Trace fossil characterization during Termination V and MIS 11 at the western Mediterranean: Connection between surface conditions and deep environment

Abstract

Trace fossil assemblages are studied at Ocean Discovery Program (ODP) Site 977 to characterize the response of the macrobenthic trace maker community to deep paleoenvironmental conditions during the Termination V (TV) and interglacial Marine Isotope Stage (MIS) 11 at the western Mediterranean Alboran Sea. An assemblage composed of Chondrites, Planolites, Scolicia, Thalassinoides and Zoophycos is identified, showing notable variations in ichnodiversity, abundance and Bioturbation Index, that were analyzed in detail. The integration of ichnological information with sediment color and high-resolution coccolithophore records from Site 977, evidenced that variations in macrobenthic trace maker community are primarily controlled by oxygen availability and surface organic productivity patterns. During TV, high surface organic productivity by intense Alboran Upwelling System enhanced the deep organic accumulation that, together with reduced deep-water removal, resulted in a decrease of bioturbation and the formation of an Organic Rich Layer. Moderate and stable surface production through MIS 11c reduced deep food availability, resulting in an oligotrophic and stable deep environment. This is reflected by relatively abundant trace fossils in lighter sediments. Intra-interglacial increase in surface organic production at ~405 ka is evidenced by increased organic matter preservation. Minor impact of western Mediterranean circulation on deep-water removal, but a plausible stronger control by Bernoulli aspiration intensities in the region, is, in overall, observed during these intervals. During the Heinrich-type (Ht) events 3 and 2, increased trace fossil diversity and ameliorated oxygenation is driven by limited surface organic production, but intense western Mediterranean deep-water circulation and enhanced regional deep-water removal.