Precursors of the 1983 Japan Sea Earthquake

The cellular macromolecular contents and energy value of phytoplankton as primary food source determine the growth of higher trophic levels, affecting the balance and sustainability of oceanic food webs. Especially, proteins are more directly linked with basic functions of phytoplankton biosynthesis and cell division and transferred through the food chains. In recent years, the East/Japan Sea (EJS) has been changed dramatically in environmental conditions, such as physical and chemical characteristics, as well as biological properties. Therefore, developing an algorithm to estimate the protein concentration of phytoplankton and monitor their spatiotemporal variations on a broad scale would be invaluable. To derive the protein concentration of phytoplankton in EJS, the new regional algorithm was developed by using multiple linear regression analyses based on field-measured data which were obtained from 2012 to 2018 in the southwestern EJS. The major factors for the protein concentration were identified as chlorophyll-a (Chl-a) and sea surface nitrate (SSN) in the southwestern EJS. The coefficient of determination (r2) between field-measured and algorithm-derived protein concentrations was 0.55, which is rather low but reliable. The satellite-derived estimation generally follows the 1:1 line with the field-measured data, with Pearson’s correlation coefficient, which was 0.40 (p-value < 0.01, n = 135). No remarkable trend in the long-term annual protein concentration of phytoplankton was found in the study area during our observation period. However, some seasonal difference was observed in winter protein concentration between the 2003–2005 and 2017–2019 periods. The algorithm is developed for the regional East/Japan Sea (EJS) and could contribute to long-term monitoring for climate-associated ecosystem changes. For a better understanding of spatiotemporal variation in the protein concentration of phytoplankton in the EJS, this algorithm should be further improved with continuous field surveys.

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Tracking a Coastal Wave Buoy, Lost from the Southern Coast of Jeju Island, Using Lagrangian Particle Modeling

Journal of Marine Science and Engineering ◽

10.3390/jmse9080795 ◽

2021 ◽

Vol 9 (8) ◽

pp. 795

Author(s):

Seongbong Seo ◽

Young-Gyu Park

Keyword(s):

Japan Sea ◽

Jeju Island ◽

East China ◽

Northwest Pacific ◽

Southern Coast ◽

Lagrangian Particle ◽

The North ◽

Particle Modeling ◽

The Usa ◽

Tracking Model

A coastal wave buoy was lost near Jeju Island, Korea, in late July 2014 and found at Cape Mendocino, USA, in April 2020. The buoy’s journey was simulated with a Lagrangian particle tracking model using surface ocean currents and wind data at 10 m above sea level. Experiments were conducted with windage values of 0, 2, and 4%. Particles were released along the southern coast of Jeju Island from 31 July to 8 August 2014. When the windage was 0 or 2%, most particles reached the northwest Pacific via the East/Japan Sea or East China Sea, respectively. With 4% windage, very few particles entered the North Pacific. Under 0% windage, particles accumulated in the Great Pacific Garbage Patch (GPGP) and never reached the USA. Under 2%, particles were able to escape the GPGP and started to reach the USA coast 2 years and 7 months after the release. The trajectory of the buoy was deduced from the trajectories of particles with a similar travel time. The buoy likely moved to East China and then to the subtropical convergence zone, where it must have circulated for approximately 2 years before being pushed toward Cape Mendocino by the intensified winter westerlies.

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Hydraulic Evaluation of the Levee System Evolution on the Kurobe Alluvial Fan in the 18th and 19th Centuries

Energies ◽

10.3390/en14154406 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4406

Author(s):

Tadaharu Ishikawa ◽

Hiroshi Senoo

Keyword(s):

Channel Capacity ◽

Flood Control ◽

River Flow ◽

Global Climate ◽

Flow Simulation ◽

Japan Sea ◽

Main Channel ◽

Alluvial Fan ◽

Flood Peak ◽

Levee System

The development process and flood control effects of the open-levee system, which was constructed from the mid-18th to the mid-19th centuries, on the Kurobe Alluvial Fan—a large alluvial fan located on the Japan Sea Coast of Japan’s main island—was evaluated using numerical flow simulation. The topography for the numerical simulation was determined from an old pictorial map in the 18th century and various maps after the 19th century, and the return period of the flood hydrograph was determined to be 10 years judging from the level of civil engineering of those days. The numerical results suggested the followings: The levees at the first stage were made to block the dominant divergent streams to gather the river flows together efficiently; by the completed open-levee system, excess river flow over the main channel capacity was discharged through upstream levee openings to old stream courses which were used as temporary floodways, and after the flood peak, a part of the flooded water returned to the main channel through the downstream levee openings. It is considered that the ideas of civil engineers of those days to control the floods exceeding river channel capacity, embodied in their levee arrangement, will give us hints on how to control the extraordinary floods that we should face in the near future when the scale of storms will increase due to the global climate change.

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Reductive dissolution of biogenic magnetite

Earth Planets and Space ◽

10.1186/s40623-020-01290-3 ◽

2020 ◽

Vol 72 (1) ◽

Author(s):

Toshitsugu Yamazaki

Keyword(s):

Japan Sea ◽

Depth Interval ◽

Reductive Dissolution ◽

Magnetic Minerals ◽

Specific Chemical ◽

Biogenic Magnetite ◽

Transmission Electron ◽

Dissolution Zone ◽

Central Ridge ◽

Redox Boundary

Abstract Reductive dissolution of magnetite is known to occur below the Fe-redox boundary in sediments. In this study, detailed processes associated with biogenic magnetite dissolution are documented. A sediment core from the Japan Sea was used for this purpose, in which reductive dissolution of magnetic minerals is known to start at depths of about 1.15 m and is mostly complete within a depth interval of about 0.35 m. Using first-order reversal curve diagrams, preferential dissolution of biogenic magnetite within this interval is estimated from the observation that a narrow peak that extends along the coercivity axis (central ridge), which is indicative of biogenic magnetite, diminishes downcore. Transmission electron microscopy is used to demonstrate that the sediments contain three magnetofossil morpho-types: octahedra, hexagonal prisms, and bullet-shaped forms. Within the reductive dissolution zone, partially etched crystals are commonly observed. With progressive dissolution, the proportion of bullet-shaped magnetofossils decreases, whereas hexagonal prisms become more dominant. This observation can be explained by the differences in resistance to dissolution among crystal planes of magnetite and the differences in surface area to volume ratios. Magnetofossil morphology may reflect the preference of magnetotactic bacterial lineages for inhabiting specific chemical environments in sediments. However, it could also reflect alteration of the original morphological compositions during reductive diagenesis, which should be considered when using magnetofossil morphology as a paleoenvironmental proxy.

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