High-resolution radiocarbon records trace episodes of Zoophycos burrowing

Abstract

The unknown Zoophycos-producing organism potentially reworks marine sediments far deeper (up to >1 m) than common bioturbational mixing of the topmost sediment layer. The Zoophycos producer displaces planktonic foraminifera tests down to deep sediment levels hence, may seriously bias the faunal and isotopic composition and in particular, the radiocarbon age (14C) of the ambient host sediment. Here we present three high-resolution 14C records from sediment cores retrieved at intermediate water depths off Brazil, New Zealand, and Norway where Zoophycos burrows have biased 14C ages by 1000–5000 years. Based on closely spaced 14C ages and 14C plateau tuning we distinguish particular episodes with enhanced Zoophycos production that coincide with time spans of decreased sedimentation and thus, with probably reduced benthic nutrition. Off New Zealand, the actual burrowing activity was dated close to the Bølling/Allerød–Younger Dryas boundary. Displaced grains are traced from the ancient sediment surface of the Younger Dryas as far back as to the onset of Heinrich Stadial 1 and the terminal Last Glacial Maximum. These displaced 14C ages and similar 14C records obtained from two other sediment cores suggest that Zoophycos producers generally mount a burrowing campaign during times when environmental conditions are switching toward a starved sedimentation regime. During these tipping points Zoophycos spreiten probably serve as storage space for nutrient-rich particles foraged at the sediment surface and bioturbational mixed layer.