Mid-latitude interhemispheric hydrologic seesaw over the past 550,000 years

Tropical and subtropical speleothems show that the latitudinal migration of the Intertropical Convergence Zone tends to produce increased precipitation in one hemisphere and drying in the other; now it is shown using speleothems from the Korean peninsula that this phenomenon extended to the mid-latitudes during the past 550,000 years. North–south wet–dry climate see-saw confirmed Prior research on tropical and subtropical speleothems — cave formations such as stalactites and stalagmites — has shown that the latitudinal (north/south) migration of the Intertropical Convergence Zone (ITCZ) tends to produce increased precipitation in one hemisphere, while the other hemisphere becomes dryer. It has been unclear whether this phenomenon extends to mid-latitudes, but now Kyung Sik Woo and colleagues show, in a study of speleothems from the Korean peninsula, that it does. The authors present a new record of the timing of peak speleothem growth for the past 550,000 years. An interhemispheric hydrologic seesaw—in which latitudinal migrations of the Intertropical Convergence Zone (ITCZ) produce simultaneous wetting (increased precipitation) in one hemisphere and drying in the other—has been discovered in some tropical and subtropical regions 1 , 2 , 3 . For instance, Chinese and Brazilian subtropical speleothem (cave formations such as stalactites and stalagmites) records show opposite trends in time series of oxygen isotopes (a proxy for precipitation variability) at millennial to orbital timescales 2 , 3 , suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics. This tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing 3 . The impacts of such an interhemispheric hydrologic seesaw on higher-latitude regions and the global climate system, however, are unknown. Here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid-latitude western Pacific Ocean. Our results are based on a new 550,000-year record of the growth frequency of speleothems from the Korean peninsula, which we compare to Southern Hemisphere equivalents 4 . The Korean data are discontinuous and derived from 24 separate speleothems, but still allow the identification of periods of peak speleothem growth and, thus, precipitation. The clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over th