Earth's position in relation to the sun influences the origin and intensity of precipitation

One important topic that is the focus of climate researchers worldwide is the hydroclimate - i.e. the totality of all long-term weather phenomena in a region that determine the amount of precipitation and humidity. As climate change progresses, the risk of hydroclimate extremes - both droughts and heavy rainfall events - is increasing. A study by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the MARUM - Centre for Marine Environmental Sciences in Bremen and Chilean universities is now looking into the palaeoclimatic past to reconstruct how the sources and distribution of precipitation have changed over time and which conditions have influenced this.

"We used sediment cores that were drilled for the international Ocean Drilling Project (ODP) off southern Chile in the early 2000s," explains Frank Lamy from the AWI, who took part in the ODP expedition at the time. "We compared these with sediment sequences further north off the southern edge of the Atacama Desert." During the investigation, the research team focussed primarily on the content of deuterium, a naturally occurring hydrogen isotope in land plants that is also deposited in marine sediments. "We know that different deuterium levels say a lot about the precipitation conditions in a region - about the amount and intensity of the precipitation, and even about the origin of the humidity from which the precipitation has formed," says Jérôme Kaiser from the IOW, lead author of the study.

The results show clear patterns for the sources of humidity and the amount of precipitation in the mid-latitude hydroclimate of the south-east Pacific: while in southern Chile it was mainly sub-Antarctic Western winds that brought precipitation, the rain in the mid-latitudes of Chile also came from the subtropics. The amount and origin of precipitation in the two regions from these sources is subject to significant fluctuations over the millennia. "Using the sediment cores, we have now been able to demonstrate these striking temporal fluctuations over the last 50,000 years for the first time," says Frank Lamy. These patterns correlate very well with the temporal cycles of the natural changes in the Earth's orbit around the sun and the Earth's orientation to the sun. Both orbital phenomena influence the 'tilt' of the earth in relation to the sun and thus the intensity of the solar radiation that reaches the various regions of the earth. And this in turn has consequences for the winds that transport humidity and rain.

"Although we have reconstructed changes in precipitation on geological time scales, we can draw important conclusions about possible future climate mechanisms," summarizes Frank Lamy. "The relative changes in subtropical and subantarctic precipitation sources are similar to present-day temporal patterns associated with the El Nino climate phenomenon in the tropical Pacific. Our data suggest that this connection of sub-Antarctic and subtropical climate patterns has fluctuated strongly in the past and this will be the case again especially in a globally warmer future."

Press release of IOW

Original publication:

J. Kaiser, E. Schefuß, J. Collins, R. Garreaud, J.-B. W. Stuut, N. Ruggieri, R. De Pol-Holz & F. Lamy (2024): „Orbital modulation of subtropical versus subantarctic moisture sources in the southeast Pacific mid-latitudes” Nat Commun 15, 7512), DOI: https://doi.org/10.1038/s41467-024-51985-4