Seamount Chain Research Articles

Phylogeography of the red alga Gracilariopsis tenuifrons (Gracilariales) along the Brazilian coast.

Changes in the sea level during the Holocene are regarded as one of the most prevalent drivers of the diversity and distribution of macroalgae in Brazil, influenced by the emergence of the Vitória-Trindade seamount chain (VTC). Gracilariopsis tenuifrons has a wide geographic distribution along the Brazilian coast, from Maranhão state (2°48'64.3" S) to Santa Catarina state (27.5°73'83" S). The knowledge of historical processes affecting diversity may allow the development of conservation strategies in environments against anthropogenic influence. Therefore, knowledge about phylogeography and populational genetic diversity in G. tenuifrons is necessary. Six populations were sampled along the northeastern tropical (Maranhão-MA, Rio Grande do Norte-RN, Alagoas-AL, and Bahia-BA States) and southeastern subtropical (São Paulo "Ubatuba"-SP1 and São Paulo "Itanhaém"-SP2 States) regions along the Brazilian coast. The genetic diversity and structure of G. tenuifrons were inferred using mitochondrial (COI-5P and cox2-3 concatenated) DNA markers. Gracilariopsis tenuifrons populations showed an evident separation between the northeast (from 2°48'64.3" S to 14°18'23" S; 17 haplotypes) and the southeast (from 23°50'14.9" S to 24°20'04.7" S; 10 haplotypes) regions by two mutational steps between them. The main biogeographical barrier to gene flow is located nearby the VTC. The southeast region (São Paulo State) is separated by two subphylogroups (SP1, three haplotypes and SP2, six haplotypes), and Santos Bay (estuary) has been considered a biogeographical barrier between them. The presence of genetic structure and putative barriers to gene flow are in concordance with previous studies reporting biogeographic breaks in the southwest Atlantic Ocean, including the genetic isolation between northeast and southeast regions for red and brown algae in the vicinity of the VTC.

Timing of carbon uptake by oceanic crust determined by rock reactivity

Abstract Carbonate formation during the alteration of oceanic crust is a global CO2 sink. Its timing and controls are not well understood, particularly in volcanic seamounts, which react with seawater over tens of millions of years. We report in situ U-Pb age dates of carbonate vein and void fill in 50–74 Ma basaltic basement of the Louisville Seamount Chain. More than 90% of the carbonate formed <20 m.y. after seamount emplacement. Vesicle carbonate precipitated within 8 m.y. (median = 2.9 m.y.) whereas vein carbonate grew over longer time spans (median = 8.1 m.y.). The duration of carbonation was hence limited despite the basement’s long-term exposure to seawater. The age dates imply a rapid infill of vesicles by alteration of confined domains around vesicles. Carbonate formation in veins extended for longer periods of time, likely due to the late opening of fractures, which exposed fresh reactive rock surface to circulating seawater long after the formation of the basement. We suggest that carbonate growth ceased after the volcanic rocks were too altered to liberate sufficient Ca2+ and generate the alkalinity required for carbonate precipitation. A critical extent of rock reactivity is required to sustain carbonate formation. Carbonate precipitation likely ends after much of the exposed basaltic substrate has been altered and the rock reactivity drops below this critical threshold. These findings help to explain the generally short duration of carbonation in the flanks of mid-ocean ridges.

Evidence for compositionally distinct upper mantle plumelets since the early history of the Tristan-Gough hotspot

Recent studies indicate that mantle plumes, which transfer material and heat from the earth’s interior to its surface, represent multifaceted upwellings. The Tristan-Gough hotspot track (South Atlantic), which formed above a mantle plume, documents spatial geochemical zonation in two distinct sub-tracks since ~70 Ma. The origin and the sudden appearance of two distinct geochemical flavors is enigmatic, but could provide insights into the structural evolution of mantle plumes. Sr–Nd–Pb–Hf isotope data from the Late Cretaceous Rio Grande Rise and adjacent Jean Charcot Seamount Chain (South American Plate), which represent the counterpart of the older Tristan-Gough volcanic track (African Plate), extends the bilateral-zonation to ~100 Ma. Our results support recent numerical models, demonstrating that mantle plumes can split into distinct upper mantle conduits, and provide evidence that these plumelets formed at the plume head-to-plume tail transition. We attribute the plume zonation to sampling the geochemically-graded margin of the African Large Low-Shear-Velocity Province.

Constraints on near-ridge magmatism using 40Ar/39Ar geochronology of enriched MORB from the 8°20' N seamount chain

Our understanding of the spatial-temporal-compositional relationships between off-axis magmatism and mid-ocean ridge spreading centers is limited. Determining the 40Ar/39Ar ages of mid-ocean ridge basalt (MORB) lavas erupting near mid-ocean ridges (MOR) has been a challenge due to the characteristically low K2O contents in incompatible element-depleted normal MORB (NMORB). High-precision 40Ar/39Ar geochronology is used here to determine ages of young, basaltic lavas erupted along the 8°20' N seamount chain west of the East Pacific Rise (EPR) axis that have a range of incompatible element enrichments (EMORB) suitable for 40Ar/39Ar geochronology (e.g., K2O contents > 0.3 wt%). 40Ar/39Ar ages were determined in 29 well-characterized basalts sampled using HOV Alvin and dredging. Detailed geochronology and geochemical analyses provide important constraints on the timing, distribution, and origins of lavas that constructed this extensive volcanic lineament relative to magmatism beneath the adjacent EPR axis. Seamount eruption ages are up to ∼1.6 Ma younger than the underlying lithosphere, supporting a model of prolonged off-axis magmatism for at least 2 Myrs at distances as great as ∼90 km from the ridge axis. Increasing geochemical heterogeneity with eruption distance reflects the diminishing effect of sub-ridge melt focusing. The range of geochemically distinct lavas erupted at given distances from the ridge highlights the dynamic nature of the near-ridge magmatic environment over Myr timescales. Linear ridge-like (EPR-parallel) morphotectonic features erupt the youngest and most incompatible element-enriched lavas of the entire seamount chain, indicating there is a recent change in the influence of mantle heterogeneity and off-axis melt metasomatism on the near-ridge lithospheric mantle. Changes in seamount morphologies are attributed to counter-clockwise rotation and southward migration of the nearby Siqueiros transform over the last few million years.

Seamount chains and hotspot tracks: Superficially similar, deeply different

Nearly 80% of the seafloor extension has not been covered by high-resolution bathymetry, impeding direct observation of seamounts. Nevertheless, lists of seamount location and height at a global scale have been produced using different techniques. In this work four of such databases (publicly available) are compared with each other to assess their differences. Results identify large differences among databases that could have exerted strong influences on models of seamount production and associated geodynamic processes. Despite those differences, it is shown that all databases allow the identification of seamount lines both along the present-day Mid Ocean Ridge (MOR) system and on intraplate settings. Notably, those seamount lines do not coincide with the so-called hotspot tracks that commonly were defined by selectively focusing attention on the larger seamounts. Examination of all the databases also shows that distinction based only on seamount size between seamounts produced at Mid-Ocean Ridge (MOR) environments from those associated with mantle-plum fed-hotspot activity has been overestimated. This, combined with the fact that most seamount lines defined by the available databases can be traced back to past locations of MOR indicates that most of the present-day intraplate linear arrays of seamounts, which include some large seamounts, were not produced by the action of underlying mantle anomalies envisaged in the form of mantle plumes. The evidence presented here calls for a reassessment of the form in which volcanic and tectonic activities are conceptually related to each other.

Deep subduction of the Philippine Sea slab and formation of slab window beneath central Japan

The geometry of the Philippine Sea slab (PHS) subducting beneath the Japanese islands has been imaged to 400 km depth beneath the Kyushu and Chugoku regions, whereas the PHS slab geometry beneath the Hokuriku region has only been determined to ~ 140 km depth, thereby indicating a large east–west asymmetry in the slab subduction. However, geologic evidence suggests that there was symmetrical east–west seafloor spreading along the axis of the Kinan seamount chain when the Shikoku basin was an active spreading center in the PHS plate. This inconsistency suggests that the PHS slab should be present beneath the Hokuriku region. Here we perform P-wave travel-time tomography across central Japan and conduct a two-dimensional plate subduction numerical simulation that reproduces the dual subduction of the PHS and Pacific (PAC) plates to elucidate the PHS slab geometry beneath central Japan. The tomography results reveal a high-velocity anomaly at ~ 150–250 km depth that extends from Wakasa bay to Noto peninsula and a slab window beneath the Hokuriku region. The numerical simulation results suggest that the PHS slab may have torn when it collided with the PAC slab, with the once leading edge of the PHS slab now present along the upper surface of the PAC slab beneath Noto peninsula. These results indicate that the PHS slab exists at ~ 250 km depth beneath the Hokuriku region, although it has been torn owing to its collision with the PAC slab, with this tear propagating westward to form a triangular slab window beneath the Hokuriku region.Graphical

Protecting the Salas y Gomez and Nazca Ridges: A review of policy pathways for creating conservation measures in the international waters of the Southeast Pacific

Seamount ecosystems host ecologically important species, including many that are found nowhere else on Earth. The Salas y Gomez and Nazca Ridges, two adjacent seamount chains in the Southeast Pacific, are biodiversity hotspots marked by the highest levels of marine endemism on Earth. Historically isolated from many human activities, this region has produced a unique biodiversity and provides an excellent opportunity for protecting a global biodiversity hotspot before it is degraded. However, no legal protection mechanism currently exists for comprehensively protecting areas beyond national jurisdiction (ABNJ) of the Salas y Gomez and Nazca Ridges. After years of negotiations at the United Nations for a legally binding instrument to address conservation in ABNJ, the Biodiversity Beyond National Jurisdiction (BBNJ) Agreement was finally agreed in March 2023. While this Agreement may provide one avenue for protecting the high seas, the Agreement has yet to be adopted and ratification may take several years. As it stands, conservation efforts in ABNJ will rest on sectoral bodies primarily set to manage large-scale industries like fishing, shipping, and mining, but that do have the ability to enact conservation measures other than restricting these industrial activities. Our study provides an overview of the major international organizations managing activities in the ABNJ of the Salas y Gomez and Nazca Ridges, identifies current conservation measures, and maps out potential policy pathways for creating conservation measures in this unique region. Our synthesis focused on identifying conservation procedures within the documents of international organizations and applying their rules and procedures to implement conservation measures. We identify three potential pathways. A regional and national pathway that relies on cooperation among international organizations spearheaded by the South Pacific Regional Fisheries Management Organization (SPRFMO), and an international pathway through the BBNJ Agreement.

The foundering of stagnant slabs bearing oceanic plateau into the lower mantle

The oceanic plateau is proposed to be produced by the plume head. Seeking the missing plume head associated with seamount chains is an important task to evaluate the plume theory. While the subduction initiation and process of the oceanic plateau is debatable, recent seismic studies suggest that the Hawaiian-Emperor Plateau has been subducted into the lower mantle. The sinking rate is higher than previously estimated and even higher than of the normal slab. It is intriguing, as the phase transitions would cause a density barrier for the basaltic materials from ∼660-km to ∼720-km depths, and slow down the subduction of the slabs, especially for the oceanic plateau with a thickened basaltic crust. Here, we perform geodynamic numerical experiments to investigate the foundering process of flat stagnant slabs from the transition zone into the lower mantle. We compare models of both the normal slab and slabs bearing oceanic plateau and suggest that a basaltic underplate beneath the peridotite mantle lithosphere in the oceanic plateau can lead to a higher foundering rate. The underplated oceanic plateau can reach ∼1000-km depth in ∼50 Myrs. These models provide a new perspective in understanding the fate of subducted oceanic plateau, suggesting that missing plume heads might be found in the lower mantle.

Distribution and Some Aspects of Biology of Hozukius guyotensis (Sebastidae) in the Area of the Emperor Seamount Chain

Distribution and Some Aspects of Biology of Hozukius guyotensis (Sebastidae) in the Area of the Emperor Seamount Chain

Membranihabitans maritimus sp. nov., a marine bacterium isolated from deep seawater.

A Gram-stain-negative, non-motile, rod-shaped bacterial strain, designated C281T, was isolated from seawater sampled at the Marshallese seamount chain. Results of 16S rRNA gene analysis revealed that strain C281T was most closely related to Membranihabitans marinus CZ-AZ5T with 92.7 % sequence similarity. Phylogenetic analysis indicated that the new isolate represented a novel species by forming a distinctive lineage within the family Saprospiraceae. The DNA G+C content of strain C281T was 38.4 mol%. The genome sizes of strain C281T and the reference strain M. marinus CZ-AZ5T were 5 962 917 and 5 395 999 bp, respectively. The average nucleotide identity and in silico DNA-DNA hybridization values between strains C281T and M. marinus CZ-AZ5T were found to be low (69.3 and 17.6 %, respectively). Different functional genes were found in the genome of strain C281T, such as CZC CBA, polysaccharide utilization loci and linear azol(in)e-containing peptide cluster coding genes. The NaCl range for growth was 0.5-15.0 %. Positive results were obtained for hydrolysis of Tween 60 and urease. MK-7 was the sole respiratory quinone. The major fatty acids were C16 : 1 ω6c and/or C16 : 1 ω7c, iso-C15 : 0 and iso-C15 : 1 F. The major polar lipids of strain C281T were phosphatidylethanolamine, phosphatidylglycerol, two unidentified lipids and five unidentified glycolipids. On the basis of its taxonomic characteristics, the isolate represents a novel species of the genus Membranihabitans, for which the name Membranihabitans maritimus sp. nov. (type strain C281T=KCTC 92171T=MCCC M27001T) is proposed.

ENSO vs glacial-interglacial-induced changes in the Kuroshio-Oyashio transition zone during the Pleistocene

The subarctic front (SAF) in the pelagic North Pacific is the northernmost front of the Kuroshio-Oyashio transition zone separating the subpolar and subtropical gyres and is marked by a strong sea surface temperature gradient. A complex interplay of e.g. variations of currents, the wind system and other forcing mechanisms causes shifts of the SAF’s position on timescales from orbital to interannual. In this study, we present proxy data from the Emperor Seamount chain, which reveal a link between long-term ENSO (El Niño/Southern Oscillation) dynamics in the tropics and shifts of the SAF. Based on sediment core SO264-45-2 from Jimmu Seamount (46°33.792’N, 169°36.072’E) located close to the modern position of the SAF, we reconstruct changes in (sub)surface temperature ((sub)SSTMg/Ca) and δ18Osw-ivc (approximating salinities) via combined Mg/Ca and δ18O analyses of the shallow-dwelling foraminifera Globigerina bulloides and the near-thermocline-dwelling Neogloboquadrina pachyderma, biological productivity (XRF-based Ba/Ti ratios), and terrigenous input via dust (XRF-based Fe). From ~600 to ~280 ka BP we observe significantly higher SSTMg/Ca than after an abrupt change at 280 ka BP. We assume that during this time warmer water from the Kuroshio-Oyashio transition zone reached the core site, reflecting a shift of the SAF from a position at or even north of our study site prior to 280 ka BP to a position south of our study site after 280 ka BP. We propose that such a northward displacement of the SAF between 600-280 ka BP was induced by sustained La Niña-like conditions, which led to increased transport of tropical ocean heat into the Kuroshio-Oyashio transition zone via the Kuroshio Current. After ~280 ka BP, the change to more El Niño-like conditions led to less heat transfer via the Kuroshio Current with the SAF remaining south of the core location. In contrast, our productivity record shows a clear glacial-interglacial pattern that is common in the North Pacific. We assume that this pattern is connected to changes in nutrient supply or utilization, which are not primarily driven by changes of the Kuroshio and Oyashio Currents or the SAF.

New insights into the age and origin of two small Cretaceous seamount chains proximal to the Northwestern Hawaiian Ridge

AbstractThe Northwestern Hawaiian Ridge is an age-progressive volcanic chain sourced from the Hawaiian mantle plume. Proximal to the Northwestern Hawaiian Ridge are several clusters of smaller seamounts and ridges with limited age constraints and unknown geodynamic origins. This study presents new bathymetric data and 40Ar/39Ar age determinations from lava flow samples recovered by remotely operated vehicle (ROV) from two east–west-trending chains of seamounts that lie north of the Pūhāhonu and Mokumanamana volcanoes. The previously unexplored Naifeh Chain (28°48′N,167°48′W) and Plumeria Chain (25°36′N, 164°35′W) contain five volcanic structures each, including three guyots in the Naifeh Chain. New 40Ar/39Ar age determinations indicate that the Naifeh Chain formed ca. 88 Ma and the Plumeria Chain ca. 85 Ma. The Cretaceous ages, coupled with a perpendicular orientation of the seamounts relative to absolute Pacific plate motion at that time, eliminate either a Miocene Hawaiian volcanic arch or Cretaceous mantle-plume origin. The seamounts lie on oceanic crust that is modeled to be 10–15 Ma older than the corresponding seamounts. Here, two models are put forth to explain the origin of these enigmatic seamount chains as well as the similar nearby Mendelssohn Seamounts. (1) Diffuse lithospheric extension results in the formation of these seamounts until the initiation of the Kula-Pacific spreading center in the north at 84–79 Ma, which alleviates the tension. (2) Shear-driven upwelling of enriched mantle material beneath young oceanic lithosphere results in an age-progressive seamount track that is approximately perpendicular to the spreading ridge. Here we show that all sampled seamounts proximal to the Northwestern Hawaiian Ridge are intraplate in nature, but their formations can be attributed to both plume and plate processes.

Distribution and Some Aspects of Biology of Hozukius guyotensis (Sebastidae) in the Area of the Emperor Seamount Chain

Based on the materials collected in the course of longline fishing in the area of the Emperor Seamount Chain, new data on the occurrence, distribution, and some features of the biology and ecology of Hozukius guyotensis have been presented. It has been shown that it is a common species in the ichthyofauna of the studied area. It is observed on the peaks and in the slope area of the Nintoku, Lira, and Koko seamounts at depths of 385–1015 m; its largest catches are typical for the range of 500–700 m. In the catches, H. guyotensis was represented by individuals 32–73 cm long and weighing 0.45–5.27 kg. Presumably, the species begins to mature at a length of 44–46 cm; the main stage of its reproduction takes place in spring.

Horizontal distribution of benthic and demersal fish assemblages on three seamounts in the Papahānaumokuākea Marine National Monument

Deep-sea fishes on seamounts have recently been shown to have strong changes in assemblage patterns with depth. However, horizontal variability patterns within a single seamount and among seamounts remain drastically understudied. The Papahānaumokuākea Marine National Monument (PMNM) is part of an extensive seamount chain that is relatively unimpacted by human activity as well as highly variable in physiographic and oceanographic characteristics. Three PMNM seamounts, Necker Island, French Frigate Shoals (FFS), and Pioneer Bank, were explored using Autonomous Underwater Vehicle surveys to document the deep-sea fish assemblages and their horizontal patterns of distribution at three different depths. Quantitative comparisons were made among the sides of the seamount and among the three seamounts while controlling for depth. The Gadiformes were the most abundant order with the highest number of individuals at 300 and 450 m on Pioneer and FFS. At 600 m the Myctophiformes showed the highest number of individuals overall and were the most abundant on FFS. Significant differences in abundance by seamount, side, and their interaction were observed at 300 and 600 m. Significant differences in some diversity metrics occurred in one, both, or the interaction of the factors of seamount and side at each depth. At all depths, the structure of the fish assemblage showed significant variation among seamounts and sides, which was explained mostly by the interaction term. After accounting for the variability explained by the confounding factor of time of day, the most common environmental factors related to assemblage structure for at least two depths were the east-west component of currents (u), latitude, chlorophyll a (chl a), and particulate organic carbon (POC). At 300 m, oxygen and salinity were also important, at 450 m mean direction of the substrate was an additional factor that was correlated with assemblage structure. At 600 m the factor that explained the most variation in community structure was percent rugosity. The results obtained in this study show significant horizontal variability in seamount fish assemblages within a given depth range; this variability should be taken into consideration in the management and conservation of the Monument and other seamounts.

Bottom-contact fisheries disturbance and signs of recovery of precious corals in the Northwestern Hawaiian Islands and Emperor Seamount Chain

Deep-sea precious corals in the octocoral family Coralliidae are among the dominant benthic megafauna at depths of 300–600 m on seamounts of the Northwestern Hawaiian Islands and lower Emperor Seamount Chain. Pleurocorallium secundum and Hemicorallium laauense were once abundant enough on these seamounts to support a targeted coral fishery in the 1960s and 1970s. Significant trawl finfish fisheries were also occurring in the same time frame on the same seamounts. Because they had high enough abundance to support a targeted fishery for two decades, these two coralliid species must have been a key component of the baseline community on these seamounts. Therefore, they provide an ideal indicator species for testing effects of large-scale disturbance and potential for recovery in deep-sea coral and seamount communities. Using AUVs and submersibles, we explored seamounts outside the US EEZ that are still actively fished by trawl, seamounts within the US EEZ that were historically trawled but have been protected since the establishment of the EEZ, and seamounts that have never been trawled, to determine population distributions and colony sizes for the targeted coral species. P. secundum had only one individual on actively trawled seamounts and occurred in low abundance on most Recovering seamounts. H. laauense was present in a few areas in Recovering and Still Trawled seamounts. Colony size distributions for H. laauense showed a smaller median size on Recovering and Still Trawled seamounts compared to the Never Trawled sites. P. secundum had a slightly smaller median colony size on the Recovering Seamounts than on the Never Trawled seamounts. These results indicate a reduction in abundance for both species in disturbed areas with some unexpected potential for recovery on protected seamounts. Recovery was uneven among sites and species with SE Hancock and Koko showing the largest populations of H. laauense among the Recovering and Still Trawled seamounts, respectively. P. secundum showed much less recovery, with its largest population on Bank 11 in the Recovering seamounts. Kammu, one of the primary seamounts of the coral fishery, had only a single coralliid observed. The other primary target, Yuryaku, had a small number of coralliids in a steeply sloped area. These two Still Trawled seamounts do not appear to be able to recover under the current levels of fishing pressure.

An emerging plume head interacting with the Hawaiian plume tail

The Hawaiian-Emperor seamount chain has shown two subparallel geographical and geochemical volcanic trends, Loa and Kea, since ∼5 Ma, for which numerous models have been proposed that usually involve a single mantle plume sampling different compositional sources of the deep or shallow mantle. However, both the dramatically increased eruption rate of the Hawaiian hotspot since ∼5 Ma and the nearly simultaneous southward bending of the Hawaiian chain remain unexplained. Here, we propose a plume-plume interaction model where the compositionally depleted Kea trend represents the original Hawaiian plume tail and the relatively enriched Loa trend represents an emerging plume head southeast of the Hawaiian plume tail. Geodynamic modeling further suggests that the interaction between the existing Hawaiian plume tail and the emerging Loa plume head is responsible for the southward bending of the Hawaiian chain. We show that the arrival of the new plume head also dramatically increases the eruption rate along the hotspot track. We suggest that this double-plume scenario may also represent an important mechanism for the formation of other hotspot tracks in the Pacific plate, likely reflecting a dynamic reorganization of the lowermost mantle.

The upper-mantle density variation beneath the South Atlantic Ocean and its implications for hotspots and large igneous provinces

The South Mid-Atlantic Ridge (SMAR), the most typical slow-spreading ridge on the earth, is a significant area to study the oceanic crust-mantle evolution. We used gravity data and the S-wave velocity model to derive a 3D density model of the upper-mantle beneath the South Atlantic Ocean to better understand the relationship between ridges, hotspots, and large igneous provinces. The density variations in the upper-mantle are related to thermal and compositional changes. The segment near the Agulhas-Falkland Fracture Zone (AFFZ) is characterized by low-density but inconspicuous low-velocity anomalies reflecting the depleted composition. Its composition is different from the northern part of the SMAR. A low-density layer at 100 km that extends 200 km from the ridge to the Discovery hotspot and that disappears near the AFFZ, is also present. The higher degree of mantle melting beneath the segment near the AFFZ is most probably influenced by the residual plume materials from the Discovery hotspot. Deep low densities beneath the Rio Grande Rise (RGR) and the Walvis Ridge (WR) indicate a higher degree of melting and their formation is probably influenced by the Tristan da Cunha plume. When the RGR is driven away from the plume, its original hot materials cool down and present as cold and dense uppermost mantle deposits. As the plume is located in the African plate, the WR was continuously formed as a seamount chain by intraplate volcanism of mantle plume.

Stratigraphy, volcanic processes and evolution of the Martin Vaz archipelago

The volcanic Martin Vaz Archipelago consists of four Plio-Pleistocene small islands (total area of 0.37 km2) in the South Atlantic Ocean in front of Brazil's coast. Together with Trindade Island, the archipelago corresponds to the easternmost portion of the Vitória-Trindade Seamount Chain (VTC).We performed geological mapping, coupled with X-ray diffraction, petrography, scanning electron microscopy, and lithogeochemistry analyses at Martin Vaz samples. Four lithostratigraphic units were identified (i) Martin Vaz Formation records older explosive phonolitic activity. It is interpreted as resulting from hydromagmatic volcanism; (ii) Subvolcanic phonolites consist of a dome (cryptodome) and plug morphologies, which represent the most voluminous rocks at Martin Vaz Archipelago; (iii) Mirante Formation records hyper-concentrated density currents of ultrabasic rocks; and (iv) Atobá Formation is composed of ultrabasic to intermediate lavas of basanitic to phonolitic composition, interpreted as a result of Strombolian (Fountain Fed)/Hawaiian volcanism.The volcanic rocks described at Martin Vaz Archipelago and Trindade Island represent the final members of the nephelinite-phonolite series, with a significant absence of intermediate phases. Basanites of the Martin Vaz, Mirante, and Atobá formations are geochemically similar to the nephelinites of Trindade Island. In the same way, the geochemical characteristics of phonolites from subvolcanic bodies and the Bandeira Member are similar to those observed on the phonolites of Trindade Island. Geochemical and thermodynamic modeling suggest cogeneticity between ultrabasic and phonolitic magmas. Fractional crystallization about 0.5 GPa and at low water pressures explain the chemical evolution trends observed. Geochemical characteristic points to melts of a metasomatized source composed of garnet wehrlite and/or hornblendite.The new data allowed for the elaboration of a novel conceptual model for the geological evolution of the Martin Vaz Archipelago, one of the last volcanic manifestations in the Brazilian territory.

New species and new records in Cerithiopsidae and Newtoniellidae (Triphoroidea, Gastropoda) from the Azores and the South Azorean Seamount Chain

New species and new records in Cerithiopsidae and Newtoniellidae (Triphoroidea, Gastropoda) from the Azores and the South Azorean Seamount Chain

Can seamounts in the Gulf of Alaska be a spawning ground for sablefish settling in coastal nursery grounds?

In addition to their prevalence on the continental shelf, adult sablefish have been found over the chain of seamounts far offshore in the Gulf of Alaska (GOA). Many of the females that were observed had recently spawned or were ready to spawn. However, to date, it is not known what role the seamounts play in sablefish life history and there are no observations of sablefish eggs or larvae over the GOA seamounts. Due to their depth and remoteness, there are no suitable shallow nursery areas in the vicinity of the seamounts. For successful recruitment, individuals hatching from eggs spawned over seamounts would need to be transported hundreds of miles to suitable areas inshore. Using an individual-based model (IBM) of sablefish, we have demonstrated that if spawning occurs over any of the seamounts in the GOA seamount province it is likely that at least some individuals will be successfully transported to shallow inshore nursery areas in the coastal GOA. As our simulated individuals only exhibit vertical movement behavior this on-shore transport results from the prevailing currents to which they were subjected and not from any geographic or environmental homing capabilities. Our analysis indicates that the strength of the on-shelf velocity is not the primary factor in determining the likelihood of transport to nursery areas. We speculate that the size, strength, location, and direction of the eddies that populate the GOA in any given year could be important in determining transport success. This idea is reinforced by our path analysis which shows that there are markedly different pathways taken by successful individuals among years. Our findings suggest that it may be necessary to expand what is considered suitable habitat for young sablefish. With seamounts being a potentially important spawning site for sablefish, future research priorities should include ground-truthing with fishery or fishery-independent data collected from seamounts. Potential applications of this expanded sablefish IBM include testing for connectivity between seamount and slope spawning areas and the Aleutian Islands and Bering Sea and contributing to the development of spatially explicit assessment models of sablefish.