TY - JOUR
T1 - Factors controlling isotopic composition of precipitation on Okinawa Island, Japan
T2 - Implications for paleoclimate reconstruction in the East Asian Monsoon region
AU - Uemura, Ryu
AU - Yonezawa, Nao
AU - Yoshimura, Kei
AU - Asami, Ryuji
AU - Kadena, Hisashi
AU - Yamada, Keita
AU - Yoshida, Naohiro
N1 - Funding Information:
We thank Aya Iwasaki (Okinawa Prefectural Institute of Health and Environment), Akira Tanahara, Hiroyuki Fujimura, Risei Matsumoto, Masashi Nakamoto (Univ. Ryukyus) for sampling and comments. This research was supported by the JSPS with a Grant-in-Aid for Scientific Research, Research Activity Start-up (22840035), and was partly supported by Yong Scientists (A) (24681005) and Young Scientists (B) (23740385) and the Rising Star Program for Subtropical Island Sciences, University of the Ryukyus.
PY - 2012/12/19
Y1 - 2012/12/19
N2 - Stable isotope ratios of oxygen (δ18O) and hydrogen (δD) in precipitation collected every week during 2008-2011, Okinawa, Japan, were analyzed. The data provide new isotope data for an oceanic island located at the eastern end of the East Asian subtropical monsoon region. The monthly averaged isotope ratio shows clear seasonal variations: lower values in summer and higher values in winter. A multiple regression model shows that the relation between the δ18O value, temperature, and precipitation amount is quantitatively similar to that found in southern China region. To elucidate factors underlying isotope seasonality, we analyzed observation results using a dataset from an isotope-incorporated Atmospheric General Circulation Model. Our analyses revealed that the East Asian Monsoon causes strong seasonal differences of moisture sources for precipitation and the water budget in the island. In winter, moisture is recharged substantially in the East China Sea because a dry air mass from the continent flows over a warm ocean current: the Kuroshio Current. The precipitation is the first condensation from the air mass, resulting in higher isotope values of precipitation. In summer, lower δ18O of precipitation results from the convergence of water vapor whose isotope ratios are depleted because of large amount of condensation from the vapor source. The vapor source of such summer precipitation with low δ18O values is expected to be a low latitude ocean: the Western Pacific Warm Pool. Overall, the results suggest that the seasonality of the isotope ratio is controlled by the strength of distillation from moisture source to the precipitation site. These results provide a basis for interpretation of the past climate record preserved in stalagmites and tree rings in this region, and underline the need for the perspective of large-scale hydrological change for climate reconstruction.
AB - Stable isotope ratios of oxygen (δ18O) and hydrogen (δD) in precipitation collected every week during 2008-2011, Okinawa, Japan, were analyzed. The data provide new isotope data for an oceanic island located at the eastern end of the East Asian subtropical monsoon region. The monthly averaged isotope ratio shows clear seasonal variations: lower values in summer and higher values in winter. A multiple regression model shows that the relation between the δ18O value, temperature, and precipitation amount is quantitatively similar to that found in southern China region. To elucidate factors underlying isotope seasonality, we analyzed observation results using a dataset from an isotope-incorporated Atmospheric General Circulation Model. Our analyses revealed that the East Asian Monsoon causes strong seasonal differences of moisture sources for precipitation and the water budget in the island. In winter, moisture is recharged substantially in the East China Sea because a dry air mass from the continent flows over a warm ocean current: the Kuroshio Current. The precipitation is the first condensation from the air mass, resulting in higher isotope values of precipitation. In summer, lower δ18O of precipitation results from the convergence of water vapor whose isotope ratios are depleted because of large amount of condensation from the vapor source. The vapor source of such summer precipitation with low δ18O values is expected to be a low latitude ocean: the Western Pacific Warm Pool. Overall, the results suggest that the seasonality of the isotope ratio is controlled by the strength of distillation from moisture source to the precipitation site. These results provide a basis for interpretation of the past climate record preserved in stalagmites and tree rings in this region, and underline the need for the perspective of large-scale hydrological change for climate reconstruction.
KW - East asian monsoon
KW - Isotopic composition
KW - Okinawa
KW - Precipitation
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U2 - 10.1016/j.jhydrol.2012.10.014
DO - 10.1016/j.jhydrol.2012.10.014
M3 - Article
AN - SCOPUS:84870247598
VL - 475
SP - 314
EP - 322
JO - Journal of Hydrology
JF - Journal of Hydrology
SN - 0022-1694
ER -
