Strait Sea Research Articles

Water Level Predictions at Both Entrances of a Sea Strait by Using Machine Learning

Water Level Predictions at Both Entrances of a Sea Strait by Using Machine Learning

Evaluation of Near-Taiwan Strait Sea Surface Wind Forecast Based on PanGu Weather Prediction Model

Evaluation of Near-Taiwan Strait Sea Surface Wind Forecast Based on PanGu Weather Prediction Model

ANALYSIS OF THE UTILIZATION OF THE HARBOR AREA AT THE PORT OF TANJUNG PERAK

Tanjung Perak Port is the initial gateway to Surabaya which handles more than 40% of international goods trade. In this case, the Kertosusilo Gate Area (GKS) has a very important position with its sea area having the busiest shipping lanes in Indonesia with 15,409 vessels operating at the end of 2021. The dense distribution of port activities in sea transportation creates complex problems which impact on delays in cargo delivery in Tanjung Perak Harbor. Problems that arise include sedimentation due to the construction of the Maspion Indonesia Port terminal, narrowing of sea water and changes in sea area which causes narrowing of the Madura Strait sea area, as well as complaints from port users regarding shipping lanes, anchoring areas in terms of depth, area, Vessel Traffic Services (VTS), services. ship guidance and security. Based on these problems, research was carried out on the utilization and needs of the anchorage area at Tanjung Perak Port. Starting with conducting research preparation, collecting data by compiling data related to the general picture of economic growth, especially in the East Java region as well as operational technicalities and conditions of the Tanjung Perak port. So that we can obtain the results of utilization research for a docking area capacity of 20,330 ships per year with a utility value of the docking area at Tanjung Perak Port of 73.5%.

West coast of Lake Baikal as a habitat for baikal seal Pusa sibirica in summer season

Using of the known rookeries on the western coast of Lake Baikal (including Olkhon Island and the isles in the Small Sea Strait) by baikal seal Pusa sibirica is assessed for modern conditions of anthropogenic pressure. All locations with geomorphological and lithological patterns suitable for rookeries are examined. For these purposes, the data from scientific literature were reviewed and the shores were researched visually with binoculars (from research boats) and from small UAVs, with particular attention to the historically known rookeries. Many new locations potentially suitable for haulouts and rookeries were found. However, the disturbance factor is significant for using these locations by seals — the most of known rookeries are visited sporadically by few seals in the short time between the floating ice disappearance and the beginning of the tourist high season. These rookeries were considered as «endangered» ones. When there is an urgent need (as in early summer 2020), seals come ashore in many locations, particularly on Olkhon Island, but don’t form new (not existed previously) rookeries. The threat of loss of the coast as a summer habitat for a significant part of the baikal seal population is possibly underestimated.

Effect of Internal Waves on the Hydrodynamics of a Mediterranean Sea Strait

In the present work, the effects of wind- and tide-induced internal waves in the Rio-Antirio Strait in western Greece were studied by using three-dimensional numerical simulations. For the wind-induced flow in the strait, it emerged that the internal waves’ initiation is associated with the direction of the wind. Tidal action, with or without the combined action of wind, also generates internal waves in the strait, with amplitudes higher than 20 m. The action of the internal waves causes a subsurface inflow of colder waters from the Gulf of Corinth to the Gulf of Patras, as has been also simulated for the case of the wind-induced flow, generating strong hypolimnetic currents. The exchange flowrate between the Gulf of Patras and the Gulf of Corinth appeared to undergo significant modification for the wind-induced flow and had little effect for the pure tidal flow (in windless conditions) due to the development and action of the internal waves at the strait. The combined action of the tide and the wind was found to marginally affect the exchange flowrate between the two gulfs compared to the pure tidal flow. The interaction between the Coriolis effect and internal waves, at least away from the strait, forms a characteristic horizontal structure of flow. The structure of turbulence in the near strait area under the action of internal waves generated by the wind and/or tide was also discussed and compared with the corresponding barotropic flow.

Ships Detection on Aerial Imagery using Transfer Learning and Selective Search

The traffic in the water area such as harbor and sea strait is highly important to be monitored because it helps to minimize unwanted ships accident. As a result, we proposed an automatic detection method to localize ships contained in sattelite image. We examine several deep learning method as the classification backbone, namely MobileNetV2, DenseNet121, VGG16, and ResNet50. Afterwards, we employed the trained model for detecting the ships. To make the detection faster, inspite of using a sliding window, we use selective search to sample the object candidates from the given scene. The experiments was done using Shipsnet dataset and tested on aerial images. We also conducted a cross domain evaluation where the images were taken using Google Earth. The results indicate that MobileNetV2 has the best performance on classification and detection tasks. The MobileNetV2 is also able to detect the ships on cross-domain scenarios.

Impact of the Nares Strait sea ice arches on the long-term stability of the Petermann Glacier ice shelf

Abstract. One of the last remaining floating tongues of the Greenland ice sheet (GrIS), the Petermann Glacier ice shelf (PGIS), is seasonally shielded from warm Atlantic water (AW) by the formation of sea ice arches in the Nares Strait. However, continued decline of the Arctic sea ice extent and thickness suggests that arch formation is likely to become anomalous, necessitating an investigation into the response of PGIS to a year-round mobile and thin sea ice cover. We use a high-resolution unstructured grid 3-D ocean–sea ice–ice shelf setup, featuring an improved sub-ice-shelf bathymetry and a realistic PGIS geometry, to investigate in unprecedented detail the implications of transitions in the Nares Strait sea ice regime, that is, from a thick and landfast sea ice regime to a mobile, and further, a thin and mobile sea ice regime, with regard to PGIS basal melt. In all three sea ice regimes, basal melt near the grounding line (GL) presents a seasonal increase during summer, driven by a higher thermal driving. The stronger melt overturning increases the friction velocity slightly downstream, where enhanced friction-driven turbulent mixing further increases the thermal driving, substantially increasing the local melt. As the sea ice cover becomes mobile and thin, wind and (additionally in winter) convectively upwelled AW from the Nares Strait enter the PGIS cavity. While its effect on basal melting is largely limited to the shallower (<200 m) drafts during winter, in summer it extends to the GL (ca. 600 m) depth. In the absence of an increase in thermal driving, increased melting under the deeper (>200 m) drafts in winter is solely driven by the increased vertical shear of a more energetic boundary layer current. A similar behaviour is noted when transitioning from a mobile to a thin mobile sea ice cover in summer, when increases in thermal driving are negligible and increases in melt are congruent with increases in friction velocity. These results suggest that the projected continuation of the warming of the Arctic Ocean until the end of the 21st century and the accompanying decline in the Arctic sea ice extent and thickness will amplify the basal melt of PGIS, impacting the long-term stability of the Petermann Glacier and its contribution to the future GrIS mass loss and sea level rise.

Climate variable relate biological respond of tropical fish: A review from small scale fisheries in Sunda Strait

The issue of climate change is currently one of the crucial issues in fisheries management to ensure potential threats and their sustainability. Various approaches have been made, one of which is by looking at the influence of the population biology parameters such as the percentage of gonad maturity, the change from the length at first maturity (Lm50), and the first length of the first capture (Lc50)and growth rate (k). The research conducted from the Sunda Strait sea collected data from 2011, 2015, 2016, 2018, and 2019. The fish species whose biological data were analyzed were turmeric, kurisi and swanggi fish. The analysis performed was the size when 50 percent reached gonad maturity (Lm50), and the size of 50 percent of the fish caught (Lc50), the percentage of fish at the gonad maturity stage (TKG3-4). Annual trend analysis and linear regression determine the relationship between year temperature parameters and Lm, Lc, and the percentage of fish to be fully cooked gonads. The analysis results showed a fluctuation of Lm50, Lc50 in both male and female kurisi, kuniran and swanggi. However, there was no significant correlation between temperature and these parameters. These results indicate that the dynamics of Lm and Lm do not follow the trend of temperature changes. It is assumed that the effect of changes in Lm, Lc is more influenced by the intensity of the catch than the temperature in Sunda Strait.

Plankton communities of the “Pregolya River – Vistula Lagoon – Kaliningrad Sea Channel (KSC) – Baltic Sea system”

The species composition, abundance and biomass, trophic relationships of phytoplankton and zooplankton, as well as the proportion of dead individuals in zooplankton were studied in the water system "Pregolya River – Kaliningrad Sea Channel (KSC) – Vistula Lagoon – Baltic Sea" in July, August and October 2021. In total 173 taxa of phytoplankton and 73 taxa of zooplankton were found during period of investigation. The maximal species diversity was observed in the summer period, in autumn it was decreasing. The maximum number of taxa for both phyto- and zooplankton was found in the Vistula Lagoon and in the KSC, the minimum – in the Baltic Sea. In summer the 3 communities in phytoplankton, 4 in zooplankton, in autumn – 3 communities in both phyto- and zooplankton were found. The plankton communities were confined to water areas with different salinity: The Pregolya River, the KSC and the Vistula Lagoon, the Baltic Sea. The dominant complex of species at the stations differed; species of a predominantly freshwater complex were noted in the Pregolya River, brackish-water species were found in the Vistula Lagoon, and a marine complex of species was identified at the stations of the sea strait and in the Baltic Sea. More abundant plankton communities both in summer and autumn were in the KSC and the Vistula Lagoon (phytoplankton biomass varied from 1.19 g/m3 to 11.89 g/m3; zooplankton biomass varied from 305 mg/m3 to 1801 mg/m3). In this area the most optimal conditions for the development of plankton were formed such as an increased nutrient content and maximum water heating. Plankton communities both in the Pregolya River and in the Baltic Sea in summer and autumn were less abundant (phytoplankton biomass varied from 0.16 g/m3 to 2.50 g/m3; zooplankton biomass varied from 34 mg/m3 to 468 mg/m3). The most intense trophic relationships in the plankton community in the summer in the Baltic Sea, optimal – in the KSC and in the Vistula Lagoon were formed. The proportion of dead individuals in the zooplankton of the studied system in both seasons was maximal in the areas, which had the critical salinity for hydrobionts and high turbulence conditions such as KSC, the Sea strait and at the exit from Sea strait.

Northern Richness, Southern Dead End-Origin and Dispersal Events of Pseudolycoriella (Sciaridae, Diptera) between New Zealand's Main Islands.

Sciaridae (Diptera) is a widespread insect family of which some species can reach high abundances in arboreal habitats. This trait, together with their (passive) mobility, enables them to quickly colonise suitable habitats. To reveal the biogeographic history of the New Zealand members of the sciarid genus Pseudolycoriella, we analysed three molecular markers of selected species and populations in a Bayesian approach. At the intra- and interspecific levels, we detected a pattern of northern richness vs. southern purity, which has probably developed as a result of Pleistocene glacial cycles. Since the late Miocene, we identified 13 dispersal events across the sea strait separating New Zealand's main islands. As nine of these dispersal events were south-directed, North Island can be considered the centre of radiation for this genus. An unequivocal re-colonisation of North Island was only observed once. Based on the inclusion of three undescribed species from Tasmania and on previously published data, three colonisations of New Zealand are likely, all of them assumed to be of Australian origin. One of these most probably took place during the late Miocene, and the other two during the late Pliocene or at the Pliocene-Pleistocene boundary.

Mesoscale weather systems and associated potential wind power variations in a mid-latitude sea strait (Kattegat)

Mesoscale weather systems and associated potential wind power variations in a mid-latitude sea strait (Kattegat)

Using Hydraulic Theory to Monitor Dense Overflows in a Parabolic Channel

Abstract Deep ocean passages are advantageous sites for long-term monitoring of deep transport and other physical properties relevant to climate. Rotating hydraulic theory provides potential for simplifying monitoring strategy by reducing the number of quantities that need to be measured. However, the applicability of these theories has been limited by idealizations such as restriction to zero or uniform potential vorticity (pv) and to channels with rectangular cross sections. Here the relationship between the flow characteristics in a canonical sea strait and its upstream condition is studied using uniform pv rotating hydraulic theory and a reduced-gravity shallow-water numerical model that allows for variation in pv. The paper is focused mainly on the sensitivity of the hydraulic solution to the strait geometry. We study the dynamics of channels with continuously varying (parabolic) cross sections to account for the rounded nature of sea-strait topographies and potentially improve monitoring strategies for realistic channel geometries. The results show that far enough from the channel entrance, the hydraulically controlled flow in the strait is insensitive to the basin circulation regardless of parabolic curvature. The controlled transport relation is derived for the case of uniform pv theory. Comparing the model to theory, we find that the measurement of the wetted edges of the interface height at the critical section can be used to estimate the volume flux. Based on this finding, we suggest three monitoring strategies for transport estimation and compare the estimates with the observed values at the Faroe Bank Channel. The results showed that the estimated transports are within the range of observed values. Significance Statement The paper investigates the relationship between the flow characteristics in an idealized sea strait and its upstream condition using rotating hydraulic theory and numerical modeling. We study the dynamics of channels with continuously varying (parabolic) cross sections to account for the rounded nature of sea-strait topographies and potentially improve monitoring strategies for realistic channel geometries. We suggest three monitoring strategies for transport estimation and apply the methods to the Faroe Bank Channel. Our estimates of dense water transport are within the range of observed values. This is significant, because the suggested monitoring strategies only require 1–3 measurements to estimate the transport at a given passage and can be used to guide observing systems.

The evolution of the Fram Strait sea ice volume export decomposed by age: estimating with parameter-optimized sea ice-ocean model outputs

Sea ice export through the Fram Strait is crucial in the dynamic evolution of Arctic sea ice and can further modulate Arctic sea ice mass balance as well as the ocean thermohaline circulation. In this study, based on outputs from a parameter-optimized and fully physical ocean–sea ice coupled model and sea ice age observation, we estimate sea ice volume (SIV) flux and its age evolution via the Fram Strait. The estimate of mean annual SIV flux is about 1605 315 km3 yr−1 without a significant trend for 1979–2021. Combining with sea ice age data, the variation of the sea ice age and its corresponding SIV flux are obtained for 1984–2020. The SIV flux of 1st-year ice significantly increases as expected, but it still contributes very little to the total flux in the 2010s with a proportion of 3.5%. SIV fluxes of different ages in multi-year ice present diverse variations. The proportions of 2nd-year ice and 3rd-year ice in the annual SIV flux show an extreme increase from 6.8% and 25.0% in the 1980s to 49.0% and 38.8% in the 2010s, respectively, while the proportions of 4th-year ice and 5th-year and older (5+ year) ice significantly decrease from 22.8% and 45.0% in the 1980s to 7.1% and 1.6% in the 2010s, respectively. Meanwhile, the prevailing age of annual volume export via Fram Strait shifts from 4th-year and 5+ year ice to 2nd-year and 3rd-year ice around 2007/2008. It is worth noticing that the variation in Fram Strait ice export modulates the variation in Arctic SIV prior to 2008, but the reverse is true after 2008, indicating a decreasing influence of Fram Strait SIV export on Artic SIV variability with decreasing sea ice age. The results are beneficial to promote the understanding of the evolution of Fram Strait SIV export under the warming Arctic.

A Review of Arctic–Subarctic Ocean Linkages: Past Changes, Mechanisms, and Future Projections

Arctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic–Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean during the 2010s. Specifically, the Pacific inflow temperature in the Bering Strait and Atlantic inflow temperature in the Fram Strait hit record highs, while the Pacific inflow salinity in the Bering Strait and Arctic outflow salinity in the Davis and Fram straits hit record lows. Both the ocean heat convergence from lower latitudes to the Arctic and the hydrological cycle connecting the Arctic with Subarctic seas were stronger in 2000–2020 than in 1980–2000. CMIP6 models project a continuing increase in poleward ocean heat convergence in the 21st century, mainly due to warming of inflow waters. They also predict an increase in freshwater input to the Arctic Ocean, with the largest increase in freshwater export expected to occur in the Fram Strait due to both increased ocean volume export and decreased salinity. Fram Strait sea ice volume export hit a record low in the 2010s and is projected to continue to decrease along with Arctic sea ice decline. We quantitatively attribute the variability of the volume, heat, and freshwater transports in the Arctic gateways to forcing within and outside the Arctic based on dedicated numerical simulations and emphasize the importance of both origins in driving the variability.

Coastal State Responsibility and Rights in Regard to Fisheries Resources in EEZ

Decreasing number of fishery resources impacted by unsustainable fisheries management, climate issues, and the sovereignty system at sea have made fishery conflicts a growing security concern, such as the conflict between Indonesia and Vietnam over the Natura Sea. This dispute is exacerbated by China's militarization efforts, as the fishing industry recognizes its ability to influence the maritime sphere around it. Other Southeast Asian coastal states, such as the Malacca Strait and the Natuna Sea, border Indonesia's EEZ, making it vulnerable to disputes. And if there is a violation of laws and regulations in the territorial sea, the coastal state can apply its criminal law to the violators if the violation has a negative impact on the coastal state or interferes with security. This EEZ regime was established to regulate long-standing disputes over maritime territory and unilateral claims, such as the dispute between Indonesia and Malaysia over the Malacca Strait Sea, which was successfully resolved. As a result, the coastal state has jurisdictional rights to make arrests, as specified in Article 73 concerning the enforcement of the coastal state's laws and regulations.

87Sr/86Sr of Lake Baikal: Evidence for rapid homogenization of water

We provide an extended 87Sr/86Sr database for the water of Lake Baikal collected along the lake and within its bays at a depth range from the surface down to 1366 m, the major tributary rivers, lake animals, and atmospheric precipitation. The water of open Lake Baikal, the Little Sea (Maloe More) Strait, and large bays are characterized by a uniform 87Sr/86Sr = 0.7086266 ± 0.0000045 (n = 44, uncertainty at 95% confidence interval). Major volumetric contributors of water to the lake (the eastern rivers and precipitation) are only slightly different from the lake value in terms of 87Sr/86Sr. In the western rivers, 87Sr/86Sr is much higher, but due to their small incoming volume, their contribution is rapidly diluted by the water currents of the lake. The exception is water with high 87Sr/86Sr from isolated Mukhor Bay at the inland end of the Little Sea Strait and water above the underwater discharge of hydrothermal springs. Benthic and pelagic Lake Baikal animals have 87Sr/86Sr similar to the values of the open lake, supporting lake water homogenization. The modelled budget of Sr suggests that 86 ± 14% of input Sr is stored in the waters of Lake Baikal. In other words, according to the estimations some Sr (from 0 to 28%) may be precipitated at the lake bottom by chemical and biochemical processes.

Flow structures and circulation due to meandering geometry in a stratified sea strait

Combining with local topography (i.e., the presence of a bar or a sill on the bottom and the shape of the coastline), the meandering geometry of straits, which have more complex geomorphological formations compared to rivers, reveals different circulation patterns in the coastal region and central part of the strait. Identifying circulation patterns in meanders is crucial to managing those waterways in several aspects (i.e. monitoring the transport of contamination, wastewater outfall, etc.). In the present study, the flow circulations in some meanders of a strait (the Bosphorus), which presents a two-layered flow, are analyzed using the calibrated 3D model. Each of the four selected meanders has a unique shape: 1) expansion on both sides, 2) expansion on one side, 3) with a constant width, and 4) an estuary connected from one side.The results showed the decisive role of some characteristic morphological formations (i.e. headland, bars on the bottom, the shape of coastline) in creating reversing flow in a meander rather than adverse along channel pressure gradient due to the sudden expansion. While extreme water level differences between both entrances of the strait reveal unidirectional flow in the main channel, the reversals may develop in the shallowness of the meanders depending on the coastline shape (e.g. smoothness), presence of a local bar, and the presence of a headland. Besides this, in the case of a meander that has expansion at both sides, the flow separates from the main channel and circulates in opposite direction either clockwise or counterclockwise in the expanded sections. The annual flow profiles show a notable difference between the main channel and the coastal part of the meanders for a significant amount of time. For the low composite Froude numbers (G2) around or less than 0.3, the main channel flow is two-layered with the upper layer flowing south and the lower layer flowing north. In the shallowness of the expansions, however, it is unidirectional. For higher G2s (> 0.6), however, it is unidirectional both in the main channel and in the expansions of the meanders.

From the sea strait to the meromictic lake: Evolution and ecosystem of a water body at the Fiard Coast (Lake Kislo-Sladkoe at the Karelian Coast of the Kandalaksha Bay, the White Sea, Russia)

Fiard coasts are common on the periphery of the areas previously covered by ice sheets. The conditions in such areas are favorable for separation of bays and straits from the sea. As a result of the glacial isostatic adjustment of the area the fiards would be transformed into coastal lakes. To discover the regularities of evolution of such water bodies, we studied topography, sea and lake sediments, hydrology and diatom associations of meromictic Lake Kislo-Sladkoe at the Karelian Coast of the Kandalaksha Bay, the White Sea, Russia (66°32′54″N, 33°08′05″E). Detailed geomorphological, geodetic, bathymetric, and aerial imagery field works have been completed on the coastal area. We built a Digital Elevation Model (DEM) of the coast and seabed. Radioisotope dating (210Pb, 14С), grain size distribution, loss on ignition, Corg/Norg ratio and diatom analysis have been completed for the entire 1.5-m sequence of the Lake's sediments. Currently, the Lake Kislo-Sladkoe communicates with the sea through a rising sill. We have established that the water body is meromictic due to its upper water layer being of variable salinity, middle layer comprising of aerated salty water, and the near-bottom water layer being anaerobic. However, several-year-long periods of water stratification alternate there with occasional late-autumn or early-winter flushes. The water body evolution falls into four stages: (1) a strait with an active hydrodynamic environment (prior to 1500–1560s), (2) a strait with a variable hydrodynamic environment (1500–1560s to 1850–1890s), (3) a semi-isolated lagoon with a quiet hydrodynamic environment (1850–1890s to early 1950s), and (4) a meromictic lake at an early stage of separation from the sea (early 1950s to present). We show how coastal processes on fiard coasts change the mode and duration of isolation of coastal water bodies from the sea. Based on the assessment of the rate of the post-glacial rebound and hydrological conditions of the coastal area we propose an approach to estimating the duration of transitional phase between a marine bay or strait and freshwater lake, including its meromictic stage. We predict that the meromictic stage of the lake will be completed no earlier than c. 100–200 years after the sill rises above the tidal zone.

Channel, dune and sand sheet architectures of a strait-adjacent delta, Rifian Corridor, Morocco

Abstract Sea straits are elongated zones where geographical constriction can amplify marine currents. Sediment deposits that formed in sea straits are relatively well studied and robust models of tidal strait depositional systems have been developed. However, models of strait-adjacent systems remain uncommon. In this study, we present such a model which is based on detailed outcrop descriptions of Miocene deposits that formed adjacent to the Rifian Corridor, an ancient sea strait that existed in what is now northern Morocco. The kilometre-scale outcrops at the Ben Allou locality (30 km north of Fez, Morocco) contain a succession of claystones, siltstones and sandstones that formed under a sea strait-adjacent process regime characterized by marine current constriction, tidal amplification and reduced wave activity. Detailed descriptions of the sandstone's sedimentary architectures reflect a development from mud drape-bearing sand sheets in the proximal regions of the system to stacked cross-strata and channel forms nearer to the basin depocentre. In the deep, distal reaches of this system, sediment grain sizes are generally fine (silt and clay) and are sparsely interbedded with sandy turbidites. These results confirm existing models which show that proximal strait-adjacent deposits tend to be tide dominated, and wave and fluvial influence can be overprinted by tidal processes. Some insights into the formation of tidal dunes are discussed. For example, it is shown that compound tidal dunes may not be preserved differently than simple tidal dunes, which is relevant for predicting sedimentary architectures and fluid flow properties of ancient tide-dominated successions.

Potential Effect of the Intrusion of the Kuroshio Current into the South China Sea on Catches of Japanese Eel (Anguilla Japonica) in the South China Sea and Taiwan Strait

This study examined the effect of the intrusion of the Kuroshio Current (KC) into the South China Sea (SCS) and the Taiwan Strait (TS) (SCS–TS region) on changes in catches of larval A. japonica in the traditional fishing ground waters of Gaoping near southwestern Taiwan in the SCS–TS region. First, the oceanic environment and recruitment trends from 1967 to 2019 were investigated based on secondary data. Then, field surveys were conducted to obtain primary data regarding the intrusion of the KC into the SCS, as well as the changes in the fishing sites and catches of A. japonica in the fall and winter of 2014–2015. Hence, the association between oceanic conditions and the number of A. japonica migrating into the SCS–TS region was explored. From 1967 to 2019, the recruitment proportion in the fishing grounds that formed due to the Kuroshio Branch Current (PKSBC) fluctuated significantly. Overall, positive values were observed for the Oceanic Niño Index for each year with a PKSBC > 50%, corresponding to El Niño conditions. In each year with a PKSBC > 70%, a looping path and a warm–core eddy appeared.