過去12万年にわたるオホーツク海南西部の表層水温変動

• Main Authors: 原田, 尚美, 坂本, 竜彦
• Format: Article in Journal/Newspaper
• Language: Japanese
• Published: 北海道大学低温科学研究所
• Subjects: 431.67; Greenland; Okhotsk; okhotsk sea; Sea ice
• Online Access: http://hdl.handle.net/2115/20462

オホーツク海南西部の海底堆積物に記録された過去12万年にわたる表層水温の変動を，北太平洋の高緯度海域では世界で初めて20-40年という高い時間分解能で復元する事に成功した．結果は，数十年程度の周期で水温にして4-5度という振幅の変動を示し，ダンスガードオシュガーサイクル（数十年-100年程度の周期で繰り返す温暖・寒冷サイクル）に連動し，氷期にしては暖かい時代が繰り返し生じていたことがわかった．このように，高緯度縁辺海は深刻な環境変動を記録しており，今後ますますその実態解明の研究に取り組む必要がある． To better understand the way in which changes in the surface environmental in the Okhotsk Sea influence climate change in East Asia,we estimated sea surface temperatures in the southwestern Okhotsk Sea for the past 120 kyr at millennial to centennial temporal resolution using a long-chain unsaturated alkyl ketone (alkenone) thermometer. The alkenone temperature, which corresponds to the SST to 20 m depth in autumn, showed repeated abrupt changes at a centennial timescale, especially during the last glacial period at 20-60 kyr before present (BP). The alkenone temperature changed in tan dem with changes from interstadials (warm events) to stadials (cold events) recorded in the δ^{18}O record of ice cores recovered from Greenland. Anomalously high alkenone temperatures occurred repeatedly during the glacial period. These warm alkenone-temperature episodes probably had multiple causes: (1) the main season of alkenone production may have shifted from autumn to midsummer over the course of the glacial period because of the expansion of sea-ice coverage to nearly all seasons except midsummer; (2) related to the expansion of the sea-ice season, the sea-ice melting season may have shifted from spring to summer and sea-ice melting during summer might have led to stratification of the surface water, resulting in a high SST; and (3) an active Asian summer monsoon may have contributed to warming the surface waters of the southwestern Okhotsk Sea. In combination, these effects could have generated anomalously high alkenone temperatures in the southwestern Okhotsk Sea during the examined glacial period. 2章 千年～10万年スケールの気候復元とモデリング