Intra-annual variations of teak cellulose δ18O in Kerala, India: implications to the reconstruction of past summer and winter monsoon rains

A seasonal cycle has been observed in the high and coarse resolution intra-annual analyses of oxygen isotopic composition (δ 18 O) of teak ( Tectona grandis ) cellulose from southern India, that receives both the south-west (SW) (summer) and the north-east (NE) (winter, more depleted in 18 O) monsoon rains. The seasonal cycle as recorded by teak, with an amplitude between 1 and 3‰, shows lower δ 18 O values at the early and late growing seasons than at the middle. This pattern is opposite to that found in central Indian teak, nurtured mostly by the SW monsoon rain. A comparison of the observed and modeled intra-annual profiles reveals that the observed pattern of intra-annual δ 18 O variation in southern India is explainable only if teak trees had sampled rainfall from both the monsoons. Thus it appears possible to detect years of past excess NE monsoon rains by analyzing the δ 18 O of cellulose from the latewood of teak trees growing in Kerala, southern India.