Spatial Variation in Sediment Organic Carbon Distribution across the Alaskan Beaufort Sea Shelf

Coffin, Richard B.; Smith, Joseph P.; Yoza, Brandon A.; Boyd, Thomas J.; Montgomery, Michael T.

doi:10.3390/en10091265

Cited by 6 publications

(4 citation statements)

References 58 publications

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“…Cryopeg brines considered here featured POC concentrations of 2–12 mM and DOC concentrations of 30–102 mM, which are high when compared to the typical micromolar concentrations in seawater ( Mathis et al, 2005 ; Goñi et al, 2021 ). The DOC concentrations are also high when compared to porewaters of nearby (unfrozen) marine sediments (e.g., < 7 mM on the Alaskan north slope; Coffin et al, 2017 ) and other Arctic marine sediments (1–6 mM, Arnosti and Jørgensen, 2006 ; < 1 mM, Rossel et al, 2020 ). Measured inorganic nutrients were also relatively high: nitrate, nitrite, and phosphate were present in micromolar concentrations, while ammonium concentrations were at millimolar levels ( Cooper et al, 2019 ).…”

Section: Physical and Biological Context For The Modelmentioning

confidence: 99%

Modeled energetics of bacterial communities in ancient subzero brines

et al. 2023

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Cryopeg brines are isolated volumes of hypersaline water in subzero permafrost. The cryopeg system at Utqiaġvik, Alaska, is estimated to date back to 40 ka BP or earlier, a remnant of a late Pleistocene Ocean. Surprisingly, the cryopeg brines contain high concentrations of organic carbon, including extracellular polysaccharides, and high densities of bacteria. How can these physiologically extreme, old, and geologically isolated systems support such an ecosystem? This study addresses this question by examining the energetics of the Utqiaġvik cryopeg brine ecosystem. Using literature-derived assumptions and new measurements on archived borehole materials, we first estimated the quantity of organic carbon when the system formed. We then considered two bacterial growth trajectories to calculate the lower and upper bounds of the cell-specific metabolic rate of these communities. These bounds represent the first community estimates of metabolic rate in a subzero hypersaline environment. To assess the plausibility of the different growth trajectories, we developed a model of the organic carbon cycle and applied it to three borehole scenarios. We also used dissolved inorganic carbon and nitrogen measurements to independently estimate the metabolic rate. The model reconstructs the growth trajectory of the microbial community and predicts the present-day cell density and organic carbon content. Model input included measured rates of the in-situ enzymatic conversion of particulate to dissolved organic carbon under subzero brine conditions. A sensitivity analysis of model parameters was performed, revealing an interplay between growth rate, cell-specific metabolic rate, and extracellular enzyme activity. This approach allowed us to identify plausible growth trajectories consistent with the observed bacterial densities in the cryopeg brines. We found that the cell-specific metabolic rate in this system is relatively high compared to marine sediments. We attribute this finding to the need to invest energy in the production of extracellular enzymes, for generating bioavailable carbon from particulate organic carbon, and the production of extracellular polysaccharides for cryoprotection and osmoprotection. These results may be relevant to other isolated systems in the polar regions of Earth and to possible ice-bound brines on worlds such as Europa, Enceladus, and Mars.

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Section: Physical and Biological Context For The Modelmentioning

confidence: 99%

Modeled energetics of bacterial communities in ancient subzero brines

et al. 2023

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“…Sediment wet (W sw ) and dry (W sd ) weights were recorded before and after freeze-drying, and used to calculate the mass of water (Ww). Sediment density (ρ s ) was held constant at 2.50 g/cm 3 , based on Coffin et al (2017) . Seawater density (ρ w ) was calculated based on bottom-water temperatures and salinities recorded at sampled sites.…”

Section: Methodsmentioning

confidence: 99%

“…These longitudinal environmental gradients from Point Barrow to Banks Island have been reflected in the benthic distributions of OM and certain epi-/infaunal groups (Naidu et al, 2000;Magen et al, 2010;Goñi et al, 2013;Bell et al, 2016). This benthic habitat may also be heavily influenced by methane derived from organic matter burial, mud volcanoes, subsurface permafrost, and/or gas hydrates (Paull et al, 2015;Brothers et al, 2016;Coffin et al, 2017;Lee et al, 2018;Retelletti Brogi et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Patterns in Benthic Microbial Community Structure Across Environmental Gradients in the Beaufort Sea Shelf and Slope

2021

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The paradigm of tight pelagic-benthic coupling in the Arctic suggests that current and future fluctuations in sea ice, primary production, and riverine input resulting from global climate change will have major impacts on benthic ecosystems. To understand how these changes will affect benthic ecosystem function, we must characterize diversity, spatial distribution, and community composition for all faunal components. Bacteria and archaea link the biotic and abiotic realms, playing important roles in organic matter (OM) decomposition, biogeochemical cycling, and contaminant degradation, yet sediment microbial communities have rarely been examined in the North American Arctic. Shifts in microbial community structure and composition occur with shifts in OM inputs and contaminant exposure, with implications for shifts in ecological function. Furthermore, the characterization of benthic microbial communities provides a foundation from which to build focused experimental research. We assessed diversity and community structure of benthic prokaryotes in the upper 1 cm of sediments in the southern Beaufort Sea (United States and Canada), and investigated environmental correlates of prokaryotic community structure over a broad spatial scale (spanning 1,229 km) at depths ranging from 17 to 1,200 m. Based on hierarchical clustering, we identified four prokaryotic assemblages from the 85 samples analyzed. Two were largely delineated by the markedly different environmental conditions in shallow shelf vs. upper continental slope sediments. A third assemblage was mainly comprised of operational taxonomic units (OTUs) shared between the shallow shelf and upper slope assemblages. The fourth assemblage corresponded to sediments receiving heavier OM loading, likely resulting in a shallower anoxic layer. These sites may also harbor microbial mats and/or methane seeps. Substructure within these assemblages generally reflected turnover along a longitudinal gradient, which may be related to the quantity and composition of OM deposited to the seafloor; bathymetry and the Mackenzie River were the two major factors influencing prokaryote distribution on this scale. In a broader geographical context, differences in prokaryotic community structure between the Beaufort Sea and Norwegian Arctic suggest that benthic microbes may reflect regional differences in the hydrography, biogeochemistry, and bathymetry of Arctic shelf systems.

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“…Cold seeps are the areas of seepage of hydrogen sulfide, methane, and other hydrocarbon-rich fluids, which originate from tens of meters to kilometers below the seafloor ( 1 , 2 ). The ecosystem here mainly depends on the anaerobic oxidation of methane (AOM) acting as an energy source, together with the organic carbon input from the water column ( 3 ). In vitro studies suggest that anaerobic methanotrophic archaea (ANME) exhibit AOM activity and are mostly associated with sulfate-reducing bacteria (SRB), which oxidize methane to bicarbonate or acetate for utilization by heterotrophs ( 4 – 7 ).…”

Section: Introductionmentioning

confidence: 99%