Fig. 2.
An ≈8,000 calyr B.P. record of δ15 N and δ13C values of Adélie penguin eggshell from Antarctica. (Upper) δ15N values of eggshell (n = 57 modern/historic and 51 fossil) organic matter dating back ≈8,000 cal yr B.P. compared with modern prey isotope values. Consistently high values persist until ≈200 years B.P., at which time they shift toward a diet with increasing amounts of krill. The spread in data at any given time persists into the modern, but the spread does not overlap significantly. Note that historic eggshell from Cape Evans collected from 1911 to 1917 also matches modern values, indicating that the isotopic shift had occurred by that time. (Lower) δ13C(CaCO3) values of eggshell (n = 77 modern/historic and 226 fossil) dating back >8,000 cal yr B.P. Note the change at ≈200 years B.P. to lower values that approach the isotope value of modern krill, similar to nitrogen. This shift is consistent with the nitrogen data away from our δ13C values of emerald rockcod [−18.8‰ Vienna Pee Dee Belemnite (VPDB)], icefish (−24.1‰ VPDB), and dragonfish (−24.1‰ VPDB) toward those of krill (−31.4‰ VPDB). The wide range in data at any given time is evidence of feeding variability (availability and dietary preference) between individuals. Note that historic eggshell from Cape Evans collected from 1911 to 1917 also matches modern values, indicating that the isotopic shift had occurred by that time.