Geochemical biomarker analyses on sediment cores PS51/154-11 and PS51/159-10 from the western Laptev Sea (Arctic Ocean)

Multi-proxy biomarker measurements were applied on two sediment cores (PS51/154, PS51/159) to reconstruct sea ice cover (IP25), biological production (brassicasterol, dinosterol) and river run-off (campesterol, beta-sitosterol) in the western Laptev Sea over the last ~17 ka with unprecedented temporal resolution. The absence of IP25 from 17.2 to 15.5 ka, in combination with minimum concentration of phytoplankton biomarkers, suggests that the western Laptev Sea shelf was mostly covered with permanent sea ice. Very minor river run-off and restricted biological production occurred during this cold interval. From ~16 ka until 7.5 ka, a long-term decrease of terrigenous (riverine) organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western Laptev Sea, caused by the onset of the post-glacial transgression. Intensified river run-off and reduced sea ice cover characterized the time interval between 15.2 and 12.9 ka, including the Bølling/Allerød warm period (14.7-12.9 ka). Prominent peaks of the DIP25 Index coinciding with maximum abundances of subpolar foraminifers, are interpreted as pulses of Atlantic water inflow on the western Laptev Sea shelf. After the warm period, a sudden return to severe sea ice conditions with strongest ice-coverage between 11.9 and 11 ka coincided with the Younger Dryas (12.9-11.6 ka). At the onset of the Younger Dryas, a distinct alteration of the ecosystem (reflected in a distinct drop in terrigenous and phytoplankton biomarkers) was detected. During the last 7 ka, the sea ice proxies reflect a cooling of the Laptev Sea spring/summer season. This cooling trend was superimposed by a short-term variability in sea ice coverage, probably representing Bond cycles (1500 ± 500 ka) that are related to solar activity changes. Hence, atmospheric circulation changes were apparently able to affect the sea ice conditions on the Laptev Sea shelf under modern sea level conditions.

本研究对两个沉积岩芯（PS51/154、PS51/159）开展多指标生物标志物测定，以重建过去约17 ka以来拉普捷夫海西部的海冰覆盖（IP25）、生物生产力（菜籽甾醇（brassicasterol）、甲藻甾醇（dinosterol））及河流径流量（菜油甾醇（campesterol）、β-谷甾醇（beta-sitosterol））记录，时间分辨率达到前所未有的水平。17.2~15.5 ka期间未检出IP25，且浮游植物生物标志物浓度处于最低值，这表明拉普捷夫海西部陆架彼时被永久海冰大范围覆盖。此寒冷时段内河流径流量极低，生物生产力受到显著限制。约16 ka至7.5 ka期间，陆源（河流输入）有机质长期减少，同时海洋有机质同步增加，反映出冰后海侵启动后，拉普捷夫海西部逐步建立起完全的海洋环境。15.2~12.9 ka（包含14.7~12.9 ka的博林-阿勒罗德暖期）的显著特征为河流径流量增强、海冰覆盖度降低。DIP25指数的显著峰值与亚极性有孔虫的最大丰度同步出现，被解读为拉普捷夫海西部陆架出现大西洋水入侵的脉冲事件。暖期结束后，11.9~11 ka期间海冰覆盖度达到峰值，海冰条件急剧恶化，这与新仙女木事件（12.9~11.6 ka）完全同步。在新仙女木事件初期，研究检测到生态系统发生显著改变，具体表现为陆源有机质与浮游植物生物标志物出现明显下降。过去7 ka以来，海冰代用指标反映出拉普捷夫海春季/夏季气候呈持续变冷趋势。该变冷趋势叠加了海冰覆盖度的短期波动，这大概率对应与太阳活动变化相关的邦德周期（Bond cycles，1500±500 ka）。因此，在现代海平面条件下，大气环流变化显然能够影响拉普捷夫海陆架的海冰状态。