Extensive exposure of the Chukchi Shelf since the last deglacial

Ice sheets and ice shelves play an important role in Earth’s climate system during the late Quaternary. The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. However, sea level estimates for the period of ice-sheet retreat after the Last Glacial Maximum (LGM) are full of uncertainties, especially in the Arctic Ocean. For example, the Bering Strait was a land bridge during the LGM, when sea level was ~130 m lower than today. Based on records from multiple sites, we suggest that the Chukchi shelf may not have been widely submerged during the late and/or post-Last deglacial.

The initial evidence comes from the less sea ice coverage and abnormal sediment accumulation rates during the early Holocene, and abnormally sedimentation rates have been observed in many records. Some cores have a very high sedimentation rate, on the contrary, there are hiatus in some records, even if a considerable number of differences due to chronological drift have been evaluated.

There were unusual sand layers before 8.2 ka, which can be associated with a rapid input of IRD in our proposed R11 core, accompanied by a fierce change in organic matter content. The coarse particle size indicates that it may be dominated by ice transition at this time.

The organic carbon record on the Chukchi sea-continental shelf/margin suggests that this model is attributed to ICD (Ice Complex Deposit), which results from the large-scale degradation and thawing of permafrost due to sea-level rise after the ice age. The early Holocene low sea source organic matter and low sea ice cover recorded in R09 indicate that the sea level rise is a long process, and the εNd, which represents the Pacific inflow also has a long-term lifting, during which part of the continental shelf may still be exposed to the surface or even covered by ice caps.

This situation continued until the last discharge of the Laurentide ice sheet during the 8.2 ka period, and the global sea level stabilized. After that, the maximum flux of PW inflow occurs between 6.0~ 5.0 ka. However, this situation may only be applicable in narrow and shallow continental shelves because we found new sedimentary records on the Chukchi borderland that show significantly different sedimentation rates compared to the cores raised from adjacent shelf. In that area, the sedimentation rate starts to rapidly decrease even though the water depth only increased by over hundreds of meters. Besides non-linear ages, the sedimentary records of the Chukchi borderland typically contain hiatus, and also include high IRD content and strong environmental changes. Furthermore, our neighboring region's records show significantly different carbonate content storage conditions compared to those from the Chukchi margin, which is similar to the micro fossil barren observed in the sedimentary record of the Chukchi plateau. Therefore, we need to be more cautious and consider the global perspective when studying the sedimentological environment of the Chukchi Sea and its continental margin.