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首页> 外文期刊>Paleoceanography >Glacial-interglacial variability in the eastern tropical North Pacific oxygen minimum zone recorded by redox-sensitive trace metals
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Glacial-interglacial variability in the eastern tropical North Pacific oxygen minimum zone recorded by redox-sensitive trace metals

机译：氧化还原敏感的痕量金属记录的东热带北太平洋氧气最低带的冰间变化

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摘要

Changes in the intensity of the oxygen minimum zone (OMZ) in the eastern tropical North Pacific over the past 140 kyr are recorded as enrichments and depletions of redox-sensitive metals in sediments of two piston cores, one within and one below the modern OMZ, from the continental margin off Mazatlán, Mexico (22°41′N, 106°28′W). Concentrations of Al (7.7 ± 0.6%), Ti (0.37 ± 0.03%), Fe (3.1 ± 0.25%), Mn (320 ± 31 ppm), and Ba (560 ± 82 ppm) in core NH15P (within the OMZ at 420 m water depth) were relatively constant over the last 110 kyr. In contrast, concentrations of Cd (4.8 ± 2 ppm), Cu (29.8 ± 9.1 ppm), U (9.1 ± 3.7 ppm), Mo (12.1 ± 5.0 ppm), V (138.2 ± 51.9 ppm), and Re (45.8 ± 25.5 ppb) were all at least 30% higher in interglacial stages compared to glacial stages. Concentrations of Al (7.4 ± 0.3%), Ti (0.35 ± 0.03%), Fe (3.5 ± 0.4%), and Mn (385 ± 77 ppm) in core NH22P (below the OMZ at 2025 m water depth) were comparable to those in core NH15P, while concentrations of Ba (1662 ± 292 ppm) were about a factor of three higher. In contrast, concentrations of Cd (0.9 ± 0.3 ppm), U (6.6 ± 0.9 ppm), Mo (3.2 ± 1.2 ppm), V (81.8 ± 10.1 ppm), and Re (25.4 ± 12 ppb) were lower in sediments of comparable age than the concentrations of these same metals in the OMZ core, and the differences in their concentrations over glacial-interglacial cycles were less pronounced than those in shallower core. Comparison of the nonlithogenic fraction of metals in the sediments with their estimated contribution from plankton suggests that organic matter is probably the major source of Cu, Ba, and perhaps Cd to the sediment, whereas the indirect effects of organic carbon and low bottom water oxygen concentrations on sediment redox state appear to be more important controls on the distributions U, Re, Mo, and V. Changes in the depth at which Re and Mo precipitated in the sediments and in the Re/Mo ratio suggest that the redox state of the surface sediment and overlying water at both core depths varied over time. Re and Mo removal depths were shallower and Re/Mo ratios were lower at the OMZ site than in deeper water, suggesting that a more reducing environment prevailed over time at the shallower site. Although the redox state of the waters and sediment at both sites varied over glacial-interglacial cycles, the OMZ likely was never anoxic in the last 140 kyr. This variability in redox state could be attributed to changes in regional export productivity, changes in ocean circulation, or a combination of both processes. A paleoproductivity reconstruction from biogenic Ba data suggests that glacial productivity was considerable lower than it was during interglacial stages. Model results suggest that the oxygen penetration depth, an indicator of sediment redox state, changed less than 1 cm as a result of the change in productivity. Changes in oxygen penetration depth estimated from Re and U removal depths are significantly larger, suggesting that changes in ventilation are a more important control on sediment redox state. Overall, trace metal results confirm the tight coupling between ocean circulation, marine productivity, and global change.
机译：在过去的140年中，热带北部太平洋东部最小氧气区（OMZ）的强度变化被记录为氧化还原敏感金属在两个活塞芯沉积物中的富集和耗尽，一个在现代OMZ内部，一个在其下方，来自墨西哥马萨特兰（22°41′N，106°28′W）的大陆边缘。 NH15P核心（在OMZ内为）中的Al（7.7±0.6％），Ti（0.37±0.03％），Fe（3.1±0.25％），Mn（320±31 ppm）和Ba（560±82 ppm）的浓度在过去的110年中，水深420 m）相对恒定。相反，Cd（4.8±2 ppm），Cu（29.8±9.1 ppm），U（9.1±3.7 ppm），Mo（12.1±5.0 ppm），V（138.2±51.9 ppm）和Re（45.8±与冰川期相比，在冰川间期，平均25.5 ppb）至少高出30％。 NH22P核心（在2025 m水深处低于OMZ）中的Al（7.4±0.3％），Ti（0.35±0.03％），Fe（3.5±0.4％）和Mn（385±77 ppm）的浓度与NH15P核心中的那些浓度较高，而Ba（1662±292 ppm）的浓度大约高三倍。相反，沉积物中Cd（0.9±0.3 ppm），U（6.6±0.9 ppm），Mo（3.2±1.2 ppm），V（81.8±10.1 ppm）和Re（25.4±12 ppb）的浓度较低。与OMZ岩心中这些相同金属的浓度相比，其年龄具有可比性，并且它们在冰川-冰晶间循环中的浓度差异不如浅岩心中的明显。通过比较沉积物中金属的非形成岩部分及其对浮游生物的贡献，表明有机物可能是沉积物中Cu，Ba和Cd的主要来源，而有机碳和低底部水氧浓度的间接影响沉积物的氧化还原状态似乎是更重要的控制分布U，Re，Mo和V的元素。Re和Mo沉积在沉积物中的深度的变化以及Re / Mo比表明表面的氧化还原状态两个岩心深度的沉积物和上覆水随时间变化。与较深水相比，OMZ站点的Re和Mo去除深度较浅，Re / Mo比率较低，这表明随着时间的推移，浅站点的还原环境普遍存在。尽管两个地点的水和沉积物的氧化还原状态在冰期至冰期之间变化，但OMZ可能在过去的140年中从未缺氧。氧化还原状态的这种变化可归因于区域出口生产力的变化，海洋环流的变化或这两种过程的结合。根据生物成因Ba数据的古生产力重建表明，冰川生产力远低于间冰期。模型结果表明，由于生产力的变化，氧渗透深度（沉积物氧化还原状态的指标）的变化小于1 cm。根据Re和U去除深度估算的氧气渗透深度变化明显更大，这表明通风变化是对沉积物氧化还原状态的更重要控制。总体而言，痕量金属的结果证实了海洋环流，海洋生产力和全球变化之间的紧密联系。

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