Unprecedented Outbreak of Harmful Algae in Pacific Coastal Waters off Southeast Hokkaido, Japan, during Late Summer 2021 after Record-Breaking Marine Heatwaves

Unprecedented large-scale harmful algae blooms (HABs) were reported in coastal waters off the south-eastern coast of Hokkaido, Japan, in mid-to-late September 2021, about a month after very intense and extensive marine heatwaves subsided. To understand the physical–biological processes associated with development of the HABs, we conducted analyses via a combination of realistic ocean circulation models, particle-tracking simulations, and satellite measurements. The satellite-derived chlorophyll concentrations (SCCs) and areal extent of the high SCCs associated with the HABs were the highest recorded since 1998. More specifically, the extent of SCCs exceeding 5 or 10 mg m−3 started to slowly increase after 20 August, when the marine heatwaves subsided, intermittently exceeded the climatological daily maximum after late August, and reached record-breaking extremes in mid-to-late September. About 70% of the SCCs that exceeded 10 mg m−3 occurred in places where water depths were <300 m, i.e., coastal shelf waters. The high SCCs were also tightly linked with low-salinity water (e.g., subarctic Oyashio and river-influenced waters). High-salinity subtropical water (e.g., Soya Warm Current water) appeared to suppress the occurrence of HABs. The expansion of the area of high SCCs seemed to be synchronized with the deepening of surface mixed layer depths in subarctic waters on the Pacific shelves. That deepening began around 10 August, when the marine heatwaves weakened abruptly. However, another mechanism was needed to explain the intensification of the SCCs in very nearshore waters off southeast Hokkaido. Particle-tracking simulations based on ocean circulation models identified three potential source areas of the HABs: the Pacific Ocean east of the Kamchatka Peninsula, the Sea of Japan, and the Sea of Okhotsk east of the Sakhalin Island. Different processes of HAB development were proposed because distance, time, and probability for transport of harmful algae from the potential source areas to the study region differed greatly between the three source areas.

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Transport and bottom accumulation of fine river sediments under typhoon conditions and associated submarine landslides: case study of the Peinan River, Taiwan

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-3-5155-2015 ◽

2015 ◽

Vol 3 (8) ◽

pp. 5155-5189

Author(s):

A. A. Osadchiev ◽

K. A. Korotenko ◽

P. O. Zavialov ◽

W.-S. Chiang ◽

C.-C. Liu

Keyword(s):

Ocean Circulation ◽

River Sediments ◽

Circulation Model ◽

Sediment Deposition ◽

Eastern Coast ◽

Submarine Landslides ◽

Coastal Circulation ◽

Study Region ◽

Sea Floor ◽

Tracking Model

Abstract. A combination of a three-dimensional Eulerian ocean circulation model (POM) and a Lagrangian particle-tracking model (STRiPE) is used to study the fate of fine river sediments discharged by the Peinan River at the north-eastern coast of the Taiwan Island. The composite model is verified against in situ measurements and applied to simulate primary sediment deposition under freshet and typhoon discharge conditions of the Peinan River. It is shown that local wind plays the crucial role in sediment transport and settling at the coastal area through its influence on the river plume dynamics and turbulent mixing in the upper layer. Wind forcing conditions generally determine the location of the sediment deposit area, while its final pattern is defined by coastal circulation with respect to coastal geometry and local bathymetry. In the study region river-born sediments are deposited to the sea floor mainly in the shallow shelf areas. A significant portion of discharged fine sediments is moved offshore to the deeper ocean where it is spread and dissipated by the strong coastal circulation governed by the Kuroshio Current. The performed numerical experiments showed that sediment accumulation rate under typhoon conditions is about two orders greater comparing to freshet condition. The simulation results were used to identify potential zones of formation of submarine landslides caused by elevated sediment deposition at the steep sea floor during and shortly after the typhoon events. Basing on these results we detected the areas of the continental shelf and continental slope which have high risk of being incised and eroded by autosuspending sediment gravity flows.

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On the World Ocean Circulation: Volume 2 The Pacific and Indian Oceans / A Global Update.

10.21236/ada323804 ◽

1996 ◽

Cited By ~ 10

Author(s):

William J. Schmitz ◽

Keyword(s):

Ocean Circulation ◽

World Ocean ◽

The Pacific ◽

The World ◽

Circulation Volume

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Waste Disposal in the Sea off Southern California

Water Science & Technology ◽

10.2166/wst.1986.0137 ◽

1986 ◽

Vol 18 (11) ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Willard Bascom

Keyword(s):

Waste Water ◽

Coastal Waters ◽

Southern California ◽

State Standards ◽

Waste Streams ◽

Cool Water ◽

Water Research ◽

The Pacific ◽

Steady Improvement ◽

Deep Cool

Southern California, with a coastal population of 12 million people, releases about 4.4 million cubic meters of treated waste water into the Pacific every day via outfalls that discharge three to six kilometers offshore at a depth of 60 meters. Diffusers cause each liter of waste to be diluted by 150 liters of deep cool water preventing it from reaching the surface except for short periods in winter. Data on the constituents of the four largest waste streams are presented and a brief account of the research done by the Southern California Coastal Water Research Project is given. Although the waste water now discharged meets rigorous state standards (with minor exceptions) and the steady improvement in sea conditions over a decade has been well documented, there is a continuing debate over whether our coastal waters are adequately protected. This is primarily because the damaging effects of DDT and PCBs that were discharged more than 14 years ago have been slow to go away. Although the amounts of DDT and PCB in sea animals are only one- tenth what they were a decade ago they tend to obscure the value of the improvements and the present discharge practices. The alternatives to sea disposal seem likely to cause greater damage to the overall environment.

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Galápagos upwelling driven by localized wind–front interactions

Scientific Reports ◽

10.1038/s41598-020-80609-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Alexander Forryan ◽

Alberto C. Naveira Garabato ◽

Clément Vic ◽

A. J. George Nurser ◽

Alexander R. Hearn

Keyword(s):

Ocean Circulation ◽

Realistic Model ◽

Surface Mixed Layer ◽

Equatorial Pacific Ocean ◽

World Heritage Sites ◽

Theory Of Evolution ◽

Heritage Sites ◽

Galapagos Archipelago ◽

Eastern Equatorial Pacific ◽

Eastern Equatorial Pacific Ocean

AbstractThe Galápagos archipelago, rising from the eastern equatorial Pacific Ocean some 900 km off the South American mainland, hosts an iconic and globally significant biological hotspot. The islands are renowned for their unique wealth of endemic species, which inspired Charles Darwin’s theory of evolution and today underpins one of the largest UNESCO World Heritage Sites and Marine Reserves on Earth. The regional ecosystem is sustained by strongly seasonal oceanic upwelling events—upward surges of cool, nutrient-rich deep waters that fuel the growth of the phytoplankton upon which the entire ecosystem thrives. Yet despite its critical life-supporting role, the upwelling’s controlling factors remain undetermined. Here, we use a realistic model of the regional ocean circulation to show that the intensity of upwelling is governed by local northward winds, which generate vigorous submesoscale circulations at upper-ocean fronts to the west of the islands. These submesoscale flows drive upwelling of interior waters into the surface mixed layer. Our findings thus demonstrate that Galápagos upwelling is controlled by highly localized atmosphere–ocean interactions, and call for a focus on these processes in assessing and mitigating the regional ecosystem’s vulnerability to 21st-century climate change.

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The Origin of Sand and Its Colour on the South-Eastern Coast of Spain: Implications for Erosion Management

Water ◽

10.3390/w12020377 ◽

2020 ◽

Vol 12 (2) ◽

pp. 377 ◽

Cited By ~ 2

Author(s):

Asensio-Montesinos ◽

Pranzini ◽

Martínez-Martínez ◽

Cinelli ◽

Anfuso ◽

...

Keyword(s):

Western Mediterranean ◽

Mediterranean Coast ◽

Eastern Coast ◽

Storm Events ◽

Colour Space ◽

Source Areas ◽

Beach Width ◽

Severe Erosion ◽

Colour Coordinates ◽

Economic Function

Sand colour can give important information about mineral composition and, consequently, sediment source areas and input systems. Beach appearance, which is mostly linked to sand colour, has a relevant economic function in tourist areas. In this paper, the colour of 66 sand samples, collected along both natural and nourished beaches in the western Mediterranean coast of Spain, were assessed in CIEL*a*b* 1976 colour space. The obtained results showed relevant differences between natural and artificially nourished beaches. The colour of many nourished beaches generally differs from the native one because the origin of the injected sand is different. The native sand colour coordinates’ range is: L* (40.16–63.71); a* (−1.47–6.40); b* (7.48–18.06). On the contrary, for nourished beaches’ the colour range is: L* (47.66–70.75); a*(0.72‒5.16); b* (5.82–18.82). Impacts of beach nourishment on the native sand colour were studied at San Juan beach, the most popular one along the study area. Nourishment works were performed after severe erosion, usually linked to anthropic activities/structures and storm events, but also to increase beach width and hence benefit tourism.

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Texture and composition of the Rosa Marina beach sands (Adriatic coast, southern Italy): a sedimentological/ecological approach

Geologos ◽

10.1515/logos-2016-0011 ◽

2016 ◽

Vol 22 (2) ◽

pp. 87-103 ◽

Cited By ~ 4

Author(s):

Massimo Moretti ◽

Marcello Tropeano ◽

A.J. (Tom) van Loon ◽

Pasquale Acquafredda ◽

Rossella Baldacconi ◽

...

Keyword(s):

Southern Italy ◽

Statistical Parameters ◽

Source Areas ◽

Potential Source ◽

Physical Study ◽

Family Level ◽

Adriatic Coast ◽

Beach Sands ◽

Shell Fragments

Abstract Beach sands from the Rosa Marina locality (Adriatic coast, southern Italy) were analysed mainly microscopically in order to trace the source areas of their lithoclastic and bioclastic components. The main cropping out sedimentary units were also studied with the objective to identify the potential source areas of lithoclasts. This allowed to establish how the various rock units contribute to the formation of beach sands. The analysis of the bioclastic components allows to estimate the actual role of organisms regarding the supply of this material to the beach. Identification of taxa that are present in the beach sands as shell fragments or other remains was carried out at the genus or family level. Ecological investigation of the same beach and the recognition of sub-environments (mainly distinguished on the basis of the nature of the substrate and of the water depth) was the key topic that allowed to establish the actual source areas of bioclasts in the Rosa Marina beach sands. The sedimentological analysis (including a physical study of the beach and the calculation of some statistical parameters concerning the grain-size curves) shows that the Rosa Marina beach is nowadays subject to erosion.

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Technical Note: Preliminary estimation of rockfall runout zones

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-819-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 819-828 ◽

Cited By ~ 59

Author(s):

M. Jaboyedoff ◽

V. Labiouse

Keyword(s):

Slope Angle ◽

Digital Terrain Model ◽

Grid Cell ◽

Technical Note ◽

Field Observations ◽

Source Areas ◽

Terrain Model ◽

Digital Terrain ◽

Energy Line ◽

Potential Source

Abstract. Rockfall propagation areas can be determined using a simple geometric rule known as shadow angle or energy line method based on a simple Coulomb frictional model implemented in the CONEFALL computer program. Runout zones are estimated from a digital terrain model (DTM) and a grid file containing the cells representing rockfall potential source areas. The cells of the DTM that are lowest in altitude and located within a cone centered on a rockfall source cell belong to the potential propagation area associated with that grid cell. In addition, the CONEFALL method allows estimation of mean and maximum velocities and energies of blocks in the rockfall propagation areas. Previous studies indicate that the slope angle cone ranges from 27° to 37° depending on the assumptions made, i.e. slope morphology, probability of reaching a point, maximum run-out, field observations. Different solutions based on previous work and an example of an actual rockfall event are presented here.

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