| Anotation: | Anoxia and hypoxia can severely reduce ecosystem functioning and increase probabilities of species extinction. The effects of oxygen depletion on benthic communities can lead to preservation of laminated strata, small size of macrobenthic organisms, outbreaks of hypoxia-tolerant, opportunistic species, and high concentrations of organic matter. However, the preservability of benthic responses to anoxia or hypoxia in the fossil record will be low if, after the renewal of oxygen concentrations, recovery time for burrowing organisms is relatively long, the depth of bioturbation is relatively large, and/or background sedimentation rates are too slow so that post-event bioturbation will lead to high time averaging, i.e., stratigraphic mixing of hypoxia-tolerant species with hypoxia-sensitive species. The ratio of sedimentation to bioturbation intensity is one of the key variables determining the preservation potential of such events in the fossil record. In this project, we will provide constraints on the range of sedimentary and mixing conditions under which benthic responses to hypoxia or anoxia can be preserved, and thus improve the identifiability of anoxic or hypoxic crises in the fossil record. First, we will evaluate preservation potential of benthic abundance and size patterns responding to oxygen depletion in sediment cores from two continental shelves, including (1) the southern California Shelf and (2) the Adriatic Sea. Second, we will assess patterns in size and abundance of benthic communities in stratigraphic successions characterized by alternations of normoxic, hypoxic, and anoxic conditions in semi-enclosed basins from the Late Triasic, Early Jurassic, and Middle Miocene. We will investigate the scales of time averaging and burial and mixing rates in Holocene sediment cores, and spatial and temporal gradients in size, abundance, and growth rate of benthic groups in habitats with varying organic enrichment and oxygen concentrations in the fossil record.
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