Masashi Tsuchiya

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (206Pb/207Pb and 208Pb/207Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Symbiotic relationships of microorganisms including eukaryotic algae and prokaryotes affect holobiont nitrogen metabolism and provide survival advantages in extreme environments; however, the influences of different symbionts on nitrogen metabolism in host organisms remain unclear. By tracing the nitrogen isotopic composition (δ ¹⁵ N) of amino acids (AAs), it is possible to constrain the biosynthetic sources and trophic interactions. We targeted reef-dwelling large benthic foraminifers hosting species-specific symbiotic algae to identify the trophic positions of multiple species with distinct feeding strategies. We measured δ ¹⁵ N in AAs of bulk organic matter and of foraminiferal shells and compared the feeding strategy of each species with its estimated trophic position (TP). Estimated TPs based on δ ¹⁵ N in AAs were inconsistent with respect to species-specific feeding strategies. In particular, Amphisorus kudakajimensis , which depends on heterotrophic feeding, showed light δ ¹⁵ N _Glu and δ ¹⁵ N _Phe and TP of ~ 1. A shared nutrient source for both host and symbionts and an interactive supply of trophic compounds may explain the low trophic position. The mixotrophic or heterotrophic TPs of Calcarinidae hosting endosymbiotic diatom with limited feeding (TP = 1.5–2.3) may be affected by bacterial heterotrophic processes. Differences in symbiotic algae (zooxanthellae and diatoms) may have influenced host’s nutritional strategies through functional variations in nitrogen metabolism. Large variations in δ ¹⁵ N _Glu and δ ¹⁵ N _Phe within single species suggested that large benthic foraminifers exploit multiple sources of nitrogen. Additional culture studies using different nitrogen sources could provide insights into detailed nitrogen metabolism of organisms with endosymbionts and role of associated organisms.

To understand the trophic interactions between various organisms in chemosynthesis-based ecosystems (CBEs) and the metabolic interaction between host animal and its symbiont, we estimated the trophic position (TP) using the stable nitrogen isotopic compositions of glutamic acid and phenylalanine. We demonstrated that estimating TP based on the isotopic composition of amino acids is a valuable tool for understanding photosynthetic prey-predator interactions among marine organisms, and it can also be applied to chemosynthesis-based food webs involving host-symbiont interactions. In CBEs, the nitrogen isotope ratio of phenylalanine ranged from − 15‰ to + 13‰, suggesting a wide variety of nutritional sources for organisms. Our results revealed that organisms in CBEs can be categorized into two main groups: those that depend on chemosynthetic organic matter and those that depend on photosynthetic organic matter from the ocean surface. Furthermore, although not clearly distinguishable, there was an intermediate group that depends on both, such as demersal fishes. CBE-endemic organisms, particularly bivalves, were notably depleted in ¹⁵N. Interestingly, two nutritional types of chemosymbiotic bivalves were identified: vesicomyid clams showed an increase in the nitrogen isotope ratio of glutamic acid and a higher TP relative to symbiotic bacteria, while Bathymodiolus and Gigantidas mussels exhibited no change in the nitrogen isotope ratio of glutamic acid and maintained a TP of ~ 1 across all tissues, including gill samples mainly composed of symbiotic bacteria. Different forms of trophic dependence on chemosynthetic bacteria were observed even among closely related bivalve species, regardless of whether the symbiotic relationship is ecto- or endo-symbiosis. Consequently, among species preying on chemosymbiotic bivalves, the TP may reach 3 or more when preying on vesicomyid clams but remains around 2 when preying on Bathymodiolus and Gigatidas mussels. The organisms inhabiting the CBE of Sagami Bay display diverse patterns of resource use.

Xenophyophores dominate the abyssal megafauna across many areas of the Pacific Ocean. These giant agglutinated foraminifera have been studied mainly in the tropics, including within the Clarion-Clipperton Zone (CCZ), from where the majority of recently described taxa have originated. Here, we describe three new species, one of them assigned to a new genus, from an area further north (30–32.5° N) near the Japanese Archipelago. Specimens were collected in pushcores during dives of the manned submersible Shinkai 6500 and preserved in the cores after removal of fragments for genetic analyses, allowing them to be examined in life position using X-ray micro-computed tomography (µCT). The three species have basically plate-like tests composed largely of mineral grains. Two, both from 32.5° N, are assigned to the genus Psammina. They are closely related to each other and to P. tenuis from the western CCZ. In Psammina yokosukae sp. nov., the test comprises curved plates, whereas in Psammina contorta sp. nov., it comprises a confusing array of contorted plates and other poorly defined structures. The third new species, Laminarena variabilis gen. et sp. nov., is genetically distinct from the others. In typical specimens from 30° N, the plates are large, curved or sinuous, relatively thin, and marked by a distinct surface pattern of concentric zones, traversed by closely spaced, radial ridges that correspond to internal partitions. A form from 32.5° N is shown to be conspecific with the 30° N specimens based on molecular evidence but is morphologically more complex, comprising elongate bar- and plate-like elements, some with fan-like terminations. A fourth taxon, resembling a bumpy pebble and occupied by bubble-like internal compartments, is described informally. These new taxa enhance our knowledge of Pacific xenophyophores, as well as our understanding of the morphological diversity of xenophyophores in general.

To mitigate marine pollution from single-use plastics, it is crucial to transition to next-generation commodity materials that are derived from biomass and are recyclable and marine biodegradable even at abyssal depths in case of the accidental release to the ocean. Here, we develop an optically transparent millimeter-thick paperboard called transparent paperboard (tPB) through dissolution and coagulation of cellulose. The tPB is made entirely of pristine cellulose and compositionally identical to paper. A cup-shaped tPB can hold just-boiled water without an internal film coating because of its high wet tensile properties and anisotropic thermal properties. In addition, the spent tPB is material recyclable in a closed system, where all chemicals and water are also recyclable. Furthermore, the marine biodegradability of tPB across shallow to abyssal depths is confirmed by on-site degradation tests and metagenomic analyses. Hence, tPB is expected to serve as a key fully circular commodity material in sustainable societies of the future.