The Temporal And Spatial Distribution And Diatom Taxa Of Vast Laminated Diatom Mat Deposits From The West Low-latitude Pacific Ocean

The diatom mat deposits are the productions of vast diatoms bloom and the samples are taken with great chances. We take the diatom mat sediment cores first found in low-latitude west pacific 136°~140°E, 15°~21°N as the research object. We ascertain the category that form the diatom mats, discuss the temporal and spatial distribution of the diatom mats, analyze and identify the category of diatoms in the cores WPD03 and WPD12. Discuss the climatic and environmental change at the time the low-latitude west pacific diatom mats formed by deep-sea deposited diatom combination change and further discuss the mechanism of the diatom mat deposits formation in this area.Based on above studies, some main conclusions were obtained as follows : 1) the diatoms forming mats in low latitude west pacific is"shade flora"diatom Ethmodiscus rex (Wallich) Hendey; 2) the sites found diatom mats are zone distributed, the direction is NW-SE and most distribute in the deep water area with flat seafloor, between 17°N～20°N and the water depth 4837-6150 m below Carbonate Compensation Depth (CCD); 3) AMS 14C dates show that the sediments rich in diatom mats occurred during 16.0 ~ 28.6 ka B.P., which means the bloom mainly occurred in last glacial maximum, while there are not diatom mats deposits in other layers; 4) A total of 101 diatom taxa (including variation) belonging to 40 genera had been identified from the 155 samples in the two cores WPD 03 and WPD 12, and the relative percentage of Thalassionema frauenfeldii are the highest, Thalassionema nitzschioides,Azpeitia nodulifera,Hemidiscus cuneiformis,Nitzschia marina take the second place. The five diatoms take about 85% of all diatom species relative percentage. It indicates the five diatoms are the easiest to coexist and bloom with the diatoms forming mats in the diatom mats deposit process of the surface water in this areas; 5) the salinity of the sea water in this area is reduced in late MIS3 and it is helpful to stratify the water and therefore make the"shade flora"diatom bloom, leading to"fall dump"; 6) Antarctic Intermediate Water (AAIW) expanded northward in last glacial period and brought silicate-rich water into the studying area, namely,"silicon leakage"processes caused the bloom of diatoms. In addition, the iron input increase is one of the main reasons of the diatom bloom.