High Resolution Studies of Late Quaternary Climate and Oceanographic Change, Santa Barbara Basin

圣巴巴拉盆地晚第四纪气候和海洋变化的高分辨率研究

• 批准号: 9509839
• 负责人: James Kennett
• 金额: --
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 1995
• 资助国家: 美国
• 起止时间: 1995-08-01 至 1999-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9509839&HistoricalAwards=false
• 关键词: Resolution; Studies; Late; Quaternary; Climate

9529839 Kennett Funds are requested to conduct high resolution paleoclimatic and paleoceanographic investigations of Site 893 (588 m water depth), a late Quaternary sediment sequence (200 m thickness) of very high quality from Santa Barbara Basin, California. Initial chronological, oxygen isotopic and foraminiferal assemblage investigations reveal a complete to near-complete climate record representing near-linear sedimentation rates at ~15 cm/100 years for the last 160 kyrs. The sequence is well located to monitor changes in upwelled intermediate waters associated with changing modes of thermohaline circulation in the north Pacific. The sediment sequence records many oscillations between low oxygen conditions, represented by sediment laminations and low oxygen tolerant benthic foraminifers, and higher oxygen conditions, represented by non-laminated bioturbated sediments and oxygen-loving benthic forminifers. Our relatively detailed studies for the last 20 ky interval suggests close coincidence between switches in basinal ventilation and global climate changes as recorded by foraminiferal 18O and planktonic forminiferal assemblages. Oxygenated conditions prevailed during colder intervals (Younger Dryas and last glacial maximum). Conversely, suboxic conditions occurred during warmer intervals (Bolling/Allerod and Holocene), Radiocarbon age differences between planktonic and benthic foraminiferal pairs are smaller (av. 90 yrs) during cool intervals; larger (av. 470 yrs) during warm intervals. We have interpreted these oscillations in sediment facies and radiocarbon ages to reflect changes in intermediate waters with a greater proportion originating from a relatively proximal source during cooler intervals compared with a distal source during warmer intervals, including the present day. Our initial studies suggest an absence of any significant lags between the ventilation and climate changes during the last 20 kyrs. This suggest that a tight coupling existed between changes i n circulation influencing Santa Barbara Basin and climate. The Santa Barbara Basin sequence has been an inherently unstable environmental system that is highly sensitive to global climate change. We have also recently discovered that the sequence of laminated sediment intervals in Site 893 closely correlated with almost the entire sequence of glacial interstadials (Dansgaard-Oeschger events) as recorded in the Greenland ice sheet and indirectly in sediment sequences in the north Atlantic. We proposed to conduct studies to test several hypotheses: 1. that the changes in ventilation in Santa Barbara Basin are intimately linked with global climate change during the last 70 kyrs; 2. that the changes in ventilation during the last 70 kyrs were linked to the north Atlantic deep sea sediment record through changes in oceanic conveyor circulation, or through thermohaline changes in Pacific intermediate waters resulting from global climate change, or to both in unison; and 3. that climate during peak-warming of the last interglacial episode (substage 5e or Eemian; 125-115 ka) was sufficiently different from that of the Holocene to affect major change in Pacific thermohaline circulation at intermediate water depths that, in turn, caused fundamental changes in basinal environmental conditions that we record in Santa Barbara Basin.

9529839肯内特请求提供资金，对893号地点（水深588米）进行高分辨率的古气候和古海洋学调查，这是加州圣巴巴拉盆地的一个晚第四纪沉积序列（厚200米），质量非常高。最初的年代学、氧同位素和有孔虫组合调查揭示了一个完整到接近完整的气候记录，代表了过去160 kyrs的近线性沉积速率约为15 cm/100年。该序列的位置很好，可以监测与北太平洋温盐环流模式变化相关的涌升中间沃茨的变化。沉积物序列记录了许多振荡之间的低氧条件下，代表沉积层和耐低氧底栖有孔虫，和较高的氧条件下，代表非层压生物扰动沉积物和喜氧底栖forminifers。我们的相对详细的研究表明，在过去的20千公里的时间间隔开关在盆地通风和全球气候变化之间的密切巧合记录有孔虫18 O和浮游forminiferal组合。在较冷的时期（新仙女木和末次冰期），氧合条件占主导地位。相反，在较温暖的时期（Bolling/Allerod和全新世）出现了亚氧条件，浮游和底栖有孔虫对之间的放射性碳年龄差异较小（av。90岁）在凉爽的间隔;更大（平均。470年）在温暖的间隔。我们已经解释了这些振荡的沉积相和放射性碳年龄，以反映中间沃茨的变化，在较冷的时间间隔，从一个相对较近的源相比，在温暖的时间间隔，包括今天的远源的比例更大。我们的初步研究表明，在过去的20 kyrs通风和气候变化之间没有任何显着的滞后。这表明影响圣巴巴拉盆地的环流变化与气候之间存在着紧密的耦合。圣巴巴拉盆地层序是一个内在不稳定的环境系统，对全球气候变化高度敏感。我们最近还发现，在现场893层沉积物间隔序列密切相关的几乎整个序列的冰川interstadials（Dansgaard-Oeschger事件）记录在格陵兰冰盖和间接沉积物序列在北大西洋。我们建议进行研究，以测试几个假设：1。圣巴巴拉盆地的通风变化与全球气候变化密切相关; 2.过去70 kyrs期间的通风变化通过海洋输送环流的变化或通过全球气候变化导致的太平洋中层沃茨的温盐变化与北大西洋深海沉积物记录有关，或与两者一致有关; 3.在最后一次间冰期（5e期或Eemian期; 125-115 ka）的气候变暖高峰期与全新世气候有很大的不同，影响了太平洋温盐环流在中间水深的重大变化，这反过来又导致了我们在圣巴巴拉盆地记录的盆地环境条件的根本变化。