Precession and atmospheric CO2 modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago

Abstract

Recent reduction in high-latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings. In order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales, here we reconstruct changes in sea ice extent and summer sea surface temperature (SSST) over the past 130,000 years in the central Okhotsk Sea. We applied novel organic geochemical proxies of sea ice (IP25), SSST (TEX L 86) and open water marine productivity (a tri-unsaturated highly branched isoprenoid and biogenic opal) to marine sediment core MD01-2414 (53 o 11.77'N, 149 o 34.80'E, water depth 1123 m). To complement the proxy data, we also carried out transient Earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors. Our results show that the central Okhotsk Sea was ice-free during Marine Isotope Stage (MIS) 5e and the early-mid Holocene, but experienced variable sea ice cover during MIS 2-4, consistent with intervals of relatively high and low SSST, respectively. Our data also show that the sea ice extent was governed by precessiondominated insolation changes during intervals of atmospheric CO2 concentrations ranging from 190 to 260 ppm. However, the proxy record and the model simulation data show that the central Okhotsk Sea was near ice-free regardless of insolation forcing throughout the penultimate interglacial, and during the Holocene, when atmospheric CO2 was above ~260 ppm. Past sea ice conditions in the central Okhotsk Sea were therefore strongly modulated by both orbital-driven insolation and CO2-induced radiative forcing during the past glacial/interglacial cycle.

A Comparison of Late Quaternary Organic Proxy‐Based Paleotemperature Records of the Central Sea of Okhotsk

“…For example, Gorbarenko (1996) Gorbarenko et al (2014) reconstructed periods of rapid warming and cooling during the Holocene and late Pleistocene, synchronous with the Greenland climatic cycles (glacial and interglacial stages as well as Heinrich events). These studies indicate that the alkenone and GDGT records reflect temperatures of different seasons, with the TEX 86 -derived temperatures representing summer subsurface temperature (Lo et al, 2018;Seki et al, 2001(Chou et al, 2011. The reconstructed temperatures range from 5-7°C to 8-12°C for the TEX 86 and from 4-7°C to 8-12°C for the U k 0 37 for the last glacial maximum and the Holocene, respectively.…”

“…SST reconstructions have been performed for the Holocene and the last glacialinterglacial interval using the δ 18 O of planktonic foraminifera (Gorbarenko, 1996), as well as the TEX 86 Lo et al, 2018;Seki et al, 2009Seki et al, , 2014 and U k 0 37 (Harada et al, 2004(Harada et al, , 2006Seki et al, 2004) temperature proxies. An age model for the core was established by Lo et al (2018) based on the correlation of XRF data (log-ratios of (Ba/Ti)) with the global benthic foraminiferal δ 18 O stack (LR04, Lisiecki & Raymo, 2005) and five accelerator mass spectrometry radiocarbon (AMS 14 C) dates of picked planktonic foraminifera (Neogloboquadrina pachyderma, sinistral). These studies indicate that the alkenone and GDGT records reflect temperatures of different seasons, with the TEX 86 -derived temperatures representing summer subsurface temperature (Lo et al, 2018;Seki et al, 2001(Chou et al, 2011.…”

“…Thirteen surface sediments were collected from the Sea of Okhotsk as described by Lo et al (2018) (Figure 1). …”

“…The sediments were previously extracted by Lo et al (2018). Briefly, sediment samples (1-10 g) were homogenized, freeze-dried, and extracted using dichloromethane (DCM): methanol (4: 1 v/v) using an accelerated solvent extractor.…”

“…We generated high-resolution records of LDI-derived and U k 0 37 -derived SST for the past 180 ka from the central Sea of Okhotsk and compared this to a previously generated TEX 86 -derived SST record (Lo et al, 2018). We generated high-resolution records of LDI-derived and U k 0 37 -derived SST for the past 180 ka from the central Sea of Okhotsk and compared this to a previously generated TEX 86 -derived SST record (Lo et al, 2018).…”