There are no historical records of changing penguin populations in the maritime Antarctic^1,2. Here we analyse^3,4 the concentration of 'bio-elements' in a lake-sediment core dating back approximately 3,000 radiocarbon years. We found that the deposition of penguin droppings had a significant effect on the geochemical composition of the sediment core. Changes in sediment geochemistry reflect fluctuations in penguin numbers and suggest that variations in climate had an impact on penguin populations, which peaked somewhere between 1,400 and 1,800 years ago.

The relative importance of north–south migrations of the intertropical convergence zone (ITCZ) versus El Niño-Southern Oscillation and its associated Pacific Walker Circulation (PWC) variability for past hydrological change in the western tropical Pacific is unclear. Here we show that north–south ITCZ migration was not the only mechanism of tropical Pacific hydrologic variability during the last millennium, and that PWC variability profoundly influenced tropical Pacific hydrology. We present hydrological reconstructions from Cattle Pond, Dongdao Island of the South China Sea, where multi-decadal rainfall and downcore grain size variations are correlated to the Southern Oscillation Index during the instrumental era. Our downcore grain size reconstructions indicate that this site received less precipitation during relatively warm periods, AD 1000–1400 and AD 1850–2000, compared with the cool period (AD 1400–1850). Including our new reconstructions in a synthesis of tropical Pacific records results in a spatial pattern of hydrologic variability that implicates the PWC.

The risk of large, devastating tsunamis in the South China Sea and its surrounding coastal region is commonly underestimated or unrecognized due to the difficulty of differentiating tsunami from storm deposits. As a consequence, few convincing records have documented tsunami deposits in this region. Here we report preliminary evidence from Xisha Islands in the South China Sea for a large tsunami around AD 1024. Sand layers in lake sediment cores and their geochemical characteristics indicate a sudden deposition event around AD 1024, temporally consistent with a written record of a disastrous event characterized by high waves in AD 1076. Heavy coral and shell fossils, which are older than AD 1024, deposited more than 200 meters into the island, further support the occurrence of a high-energy event such as a tsunami or an unusually large storm. Our results underscore the importance of acknowledging and understanding the tsunami hazard in this area.