Claudio Augustino represented EMAN7 during EGU25 where he presented his poster entitled “Methane-related seafloor habitats and sediment microbiome at a cold-water corals site off the Vesterålen coast, northern Norway“

Bénédicte Ferré, Claudio Argentino, Luca Fallati, Giuliana Panieri, Sebastien Petters, Hans C.
Bernstein, Ines A. Barrenechea, and Alessandra Savini

Cold-water corals in the Hola area off the coast of Vesterålen (N. Norway), thrive on a substrate made of methane-derived carbonate and are closely associated with microbial mats. High resolution seafloor imagery and sediment samples collected during the EMAN7 expedition in June 2022 allowed us to reconstruct the spatial relationships between methane seepage and seafloor habitats and gain insights into subsurface biogeochemical processes directly influencing benthic ecosystems. Here, we present the fine-scale orthomosaics and habitat maps covering 1680 m2 of seafloor in proximity to the coral mounds and the geochemistry (sedimentary carbon and nitrogen, pore waters) of a pushcore and blade core collected from a microbial mat and a reference area, respectively. The push core revealed the presence of a macroscopic microbial biofilm at 9 cm depth within the sediment, which is associated with a sharp drop in downcore δ13C of sedimentary organic matter and dissolved inorganic carbon and in C/N ratios. Results from 16S rRNA gene analyses conducted on the uppermost 10 cm of sediment in the pushcore showed a drop in alpha diversity and a compositional change from high abundance of ASVs representing Protebacteria to those representing Halobacterota that we ascribe to the occurrence of methanotrophic consortia performing anaerobic oxidation of methane.

Many of us met during EGU in 2024 in Vienna for posters or presentations. Below are the abstracts:

Biogeochemistry of seep-impacted sediments at a cold-water coral site off the Vesterålen coast, Northern Norway

Claudio Argentino, Giuliana Panieri, Luca Fallati, Alessandra Savini, Ines Barrenechea Angeles, Abidemi Akinselure, and Benedicte Ferré

Methane seepage in the Hola area off the coast of Vesterålen (N. Norway) has long been known for its peculiar association with cold-water coral mounds, but only recently it was possible to explore the distribution of seafloor ecosystems using a Remotely Operated Vehicle (ROV) and to conduct microhabitat-specific samplings for biogeochemical investigations. Here, we describe the results from sediment (carbon-nitrogen systematics) and pore fluid geochemistry (sulfate, dissolved inorganic carbon, methane) and interpret them in relation to the seafloor ecosystems. Microbial mats are the dominant seep-related community and form small white patches of a few tens of cm in diameter located at various distances from the coral mounds. Seep carbonates are widespread at this location and form extensive pavements. The seafloor distribution of methane bubbling and chemosynthetic communities seem controlled by fractures in the carbonates. Microbial mats are associated with intense sulfate-driven anaerobic oxidation of methane producing shallow sulfate-methane transitions coupled with highly ¹³C-depleted dissolved inorganic carbon in the pore water.

Modeling the fate of methane in the water column by model coupling

Knut Ola Dølven, Håvard Espenes, Magnus Drivdal, Muhammed Fatih Sert, and Bénédicte Férré

Estimates of atmospheric methane emissions due to seabed methane seepage are hard to constrain. Additionally, high concentrations of methane can have an impact on local biology due to local ocean acidification. In both cases, better tools for modeling the fate of methane in the water column are needed.  

We present a new approach where we include and couple a wide range of water column processes by using several already verified models in tandem, attempting to form a complete modelling framework for the fate of methane in the water column. Included processes are gas phase changes, advection, dilution, direct and diffusive atmospheric flux and microbial oxidation. The modelling framework allows for a complete estimate of atmospheric emissions, both direct and diffusive fluxes, as well as the 3-dimensional distribution of methane in the water column. The framework can be applied to specific seep sites of interest using hydroacoustic data as input. Additionally, it is also possible to simulate atmospheric fluxes in potential edge cases and future scenarios in areas where local seepage is expected to change or is unknown.

We tested the methodology using hydroacoustic field data from a seep site in the Hola trough offshore North-Western Norway in Spring 2020. We calculated both direct and diffusive atmospheric methane fluxes, distribution of methane in the water column and its potential for affecting local biology due to acidification.

Carbon cycling in coexisting marine ecosystems: Cold seeps and coral reefs in Northern Norway

Muhammed Fatih Sert, Knut Ola Dølven, Sebastian Petters, Timo Kekäläinen, Janne Jänis, Jorge Corrales-Guerrero, and Bénédicte Ferré

Cold seeps and cold water corals (CWCs) coexist on Northern Norway’s continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet only a limited amount reaches the atmosphere. The remaining methane dissolves and disperses in nearby seeps. Methane is unreactive for most microorganisms in the water column, yet it is a unique energy and carbon source for methane-oxidizing bacteria (MOB). MOBs metabolize methane and release carbon dioxide as the end product of oxidation. Increasing carbon dioxide may constrain pH-sensitive CWCs in the region. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, dissolved organic matter (DOM) compositions and microbial diversity through water column profiles and water samples collected in June 2022. Preliminary results indicated that elevated methane increases dissolved inorganic carbon concentrations and modifies carbon isotopic compositions. Additionally, DOM compositions implied a positive correlation between prokaryotic diversity and protein-like DOM components at cold seeps and the entire water column near CWCs, suggesting analogous microbial modifications. Our preliminary conclusion suggests cold seeps and CWCs symbiotically coexist in Northern Norway continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may mitigate the functioning of CWCs in future.

EMAN7: understanding methane seepage dynamics in the Hola Trough

Bénédicte Ferré, Thibaut Barreyre, stefan Bünz, Claudio Argentino, Jorge Corrales-Guerrero, Knut Ola Dølven, Marie Stetzler, Luca Fallati, Muhamed Fatih Sert, Giuliana Panieri, Samuel Rastrick, Tina Kutti, and Manuel Moser

The Hola Trough, offshore Norway’s Lofoten-Vesterålen (LoVe) area, has been of interest for many years due to its rich marine life and potential oil and gas resources. There, coral mounds thrive around methane seepage. The LoVe observatory network monitors this unique environment. Using this observatory platform, associated dataset and research expeditions at sea, the project EMAN7 (Environmental impact of Methane seepage and sub-seabed characterization at LoVe-Node 7) aims to understand the environmental impact of methane seepage as well as its spatio-temporal variability.

The comparison of methane seep activity during two summers with different environmental conditions revealed 3.5 times more seeps when a combination of warmer bottom water and low tide changes the sediment pore pressure. Piezometer data, recording subseafloor pore pressure and bottom temperature, support these findings. Sub-seafloor investigations identified pathways for gas migration in methane seep areas, influenced by topography.

Claudio Argentino presented data from the Hola area off the coast of Vesterålen (N. Norway) at the conference GIMS15: Gas in Marine Sediments (2023, Cadiz, Spain). He described imagery, sediment and pore fluid datasets collected in 2022 that were combined to reconstruct biogeochemical processes in the sediment and their control over seafloor ecosystems. The title of his talk was “Biogeochemical processes affecting the distribution of chemosynthetic communities at a cold-water coral site off the Vesterålen coast, Northern Norway”