Verified answer

δ13C means "delta C-13" which refers to a change (delta) in the levels of the isotope carbon-13. Normally the isotopes of the naturally occurring elements maintain a relatively constant ratio. This is the basis for the computation of average atomic weights (the values printed on periodic tables).

But some isotopic ratios have not been constant over geologic time, and that is the case with C-12 and C-13, the two naturally occurring, stable isotopes of carbon that are found in methane. The isotopic ratio in methane depends in part on the organisms that contributed to the formation of the methane.

Methane clathrate is an undersea formation where ice molecules trap methane molecules. The methane-ice, as it is sometimes called, is trapped under sediments on the ocean floor. On the plus side, It may be an important source of energy. But on the negative side, the natural release of methane, a "greenhouse gas," may accelerate global warming.

To find out more about methane clathrates, start here: https://en.wikipedia.org/wiki/Methane_clathrate#Oc...