Expedition 302 summary
Expedition 302 summary
复制标题
远征302概要
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Masanobu Yamamoto
中科院分区：
文献类型：
--
作者：
J. Backman;K. Moran;D. McInroy;H. Brinkhuis;S. Clemens;T. Cronin;G. Dickens;F. Eynaud;J. Gattacceca;M. Jakobsson;R. Jordan;M. Kaminski;J. King;N. Koç;N. Martinez;J. Matthiessen;T. C. Moore;Jonaotaro Onodera;M. O’Regan;H. Pälike;B. Rea;D. Rio;T. Sakamoto;David C. Smith;R. Stein;K. S. John;I. Suto;N. Suzuki;Kozo Takahashi;Mahito Watanabe;Masanobu Yamamoto
2004年9月完成了对北冰洋中部的第一次科学钻探考察。综合大洋钻探计划探险302，北极取芯探险(ACEX)，在距北极250公里的约1300米水深的海底(MBsf)下发现了428米的沉积物岩芯。S探险队的目的地是洛蒙诺索夫山脊，假设它是大约56 Ma时从欧亚板块分离出来的一片大陆地壳。随着海脊向北移动并下沉，海洋沉积发生并持续到现在，导致了从地震数据中预期的连续的古海洋记录。海脊的高度高于周围的深海平原(约3公里)，确保了海脊上的沉积物没有浑浊。探险302的主要科学目标是不断恢复这一沉积物记录，并通过从静止的钻井船上钻探和取芯来采样下面的沉积基岩。在探险302期间，最大的挑战是在2-4米厚的海冰中进行钻探和取芯时保持钻井船的位置，这些海冰的移动速度接近0.5kt。洛蒙诺索夫海脊上的海冰覆盖与北极两个主要海冰环流系统之一--跨极漂移--一起移动，并对风、潮汐和洋流做出局部反应。到目前为止，在科学界被称为“隐姓埋名的母马”的北冰洋高地盆地，以前从未因为这些具有挑战性的海冰条件而被深入钻探。初步研究结果表明，生物碳酸盐仅存在于全新世-更新世之间。上部198 Mbsf代表了过去18英里以来相对较高的沉积速率记录。由带有冰筏碎片和落石的沉积物组成，这表明被冰覆盖的条件至少在时间上延续了这么久。冰的类型(例如，冰山与海冰)、时间和特征(例如，常年与季节性)的细节有待进一步研究。间断出现在193.13 Mbsf，跨度为25英里。早中新世至中始新世，约18~43 Ma。始新世中期的沉积记录为暗色、富含有机的生物硅质成分。孤立的鹅卵石，被解释为冰排下落的石头，存在于239 Mbsf，很好地进入这个始新世中期。在始新世中、下界附近有丰富的满江红藻类。这表明，在这一时期，淡水和/或低盐度的地表水环境主导了该区域。尽管基于地球物理数据的钻探前预测将沉积柱的底部定为50 Ma，但钻探表明，恢复了古新世至始新世最高至最低的界线区间，即众所周知的古新世/始新世最高温度(PETM)。在PETM期间，北冰洋表层海水温度超过20℃。302探险期间的钻探也深入到下伏的沉积基岩中，揭示了晚白垩世的浅水沉积环境。
The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole. Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship. The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions. Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C. Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age.