The alkenone derived sea surface temperature and UK'37 index for the sediment core, MD01-2412 collected in the southwestern Okhotsk Sea.

Sea-ice expansion in the Okhotsk Sea in winter is sensitively affected by global warming and cooling. Regionally, the southwestern Okhotsk Sea is closely linked to climate change in East Asia, including Japan, because the cold sea surface temperature (SST) in the southwestern Okhotsk Sea influences directly the development of the Okhotsk atmospheric high-pressure system, and the activated Okhotsk high causes cold climatic conditions in northern Japan. Therefore, environmental change in the Okhotsk Sea indicates two-way interactions as a sensitive mirror reflecting global climate change and as a driving force of regional climate change. To better understand how surface environmental changes in the Okhotsk Sea can influence climate change in East Asia, SSTs were estimated in the southwestern Okhotsk Sea for the past 120 ky with millennial to centennial time resolution using the long-chain unsaturated alkyl ketone (alkenone) thermometer. The alkenone temperature, which corresponds to the SST to 20m depth in autumn, showed repeated abrupt changes at a centennial timescale, especially during the last glacial period, 20?60 ky before present (BP). The alkenone temperature changed concurrently with changes from interstadials (warm events) to stadials (cold events) in the d18O record of the ice cores from Greenland, although some interstadials could not be identified in the alkenone temperature record. A wavelet power spectrum analysis showed that a periodicity of about 8 ky was prominent during 10?90 ky BP, and a 4- to 5- ky cycle was characteristic during 30?40 ky BP in the alkenone temperature records. These periodicities were both similar and dissimilar to those in the Polar Circulation Index, which is based on the atmospheric circulation intensity at high latitudes, as recorded by major-ion concentrations in GISP2. Both the similarity and dissimilarity imply that the SST in the southwestern Okhotsk Sea is controlled mainly by the atmosphere?ocean circulation system in the Northern Hemisphere; however, the relationship between the SST in the Okhotsk Sea and the climate in the Greenland is not linear. Anomalously high alkenone temperatures occurred repeatedly in the glacial period. These warm alkenone temperature episodes would have had multiple causes. In particular, high alkenone temperatures during the last glacial maximum (LGM) have been reported previously for locations near this study site. More investigations are necessary to understand what happened in the Okhotsk Sea and in adjacent seas at the time of the LGM.鄂霍次克海冬季海冰扩张对全球变暖和冷却响应敏感。区域层面，鄂霍次克海西南部与包括日本在内的东亚气候变化密切相关：该区域的低温海表温度（Sea Surface Temperature, SST）直接调控鄂霍次克海高压大气系统的发育，而活跃的鄂霍次克海高压会引发日本北部的寒冷气候。因此，鄂霍次克海的环境变化兼具双重属性：既是反映全球气候变化的敏感镜像，亦是区域气候变化的驱动因子。 为深入解析鄂霍次克海表层环境变化对东亚气候变化的影响机制，本研究依托长链不饱和烷基酮（alkenone）温度计，以千年至百年的时间分辨率，重建了过去12万年以来鄂霍次克海西南部的海表温度序列。对应秋季20米水深海表温度的烯酮温度记录显示，其在百年尺度上存在多次突变事件，尤其在末次冰期（距今2万至6万年）期间。该烯酮温度变化与格陵兰冰芯d¹⁸O记录中由间冰阶（interstadials，暖事件）向冰阶（stadials，冷事件）的转变过程同步，尽管部分间冰阶未能在烯酮温度序列中被识别。小波功率谱分析（wavelet power spectrum analysis）结果显示：在距今10万至9万年期间，烯酮温度记录中约8千年的周期特征显著；而在距今3万至4万年期间，4至5千年的周期为主要特征。上述周期特征与基于高纬度大气环流强度（由GISP2冰芯主要离子浓度记录重建的极地环流指数（Polar Circulation Index））的周期特征既存在相似性，也存在差异。这种相似性与差异性共同表明，鄂霍次克海西南部的海表温度主要受北半球大气-海洋环流系统调控，但鄂霍次克海海表温度与格陵兰气候之间的关联并非线性。冰期阶段反复出现异常偏高的烯酮温度，这类暖期事件的成因具有多重性。其中，末次冰盛期（Last Glacial Maximum, LGM）期间的高烯酮温度在本研究区域附近的既往研究中已有报道。未来仍需开展更多研究，以厘清末次冰盛期鄂霍次克海及邻近海域的环境演化过程。