East Asian Winter Monsoon Variations and Their Links to Arctic Sea Ice During the Last Millennium, Inferred From Sea Surface Temperatures in the Okinawa Trough

Abstract

The East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05‐2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.

Decadal‐ to Centennial‐Scale East Asian Summer Monsoon Variability Over the Past Millennium: An Oceanic Perspective

“…The EASM record from Lake Nakaumi (Japan; Yamada et al, ) shows remarkably similar trends with the Lake Hwajinpo record, displaying the same EASM strengthened events, except for Event 4 (Figure ). The diatom‐based reconstructed winter sea surface temperature in the Okinawa Trough (Li et al, ) also shows striking similarity to the Hwajinpo record (Figure ), even though there are slight age discrepancies for Events 1 and 4. Higher winter sea surface temperature is associated with a weakened East Asian winter monsoon (EAWM; Li et al, ), and an inverse relationship between the centennial‐scale variabilities of the EAWM and the EASM was previously reported (Kang et al, ; Sagawa et al, ).…”

“…The diatom‐based reconstructed winter sea surface temperature in the Okinawa Trough (Li et al, ) also shows striking similarity to the Hwajinpo record (Figure ), even though there are slight age discrepancies for Events 1 and 4. Higher winter sea surface temperature is associated with a weakened East Asian winter monsoon (EAWM; Li et al, ), and an inverse relationship between the centennial‐scale variabilities of the EAWM and the EASM was previously reported (Kang et al, ; Sagawa et al, ). Among Chinese continental records, the Wanxiang Cave stalagmite record (Zhang et al, ) shows the greatest overall similarity with the Lake Hwajinpo record including all four events, while many other Chinese continental records do not show substantial similarity (F. Chen et al, ; Chu et al, ; Wang et al, ; Yi et al, ; Zheng et al, ; Figure ).…”

“…(b) δ 18 O of ostracode Bicornucythere bisanensis (Okubo) in Lake Nakaumi, Japan (Yamada et al, ). (c) Reconstructed sea surface temperature based on diatom data of Core MD05‐2908 from the Okinawa Trough (Li et al, ). (d) Wanxiang Cave stalagmite δ 18 O (Zhang et al, ).…”

“…These may result in complicated spatial monsoon patterns in continental China (J. Chen et al, , ). Because the limit of monsoonal influence may vary with relative strength of the EASM and ISM, it is possible that oceanic proxies (Li et al, ; Yamada et al, ) and Chinese continental records (Wang et al, ; Yi et al, ; Zheng et al, ) might better represent two alternate sources of precipitation, respectively. This may be consistent with spatial difference of wetness between southeastern (comparatively more coastal) and northwestern (comparatively more continental) parts of monsoonal eastern China (J. Chen et al, ).…”

A multi‐model analysis of the East Asian monsoon changes in the Medieval Climate Anomaly and Little Ice Age

“…By comparing the EASM evolution with other proxy data, it is further proposed that external forcing factors such as solar activity (Wang et al, 2005;Zhang et al, 2008;Li et al, 2017) and internal variability modes such as the Asia-Pacific Oscillation (Fang et al, 2014) and Pacific Decadal Oscillation (Lee and Park, 2015;Zhao et al, 2015) may affect the EASM variation. On the other hand, the sequences of the Holocene EAWM are less well established than those of the EASM because of unsuitable archives and proxies (Sagawa et al, 2014), and discrepancies are evident among different reconstruction results (Xiao et al, 2006;Liu et al, 2009;Sagawa et al, 2014;Tu et al, 2017;Li et al, 2018). It is also implied that changes in the Holocene EAWM were likely forced by the reduction in solar irradiance through changes in the oceanic-atmospheric circulation patterns on the centennial scale (Sagawa et al, 2014), and Arctic Sea ice may have modulated the relationship between the EAWM and the Atlantic Oscillation (Li et al, 2018).…”