Influences of the Kuroshio on Interisland Remote Connectivity of Corals Across the Nansei Archipelago in the East China Sea

For the preservation and protection of coral habitats along the Nansei Archipelago in the East China Sea, a submesoscale eddy‐resolving synoptic ocean model was developed based on the Regional Oceanic Modeling System coupled with a 3‐D Lagrangian particle tracking model. Millions of neutrally buoyant particles representing coral spawn and larvae were released from 19 major islands and one lagoon every spring from 2012 to 2015. The model results were compared to satellite data, in situ observation, and surface drifters to confirm reasonable agreement. The connectivity matrix across the archipelago was quantified using Lagrangian probability density functions of the modeled particle displacement. Most particles remained near the release areas, while some traveled long distances by the northeastward drifting Kuroshio, leading to notable interisland coral transport across the archipelago that promotes interisland connectivity. A possible mechanism was examined by analyzing the transition from coastal to pelagic transport of the particles released from the Yaeyama Islands, the southernmost area of the archipelago. The Kuroshio trapped the particles released from the northern coast of the islands with considerable temporal variability in the entrainment rate. By contrast, particles released from the southern coast are markedly affected by the eastward current around the release sites, which significantly reduces their entrainment in the Kuroshio and, thus, long‐distance transport. Some entrained particles were expelled abruptly from the Kuroshio, trapped by the southwestward drifting Kuroshio Counter Current developed between the Kuroshio and the archipelago, and subsequently transported eastward to the islands

Identification of coral spawn source areas around Sekisei Lagoon for recovery and poleward habitat migration by using a particle-tracking model

A massive coral bleaching event occurred in 2016 in the interior of Japan\u27s largest coral lagoon, the Sekisei Lagoon, located in the Kuroshio upstream region in southwestern Japan. Recovery of the coral lagoon will require the influx of coral spawn and larvae; therefore, it is important to identify and conserve source sites. A surface-particle-tracking simulation of coral spawn and larvae was used to identify source areas of coral spawn outside of the Sekisei Lagoon for potential recovery of the interior lagoon. The northern coastal zone of Iriomote Island, including Hatoma Island, was identified as a major source area. Hatoma Island was also identified as a key source for the Kuroshio downstream region and for aiding the poleward migration of coral habitat under ongoing global climate change, making it one of the most important source areas in the Nansei Archipelago

Interannual variability of mesoscale eddy activity at the subtropical fronts region and its influence on the generation of Kuroshio large meander

The Kuroshio off Enshunada, south of Japan Main Island, is well known to take two major paths, the nearshore path and the large meander path. The Kuroshio changed its path from the nearshore to the large meander during July 2004 (KLM04). The 9.25 MHz high frequency ocean radar developed by the National Institute of Communication and Technology observed a significant increase of the Kuroshio surface transport northeast of Taiwan, which is considered to induce KLM04, after the anticyclonic eddies from the subtropical fronts region collided with the Kuroshio east of Taiwan during August-September 2003. Interannual variability of mesoscale eddy activity at the subtropical fronts region was detected from altimeter data and the anticyclonic eddies which induced the Kuroshio increase were generated during the high eddy activity period, inevitably

Variations of velocity and transport associated with coastal cyclonic eddies off Shikoku, Japan estimated from moored current meter and IES data

Data from three moored current meters and four inverted echo sounders deployed south off Shikoku, Japan during October 1993 through November 1995 were used to investigate the variations of velocity and transport associated with coastal cyclonic eddies. The averages of the velocity near the bottom across the ASUKA line were about 5 cm/s for southwest on the continental slope, The vertical profiles of the geostrophic velocity were nearly barotropic at two coastal current meter stations when the coastal cyclonic eddies passed through the ASUKA line. Directions of the velocity anomaly near the bottom were then southwest at the most coastal station and northeast at the two relatively offshore stations. Variations of the barotropic transport anomaly associated with the coastal cyclonic eddies and the decrease of the geostrophic transport anomaly associated with southward shift of the Kuroshio axis were seen simultaneously

Variations of velocity and transport associated with coastal cyclonic eddies off Shikoku, Japan estimated from moored current meter and IES data

Data from three moored current meters and four inverted echo sounders deployed south off Shikoku, Japan during October 1993 through November 1995 were used to investigate the variations of velocity and transport associated with coastal cyclonic eddies. The averages of the velocity near the bottom across the ASUKA line were about 5 cm/s for southwest on the continental slope, The vertical profiles of the geostrophic velocity were nearly barotropic at two coastal current meter stations when the coastal cyclonic eddies passed through the ASUKA line. Directions of the velocity anomaly near the bottom were then southwest at the most coastal station and northeast at the two relatively offshore stations. Variations of the barotropic transport anomaly associated with the coastal cyclonic eddies and the decrease of the geostrophic transport anomaly associated with southward shift of the Kuroshio axis were seen simultaneously

日本南方黒潮域における慣性周期近傍の流速変動

Velocity fluctuations having near inertial frequency are studied on the basis of moored current meter data obtained at mid-depths in the Kuroshio and its recirculation regions south of Japan. Spectra of velocities with tidal currents removed show remarkable peaks near the inertial frequency, having mostly the clockwise rotation component. The energy associated with these fluctuations increases toward the offshore side, or southward. There are several peaks on the higher-frequency side, which seem to be associated with harmonics of the inertial oscillation

直接測定による四国沖の黒潮流速の変動特性

Direct current measurements were carried out along ASUKA(Affiliated Surveys of the Kuroshio off cape Ashizuri) line crossing the Kuroshio from Shikoku coast, Japan to 25 °N, during 1993-1995. The temporally averaged views of the Kuroshio show that most strongly flowing part, the Kuroshio flow axis, at about 700 m depth is located around 32 °N and it spreads down to about 2000 m depth. Weak countercurrents are detected just above the continental slope and strong countercurrents are also detected near the deepest end of the continental slope. At a reference depth of 650 m, the Kuroshio flow axis coincides with 7° C isotherm. The Kuroshio takes two distinct paths: a near-coast path and a far offshore path. For each case, a horizontal velocity profile at 650 m depth is estimated on a stream coordinate that denotes the component parallel to the velocity at the Kuroshio flow axis.1. 緒言 / 2. RIAM-COMPACTの概要 / 3. 壁面せん断乱流場によるRIAM-COMPACTの計算精度の検証 / 4. 実地形上の風況場解析への適用 / 5. まと