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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Nd- and Pb-isotope time series from Atlantic ferromanganese crusts: implications for changes in provenance and paleocirculation over the last 8 Myr
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Nd- and Pb-isotope time series from Atlantic ferromanganese crusts: implications for changes in provenance and paleocirculation over the last 8 Myr

机译：大西洋铁锰结壳的Nd和Pb同位素时间序列：对最近8 Myr物源和古循环变化的影响

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High-resolution Nd- and Pb-isotope time series for the last 8 Myr are reported for four Atlantic ferromanganese crusts, dated by ~(10)Be/~9Be chronology. These are compared to new high-resolution and high-precision Pb-isotope time series and recently published Nd-isotope time series for two previously studied crusts from the NW Atlantic Ocean. These records allow a more detailed examination of Atlantic deepwater variability over the time period of intensification of Northern Hemisphere Glaciation (NHG). Changes in the Pb-isotope time series started after 3 Ma, but were most dramatic over the last 1.8 Myr, coinciding with changes of Pb-isotopes in the Arctic Ocean. this latter change post-dates the intensification of NHG at 3.1 to 2.5 Ma and reflects an increase in the input of material eroded from the Archean Shield of Canada and Greenland. Shifts in Nd- and Pb-isotope compositions in a crust from the Blake Plateau occur before approx 5 Ma and most prominent at approx 8 Ma suggest that water masses from either the Pacific or Southern Ocean influenced the isotope composition of this crust. The relatively high #epsilon#_(Nd) values around 8 Ma recorded by the Blake Plateau crust are explained by a contribution of eastward flowing Pacific water through the Panama Gateway into the Caribbean Sea. This high #epsilon#_(Nd) signal decreased between 8 and 5 Ma suggesting that the supply of Pacific water into the Caribbean became restricted. This is earlier than the Caribbean seawater salinity increase at 4.2 Ma deduced from #delta#~(18)O data, and may indicate that there was only a surface water connection between the Caribbean and Pacific between approx 5 and 4.2 Ma. The closure of the Panama Gateway to intermediate and deep water exchange (> 200 m depth) apparently occurred much earlier than the intensification of Northern Hemisphere Glaciation at 3.1-2.5 Ma, and cannot therefore have been a direct cause of this climatic change, but may, as recently
机译：报告了四个大西洋铁锰结壳的最后8 Myr的高分辨率Nd和Pb同位素时间序列，按〜（10）Be /〜9Be年表排序。这些与新的高分辨率和高精度的Pb同位素时间序列进行了比较，并且最近针对来自西北大西洋的两个先前研究的地壳发布了Nd同位素时间序列。这些记录可以更详细地检查北半球冰川（NHG）强化期间的大西洋深水变化。铅同位素时间序列的变化在3 Ma之后开始，但在最近的1.8 Myr时变化最大，这与北冰洋中Pb同位素的变化相吻合。后者的变化是在NHG从3.1增强到2.5 Ma之前的，并且反映了加拿大和格陵兰太古宙盾侵蚀的材料输入量的增加。布莱克高原地壳中Nd和Pb同位素组成的变化发生在大约5 Ma之前，最显着的发生在大约8 Ma之前，这表明来自太平洋或南洋的水团影响了这种地壳的同位素组成。布莱克高原地壳记录的大约8 Ma的#epsilon #_（Nd）值相对较高，这是通过向东流动的太平洋水通过巴拿马门户进入加勒比海的作用来解释的。这种高#epsilon #_（Nd）信号在8至5 Ma之间下降，表明向加勒比海供应的太平洋水受到限制。这是从#delta（〜）（18）O数据推断的加勒比海水盐度增加到4.2 Ma之前的，并且可能表明加勒比海和太平洋之间只有大约5至4.2 Ma之间的地表水连接。巴拿马中转和深水交换（> 200 m深度）通道的关闭显然发生在北半球冰川在3.1-2.5 Ma强化之前，因此，不可能是造成这种气候变化的直接原因，但可能，最近

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