3‐D Seismic Investigation of a Gas Hydrate and Fluid Flow System on an Active Mid‐Ocean Ridge; Svyatogor Ridge, Fram Strait

Tectonic settings play a large role in the development of fluid flow pathways for gas migrating through sedimentary strata. Gas hydrate systems worldwide are located on either the slopes of passive continental margins, often in large contourite deposits, or in accretionary wedges on subduction margins. The Svyatogor Ridge, however, located at the northwestern flank of the Knipovich Ridge and south of the Molloy Transform Fault (Fram Strait), is a gas hydrate system which is located on an actively spreading margin. Svyatogor Ridge has evidence of shallow gas accumulations; a strong BSR indicating a gas hydrate and underlying free gas system, and fluid flow pathways to the seafloor culminating in pockmarks. Using a high‐resolution P‐Cable 3‐D seismic survey, we investigate how tectonic and sedimentary regimes have influenced the formation of this well‐developed gas hydrate system. Large‐scale basement faults identified in the seismic data are interpreted as detachment faults, which have exhumed relatively young ultramafic rocks. These detachment faults act as conduits for fluid flow, and are responsible for the formation of folds in the overlying sediments that are breached by faults. We propose a model for fluid flow within this system whereby as sedimentary faults breach upward through the sedimentary strata, fluid is able to migrate further upward. We find that the tectonic regime on Svyatogor Ridge is the dominant driver of fluid migration and episodic release at the seafloor

Hot Vents Beneath an Icy Ocean: The Aurora Vent Field, Gakkel Ridge, Revealed

Evidence of hydrothermal venting on the ultra-slow spreading Gakkel Ridge in the Central Arctic Ocean has been available since 2001, with first visual evidence of black smokers on the Aurora Vent Field obtained in 2014. But it was not until 2021 that the first ever remotely operated vehicle (ROV) dives to hydrothermal vents under permanent ice cover in the Arctic were conducted, enabling the collection of vent fluids, rocks, microbes, and fauna. In this paper, we present the methods employed for deep-sea ROV operations under drifting ice. We also provide the first description of the Aurora Vent Field, which includes three actively venting black smokers and diffuse flow on the Aurora mound at ~3,888 m depth on the southern part of the Gakkel Ridge (82.5°N). The biological communities are dominated by a new species of cocculinid limpet, two small gastropods, and a melitid amphipod. The ongoing analyses of Aurora Vent Field samples will contribute to positioning the Gakkel Ridge hydrothermal vents in the global biogeographic puzzle of hydrothermal vents

Repeatability of high-resolution 3D seismic data

High-resolution 4D (HR4D) seismic data have the potential for improving the current state-of-the-art in detecting shallow (≤500−1000  m below seafloor) subsurface changes on a very fine scale (approximately 3–6 m). Time-lapse seismic investigations commonly use conventional broadband seismic data, considered low to moderate resolution in our context. We have developed the first comprehensive time -lapse analysis of high-resolution seismic data by assessing the repeatability of P-cable 3D seismic data (approximately 30–350 Hz) with short offsets and a high density of receivers. P-cable 3D seismic data sets have for decades been used to investigate shallow fluid flow and gas-hydrate systems. We analyze P-cable high-resolution 4D (HR4D) seismic data from three different geologic settings in the Arctic Circle. The first two are test sites with no evidence of shallow subsurface fluid flow, and the third is an active seepage site. Using these sites, we evaluate the reliability of the P-cable 3D seismic technology as a time-lapse tool and establish a 4D acquisition and processing workflow. Weather, waves, tide, and acquisition-parameters such as residual shot noise are factors affecting seismic repeatability. We achieve reasonable quantitative repeatability measures in stratified marine sediments at two test locations. However, repeatability is limited in areas that have poor penetration of seismic energy through the seafloor, such as glacial moraines or rough surface topography. The 4D anomalies in the active seepage site are spatially restricted to areas of focused fluid flow and might likely indicate changes in fluid flow. This approach can thus be applied to detect migration of fluids in active leakage structures, such as gas chimneys

3D Seismic Investigation of a Gas Hydrate and Fluid Flow System on an Active Mid‐Ocean Ridge; Svyatogor Ridge, Fram Strait

Tectonic settings play a large role in the development of fluid flow pathways for gas migrating through sedimentary strata. Many gas hydrate systems worldwide are located on either passive continental margins, in large contourite deposits on the slopes of passive continental margins or on subduction margins. The Svyatogor Ridge, however, located at the northwestern flank of the Knipovich Ridge and south of the Molloy Transform Fault (Fram Strait), is a gas hydrate system which is located on an actively spreading margin. Svyatogor Ridge has evidence of shallow gas accumulations; a strong BSR indicating a gas hydrate and underlying free gas system, and fluid flow pathways to the seafloor culminating in pockmarks. Using a high‐resolution P‐Cable 3D seismic survey, we investigate how tectonic and sedimentary regimes have influenced the formation of this well‐developed gas hydrate system. Large‐scale basement faults identified in the seismic data are interpreted as detachment faults, which have exhumed relatively young ultramafic rocks. These detachment faults act as conduits for fluid flow, and are responsible for the formation of folds in the overlying sediments that are breached by faults. We propose a model for fluid flow within this system whereby as sedimentary faults breach upwards through the sedimentary strata, fluid is able to migrate further upwards. We find that the tectonic regime on Svyatogor Ridge is the dominant driver of fluid migration and episodic release at the seafloor