The evolution of climatically driven weathering inputs into the western Arctic Ocean since the late Miocene: Radiogenic isotope evidence
The evolution of climatically driven weathering inputs into the western Arctic Ocean since the late Miocene: Radiogenic isotope evidence
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DOI：
10.1016/j.epsl.2015.03.007
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发表时间：
2015-06
影响因子：
5.3
通讯作者：
V. Dausmann;M. Frank;C. Siebert;M. Christl;J. Hein
中科院分区：
文献类型：
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作者：
V. Dausmann;M. Frank;C. Siebert;M. Christl;J. Hein
我们首次连续记录了北冰洋西部深水中溶解放射性成因钕、铪和铅的同位素组成，时间跨度从晚中新世到现在。数据来自加拿大盆地北风脊最北端海底山的三个含氢锰铁（Fe-Mn）地壳，水深分别为2200、2400和3600 m。利用宇宙成因10 Be测定地壳年代记录了未受干扰的现今生长表面，并得出生长速率在27至2.2 mm/Myr之间。3个地壳的Nd （Hf）同位素时间序列从最老部分的- 8.5（+ 4）到地表的- 11.5(- 4)，呈现出相似的演化趋势，从~ 4 Ma开始有明显的低放射成因趋势。这与Pb同位素向206pb / 204pb、207pb / 204pb、208pb / 204pb演化趋势一致。推断加拿大盆地北极深水（ADW）放射性成因同位素组成的主要变化是由气候控制的北美大陆风化机制和沉积物输运的变化引起的。根据这些记录，我们得出结论，与冰川条件增强有关的北美大陆的风化输入在约400万年前开始增加并影响ADW的放射性成因同位素组成，并在约1 Ma进一步加强。这些新的时间序列与在罗蒙诺索夫海岭记录的北极中间水的放射性成因同位素演化明显不同，表明北冰洋水团之间的同位素差异比过去普遍存在的要大得多。
We present the first continuous records of dissolved radiogenic neodymium, hafnium, and lead isotope compositions of deep waters in the western Arctic Ocean, spanning the time from the late Miocene to the present. The data were obtained from three hydrogenetic ferromanganese (Fe–Mn) crusts recovered from seamounts along the northernmost edge of the Northwind Ridge in the Canada Basin from water depths of 2200, 2400, and 3600 m. Dating the crusts using cosmogenic 10 Be documents undisturbed present-day growth surfaces and yields growth rates between 27 and 2.2 mm/Myr. The Nd (Hf) isotope time series of the three crusts show similar evolutions from ε Nd (ε Hf) of− 8.5 (+ 4) in the oldest parts to− 11.5 (− 4) at the surfaces and a pronounced trend to less radiogenic values starting at∼ 4 Ma. This coincided with a trend of the Pb isotope evolution towards more radiogenic 206 Pb/204 Pb, 207 Pb/204 Pb, and 208 Pb/204 Pb. It is inferred that climatically controlled changes in weathering regime and sediment transport along the North American continent were responsible for the major change of the radiogenic isotope composition of the Arctic Deep Water (ADW) in the Canada Basin. Based on these records we conclude that weathering inputs from the North American continent linked to enhanced glacial conditions started to increase and to influence the radiogenic isotope composition of ADW∼ 4 million years ago and were further intensified at∼ 1 Ma. These new time series differ markedly from the radiogenic isotope evolution of Arctic Intermediate Water recorded on the Lomonosov Ridge and suggest that much larger isotopic differences between the water masses of the Arctic Ocean than today prevailed in the past.