Trace fossils evidence of a complex history of nutrient availability and oxygen conditions during Heinrich Event 1

Abstract

The relationship between the behavior of tracemakers and paleoenvironmental conditions has been shown to be a useful tool in paleoceanographic studies. Here we present a detailed ichnological analysis of Heinrich Event 1 (H1), the youngest glacial North Atlantic large iceberg discharge, from Integrated Ocean Drilling Program Site U1308 in the central North Atlantic, located 2800 km from the mouth of the Hudson Strait. The ichnoassemblage consists of small trace fossils such as Phycosiphon, “Mycellia”/Trichichnus and Chondrites, and large ones including Planolites and Thalassinoides. The bioturbation index is generally low, from no bioturbation, to 30% of total bioturbated surface. Significant variations in composition, diversity and abundance of trace fossils are recorded, associated with the dual nature of H1 (comprising H1.1 and H1.2) and the period intervening between the two. Bottom- and pore-water oxygenation and benthic food availability are found to be the main limiting conditions for the tracemaker community, with some variations during the time span of H1, while factors such as sea water temperature had a minor impact.