Description: The Arctic marine food web is based on organic matter produced by both phytoplankton and sea-ice algae. With the decline of Arctic sea ice, the sustained availability of organic carbon of sea-ice origin is unclear. Recently, the detection of the sea-ice diatom biomarker IP25 in a range of Arctic benthic macrofauna indicated that this is a highly suitable biomarker for the identification of organic carbon derived from sea-ice primary production in Arctic food webs. However, the data presented previously were restricted to a single geographical region in the Canadian Arctic. Here, we show that IP25 is present in sea urchins of the genus Strongylocentrotus collected from ten locations with seasonal sea-ice cover from the Canadian Archipelago, Greenland and Spitsbergen. In contrast, IP25 was not found in specimens of Echinus esculentus collected from the southwest UK, where sea ice is absent. Our findings provide evidence that the presence of IP25 in macrobenthic organisms can be used across different Arctic regions as a versatile indicator of a diet containing carbon of sea-ice origin.

Description: The effects of climate change on Arctic marine ecosystems and their biogeochemical cycles are difficult to predict given the complex physical, biological and chemical interactions among the ecosystem components. We studied benthic biogeochemical fluxes in the Arctic and the influence of short-term (seasonal to annual), long-term (annual to decadal) and other environmental variability on their spatial distribution to provide a baseline for estimates of the impact of future changes. In summer 2009, we measured fluxes of dissolved oxygen, nitrate, nitrite, ammonia, soluble reactive phosphate and silicic acid at the sediment–water interface at eight sites in the southeastern Beaufort Sea at water depths from 45 to 580 m. The spatial pattern of the measured benthic boundary fluxes was heterogeneous. Multivariate analysis of flux data showed that no single or reduced combination of fluxes could explain the majority of spatial variation, indicating that oxygen flux is not representative of other nutrient sink–source dynamics. We tested the influence of eight environmental parameters on single benthic fluxes. Short-term environmental parameters (sinking flux of particulate organic carbon above the bottom, sediment surface Chl a) were most important for explaining oxygen, ammonium and nitrate fluxes. Long-term parameters (porosity, surface manganese and iron concentration, bottom water oxygen concentrations) together with δ13Corg signature explained most of the spatial variation in phosphate, nitrate and nitrite fluxes. Variation in pigments at the sediment surface was most important to explain variation in fluxes of silicic acid. In a model including all fluxes synchronously, the overall spatial distribution could be best explained (57%) by the combination of sediment Chl a, phaeopigments, δ13Corg, surficial manganese and bottom water oxygen concentration. We conclude that it is necessary to consider long-term environmental variability along with rapidly ongoing environmental changes to predict the flux of oxygen and nutrients across Arctic sediments even at short timescales. Our results contribute to improve ecological models predicting the impact of climate change on the functioning of marine ecosystems.

Description: The diversity-ecosystem function relationship is an important topic in ecology but has not received much attention in Arctic environments, and has rarely been tested for its stability in time. We studied the temporal variability of benthic ecosystem functioning at hotspots (sites with high benthic boundary fluxes) and coldspots (sites with lower fluxes) across two years in the Canadian Arctic. Benthic remineralisation function was measured as fluxes of oxygen, silicic acid, phosphate, nitrate and nitrite at the sediment-water interface. In addition we determined sediment pigment concentration and taxonomic and functional macrobenthic diversity. To separate temporal from spatial variability, we sampled the same nine sites from the Mackenzie Shelf to Baffin Bay during the same season (summer or fall) in 2008 and 2009. We observed that temporal variability of benthic remineralisation function at hotspots is higher than at coldspots and that taxonomic and functional macrobenthic diversity did not change significantly between years. Temporal variability of food availability (i.e., sediment surface pigment concentration) seemed higher at coldspot than at hotspot areas. Sediment chlorophyll a (Chl a) concentration, taxonomic richness, total abundance, water depth and abundance of the largest gallery-burrowing polychaete Lumbrineris tetraura together explained 42% of the total variation in fluxes. Food supply proxies (i.e., sediment Chl a and depth) split hot- from coldspot stations and explained variation on the axis of temporal variability, and macrofaunal community parameters explained variation mostly along the axis separating eastern from western sites with hot- or coldspot regimes. We conclude that variability in benthic remineralisation function, food supply and diversity will react to climate change on different time scales, and that their interactive effects may hide the detection of progressive change, particularly at hotspots. Time-series of benthic functions and its related parameters should be conducted at both hot- and coldspots to produce reliable predictive models.

Description: Epibenthos communities play an important role in the marine ecosystems of the Weddell Sea. Information on the factors controlling their structure and distribution are, however, still rare. In particular, the interactions between environmental factors and biotic assemblages are not fully understood. Nachtigaller Hill, a newly discovered seabed structure on the over-deepened shelf of the northwest Weddell Sea (Southern Ocean), offers a unique site to study these interactions in a high-latitude Antarctic setting. Based on high-resolution bathymetry and georeferenced biological data, the effect of the terrain and related environmental parameters on the epibenthos was assessed. At Nachtigaller Hill, both geomorphological and biological data showed complex distribution patterns, reflecting local processes such as iceberg scouring and locally amplified bottom currents. This variability was also generally reflected in the variable epibenthos distribution patterns although statistical analyses did not show strong correlations between the selected environmental parameters and species abundances. By analysing the interactions between environmental and biological patterns, this study provides crucial information towards a better understanding of the factors and processes that drive epibenthos communities on the shelves of the Weddell Sea and probably also on other Antarctic shelves.

Description: Polar coralline red algae (Corallinales, Rhodophyta) that form rhodoliths have received little attention concerning their potential as ecosystem engineers and carbonate factories; although, recent findings revealed that they are much more widespread in polar waters than previously thought. The present study deals with the northernmost rhodolith communities currently known, discovered in 2006 at 80 degrees 31'N in Nordkappbukta (North Cape Bay) at Nordaustlandet, Svalbard. These perennial coralline algae must be adapted to extreme seasonality in terms of light regime (c. 4 months winter darkness), sea ice coverage, nutrient supply, turbidity of the water column, temperature and salinity. The rhodolith communities and their environment were investigated using multibeam swath bathymetry, CTD measurements, recordings of the photosynthetic active radiation (PAR) and determination of the water chemistry, seabed imaging and targeted sampling by means of the manned submersible JAGO as well as benthic collections with a dredge. The coralline flora was composed mainly of Lithothamnion glaciale, with a lesser amount of Phymatolithon tenue. Based on their distribution and development at different depth levels, a facies model was developed. Rhodoliths occurred between 30 and 51 m, while coralline algae attached to cobbles were present as deep as 78 m. Measurements of the PAR indicated their adaptation to extreme low light levels. Ambient waters were always saturated with reference to calcite and aragonite for the whole area. The rhodolith-associated macrobenthic fauna samples yielded 59 species, only one of which was typically Arctic, and the concomitant appearance of corallines and grazers kept the corallines free from epiphytes and coequally provided feeding grounds for the grazers. Overall, L. glaciate and P. tenue appeared to be well adapted to the extreme environment of the Arctic.

Description: The epibenthic megafauna of the Great Meteor Seamount top region was investigated by means of the quantitative analysis of seabed photographs taken during cruise M42/3 of th RV "Meteor" at 15 stations, at water depths of 285 to 603 m in September 1998. The invertebrate megabenthos is rather poor in both abundance and diversity. Mean abundances per station fall in the range of2.5 to 71.3 ind.·m-2• A total of 52 putative species were identified in the photographs. Species numbers per station varied between 11 and 22. The most prominent megafaunal taxa were sponges, gorgonarian, antipatharian and madreporarian corals, and sea urchins. Small-scale distribution patterns (100-m scale) of dominant species were characterised by a pronounced patchiness. The meso-scale pattern (10-km scale) featured three distinct faunistic zones: Slope(〉 450 m), Southern Plateau (290 to 300 m), and Northern Plateau (290 to 470 m). This pattern corresponds with the distribution of morphology-driven circulation cells, strongly affecting pelagic processes such as primary production, sedimentation (and, hence, food supply to the benthos), as well as retention of meroplanktonic larvae.

Description: Increased public awareness of the global significance of polar regions and opening of the Russian Arctic to foreign researchers have led to a pronounced intensification of benthic research in Arctic seas. The wealth of information gathered in these efforts has markedly enhanced our knowledge on the Arctic benthos. While some scientific concepts have been corroborated by the novel findings (e.g., low endemism and high faunistic affinity to northern Atlantic assemblages), other common notions need to be revised, particularly with regard to the often-cited differences between Arctic seas and the Southern Ocean. It has been demonstrated that benthos assemblages vary broadly in diversity between Arctic regions and that, hence, the idea of a consistently poor Arctic benthos—being in stark contrast to the rich Antarctic bottom fauna—is an undue overgeneralization. In terms of biogeographic diversity, both Arctic and Antarctic waters seem to be characterized by intermediate species richness. Levels of disturbance—a major ecological agent known to heavily affect benthic diversity and community structure—have been assumed to be relatively high in the Arctic but exceptionally low in the Southern Ocean. The discovery of the great role of iceberg scouring in Antarctic shelf ecosystems, which has largely been overlooked in the past, calls for a reconsideration of this notion. The novel data clearly demonstrate that there are marked differences in geographical and environmental setting, impact of fluvial run-off, pelagic production regime, strength of pelago–benthic coupling and, hence, food supply to the benthos among the various Arctic seas, impeding the large-scale generalization of local and regional findings. Field evidence points to the great significance of meso-scale features in hydrography and ice cover (marginal ice zones, polynyas, and gyres) as ‘hot spots’ of tight pelago–benthic coupling and, hence, high benthic biomass. In contrast, the importance of terrigenic organic matter discharged to the Arctic seas through fluvial run-off as an additional food source for the benthos is still under debate. Studies on the partitioning of energy flow through benthic communities strongly suggest that megafauna has to be adequately considered in overall benthic energy budgets and models of carbon cycling, particularly in Arctic shelf systems dominated by abundant echinoderm populations. Much progress has been made in the scientific exploration of the deep ice-covered Arctic Ocean. There is now evidence that it is one order of magnitude more productive than previously thought. Therefore, the significance of shelf–basin interactions, i.e., the importance of excess organic carbon exported from productive shelves to the deep ocean, is still debated and, hence, a major topic of on-going research. Another high-priority theme of current/future projects are the ecological consequences of the rapid warming in the Arctic. Higher water temperatures, increased fluvial run-off and reduced ice cover will give rise to severe ecosystem changes, propagating through all trophic levels. It is hypothesized that there would be a shift in the relative importance of marine biota in the overall carbon and energy flux, ultimately resulting in a switch from a ‘sea-ice algae–benthos’ to a ‘phytoplankton–zooplankton’ dominance.