Abstract: During sea-ice melt in the Arctic, primary production by sympagic (sea-ice) algae can be exported efficiently to the seabed if sinking rates are rapid and activities of associated heterotrophic bacteria are limited. Salinity stress due to melting ice has been suggested to account for such low bacterial activity. We further tested this hypothesis by analyzing samples of sea ice and sinking particles collected from May 18 to June 29, 2016, in western Baffin Bay as part of the Green Edge project. We applied a method not previously used in polar regions—quantitative PCR coupled to the propidium monoazide DNA-binding method—to evaluate the viability of bacteria associated with sympagic and sinking algae. We also measured cis-trans isomerase activity, known to indicate rapid bacterial response to salinity stress in culture studies, as well as free fatty acids known to be produced by algae as bactericidal compounds. The viability of sympagic-associated bacteria was strong in May (only approximately 10% mortality of total bacteria) and weaker in June (average mortality of 43%; maximum of 75%), with instances of elevated mortality in sinking particle samples across the time series (up to 72%). Short-term stress reflected by cis-trans isomerase activity was observed only in samples of sinking particles collected early in the time series. Following snow melt, however, and saturating levels of photosynthetically active radiation in June, we observed enhanced ice-algal production of bactericidal compounds (free palmitoleic acid; up to 4.8 mg L–1). We thus suggest that protection of sinking sympagic material from bacterial degradation early in a melt season results from low bacterial activity due to salinity stress, while later in the season, algal production of bactericidal compounds induces bacterial mortality. A succession of bacterial stressors during Arctic ice melt helps to explain the efficient export of sea-ice algal material to the seabed.

Abstract: Measurements of net community production (NCP) provide an upper constraint on the strength of the oceanic biological pump, the dominant mechanism for removing CO2 from the ocean surface and sequestering it at depth. In this investigation, our objectives were to describe the spatial and temporal variability of NCP associated with the spring ice-edge bloom in Baffin Bay and to identify the key environmental drivers controlling its variability. Using data collected between June 9 and July 10, 2016, we estimated NCP based on (1) underway measurements of surface water oxygen to argon ratios (O2:Ar), (2) underway measurements of the partial pressure of CO2, and (3) seasonal nitrate drawdown from discrete samples. These multiple approaches displayed high NCP (up to 5.7 mol C m–2) in eastern Baffin Bay, associated with modified Atlantic waters, and low NCP (<1 mol C m–2) in the presence of Arctic outflow waters in western Baffin Bay. Arctic outflow waters were characterized by low surface salinities and nitrate concentrations, suggesting that high freshwater content may have limited the nutrient availability of these waters. Different integration depths and timescales associated with each NCP approach were exploited to understand the temporal progression and succession of the bloom, revealing that the bloom was initiated under ice up to 15 days prior to ice retreat and that a large portion of NCP in eastern Baffin Bay (potentially up to 70%) was driven by primary production occurring below the surface-mixed layer.

Abstract: Bioluminescence, which occurs in approximately 80% of the world's mesopelagic fauna, can take the form of a low-intensity continuous glow (e.g. for counter-illumination or signalling) or fast repetitions of brighter anti-predatory flashes. The southern elephant seal (SES) is a major consumer of mesopelagic organisms, in particular the abundant myctophid fish, yet the fine-scale relationship between this predator's foraging behaviour and bioluminescent prey remains poorly understood. We hypothesised that brief, intense light emissions should be closely connected with prey strikes when the seal is targeting bioluminescent prey that reacts by emitting anti-predator flashes. To test this, we developed a biologging device containing a fast-sampling light sensor together with location and movement sensors to measure simultaneously anti-predator bioluminescent emissions and the predator's attack motions with a 20 ms resolution. Tags were deployed on female SES breeding at Kerguelen Islands and Península Valdés, Argentina. In situ light levels in combination with duration of prey capture attempts indicated that seals were targeting a variety of prey types. For some individuals, bioluminescent flashes occurred in a large proportion of prey strikes, with the timing of flashes closely connected with the predator's attack motion, suggestive of anti-predator emissions. Marked differences across individuals and location indicate that SES do exploit bioluminescent organisms but the proportion of these in the diet varies widely with location. The combination of wideband light and acceleration data provides new insight into where and when different prey types are encountered and how effectively they might be captured.

Abstract: The objective of this contribution is to get new insights into the effects of magnetic field variations of natural and anthropogenic origin on broad-band seismic stations. Regarding natural sources of magnetic perturbations, we have investigated if the Sudden Storm Commencements (SSC) cataloged during the 24th solar cycle (2008–2019) can be systematically identified in broad-band seismic stations distributed worldwide. The results show that the 23 SSC events with a mean amplitude above 30 nT and most of those with lower energy but still clearly identified in the magnetometer detection network can be observed at broad-band stations’ network using a simple low-pass filter. Although the preliminary impulse of those signals is usually stronger at stations located at high latitudes, major SSC are observed at seismic stations distributed worldwide. Regarding anthropogenic sources, we focus on the short period seismic signals recorded in urban environments which are correlated with the activity of the railway transportation system. We have analyzed collocated measurements of electric field and seismic signals within Barcelona, evidencing that significant changes in the electric field following the activity of the transportation systems can be attributed to leakage currents transmitted to the soil by trains. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations inducing telluric currents near the Earth surface, which in turn generate a secondary magnetic field. In the case of underground trains, leakage currents are transmitted to the soil, which in turn can result in local variations in the magnetic field. The observed signals in modern seismometers can be related to the reaction of the suspension springs to these magnetic field variations or to the effect of the magnetic field variations on the force transducers used to keep the mass fixed.

Abstract: In this paper, we provide a comprehensive overview of the state-of-knowledge of dust flux and variability in time and space in different sectors of East Antarctica during the Holocene. By integrating the literature data with new evidences, we discuss the dust flux and grain-size variability during the current interglacial and its provenance in the innermost part of the East Antarctic plateau as well as in peripheral regions located close to the Transantarctic Mountains. The local importance of aeolian mineral dust aerosol deflated from low-elevation areas of peripheral East Antarctica is also discussed in the light of new data from several coastal, low-elevation sites.