Abstract
Foraminifera are numerically abundant components of the benthic fauna; thus, they are very important compounds in glaciomarine environments. However, ongoing oceanographic changes may influence their distribution, abundances and diversity differently at different times of the year. In the present study, we aimed to assess seasonal environmental changes in an Arctic fjord (Adventfjorden, W Spitsbergen) and the structure and distribution of benthic foraminiferal assemblages during four seasons (January, May, August, November). The study revealed that the benthic foraminiferal assemblages in Adventfjorden are susceptible to environmental changes related to enhanced inflow of shelf-transformed water (STW). We distinguished three zones in the fjord: (1) the deeper outer part influenced by STW, with living specimens staying in the few uppermost layers of sediment, (2) the shallower interior influenced by freshwater outflows and high sediment load, resulting in the dominance of opportunistic glaciomarine taxa constantly buried in the sediment, and (3) the central part, where the seasonal variation in the foraminifera assemblage reflects the interplay between the influence of riverine inputs and STW. Our study also revealed that the presence of STW in Adventfjorden favours an early spring appearance of juvenile foraminifera; however, the majority of the specimens are later withered and do not contribute to the summer pool of mature individuals. On the other hand, the majority of the mature specimens can survive during the winter because of sufficient organic matter stocks and year-long ice-free conditions.
Highlights
Arctic fjords encompass several distinctive oceanographic environments, with strong gradients in many key environmental parameters, including salinity, suspension load and sedimentation (Syvitski and Skei 1983)
We investigated the horizontal and vertical seasonal patterns of the distribution of the benthic foraminiferal assemblages in Adventfjorden (Spitsbergen, Svalbard)
The foraminiferal assemblages in Adventfjorden clearly reflected the spatial variability of the environmental conditions, from the innermost part of the fjord that was strongly impacted by riverine input and high sediment loads to the outer part that was mainly shaped by the inflows of shelf-transformed water (STW) from the central basin of Isfjorden
Summary
Arctic fjords encompass several distinctive oceanographic environments, with strong gradients in many key environmental parameters, including salinity, suspension load and sedimentation (Syvitski and Skei 1983). The oceanographic conditions of west Spitsbergen fjords are mainly shaped by the inflow of warm and saline Atlantic Waters (AW). According to Nilsen et al (2016), Isfjorden is one of the fjord systems that is most affected by AW in Spitsbergen due to the deep trough at its entrance. Majewski and Zajączkowski (2007) noticed the intrusions of AW in central Adventfjorden (southern arm of Isfjorden) over the last 50 years, which caused pronounced oceanographic changes that affected the foraminiferal assemblages and mainly resulted in a higher biodiversity of foraminiferal fauna and a higher number of agglutinated species. A similar pattern was described by Łącka and Zajączkowski (2016) and Pawłowska et al (2017a) in the Hornsund fjord (S Spitsbergen). Recent studies have suggested that these changes may have a tremendous influence on the seasonal variability in fjord systems (e.g. Zajączkowski et al 2010a; Pawłowska et al 2011)
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