HBIs and Sterols in Surface Sediments Across the East Siberian Sea: Implications for Palaeo Sea‐Ice Reconstructions

Abstract

Since the beginning of the twentieth century, the global ocean has undergone unprecedented changes caused by global warming (Gillett et al., 2021;Stocker et al., 2013). These changes are notably pronounced in the Arctic region due to polar amplification with major consequences for sea-ice cover and the thermohaline circulation (Cavalieri et al., 1997;Shindell & Faluvegi, 2009). The Arctic Ocean and its marginal seas are characterized by large seasonal sea-ice changes. Melting in summer and sea-ice formation in winter, including coastal polynyas, through the production of cold and saline waters, alter deep-water formation and subsequently the Arctic Ocean circulation (Arrigo, 2014;Cai et al., 2010;Overland & Wang, 2013;Xiao et al., 2013). At the current rate of decline (0.42% year −1 ), the Arctic Ocean may be ice-free in summer season in the next 50 or even 30 years (Comiso, 2012;Wang et al., 2019), which will profoundly impact the global climate and carbon cycle and further accelerate global warming causing damages to the polar ecosystems (Moline et al., 2008). In Arctic marginal seas changes in sea-ice cover and thickness involve different thermodynamic and dynamic factors (Polyakov et al., 2003). In the case of the East Siberian Sea (ESS), land run-off and atmospheric circulation are controlling factors of the sea-ice distribution (Park et al., 2020;Rigor & Wallace, 2004).Our knowledge on natural variability of Arctic sea ice and on-going changes are limited by the lack of long time series observations. Information on past sea-ice distribution can be obtained from micropaleontological fossils (

Centennial-scale variability of sea-ice cover in the Chukchi Sea since AD 1850 based on biomarker reconstruction

“…The P D IP 25 values show similar features as P B IP 25, despite discrepancies between dinosterol and brassicasterol profiles, except since the 1980s when P D IP 25 indicates increased sea ice contrary to observations (Walsh et al 2016) (figures 4(d), (e) and 6(d)). Diverging spatial distribution of these two sterols has also been underlined by Su et al (2022) in the Eastern Siberian Sea. It has been speculated that dinosterol in the Arctic Ocean might be produced by other organisms than dinoflagellates (Nichols et al 1990).…”

“…brassicasterol or dinosterol), in the so called 'PIP 25 (Phytoplankton-IP 25 ) index' to produce semi-quantitatively seasonal seaice estimates (see reviews of Müller 2013, Belt 2018). More recently, a tri-unsaturated HBI (HBI III) has been proposed as an alternative to represent pelagic phytoplankton in order to improve the PIP 25 index (Belt et al 2015, Smik et al 2016, Bai et al 2019, Koch et al 2020, Su et al 2022 while Belt (2018) hypothesized that HBI II, also associated with sympagic algae, might provide an even better seasonal sea ice proxy than IP 25 .…”

Climate and ice conditions of East Siberian Sea during Holocene: Reconstructions based on sedimentary geochemical multiproxy

“…The transfer functions for the reconstruction of ice cover and air temperature based on the variations in the elemental composition of sediments in the core LV77-36-2 (Figure 2), include biogenic (Sr), redox-sensitive (Fe), and lithogenic (K, Nb, Zr, Y) elements. The main processes responsible for the ice cover effect on the elemental composition of sediments accumulated on the East Siberian shelf were characterized earlier (Astakhov et al, 2019a, 2021, 2022; Su et al, 2022). They are changes in the primary bioproductivity of surface waters, as a result of a longer vegetation period, and changes in the redox conditions of bottom waters toward more oxide ones due to better ventilation of the water column with a decreased ice cover.…”

“…The main processes responsible for the ice cover effect on the elemental composition of sediments accumulated on the East Siberian shelf were characterized earlier (Astakhov et al, 2019a(Astakhov et al, , 2021(Astakhov et al, , 2022Su et al, 2022). They are changes in the primary bioproductivity of surface waters, as a result of a longer vegetation period, and changes in the redox conditions of bottom waters toward more oxide ones due to better ventilation of the water column with a decreased ice cover.…”

“…Reconstructions of Arctic ice conditions are based on various proxies in marine sediments, dinocyst species composition (de Vernal, 2017; Farmer et al, 2011; Stroeve et al, 2007), and other biomarkers (Hörner et al, 2016; Polyak et al, 2016; Stein et al, 2017; Su et al, 2022). However, these methods provide only a qualitative assessment of ice condition changes, without a comparison with digital hydrometeorological data.…”