scholarly journals Phytoplankton Increase Along the Kuroshio Due to the Large Meander

2021 ◽  
Vol 8 ◽  
Author(s):  
Daniel Andres Lizarbe Barreto ◽  
Ricardo Chevarria Saravia ◽  
Takeyoshi Nagai ◽  
Takafumi Hirata
Keyword(s):  
Chlorophyll A ◽  
Mixed Layer Depth ◽  
Local Environment ◽  
Trophic Levels ◽  
Large Meander ◽  
The Mean ◽  
Western Side ◽  
The Kuroshio ◽  
Cold Core ◽  
Kuroshio Region

The Kuroshio Large Meander (LM) is known to be highly aperiodic and can last from 1 to 10 years. Since a stationary cold core formed between the Kuroshio and the southern coast of Japan off Enshu-Nada and approaching warm saltier water on the eastern side of the LM changes the local environment drastically, many commercially valuable fish species distribute differently from the non-LM period, impacting local fisheries. Despite this importance of the LM, the influences of the LM on the low trophic levels such as phytoplankton and zooplankton have still been unclear. In this study, satellite daily sea surface chlorophyll data are analyzed in relation to the LM. The results show positive anomalies of the chlorophyll-a concentration along the Kuroshio path during the LM periods, 2004–2005 and 2017–2019, from the upstream off Shikoku to the downstream (140°E). These positive anomalies are started by the triggering meander generated off south of Kyushu, which then slowly propagates to the downstream LM region in both the LM periods. Even though the detailed patterns along the Kuroshio region in the two LM periods were different, similar formations of the positive anomalies on the western side of the LM with shallower mixed layer depth are observed. Furthermore, we found clear relationships between the minimum distance from several stations along the coast to the Kuroshio axis and the mean chlorophyll-a anomaly, with significant correlations with the distance from different stations.

scholarly journals An Objective Method for Probabilistic Forecasting of Multimodal Kuroshio States using Ensemble Simulation and Machine Learning

2020 ◽  
Vol 50 (11) ◽  
pp. 3189-3204
Author(s):  
Kunihiro Aoki ◽  
Yasumasa Miyazawa ◽  
Tsutomu Hihara ◽  
Toru Miyama
Keyword(s):  
Machine Learning ◽  
Baroclinic Instability ◽  
Mixture Distribution ◽  
Gaussian Mixture ◽  
Distribution Model ◽  
Probabilistic Forecasting ◽  
Large Meander ◽  
Mixture Distribution Model ◽  
The Kuroshio ◽  
Kuroshio Region

AbstractThis paper presents a method for detecting the ensemble means, spreads, and occurrence probabilities for each of the multiple Kuroshio states. This is accomplished by classifying the forecasts of the ensemble members with a Gaussian mixture distribution model, a machine learning method. Ensemble simulations with 80 members are conducted to reproduce possible occurrences of the multiple Kuroshio states, targeting the large meander event in 2017. To test its performance, first, the method is applied for the southernmost latitude, a conventional index that represents meander intensity. The results show that the Kuroshio initially taking the nearshore nonlarge meander state bifurcates into the large meander and offshore nonlarge meander states, which occur with similar probabilities. Both developments are accompanied by positive potential energy extraction rates, consistent with baroclinic instability. As a more objective approach, the method is then applied for the dominant modes derived from empirical orthogonal function (EOF) analysis of the sea surface height field in the entire Kuroshio region. Importantly, almost identical results can be achieved. In particular, the bimodality between the large meander and nonlarge meander is shown to appear on the axis of the first EOF mode. From a mathematical perspective, this mode can be interpreted as the singular vector which grows most rapidly following the time-evolution operator. Finally, the multimodality of the Kuroshio is reinterpreted as a phase transition phenomenon where the nearshore nonlarge meander constitutes the basic state.

scholarly journals Subtropical Mode Water Variability in a Climatologically Forced Model in the Northwestern Pacific Ocean

2012 ◽  
Vol 42 (1) ◽  
pp. 126-140 ◽  
Author(s):  
Elizabeth M. Douglass ◽  
Steven R. Jayne ◽  
Synte Peacock ◽  
Frank O. Bryan ◽  
Mathew E. Maltrud
Keyword(s):  
Pacific Ocean ◽  
Mixed Layer Depth ◽  
Northwestern Pacific ◽  
Northwestern Pacific Ocean ◽  
Large Meander ◽  
The West ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
South Of Japan ◽  
The Kuroshio

Abstract A climatologically forced high-resolution model is used to examine variability of subtropical mode water (STMW) in the northwestern Pacific Ocean. Despite the use of annually repeating atmospheric forcing, significant interannual to decadal variability is evident in the volume, temperature, and age of STMW formed in the region. This long time-scale variability is intrinsic to the ocean. The formation and characteristics of STMW are comparable to those observed in nature. STMW is found to be cooler, denser, and shallower in the east than in the west, but time variations in these properties are generally correlated across the full water mass. Formation is found to occur south of the Kuroshio Extension, and after formation STMW is advected westward, as shown by the transport streamfunction. The ideal age and chlorofluorocarbon tracers are used to analyze the life cycle of STMW. Over the full model run, the average age of STMW is found to be 4.1 yr, but there is strong geographical variation in this, from an average age of 3.0 yr in the east to 4.9 yr in the west. This is further evidence that STMW is formed in the east and travels to the west. This is qualitatively confirmed through simulated dye experiments known as transit-time distributions. Changes in STMW formation are correlated with a large meander in the path of the Kuroshio south of Japan. In the model, the large meander inhibits STMW formation just south of Japan, but the export of water with low potential vorticity leads to formation of STMW in the east and an overall increase in volume. This is correlated with an increase in the outcrop area of STMW. Mixed layer depth, on the other hand, is found to be uncorrelated with the volume of STMW.

scholarly journals New Perspectives on the Generation and Maintenance of the Kuroshio Large Meander

2019 ◽  
Vol 49 (8) ◽  
pp. 2095-2113 ◽  
Author(s):  
Yang Yang ◽  
X. San Liang
Keyword(s):  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Low Frequency ◽  
Analysis Tool ◽  
Mean Flow ◽  
Large Meander ◽  
Kuroshio Large Meander ◽  
The Mean ◽  
The Kuroshio ◽  
Canonical Transfer

AbstractThe internal dynamical processes underlying the Kuroshio large meander are investigated using a recently developed analysis tool, multiscale window transform (MWT), and the MWT-based canonical transfer theory. Oceanic fields are reconstructed on a low-frequency mean flow window, a mesoscale eddy window, and a high-frequency synoptic window with reference to the three typical path states south of Japan, that is, the typical large meander (tLM), nearshore non-large meander (nNLM), and offshore non-large meander (oNLM) path states. The interactions between the scale windows are quantitatively evaluated in terms of canonical transfer, which bears a Lie bracket form and conserves energy in the space of scale. In general, baroclinic (barotropic) instability is strengthened (weakened) during the tLM state. For the first time we found a spatially coherent inverse cascade of kinetic energy (KE) from the synoptic eddies to the slowly varying mean flow; it occupies the whole large meander region but exists only in the tLM state. By the time-varying multiscale energetics, a typical large meander is preceded by a strong influx of mesoscale eddy energy from upstream with a cyclonic eddy, which subsequently triggers a strong inverse KE cascade from the mesoscale window to the mean flow window to build up the KE reservoir for the meander. Synoptic frontal eddies are episodically intensified due to the baroclinic instability of the meander, but they immediately feed back to the mean flow window through inverse KE cascade. These results highlight the important role played by inverse KE cascades in generating and maintaining the Kuroshio large meander.

scholarly journals Mixed layer depth and chlorophyll a: Profiling float observations in the Kuroshio–Oyashio Extension region

2015 ◽  
Vol 151 ◽  
pp. 1-14 ◽  
Author(s):  
Sachihiko Itoh ◽  
Ichiro Yasuda ◽  
Hiroaki Saito ◽  
Atsushi Tsuda ◽  
Kosei Komatsu
Keyword(s):  
Chlorophyll A ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Profiling Float ◽  
The Kuroshio

scholarly journals Water Column Profiles of Dissolved Inorganic Radiocarbon for the Kuroshio Region, Offshore of the Southern Japanese Coast

Radiocarbon ◽  
2011 ◽  
Vol 53 (4) ◽  
pp. 679-690 ◽  
Author(s):  
Tatsuya Tsuboi ◽  
Hiroshi Iwata ◽  
Hideki Wada ◽  
Hiroyuki Matsuzaki ◽  
Rumi Sohrin ◽  
...  
Keyword(s):  
Water Column ◽  
Intermediate Layer ◽  
Large Meander ◽  
Study Region ◽  
Japanese Coast ◽  
Kuroshio Large Meander ◽  
The Kuroshio ◽  
Kuroshio Region

We present the water column profiles (surface to 2000 m depth) for dissolved inorganic radiocarbon (14CDIC) from 2 stations in the Kuroshio region including the Kuroshio large meander (LM) of 2004–2005. Surprisingly, the Δ14CDIC value varied up to 125‰ in the intermediate layer, especially near 600 m depth. In addition, the Δ14CDIC value was approximately − 150‰ at 200 m depth at the northern station of Kuroshio in August 2005. This value is ∼100‰ less than other Δ14CDIC values for the same depth. In comparison, the Δ14CDIC water column profiles for the southern station of Kuroshio and GEOSECS station 224 decrease down to 600 m depth and were similar below 600 m depth. Our results suggest that strong upwelling associated with the Kuroshio LM has a powerful influence on the Δ14CDIC water column profiles in the study region.

scholarly journals Asynchrony of Gambierdiscus spp. Abundance and Toxicity in the U.S. Virgin Islands: Implications for Monitoring and Management of Ciguatera

Toxins ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 413
Author(s):  
Justin D. Liefer ◽  
Mindy L. Richlen ◽  
Tyler B. Smith ◽  
Jennifer L. DeBose ◽  
Yixiao Xu ◽  
...  
Keyword(s):  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Environmental Parameters ◽  
Virgin Islands ◽  
Coastal Communities ◽  
Trophic Levels ◽  
Us Virgin Islands ◽  
Benthic Dinoflagellates ◽  
The Mean ◽  
The U.S

Ciguatera poisoning (CP) poses a significant threat to ecosystem services and fishery resources in coastal communities. The CP-causative ciguatoxins (CTXs) are produced by benthic dinoflagellates including Gambierdiscus and Fukuyoa spp., and enter reef food webs via grazing on macroalgal substrates. In this study, we report on a 3-year monthly time series in St. Thomas, US Virgin Islands where Gambierdiscus spp. abundance and Caribbean-CTX toxicity in benthic samples were compared to key environmental factors, including temperature, salinity, nutrients, benthic cover, and physical data. We found that peak Gambierdiscus abundance occurred in summer while CTX-specific toxicity peaked in cooler months (Feb–May) when the mean water temperatures were approximately 26–28 °C. These trends were most evident at deeper offshore sites where macroalgal cover was highest year-round. Other environmental parameters were not correlated with the CTX variability observed over time. The asynchrony between Gambierdiscus spp. abundance and toxicity reflects potential differences in toxin cell quotas among Gambierdiscus species with concomitant variability in their abundances throughout the year. These results have significant implications for monitoring and management of benthic harmful algal blooms and highlights potential seasonal and highly-localized pulses in reef toxin loads that may be transferred to higher trophic levels.

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