Distribution of thermochemical output and associated ecosystems at the Loki’s Castle hydrothermal field
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- Department of Earth Science 
Loki’s Castle is a hydrothermal vent field situated on the ultra-slow Arctic mid-Ocean ridges, at the boundary of the Mohns- and Knipovich segments (73◦30’N, 08◦E), and consists of two sulfide mounds and associated black smoker chimneys with extensive diffusive fluid emission in the surrounding area. Though the site has been the target of extensive research since its discovery in 2008, constraints on the quantity and distribution of thermal output from the vent field are poor. In this study a method of image processing of 3500 images captured of the seafloor in 2018, is used to identify the distribution and types of hydrothermal venting at the site. The orthomisac generated from the seafloor images provides a full-resolution map of the vent field, allowing highly detailed digitization of biomarkers and hydrothermal deposits associated with hydrothermal outflow across the site. In-situ temperature measurements were integrated to place constraints on the total heat output and its partition between diffuse and focused outflow. Compared to previous estimates of the total heat flux, the results presented here are highly conservative, with a total thermal output of 146-403 MW. ∼90% of the thermal output is through diffuse outflow, indicating a substantial amount of subsurface seawater mixing with the high-temperature (∼300◦C) fluids. From the heat flux constraints, the mass-, volumetric- and chemical fluxes were constrained as well, providing quantitative data on the major elements emitted through the vent field. Results presented here show that image surveys, and subsequent photomosaic-generation, is a powerful method to provide good constraints on the hydrothermal fluxes, and its implications on the overall heat loss on the ridge.