Monthly anomalies of sea surface chlorophyll-a concentration in the Khanh Hoa waters of Vietnam related to ENSO phenomenon
Keywords:Southeast Asian studies, climate change, Khanh Hoa, chlorophyll-a anomaly, ENSO events.
Based on the monthly averaged sea surface chlorophyll-a concentration data continuously for more than 17 years (Jul. 2002–Dec. 2019), the analyzed results show that the averaged chlorophyll-a concentration in Khanh Hoa waters was 0.58 mg/m3, and the monthly average variation was ± 0.14 mg/m3 (that is equivalent to about ± 24%). Under the impact of ENSO phenomena, in the years when the double La Niña events occurred (two consecutive years in the La Nina event occurs), the chlorophyll-a anomaly index fluctuated from -0.99 mg/m3 to 1.62 mg/m3. These are very strong fluctuation levels, corresponding to the decrease or increase in chlorophyll-a concentration from 86% to 279%. In the El Niño years, the fluctuations of chlorophyll-a concentration were little affected unless the two previous years in which the double La Niña event occurred. These fluctuations have significantly impact nutritional resources and water quality because chlorophyll-a concentration is one of the key indices in studying the health status of any natural marine ecosystem. In addition, chlorophyll-a concentration in Khanh Hoa waters often varies between seasons. The averaged chlorophyll-a concentration reaches its maximum value in the winter, then decreases gradually in the spring and usually reaches the minimum value in the summer, then rises gradually again in the autumn.
 Eckstein, D., Künzel, V., Schäfer, L., and Winges, M., 2020. Global Climate Risk Index 2020: who suffers most from extreme weather events? Weather-related loss events in 2018 and 1999–2018. Germanwatch, Bonn.
 L’Heureux, M., 2014. What is the El Niño–Southern Oscillation (ENSO) in a nutshell?; Available from: https://www.climate.gov/news-features/bl-ogs/enso/what-el-ni%C3%B1o%E2%80% 93southern-oscillation-enso-nutshell; accessed February 12, 2020.
 Advisory Panel for the Tropical Oceans and Global Atmosphere Program National Research Council, 1996. Learning to predict climate variations associated with El Niño and the southern oscillation: accomplishments and legacies of the TOGA program. National Acad. Press.
 Behrenfeld, M. J., Randerson, J. T., McClain, C. R., Feldman, G. C., Los, S. O., Tucker, C. J., Falknowski, P. G., Field, C. B., Frouin, R., Esaias, W. E., Kolber, D. D., and Pollack, N. H., 2001. Biospheric primary production during an ENSO transition. Science, 291(5513), 2594–2597. Doi: 10.1126/science.1055071.
 Field, C. B., Behrenfeld, M. J., Randerson, J. T., and Falkowski, P., 1998. Primary production of the biosphere: integrating terrestrial and oceanic components. Science, 281(5374), 237–240. Doi: 10.1126/science.281.5374.237.
 Dilley, M., and Heyman, B. N., 1995. ENSO and disaster: Droughts, floods and El Niño/Southern Oscillation warm events. Disasters, 19(3), 181–193. https://doi.org/10.1111/j.1467-7717.1995.t b00338.x.
 Ward, P. J., Kummu, M., and Lall, U., 2016. Flood frequencies and durations and their response to El Niño Southern Oscillation: Global analysis. Journal of Hydrology, 539, 358–378. https://doi.org/10.1016/j.jhydrol.2016.05.045.
 Domeisen, D., Garfinkel, C. I., and Butler, A. H., 2019. Global impacts of ENSO reach into the stratosphere. EOS: Earth & Space Science News, 100. https://doi.org/10.1029/2019EO115943.
 Yapa, K. K., 2000. Seasonal variability of sea surface chlorophyll-a of waters around Sri Lanka. Journal of Earth System Science, 109(4), 427–432.
 NOAA National Marine Fisheries Service; NASA, 2019. About Ocean Chlorophyll Concentrations. 1998–2018. Available from: https://www.globalchange.gov/bro-wse/indicators/ocean-chlorophyll-concen-trations; accessed February 15, 2020.
 Liu, Y., Liu, B., Yang, X., Bai, W., and Wang, J., 2015. Relationships between drought disasters and crop production during ENSO episodes across the North China Plain. Regional environmental change, 15(8), 1689–1701. https://doi.org/10.1007/s10113-014-0723-8.
 Karati, K. K., Vineetha, G., Madhu, N. V., Anil, P., Dayana, M., Shihab, B. K., Muhsin, A. I., Riyas, C., and Raveendran, T. V., 2017. Variability in the phytoplankton community of Kavaratti reef ecosystem (northern Indian Ocean) during peak and waning periods of El Niño 2016. Environmental monitoring and assessment, 189(12), 1–17. https://doi.org/10.1007/s10661-017-6369-5.
 Liu, Y., Yang, X., Wang, E., and Xue, C., 2014. Climate and crop yields impacted by ENSO episodes on the North China Plain: 1956–2006. Regional Environmental Change, 14(1), 49–59. Doi: 10.1007/s10113-013-0455-1.
 Pandey, S., Bhagawati, C., Dandapat, S., and Chakraborty, A., 2019. Surface chlorophyll anomalies associated with Indian Ocean Dipole and El Niño Southern Oscillation in North Indian Ocean: a case study of 2006–2007 event. Environmental Monitoring and Assessment, 191(3), 1–14. https://doi.org/10.1007/s10661-019-7754-z.
 Park, M., and Choi, M., 2015. The relationships between El Niño Southern Oscillation and extreme storm events in Korea. Environmental Earth Sciences, 74(1), 351–362. https://doi.org/10.1007/s12665-015-4040-4.
 Dewi, D. M. P. R., Fatmasari, D., Kurniawan, A., and Munandar, M. A., 2018. The impact of ENSO on regional chlorophyll-a anomaly in the Arafura Sea. In IOP Conference Series: Earth and Environmental Science (Vol. 139, No. 1, pp. 012020). IOP Publishing.
 Park, J. Y., Kug, J. S., Park, J., Yeh, S. W., and Jang, C. J., 2011. Variability of chlorophyll associated with El Niño-Southern Oscillation and its possible biological feedback in the equatorial Pacific. Journal of Geophysical Research (Oceans), 116(C10), C10001. Doi: 10.1029/2011JC007056.
 Van Chung, T., and Long, B. H., 2019. Studies on the variability of upwelling system in the South Central Vietnam waters under the impact of ENSO events and its impact on hydrographic conditions of the Ninh Thuan-Binh Thuan waters. Vietnam Journal of Marine Science and Technology, 19(4A), 17–33. Doi: 10.15625/1859-3097/19/4A/14595.
 Son, T. P. H., Van Chung, T., Huan, N. H., Tien, N. M., Van Tac, V., Khang, N. H. T., Hoi, N. T. T., Herrmann, M., and Siswanto, E., 2017. Abnormal features of oceanographic characteristics in upwelling Vietnam waters under impact of El Niño events. Vietnam Journal of Earth Sciences, 39(3), 225–239. DOI: 10.15625/0866-7187/39/3/10268.
 Vu, T. V., Nguyen, H. T., Nguyen, T. V., Nguyen, H. V., Pham, H. T. T., and Nguyen, L. T., 2015. Effects of ENSO on autumn rainfall in central Vietnam. Advances in Meteorology, 2015. https://doi.org/10.1155/2015/264373.
 Van Tac, V., and Hai, D. N., 2018. Chlorophyll concentration anomaly in coastal marine area of Vietnam South Centre related to ENSO phenomenon. Vietnam Journal of Marine Science and Technology, 18(1), 70–78. https://doi.org/10.15625/1859-3097/18/1/8786.
 Van Tac, V., 2020. Variability of sea surface chlorophyll_a concentration in the South Vietnam coastal waters related to enso phenomenon. Vietnam Journal of Earth Sciences, 42(1), 67–74. https://doi.org/10.15625/0866-7187/42/1/14759.
 Khanh, V. N. G., 2003. The People's Committee of Khanh Hoa province, Vietnam. Khanh Hoa Geography, 2003; Available from: https://en.khanhhoa.gov.vn/vi/introduction/natural-conditions; accessed 30/12/2020.
 NASA OBPG, NGSFC, Ocean Ecology Laboratory, Ocean Biology Processing Group. (2018). Moderate‐resolution Imaging Spectroradiometer (MODIS) Aqua Chlorophyll Data; 2018 Reprocessing. 23/06/2020.
 Enfield, D. B., 2020. El Niño. Available from: https://www.britannica.com/ science/El-Nino; accessed December 01, 2020; March 05, 2020.
 Boyer, T. P., Antonov, J. I., Baranova, O. K., Coleman, C., Garcia, H. E., Grodsky, A., Johnson, D. R. Locarnini, R. A., Mishonov, A. V., O’Brien,T. D., Paver, C. R., Reagan,J. R., Seidov, D., Smolyar, I. V., and Zweng, M. M., 2013. World Ocean Database 2013. Silver Spring, MD, National Oceanographic Data Center, 208 p. (NOAA Atlas NESDIS, 72). Doi: https://doi.org/10.25607/OBP-1454.
 Van Lanh, V., Quang, P., Van Tac, V., Khin, L. V., Tien, N. M., and Thanh, D. N., 2000. The oceanographic database of the South China Sea and adjacent waters. Collection of Marine Research Works, 10, 254–259.
 Golden Gate Weather Services, 2020. El Niño and La Niña Years and Intensities. Available from: http://ggweather.com/ enso/oni.htm; accessed Feburay 2020.
 Thuy, N., 2018. The floods that “attacked” the “capital” of Khanh Hoa tourism, Vietnam. 2018; Available from: https://anninhthudo.vn/doi-song/nhung-tran-lu-tung-tan-cong-thu-phu-du-lich-khanh-hoa/790541.antd; accessed 20/12/2020.