Journal of Geophysical Research: Solid Earth
Numerical simulation of cool hydrothermal processes in the upper volcanic crust beneath a marine sediment pond: North Pond, North Atlantic Ocean - NEW!
Price, A. N.*, Fisher, A. T.*, Stauffer, P. H., & Gable, C. W.
*C-DEBI Contribution 580

Low temperature hydrothermal systems hosted in the volcanic oceanic crust are responsible for ∼20% of Earth's global heat loss. Marine sediment ponds comprise an important type setting on young ridge flanks where hydrothermal circulation advectively extracts lithospheric heat, but the nature of coupled fluid-heat transport in these settings remains poorly understood. Here we present coupled (fluid-heat) numerical simulations of ocean crustal hydrogeology in and below North Pond, a sediment pond on ∼8 Ma seafloor of the North Atlantic Ocean. Two- and three-dimensional simulations show that advective transport beneath North Pond is complex and time varying, with multiple spatial and temporal scales, consistent with seafloor and borehole observations. A unidirectional, single-pass flow system is neither favored nor needed to match the spatial distribution of seafloor heat flux through North Pond sediments. When the permeability of the crustal aquifer is relatively high (10⁻¹⁰–10⁻⁹ m²), simulations can replicate much of the observed variability and suppression of seafloor heat flux and can explain basement overpressures and transient perturbations in pressure and temperature in the upper volcanic crust. Simulation results can also help explain heterogeneity in pore fluid chemistry and microbiology in the crust. Although driven by the same physical processes, the dynamics of hydrothermal circulation below North Pond are different from those seen on "discharge-dominated" ridge flanks, where the permeability and exposed area of isolated basement outcrops control the extent of regional heat extraction.
 

Nature Microbiology
Unique mobile elements and scalable gene flow at the prokaryote–eukaryote boundary revealed by circularized Asgard archaea genomes - NEW!
Fabai Wu*, Daan R. Speth*, Alon Philosof, Antoine Crémière, Aditi Narayanan*, Roman A. Barco*, Stephanie A. Connon, Jan P. Amend*, Igor A. Antoshechkin & Victoria J. Orphan*
*C-DEBI Contribution 590

Eukaryotic genomes are known to have garnered innovations from both archaeal and bacterial domains but the sequence of events that led to the complex gene repertoire of eukaryotes is largely unresolved. Here, through the enrichment of hydrothermal vent microorganisms, we recovered two circularized genomes of Heimdallarchaeum species that belong to an Asgard archaea clade phylogenetically closest to eukaryotes. These genomes reveal diverse mobile elements, including an integrative viral genome that bidirectionally replicates in a circular form and aloposons, transposons that encode the 5,000 amino acid-sized proteins Otus and Ephialtes. Heimdallaechaeal mobile elements have garnered various genes from bacteria and bacteriophages, likely playing a role in shuffling functions across domains. The number of archaea- and bacteria-related genes follow strikingly different scaling laws in Asgard archaea, exhibiting a genome size-dependent ratio and a functional division resembling the bacteria- and archaea-derived gene repertoire across eukaryotes. Bacterial gene import has thus likely been a continuous process unaltered by eukaryogenesis and scaled up through genome expansion. Our data further highlight the importance of viewing eukaryogenesis in a pan-Asgard context, which led to the proposal of a conceptual framework, that is, the Heimdall nucleation–decentralized innovation–hierarchical import model that accounts for the emergence of eukaryotic complexity.