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Subtropical coral reveals abrupt early-twentieth-century freshening in the western North Pacific Ocean
Geology
Vol. 37, No. 6, pp. 527-530, June 2009. doi:10.1130/G25581A.1
Thomas Felis1, Atsushi Suzuki2, Henning Kuhnert1,
Mihai Dima3,4, Gerrit Lohmann3, and Hodaka Kawahata2,5,6
1 MARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
2 Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8567, Japan
3 Alfred Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany
4 Department of Atmospheric Physics, Faculty of Physics, University of Bucharest, 77125 Bucharest, Romania
5 Graduate School of Frontier Sciences, University of Tokyo, Tokyo 164-8639, Japan
6 Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan
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ABSTRACT:
Instrumental climate observations provide robust records of global
land and ocean temperatures during the twentieth century. Unlike for
temperature, continuous salinity observations in the surface ocean
are scarce prior to 1970, and the magnitude of salinity changes
during the twentieth century is largely unknown. Surface ocean
salinity is a major component in climate dynamics, as it influences
ocean circulation and water mass formation. Here we present an
annually resolved reconstruction of salinity variations in the
surface waters of the western subtropical North Pacific Ocean
since 1873, based on bimonthly records of δ18O, Sr/Ca, and U/Ca
in a coral from the Ogasawara Islands. The reconstruction indicates
that an abrupt regime shift toward fresher surface ocean conditions
occurred between 1905 and 1910. Observational atmospheric data suggest
that the abrupt freshening was associated with a weakening of the
winds that drive the Kuroshio Current system and the associated
subtropical gyre circulation. We note that the abrupt early-twentieth-
century freshening in the western subtropical North Pacific precedes
abrupt climate change in the northern North Atlantic by a few years.
The potential for abrupt regime shifts in surface ocean salinity
should be considered in climate predictions for the coming decades.
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