Stress factors resulting from the Arctic vernal sea-ice melt

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.

Singlet oxygen‐induced alteration of bacteria associated with phytodetritus: Effect of irradiance

“…Sinking particulate matter samples were collected: (i) in summer at 100 m in open water in the Beaufort Sea (Rontani et al, 2016), (ii) in summer at 25 m in the marginal ice zone of central Baffin Bay (Rontani et al, 2022), and (iii) in spring at 5 and 30 m in ice‐covered Resolute Passage (Rontani et al, 2016). Sea‐ice samples (0–10 cm) were collected in spring during the GreenEdge campaign at Qikiqtarjuaq (Baffin Bay, Arctic Ocean; Amiraux et al, 2020). To compare the efficiency of type II photooxidation processes in algal and bacterial material, we used the ratio of % vaccenic acid photooxidation to % palmitoleic acid photooxidation.…”

“…In this solid habitat, the bacteria–sympagic algae association may be maintained at relatively high irradiances during long periods; these conditions strongly favoring the photooxidation of bacteria. It was previously demonstrated that during the early stages of ice melt, sympagic bacteria undergo an intense osmotic stress in hypersaline ice brines (Amiraux et al, 2017) and are affected later in the season by the release of bactericidal free palmitoleic acid by sympagic algae under the effect of light stress (Amiraux et al, 2020). Our results show that these organisms may also undergo a strong photooxidative stress in the ice resulting from a strong and efficient transfer of 1 O 2 from senescent sympagic algae.…”

“…Briefly, sinking particles were collected (i) in Resolute Passage under first‐year ice at 5‐ and 30‐m depths with Hydro‐Bios MS12‐model multisediment traps (Rontani et al, 2016), (ii) in central Baffin Bay under the marginal ice zone at 25‐m depth with a Technicap PPS4 drifting sediment trap (Rontani et al, 2022), and (iii) in the Beaufort Sea in open water at 100‐m depth with Technicap PPS traps (Rontani et al, 2012). Sea‐ice samples were collected at GreenEdge Project landfast ice station located near Broughton Island in the Davis Strait using a Kovacs Mark V 14‐cm‐diameter corer and focusing on the bottommost 10 cm of sea ice (Amiraux et al, 2020; Figure 1).…”

“…Detailed descriptions of the Arctic marine particulate matter and sea-ice sample collection processes (e.g., sampling dates, depths, and volumes) can be found in previously published works (Amiraux et al, 2020;Rontani et al, 2012Rontani et al, , 2016Rontani et al, , 2022. Briefly, sinking particles were collected (i) in Resolute Passage under first-year ice at 5-and 30-m depths with Hydro-Bios MS12-model multisediment traps (Rontani et al, 2016), (ii) in central Baffin Bay under the marginal ice zone at 25-m depth with a Technicap PPS4 drifting sediment trap (Rontani et al, 2022), and (iii) in the Beaufort Sea in open water at 100-m depth with Technicap PPS traps (Rontani et al, 2012).…”