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肯尼特基金要求对位点893（588 m水深）进行高分辨率古气候和古志研究，这是加利福尼亚州圣塔芭芭拉盆地的晚期季学序列（200 m厚度）。最初的年代，氧同位素和有孔虫组装研究显示，最后160尔斯的近乎线性沉积速率在近15 cm/100年中均显示出完整至完整的气候记录。该序列位置良好，可以监测与北太平洋中热盐循环模式变化相关的上升中间水域的变化。沉积物序列记录了低氧条件之间的许多振荡，这些氧气条件由沉积物层压和低氧底栖有孔虫和较高的氧气条件和较高的氧气条件表示，以非层压生物扰动的沉积物和较高的氧气状况为代表。我们对最后20个ky间隔的相对详细的研究表明，如有孔虫18O和浮游生物福利式组合所记录的基础通风开关与全球气候变化之间的巧合。在较冷的间隔（年轻的Dryas和最后的冰川最大值）中，氧化条件占了上风。相反，在温暖的间隔（孔/allerod和全新世）中发生了亚氧化条件，浮游生物和底栖有孔虫对之间的放射性碳年龄差异在凉爽的间隔中较小（AV。90年）。在温暖的间隔内较大（4​​70年）。我们已经解释了这些振荡在沉积物相和放射性碳年龄中的这些振荡，以反映中间水的变化，比在较温暖的间隔（包括当今）的远端源相比，在较冷的时间间隔内，其比例较大的源自相对近端的来源。我们的初步研究表明，在过去的20个学差期间，通风和气候变化之间没有任何明显的滞后。这表明在影响圣塔芭芭拉盆地的循环和气候之间存在紧密的耦合。圣塔芭芭拉盆地序列一直是一种天生的不稳定环境系统，对全球气候变化非常敏感。我们最近还发现，现场893中层压沉积物间隔的序列与格陵兰冰盖中记录的几乎整个冰川间座序（Dansgaard-Oeschger事件）密切相关，并在北大西洋的沉积物序列中独立地记录。我们建议进行研究以检验几种假设：1。圣塔芭芭拉盆地的通风变化与最后70台学家期间的全球气候变化密切相关。 2。在过去的70尔kyr中的通风变化与北大西洋深海沉积物通过海洋传送带循环的变化或通过全球气候变化导致的太平洋中间水域的热盐发生变化联系在一起，或者两者都与一致相关；和3。在上一场冰川间发作（替代品或eemian; 125-115 ka）的高峰期间的气候与全新世的气候完全不同，以影响中等水深的太平洋热氨基循环的重大变化，这反过来又导致了我们在Santa Basana Basine中造成基本环境中的根本变化。