5:15 PM - 7:15 PM
[ACG52-P07] Revaluation of sea-ice proxies using IP25 in the Chukchi Sea
Keywords:sea ice, biomarker, Chukchi Sea
Reconstruction of sea ice change in the past is important to evaluate retreat of sea ice in the Arctic Ocean at the recent. HBIs (highly branched isoprenoidal alkenes) originated from diatoms have differences in position and number of C=C bonds related to their living environments. IP25 is monounsaturated HBI biosynthesized by diatom genus Haslea and useful to reconstruct sea ice in the past. Especially, sediments deposited under ice edge and/or seasonal sea-ice have higher concentrations of IP25 (Vare et al., 2008). Müller et al. (2011) suggested sea-ice proxies, named as PIP25, using IP25 and other phytoplankton biomarkers. PIP25 values vary among sediments deposited under ice-free, seasonal ice and multi-year ice. Especially, PBIP25 using brassicasterol (diatom/haptophyta) and PDIP25 using dinosterol (dinoflagellate) have relationships with changes in sea-ice volume at the recent from satellite data (Kolling et al., 2020). In this study, we revaluated sea-ice proxies including PIP25 using surface sediments collected from the Chukchi Sea.
We used surface sediment samples along a latitudinal transect were collected around the Chukuchi Sea by R/V Mirai Expeditions in 2012 and 2020. IP25 were detected from 3 samples deposited around 73°N located nearby ice edge in the summer season. On the other hand, diunsaturated HBI-II were detected at lower latitudes than 73°N. These results are consistent with previous researches. PBIP25 and PDIP25 have similar values between samples collected in 2012 and 2020. In addition, we suggested new proxies using n-C21 alkane and HBI-II. The values of new proxies were lower in samples collected in 2012 compared with those in 2020. These proxies were possibly influenced by short-term changes in sea-ice. In fact, in the summer season, the ice edge was located farther north in 2011 than in 2019. Moreover, dinosterol/brassicasterol ratios, showing dinoflagellate productivity, are higher in the samples without both IP25 and HBI-Ⅱ. One of those was deposited under marginal ice zone in which dinoflagellate have higher percentage among eukaryotes. Other two samples were deposited nearby the Hope Valley, characterized by higher organic matter concentration enhanced by high productivity, in which heterotrophic dinoflagellate possibly flourished. Therefore, comparisons between sea-ice proxies and other proxies using algal biomarkers have the potential to evaluate variations in the main primary producers in specific areas of the Arctic Ocean in detail.
We used surface sediment samples along a latitudinal transect were collected around the Chukuchi Sea by R/V Mirai Expeditions in 2012 and 2020. IP25 were detected from 3 samples deposited around 73°N located nearby ice edge in the summer season. On the other hand, diunsaturated HBI-II were detected at lower latitudes than 73°N. These results are consistent with previous researches. PBIP25 and PDIP25 have similar values between samples collected in 2012 and 2020. In addition, we suggested new proxies using n-C21 alkane and HBI-II. The values of new proxies were lower in samples collected in 2012 compared with those in 2020. These proxies were possibly influenced by short-term changes in sea-ice. In fact, in the summer season, the ice edge was located farther north in 2011 than in 2019. Moreover, dinosterol/brassicasterol ratios, showing dinoflagellate productivity, are higher in the samples without both IP25 and HBI-Ⅱ. One of those was deposited under marginal ice zone in which dinoflagellate have higher percentage among eukaryotes. Other two samples were deposited nearby the Hope Valley, characterized by higher organic matter concentration enhanced by high productivity, in which heterotrophic dinoflagellate possibly flourished. Therefore, comparisons between sea-ice proxies and other proxies using algal biomarkers have the potential to evaluate variations in the main primary producers in specific areas of the Arctic Ocean in detail.