T58 Divided Oceans and Connected Continents: Advances in Geology and Paleontology of the Tropical Americas II

Sunday, 4 November 2012
1:30 PM - 5:30 PM
218AB

STABLE ISOTOPE PROFILING IN MODERN MARINE BRYOZOAN COLONIES ACROSS THE ISTHMUS OF PANAMA

Paper number: T58-13
Program: Technical Sessions
Time: 4:35 PM – 4:50 PM

Authors

Abstract

In the tropics, upwelling of cold, deep water is the only source of major seasonal fluctuations in temperature. Along the equatorial Pacific coast of the Isthmus of Panama, for example, upwelling drives seasonal drops in temperature. The strength of upwelling is regulated by trade wind direction and the elevation of the Isthmus, so that upwelling does not occur along the Caribbean coast of the Isthmus. The geological history of upwelling in the region is therefore of great interest because it relates to the closure of the Central American Seaway and the paleogeography of the protoisthmus, as well as the evolution of biological communities. Our goal was to test the use of stable isotope profiling in free-living cupuladriid bryozoans as a method for quantifying paleo-upwelling. We analyzed C and O stable isotopes from micromilled carbonates profiled along the line of growth in three modern colonies of Cupuladria exfragminis near Isla San Jose, Archipelago de Las Perlas, in the upwelling Gulf of Panama in the northeastern equatorial Pacific and three modern colonies of C. surinamensis (var. gigante) from the non-upwelling Almirante Bay, Bocas del Toro Archipelago, in the southwestern Caribbean. The colonies came from 10-23 m water depth. The number of micromill paths for each of the 16-22 mm diameter colonies ranged from 8 to 18 (mean: 14).

Pacific colonies had inter-colony δ18O values ranging from -2.1 to -0.2 (mean: -1.1) ‰ V-PDB, whereas Caribbean colonies ranged from -1.7 to -0.6 (mean: -1.1) ‰ V-PDB. Using published values for the isotopic compostion of the seawater on each side of the isthmus, we calculated temperatures of 19-26°C in the Pacific and 28-31°C in the Caribbean. These estimates accurately reflect observed temperatures, and Pacific colonies consistently reveal cyclical trends in δ18O that presumably reflect seasonal upwelling. Such cyclical trends are absent in the Caribbean colonies. This approach therefore has considerable potential for inferring patterns in seasonal upwelling during the history of the Isthmus of Panama, especially given the great abundance of well-preserved fossil cupuladriid bryozoans from before, during, and after the rise of the Central American Isthmus.