Bidenichthys okamotoi, a New Species of the Bythitidae (Ophidiiformes, Teleostei) from the Koko Seamount, Central North Pacific

Two specimens from the Koko Seamount (Koko Guyot), in the Hawaiian-Emperor seamount chain, Central North Pacific, caught in 2009 and 2010 are here described as a new species, Bidenichthys okamotoi. The taxonomy of the species in the genera Bidenichthys Barnard, 1934, and Fiordichthys Paulin, 1995, has been confusing due to the lost type of B. consorbrinus (Hutton, 1876) and the rarity of some of the species. Following the synonymization of Fiordichthys Paulin, 1995, with Bidenichthys by Møller and Nielsen 2015 and of Bidenichthys beeblebroxi Paulin, 1995, with Bidenichthys consobrinus Hutton, 1876, the genus Bidenichthys now comprises five species: B. capensis, B. consobrinus, B. okamotoi, B. paxtoni and B. slartibartfasti. Bidenichthys okamotoi differs from its congeners in, e.g., the fewer precaudal vertebrae (12 vs. 13), more palatine teeth rows (4–6 vs. 2–3), shorter pelvic fins (12.1–13.4% vs. 14.4–21.0% SL), max size (187 vs. 147 mm SL) and the shape of the sulcus of the otolith. We here present an updated diagnosis of the genus. A computed tomography (CT) scan of the holotype of B. okamotoi provides for additional anatomical details. The disjunctive occurrence of Bidenichthys okamotoi on the Emperor Seamount chain about 7500 km from the nearest congeneric taxon in New Zealand is discussed. The fossil otolith-based record of the genus Bidenichthys and its systematic implications is briefly discussed.

Geochemistry of Surface Sediments From the Emperor Seamount Chain, North Pacific

Investigating the composition and distribution of pelagic marine sediments is fundamental in the field of marine sedimentology. The spatial distributions of surface sediment are unclear due to limited investigation along the Emperor Seamount Chain of the North Pacific. In this study, a suite of sedimentological and geochemical proxies were analyzed, including the sediment grain size, organic carbon, CaCO3, major and rare earth elements of 50 surface sediment samples from the Emperor Seamount Chain, spanning from ∼33°N to ∼52°N. On the basis of sedimentary components, we divide them into three Zones (I, II, and III) spatially with distinct features. Sediments in Zone I (∼33°N–44°N) and Zone III (49.8°N–53°N) are dominated by clayey silt, and mainly consist of sand and silty sand in Zone II. The mean grain size of the sortable silt shows that the hydrodynamic condition in the study area is significantly stronger than that of the abyssal plain, especially at the water depth of 1,000–2,500 m. The CaCO3 contents in sediments above 4,000 m range from 20 to 84% but decrease sharply to less than 1.5% below 4,000 m, confirming that the water depth of 4,000 m is the carbonate compensation depth of the study area. Strong positive correlations between Al2O3 and Fe2O3, TiO2, MgO, and K2O (R > 0.9) in the bulk sediments indicate pronounced contributions of terrigenous materials from surrounding continent mass to the study area. Furthermore, the eolian dust makes contributions to the composition of bulk sediments as confirmed by rare earth elements. There is no significant correlation between grain size and major and minor elements, which indicates that the sedimentary grain size does not exert important effects on terrigenous components. There is significant negative δCe and positive δEu anomalies at all stations. The negative Ce anomaly mainly exists in carbonate-rich sediments, inheriting the signal of seawater. The positive Eu anomaly indicates widespread volcanism contributions to the study area from active volcanic islands arcs around the North Pacific. The relative contributions of terrestrial, volcanic, and biogenic materials vary with latitude and water depth in the study area.

Contrasting spatial distributions of surface sediment compositions from the Emperor Seamount Chain, North Pacific

<p>The Emperor Seamount chain is located in the North Pacific Ocean and beneath the Northern Westerly wind belt. It extends from the subtropical to subarctic North Pacific oceans between 30°N-50°N. Modern observations have shown this region has complex physical oceanic processes, including the Kuroshio Extension, the Oyashio Current, the polar front and the subarctic front. A large amount of dust from the central Asian continent is delivered to this area, which affects the regional marine ecosystem and the global carbon cycle. Due to the lack of sediments from the Emperor Seamount chain, few studies have examined the composition of surface sediments in this ocean realm. On the basis of 50 samples collected during the SO264 Expedition in 2018 using multicorers, we investigate the spatial distributions of sediment grainsize, total organic carbon, CaCO<sub>3</sub> and major and minor elements in surface sediments of this ocean realm. Our data show that the detritus sediments mainly consist of siltly sand and clayey silt with more coarse fractions between ~45°N and 48°N, which has strong negative correlations with water depth. The content of CaCO<sub>3</sub> varies between 0.04% and 83.67% with higher values at the south of 48°N. The TOC content ranges between 0.07% and 1.36% with lower values (<0.3%) occurring at the north of ~45°N. The concentration of ∑REEs ranges from 31 ppm to 136 ppm with lower values between ~45° N and 48°N. There is significant positive Eu anomaly at all stations, indicating widespread occurrence of volcanic detritus. A significant negative correlation between sediment grainsize and ∑REEs and some lithophile elements, such as Al<sub>2</sub>O<sub>3</sub>, Fe<sub>2</sub>O<sub>3</sub>, K<sub>2</sub>O, Th, REEs, etc., indicates a strong effect of sediment grainsize on sediment geochemical composition. A strong negative correlation between Al and CaCO<sub>3</sub> suggests contrasting sources, such as terrigenous vs biogenic sources, respectively. Our data confirms the contributions of terrigenous, volcanic and biogenic materials to the bulk sediment with contrasting spatial distribution along the Emperor Seamount Chain.</p><p>Note: This study was supported by the National Natural Science Foundation of China (Grant No.41876065, U1606401) and National Program on Global Change and Air-Sea Interaction(GASI-GEOGE-04). </p>

Diagenetic manganese and iron cycling and implications for past redox conditions in sediments along the Emperor Seamount Chain, NW Pacific Ocean

<p>The deep water of the North Pacific Ocean is enriched in CO<sub>2</sub> and nutrients as a result of organic matter degradation in the water column and surface sediments. Due to its large volume, the deep North Pacific may have played a fundamental role for the postulated glacial carbon sequestration leading to the observed drawdown of atmospheric CO<sub>2</sub>. As a consequence of increased CO<sub>2</sub> levels in the deep glacial ocean, bottom-water oxygen concentrations must have been correspondingly low compared to current oxygenated conditions (e.g., Anderson et al., 2019). Previous studies on sediments from the NW Pacific Ocean have provided evidence that glacial bottom‑water O<sub>2</sub> concentrations were significantly lower than today, which have induced suboxic surface sediment redox conditions (Jaccard et al., 2009) and have altered the primary sediment composition and properties of glacial deposits (e.g., magnetic susceptibility) due to diagenetic processes (Korff et al., 2016).</p><p>We have investigated seven 10- to 15-m-long sediment cores along a S-N transect at the Emperor Seamount Chain taken during RV SONNE cruise SO264 in order to (1) geochemically characterize the sediments and, (2) reconstruct past sediment redox conditions. The cores were retrieved from water depths between 3.5 and 5.7 km from organic-poor siliciclastic‑carbonaceous sediments in the South to more organic-rich siliciclastic‑siliceous sediments in the North with tephra layers found throughout all cores (Nürnberg et al., 2018).</p><p>Mn<sup>2+</sup> is released into the pore water at all study sites with increasing Mn<sup>2+</sup> concentrations below 20‑30 cm sediment depth. Pore-water Mn<sup>2+</sup> reraches up to 190 µM in siliciclastic‑siliceous sediments most likely associated with high rates of dissimilatory Mn(IV) reduction. The solid‑phase composition of a core taken from the Minnetonka Seamount (47°44’N, 168°40’E) at 4 km water depth shows Mn/Al ratios below 0.0003. These ratios are much lower than the average MORB Mn/Al value of 0.013 (Klein, 2004), which further indicates that Mn has been diagenetically lost from these sediments. As pore-water Fe<sup>2+</sup> concentrations are below detection limit at the Minnetonka Seamount and the depth distribution of solid-phase Fe/Al is mostly constant with ratios close to the average MORB Mn/Al value of 0.59 (Klein, 2004), Fe has probably not been diagenetically redistributed at this site. Pore‑water Fe<sup>2+</sup> concentrations of up to 20 µM are only found at two sites most likely as a result of dissimilatory Fe(III) reduction due to higher fluxes of organic material to the seafloor compared to the other sites.</p><p>References</p><p>Anderson, R.F., et al., 2019. Deep-sea oxygen depletion and ocean carbon sequestration during the last ice age. Global Biogeochem. Cycles 33, 301-317. </p><p>Jaccard, S.L., et al., 2009. Subarctic Pacific evidence for a glacial deepening of the oceanic respired carbon pool. Earth Planet. Sci. Lett. 277, 156‑165. </p><p>Klein, E.M., 2004. Geochemistry of the Igneous Oceanic Crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, Vol.3. Elsevier, Amsterdam, pp. 433‑463.</p><p>Korff, L., et al., 2016. Cyclic magnetite dissolution in Pleistocene sediments of the abyssal northwest Pacific Ocean: evidence for glacial oxygen depletion and carbon trapping. Paleoceanography 31, 600‑624. </p><p>Nürnberg, D., 2018. RV SONNE Fahrtbericht /Cruise Report SO264, SONNE-EMPEROR, 30.6. – 24.8.2018. </p>