Testing ecological and environmentalchanges during the last 6000 years: a multiproxi approach based on the bivalve Tawera gayi from southern South America

GORDILLO S., MARTINELLI J., CÁRDENAS J., BAYER M.S.

JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM

CAMBRIDGE UNIV PRESS

Lugar: Cambridge; Año: 2011 p. 1 - 15

0025-3154

This paper evaluates if the bivalve Tawera gayi from southern South America represents an opportunity to test ecologicalvariability and environmental changes during the last 6000 years in southern South America. For this purpose, weanalyse both modern and fossil (mid-to-late Holocene) T. gayi shells from Tierra del Fuego using different techniques, includingtaphonomy, stable isotopes, cathodoluminiscence (CL) and linear morphometrics. Taphonomic analysis shows that differencesbetween modern and fossil shells appear best related to local variations of physical factors such as current speed, waveaction and freshwater input along the non-uniform Beagle Channel coast. However, slight changes of hydraulic energyregimes throughout the Holocene cannot be ruled out. The analysis of stable isotopes on T. gayi shells indicates a mixingof oceanic waters with freshwater from precipitation, river runoff and glacier meltwater during the mid-to-late Holocene.The high depletion of d18O at 4400 years before present would be associated with a period of warmer temperatures, theso-called Hypsithermal. Under CL modern and fossil T. gayi shells show a well defined pattern related to the growth dynamicsof the shell, which can lead to a better understanding of its biology, adding details to further palaeoenvironmental analysis.Finally, conventional metrics shows that fossil T. gayi shells are smaller and shorter than modern shells. These differencescould be related to Holocene environmental changes, but here are best explained on the basis of a predator–prey relationship.This study shows that T. gayi may be a good candidate for looking at evidences of environmental changes in southern SouthAmerica, and multi-proxy data are necessary to better understand the driving mechanisms of ecological variability andchanges over short geological time intervals of few thousands of years.