Diatom distribution as an environmental indicator in surface sediments of the West Philippine Basin

The distribution of diatoms from surface sediments of the West Philippine Basin was analyzed,with 68 species and varieties of diatoms from 26 genera identified.Diatom abundance varied spatially,with the absolute abundance of diatoms ranging from 0 to 3.4×10~4 frustules/g.The seven tropical pelagic diatoms were Alveus marinus,Azpeitia africana,Azpeitia nodulifera,Hemidiscus cuneiformis,Hemidiscus cuneiformis var.ventricosus,Roperia tesselata and Rhizosolenia bergonii.The relative abundance of these species was greater than 20%,and their distribution pattern in the sediments was overlaid by the flow of the Kuroshio Current.Ethmodiscus rex was present at 159 stations,formed the most abundant and dominant species in the diatomaceous ooze,and thus referred to as Ethmodiscus ooze.Ethmodiscus rex was also a major contributor to primary production in the region.A principal component analysis was employed to explain the relationship between samples and variations in diatom species from the WPB.Four diatom assemblages were distinguished,representing different oceanographic conditions;their spatial distributions were closely related with the North Equatorial Current and Kuroshio Current patterns in the region.These diatom assemblages can therefore be useful in deciphering late Quaternary palaeoceanographic reconstructions of the West Philippine Basin.

Diatom distribution and its relationship to sediment property in the Minjiang Estuary, southeast China

The distribution of diatoms in surface sediments in the Minjiang Estuary, southeast China, was investigated in2009. Total 56 species and other species belonging to 25 genera were identified, among them 11 species were dominant over 5%. Dominant species included Actinocyclus ehrenbergii, Coscinodiscus curvatulus, C. divisus, C.jonesianus, C. radiatus, C. rothii, C. subtilis, Cyclotella stylorum, Epithemia hyndmanii, Hydrosera whampoensis,and Trachyneis aspera. Diatom abundance varied spatially, with the absolute abundance of diatoms ranging from13 valves/g to 11×104 valves/g, and averaging 2.5×104 valves/g. A canonical correspondence analysis（CCA） was used to explain the relationships between diatom distribution and sediment properties in the Minjiang Estuary.CCA revealed that the major elements（Fe_2O_3, Na_2O, CaO, MgO, TiO_2, SiO_2, Al_2O_3, and K_2O） were closely related to diatom abundance. Four diatom assemblages were distinguished, representing different sediment properties,which may assist late Quaternary palaeoceanographic reconstructions of the Minjiang Estuary.

Diatom distribution in surface sediments from Chinese inshore waters and the relationship to modern environmental variables

Diatoms are widely used to study past and present changes in the marine environment. Unimodal models are appropriate for exploring the relationship between environmental properties in Chinese inshore waters and fossil diatom species derived from modern surface sediments. The best-fit relationships between two multivariate datasets(diatom species and environmental variables) were identified using canonical correspondence analysis(CCA), which is a constrained ordination technique. The absolute abundance of diatoms in the Chinese inshore waters ranged from 500 to 48 000 valves/g, and the average absolute abundance of all the 29 sites was 11 300 valves/g. 153 species and varieties of diatoms belonging to 42 genera in all were identified in the Chinese inshore waters. There were 28 dominant diatom species in all. According to the absolute abundance of the dominant species and the spatial distribution of the currents from the Chinese inshore waters, 12 diatom assemblages were distinguished from north to south, which refl ected the different oceanographic conditions at the regional scale. Of the eight environmental variables considered, the most important environmental variable is winter sea surface salinity(WSS), which was also the only environmental variable with statistical significance. Therefore, it may be used to establish a transfer functions for the Chinese inshore waters in future paleoclimate studies.