Aiming at two types of typhoon field parameters used in parametric typhoon wind field model, such as radius to maximum wind speed ${R}_{{\rm{max}}}$ and radial pressure distribution coefficient $(B)$, the process of two typhoon was reproduced with different combinations of parameters ${R}_{{\rm{max}}}$ and $ B $, and compared with the field observation data of three observation sites. The constructed typhoon wind field was used as the driving wind field in the MIKE 21 model, which was used to complete numerical simulation of the storm surge of two typhoons in Zhejiang Province. The tide level and storm tide level were verified and analyzed with the observation data. The results show that the parametric model selected in this paper is suitable for calculating typhoon wind field which affect the coast of Zhejiang, and the simulation results of storm surge model established on this basis meet the requirement of accuracy.

Seawater and surface sediment samples at 30 stations in the Jiaozhou Bay (JZB) and river water and coastal water samples at 18 stations along the JZB were collected in August 2019 and May 2021, respectively. Dissolved inorganic nutrient concentrations and structure in the water and the contents of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), biogenic silica (BSi), and stable isotopes of carbon and nitrogen (δ¹³C, δ¹⁵N) in surface sediments were analyzed to clarify the present nutritional environment of seawater and surface sediment and its main influencing factors in the JZB. The results show that the spatial distribution of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), and dissolved silicate (DSi) in seawater is consistent with that in the coastal water of JZB. The high values that occur northeast of the bay are mainly caused by river input and sewage discharge, and the low values mainly occur at the center and bay mouth. Combined with the analysis of historical data, we found that the nutrient concentrations of JZB in summer continued to rise from 1990 to 2008 and then declined since 2006 because of the declining nutrient loadings related to the implementation of total pollutant load control management and freshwater loadings from surrounding rivers. The decreased nutrient loadings were mainly found in rivers such as the Dagu River, causing the disappearance of high concentrations in the western region after 2010. The phosphorus limitation accelerated after 2000 as a result of the imbalanced input of nitrogen and phosphorus. The high values of TOC, TN, and TP in the surface sediments of JZB are concentrated along the northeast and east coasts, combined with BSi and water nutrient analysis, which is mainly caused by the river input and sewage discharge and the high primary productivity they bring. Sediment biogenic elements are well coupled with water column nutrients in spatial distribution. The adverse effect of coarse sediment grain size on the preservation of organic matter and the strong hydrodynamic effect of the bay mouth jointly lead to the low content of biogenic elements in the west, middle, and mouth of the bay. The δ¹³C and two-endmember mixing model show that the source of organic matter in the surface sediments of JZB is mainly marine-derived, accounting for an average of 64%. The eastern coast is obviously affected by terrestrial input. The spatial distribution of δ¹⁵N shows that the nitrogen in the surface sediment of JZB is jointly affected by mariculture and sewage discharge. The current situation of the water body and sediment nutrient environments shows that the control of sewage discharge from the northeast river and the coastal area is the key to the later pollution control of JZB.

Changes in the content of redox sensitive elements (RSE) in sediments are good surrogate indicators for the redox environment of the overlying water. The RSE in the columnar sediments under complex environmental backgrounds through the grain size, total organic carbon and total nitrogen and its isotopes contents, and redox sensitive elements contents of the two columnar sediments (30 cm) in South Central Okinawa Trough are explored in this paper. And to explore the occurrence mechanism and environmental indication significance. The study found that in addition to the depletion of Cr in the columnar sediments, other RSEs showed different degrees of enrichment. The “grain size effect” has little effect on the RSE content of columnar sediments in the Okinawa Trough; analysis and judgment show that seawater surface productivity is the main factor affecting the redox environment of sediments, and RSE is achieved through the adsorption or desorption of Mn (hydrogen) oxides enrichment and loss. Indicators such as δCe, V/(V+Ni), Ni/Co and V/Cr indicate that the sediment is in an oxic-dysoxic water environment. The Mn element in the sediment diffuses upward in the form of Mn²⁺ through reduction, and is oxidized and enriched by oxygen-containing interstitial water at 25−30 cm to form a manganese peak. The 0−25 cm columnar sediment is in an oxic water column, and 25−30 cm is in a dysoxic water column.

This study utilizes a new functional analysis tool, multiscale window transform (MWT), to decompose the ocean circulation system in the Bay of Bengal (BOB) into three scale windows, namely, the background flow window (>96 days), the mesoscale window (24–96 days) and the high-frequency window (<24 days), and then uses the canonical energy transfer theory to investigate the intrinsic nonlinear multiscale interactions among these windows, on the basis of an eddy-resolving model simulation. It is found that multiscale interactions are strongest along the northwestern boundary and east of Sri Lanka. With intense barotropic and baroclinic instabilities, the canonical transfers of kinetic energy (KE) and available potential energy (APE) are mainly forward in these two regions. Mesoscale eddy kinetic energy (EKE) reservoir is mainly filled by the barotropic energy pathway with the kinetic energy of the background flow transferring to EKE, and secondarily from the baroclinic energy pathway with APE of the background flow transferring to the mesoscale APE and further converting to EKE. The gained EKE is found to further cascade to high-frequency motions, acting as an important dissipation mechanism of the mesoscale eddies in these regions. In contrast, the central BOB is mainly characterized by inverse KE cascades, where EKE and high-frequency kinetic energy (HKE) are gained via the baroclinic energy pathway, and then feed the background flow through inverse cascade processes. The northwest of Sumatra is also an area with strong mesoscale and high-frequency variability. Both barotropic and baroclinic energy pathways are the sources for EKE and HKE reservoirs in this region, with the baroclinic energy pathway playing the dominant role.

Fe is the most abundant variable-valence element in igneous rocks, and is also an important mineralizing element, mainly in the solid (mineral) and liquid (fluid) phases in Fe²⁺ or Fe³⁺ valence state, and participates in magmatic processes and various mineralization throughout. With the development of test analytical techniques (e.g. MC-ICPMS), the analysis of non-traditional stable isotope compositions such as Fe has become possible and has been successfully applied to the study of important geological processes such as magma source tracing, tracing of crystallization evolutionary processes and mineralization analysis in the last decade or so. Based on the analysis of the fractionation effect of Fe isotopes during magmatism, this paper summarized the latest results of Fe isotope composition studies in tracing the action of seafloor basaltic magmas (MORB, OIB, IAB and BABB, etc.) and discussed the main problems in the application of Fe isotope composition in tracing the action of seafloor magmas. The results of the comprehensive analysis show that the Fe isotope fractionation effect in igneous rocks is influenced not only by the processes of partial melting of magma source material, magma diffusion, fluid exsolution and crystallization differentiation, but also by the assimilation of surrounding rock material and seafloor alteration. Since Fe isotope analysis techniques (methods) have yet to be further refined, and the available data are limited and need to be screened for artifacts, caution is still needed when using Fe isotope compositions to analyze or recover magmatic sources and processes. It is urgent to establish a complete and reliable Fe isotope tracing system, which requires the recent work to select as many suitable samples as possible representing different tectonic environments and different rock types, to obtain (accumulate) more fine analytical data of original (unmodified or altered) samples, and to pay attention to the combination or mutual corroboration of multiple data in the process of using Fe isotope tracing for seafloor magmatism.

The Atlantic meridional overturning circulation (AMOC) is an important component of the climate system, of which change in the strength can affect meridional heat distribution between the northern and southern hemispheres. Proxy records show that changes in Atlantic Ocean circulation during the Late Pleistocene is associated with precessional cycle, but its physical mechanism remains unclear. Here we use a fully coupled climate model to investigate dynamics associated with AMOC changes in precessional band under glacial-interglacial climate conditions. Our results show that increase in boreal summer insolation can effectively weaken the AMOC during warm interglacial periods, while this weakening effect is reduced under glacial maximum. We further demonstrate that during the warm interglacial period increase in boreal summer insolation leads to sea surface warming and subpolar rainfall increase in North Atlantic, which jointly reduces sea surface density and hence the strength of deep water formation. During the glacial maximum period, climate responses to precessional change is of anti-phase impacts on the AMOC. At the low latitudes, a low pressure anomaly triggered by subtropical warming weakens atmospheric moisture export from the subtropical Atlantic to Pacific, increasing in net precipitation and hence freshening tropical sea surface in the North Atlantic. At the high latitudes, the warming-induced sea ice retreat promotes ocean heat loss via the enlarged ice-free area, and hence tends to strengthen the vertical mixing. The combined effects of low- and high-latitude responses finally leads to a trivial weakening of the AMOC. Overall, our results provide a systematic understanding of governing mechanism for precessionally-induced AMOC change under glacial-interglacial climatic backgrounds, shedding light on our interpretation of precessional periodicity in reconstructed ocean circulation changes during the Pleistocene.

Previous studies have shown that the decadal modulation of the Kuroshio extension (KE) system is controlled by the Pacific decadal oscillation-associated forcing from downstream. However, recent observation reveals that this mechanism ceases to function after August 2017. Meanwhile, a large meander is under development in the KE’s upstream, i.e., south of Japan. Using the self-organizing map (SOM), we investigate the characteristic spatial and temporal patterns of the Kuroshio south of Japan and the KE and their causal relations, based on the 26-year (1993−2018) satellite altimetry data of sea level anomaly (SLA). The typical spatial patterns are well extracted, and their temporal trajectories indicate that the KE tends to be stable (unstable) when the upstream Kuroshio takes a large meander (an offshore nonlarge meander) path. To further unravel the underlying cause-and-effect relation between the two systems, we apply the information flow-based causality analysis to the typical regions of SLA and its associated temporal modes identified with the SOM. It is found that during the large meander event, the Kuroshio south of Japan and the KE are mutually causal, but have different hotspots. The information flows from the former to the latter mainly occur in the southeastern area off the Kii Peninsula and the time-mean ridge and trough of the KE jet, while those from the latter to the former are mainly concentrated in the time-mean ridge and trough of the KE jet, and the recirculation gyre of the Kuroshio. These results indicate that the Kuroshio large meander is an important factor influencing the KE’s stability, while the KE affects its upstream Kuroshio via modulating the associated recirculation gyres. In contrast, when the offshore nonlarge meander path is taken, a one-way causality is identified from the Kuroshio to the KE, mainly occurring over the Izu-Ogasawara Ridge and in the recirculation gyres. This may be attributed to the constantly downstream transport of negative SLAs into the KE’s recirculation gyre, which leads to an unstable KE.

In order to improve the study of the interaction between internal solitary waves and submarine slope sediments, the stage of continued motion on the slope after internal solitary waves fragmentation is focused on in this paper, and conducts physical simulation experiments to analyse the changes in earth pressure and super-pore water pressure in response to the slope to reveal the process of internal wave action. The results show that the sediment particles on the slope are resuspended under the combined action of vortex and seepage caused by the internal solitary waves fragmentation, and the change in slope gradient does not change the dominant dynamic role of the sediment in generating the dynamic response; the amplitude of the internal solitary waves affect the ratio between vortex and seepage, i.e. the vortex is dominant under small amplitude conditions and the seepage is dominant under large amplitude conditions; the fragmented fluid forms a new dynamic role when it rushes out along the slope. The dynamic response of the sediment to the new vorticity is influenced by the slope of the slope. The results of this paper are useful for the study of internal solitary waves resuspension transporting seafloor sediments and modifying seafloor topography.

The applicability of environmental DNA (eDNA) metabarcoding fragments to relative fish species had not been compared. There was a risk of “species loss” in diversity surveys. In order to screen out the best fragments, we compared the resolution rate differences of 15 eDNA metabarcoding fragments in 106 genera (a total of 935 species). The results were as follows: (1) the protein-coding gene (COI, fragment 15) had the highest resolution rate, but the universality of its corresponding primer pairs was the worst; the overall mean distance based on primer pair sequence of fragment 09, fragment 11, fragment 07, fragment 03 and fragment 12 were obviously large, suggesting their eDNA amplification efficiency were possibly low. (2) The resolution rates were significantly affected by the length of fragments, and the fragment 05, fragment 06, fragment 01, fragment 02 and fragment 13 of ribosomal genes had a higher resolution rate except fragment 15. (3) Non-metric multidimensional scaling analysis (NMDS) showed that there were great differences among different genes and different fragments belonging to the same gene. Therefore, the combination application of multi-fragment and multi-gene should be considered; besides, fragment 01 and fragment 02, and fragment 05 and fragment 06 were close to each other in the NMDS plot. They function of fish resolution were overlapped. (4) Species groups affected the resolution results, and eDNA studies stilled need to develop fragments with higher resolution rates. Based on the resolution rate of relative species, the universality of primer pairs and NMDS analysis, this study recommended fragment 01 (Mifish-U) for 2×150 bp sequencing platform and fragment 05 (Ac12S) for 2×250 bp sequencing platform, supplemented by fragment 13 (Vert-16S-eDNA) to investigate the diversity of relative fish. This study provided some support for improving the accuracy of fish eDNA survey results.

During the past decades of years, the widespread restrictions and ban on the use of legacy persistent organic pollutants (POPs) such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) around the world have resulted in gradual decrease in their concentration in various environmental media. As an open sea area, the Northwest Pacific Ocean is far away from the continental area without obvious pollution point source, the ocean currents play an important role in the transportation and diffusion of POPs. In this study, the surface waters (2−5 m) and subsurface waters (150 m) in the Kuroshio area of the Northwest Pacific Ocean were collected and analyzed for dissolved OCPs and PCBs. The results showed that the concentrations of HCHs, DDTs, CHLs and PCBs in the surface waters ranged from 30.7 pg/L to 68.8 pg/L, 6.16 pg/L to 23.8 pg/L, 1.07 pg/L to 5.75 pg/L and 49.8 pg/L to 124 pg/L, respectively; the concentrations in the subsurface waters ranged from 27.3 pg/L to 68.4 pg/L, 7.06 pg/L to 14.1 pg/L, 0.518 pg/L to 10.1 pg/L and 34.1 pg/L to 68.4 pg/L, respectively. The concentration levels of OCPs in different water bodies were comparable, which may be related to the huge water body and internal homogeneity of the Kuroshio. The ratios of the various isomers of HCHs indicated that the sea area was dominated by lindane input, while the ratio of DDTs and CHLs showed that the DDTs and CHLs in the waters of the sea area were mainly derived from the residues of legacy. PCBs were dominated by tri-PCBs and tetra-PCBs, which consistented with the use of PCBs in East Asia. The large volume and uniform internal distribution of Kuroshio water mass have an important impact on the vertical distribution of pollutants, that is, the concentration and composition of OCPs in water at different depths are similar. At the same time, Kuroshio brings high temperature and high nutrient salt water masses, forming potential risks to the enrichment of pollutants in the marine organisms.