Stott L D, Berelson W, Douglas R, Gorsline D
Department of Earth Sciences, University of Southern California, Los Angeles 90089, USA.
Nature. 2000 Sep 21;407(6802):367-70. doi: 10.1038/35030084.
Concentrations of dissolved oxygen in the ocean seem to correlate well with climate instabilities over the past 100,000 years. For example, the concentration of dissolved oxygen in Pacific intermediate waters was considerably higher during Pleistocene glacial periods than it is today. This has been inferred from the presence of bioturbated sediments, implying that oxygen levels were sufficient for burrowing organisms to live. Today, basins in the northeastern Pacific Ocean are floored by laminated sediments implying lower oxygen levels, which may be explained by reduced ventilation. Here we report a recent return to bioturbated sediments in the northeastern Pacific Ocean since the late 1970s. From the carbon isotope composition of benthic foraminifers living in the sediment, we infer a twofold decrease in the carbon oxidation rate occurring within sediments, equivalent to an increase in dissolved oxygen concentration of 15-20 micromoles per litre. These changes, at the edges of the Santa Barbara, Santa Monica and Alfonso basins, are coincident with a change in North Pacific climate which has reduced upwelling by 20-30% and increased sea surface temperatures by 1.5-3 degrees C. This suggests that climate effects on surface productivity, reducing the supply organic matter to sediments, may have had a greater effect on benthic oxygen levels than changes in ocean circulation patterns.
海洋中溶解氧的浓度似乎与过去10万年的气候不稳定状况密切相关。例如，更新世冰川期期间太平洋中层水域的溶解氧浓度比现在高得多。这是从生物扰动沉积物的存在推断出来的，这意味着氧气水平足以让穴居生物生存。如今，东北太平洋的盆地底部是纹层状沉积物，这意味着氧气水平较低，这可能是由于通风减少所致。在此，我们报告自20世纪70年代末以来东北太平洋近期又出现了生物扰动沉积物。根据生活在沉积物中的底栖有孔虫的碳同位素组成，我们推断沉积物中发生的碳氧化速率下降了两倍，相当于溶解氧浓度每升增加了15 - 20微摩尔。圣巴巴拉、圣莫尼卡和阿方索盆地边缘的这些变化，与北太平洋气候的变化同时出现，北太平洋气候的变化使上升流减少了20 - 30%，海面温度升高了1.5 - 3摄氏度。这表明气候对表层生产力的影响，减少了向沉积物供应的有机物质，可能对底栖氧气水平的影响比海洋环流模式的变化更大。
