OXYGEN STABLE ISOTOPE ANALYSES ON AMEGHINOMYA ANTIQUA SHELLS: A PROMISING TOOL FOR PALAEOENVIRONMENTAL RECONSTRUCTION ALONG THE QUATERNARY PATAGONIAN ARGENTINA COAST?

GABRIELLA BORETTO 1 1, 2 , ILARIA CONSOLONI 3 , GISELA ARIANNA MORÁN 1, 2 , ELEONORA REGATTIERI , SANDRA GORDILLO 1, 2 , ENRIQUE FUCKS 5 , GIOVANNI ZANCHETTA 3, 5 , LUIGI DALLAI

Alpine and Mediterranean Quaternary

AIQUA - Italian Association for Quaternary Research

Año: 2019 vol. 32 p. 1 - 16

2279-7327

There are only a few data concerning the Quaternary climate fluctuations in the marine environments of the AtlanticPatagonian coast. In this regard, the aragonitic shell of the Ameghinomya antiqua bivalve offers the possibility to study the climatevariability and the seasonal cycles of sea water temperature in the region at different geological times. We compared oxygen isotopicprofiles along the shell-growth axis on four well-preserved A. antiqua bivalves collected from marine coastal deposits of MarineIsotope Stage (MIS) 7, MIS 5, Holocene (7.284 ±140 yr cal BP), and from the present-day active beach of Bahía Bustamante(Patagonia Argentina). Shell ontogeny was determined through the annual growth lines recorded along the external region of theshell, and was also verified by cross-section analyses. The fossil bivalves were around 15 years old, while the Present day shellwas 10 years old. When the modern climatic data available are compared, the higher δ18Oshell values represent the cold season,while the lower δ18Oshell values indicate the warm season. The δ18Oshell ranges indicate different environmental conditions and seasonaltemperature variations between specimens. By assuming, a constant δ18Ow calculated with the limited environmental dataavailable, superficial seawater temperatures are estimated from the specimens. These paleotemperatures may overestimate watertemperatures, and shell formation seems to occur with an offset from expected oxygen isotopic equilibrium with the water in whichthey lived. Meanwhile, A. antiqua shells are suitable bioarchives for the comparison of seasonal patterns throughout the Quaternary,thus constituting another proxy for the evaluation of paleoclimatic and paleoenvironmental changes in the Patagonia region.