“Compared to the present climate, the Arctic climate in MH [Mid-Holocene] summer became warmer and had less sea ice” (Dong et al., 2022).
While the modern Arctic “remains largely covered by sea ice in June and July,” the higher summer sea surface temperatures (SSTs) from about 3,000 to 7,000 years ago meant the East Siberian Sea had “sea-ice free conditions throughout the MH summer.”
Image Source: Dong et al., 2022
Other studies assessing the paleoclimate and sea ice cover trends for the Chukchi Sea region provide more detailed quantification.
McKay et al. (2008) reported the modern Arctic sea ice coverage lasts 10.6 months per year, and present-day summer SSTs average 1.1°C.
But throughout most of the last 9,000 years the Chukchi SSTs ranged from 3 to 7.5°C (2 to 6.5°C warmer than present), and sea ice coverage lasted 5.5 to 9 months per year, or 1.5 to 5 fewer months than modern.
Image Source: McKay et al, 2008
Porter et al. (2019) also conclude modern Chukchi Sea summer sea ice endures for about 11 to 11.5 months per year, a duration that has remained stable for the last 200 years. In contrast, during the 1500s, 1600s, and 1700s sea ice coverage lasted only 7 to 9 months per year.
Image Source: Porter et al., 2019
Finally, Zhou et al. (2021) indicate that while the surface water of the Chukchi Plateau is “covered by perennial sea ice” today, this region had “probably summer sea-ice-free conditions during the Holocene.”