• Journal of the Korean earth science society
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• v.42 no.1
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• pp.1-10
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• 2021

Silicon (Si) is the second most abundant element in the crust and consists of three stable isotopes, 28Si (92.23%), 29Si (4.67%), and 30Si (3.10%). Si isotopes are widely studied worldwide as a proxy for the biogeochemical cycle of Si to reconstruct the paleoenvironment and paleoclimate. However, in Korea, there have been no studies on biogenic silica using Si isotopes. In this study, we carried out Si isotope measurements of giant diatoms, summarizing the previously reported alkali fusion methods and establishing the best Si separation method for biogenic silica. Samples were completely digested using alkali fusion at high temperatures, effectively separating Si using an AG® 50W-X8 cation exchange resin. To evaluate the precision and accuracy of our measurements, Si isotope standard material (NBS-28) and USGS reference materials (AGV-2, GSP-2, BHVO-2) were analyzed. The results are in excellent agreement with the reported values within the acceptable error. The Si isotope measurement method developed in this study is expected to help in understanding the paleoclimate and paleoenvironment by tracing the Si cycle.

• Korean Journal of Environmental Biology
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• v.38 no.4
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• pp.567-577
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• 2020

The infection of marine diatom Coscinodiscus wailesii by a parasitic protist from the Yongho Bay of Busan, Korea was observed during the diatom bloom events in 2017 through 2018. The morphological and molecular features suggested that the parasitic nanoflagellate Pirsonia diadema was responsible for the infection. During the study period, the parasite prevalence ranged from 0.3% to 3.3%, and infected C. wailesii cells were observed only at surface seawater temperatures ranging between 10.9 and 19.9℃, although the host population appeared at temperatures above 25℃. The parasite and host system was successfully established as cultures. Using the cultures, we determined the morphological features over the infection cycle, parasite generation time, parasite prevalence as a function of inoculum size, and zoospore infectivity and survival time. The diatom C. wailesii was readily infected by the parasite P. diadema, with a parasite prevalence reaching up to 100% and a zoospore to host inoculum ratio above 20:1. The survival and infectivity of the parasite zoospores decreased with age. While the zoospores could survive up to 88 hours, they quickly lost their ability to infect after 48 hours. These results could lead to a better understanding of the biology and ecology of the parasitoid infecting the giant-sized diatoms in coastal waters.