalen near Longyearbyen (78°11’11”N, 15°55’20”E), 2. to determine the present-day hydrochemical and sedimentary characteristics of ostracod habitats, and 3. to witness temporal variability in a polygon pond during the Arctic summer season 2013. The study site was located near the University Centre on Svalbard (UNIS)-run monitoring site for thermal contraction cracking in ice-wedge polygons on a river terrace in outer Adventdalen (Christiansen 2005). Permafrost on Svalbard is estimated to be of late Holocene age with temperatures of -5.2 to -5.6 °C in boreholes in the Adventdalen area (Christiansen et al. 2010). Ice-wedge polygons form in cold-climate environments under permafrost conditions and are the most common periglacial patterned ground features in the Arctic (Minke et al. 2007). Since the permafrost table efficiently blocks drainage pathways, surface depressions hold ponding water during summer, and freeze solid in winter. Those shallow periglacial surface freshwaters, called polygon ponds, are hotspots of biological activity in the otherwise hostile tundra. They provide diverse habitats to aquatic communities including freshwater ostracods. For this study, we choose an area with polygon ponds that are known to persist during the summer season. Our sampling scheme of 13 ponds in total comprised collecting freshwater ostracod individuals, pond water and sediment samples. One species, Tonnacypris glacialis (SARS, 1890), was found in only one of the sampled sites, the pond AD-01 (Fig. 1). Continuous water temperature records directly below the water surface in AD-01, and at the sediment surface in about 25cm water depth were collected between July 20 and September 25, 2013. We measured water and thaw depth in the pond centre and the thaw depth of the surrounding polygon rim. The last record at September 25, 2013 completed the observation season with the presence of 2-3cm lake ice. Preliminary results suggest the pond water is welloxygenated and dilute with slightly acidic pH. The hydrochemical fingerprint and sedimentary characteristics of inter- and intrapolygon ponds may allow a differentiation between the two subtypes for the first time, and are subject of ongoing work. Active-layer thickness was around 40-100 cmin polygon rims, we measured about 50-80 cm thaw depth under pond centres. A considerable increase in water surface area extend occurred in the monitored pond after a rain period. The records obtained from this and similar studies in the Siberian Arctic demonstrate that small and shallow periglacial surface waters are sensitive to local permafrost and climate variations. References Christiansen HH. 2005. Thermal regime of icewedge cracking in Adventdalen, Svalbard. Permafrost and Periglacial Processes 16: 87-98. Christiansen HH, Etzelmüller B, Isaksen K, Juliussen H, Farbrot H, Humlum O, Johansson M, Ingeman-Nielsen T, Kristensen L, Hjort J, Holmlund P, Sannel ABK, Sigsgaard C, Åkerman HJ, Foged N, Blikra LH, Pernosky MA, Ødegård RS. 2010. The thermal state of permafrost in the Nordic Area during the International Polar Year 2007–2009. Permafrost and Periglacial Processes 21: 156–181. Minke M, Donner N, Karpov N, de Klerk P, Joosten H. 2007. Distribution, diversity, development and dynamics of polygon mires: examples from Northeast Yakutia (NE Siberia). Peatlands International 1: 36-40.