RELIABILITY OF MULTITAXON, MULTIPROXY RECONSTRUCTIONS OF ENVIRONMENTAL CONDITIONS FROM ACCRETIONARY BIOGENIC SKELETONS

Abstract

Evaluation and quantification of climate change require data on subseasonal to daily environmental extremes from those periods before instrumental records were available. This study employs a high-resolution, multitaxon, multiproxy approach and analyzes how faithfully accretionary biogenic skeletons record environmental extremes. Six specimens of two bivalve mollusks (Chione fluctifraga, Mytella guyanensi) and one barnacle species (Chthamalus fissus) from a single habitat (northern Gulf of California, Mexico) were collected. Contemporaneous shell portions from these specimens were analyzed for shell growth rates (sclerochronology) and stable isotopes (δ18O, δ13C) and were compared to instrumental records. The results of these analyses included some significant observations. First, shell δ18O values overestimate winter temperatures and underestimate summer temperatures. Second, the actual diurnal temperature range is not recorded in the biogenic skeletons. Third, skeletal growth is biased toward a species-specific optimum growth temperature (24°-30.9°C. Therefore, higher sampling resolution will not necessarily capture actual environmental extremes. Despite measured temperature extremes of 37.8° and 4.5°C, none of the studied species recorded temperatures above 30.9° or below 12.2°C. Duration and timing of the annual growing period is species specific as well. Faster shell growth occurred at higher temperatures. Up to 58% (C. fissus) of the variability in shell growth can be explained by water temperature during growth. Contemporaneous trends in shell δ13C show a weak correlation with pigment concentration (R2 = 0.17). Higher levels of chlorophyll appear to increase shell production. rates. Our study highlights the difficulties inherent in using biogenic skeletons for the reconstruction of paleoenvironmental extremes and demonstrates the power and utility of multiproxy and multitaxon approaches. © 2006 by The University of Chicago. All rights reserved.