State of the Arctic - Arctic marine ecology
- 13:00 Climate based multi-year predictions of the Barents Sea cod stock
Authors: Marius Årthun ( Geophysical Institute, University of Bergen, and Bjerknes Centre for Climate Research ); Bjarte Bogstad ( Institute of Marine Research ); Ute Daewel ( Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research ); Noel Keenlyside ( Geophysical Institute, University of Bergen, and Bjerknes Centre for Climate Research ); Anne Britt Sandø ( Institute of Marine Research ); Corinna Schrum ( Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research ); Geir Ottersen ( Institute of Marine Research )
Predicting fish stock variations on interannual to decadal time scales is one of the major issues in fisheries science and management. Although the field of marine ecological predictions is still in its infancy, it is understood that a major source of multi-year predictability resides in the ocean. Here we show the first highly skilful long-term predictions of the commercially valuable Barents Sea cod stock. The 7-year predictions are based on the propagation of ocean temperature anomalies from the subpolar North Atlantic toward the Barents Sea, and the strong co-variability between these temperature anomalies and the cod stock. Retrospective predictions for the period 1957-2017 capture well multi-year to decadal variations in cod stock biomass, with cross-validated explained variance of over 60%. For lead times longer than one year the statistical long-term predictions show more skill than operational short-term predictions used in fisheries management and lagged persistence forecasts. Our results thus demonstrate the potential for ecosystem-based fisheries management, which could enable strategic planning on longer time scales. Future predictions show a gradual decline in the cod stock towards 2024.
- 13:30 Wind-driven variability of advection and sea-ice cover in the Barents Sea and impacts on productivity
Authors: Vidar S. Lien ( Institute of Marine Research ); Pawel Schlichtholz ( Institute of Oceanology, Polish Academy of Sciences ); Øystein Skagseth ( Institute of Marine Research ); Frode Vikebø ( Institute of Marine Research )
Variability in the Barents Sea ice cover on inter-annual and longer time-scales has previously been shown to be governed by oceanic heat transport. Based on analysis of observations and results from an ocean circulation model we show that the ocean also plays a direct role within seasons. Positive wind stress curl and associated Ekman divergence causes a coherent increase in the Atlantic water transport along the negative thermal gradient through the Barents Sea. The immediate response connected to the associated local winds in the north-eastern Barents Sea is a decrease in the sea-ice cover due to advection. Despite a subsequent anomalous ocean to air heat loss due to the open water, increased ocean heat content contributes to maintaining a reduced sea-ice cover. These changes in circulation and ice cover potentially affect biological productivity both directly through advection, and indirectly through changes in ice cover and subsequent physical changes in the water column including light conditions.
- 13:45 Pelagic-benthic coupling over winter in Kaldfjorden, Northern Norway
Authors: Zoe Walker ( UiT - The Arctic University of Norway, Tromsø ); Ingrid Wiedmann ( UiT - The Arctic University of Norway, Tromsø ); Angelika Renner ( Institute of Marine Research )
Global aquaculture is projected to double by 2050 to meet the demand of a growing human population. Norway has stated its interest in expanding its aquaculture sector to supply this growing international and domestic demand. The environmental impact of aquaculture by-products is determined by their concentration and distribution, which are affected by seasonal signals in pelagic-benthic coupling. Spring and summer studies of pelagic-benthic coupling in Norwegian fjords are significantly more abundant than those focusing on late autumn and winter. This study compared meteorology, hydrography, concentration of suspended and sinking biomass, and total particulate matter flux from October 2017 to May 2018 in Kaldfjorden, Norway (69.746ºN, 18.683ºE) to explore the physical and biological drivers of pelagic-benthic coupling. Stratification of the water column in Kaldfjorden weakened between October and December before disappearing completely in January and February, identifying winter as a time of high mixing. Changes to the physical environment coincided with a steep decline in suspended chlorophyll a concentration (Oct: 0.09-3.15 mg m-3, Dec-Feb: 0.03-0.12 mg m-3) and zooplankton abundance (Nov: 4502.8 ind. m-3, Jan-Feb: <101.7 ind. m-3). Sinking material was sampled using short-term sediment traps (24hrs). The downward biomass flux decreased throughout winter and particulate matter became more degraded, most likely due to zooplankton grazing. Sediment trap samples also showed evidence of resuspension following episodic winds throughout winter. The observed decrease in stratification and biological activity in this study is considered characteristic of a Northern Norwegian fjord. Results indicate the importance of including seasonally and regionally appropriate environmental baselines in the management of open circuit aquaculture to mitigate environmental impacts at high-latitudes.
- 14:00 The role of sympagic fauna for ecosystem functions in the Arctic Ocean, north of Spitsbergen
Authors: Julia Ehrlich ( Alfred-Wegener-Institut/ Universität Hamburg ); Hauke Flores ( Alfred-Wegener-Institut ); Bodil Bluhm ( The Arctic University of Norway ); Angelika Brandt ( Senckenberg Institut )
In the Arctic ocean, sea-ice habitats are deteriorating rapidly. The sea ice hosts specific ice-associated communities known as ‘sympagic fauna’, which performs important ecosystem functions (e.g., carbon cycling). Those ecosystem functions are often enhanced by biodiversity and decline of sea ice can alter the composition and biodiversity of the sympagic fauna. Thus, understanding the relationship of biodiversity with ecosystem functions is important for predicting consequences of climate change in polar ecosystems.
During the Polarstern expedition ‘The Transitions in the Arctic Seasonal Sea-Ice Zone’ (TRANSSIZ) in the north of Spitsbergen, material from under‑ice and in‑ice biota was sampled (PS92, 5/2015-6/2015). This study gives an integrated inventory of the biodiversity and community structure of sympagic protist-, meio- and macrofauna applying morphological techniques and relates them to habitat properties and ecosystem functions.
The knowledge of the linkage between biodiversity and ecosystem function in ice‑covered areas in the Arctic Ocean is highly warranted for the resource and conservation management of polar sea-ice ecosystems.
- 14:15 The photosynthetic response of ice algae varies with sample melt procedure
Authors: Karley Campbell ( University of Bristol ); C.J. Mundy ( University of Manitoba ); Andy Juhl ( Columbia University ); Laura Dalman ( University of Manitoba ); Christine Michel ( Department of Fisheries and Oceans ); Ryan Galley ( University of Manitoba ); Brent Else ( University of Calgary ); Nicolas Geilfius ( University of Manitoba ); Soren Rysgaard ( Aarhus University )
The accuracy of sea ice algal production estimates is influenced by the range of melting procedures used in studies to obtain a liquid sample for incubation, particularly in relation to the duration of melt and the approach to buffering for osmotic shock. In this research, field measurements of first-year ice from the Canadian Arctic Archipelago were examined and then tested using controlled laboratory experiments on cultures of Nitzschia frigidato comprehensively investigate the impact of three commonly applied melt procedures on the photophysiology, and thus modeled productivity, of sea ice algae. The field techniques examined included: i) a rapid 4 h melt of the bottommost (< 1 cm) ice algal layer scraped into a large volume of filtered seawater (salinity 27 - 30), ii) melt of a bottom 5 cm section diluted in filtered seawater (salinity 20 - 24) over 24 h, and iii) melt of a bottom 5 cm section with no filtered seawater dilution (salinity 10 -12) over 48 h. Field-based and experimental results consistently showed that maximum photosynthetic rate and photosynthetic efficiency varied significantly between growth conditions created by the melt treatments, having the greatest values in the highly diluted scrape sample and lowest values in the bulk-ice sample melted without filtered seawater. These responses are largely attributed to the rapid (<4 h) adverse effect of exposing cells to salinities much fresher than in situconditions. The observed differences in primary production between melt treatments examined were estimated to account for over 60% of the variability in production estimates reported for the Arctic. To limit the influence of ice melt procedure on estimates of primary production, future studies are strongly encouraged replicate in situsalinity conditions during the melting process in an effort to minimize the negative effects of hypoosmotic stress.
Thursday 24th January 2019
13:00 - 14:30