The biogeochemical role of a microbial biofilm in sea ice

Abstract

A paradox is commonly observed in productive sea ice in which an accumulation in the macro-nutrients nitrate and phosphate coincides with an accumulation of autotrophic biomass. This paradox requires a new conceptual understanding of the biogeochemical processes operating in sea ice. In this study, we investigate this paradox using three time series in Antarctic landfast sea ice, in which massive algal blooms are reported (with particulate organic carbon concentrations up to 2,600 µmol L–1) and bulk nutrient concentrations exceed seawater values up to 3 times for nitrate and up to 19 times for phosphate. High-resolution sampling of the bottom 10 cm of the cores shows that high biomass concentrations coexist with high concentrations of nutrients at the subcentimeter scale. Applying a nutrient-phytoplankton-zooplankton-detritus model approach to this sea-ice system, we propose the presence of a microbial biofilm as a working hypothesis to resolve this paradox. By creating microenvironments with distinct biogeochemical dynamics, as well as favoring nutrient adsorption onto embedded decaying organic matter, a biofilm allows the accumulation of remineralization products (nutrients) in proximity to the sympagic (ice-associated) community. In addition to modifying the intrinsic physicochemical properties of the sea ice and providing a substrate for sympagic community attachment, the biofilm is suggested to play a key role in the flux of matter and energy in this environment.

Modeling Virus and Bacteria Populations in Europa’s Subsurface Ocean

“…We imagine the sub-ice biosphere to resemble either a shallow biosphere just beneath the ice, or perhaps biofilms growing on the underside of Europa’s ice cover [ 18 ], where prokaryotic analogs can receive an influx of oxidants from the convection of the ice above and an influx of DOM from the ‘viral elevator’ below. In sea-ice environments on Earth, biofilms have already been shown to play an important role in the flux of energy and matter [ 29 ].…”

Effects of Snow and Remineralization Processes on Nutrient Distributions in Multi‐Year Antarctic Landfast Sea Ice

“…Such vertical nutrient distributions are considered to be closely related to physical characteristics such as salinity, δ 18 O value, and ice structure (discussed in Section 3.3). Furthermore, the high concentrations of various nutrients at the bottom of both first-year and multi-year ice columns are most likely related to the high concentrations of chl a in the bottommost ice column (Figures 4d and 4h), indicating both photosynthesis by the ice algae and remineralization by the degradation of organic matter (Roukaerts et al, 2021;Rysgaard & Glud, 2004;Rysgaard et al, 2008;Thomas et al, 1995). Roukaerts et al (2021) proposed the microbial biofilm in sea ice.…”

“…In addition to the consumption of nutrients by ice algae, high‐salinity and high‐nutrient brines are discharged beneath the sea ice over time (Fripiat et al., 2017). Nutrients are resupplied by remineralization during the degradation of organic matter within sea ice by heterotrophs and bacteria (Roukaerts et al., 2021; Thomas et al., 1995), as well as by convection through brine channels (Nomura et al., 2009; Vancoppenolle et al., 2010).…”

Monitoring a changing Arctic: Recent advancements in the study of sea ice microbial communities

“…Nutrient availability is difficult to assess, as this depends both on how the brine channel system is connected with the underlying ocean, and how microscale processes like microbial recycling and the creation of microenvironments with distinct biogeochemical dynamics (e.g. Fripiat et al 2017 ; Roukaerts et al 2021 ) control nutrient concentrations in the brine. In addition, there are a number of other factors influencing nutrient availability, such as: regional proximity of the sea ice to Pacific or Atlantic inflow (Fig.…”

“…Microbial adaptations for life in sea ice require modifications to intracellular processes, but also to extracellular controls. For example, this includes the exudation of gelatinous extracellular polymeric substances or production of ice-binding proteins that have been shown to modify the functioning of the microbial community and the structure of their ice environment (Krembs et al 2011 ; Ewert and Deming 2013 ; Roukaerts et al 2021 ). In this paper, we provide an overview on the complexities of sea ice microbial communities while introducing innovative methods that may be used to characterise their presence and function within Arctic sea ice.…”