Epibenthos Dynamics and Environmental Fluctuations in Two Contrasting Polar Carbonate Factories (Mosselbukta and Bjørnøy-Banken, Svalbard)

Max Wisshak,Janina V Büscher,Peter Linke,Hermann Neumann,Andres Rüggeberg,Jacek Raddatz

doi:10.3389/fmars.2019.00667

Abstract

The Arctic Svalbard Archipelago hosts the world’s northernmost cold-water ‘carbonate factories’ thriving here despite of presumably unfavourable environmental conditions and extreme seasonality. Two contrasting sites of intense biogenic carbonate production, the rhodolith beds in Mosselbukta in the North of the archipelago and the barnacle-mollusc dominated carbonate sediments accumulating in the strong hydrodynamic regime of the Bjornoy-Banken south of Spitsbergen, were the targets of the RV Maria S. Merian cruise 55 in June 2016. By integrating data from physical oceanography, marine biology, and marine geology, the present contribution characterises the environmental setting and biosedimentary dynamics of these two polar carbonate factories. Repetitive CTD profiling in concert with autonomous temperature/salinity loggers on a long-term settlement platform identified spatiotemporal patterns in the involved Atlantic and Polar water masses, whereas short-term deployments of a lander revealed fluctuations of environmental variables in the rhodolith beds in Mosselbukta and at same depth (46 m) at Bjornoy-Banken. At both sites, dissolved inorganic nutrients in the water column were found depleted (except for elevated ammonium concentrations) and show an overall increase in concentration and N:P ratios towards deeper waters. This indicates that a recycling system was fuelling primary production after the phytoplankton spring bloom at the time of sampling in June 2016. Accordingly, oxygen levels were found elevated and carbon dioxide concentrations (pCO2) markedly reduced, on average only half the expected equilibrium values. Backed up by seawater stable carbon and oxygen isotope signatures, this is interpreted as an effect of limited air-sea gas exchange during seasonal ice cover in combination with a boost in community photosynthesis during the spring phytoplankton bloom. The observed trends are enhanced by the onset of rhodophyte photosynthesis in the rhodolith beds during the polar day upon retreat of sea-ice. Potential adverse effects of ocean acidification on the local calcifier community are thus predicted to be seasonally buffered by the marked drop in pCO2 during the phase of sea-ice cover and spring plankton bloom, but this effect will diminish should the seasonal sea-ice formation continue to decline. (Abstract truncated here - please see comments for our arrangement of excess word count)

Highlights

Arctic Carbonate FactoriesBiogenic carbonate production by benthic skeletal organisms on the shelf and in coastal waters of the Arctic Svalbard Archipelago supports the northernmost cold-water ‘carbonate factories’ known to date
The Svalbard C factories have evolved between Bjørnøya (Bear Island) and northern Spitsbergen upon retreat of the last glacial ice sheet during the early Holocene, despite presumably unfavourable environmental conditions characterised by cold waters with low carbonate saturation, iceberg ploughing, high aeolian and glacial terrigenous input, as well as extreme seasonality (e.g., Henrich et al, 1995, 1996, 1997; Teichert et al, 2012, 2014)
Ice charts indicate the presence of drift ice in Mosselbukta in February and from April to early June 2007 (Figure 3F)

Summary

Introduction

Biogenic carbonate production by benthic skeletal organisms on the shelf and in coastal waters of the Arctic Svalbard Archipelago supports the northernmost cold-water ‘carbonate factories’ known to date. Among the most significant carbonate producers in polar C factories are calcifying crustose coralline red algae (Rhodophyta), and their non-attached mobile sedimentary aggregates, called rhodoliths They serve as ‘bioengineers’ that provide habitat for a great variety of invertebrate species (Foster, 2001; Barbera et al, 2003). Lithothamnion glaciale has a widespread distribution and contributes substantially to cold-temperate and polar carbonate production It is the key species in the extensive Svalbard rhodolith beds (Teichert et al, 2014; Teichert and Freiwald, 2014). Among the invertebrate calcifiers it is mainly the large clam Chlamys islandica, the thick-shelled Mya truncata, and the bioeroding bivalve Hiatella arctica, as well as the barnacle Balanus balanus that contribute to the intense carbonate production, complemented by various species of serpulid worms, bryozoans, benthic foraminiferans, gastropods, and echinoderms (e.g., Andruleit et al, 1996; Henrich et al, 1996, 1997; Teichert et al, 2012, 2014)

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