Pollen transport to deep-marine environments: Considerations for reconstructing past vegetation from marine sediment cores

Abstract

Deep-marine sedimentary records provide a unique opportunity to investigate long-term vegetation changes in response to climate through pollen analysis. In contrast to pollen records from terrestrial sites which capture a local vegetation signature, deep-marine records typically capture a regional vegetation signature, with pollen often taking long and complex transport pathways before depositing on the seafloor. To use deep-marine pollen records to their full potential, we need to understand how pollen is reaching deep-marine sites and whether different transport processes (i.e. ocean currents or gravity flows) impact or bias the final palaeovegetation record. We compare three deep-marine pollen records from offshore eastern Aotearoa-New Zealand from different depths, proximities from land and sedimentary settings to understand whether these different factors influence the final palaeovegetation records. We focus on the glacial-interglacial transitions from Marine Isotope Stages 6-5 and 2-1, and present a new 135 ka pollen record from the turbidite-dominated sediment core IODP-U1520D. We find that pollen assemblages in the three cores show consistent changes over glacial-interglacial cycles, with pollen assemblages showing greater similarities in interglacial periods and varying during glacial periods. The general consistency in pollen assemblages is surprising given the vastly different nature of the three sediment cores and shows that deep-marine records, including fine-grained turbidite-dominated records from active margins, can yield reliable palaeovegetation records