New insights into the application of the PIP25 index in the Arctic Ocean

Abstract

In this study we investigated suspended particulate matter (SPM) collected along a transect from the East Sea of Korea to the Bering Sea from 18 to 28 July in 2015, a multicore (ARA01B-3MUC) retrieved from the Chukchi shelf region, and a piston core (MD95-2009) taken from the Nordic Seas. We analyzed the samples for the Arctic sea ice proxy IP25 together with a tri-unsaturated highly branched isoprenoid (HBI triene) and two sterols (epi-brassicasterol and dinosterol) to assess the suitability of these compounds for the so-called PIP25 index in the Arctic region as a proxy for sea ice change in the past. Our results highlight that the use of HBI triene, epi-brassicasterol, and dinosterol, as strict phytoplankton markers for the PIP25 index (i.e. PTIP25, PBIP25 and PDIP25, respectively), might result in misleading outcomes. Accordingly, our study highlights that more work is needed to better constrain the use of HBI triene, epi-brassicasterol, and dinosterol, as strict ice-free, open ocean phytoplankton biomarkers when applying the PIP25 index for reconstructing past sea ice changes.