Paleoceanographic Productivity Reconstructions Using Marine Mammal Bone Collagen

Changes in primary ocean productivity play a key role in determining the structure and biomass yield of the North Pacific ecosystem. Archaeofaunal remains of marine mammals from the Aleutian Islands, Alaska were used as a proxy for marine productivity changes over decade, century and millennial scales throughout the Holocene. Marine vertebrate remains from several previously excavated, well-dated archaeological deposits on Unalaska Island span the period AD 1912-5500 BP. Stable carbon and nitrogen isotope ratios (δ13C and δ15N) derived from marine mammal bone and tooth collagen provide information about changes in food web dynamics and marine productivity levels and, through inference, about ecosystem changes. The paleorecord of phytoplankton production, in response to changes in atmospheric and oceanic fluctuations, is reflected in the stable isotope composition of the skeletal remains of these animals. An analysis of three hundred pinniped and cetacean individuals over the six thousand year period indicated a consistent inverse relationship existed between the two isotopes. A minimum of five time periods occurred when both stable isotopes changed from either a positive to negative slope or negative to positive slope.