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肯内特基金被要求对加利福尼亚州圣巴巴拉盆地晚第四纪沉积层序(水深588m)进行高分辨率古气候和古海洋调查。初步的年代学、氧同位素和有孔虫组合研究揭示了一个完整的到接近完整的气候记录，代表了过去160年来近15厘米/100年的近线性沉积速率。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有关的上升中间水的变化。沉积物层序记录了以沉积物纹层和低耐氧底栖有孔虫为代表的低氧条件和以非层理生物扰动沉积物和喜氧底栖有孔虫为代表的高氧条件之间的多次振荡。我们对过去20Ky间隔的相对详细的研究表明，盆地通风的开关与全球气候变化之间存在密切的吻合，如有孔虫18O和浮游有孔虫组合所记录的那样。充氧条件在较冷的时段(较年轻的仙女木和最后一次冰川高峰期)占优势。相反，亚缺氧条件发生在较温暖的时期(Bolling/Allerod和全新世)，浮游有孔虫和底栖有孔虫对之间的放射性碳年龄差异较小(av。90年)；较大的(平均470年)在温暖的间歇期。我们对沉积相和放射性碳测年中的这些振荡进行了解释，以反映中间水域的变化，与温暖时期(包括今天)来自相对较近的来源的比例较大，而来自较温暖的时间间隔的较远来源的比例较大。我们的初步研究表明，在过去的20年里，通风和气候变化之间没有任何明显的滞后。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。圣巴巴拉盆地层序一直是一个天生不稳定的环境系统，对全球气候变化高度敏感。我们最近还发现，893站位的层状沉积物序列与格陵兰冰盖记录的几乎整个冰川间期序列(Dansgaard-Oeschger事件)密切相关，间接地与北大西洋的沉积物序列密切相关。我们建议进行研究来检验几个假说：1.圣巴巴拉盆地的通风变化与过去70年期间的全球气候变化密切相关；2.过去70年期间的通风变化与北大西洋深海沉积物记录有关，是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间水域的温盐变化，或两者的统一；以及3.最后一次间冰期事件(5E亚期或Eemian亚期)峰温变暖期间的气候；125-115ka)与全新世有很大的不同，影响了中等水层太平洋温盐环流的重大变化，进而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。