Search

The lack of suitable indicators of changes in such as sea‐level and circulation has been a major limit to paleoenvironmental and paleoceanographic investigations in continental shelf regions. This paper presents an environmental magnetic study by comparing two late‐Quaternary sediment cores (DH02 and DH03) from the outer shelf of the East China Sea (ECS). Late and early Marine Isotope Stage (MIS) 3 sediments were deposited in a prodelta under cold coastal currents and an open‐shelf with the Taiwan Warm Current and upwelling. The dominant iron‐bearing minerals of the late and early MIS 3 sediments are authigenic greigite (Fe3S4) and pyrite (FeS2), respectively, which were assumed to be formed nearly syndepositionally. The overlying sediments, however, are magnetically dominated by detrital magnetite. This pattern corresponds well to the temporal changes in sea‐level over this period. The widespread occurrence of greigite in the late MIS 3 sediments can also be used for future stratigraphic division and correlation in the ECS. Additionally, compared to microfossil assemblages, rock magnetic parameters based on greigite may be more sensitive to environmental changes on continental shelves. Furthermore, the inter‐borehole spatial comparisons imply not only a sedimentary hiatus/erosion of at least 30‐m thickness in core DH02, most probably during the Last Glacial Maximum, but also that core DH02 was in a more reductive environment than core DH03 during late MIS 3. The findings highlight the potential of authigenic greigite as an indicator of spatiotemporal changes in paleoenvironmental and paleoceanographic conditions on the continental shelf at orbital or even suborbital timescales. Plain Language Summary: Environmental and oceanographic conditions on continental shelves are vital for sedimentation processes and human settlements, but the reconstruction of their evolution is hindered by the lack of effective indicators. Recent studies have indicated that syndepositional formation of greigite, a precursor to pyrite, is highly likely in shallow‐water environments with rapid sedimentation. Here, two sediment cores meridionally traversing the outer shelf of the East China Sea were investigated. The magnetic mineral assemblage and sedimentary environment exhibited almost identical change patterns, with pyrite, greigite, and magnetite as the major magnetic minerals of the early and late Marine Isotope Stage 3, and Last Glacial Maximum/last deglacial deposits, respectively. This agreeably reflects the temporal fluctuations in sea‐level and ocean circulation. By comparing the two cores, the spatial characteristics of stratigraphy and redox conditions could be determined clearly. This study thus provides a good reference for paleoenvironmental and paleoceanographic research based on authigenic greigite in continental shelf sediments. Key Points: Greigite was further confirmed as the major magnetic mineral of the late Marine Isotope Stage 3 deposits widespread on the outer shelf of the East China SeaSpatiotemporal changes in environmental and oceanographic conditions on the continental shelf are well revealed by greigite‐based parametersAuthigenic greigite can serve as a sensitive indicator for paleoenvironmental and paleoceanographic studies in continental shelf regions [ABSTRACT FROM AUTHOR]

Sedimentary deposits from the northern South China Sea (SCS) can provide important constraints on past changes in ocean currents and the East Asian summer monsoon (EASM) in this region. However, the interpretation of such records spanning the last deglaciation is complicated because sea‐level change may also have influenced the depositional processes and patterns. Here, we present new records of grain size, clay mineralogy, and magnetic mineralogy spanning the past 24 kyr from both shallow and deep‐water sediment cores in the northern SCS. Our multi‐proxy comparison among multiple cores helps constrain the influence of sea‐level change, providing confidence in interpreting the regional climate‐forced signals. After accounting for the influence of sea‐level change, we find that these multi‐proxy records reflect a combination of changes in (a) the strength of the North Pacific Intermediate Water inflow, (b) the EASM strength, and (c) the Kuroshio Current extent. Overall, this study provides new insights into the roles of varying terrestrial weathering and oceanographic processes in controlling the depositional record on the northern SCS margin in response to climate and sea‐level fluctuations. Plain Language Summary: Sediments in the South China Sea (SCS) provide important records of past changes in the ocean circulation and atmospheric patterns in the Pacific Ocean. However, the interpretation of sedimentary archives from this region in terms of changes in the ocean currents or the climate‐driven sediment supply can be challenging because of the potential influence of global sea‐level fluctuations. In order to better constrain these multiple controls on the sedimentary regime of the northern SCS, we present new mineralogical records from sediment cores collected from both shallow‐ and deep‐water sites. After assessing the effects of sea‐level change, we find that the clay mineral assemblage in shallow sites from the northern SCS can generally be used to reconstruct the evolution of the East Asian summer monsoon. In deep‐water sites, the clay mineralogy instead reflects changes in the relative abundance of sediment supplied from Taiwan compared to Luzon, revealing an enhanced inflow of the Kuroshio Current during the mid‐late Holocene. Furthermore, millennial‐scale variability in the North Pacific Intermediate Water inflow can be traced using changes in magnetic mineralogy and the inflow appears to have been stronger at the end of the last ice age. Key Points: Sedimentary records from shallow and deep‐water sites have differing sensitivities to changes in ocean currents and the East Asian monsoonClay mineralogy in shallow sites reflects sea‐level change, while deep‐water records respond to incursion of the Kuroshio CurrentMagnetic grain‐size indicates stronger deep currents during Heinrich Stadial 1, associated with the North Pacific Intermediate Water [ABSTRACT FROM AUTHOR]

Abstract Harmful effects of water pollutants are myriad. Sulfide from water bodies affects the aquatic animals. Intestine barrier function serves as the front-line of animals defense. Our previous study confirmed the toxic effect of sulfide on intestine immune response of Litopenaeus vannamei , but the underlying mechanisms remained elusive. Therefore, in this study, we investigated the transcriptomic and microbiota responses of the L. vannamei intestine subjected to acute sulfide exposure. Sulfide decreased bacterial richness and altered the intestine microbiota composition. Specifically, sulfide increased the abundances of Bacteroidetes and Actinobacteria, but decreased the abundance of Proteobacteria. At the genus level, sulfide increased typical cellulolytic characteristics bacteria, such as Formosa , Sphingomonas , and Demequina. RNA-seq analysis identified differential expression of 1799 genes (701 up-regulated and 1098 down-regulated) were grouped into 267 pathways. The most enriched pathway 'amoebiasis' was related to the intestine mucus homeostasis. A number of immune-related genes associated with antimicrobial, antioxidant, pathogen attachment and recognition, and apoptosis processes in contrasting accessions; they were correlated with the abundance of intestine bacterial at the phylum level. This study provides an insight into the mechanisms associated with molecular and microbiota response and processes involved in adaptation strategies towards sulfide stress. Highlights • Transcriptomic and microbiome responses of the Litopenaeus vannamei intestine exposed to sulfide stress was studied. • Sulfide decreased bacterial richness and altered the intestine microbiota composition. • 701 up-regulated and 1098 down-regulated genes differentially expressed in response to sulfide exposure. • The most enriched pathway "amoebiasis" was related to the intestine mucus homeostasis. • We speculated a potential mechanism of intestine barrier function in the contrasting accessions towards sulfide exposure. [ABSTRACT FROM AUTHOR]

The sediment in the Okinawa Trough (OT) preserves considerable information regarding land–ocean interactions and palaeoenvironmental evolution in the East Asian marginal seas. More specifically, the sediment provenance in the OT must be studied to recover this information. However, arguments about this remain, especially regarding the contribution of Yellow River (YR)-derived materials to middle OT depositions. To resolve this problem, we systematically investigated a gravity core (M063-05; 3.87 m in length, since the last deglaciation) collected from the middle OT by integrating environmental magnetism, diffuse reflectance spectroscopy, and transmission electron microscopy, as well as analyses of sediment grain size, clay mineralogy, and major elements. Our results indicated that sediment from the YR has contributed dominantly to this core since the last deglaciation. Limited contributions were also made from the Yangtze River and Taiwan rivers during the Holocene. Terrigenous inputs derived from the YR could be well characterized by the ratio of hematite/(hematite + goethite). Additionally, the Kuroshio Current (KC) activity since the last deglaciation, which is an important influencing factor for sediment provenance changes, was well deciphered using a new proxy Rel DM (relative contribution of detrital ferrimagnetic minerals to bulk magnetic properties). Based on comprehensive analyses of our results and previously published studies, we hypothesised that, during the last deglaciation, abundant resuspended sediment from the palaeo-YR mouth was transported to the East China Sea (ECS) continental shelf edge and the northern OT through seaward bottom flow and further spread into the middle OT. Since the Middle to Late Holocene, the central mud area of the South Yellow Sea and the mud area southwest off Cheju Island may have become the main sources to provide YR-derived materials to the middle OT. However, the mud-area-derived sediment could only be restricted to a small range owing to the hindrance of the strengthened KC. This study provides a new perspective for sediment provenance evolution of the middle OT since the last deglaciation and proposes new methods and parameters for future research on palaeoenvironmental evolution in the ECS. • Integrated methods are used for Okinawa Trough (OT) sediments provenance analyses. • Yellow River (YR) contributed dominantly to middle OT since the last deglaciation. • Hematite/(Hematite + Goethite) can well evaluate the inputs of YR-derived materials. • A new magnetic proxy (Rel DM) is utilized to decipher Kuroshio Current activity. • Sediment transportation pattern in the OT is explored combined with previous results. [ABSTRACT FROM AUTHOR]