Patterns of Benthic Communities in Arctic Fjords (Novaya Zemlya Archipelago, Kara Sea): Resilience vs. Fragility

Despite a large number of studies, a detailed overall picture of benthic communities zonation in the Arctic fjords is currently lacking. Our study aimed to find out whether there is a universal model for the distribution of benthic communities based on the structural features of the fjords. We examined benthic macrofaunal communities in fjords with various environmental settings on the eastern coast of Novaya Zemlya Archipelago, Kara Sea. The material was collected during five cruises undertaken from 2013 to 2016. A total of 50 stations located in the five fjords were taken. In all five fjords, macrofauna had a similar composition assembled from a regional species pool, with a predominance of species tolerant to glacial sedimentation and fluctuations in temperature and salinity. Benthic communities changed consistently along the axis of the bay from the outer slope to the inner parts. Biodiversity and quantitative characteristics of the macrofauna decreased along the environmental gradient related to terrigenous and glacial runoff, consistent with patterns reported in other studies of Arctic glacial fjords. The most impoverished communities were dominated by bivalve Portlandia arctica and isopod Saduria sabini. At the same time, fjord walls and sills, characterized by low sedimentation rates, strong currents and the presence of ice-rafted debris, were inhabited by patchy distributed benthic communities dominated by species confined to hard substrates. In general, the distribution of communities corresponded to five zones: depleted inner periglacial areas, the upper subtidal belt with stony substrates, deep inner semi-isolated basin, outer non-isolated basins and upper slope transitioning to lower slope. Our study can provide a reference point for monitoring changes in fjord ecosystems in response to climate change and the potential impact of human activities.

Studying Arctic Fjords with Crowdsourced Science and Sailboats

A new study demonstrates the benefits of crowdsourcing science using sailboats to better understand the impact of melting sea ice in the Arctic.

Cells of matter and life – towards understanding the internal structure and spatial patchiness of particles and plankton distribution in the Arctic fjords

Nothing is homogenous, neither the oceans, nor the distribution pattern of particles and plankton, both in the water column and within their patches. Here we analyse and map the spatio-temporal distribution patterns and the internal structure of 94 patches of various size fractions of particles and plankton studied in two Arctic fjords over six summer seasons. Observed patches generally occupied only the minor part of the studied upper water column (on average 12 %), and frequently occurred as multi-fraction forms. They varied among years and regions in terms of their position in a water column, size, shape, and structure. Consequently, we propose completely novel insight into their internal structure, by classifying them according to their shapes and the location of their cores. We distinguished seven types of patches: Belt, Triangle, Diamond, Flare, Fingers, Flag, and Rosette. The observed increasing role of the smallest size fractions (steepening size spectra slopes) over years implies that Atlantic water advection played the crucial role on compositional dynamics on temporal scale. The recurring feature of the elevated concentrations of particles and plankton near glacier fronts suggest that it, together with local biological production, is the strongest mechanism generating patchiness on the local scale. Even though we significantly extended our comprehension of the phenomenon of patchiness, it still remains an ambiguous matter, when, why, and if the mechanistic or ecological forcing prevails in shaping the patterns of particles and plankton distribution. Regardless of the mechanism, our results show that particles and plankton are not purely dye-like passive objects and that the type of their structuring in a water column may have only short term and local validity.

Seasonal variability of the Rossby radius deformation in the Hornsund fjord

<p>The Earth's rotation affects the water circulation in the Arctic fjords. It can be described by means of the baroclinic Rossby radius deformation (R<sub>1</sub>) expressed as the ratio of the internal wave velocity to the Coriolis parameter.</p><p>The influence of the rotational effects on the water‐mass distribution depends on the width of the fjord in relation to the baroclinic radius of deformation (Gilbert, 1983). Most often the Rossby radius deformation in the Arctic fjords is 2-3 times smaller than the width of the fjord entrance, which allows the rotation of water masses within such fjords (Cottier, 2010). Such a situation exists in the small, western fjord of Svalbard - Hornsund, where the rotation makes the Atlantic and the Arctic waters flow from the shelf into the fjord along the southern bank and flow out of the fjord along the northern bank. The impact of the Coriolis force on the Hornsund environment was observed in a sedimentary record from the last century (Pawłowska et al. 2017). Literature estimates indicate that Hornsund is a typical fjord with an internal baroclinic Rossby radius between 3.5 and 6 km (Cottier, 2005, Nilsen, 2008).</p><p>The spatial and seasonal variation of the R<sub>1</sub> in the Hornsund fjord was carried out based on data from the numerical model (Jakacki et al. 2017) for the period 2005-2010 and for the selected actual data collected during the AREX survey campaigns.  The analysis of the actual data and model data confirms the seasonal variability of the vertical water structure in the fjord, which leads to cyclic changes of the vertical <strong>Brunta-Vaisali </strong>frequency structure and consequently to seasonal variability of R<sub>1</sub>. In the Hornsund fjord seasonality strongly influences the Rossby radius, which reaches maximum values in summertime and minimum values in wintertime. Moreover, R<sub>1</sub> values can be different even at points close to each other.  The values of the baroclinic Rossby radius of deformation also differ depending on the adopted calculation method.<br><br>Calculations were carried out at the Academic Computer Centre in Gdańsk.</p><p> </p><p> </p>