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首页> 外文期刊>Paleoceanography >Southward shift of the Intertropical Convergence Zone in the western Pacific during the late Tertiary: Evidence from ferromanganese crusts on seamounts west of the Marshall Islands
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Southward shift of the Intertropical Convergence Zone in the western Pacific during the late Tertiary: Evidence from ferromanganese crusts on seamounts west of the Marshall Islands

机译：第三纪晚期西太平洋热带融合带的南移：马绍尔群岛以西海山上的锰铁结壳的证据

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+AFs-1+AF0- Hydrogenetic ferromanganese crusts were dredged from four seamounts in the western Pacific, OSM7, OSM2, Lomilik, and Lemkein, aligned in a NW-SE direction parallel to Pacific Plate movement. The crusts consist of four well-defined layers with distinct textural and geochemical properties. The topmost layer 1 is relatively enriched in Mn, Co, Ni, and Mo compared to the underlying layer 2, which is relatively enriched in Al, Ti, K, and Rb and Cu, Zn, and excess Ba. Textural and geochemical properties of layer 2 suggest growth conditions under high biogenic and detrital flux. Such conditions are met in the equatorial Pacific (i.e., between the Intertropical Convergence Zone (ITCZ) and equatorial high-productivity zone). Layer 2 likely formed when each seamount was beneath the equatorial Pacific along its back track path. On the other hand, layer 1 probably started to grow after seamounts moved northwest from the ITCZ. This interpretation is consistent with the thickness of layer 1 across the four crusts, which increases to the northwest. Ages of the layer 1 - layer 2 boundary in each crust, a potential proxy for northern margin of the ITCZ, also increase to the northwest at 17, 11, 8, and 5 Ma for OSM7, OSM2, Lomilik, and Lemkein, respectively. Assuming Pacific Plate motion of 0.3 degrees/Myr, the seamounts were located at 12 degrees N, 11 degrees N, 9 degrees N, and 8 degrees N at the time of boundary formation. This result suggests that the north edge of the ITCZ has shifted south since the middle Miocene in the western Pacific, which agrees with information from the eastern Pacific.
机译：+ AFs-1 + AF0-从西部太平洋的四个海山，OSM7，OSM2，Lomilik和Lemkein挖出了氢锰铁结壳，并沿与太平洋板块运动平行的NW-SE方向对齐。地壳由四个定义明确的层组成，这些层具有明显的纹理和地球化学特性。与下面的层2相比，最顶层1相对富含Mn，Co，Ni和Mo，下面的层2相对富含Al，Ti，K和Rb以及Cu，Zn和过量的Ba。第2层的质地和地球化学性质表明在高生物成因和碎屑通量下的生长条件。在赤道太平洋（即在热带辐合带（ITCZ）和赤道高产区之间）满足了这些条件。当每个海山沿赤道太平洋沿其回航路径在下方时，可能形成了第2层。另一方面，海山从ITCZ向西北移动后，第1层可能开始增长。这种解释与横跨四个地壳的第1层厚度一致，该厚度向西北方向增加。每个地壳的第1层到第2层边界的年龄（可能是ITCZ北缘的代表）的年龄也分别在OSM7，OSM2，Lomilik和Lemkein的西北向增加，分别为17、11、8和5 Ma。假设太平洋板块运动为0.3度/米尔，则在形成边界时海山位于12度北，11度北，9度北和8度北。这一结果表明，自西太平洋中新世中期以来，ITCZ的北边缘已向南偏移，这与东太平洋的信息一致。

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