Preliminary evidence for the microbial loop in Antarctic sea ice using microcosm simulations

Abstract

<jats:title>Abstract</jats:title><jats:p>Sea ice microalgae actively contribute to the pool of dissolved organic matter (DOM) available for bacterial metabolism, but this link has historically relied on bulk correlations between chlorophyll<jats:italic>a</jats:italic>(a surrogate for algal biomass) and bacterial abundance. We incubated microbes from both the bottom (congelation layer) and surface brine region of Antarctic fast ice for nine days. Algal-derived DOM was manipulated by varying the duration of irradiance, restricting photosynthesis with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or incubating in the dark. The bacterial response to changes in DOM availability was examined by performing cell counts, quantifying bacterial metabolic activity and examining community composition with denaturing gradient gel electrophoresis. The percentage of metabolically active bacteria was relatively low in the surface brine microcosm (10–20% of the bacterial community), the treatment with DCMU indirectly restricted bacterial growth and there was some evidence for changes in community structure. Metabolic activity was higher (35–69%) in the bottom ice microcosm, and while there was no variation in community structure, bacterial growth was restricted in the treatment with DCMU compared to the light/dark treatment. These results are considered preliminary, but provide a useful illustration of sea ice microbial dynamics beyond the use of ‘snapshot’ biomass correlations.</jats:p>

Nutrient Distribution in East Antarctic Summer Sea Ice: A Potential Iron Contribution From Glacial Basal Melt

“…Therefore, PEPS could be used as a carbon source for bacteria, also facilitating grazing by heterotrophic and mixotrophic protists. Tightly coupled bacteria‐algae interactions have been reported in sea‐ice systems (Stewart & Fritsen, 2004) and the microbial loop is considered an important mechanism for recycling of organic matter in sea ice (Martin et al., 2012; Meiners and Michel, 2016).…”

Sea Ice Melting Drives Substantial Change in Dissolved Organic Matter in Surface Water off Prydz Bay, East Antarctic

“…Thus, both FT‐ICR MS‐derived molecular formulas and optical parameters suggest that the DOM of the SIM water samples is enriched in fresh, biolabile compounds, whereas the DOM of the post‐SIM water samples contains more refractory, humic‐like compounds. Taken together these observations suggest that heterotrophic bacteria in the surface water of the Southern Ocean preferentially consume smaller molecular weight compounds with low aromaticity characteristics under seasonal sea ice cover, causing selective accumulation of higher‐molecular‐weight compound with higher humification degrees (Barker et al., 2013; Imbeau et al., 2021; Martin et al., 2012).…”

It's what's inside that matters: physiological adaptations of high‐latitude marine microalgae to environmental change

“…The switch from lysogenic to lytic infection of bacteriophages during a spring bloom in the Western Antarctic Peninsula is a major control on bacterial populations and, through regenerated nutrients, indirectly influences primary production (Brum et al, 2016). It is unknown how warming oceans and reduced sea-ice thickness and duration could affect these interactions, ultimately impacting biogeochemical cycles (Martin et al, 2012a). For example, a study by Maat et al (2017) found that warmer temperatures shortened latent periods and increased burst size of Micromonas polaris viruses.…”