The new Arctic in the global context - Ecosystem Part 2
- 11:00 The ice-water interface -- new approaches to investigate a crucial node in the Arctic ecosystem
Authors: Hauke Flores ( AWI ); Barbara Niehoff ( AWI ); Ilka Peeken ( AWI ); Fokje Schaafsma ( Wageningen Marine Research ); Nicoloe Hildebrandt ( AWI ); Jutta Wollenburg ( AWI ); Erin Kunisch ( UiT ); Rolf Gradinger ( UiT ); Marcel Nicolaus ( AWI ); Christian Katlein ( AWI )
The Arctic sea ice environment is changing faster than we can gain knowledge about its role for biodiversity and ecosystem functions. In the present Arctic Ocean sea ice plays a crucial role as a habitat hosting a unique diversity of life, and supporting major life stocks through the primary production of ice algae. Which ecological role sea ice played in the past, and how it may develop in the future, is largely unknown. Major carbon transmitters of the food web, such as Calanus spp., ice amphipods and polar cod, depend on the ice-water interface as a habitat and foraging ground. This makes the ice-water interface a functional node in the Arctic ecosystem. Sampling this environment, however, has been a challenge due to its inaccessibility to traditional sampling tools, such as nets, flasks and sensors. The rise of automated under-ice profilers and recent technological developments have made it possible to obtain a more quantitative view of the life in the ice-water interface layer, from microscopic protists to polar cod. This presentation will review recent developments in under-ice sampling with under-ice nets and ROVs, and the scientific knowledge that has been gained with them. A special focus will be laid on first experiences newly developed ROV-operated sampling devices suitable to be used during MOSAiC and other drift stations.
- 11:15 Tight coupling and distinct differences: Ecophysiological traits of sea ice algae blooms vs. pelagic under-ice blooms in Arctic landfast sea ice
Authors: Eva Leu ( Akvaplan-niva ); Ane Cecilie Kvernvik ( UNIS/ UiT ); Sander Verbiest ( University of Utrecht ); Thomas Brown ( Scottish Association of Marine Sciences ); Hoppe Clara Jule Marie ( Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine Research ); Jozef Wiktor ( Institute of Oceanology, Polish Academy of Science ); Tove Gabrielsen ( UNIS - The University Centre in Svalbard )
Decreasing Arctic sea ice changes the environmental conditions that control timing, quantity and quality of future Arctic algae blooms. In the FAABulous project, we try to gain a mechanistic understanding of how these changes will alter algal production regimes. In spring 2017, we observed a strong sea ice algal bloom occurring simultaneously with a pelagic algal bloom in Van Mijenfjorden in Svalbard. We found strong indications for a tight cryo-pelagic coupling in the bottom part of the sea ice, as indicated by species composition and biochemical tracers. At the same time, sea ice algae and phytoplankton seem to have distinct differences in their photophysiological traits, even if their surrounding conditions with respect to light and nutrient availability are very similar. These findings were confirmed by field experiments with natural communities, as well as laboratory experiments with unialgal cultures of dominating diatom species. Sea ice algae are superior in their ability to take advantage of even very low light intensities – whereas they are much more sensitive to high light stress, and have a lower maximum photosynthetic rate. Such intrinsic differences indicate that a transition from predominantly sympagic to more pelagic algal bloom regimes at high latitudes might have complex implications for ecosystems.
- 11:30 Emerging physical and biological properties in a new Arctic ice regime
Authors: Philipp Assmy ( Norwegian Polar Institute ); N-ICE2015 team ( N-ICE2015 )
One of the most prominent manifestations of climate change is the drastic decrease in Arctic sea-ice thickness and summer sea-ice extent. These fundamental changes in the physical properties of the ice pack will have unforeseen consequences for the entire Arctic marine food web. During the Norwegian young sea ICE (N-ICE2015) drift expedition from January to June 2015, we studied ice-algal and phytoplankton blooms under the new ice regime in the Arctic Ocean north of Svalbard, consisting of young ice, first- and second year ice. The most pertinent emerging physical properties observed during N-ICE2015 were the thinner and more dynamic ice pack, relatively thick snow cover, and the frequent formation of leads and ridges due to a more dynamic thin ice pack. This regime shift was reflected in the fact that light penetration through the open leads allowed for a phytoplankton bloom to develop in late May despite the snow-covered sea ice. On the other hand, ice-algal assemblages that developed in the high-light young ice environment of a refrozen lead were characterized by elevated levels of UV-protecting compounds, indicative of light stress by the shade-acclimated ice algae. The ice algal bloom of the young lead ice was apparently facilitated by recruitment of ice algae from adjacent older ice, highlighting the importance of the older ice for seeding of the ice algal bloom. Empirical and model results suggest that maximum growth rates of ice algae will increase whilst vertically integrated NPP and biomass will decrease under the thinner ice regime, as a result of the predictable increase in the area covered by refrozen leads in the Arctic Ocean. Furthermore, we have identified pressure ridges as biological hotspots which merit further investigation as the probability of their formation is expected to increase under the new, more dynamic Arctic sea ice regime. The heavy snow load on the sea ice caused negative ice-freeboard throughout the drift. In early June this led to infiltration of seawater through cracks in the ice and growth of phytoplankton at the snow-ice interface. These snow-infiltration communities have rarely been reported from the Arctic and could be another harbinger of a new Arctic sea ice regime. The observed changes in ice algal and phytoplankton bloom dynamics will potentially have cascading effects on the entire Arctic food web and may alter the uptake and release of climate-relevant gases from ocean and sea ice.
- 11:45 Benthic foraminifera as proxies of brine-enriched shelf waters cascading: promising tools for reconstructing historical changes in sea-ice production in the Storfjorden polynya (Svalbard)
Authors: Maria Pia Nardelli ( UMR CNRS 6112 - LPG-BIAF, University of Angers (France) ); Arbia Jouini ( University of Angers ); Hélène Howa ( UMR CNRS 6112 - LPG-BIAF, University of Angers (France) ); Bruno Lansard ( UMR CNRS 8212 – LSCE, Université de Versailles (France) ); Elisabeth Michel ( UMR CNRS 8212 – LSCE, Université de Versailles (France) ); Thierry Garlan ( ervice Hydrographique et Océanographique de la Marine (SHOM), Brest ); Frédéric Vivier ( UMR CNRS 7159 - LOCEAN, Université Paris 6 (UMPC) (France) ); Agnès Baltzer ( LETG - UMR6554 CNRS, Université de Nantes (France) ); Meryem Mojtahid ( UMR CNRS 6112 - LPG-BIAF, University of Angers (France) )
Nowadays, the Storfjorden (Svalbard) is a first-year sea-ice production zone characterized by
intenseproduction of brine and cascading of brine-enriched shelf waters (BSW). Brine formation, and the consequent injection of salty and relatively acid dense water into the deepest ocean,was likely more important during the cold climatic periods of Holocene, because of the higher sea-ice production. In this study, we explore the potential of benthic foraminifera (fossilizing meiofauna), as indicators of brine water circulation on the sea floor. Consequently, the identification of benthic foraminiferal species sensitive to brine waters properties would allow the reconstruction of the extent and the temporal variability of Arctic sea-ice cover, and therefore a better understanding of the ongoing climatic change on historical time scales (hundred to thousand years). Therefore, this study aims at calibrating the ecological response of living benthic foraminifera to sinking brine waters,and estimating the taphonomic loss during early stages of test fossilization. Sediments from 7 interface cores sampled along a N-Stransect across the Storfjorden were analyzed for livingand modern dead foraminiferal assemblages. Results from the living fauna show two major biozones: an “inner-basin” fauna characterized by the dominance of calcareous species, with more or less dissolved tests; and an “outer-basin” fauna, characterized by a strong dominance of agglutinated species, potentially due to persistent relatively low pH conditions hampering the development of calcareous species. Down-core dead faunas from the inner-basin show low amplitude temporal changes, while in the outer-basin some abrupt changes in agglutinated/calcareous ratios occur. High ratios suggest large brine production and higher BSW residence times in the inner basin, whereas low ratios (more calcareous) might correspond with low to no sea-ice cover periods due to warmer and organic enriched Atlantic water intrusions into the fjord. Indeed, the ratio between agglutinated and calcareous benthic foraminiferal species is potentially a good bio-indicatorof BSW circulation in Arctic shelf areas.
Wednesday 24th January 2018
11:00 - 12:00