The unexpected observation of colder winters in midlatitude Eurasia despite rapid Arctic sea ice decline in recent decades, a phenomenon known as the "warm Arctic-cold continents" pattern, has spurred significant research. While regression analysis and climate simulations suggest a link between Arctic sea ice decline and colder midlatitude Eurasian winters through mechanisms involving planetary waves, storms, and jet streams, this relationship remains controversial due to limited observational data, high climate system variability, and the influence of other factors such as lower-latitude climate change, human activities, and lagged effects of ocean-atmospheric circulation. The mid-Holocene warm period (8.2–4.2 ka), characterized by warmer global temperatures driven by increased summer insolation and amplified Arctic warming leading to intensified Arctic sea ice decline, presents a valuable natural experiment to investigate the long-term effects of Arctic sea ice reduction on midlatitude winter climate without significant human influence. Statistical analyses and models suggest that Arctic amplification may lead to more stable climate in warm periods, reducing the impact of internal variability and lagged effects. The winter climate in Central Asia and Siberia is primarily regulated by the Siberian High and East Asian Trough, with the East Asian Winter Monsoon (EAWM) serving as an indicator of East and Central Asian winter temperatures. Since EAWM intensity is linked to the Siberian High and East Asian Trough but inversely related to Central Asian winter temperatures, it provides an independent proxy for winter climate evolution in temperate Asia. This study focuses on millennial-scale Holocene changes in Arctic sea ice and EAWM to examine their relationship. The East Siberian Sea, a key region for Arctic sea ice export, and the East China Sea, a core pathway for the EAWM, are selected for study due to the availability of suitable proxy data.

Existing literature highlights the complex relationship between Arctic sea ice decline and mid-latitude winter weather. Some studies have shown a link between Arctic sea ice loss and colder winters in mid-latitude Eurasia, attributing it to changes in atmospheric circulation patterns such as planetary waves and jet stream behavior. However, other studies have found little or no significant correlation, emphasizing the limitations of observational data and the influence of other climatic factors. The mid-Holocene warm period, characterized by increased summer insolation, amplified Arctic warming, and resulting sea ice decline, provides a unique opportunity to understand the long-term impacts of Arctic changes on mid-latitude climate in a warmer-than-present context. Previous studies using loess records and climate models have investigated the relationship between Arctic sea ice, atmospheric temperatures, solar insolation, and the EAWM in the mid-Holocene. These investigations have explored the role of meridional temperature gradients and the influence of Arctic heat transport on atmospheric circulation patterns. Existing models have produced contrasting results regarding the link between Arctic sea ice loss and mid-latitude winter temperature.

This study utilizes two sediment cores: LV77-36-1 from the East Siberian Sea shelf and ECMZ from the East China Sea shelf. The age of the sediment cores was determined using accelerator mass spectrometry ¹⁴C dating of bivalve shells and foraminifera, calibrated using the Marine 20.14 C dataset and accounting for reservoir ages. In the East Siberian Sea core (LV77-36-1), ice-rafted detritus (IRD) content in the 125–250 µm fraction was analyzed as a proxy for sea ice changes. Authigenic minerals and grains >250 µm were excluded to focus on seasonal sea ice variations. In the East China Sea core (ECMZ), the Zr/Rb ratio was used as a proxy for East Asian Winter Monsoon (EAWM) strength, based on the understanding that Zr and Rb are concentrated in coarse and fine-grained sediments, respectively, reflecting the strength of the EAWM-driven alongshore current. The changes observed in Zr/Rb ratio and grain size are interpreted against the backdrop of stable regional tidal conditions and are thus attributed to hydrodynamic differentiation within the alongshore current. Results from both cores cover the period from ~7.5 ka to present, excluding the early Holocene due to rapid sea-level rise affecting the sedimentary record. The reconstructions are compared with a compilation of existing paleoclimate datasets to expand the spatial coverage and improve the robustness of conclusions. The Community Earth System Model Version 1.0 (CESM1.0) and CMIP6-PMIP4 were employed to simulate East Asian winter surface air temperatures in the mid-Holocene and to examine the physical mechanisms linking Arctic sea ice and the EAWM. CESM1.0 sensitivity simulations were conducted by reducing the surface albedo over the ice-covered ocean to 0.8 times its original value, reflecting reduced sea ice extent, while other parameters were held constant at preindustrial values. A control run (CTRL) was also performed. Simulated results were then analyzed to understand heat absorption, release, and atmospheric changes related to Arctic sea ice decline.

Analysis of IRD in the East Siberian Sea core revealed an increase in IRD content since the mid-Holocene, indicating a decrease in sea ice extent during that period. This finding aligns with other studies showing enhanced sea ice melting and even summer sea ice-free conditions in the eastern Arctic during the mid-Holocene. Analysis of the Zr/Rb ratio in the East China Sea core showed a lower ratio during the mid-Holocene than in the late Holocene, signifying a weaker EAWM and suggesting warmer winters in East Asia during the mid-Holocene. This is supported by other proxy data indicating a weakened EAWM and warmer midlatitude Asian winters during this period. CESM1.0 simulations showed that reduced Arctic sea ice in the mid-Holocene led to increased absorption of summer solar radiation and enhanced seasonal heat storage in the upper ocean. This heat was released in autumn and winter, warming the Arctic atmosphere. The increased heat flux from the ocean to the atmosphere suppressed meridional heat transport, leading to intensified westerlies and dampened planetary wave activity. The weaker planetary waves resulted in a weaker East Asian trough and Siberian High, reducing the southward transport of cold air and resulting in warmer winters in East and Central Asia. The simulations reproduced the observed mid-Holocene warming in the eastern Arctic and weakening of the EAWM.

The findings contradict short-term observations of the "warm Arctic-cold continents" pattern but provide evidence for a "warm Arctic-warm continents" pattern on millennial timescales. This study suggests that while short-term variations may show a different relationship, the long-term trend is for warmer East Asian winters in response to Arctic sea ice decline. The increased heat flux from the ocean to the atmosphere, driven by the reduction in sea ice, plays a crucial role in suppressing meridional heat transport and influencing the behavior of atmospheric waves. Previous studies using atmospheric models alone have produced contrasting results, highlighting the importance of coupled ocean-atmosphere models for better understanding these climate dynamics. The impact of sea ice loss in different Arctic regions on the Northern Hemisphere tropospheric circulation is complex, but focusing on the overall eastern Arctic sea ice loss allows us to consider the primary large-scale influence. The mid-Holocene serves as an analog for the current period of sea ice decline and warming, aiding in projections of long-term climate change.

This study provides compelling evidence, using proxy data and climate model simulations, that enhanced Arctic sea ice decline in the mid-Holocene warmed temperate East Asian winters. This contrasts with short-term observations, demonstrating the complexity of Arctic-midlatitude climate interactions. The mechanism involves increased absorption and release of heat from the Arctic Ocean, influencing atmospheric circulation patterns and ultimately leading to weaker winter monsoons and warmer winters in East Asia. Future research should focus on higher-resolution simulations and refined proxy reconstructions to improve the understanding of these dynamic climate interactions and refine projections of future climate change in the context of continued Arctic sea ice loss.

The study focuses on a specific region within the Arctic, and the generalizability of the findings to other parts of the Arctic might be limited. The reliance on proxy data, despite its extensive use and validation, involves inherent uncertainties. The climate model used has its own limitations, and the specific parameterizations might affect the results. Additionally, other potential climatic factors besides Arctic sea ice decline may have influenced the mid-Holocene climate.