Individual to Community-Level Faunal Responses to Environmental Change from a Marine Fossil Record of Early Miocene Global Warming

Abstract

Modern climate change has a strong potential to shift earth systems and biological communities into novel states that have no present-day analog, leaving ecologists with no observational basis to predict the likely biotic effects. Fossil records contain long time-series of past environmental changes outside the range of modern observation, which are vital for predicting future ecological responses, and are capable of (a) providing detailed information on rates of ecological change, (b) illuminating the environmental drivers of those changes, and (c) recording the effects of environmental change on individual physiological rates. Outcrops of Early Miocene Newport Member of the Astoria Formation (Oregon) provide one such time series. This record of benthic foraminiferal and molluscan community change from continental shelf depths spans a past interval environmental change (∼20.3-16.7 mya) during which the region warmed 2.1–4.5°C, surface productivity and benthic organic carbon flux increased, and benthic oxygenation decreased, perhaps driven by intensified upwelling as on the modern Oregon coast. The Newport Member record shows that (a) ecological responses to natural environmental change can be abrupt, (b) productivity can be the primary driver of faunal change during global warming, (c) molluscs had a threshold response to productivity change while foraminifera changed gradually, and (d) changes in bivalve body size and growth rates parallel changes in taxonomic composition at the community level, indicating that, either directly or indirectly through some other biological parameter, the physiological tolerances of species do influence community change. Ecological studies in modern and fossil records that consider multiple ecological levels, environmental parameters, and taxonomic groups can provide critical information for predicting future ecological change and evaluating species vulnerability.

Stratigraphic and environmental control on marine benthic community change through the early Toarcian extinction event (Iberian Range, Spain)

“…The study sites were selected because they record deposition at different water depths along an onshore-offshore gradient of the western Tethyan shelf, which enables us to better understand the role of sedimentary and stratigraphic processes on the distribution of fossils through the extinction event (i.e., Holland 2000;, Nawrot et al 2017. Furthermore, the presence of both bivalves and brachiopods at both study sites (Comas-Rengifo et al 1988;, enables us to test whether these different taxonomic groups responded differently to the same event and/or to the same environmental drivers or not, providing a test of the generality of faunal responses (e.g., Belanger 2012;Danise et al 2015). For this purpose, faunal data were integrated with high-resolution geochemical proxies on the bulk rock (TOC, δ 13 C, δ 18 O) and on calcitic brachiopod and belemnite shells (δ 13 C, δ 18 O), to test for possible correlations between biotic and environmental change.…”

The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)

“…Data from the largest temporal, spatial and ecological scales can, however, be sourced from the fossil record, which provides an archive of natural data from a number of past episodes of climatic and environmental change [10]–[12]. A detailed fossil record with good temporal resolution that spans past climate change events can help in forecasting future ecosystem changes, especially if predicted climate changes move outside the parameters experienced by modern ecosystems and into regimes known only from the deeper geological record [13].…”

Differential drivers of benthic foraminiferal and molluscan community composition from a multivariate record of early Miocene environmental change

“…In addition, sediments younger than ca. 18.20 Ma are well laminated, suggesting that dysoxic conditions developed in the benthos (Belanger 2011a). Strata older than ca.…”

“…We used a combination of lithostratigraphic comparisons and Sr-isotope ages derived from molluscan aragonite to correlate stratigraphic sections (Belanger 2011a). Each stratigraphic unit is assigned an age based on 12 Sr-isotope measurements across~80 m of unique section and an assumption of constant sedimentation rates between ages within the same stratigraphic section.…”

“…Previous paleoecological work in the Newport Member recognized three benthic foraminiferal and three molluscan communities by using a maximum likelihood approach for finding abrupt temporal shifts in community metrics (Belanger 2012). Organic carbon flux was identified as having the greatest relationship to foraminiferal faunal change (Belanger 2012).…”