  In this paper we report direct measurement of large low frequency temperature
fluctuations in double stranded (ds) DNA when it undergoes thermal denaturation
transition. The fluctuation, which occurs only in the temperature range where
the denaturation occurs, is several orders more than the expected equilibrium
fluctuation. It is absent in single stranded (ss) DNA of the same sequence. The
fluctuation at a given temperature also depends on the wait time and vanishes
in a scale of few hours. It is suggested that the large fluctuation occurs due
to coexisting denaturated and closed base pairs that are in dynamic equilibrium
due to transition through a potential barrier in the scale of
25-30k_{B}T_{0}(T_{0}=300K).
