David H. Goodwin

Cross-Calibration of Daily Growth Increments, Stable Isotope Variation, and Temperature in the Gulf of California Bivalve Mollusk Chione cortezi: Implications for Paleoenvironmental Analysis

Abstract Annual-oxygen isotope profiles from two live-collected specimens of Chione cortezi Carpenter were analyzed in conjunction with daily growth-increment width profiles and high-resolution temperature records from the same site in the northern Gulf of California. The daily growth-increment profiles serve to date the deposition of the δ18O samples. Then the δ18O values were compared with high-resolution temperature records from the same site. Shell deposition began in late March or early April and ended in late November or early December. δ18O-derived estimates of the maximum and minimum temperature thresholds of growth agree well with those obtained from the dated increment width profile. Shell deposition in these two specimens of C. cortezi from the northern Gulf began when temperature warmed above ∼17°C and slowed or halted when temperature rose above ∼31°C. The temporal resolution of stable isotope samples varies throughout the year. Samples with the coarsest resolution (>3 weeks) were taken from parts of the shell deposited near the minimum and maximum temperature thresholds of growth. Higher resolution samples have intermediate δ 18O values and most represent less than five days of growth. Calculated temperatures from the dated oxygen-isotope samples are similar to observed temperatures. Differences reflect the effects of daily temperature variation, tidal emergence, and enrichment in δ18O of the water in which the clams grew. Stable oxygen-isotope samples used in conjunction with increment-width profiles can provide paleoenvironmental information at sub-weekly to sub-monthly resolution.

Resolution and Fidelity of Oxygen Isotopes as Paleotemperature Proxies in Bivalve Mollusk Shells: Models and Observations

Abstract Bivalve mollusks are biological chart recorders: their shells contain a record of environmental conditions in the form of geochemical variation. However, these records are often incomplete. Growth cessations and/or changing growth rates can reduce the range and resolution of the recorded environmental conditions. To investigate the effects of these variables on geochemical profiles, stable oxygen isotope (δ18O) profiles were modeled using several growth parameters. Two sets of profiles were calculated: one with constant daily increment widths, the other based on the annual pattern of daily increment width variation observed in the northern Gulf of California bivalve mollusk Chione cortezi. In both sets of models, multi-year δ18O profiles were calculated assuming that the bivalve shell grows continuously throughout its life. Other profiles were calculated to simulate an ontogenetic decrease in growth rate by decreasing the growth period, daily growth rate, or both. Altering the growth period simulates the effects of thermal thresholds, above or below which no shell material is deposited. Decreasing the daily growth rate results in lower annual shell growth rates while keeping the growth period constant. Combining the two provides a more accurate representation of bivalve shell growth in many subtropical and temperate species. In addition to the modeling exercise, the shell of a Chione cortezi that lived in the northern Gulf of California was sampled in two ways. First, low-resolution (300 micron) samples were recovered from the entire growth profile along the axis of maximum shell height (umbo to the commissure). Second, high-resolution (50 micron) samples were taken from regions of the shell representing winter growth from late in the bivalves life. Modeling results and observations indicate that the fullest range of environmental conditions only is reflected in the earliest years of growth; profiles from successive years have reduced amplitudes, sample resolutions, or both. Variation of intra-annual growth rate in models simulating continuous growth can produce cuspate δ18O profiles that mimic shutdowns. More detailed sampling in later stages of ontogeny can reconstruct a fuller range of environmental conditions. Finally, within-shell trends in isotopic amplitudes and averages may reflect decreases in growth rate rather than environmental fluctuations. Therefore, particular care should be taken when interpreting inter-annual isotope profiles from long-lived species.

Reconstructing daily temperatures from growth rates of the intertidal bivalve mollusk Chione cortezi (northern Gulf of California, Mexico)

Abstract We establish a model for the reconstruction of average daily sea surface temperatures from calcification rates of an intertidal bivalve mollusk. The rate of shell production in Chione cortezi (Carpenter, 1864, ex Sloat MS) is mainly controlled by water temperature, ontogenetic age and the effect of tidal cycles. Statistical methods developed by dendrochronologists can successfully extract the water temperature signal from daily growth increment chronologies. After removal of noise, the growth rates are expressed as scaled daily growth indices. Average daily water temperatures during the first half of the year are highly correlated with the scaled daily growth index values of recent and subrecent specimens, using the multi-valued function presented here. Increment width analysis can reconstruct daily average water temperatures with a mean error of less than 3%. This technique provides an independent method for reconstructing temperatures in fossil specimens of species with living representatives and can supplement high-resolution temperature reconstructions based on geochemical analysis.

Upstream dams and downstream clams: Growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico)

We studied how the extensive diversion of Colorado River water, induced by dams and agricultural activities of the last 70 years, affected the growth rates of two abundant bivalve mollusk species (Chione cortezi and Chione fluctifraga) in the northern Gulf of California. Shells alive on the delta today (Post-dam shells) grow 5.8–27.9% faster than shells alive prior to the construction of dams (Pre-dam shells). This increase in annual shell production is linked to the currently sharply reduced freshwater influx to the Colorado River estuary. Before the upstream river management, lower salinity retarded growth rates in these bivalves. Intra-annual growth rates were 50% lower during spring and early summer, when river flow was at its maximum. Growth rates in Chione today are largely controlled by temperature and nutrients; prior to the construction of dams and the diversion of the Colorado River flow, seasonal changes in salinity played an important role in regulating calcification rates. Our study employs sclerochronological (growth increment analysis) and geochemical techniques to assess the impact of reduced freshwater influx on bivalve growth rates in the Colorado River estuary. A combination of both techniques provides an excellent tool to evaluate the impact of river management in areas where no pre-impact studies were made. 2003 Elsevier Ltd. All rights reserved.

Reliability of Multitaxon, Multiproxy Reconstructions of Environmental Conditions from Accretionary Biogenic Skeletons

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 ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Evolutionary origins of novel conchologic growth patterns in tropical American corbulid bivalves

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The organic carbon isotopic and paleontological record across the Triassic–Jurassic boundary at the candidate GSSP section at Ferguson Hill, Muller Canyon, Nevada, USA

\end{document} ). 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.

Sclerochronology and Growth of the bivalve mollusks Chione (Chionista) fluctifraga and C. (Chionista) cortezi in the northern Gulf of California, Mexico

Abstract Stable oxygen- and carbon-isotope profiles from recent specimens of the exotic oyster Crassostrea gigas collected in southern San Francisco Bay were analyzed in conjunction with in situ records of environmental variability to determine the timing of the initial biological invasion and the number of annual cohorts present. Two distinct patterns of isotopic (18O/16O and 13C/12C) variation were identified. The first, found in specimens collected alive from two sites in 2006, is characterized by several unique features that correlate with predicted oxygen-isotope values calculated from temperature and salinity measurements and with records of phytoplankton blooms, indicating that these oysters were recruited at the end of 2001 or early in 2002. The isotope profiles from other specimens differ from these, and do not show evidence of significant environmental events that occurred in 2003, 2004, and 2006, despite the fact that some of these oysters were also collected alive in 2006. These oysters were likely recruited between 1998 and 2000, based on shell growth rates estimated with the von Bertalanffy growth function and on the record of phytoplankton blooms. Poor resolution due to slowed shell growth associated with senescence probably accounts for the absence of the 2003–2006 environmental events in these shell isotope records. These findings indicate that at least two cohorts of C. gigas settled in San Francisco Bay in recent years. That two successful recruitment events occurred over a relatively short time suggests that further recruitment may occur. Such studies as the one conducted here can potentially be used to identify favorable environmental conditions or circumstances associated with past biological invasions as well as those likely to come.