Abstract
Stable isotope analyses (δ18O, δ13C) of Spirula spirula, a mesopelagic cephalopod with a loosely coiled internal calcareous (aragonitic) shell, suggest that δ18O is precipitated in equilibrium with the surrounding water, recording the temperature of the seawater inhabited by the animal through its life. The δ18O trends are interpreted to reveal a life that begins in deep waters characterized by cool temperatures before rising to warm surface waters to feed during its juvenile stage. Following this brief period in warmer waters, the isotopes suggest that the remainder of the organism's life is spent in progressively cooler (deeper) waters. The incorporation of isotopically light metabolic carbon, however, significantly affects the stable carbon isotope signal recorded in S. spirula, effectively obscuring the record of δ13C of seawater dissolved inorganic carbon archived in the shell carbonate. This may relate to the internal position of the shell, in which the growing margin is anchored in soft tissue and ...
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