Warm Water Mass Research Articles

Distribution, biomass, and species composition of salps and doliolids in the Oyashio–Kuroshio transitional region: potential impact of massive bloom on the pelagic food web

The Oyashio–Kuroshio Transitional Region (OKTR) is a nursery ground for pelagic fishes; thus, community succession of mesozooplankton is pivotal to understand prey availability, and it subsequently affects recruitment success. We investigated the surface distribution, biomass, and species composition of thaliaceans (salps and doliolids) that potentially have a significant impact on the food web and biogeochemical cycle by forming intensive blooms. A total of 11 thaliacean species were recorded from 62 locations along two transects at 36° N and 38.5° N extending from 142° E to 180° in May to June 1993. Salps and doliolids were found at 93% and 84% of the stations, respectively, and their biomass values varied widely in space (0.00011–79.56 and 0.00001–5.11 mg C m−3 for salps and doliolids, respectively). Thalia democratica was the most dominant salp and particularly abundant at stations east of 165°E on the 36°N-line; the abundance varied from 103 to 1379 ind m−3. Dolioletta gegenbauri and Doliolum denticulatum were dominant doliolids, although their biomass values were far lower than that of salps. Multivariate statistical analysis with PRIMER revealed that the distribution of thaliaceans in the OKTR was not uniform in space and was affected by oceanographic conditions; doliolids tended to occur in much warmer (14.10–15.63 °C) and saline water mass (34.54–34.72) than salps (13.16–14.95 °C and 34.40–34.53). In terms of population clearance rates, the most dense salp blooms have the potential to sweep > 200% of their resident water per day, indicating that salp blooms cause deleterious feeding conditions for pelagic fishes through non-selective filter feeding.

Structure and Seasonal Variation of the Indian Ocean Tropical Gyre Based on Surface Drifters

AbstractUsing the Gauss‐Markov decomposition method, this study investigates the mean structure and seasonal variation of the tropical gyre in the Indian Ocean based on the observations of surface drifters. In the climatological mean, the clockwise tropical gyre consists of the equatorial Wyrtki Jets (WJs), the South Equatorial Current (SEC), and the eastern and western boundary currents. This gyre system redistributes the water mass over the entire tropical Indian Ocean basin. Its variations are associated with the monsoon transitions, featuring a typical clockwise pattern in the boreal spring and fall seasons. The relative importance of the geostrophic and Ekman components of the surface currents as well as the role of eddy activity were further examined. It was found that the geostrophic component dominates the overall features of the tropical gyre, including the SEC meandering, the broad eastern boundary current, and the axes of the WJs in boreal spring and fall, whereas the Ekman component strengthens the intensity of the WJs and SEC. Eddies are active over the southeastern tropical Indian Ocean and transport a warm and fresh water mass westward, with direct impact on the southern branch of the tropical gyre. In particular, the trajectories of drifters reveal that during strong Indian Ocean Dipole or El Niño‐Southern Oscillation events, long‐lived eddies were able to reach the southwestern Indian Ocean with a moving speed close to that of the first baroclinic Rossby waves.

ОСНОВНЫЕ НАПРАВЛЕНИЯ И РЕЗУЛЬТАТЫ ИССЛЕДОВАНИЙ ЗООБЕНТОСА БАРЕНЦЕВА МОРЯ МУРМАНСКИМ МОРСКИМ БИОЛОГИЧЕСКИМ ИНСТИТУТОМ В 2015–2019 гг.

The results of five-year studies (2015–2019) of the laboratory of zoobenthos MMBI RAS on the impact of environmental factors, climate change and pollution on the species diversity, structure and abundance of bottom fauna in the Barents Sea were considered. The abundance and diversity of bottom communities and taxocenoses were higher in the most warm Atlantic water masses. The warming of the Arctic contributes to increased diversity of the Barents Sea benthos, increased biological invasion in the northern seas, and maintenance of diversity in the polluted ecosystem of the Kola Bay. The technology of biomonitoring of climate change using littoral populations of invertebrates is proposed.

The observed recent surface air temperature development across Svalbard and concurring footprints in local sea ice cover

AbstractThe Svalbard archipelago in the Arctic North Atlantic is experiencing rapid changes in the surface climate and sea ice distribution, with impacts for the coupled climate system and the local society. This study utilizes observational data of surface air temperature (SAT) from 1980–2016 across the whole Svalbard archipelago, and sea ice extent (SIE) from operational sea ice charts to conduct a systematic assessment of climatologies, long‐term changes and regional differences. The proximity to the warm water mass of the West Spitsbergen Current drives a markedly warmer climate in the western coastal regions compared to northern and eastern Svalbard. This imprints on the SIE climatology in southern and western Svalbard, where the annual maxima of 50–60% area ice coverage are substantially less than 80–90% in the northern and eastern fjords. Owing to winter‐amplified warming, the local climate is shifting towards more maritime conditions, and SIE reductions of between 5 and 20% per decade in particular regions are found, such that a number of fjords in the west have been virtually ice‐free in recent winters. The strongest decline comes along with SAT forcing and occurs over the most recent 1–2 decades in all regions; while in the 1980s and 1990s, enhanced northerly winds and sea ice drift can explain 30–50% of SIE variability around northern Svalbard, where they had correspondingly lead to a SIE increase. With an ongoing warming it is suggested that both the meteorological and cryospheric conditions in eastern Svalbard will become increasingly similar to what is already observed in the western fjords, namely suppressed typical Arctic climate conditions.

Diel quenching of Southern Ocean phytoplankton fluorescence is related to iron limitation

Abstract. Evaluation of photosynthetic competency in time and space is critical for better estimates and models of oceanic primary productivity. This is especially true for areas where the lack of iron (Fe) limits phytoplankton productivity, such as the Southern Ocean. Assessment of photosynthetic competency on large scales remains challenging, but phytoplankton chlorophyll a fluorescence (ChlF) is a signal that holds promise in this respect as it is affected by, and consequently provides information about, the photosynthetic efficiency of the organism. A second process affecting the ChlF signal is heat dissipation of absorbed light energy, referred to as non-photochemical quenching (NPQ). NPQ is triggered when excess energy is absorbed, i.e. when more light is absorbed than can be used directly for photosynthetic carbon fixation. The effect of NPQ on the ChlF signal complicates its interpretation in terms of photosynthetic efficiency, and therefore most approaches relating ChlF parameters to photosynthetic efficiency seek to minimize the influence of NPQ by working under conditions of sub-saturating irradiance. Here, we propose that NPQ itself holds potential as an easily acquired optical signal indicative of phytoplankton physiological state with respect to Fe limitation. We present data from a research voyage to the Subantarctic Zone south of Australia. Incubation experiments confirmed that resident phytoplankton were Fe-limited, as the maximum quantum yield of primary photochemistry, Fv∕Fm, measured with a fast repetition rate fluorometer (FRRf), increased significantly with Fe addition. The NPQ “capacity” of the phytoplankton also showed sensitivity to Fe addition, decreasing with increased Fe availability, confirming previous work. The fortuitous presence of a remnant warm-core eddy in the vicinity of the study area allowed comparison of fluorescence behaviour between two distinct water masses, with the colder water showing significantly lower Fv∕Fm than the warmer eddy waters, suggesting a difference in Fe limitation status between the two water masses. Again, NPQ capacity measured with the FRRf mirrored the behaviour observed in Fv∕Fm, decreasing as Fv∕Fm increased in the warmer water mass. We also analysed the diel quenching of underway fluorescence measured with a standard fluorometer, such as is frequently used to monitor ambient chlorophyll a concentrations, and found a significant difference in behaviour between the two water masses. This difference was quantified by defining an NPQ parameter akin to the Stern–Volmer parameterization of NPQ, exploiting the fluorescence quenching induced by diel fluctuations in incident irradiance. We propose that monitoring of this novel NPQ parameter may enable assessment of phytoplankton physiological status (related to Fe availability) based on measurements made with standard fluorometers, as ubiquitously used on moorings, ships, floats and gliders.

Observational Insight Into the Subsurface Anomalies of Marine Heatwaves

Marine heatwaves (MHWs) are extreme ocean warming events that can have devastating impacts, from biological mortalities to irreversible redistributions within the ocean ecosystem. MHWs are an added concern because they are expected to increase in frequency and duration. To date, our understanding of these extreme ocean temperature events is mainly limited to the surface layers, despite some of the consequences they are known to have on the deep marine environment. In this paper, using data from sea surface temperature (SST) and in situ observations from Argo floats, we investigate the anomalous water characteristics during MHWs down to 2000 m in the western Tasman Sea which is located off the east coast of Australia. Focusing on their vertical extensions, characteristics and potential drivers, we break MHWs down into three categories (1) shallow [0 – 150 m], (2) intermediate [150 – 800 m], and (3) deep events [> 800 m]. Only shallow events show a relationship between surface temperature anomalies and depth extent, in agreement with a likely surface origin in response to anomalous air-sea fluxes. By contrast, deep events have greater and deeper maximum temperature anomalies than their surface signal (mean of almost 3.4oC at 165 m depth) and are more frequent than expected (>45%), dominating MHWs in winter. They predominantly occur within warm core eddies, which are deep mesoscale anticyclonic structures carrying warm water-mass from the East Australian Current. This study highlights the importance of MHWs down to 2000 m and the influence of oceanographic circulation on their characteristics. Consequently, we recommend a complementary analysis of sea level anomalies and SST be conducted to improve the prediction of MHW characteristics and impacts, both physical and biological.

Effects of the 2013–2016 Northeast Pacific warm anomaly on physical and biogeochemical variables off northwestern Baja California, derived from a numerical NPZD ocean model

Interannual climatic anomalies have important physical and biological consequences for the southern part of the California Current System (CCS). Two examples of these anomalies are “The Blob” and El Niño phenomena. The Blob was an anomalously warm water mass that formed in the Gulf of Alaska during fall 2013 and then affected most of the eastern North Pacific, including the waters off Baja California, Mexico. In this work we use a biogeochemical nutrient-phytoplankton-zooplankton-detritus (NPZD) model coupled to a three-dimensional hydrodynamic model, which allowed the simulation of some of the physical and biological consequences of the anomalous warm 2013–2016 period (The Blob was observed in 2014 and El Niño by mid-2015). A model-observation comparison showed that in some cases the model solution deviates substantially from the observed vertical thermal structure, but the temporal evolution of the spatially-averaged variables diagnosed by the model shows good agreement with the observations, except for the period from late 2015 to mid-2016, when the sea surface temperature (SST) is underestimated and the model failed to reproduce the correct sign of the surface chlorophyll-a (sCHL) anomalies. An EOF analysis of the 15-year (2003–2017) record of monthly mean modeled variables allowed the identification of two main contributions to the model variability: one mode mostly correlated with the Multivariate El Niño-Southern Oscillation (ENSO) Index (MEI), explaining ~50% of the variance of temperature (T) and dissolved nitrogen (N) and ~10% of the variance of chlorophyll-a (CHL), and another mode mostly correlated with the Coastal Upwelling Index (CUI) anomaly, explaining ~50-70% of variance of CHL and only ~10-20% of variance of T and N. In the 2013–2016 period, an El Niño signal diagnosed by the MEI induced a remarkable warming off northwestern Baja California. As a consequence, the thermocline and the nutricline deepened during this period and caused a deepening and weakening of the subsurface CHL maximum (SCM). Around the southern region of the study area (near Punta Baja) these effects were more intense at the surface over the shelf, but in the northern region (south of Southern California Bight) the effects were more intense subsurface seaward of the shelf break. This ENSO-modulated subsurface warming tends to weaken the Southern California Eddy during El Niño events, and intensify it during La Niña episodes. During the 2013–2015 period there was also a weakening of the upwelling-favorable winds, which caused a prolonged negative anomaly of the wind forcing, reducing the nutrient flux and causing negative CHL anomalies. Finally, in addition to the partial relation between the ENSO and the warming observed along the Baja California coast, the anomalies were observed in this area 4–6 months before the onset of the El Niño conditions (MEI>0.5) period, when the Blob was affecting the southern part of the CCS.

Azimuthal, spatial, and temporal variability of acoustic intensity in along-the-shelf direction of Chukchi shelf from June to August 2017

Spatial, temporal, and azimuthal variability of sound propagation with simultaneously measured oceanography on the Chukchi shelf is reported. Broadband acoustic signals (0.7 to 1.1 kHz) were transmitted from a single sound source placed near the sound channel axis in 150 m water depth and received by two arrays about 32 km away at different angles forming two acoustic tracks. One was along the 120–150 m isobath and the other crossing 120 to 220 m isobath. The angle between the two acoustic paths was 30 deg. Sound emitted from the common source shows different behavior along each acoustic track. Concurrently detailed water column environmental parameters (i.e., salinity and temperature) were measured in the region in both “along” and “cross-shelf” directions. Emergence of a warm water masses during from late June to July caused a variable channel where transmissions showed markedly large intensity variations (∼20 dB). This presentation quantifies data analysis using correlation between acoustics and environmental signals. [Work supported by ONR 322OA.]Spatial, temporal, and azimuthal variability of sound propagation with simultaneously measured oceanography on the Chukchi shelf is reported. Broadband acoustic signals (0.7 to 1.1 kHz) were transmitted from a single sound source placed near the sound channel axis in 150 m water depth and received by two arrays about 32 km away at different angles forming two acoustic tracks. One was along the 120–150 m isobath and the other crossing 120 to 220 m isobath. The angle between the two acoustic paths was 30 deg. Sound emitted from the common source shows different behavior along each acoustic track. Concurrently detailed water column environmental parameters (i.e., salinity and temperature) were measured in the region in both “along” and “cross-shelf” directions. Emergence of a warm water masses during from late June to July caused a variable channel where transmissions showed markedly large intensity variations (∼20 dB). This presentation quantifies data analysis using correlation between acoustics and enviro...

Brief communication: A submarine wall protecting the Amundsen Sea intensifies melting of neighboring ice shelves

Abstract. Disintegration of ice shelves in the Amundsen Sea, in front of the West Antarctic Ice Sheet, has the potential to cause sea level rise by inducing an acceleration of ice discharge from upstream grounded ice. Moore et al. (2018) proposed that using a submarine wall to block the penetration of warm water into the subsurface cavities of these ice shelves could reduce this risk. We use a global sea ice–ocean model to show that a wall shielding the Amundsen Sea below 350 m depth successfully suppresses the inflow of warm water and reduces ice shelf melting. However, these warm water masses get redirected towards neighboring ice shelves, which reduces the net effectiveness of the wall. The ice loss is reduced by 10 %, integrated over the entire Antarctic continent.

ENSO impacts during west and east monsoon to the ocean current and water mass characteristics in the Makassar Strait

Ocean and atmospheric interactions are known by the presence of El-Nino Southern Oscillation (ENSO) in the Pacific Ocean, dipole mode in the Indian Ocean, and Indonesian-Throughflow (ITF). Those interactions have impacts to oceanographic conditions of Indonesian waters, especially Makassar Strait as main route of ITF which carries warm water masses to Indian Ocean due to the El-Nino and La-Nina as part of global scale oceanic belt. The purpose of this research is to understand the ENSO effect on spatio-temporal of current patterns and characteristics of water mass, namely temperature and salinity during west and east monsoon in the Makassar Strait. This study are using the ENSO index data from NOAA between year 2000-2015 and 1/4 degrees resolution of temperature, salinity, and currents monthly model from Copernicus Marine Environment and Monitoring System (CMEMS) with focus in February and August 2010 and 2015 to represents respectively for west and east monsoon period during the ENSO year. The results showed that surface currents were stronger during La-Nina with speeds of 0.8 to 1.2 m/s compared to El-Nino event with speeds of 0.6-0.7 m/s and it is higher in east monsoon. During west monsoon the current leads to the east and reversely the current pattern changes to the west during east monsoon. The temperature and salinity when La-Nina events are about 1°C higher and 0.7 psu lower than El-Nino events. Based on the results, in general that the impacts of El-Nino an La-Nina events to the Makassar Strait are clearly shown during east monsoon.

Copepod carcasses in the subtropical convergence zone of the Sargasso Sea: implications for microbial community composition, system respiration and carbon flux

Abstract The oligotrophic subtropical gyre covers a vast area of the Atlantic Ocean. Decades of time-series monitoring have generated detailed temporal information about zooplankton species and abundances at fixed locations within the gyre, but their live/dead status is often omitted, especially in the dynamic subtropical convergence zone (STCZ) where the water column stratification pattern can change considerably across the front as warm and cold water masses converge. We conducted a detailed survey in the North Atlantic STCZ and showed that over 85% of the copepods were typically concentrated in the upper 200 m. Copepod carcasses were present in all samples and their proportional numerical abundances increased with depth, reaching up to 91% at 300–400 m. Overall, 14–19% of the copepods within the upper 200 m were carcasses. Shipboard experiments showed that during carcass decomposition, microbial respiration increased, and the bacterial community associated with the carcasses diverged from that in the ambient water. Combining field and experimental data, we estimated that decomposing copepod carcasses constitute a negligible oxygen sink in the STCZ, but sinking carcasses may represent an overlooked portion of the passive carbon sinking flux and should be incorporated in future studies of carbon flux in this area.

Composition of Indonesia throughflow in North Sulawesi water masses and heat content

In this research the composition of water masses in the North Sulawesi (Sangihe Talaud) waters as part of the Indonesian Throughflow is investigated and analysed by using the Optimum Multi Parameter Analysis (OMP). The data used is the World Ocean Atlas data (WOA 13) in 1° x 1° latitude longitude resolution. Main data are the salinity, temperature and pressure. The Optimum Multiparameter analysis was used to calculate the percentage of each water mass contribution in the study waters. The contributions are 20-60% at 200-500 m depth for The North Pacific Intermediate Water (NPIW), 90-100%at around 0-100 meters depth for The North Pacific Subtropical Water (NPSW),100%at 900-1500 meters depth for the South Pacific Intermediate Water (SPIW)and 80-100% at 1100-1500 meters depth for TheAntartic Intermediate Water (AAIW). Surprisingly, the South Pacific Subtropical Water (SPSW) does not have any contribution and largest heat content comes from the AAIW. Magnitudes for each heat content of water types calculated in this study for NPIW, NPSW, AAIW, SPSW, and SPIW are in the range of 1.5 × 1014∼ 1.7 × 1014 J/m2, 2 × 1012∼ 9.9 × 1012 J/m2, 2.7 × 1014∼ 3.1 × 1014 J/m2, 0 ∼ 4.3 × 1011 J/m2, and 1.8 × 1014∼ 2 × 1014 J/m2, respectively. Eventhough the AAIW has the lowest temperature range but its large contribution in the waters outnumbers the warmer water masses.

Distribution of Deep-Sea Sponge Aggregations in an Area of Multisectoral Activities and Changing Oceanic Conditions

Discovery and understanding of fragile deep-sea habitats like sponge aggregations, are being outpaced by anthropogenic resource exploitation. Sustainable ocean development in the Faroe-Shetland Channel Nature Conservation Marine Protected Area (FSC NCMPA; northeast Atlantic), which harbours sponge aggregations, now requires adaptive management in the face of encroachment of multisectorial activities in this area (e.g. fishing, oil and gas, shipping) and climate change. We examined sponge morphotype composition, richness, diversity, density and body-size distribution inside and outside the FSC NCMPA, and the role of environmental variability and human impact in these sponge aggregations. Analyses were based on the examination of 465 high resolution images from 13 towed-camera transects. A catalogue for regional sponge morphotypes was also developed and applied for these analyses. Analysis revealed that morphotype composition did not differ between inside and outside the FSC NCMPA but richness, diversity and densities of massive/spherical/papillate and flabellate/caliculate sponges were higher inside than outside the boundary. The sponge aggregations occurred within a narrow zone between 450 and 530 m depth, within relatively warm and saline water masses. Furthermore, multiple size cohorts of sponges were recorded inside the FSC NCMPA, in contrast to the single cohort outside. Distance-based linear modelling showed that demersal fisheries, substratum, salinity and temperature explained a statistically-significant amount of variation (48%, p<0.001) of sponge density across the study area. Findings on density and size cohorts suggest that the FSC NCMPA boundary currently encloses the most vulnerable area, which also demonstrates normal ecosystem functions (e.g. recruitment). However, sponges were constrained to a narrow environmental niche shaped by fisheries and interactions of FSC NCMPA water masses with the slope that in turn likely determine, food supply to the sponge aggregations. Our study illustrated the vulnerability of the FSC NCMPA sponge aggregations to fisheries and changes to water mass properties over time. The morphotype catalogue and suite of indicators (i.e. density and body-size distribution) allow for baseline and future assessments of anthropogenic and climate change impacts on sponge aggregations’ environmental status in the FSC NCMPA, thus guiding management as sectoral encroachment continues in this area.

Campanian carbon isotope calibrated paleofertility estimates from northwestern Tunisia: Inferences from calcareous nannofossils

Abstract The δ13C calibrated Campanian (upper part of CC17/UC13 to CC23a/UC16 zones) calcareous nannofossil assemblages were analyzed to reconstruct paleofertility, paleoenvironment, and sea–level changes from the Jebil section, north–western Tunisia. Seven globally–recognized δ13C events are noted: three positive [Santonian–Campanian Boundary Event (SCBE); Early–Campanian Event (ECE); Mid–Campanian Event (MCaE)] and four negative excursions (Pillula Event; Conica Event; Late–Campanian Event (LCE); Epsilon Event or the C1– Event). The nannofossil assemblage is dominated by Watznaueria barnesae (28%), Lucianorhabdus cayeuxii (8%), Micula decussata (6%), Cyclagelosphaera reinhardtii (5%) and Micula concava (4%). In spite of the dominance of W. barnesiae (range: 33–46.5%), the signal given by the nannofossil assemblage is primary. All species–based proxies (the percentage abundances of stressed/opportunistic taxa, high and low fertility taxa, cool and warm watermass taxa, and Nannoconus spp.) along with the inferred Paleotemperature Index, suggests a cooling trend for the Campanian. Data suggests that oligotrophy was a greater influencing factor than paleotemperature, for the observed changes within the nannofossil assemblage. As a result of this extreme oligotrophy, a distinct assemblage is recorded that is marked by the absence of Biscutum, reduced % abundances of Prediscosphaera (0.7%), Retecapsa (2.3%), and Zeugrhabdotus (1.8%), but with the dominance of W. barnesiae.

Pliocene integrated chronostratigraphy from the Anno Formation, Awa Group, Boso Peninsula, central Japan, and its paleoceanographic implications

The Pliocene climate is one of the best analogs for the climate of a globally warmer future. Here, we present a new Pliocene integrated chronostratigraphy from the Anno Formation in the uppermost Awa Group, which is distributed throughout the Boso Peninsula, central Japan, based on paleomagnetic and benthic foraminiferal oxygen isotope records. This new chronostratigraphy provides valuable constraints for paleoceanographic and paleoclimatic studies in the northwestern Pacific Ocean, where the number of paleoceanographic records is limited due to the lack of calcareous microfossils from deep-sea sediment cores, with the exception of some plateaus at water depths above the calcite compensation depth (CCD). Paleomagnetic results indicate that the Anno Formation corresponds to the period extending from the Nunivak normal polarity subchronozone (4.493–4.631 Ma) to Chron C2An.2n (3.116–3.207 Ma), which is just above the Mammoth reversed polarity subchronozone. Although foraminifera are not found in the middle Anno Formation, our oxygen isotope records from the upper and lower Anno Formation demonstrate the recording of glacial–interglacial cycles. However, the amplitude of our δ18O profile is much larger than that of the LR04 stack, with similar to slightly lower glacial values and much lower interglacial values. This observation implies that the bottom water had lower δ18O values and/or a warmer water mass during interglacials compared with global average deep-water regions.

First-Order Estimates of Coastal Bathymetry in Ilulissat and Naajarsuit Fjords, Greenland, from Remotely Sensed Iceberg Observations.

Warm water masses circulating at depth off the coast of Greenland play an important role in controlling rates of mass loss from the Greenland Ice Sheet through feedbacks associated with the melting of marine glacier termini. The ability of these warm waters to reach glacier termini is strongly controlled by fjord bathymetry, which was unmapped for the majority of Greenland’s fjords until recently. In response to the need for bathymetric measurements in previously uncharted areas, we developed two companion methods to infer fjord bathymetry using icebergs as depth sounders. The main premise of our methods centers around the idea that deep-drafted icebergs will become stranded in shallow water such that estimates of iceberg surface elevation can be used to infer draft, and thus water depth, under the assumption of hydrostatic equilibrium. When and where available, surface elevations of icebergs stranded on bathymetric highs were extracted from digital elevation models (DEMs) and converted to estimates of iceberg draft. To expand the spatial coverage of our inferred water depths beyond the DEM footprints, we used the DEMs to construct characteristic depth–width ratios and then inferred depths from satellite imagery-derived iceberg widths. We tested and applied the methods in two fjord systems in western Greenland with partially constrained bathymetry, Ilulissat Isfjord and Naajarsuit Fjord, to demonstrate their utility for inferring bathymetry using remote sensing datasets. Our results show that while the uncertainties associated with the methods are high (up to ±93 m), they provide critical first-order constraints on fjord bathymetry.

Climatological oceanic-driven upwelling in the Western North Sumatera Waters using INDESO (2008-2014)

It is widely known that during upwelling feature, two different water-masses exchange simultaneously, on the one side surface warm-water mass sink downward and on the other side, deep cold-water-mass rise toward the surface which also bring demanded nutrients upward that may further locate areas of rich in marine productivity. Western North Sumatera Waters (WNSW) is considered as potential upwelling zones in Western and Northern Provinces of Sumatera. However, studies on upwelling as well as its physical mechanisms associated with ocean-atmosphere interaction that might govern the upwelling system in the region is yet to perform. A three-dimensional numerical model outputs are utilized in the present research to address the emergence of upwelling feature throughout the WNSW. The purpose of the research are to identify the thermal front associated with cyclonic and anti-cyclonic eddies.

High-Resolution Benthic Mg/Ca Temperature Record of the Intermediate Water in the Denmark Strait Across D-O Stadial-Interstadial Cycles.

Dansgaard‐Oeschger (D‐O) climate instabilities that took place during Marine Isotope Stage 3 are connected to changes in ocean circulation patterns and sea ice cover. Here we explore in detail the configuration of the water column of the Denmark Strait during D‐O events 8–5. How the ocean currents and water masses within the Denmark Strait region responded and were connected to the North Atlantic are discussed. We investigate sediment core GS15‐198‐36CC, from the northern side of the Greenland‐Iceland Ridge, at 30‐year temporal resolution. Stable carbon and oxygen isotope reconstructions based on benthic foraminifera, together with a high‐resolution benthic foraminiferal record of Mg/Ca paleothermometry, is presented. The site was bathed by warm intermediate waters during stadials and cool but gradually warming intermediate water during interstadials. We suggest that stadial conditions in the Denmark Strait are characterized by a well‐stratified water column with a warm intermediate water mass that lies beneath a cold fresh body of water where sea ice and brine rejection work in consort to uphold the halocline conditions. Interstadial periods are not a pure replicate of modern times, but rather have two modes of operation, one similar to today, and the other incorporating a brief period of warm intermediate water and increased ventilation.

Relationship between recruitment of Japanese sardine (Sardinops melanostictus) and environment of larval habitat in the low‐stock period (1995–2010)

AbstractStock level of Japanese sardine (Sardinops melanostictus) was high from 1980s to early 1990s and low from late 1990s to 2000s. The warm and cold water masses in the vicinity of the Kuroshio axis from winter to early spring used to be critical for the recruitment in the high‐stock period, because most of the larvae were distributed there. However, the environmental fluctuation might not affect the recruitment in the low‐stock period. Some studies reported that spawning location and spawning season, and hence the larval habitat, differ depending on the stock level. Three points were investigated in this study: (a) how spawning location and spawning season shifted from the late 1990s, (b) confirmation of the distribution area of larvae in the recent low‐stock period and (c) whether the water temperature in the vicinity of the Kuroshio axis was still related to the recruitment in the low‐stock period. The spawning location and spawning season clearly changed after 1995. Consequently, particle tracking experiments suggested that the larvae appeared in the vicinity of the Kuroshio axis from winter to early spring decreased. Nevertheless, only the ambient temperature of larvae that appeared in the vicinity of the Kuroshio axis from winter had a significant negative correlation with an index of the recruitment in the low‐stock period. It is suggested that the warm and cold masses in the vicinity of the Kuroshio axis are critical for the recruitment regardless of the stock level.

Parmales abundance and species composition in the waters surrounding Hokkaido, North Japan

The abundance and species composition of Parmales (Bolidophyceae), a siliceous marine phytoplankton, were investigated in the waters surrounding Hokkaido, North Japan. In the Pacific Ocean, high Parmales abundances were observed in the Oyashio region (84.9–95.2 cells mL−1), in the surrounding area of the cold Oyashio Current, and in the Coastal Oyashio Water (35.1–41.4 cells mL−1) being low temperature and salinity in spring. In the Okhotsk Sea, Parmales abundance was moderate (>5 cells mL−1) in the Intermediate Cold Water, which is formed by convective mixing under the pack ice. On the other hand, their abundance was quite low in warm water masses, such as the Tsushima Warm Current in the Sea of Japan and the Soya Warm Current in the Okhotsk Sea. Parmales cells were also found in the sea ice in the Notoro-ko Lagoon connected to the Okhotsk Sea, suggesting that they have an ice algal life cycle. Triparma spp. were almost dominant in the study areas with the occasional contribution of Tetraparma spp. in the Okhotsk Sea. These results indicate that Parmales abundance and species composition are significantly influenced by water currents.