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The western coast of the Korean Peninsula has some of the highest tidal ranges in the world. Gomso Bay, located along the western coast of Korea, is a semi-enclosed embayment. Tidal deposits occur under most lowland rural areas along Gomso Bay. In this study, the diatom assemblage and grain size distributions of surface sediments along a tributary of Gomso Bay called Jujin Stream were examined to identify their relationships with tidal levels. Consequently, riverside sediments of Jujin Stream could be separated into four tidal level zones based on their diatom assemblage and grain size distribution. Clear diatom and grain size distribution gaps were found between the tidal (zones 1 and 2), fluvio-tidal transition (zone 3), and freshwater (zone 4) zones. The tidal zone was characterized by allochthonous marine diatom taxa. These marine taxa, and the sand content, gradually decreased in the upstream direction. Sediment in the fluvio-tidal transition zone has particularly distinctive features. Extremely high numbers of diatoms are present, which are dominated by freshwater taxa, with rare marine and marine-brackish taxa. Grain sizes in this zone increase sharply in the upstream direction. Combining diatom and grain size data can provide accurate paleo sea-level information for strongly tidal areas. • Diatom and grain size distributions in an area of large tidal range along Jujin Stream, which flows into Gomso Bay. • Limit of sea-water incursion is appear by the fluvio-tidal transition zone, which has extremely high diatom abundance with a majority of freshwater diatoms and rare marine diatom. • The elevation of the fluvio-tidal transition zone is between the extreme high-water level of spring tide and the maximum tidal level of neap tide, although the distance from the river mouth is stronger factor. • In an area of large tidal range, appearance of marine diatom in sediment suggests the elevation was under extreme high-water level of spring tide. [ABSTRACT FROM AUTHOR]

Detailed diatom records within surface and core sediments from the Southern Bering Continental Shelf (SBCS) reveal that the Holocene evolution of sea-ice distribution is associated with low pressure patterns. Holocene sea-ice distribution over the SBCS was mainly controlled by the location of the Aleutian Low. The corresponding paleoceanographic and paleoclimate conditions can be divided into three stages: (1) the early Holocene (before 7000 cal. yr BP) was characterized by extensive sea-ice distribution under two low-pressure cells, which covered the western Bering Sea and the Gulf of Alaska, respectively. (2) Between 3000 and 7000 cal. yr BP, the low-pressure system over the Gulf of Alaska became weak, causing total sea-ice mass over the SBCS to retreat. (3) In the past 3000 years, prevailing southwesterly winds over the SBCS due to the developing Aleutian Low have reduced further sea-ice cover on the SBCS. These paleoclimatic changes were probably a response to ENSO variation. The timings of water mass exchanges on the SBCS coincided with sea-level change along the Alaskan Peninsula. As a result, subsequent morphologic alterations have also influenced the paleoceanographic condition of the SBCS. The effect of the surface coastal water and bottom marine water on the SBCS intensified about 6000 cal. yr BP when sea level increased. [ABSTRACT FROM AUTHOR]

Abstract: Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake''s water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10years, which suggests that Lake Saroma''s present-day deterioration and eutrophication will continue or become even worse. [Copyright &y& Elsevier]

Fossil benthic and planktonic foraminifera from a part of core ND-02 and the published data of core ND-01 from the Nakdong River delta, southeast Korea were analyzed to evaluate the impact of the Tsushima Warm Current on coastal environments in the Korea/Tsushima Strait between Korea and Japan during the early to middle Holocene. Based on cluster analysis, four sample clusters (A, B, C, and D), suggestive of a landward–seaward gradient of environmental conditions, can be defined. According to the spatio-temporal and cluster distributions of benthic foraminifera in faunal compositions, the landward occurrence of benthic foraminifera was delimited in the inner part of the Nakdong River delta at ∼8–7 ka. The common occurrence of warm-water planktonic foraminifera suggests that this maximum landward expansion of benthic foraminifera within the delta was caused by the intensification of the Tsushima Warm Current in addition to sea level rise during the early to middle Holocene. Changes in both marine biota and sedimentation were reported in the coastal areas of southwestern Japan in that period. They were also caused by a precursor of the enhanced Tsushima Warm Current at ∼8 ka. Thus, the evolution of the Tsushima Warm Current during the early to middle Holocene is important for understanding various phenomena in the coastal environments of the Korea/Tsushima Strait. [ABSTRACT FROM AUTHOR]