Climate signals in oxygen isotopic tree-ring chronologies of Polylepis tarapacana from the South American Altiplano

MILAGROS RODRÍGUEZ-CATÓN; LAIA ANDREU HAYLES; MARIANO S. MORALES; DUNCAN A. CHRISTIE

San Francisco

Conferencia; AGU fall meeting; 2019

Trees of Polylepis tarapacana (queñoa) in the Southamerican Altiplano, are the highest elevation tree-ring archive worldwide growing up to 5200 m a.s.l. The rain that P. tarapacana forests receive in the Altiplano is of monsoon type, more intense during the austral summer season (December to March), coming mainly from the Amazon basin. An extensive network of P. tarapacana ring width (RW) chronologies, ranging from 16-22ºS and 67-69 ºW, have been used to reconstruct precipitation and drought variability for the last 700 years. The models for these reconstructions rely on the positive relationships between RW variations and previous summer-season precipitation. Current growth period responses are messier, since opposite sign (negative) correlations exists between RW and current summer-season precipitation. This contrasting pattern is also observed between growth and temperature, but inverse to the precipitation-growth response, being positive for the current and negative for the prior season of growth. Here, we analyzed the stable oxygen (δ18O) and carbon (δ13C) isotopic composition of tree-ring cellulose from P. tarapacana for the period 1950-2015 to provide physiological insights on how this tree is responding to climate variability. We generated isotopic tree-ring chronologies for four sites located along a 500km latitudinal gradient from 18 to 22ºS along the Chilean and Bolivian Altiplano. The δ18O records show similar positive (negative) response with temperature (precipitation) for both, the previous and the current summer season. These results demonstrate the consistency of the isotope response to climatic variations during previous and current growing seasons; and resolve the complex relationship between RW and climatic variables.Accordingly, the highest correlations between δ18O and precipitation were found from January to March and were negative reflecting more d18O depleted values in periods of higher monsoon intensity as has been described with other paleo records. The current year response to temperature embrace a longer season starting about October-December and ending in April. The comparison between the correlation functions and the dominant patterns of the three tree-ring proxies RW, δ18O and δ13C suggest differential influence of climate along the gradient possibly related to physiological processes associated with sugars production at leaf level, and starch accumulation and use.