Implications for sedimentation changes on the Iberian margin over the last two glacial/interglacial transitions from (230Thexcess)0 systematics
Implications for sedimentation changes on the Iberian margin over the last two glacial/interglacial transitions from (230Thexcess)0 systematics
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DOI：
10.1016/s0012-821x(98)00265-9
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发表时间：
1999-02
影响因子：
5.3
通讯作者：
J. Thomson;S. Nixon;C. Summerhayes;J. Schönfeld;R. Zahn;P. Grootes
中科院分区：
文献类型：
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作者：
J. Thomson;S. Nixon;C. Summerhayes;J. Schönfeld;R. Zahn;P. Grootes
葡萄牙边缘非常适合研究冰期和间冰期北大西洋环流的对比，因为它的沉积物积累速度很快。本文报道了一项基于（230 theexcess）0的研究，在过去140天（包括最后两次冰期/间冰期转变）中，在40°N的斜坡样带上水深2.4和3.5 km的两个岩心中进行了沉积物堆积研究。虽然独立确定的过去140天的平均沉积物堆积通量明确很高，在两个岩心中平均值为13.2和10.5 g cm - 2ky - 1，但传统的（230 - the - ess）0方法产生的通量始终较低，平均值为3.5和3.8 g cm - 2ky - 1。这些估算值被解释为随时间变化的区域沉积通量的表示。该区域通量由<1 g cm - 2ky - 1的碳酸盐通量和较大且多变的粘土输入组成，这表明海平面控制对盆地粘土输入的重要性。粘土通量主导区域沉积物堆积，在间冰期总通量为~ 2 g cm−2ky−1，caco3含量高达50%，在冰期总通量高达~ 5 g cm−2ky−1，caco3含量低至10%。这种沉积物组成随时间变化的模式也是东北大西洋的典型特征，沉积物聚焦（等长岩形成）似乎是伊比利亚边缘在冰期与间冰期相比观察到的高实际通量的原因。在两个岩心中，通过×3.2和×4.0的因子，（230theexcess）0的库存量超过了仅由上覆水柱提供的库存量。这是由于在气候强迫下深海环流系统变化导致的冰川时期细沉积物质的优先洋流聚焦。海因里希事件在沉积物中的存在是显而易见的，但在这个南纬，除了大海因里希事件4在环境背景水平上增加了10-20 g cm - 2ky - 1之外，它们只产生了微弱的区域累积通量增加（<2 g cm - 2ky - 1）。
The Portuguese margin is well-suited for studies of the contrasts in North Atlantic circulation during glacial and interglacial times because of its rapid sediment accumulation rate. This paper reports a (230Thexcess)0-based study of sediment accumulation over the past 140 ky, a period which includes the last two glacial/interglacial transitions, in two cores at 2.4 and 3.5 km water depth on a slope transect at 40°N. Although the independently-determined mean sediment accumulation fluxes over the past 140 ky are unequivocally high with means of 13.2 and 10.5 g cm−2ky−1in the two cores, conventional application of the (230Thexcess)0method yields consistently lower fluxes with means of 3.5 and 3.8 g cm−2ky−1. These (230Thexcess)0estimates are interpreted as representations of the regional depositional flux through time. This (230Thexcess)0regional flux is composed of a carbonate flux of <1 g cm−2ky−1and a larger and variable clay input which indicates the importance of the sea level control on the clay input to the basin. Clay flux dominates the regional sediment accumulation which has a total flux of ∼2 g cm−2ky−1and a CaCO3content up to 50% in interglacial times, and a total flux up to ∼5 g cm−2ky−1and a CaCO3content down to 10% in glacial times. This pattern of change of sediment composition through time is also typical of the NE Atlantic, and sediment focusing (contourite formation) appears responsible for the high actual fluxes observed in glacial compared with interglacial times on the Iberian margin. The inventories of (230Thexcess)0exceed those which could have been supplied from the overlying water column alone over 140 ky by factors of ×3.2 and ×4.0 in the two cores. This is ascribed to preferential current focusing of fine sedimentary material in glacial times as a result of a systematic change in deep ocean circulation in response to climatic forcing. The presence of Heinrich events in the sediments is clearly evident, but at this southerly latitude they produce muted regional increases in accumulation flux (<2 g cm−2ky−1), apart from the large Heinrich event 4 which introduced an additional 10–20 g cm−2ky−1over ambient background levels.