Cold Water Mass Research Articles

The impact of Holocene interactions among climate, ocean current, and shear front factors on fine sediment dispersal in the central South Yellow Sea

The South Yellow Sea (SYS) is strongly influenced by large amounts of sediment input from surrounding rivers, but the dispersal patterns of these sediments, especially how they accumulate in the central Yellow Sea mud (CYSM) region, have not been well illustrated. Here, we present a detailed temporal variation record of the clay mineral compositions from core YSC-10 of the northern SYS near the western margin of the CYSM, trying to investigate sediment provenance and to discuss transport processes occurring during the Holocene. The clay mineral assemblages of core YSC-10 mainly consist predominantly of illite (68 ± 3%), followed by chlorite (15 ± 2%) and kaolinite (10 ± 2%), with scarce amounts of smectite (6 ± 3%). Combined with published data, our results suggest that the fine sediments of core YSC-10 are most likely a mixing product of the Huanghe (Yellow River), Changjiang (Yangtze River) and Korean Peninsula small river sediments, with notable temporal changes. During 8.4–6.4 ka, the Huanghe sediments from the Bohai Sea flowed directly into the SYS and played major roles in the sedimentation therein. In addition, as the modern ocean circulation pattern was formed ∼6 ka, the ocean front developed along the Shandong Peninsula coastal area of the SYS, which would have prevented the dispersal of the Huanghe sediments to the CYSM. The Changjiang sediments delivered by the diluted water replaced those from the Huanghe as the main source of the CYSM during the period of 6.4–4.2 ka. After 4.2 ka, the coastal shear front weakened and moved seawards due to the weakening and eastward shift of the Yellow Sea Warm Current (YSWC) in winter and the weakening and shrinking of the Yellow Sea Cold Water Mass (YSCWM) in summer. The Huanghe sediments seem to have increased and fluctuated frequently to core YSC-10 since then. Our study thus highlights that the coastal shear front may have played an important role in the source-to-sink processes of the SYS.

Numerical study on advective fog formation and its characteristic associated with cold water upwelling.

Recent rapid industrial development in the Korean Peninsula has increased the impacts of meteorological disasters on marine and coastal environments. In particular, marine fog driven by summer cold water masses can inhibit transport and aviation; yet a lack of observational data hinders our understanding of this phenomena. The present study aimed to analyze the differences in cold water mass formation according to sea surface temperature (SST) resolution and its effects on the occurrence and distribution of sea fog over the Korean Peninsula from June 23-July 1, 2016, according to the Weather Research and Forecasting model. Data from the Final Operational Model Global Tropospheric Analyses were provided at 1° and 0.25° resolutions and NOAA real-time global SST (RTG-SST) data were provided at 0.083°. While conventional analyses have used initial SST distributions throughout the entire simulation period, small-scale, rapidly developing oceanic phenomena (e.g., cold water masses) lasting for several days act as an important mediating factor between the lower atmosphere and sea. RTG-SST was successful at identifying fog presence and maintained the most extensive horizontal distribution of cold water masses. In addition, it was confirmed that the difference in SST resolution led to varying sizes and strengths of the warm pools that provided water vapor from the open sea area to the atmosphere. On examining the horizontal water vapor transport and the vertical structure of the generated sea fog using the RTG-SST, water vapors were found to be continuously introduced by the southwesterly winds from June 29 to 30, creating a fog event throughout June 30. Accordingly, high-resolution SST data must be input into numerical models whenever possible. It is expected that the findings of this study can contribute to the reduction of ship accidents via the accurate simulation of sea fog.

Palynological implications for paleoenvironmental changes over the past 81,000 years on the Jeju Strait shelf, off southwestern Korea

Age-controlled palynostratigraphy has revealed changes in the depositional environment, vegetation, and climate of the southwestern Korean Peninsula since marine isotope stage (MIS) 5a. During MIS 5a (ca. 74–81 ka), the Jeju Strait shelf was an inner shelf with deposition influenced by the Jeju Warm Current (JWC), surrounded by land covered by mixed conifer and deciduous broadleaf forests under warm temperate conditions. The paleoenvironment during MIS 4 (57–71 ka) remains unknown due to a lack of palynomorphs from this stage. During mid–late MIS 3 (ca. 29–50 ka), the Jeju Strait shelf was an inner shelf influenced by cold-water masses from the Korean Coastal Current combined with weaker influences by the JWC, and the surrounding land was covered by mixed conifer and deciduous broadleaf forests that were less dense than in MIS 5a under warm and relatively dry conditions. A cold, slightly wet climate during MIS 2 (ca. 12–29 ka) led to the extension of predominantly cold-tolerant conifer forests due to lowstand sea levels, although inland East Asia remained cold and dry. During MIS 1 (ca. 0–12 ka), cold-tolerant conifer forests persisted into the early Holocene, and were subsequently replaced by mixed conifer and deciduous broadleaf forests as a warm climate was restored in the mid–late Holocene, when the depositional environment became an outer shelf due to highstand sea levels, as it remains today.

Occurrence and abundance of the gymnosome pteropod genus Clione in the coastal waters of Mombetsu, southern Okhotsk Sea, from 2004 to 2012

Patterns in the seasonal occurrence and abundance of gymnosome pteropods of the genus Clione are described from samples collected during routine monitoring in Mombetsu Harbor, northeastern Hokkaido, Japan, from 2004 to 2012. In this study area of the southern Okhotsk Sea is a unique region where water masses are exchanged seasonally, driven by the East Sakhalin Current (ESC) in winter and the Soya Warm Current (SWC) in summer. Clione elegantissima adults were found between December and early April within a narrow temperature range of −1.79 to 3.78 °C. Most (90.9%) of these individuals occurred in the cold-water mass of the ESC. Veliger and polytrochous larval stages of Clione spp. were observed in all periods, except for late August to early October when the SWC dominated. A positive correlation was found between chlorophyll a concentration and larval abundance using 10-day averaged data. The results indicate that food availability was sufficient to support Clione spp. larval stages in the sampling region. Seasonal exchanges of water mass in the sampling area influence the occurrence of Clione species.

An extreme warm event of the Yellow Sea Cold Water Mass in the summer of 2007 and its causes

A high-resolution numerical model based on the Regional Ocean Modeling System (ROMS) was used to simulate the Yellow Sea Cold Water Mass (YSCWM) and revealed an extreme warm event of the YSCWM in the summer of 2007. This event was also captured by in situ observations. In August 2007, the average temperature of the YSCWM was above 1 °C higher than its climatological mean. The unusually-high temperature anomaly of the YSCWM could trace back to the winter 2006–07. Heat budget of the Yellow Sea deep water (YSDW) below 50 m depth, indicated that vertical mixing, rather than advection, in the winter 2006–07 played a crucial role in the generation of the warm event. With the seasonal thermocline disappearing in the winter 2006–07, a weak vertical mixing effect due to weak wind speeds and high heat content in the Yellow Sea upper water (YSUW) above the YSDW, together with strong advection effect, caused the YSDW to become quite warmer than its climatological mean. After that, the seasonal thermocline above the YSDW formed again and the warm YSDW persisted until the summer of 2007, resulting in the extreme warm event of the YSCWM.

Regional projection of climate warming effects on coastal seas in east China

The coastal region in east China experiences massive anthropogenic eutrophication, and the bottom water off the Changjiang River Estuary in the East China Sea faces the threat of severe seasonal hypoxia. We find that projected future climate changes will work in parallel with anthropogenic eutrophication to exacerbate current hypoxia and increase shelf vulnerability to bottom hypoxia. We use a coupled physical-biogeochemical regional model to investigate the differences of shelf hydrography and oxygen dynamics between present and future projected states. Model results indicate that the Yellow Sea Cold Water Mass which plays essential roles in nekton migration and shellfish farming practically disappears by the end of the 21st century, and shelf vertical stratification strengthens by an average of 12.7%. Hypoxia off the Changjiang River Estuary is exacerbated with increased (by one month) hypoxia duration, lower dissolved oxygen minima, and significant lateral (202%) and vertical (60%) expansions of hypoxic water. Reduced oxygen solubility, and accelerated oxygen consumption under increased primary production and rising water temperature contribute 42% and 58%, respectively, of bottom dissolved oxygen decrease in the East China Sea. Model results also show increased vertical diffusion of oxygen, despite vertical stratification strengthening, due to increased surface-bottom oxygen concentration gradient associated with increased oxygen release in surface water and exacerbated oxygen consumption in subsurface water.

Interannual variation of a bottom cold water mass in the Seto Inland Sea, Japan

Abstract. A bottom cold water mass (BCWM) is a widespread physical oceanographic phenomenon in coastal seas, and its temperature variability has an important effect on the marine ecological environment. In this study, the interannual variation of the BCWM in Iyo-Nada (INCWM), a semi-enclosed bay in the Seto Inland Sea, Japan, from 1994 to 2015 and its response to air–sea heat flux change were investigated using monthly observational data and a hydrodynamic model. Surrounded by the isotherm of 18 ∘C, the observed multi-year average water temperature inside the INCWM was 17.58 ∘C with a standard deviation of 0.27 ∘C, while the mean area of INCWM was 5.73 × 105 m2 with a standard deviation of 4.35 × 105 m2. The interannual variation of average water temperature of INCWM showed a negative correlation with its area that indicates a low temperature corresponds to a big area. In addition, the interannual variation of the average temperature inside INCWM showed positive correlations with the local water temperature from April to July and with remote water temperature below 10 m in an adjacent strait in July. Differing from previously studied BCWMs, which had interannual variations depending closely on the water temperature before the warming season, the interannual variation of INCWM is more sensitive to the air–sea heat flux during the warming season than that in the previous winter. Further, by comparing several BCWMs, we found that the BCWM size is a key factor in understanding the heat transfer process responsible for the interannual variation of BCWMs in coastal seas. These findings will help us to understand the response of bottom cold water mass in coastal seas to sea surface forcing change.

Quasi-Synchronous Accumulation of Apparent Oxygen Utilization and Inorganic Carbon in the South Yellow Sea Cold Water Mass From Spring to Autumn: The Acidification Effect and Roles of Community Metabolic Processes, Water Mixing, and Spring Thermal State

To better understand seasonal acidification in the South Yellow Sea (SYS), four field surveys conducted in 2019 and the historical data obtained in 2018 were incorporated in this study. The lowest aragonite saturation state (Ωarag) value of 1.15 was observed in the central SYS in late autumn. Despite interannual variations in the rate of net community respiration, the quasi-synchronous accumulation of apparent oxygen utilization and excess dissolved inorganic carbon (DIC) relative to the air equilibrium were revealed in the SYS cold water mass (SYSCWM) from late spring to autumn. Correspondingly, the two acidification indexes (Ωarag and pH) decreased in logarithmic forms in the SYSCWM in warm seasons. To examine the potential influences of hydrological dynamics on seasonal acidification in the SYSCWM, a three-endmember water-mixing model was applied. The results showed that the cumulative effect of various non-conservative processes on DIC was comparable with the excess DIC relative to the air equilibrium. This implied that the summer and autumn carbonate dynamics and the acidification status of the cold water mass were almost free from the potential impacts of the weak water mixing and internal circulation in summer and autumn in a given year. The Yellow Sea Warm Current carries oceanic DIC into the SYS only in winter and early spring. This study also showed that the re-equilibrium with atmospheric CO2 at given temperature in early spring determined the initial Ωarag of the SYS before Ωarag declining in late spring, summer, and autumn. The sensitivity of coastal Ωarag changes to DIC addition is subject to both spatial and temporal variations.

Stable oxygen isotopes in planktonic foraminifera from surface sediments in the California Current system

Stable oxygen isotopes of Globigerinoides ruber s.l. and Globigerina bulloides have been widely used to infer the variability of the water column hydrographic structure over various time scales. However, the reliability of this geochemical tool requires a regional analysis since the inferred calcification depth and temperature of planktonic foraminifera depend on local environmental conditions. In the present study, δ18O values of G. ruber s.l and G. bulloides collected from 21 surface sediment samples were used to infer their calcification depth in the southwestern margin of the Baja California peninsula. The δ18O values of G. ruber s.l. represented oceanographic conditions from warm tropical water masses (summer-autumn), while G. bulloides represented upwelling conditions and cold-water masses (winter-spring). Estimated calcification depths ranged from 0 to 30 m for both species. The isotopic difference between them (1.2‰ in this study and 1.1‰ in the Guaymas basin sediment trap) suggests a sea temperature difference of ~5 °C, which is very similar to the difference inferred from the Mg/Ca ratio for both species 3 to 14 ka. This suggests that G. ruber s.l. and G. bulloides have calcified over the same depth interval but under contrasting seasonal oceanographic conditions i.e. upwelling (winter-spring) and stratification of the water column (summer-autumn).

Ocean model-based covariates improve a marine fish stock assessment when observations are limited

Abstract The productivity of many fish populations is influenced by the environment, but developing environment-linked stock assessments remain challenging and current management of most commercial species assumes that stock productivity is time-invariant. In the Northeast United States, previous studies suggest that the recruitment of Southern New England-Mid Atlantic yellowtail flounder is closely related to the strength of the Cold Pool, a seasonally formed cold water mass on the continental shelf. Here, we developed three new indices that enhance the characterization of Cold Pool interannual variations using bottom temperature from a regional hindcast ocean model and a global ocean data assimilated hindcast. We associated these new indices to yellowtail flounder recruitment in a state–space, age-structured stock assessment framework using the Woods Hole Assessment Model. We demonstrate that incorporating Cold Pool effects on yellowtail flounder recruitment reduces the retrospective patterns and may improve the predictive skill of recruitment and, to a lesser extent, spawning stock biomass. We also show that the performance of the assessment models that incorporated ocean model-based indices is improved compared to the model using only the observation-based index. Instead of relying on limited subsurface observations, using validated ocean model products as environmental covariates in stock assessments may both improve predictions and facilitate operationalization.

Nitrate Regeneration and Loss in the Central Yellow Sea Bottom Water Revealed by Nitrogen Isotopes

The Yellow Sea (YS) is an epicontinental sea framed by the densely populated mainland of China and the Korean peninsula. Human activities over the last decades resulted in heavily increasing discharge of reactive nitrogen into the YS, which created numerous ecological problems. To elucidate the role of central YS in the cycling of reactive nitrogen, specifically the Yellow Sea Cold Water Mass (YSCWM), we determined nutrient concentrations, dual stable isotopes of nitrate (δ15N-NO3- and δ18O-NO3-), and stable isotopes of particulate and sedimentary nitrogen in spring and summer, i.e., in biologically inactive and active periods. The nitrate concentration in spring was higher than that in summer in the northern part of the YSCWM, Nitrate increased in the southern part accompanied by a decrease in δ15N-NO3- and δ18O-NO3-, which are indicative of nitrification that was a significant source of recycled nitrate in the south part of YSCWM. To quantify this regenerated nitrate, we use a mixing model with end members of preformed nitrate in spring and regenerated nitrate in summer, both with their distinct dual isotope values. The results suggest that only 35% nitrate was a residual of nitrate preformed in spring and 65% in summer in the southern branch of YSCWM was regenerated. The northern part of YSCWM has low concentrations of dissolved inorganic nitrogen, mainly because of denitrification in sediments. In contrast, the southern pool of YSCWM is a growing reservoir of regenerated terrestrial reactive nitrogen, the addition of which compensates the removal by co-occurring sediment denitrification. In consequence, the southern branch of YSCWM is facing a higher ecological risk than the northern branch, when excess reactive nitrogen discharge from Changjiang River continues at present levels or even increases.

COASTAL OCEAN ACIDIFICATION IN BRAZIL: A BRIEF OVERVIEW AND PERSPECTIVES

This perspective paper aims at presenting the current knowledge on the processes of ocean acidification (OA) and coastal acidification (CA) in the Brazilian coastal ocean. We define and differentiate the processes of OA and CA: the first driven by the actual global increase of atmospheric carbon dioxide (CO2); the second driven by a combination of ocean uptake of atmospheric CO2 and other local/regional chemical additions or subtractions in aquatic ecosystems at the land-ocean interface. Regarding OA, we have centered our analysis on the data available for the main water masses along the Brazilian coast: South Atlantic Central Water (SACW), Tropical Water (TW), and Coastal Water (CW). The few data available for the shallow coastal waters (< 200 m depth) of the continental shelf reveal an increase in the anthropogenic component of the total dissolved inorganic carbon (DIC) pool in the SACW, with a decline in the ocean pH (over two decades; 1993-2013), and in the saturation state of calcium carbonate (CaCO3) minerals. We could not find OA trends for TW and CW because no data was available. Overall, the colder water masses (SACW, Plata Plume) have lower buffering capacity and simulations show that will potentially experience earlier negative OA impacts than the warmer waters masses (TW, Amazon Plume). Regarding CA, we have identified some local/regional studies investigating the carbonate chemistry in nearshore/estuarine ecosystems, particularly on the quantification of sources and sinks of CO2 , and determining short-term variabilities. Apparently, spreading coastal eutrophication in Brazil can enhances or reduces the process of OA, depending on the net ecosystem metabolism in combination with other chemical alterations. However, we could not find medium-long term acidification trends due to the limited data. There is a limited capacity to produce long time-series of carbonate chemistry parameters in key ecosystems and regions along the Brazilian coast. This lack of past information hinders and impairs the scientific community for identifying potential patterns of acidification along the Brazilian coast. We call for an urgent action in Brazil, with emphasis on the establishment of moored buoys/stations and/or scientific programs in the long term with continuous, real-time measurements of the main carbonate chemistry parameters.
 Keywords: ocean acidification, coastal acidification, coastal eutrophication, continental shelf, Southwestern Atlantic Ocean

Horizontal and Vertical Migration of Anglerfish Lophius piscatorius in Relation to Hydrography in Faroese Waters

Adult anglerfish conduct annual migrations between spawning areas and feeding areas; for Faroese waters this migration has so far not been described. Therefore, anglerfish migration and distribution in Faroese waters was investigated by mark-recapture studies, including data storage tags, as well as data from scientific trawl surveys, commercial trawlers and gillnetters. The fish distribution was compared to hydrographical conditions such as sea surface- and bottom temperature. A clear seasonal offshore-onshore migration was observed. Anglerfish occupied shallower waters (<200 m) during summer and deeper waters, especially on the western side of the Faroe shelf, during winter. This seasonal movement was most evident for sexually mature fish longer than 70 cm indicating spawning in deep waters during winter. Further, during winter anglerfish experienced cold water, which indicated that they were distributed close to the main interface of cold water masses surrounding the shelf. The fish were mostly located in warm water (6.5–11°C) and seldom occurred in colder waters than 4°C. Anglerfish appeared generally inactive, only around 5% of the total data storage tag recordings showed more than 5 m vertical movement between two subsequent hourly recordings. This vertical activity varied seasonally by being higher during winter than summer and diurnally by being higher during night time than day time, indicating that sunrise and day length played an important role in vertical movements.

Functional diversity and groups of crustacean zooplankton in the southern Yellow Sea

Functional trait and functional diversity indices reflect the variations of community structure and indicate their responses to environmental stress. In this study, based on four functional traits, including body length, feeding type, trophic group, and reproductive mode, the functional diversity and functional groups of crustacean zooplankton from the southern Yellow Sea (SYS) were explored over four seasons of 2019. A total of 53 species were identified and categorized into six functional groups. Copepods with ambush-feeding and omnivore–carnivore diet (Group Ⅱ) were dominant in spring (55.6%), while omnivore–herbivore copepods (Group Ⅰ) were the most abundant group in the other three seasons (>54.7%). The comparable distributions of functional diversity indices in different seasons were most likely due to hydrological variations. The Changjiang River Diluted Water promoted the coexistence of multiple traits carried by different functional groups (high functional richness (FRic) and functional dispersion (FDis)), but the stability of ecosystem function in this water mass was vulnerable to the loss of individual species (low functional evenness (FEve)) in summer. In winter, as a result of the Yellow Sea Warm Current, warm-water taxa increased FRic and FEve, suggesting that the community could buffer environmental fluctuations more effectively. Moreover, distribution of FRic values indicates the possible range and influence intensity of the Yellow Sea Cold Water Mass.

Effect of bottom counterweight and cable distribution on the hydrodynamic response of the gravity net cage

ABSTRACT To investigate the influence of the bottom counterweight and cable distribution on hydrodynamic response of the gravity net cage, a single cylindrical gravity net cage with different cable distributions and counterweights was analysed by numerical simulation. The floating collar was simplified as a hollow ring that has the same mechanical properties as one double-row floating pipe. The influence of the current, wave and cable distribution on the floating collar motions and cable loads were investigated. Analysis results illustrated that the volume reduction coefficient of net structure and the maximum tension of cable are mainly affected by the counterweight and cable distribution, respectively. In addition, the deformation of the floating collar is mainly affected by the wave height. The cylindrical gravity net cage with the 80 kg × 32 bottom counterweight and the ‘*’-layout cable distribution is fit for the sea state of the Yellow Sea Cold Water Mass.

Tight coupling between primary productivity, export production, and the growth of benthic scallops in the coastal region of the Okhotsk Sea along Hokkaido

AbstractScallop culture is conducted worldwide, nonfeeding and depending on the natural phytoplankton production for the diet. It is necessary for sustainable culture of this species to understand how the phytoplankton production and subsequent vertical transport to the bottom (export production) are regulated by environmental factors. A 3‐year time series monitoring of chlorophyll and temperature, as well as sinking particle flux, was conducted to elucidate the relationship between surface primary production, the subsequent export, and the growth of benthic cultured scallops in spring in the coastal region of the Okhotsk Sea along Hokkaido, Japan. Five times larger export fluxes were observed in 2013 than those in other years. Coscinodiscus spp., diameter >200 μm, was the quantitatively dominant phytoplankton in 2013. This species contributed to the high export flux due to a higher settling velocity. The sudden drops in temperature by >2°C were observed during the study period. These indicated that the supply of nutrients from Intermediate Cold Water (ICW), a cold and nutrients rich water mass, accelerated the primary productivity in this area. This intensity was strongest in 2013, contributing to the high export flux. The large export flux in 2013 provided a more sufficient food to the benthic cultured scallops, resulting in a two times higher growth of the scallops than in other years. This study demonstrated that the size of the dominant diatom species and the supply from ICW strongly influenced the export ratio and the growth of cultured scallops.

Holocene palaeoceanography of the Northeast Greenland shelf

Abstract. The Northeast Greenland shelf is highly sensitive to climate and ocean variability because it is swept by the East Greenland Current, which, through the western Fram Strait, forms the main pathway of export of sea ice and cold water masses from the Arctic Ocean into the North Atlantic Ocean. In order to reconstruct the variability of the East Greenland Current and general palaeoceanographic conditions in the area during the Holocene, we carried out benthic foraminiferal assemblage, stable isotope, and sedimentological analyses of a marine sediment core retrieved from the Northeast Greenland shelf (core DA17-NG-ST07-73G). The results reveal significant variations in the water masses and thus in the strength of the East Greenland Current over the last ca. 9.4 kyr. Between 9.4 and 8.2 ka the water column off Northeast Greenland was highly stratified, with cold, sea-ice-loaded surface waters and a strong influx of warm Atlantic Water in the subsurface. At ∼ 8.4 ka a short-lived peak in terrestrial elements may be linked to an influx of iceberg-transported sediments and thus to the so-called 8.2 ka event. Conditions similar to those of the Holocene Thermal Maximum prevailed from 8.2 to 6.2 ka, with a strong influence of the Return Atlantic Current and a weakened transport of Polar Water in the upper East Greenland Current. After 6.2 ka we recorded a return to a more stratified water column with sea-ice-loaded surface waters and still Atlantic-sourced subsurface waters. After 4.2 ka increased Polar Water at the surface of the East Greenland Current and a reduction in the Return Atlantic Water at subsurface levels signifies freshening and reduced stratification of the water column and (near) perennial sea-ice cover. The neoglaciation started at 3.2 ka at our location, characterized by a strengthened East Greenland Current. Cold subsurface-water conditions with possible sea-ice cover and minimum surface-water productivity persisted here throughout the last ∼ 3 kyr.

The Sandwich Structure of the Southern Yellow Sea Cold Water Mass and Yellow Sea Warm Current

The southern Yellow Sea Cold Water Mass (YSCWM) and the Yellow Sea Warm Current (YSWC) are prominent features in the southern Yellow Sea. The traditional viewpoint is that the southern YSCWM exists in the warm half of the year and the YSWC exists in the cold half of the year; the most existing studies have regarded these features as independent ocean phenomenon. Through marine investigations conducted in the recent years in the southern Yellow Sea, the southern YSCWM was found to exist in the early winter in 2010, and the YSWC was observed in the early summer in 2013, 2014. For approximately half the year, the southern YSCWM and YSWC existed simultaneously, and the YSWC was located in a slightly high-temperature region in the middle of the southern YSCWM. A sandwich-shaped temperature structure formed in the middle of the southern Yellow Sea from spring to autumn. This article studies the seasonal variation characteristics of the three-dimensional southern YSCWM and YSWC structures using ocean survey data collected in the recent years. The new perspective of the seasonal variations in the southern YSCWM and YSWC obtained herein will promote the recognition of southern Yellow Sea water exchanges and support biogeochemical cycle research in the Yellow Sea.

Seasonal variation in fish school spatial distribution and abundance under the Kuroshio regular pattern and the large meander in Suzu coastal waters

The Kuroshio Current can take two paths; usually it follows the regular pattern but occasionally it follows a pattern known as the large meander. In this study, we investigated the abundance of fish that migrate to coastal waters and the spatial distribution of fish schools under both Kuroshio patterns in Suzu district, Kochi prefecture, where the set net is the main fishery industry. We clarified the seasonal variation in the density and distribution of fish schools using a quantitative echo sounder. The effects of the Kuroshio large meander (LM) depended on the season. There was no effect of current pattern in summer or autumn, but in winter and spring the LM altered the marine environment and fish distributions. Cold water masses were formed in the survey area during winter and spring during the LM, and the water temperature dropped significantly compared with during the Kuroshio non-large meander (NLM). This altered the fish species and the distribution of fish schools in the survey area. The catches of Japanese horse mackerels (Trachurus japonicus) and Yellowtails (Seriola quinqueradiata) were much higher during the LM compared with those during the NLM. Unlike these two species, the small-sized pelagic fishes in spring has decreased significantly during the LM.

International megabenthic long-term monitoring of a changing arctic ecosystem: Baseline results

The sustainable development and environmental protection of the Arctic ecosystem is on the agenda globally. The Convention of Biological Diversity (CBD) and the UN Sustainable Development Goals call for conserving at least 10 per cent of coastal and marine areas globally. Management tools to achieve this goal include marine protected areas (MPAs) and “other effective area-based conservation measures” (OECMs) of structural megabenthic organisms (e.g. corals, sea pens, sponges, anemones, etc.). But large areas of the ocean are lacking information about seabed communities. Here we show that this data gap can potentially be filled by collecting data on megabenthic organisms that are “bycatch” (not the target species) on government research vessels monitoring commercial fish and shellfish. For this paper, several Arctic and sub-arctic nations contributed megabenthos data from a total of 12.569 fish assessment trawls and associated bottom water temperature data. The latter outline areas of warm sub-Arctic inflow versus colder Arctic waters, which we align with temperature affinities of community. We also found that maximum levels of shared taxa were higher between Atlantic and Eurasian Arctic Seas than with Pacific Arctic Seas. Areas of high standardized species richness generally, but not everywhere, coincided with areas of high standardized biomass and/or high current velocity and in transition zones between water masses. We did not find that standardized taxon richness declined with latitude (from 60 to 81°N) as has been previously hypothesized. High biomass was generally associated with Arctic outflow shelves and/ or (within-region) colder water masses. We identify areas with high proportions of sessile and upright taxa that may be susceptible to damage by bottom trawl gear, taxa with calcareous skeletons that may be susceptible to ocean acidification, and 'cold-water' taxa that may be most vulnerable to ocean warming. Our results demonstrate the feasibility and value of international collaboration and cooperation in understanding large-scale patterns of Arctic megabenthic communities and providing scientific advice for management of human activities in the global Arctic ecosystem.