What controls precipitation δ18O in the southern Tibetan Plateau at seasonal and intra-seasonal scales? A case study at Lhasa and Nyalam

Jing Gao,Valerie Masson-Delmotte,Camille Risi,You He,Tandong Yao

doi:10.3402/tellusb.v65i0.21043

Abstract

Understanding the spatial and temporal controls of precipitation δ18O in the southern Tibetan Plateau of central Asia is necessary for paleoclimate reconstructions from the wealth of regional archives (ice cores, lake sediments, tree ring cellulose, and speleothems). While classical interpretations of such records were conducted in terms of local precipitation, simulations conducted with atmospheric general circulation models enabled with water stable isotopes have suggested that past changes in south Asia precipitation δ18O may be driven by remote processes linked to moisture transport. Studies conducted at the event scale can provide constraints to assess the drivers of precipitation δ18O and the validity of simulated mechanisms. Here, we take advantage of new event precipitation δ18O monitored from January 2005 to December 2007 at two southern Tibetan Plateau stations (Lhasa and Nyalam). The drivers of daily to seasonal variations are investigated using statistical relationships with local and regional temperature, precipitation amount and convective activity based on in situ data and satellite products. The strongest control on precipitation δ18O at Lhasa during the monsoon season at event and seasonal scales is provided by the integrated regional convective activity upstream air mass trajectories, cumulated over several days. In contrast, the integrated convection appears to be the main driver of precipitation δ18O at Nyalam only in July and August, and the situation is more complex in other months. Local climate variables can only account for a small fraction of the observed δ18O variance, with significant differences between both stations. This study offers a better constraint on climate archives interpretation in the southern Tibetan Plateau. The daily data presented here also provides a benchmark to evaluate the capacity of isotopically enabled atmospheric general circulation models (iGCMs) to simulate the response of precipitation δ18O to convection. This is illustrated using a nudged and zoomed simulation with the LMDZiso model. While it successfully simulates some seasonal and daily characteristics of precipitation δ18O in the southern Tibetan Plateau, it fails to simulate the correlation between δ18O and upstream precipitation. This calls for caution when using atmospheric models to interpret precipitation δ18O archives in terms of past monsoon variability.

Highlights

Records of precipitation d18O in natural archives provide key paleoclimate information in mid and low latitudes
Taking advantage of several years of event precipitation sampling at two southern Tibetan Plateau (TP) stations, we have investigated the meteorological drivers of precipitation d18O at seasonal and intra-seasonal scales
While a local amount effect is only evident for Lhasa at the event scale, local precipitation only accounts for a small fraction of d18O variability

Summary

Introduction

Records of precipitation d18O in natural archives provide key paleoclimate information in mid and low latitudes. Temperature-driven distillation effects dominate the variability of temperate to polar precipitation d18O, and were shown to be the main control on northern TP precipitation d18O (Yao et al, 1996; Thompson et al, 1997; Tian et al, 2001; Wang et al, 2003; Aizen et al, 2006). Some studies suggested that southern TP ice core d18O reflects long-term changes in regional temperature (Thompson et al, 2000; Aizen et al, 2006; Yao et al, 2006), while others interpreted the ice core data in terms of amount effect (the anti-correlation between d18O and local precipitation amount) and Indian monsoon intensity (Vuille et al, 2005; Zhang et al, 2005; Kaspari et al, 2007; Joswiak et al, 2010). Large uncertainties remain on the ability of these models to resolve correctly the processes controlling precipitation d18O, in particular convective processes (Bony et al, 2008; Lee et al, 2009; Vimeux et al, 2011)

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