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

Evolutionary history, connectivity and habitat-use of annelids from deep-sea chemosynthesis-based ecosystems, with an emphasis on the Arctic mid-Ocean Ridge and the Nordic Seas

The enigmatic fauna of chemosynthesis-based ecosystems (CBEs), i.e. hydrothermal vents, cold seeps and organic falls, has been the subject of intensive research over the last decades. However, there are still many aspects of these ecosystems that are poorly understood. There are many shared families and genera of animals between the different types of CBEs, which shows that there is an evolutionary link between them, but the prevalence of shared species and present-day connectivity between different CBEs is debated. The existence of “intermediate” habitats such as sedimented hydrothermal vents and hydrothermal seeps, led to the suggestion that CBEs should be considered a continuum of reducing conditions, rather than completely distinct phenomena. However, it is not clear which environmental factors are most important in structuring the fauna of CBEs, or what determines the habitat specificity of taxa. Evolutionary studies of CBE-adapted taxa often show a gradual adaptation to more extreme environments, with organic falls or cold seeps serving as evolutionary stepping-stones into the hydrothermal vent habitat. Most of these studies, however, have been focused on symbiotrophic taxa, and the evolutionary role of intermediate habitats has not been assessed in a phylogenetic context. Sampling of CBEs is still patchy and biased, both in terms of geographic regions and habitats, which hampers our understanding of biogeographic patterns. The main objective of this project was to contribute to filling these knowledge gaps by focusing on the annelid fauna of CBEs on the Arctic Mid-Ocean Ridge and in the Nordic Seas. The target taxa were worms in the family Ampharetidae, which are commonly found in all types of CBEs around the world, and Sclerolinum contortum and Nicomache lokii, which are abundant habitat-builders in Arctic CBEs. The project aimed to: 1 – describe the new species of Ampharetidae from Loki’s Castle Vent Field (LCVF), 2 – reconstruct the evolutionary history of Ampharetidae, 3 – assess the relationship between the Arctic populations of Sclerolinum contortum and Nicomache lokii, and populations in other oceans, 4 – reassess the links between the annelid fauna of Loki’s Castle Vent Field and vent faunas of other oceans, and 5 – evaluate which environmental factors may be driving the habitat-specificity and distributions of the studied species. The new species of Ampharetidae from Loki’s Castle were formally described as Pavelius smileyi sp. nov. and Paramytha schanderi gen. et sp. nov. Phylogenetic reconstructions and inference of ancestral habitats revealed that adaptation to CBEs has happened multiple times independently within Ampharetidae. Multiple independent colonisations of CBEs within a family is unusual, but may be more common in heterotrophic taxa. The habitat transitions recovered were both from seep to vent and vent to seep, which contradicts the notion of gradual adaptation into more and more extreme habitats, with hydrothermal vents considered the most extreme. Sedimented vents were involved in two of the three transitions inferred, which supports the hypothesis that sedimented vents are important in linking vents and seeps, and a novel link between organic falls and sedimented vents was also shown in a clade comprising the genera Paramytha and Decemunciger. Both Sclerolinum contortum and Nicomache lokii were shown to be distributed all the way from the Arctic to the Antarctic, which is the widest geographic range of animals from CBEs known to date. This corroborates findings by other authors indicating that wide geographic ranges might not be unusual for annelids from CBEs. S. contortum shows a stronger geographic structure in the haplotype networks than N. lokii, but whether this is due to different dispersal capacities or reflects the geographic isolation of the sampled localities is unclear. Two distinct mitochondrial lineages of N. lokii are present in the Antarctic, which may be the result of two independent colonization events. The wide ranges observed in these species may be facilitated by their ability to colonize different types of CBEs, and it is likely that population connectivity is maintained through presently unknown populations. The presence of taxa at LCVF belonging to genera common at Pacific vents such as Amphisamytha and Nicomache, led to the hypothesis that the fauna at LCVF was partly formed by migrations from the Pacific. However, the results presented here show that ampharetid species from LCVF belong to globally distributed clades and have no clear geographic affinities. In addition, the wide distributions of Sclerolinum contortum and Nicomache lokii indicate a higher degree of connectivity between Arctic and Atlantic CBEs than previously recognized. Although most ampharetids are specific to one type of CBE, a review of the habitatuse of ampharetid species showed that they are quite flexible in terms of substratum, temperature and fluid flux. Depth and biological interactions may play a role in determining the habitat specificity and distributions of ampharetids, but we will probably find more examples of ampharetids inhabiting multiple CBEs in the future. Observations on the environmental conditions inhabited by Sclerolinum contortum and Nicomache lokii indicates that S. contortum may be able to occupy areas of lower sulphide levels, but is limited by high temperatures. On the other hand, N. lokii seems to be more temperature tolerant, but may require higher levels of sulphide. These findings support the notion that environmental factors varying across habitats, such as fluid flux, are important in shaping the faunal composition of CBEs. The results presented in this thesis shows that there is still a lot of undescribed biodiversity in CBEs, and illustrates the need for integrative taxonomic work. The importance of comparing across habitats and geographic regions is also demonstrated, and future collaborative projects will hopefully enable a better understanding of large scale patterns and the underlying processes in CBEs

A New Species of Osedax (Siboglinidae: Annelida) From Colonization Experiments in the Arctic Deep Sea

Large parcels of organic matter in the deep sea, such as whale carcasses, harbor a very specialized fauna, most famously the bone-eating worms in the genus Osedax (Annelida, Siboglinidae). Although Osedax was first described only 15 years ago, there are already 26 described species from the Pacific, Atlantic, and Southern Oceans. The high discovery rate of new Osedax species indicates that there is still a lot of undescribed diversity. In this study we describe the most northerly species of Osedax to date, Osedax fenrisi sp. nov. from 73°N on the Arctic Mid-Ocean Ridge. We also present an updated molecular phylogeny of Osedax based on cytochrome oxidase subunit I and 18S rRNA, including all described species in the genus. The molecular results support that O. fenrisi sp. nov. is distinct from the previously known species of Osedax. Both morphological characters and the molecular phylogeny support the placement of O. fenrisi sp. nov. in clade V. The most striking morphological character shared with other described species in this clade (Osedax rubiplumus, Osedax roseus, and Osedax bryani) is the presence of long pinnules inserted on the outside of the palps. Nomenclatural act recorded in Zoobank. LSID: E55A5C87-0CB6-4146-B3D9-7E3B19B68628.publishedVersio

A New Species of Osedax (Siboglinidae: Annelida) From Colonization Experiments in the Arctic Deep Sea

Large parcels of organic matter in the deep sea, such as whale carcasses, harbor a very specialized fauna, most famously the bone-eating worms in the genus Osedax (Annelida, Siboglinidae). Although Osedax was first described only 15 years ago, there are already 26 described species from the Pacific, Atlantic, and Southern Oceans. The high discovery rate of new Osedax species indicates that there is still a lot of undescribed diversity. In this study we describe the most northerly species of Osedax to date, Osedax fenrisi sp. nov. from 73°N on the Arctic Mid-Ocean Ridge. We also present an updated molecular phylogeny of Osedax based on cytochrome oxidase subunit I and 18S rRNA, including all described species in the genus. The molecular results support that O. fenrisi sp. nov. is distinct from the previously known species of Osedax. Both morphological characters and the molecular phylogeny support the placement of O. fenrisi sp. nov. in clade V. The most striking morphological character shared with other described species in this clade (Osedax rubiplumus, Osedax roseus, and Osedax bryani) is the presence of long pinnules inserted on the outside of the palps. Nomenclatural act recorded in Zoobank. LSID: E55A5C87-0CB6-4146-B3D9-7E3B19B68628

Additional datasets from 'Do ampharetids take sedimented steps between vents and seeps? Phylogeny and habitat use of Ampharetidae (Annelida, Terebelliformia) in chemosynthesis-based ecosystems' BMC Evolutionary Biology

Geographic coordinates of records of Ampharetids in chemosynthesis-based ecosystems.<div><br></div><div>Concatenated alignments of COI, 16S, 28S and 18S for the complete dataset and Clade A and C separately.</div

An Arctic natural oil seep investigated from space to the seafloor

Due to climate change, decreasing ice cover and increasing industrial activities, Arctic marine ecosystems are expected to face higher levels of anthropogenic stress. To sustain healthy and productive ocean ecosystems, it is imperative to build baseline data to assess future changes. Herein, a natural oil seep site offshore western Svalbard (Prins Karls Forland, PKF, 80–100 m water depth), discovered using satellite radar images, was investigated using an extensive multiscale and multisource geospatial dataset collected by satellite, aerial, floating, and underwater platforms. The PKF seep covers roughly a seafloor area of 30,000 m2 and discharges oil from Tertiary or younger source rocks. Biomarker analyses confirm that the oil in the slicks on the sea surface and from the seep on the seafloor have the same origin. Uranium/Thorium dating of authigenic carbonate crusts indicated that the seep had emanated since the Late Pleistocene when ice sheet melting unlocked the hydrocarbons trapped beneath the ice. The faunal communities at the PKF seep are a mix of typical high latitude fauna and taxa adapted to reducing environments. Remarkably, the inhospitable oil-impregnated sediments were also colonized by abundant infaunal organisms. Altogether, in situ observations obtained at the site provide essential insights into the characteristics of high–latitude oil seeps and can be used as a natural laboratory for understanding the potential impacts of human oil discharge into the ocean

Diversity, habitat endemicity and trophic ecology of the fauna of Loki’s Castle vent field on the Arctic Mid-Ocean Ridge

Loki’s Castle Vent Field (LCVF, 2300 m) was discovered in 2008 and represents the first black-smoker vent field discovered on the Arctic Mid-Ocean Ridge (AMOR). However, a comprehensive faunal inventory of the LCVF has not yet been published, hindering the inclusion of the Arctic in biogeographic analyses of vent fauna. There is an urgent need to understand the diversity, spatial distribution and ecosystem function of the biological communities along the AMOR, which will inform environmental impact assesments of future deep-sea mining activities in the region. Therefore, our aim with this paper is to provide a comprehensive inventory of the fauna at LCVF and present a first insight into the food web of the vent community. The fauna of LCVF has a high degree of novelty, with five new species previously described and another ten new species awaiting formal description. Most of the new species from LCVF are either hydrothermal vent specialists or have been reported from other chemosynthesis-based ecosystems. The highest taxon richness is found in the diffuse venting areas and may be promoted by the biogenic habitat generated by the foundation species Sclerolinum contortum. The isotopic signatures of the vent community of LCVF show a clear influence of chemosynthetic primary production on the foodweb. Considering the novel and specialised fauna documented in this paper, hydrothermal vents on the AMOR should be regarded as vulnerable marine ecosystems and protective measures must therefore be implemented, especially considering the potential threat from resource exploration and exploitation activities in the near future.publishedVersio