Community benthic paleoecology from high-resolution climate records: Mollusca and foraminifera in post-glacial environments of the California margin

Abstract

Paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence. Less is known about the relationship between multi-taxon community-wide change and climate variability. Here we reconstruct paleoecological change in a Late Quaternary (16.1-3.4 ka) sediment core from the California margin (418 meters below sea level) of Santa Barbara Basin (SBB), USA, using Mollusca (Animalia) and Foraminifera (Rhizaria) microfossils. Building upon previous investigations, we use multivariate ordination and cluster analyses to interpret community-scale changes in these distinctly different taxonomic groups across discrete climate episodes. The strongest differences between seafloor biological communities occurred between glacial (prior to Termination IA, 14.7 ka) and interglacial climate episodes. Holocene communities were well partitioned, indicating that sub-millennial oceanographic variability was recorded by these microfossils. We document strong evidence of chemosynthetic trophic webs and sulfidic environments (from gastropod Alia permodesta and bivalve Lucinoma aequizonata), which characterized restricted intervals previously interpreted as well oxygenated (such as the Pre-Bølling Warming). Mollusc records indicate first-order trophic energetic shifts between detrital and chemosynthetically-fixed carbon. Molluscs associated with widely different physiological preferences occur here within single, decadal intervals of sediment, and as such mollusc assemblages may reflect significant inter-decadal oceanographic variability. Foraminifera assemblages provide exceptional records of the sequential, chronological progression of the deglacial climatic and oceanographic events, whereas mollusc assemblages reflect non-chronological similarities in reoccurring communities.Foraminifera taxa that drive community similarity here are also independently recognized

Benthic Biotic Response to Climate Changes Over the Last 700,000 Years in a Deep Marginal Sea: Impacts of Deoxygenation and the Mid‐Brunhes Event

“…This observation in the Sea of Japan ostracode fauna is similar with the benthic foraminiferal faunal succession related to Mediterranean deoxygenation, especially the sapropel S1 in intermediate water depths (Jorissen, 1999). The biotic history reconstructed here suggests a general implication on the climatic sensitivity of deep-sea ecosystems in marginal seas (e.g., the Sea of Japan and Mediterranean Sea; this study, and references herein) and oceanic basins (Cannariato et al, 1999;Moffitt et al, 2015;Myhre et al, 2017) characterized by the periodic oxygen depletion. 2.…”

Climate and Anthropogenic Controls of Coastal Deoxygenation on Interannual to Centennial Timescales

“…At~1840 Macoma bivalve shells were found preserved in situ (Schimmelmann et al, 1992). These bivalves are intolerant of hypoxia (<65 μmol/kg) (Coan, 2000;Myhre et al, 2017), indicating a relatively well-oxygenated benthic environment existed for <3 years. Less reducing sedimentary conditions at this time may have been attributed to the abrupt deposition of a seismically triggered turbidite in 1812 (Borrero et al, 2001).…”

“…Measurements by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) indicate persistent low-oxygen concentrations (typically <20 μmol kg À1 ) in the bottom water of central SBB. This low-oxygen environment is inhospitable for most benthic megafauna and macrofauna (notably burrowing organisms) except the sediment surface-dwelling gastropod Alia permodesta (Bernhard et al, 2000;Bernhard et al, 2003;Myhre et al, 2017), preserving the seasonally distinct varved laminations for high-resolution reconstructions (Schimmelmann et al, 1990). With a sill depth of~450 m to the west, bottom water in the basin is either supplied from the California Undercurrent (CUC) (Bograd et al, 2008;Lynn & Simpson, 1990;Nam et al, 2015) or "flushing events"-uplifted cold intermediate water (Auad et al, 2003) that flush SBB when dense subsurface waters displace more buoyant water in the basin (Bograd, 2002).…”

Millennial‐Scale Age Offsets Within Fossil Assemblages: Result of Bioturbation Below the Taphonomic Active Zone and Out‐of‐Phase Production

“…Continental shelf sediments are valuable archives of oceanographic and biological history that allow inferences about the timing and causes of changes in climate, productivity, and seawater chemistry (Birks & Koç, ; Keigwin & Jones, ; Knies et al, Kobashi et al, ) and about evolutionary and ecological dynamics (e.g., Myhre et al, ; O'Dea et al, ; Pandolfi, ). However, as in pelagic sediments, bioturbational mixing by diffusion or advection increases time averaging (i.e., age offsets among co‐occurring individuals and species) of fossil assemblages and can alter the distribution of species in stratigraphic successions, thereby modifying community composition, co‐occurrence patterns, patterns of first and last appearances, and turnover rates (Alegret et al, ; Anderson et al, ; Lazarus et al, ; MacLeod & Huber, ; Nawrot et al, ; Tomašových & Kidwell, ).…”