Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling
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DOI：
10.1029/93pa03524
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发表时间：
1994-06
期刊：
影响因子：
--
通讯作者：
W. Howard;W. Prell
中科院分区：
文献类型：
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作者：
W. Howard;W. Prell
最近的地球化学模型利用海洋碱度变化，特别是南大洋表面的碱度变化，来解释冰川时代 pCO2 的减少。在此类模型中，冰期碱度增加是由北大西洋深水（NADW）供应减少驱动的，这导致深水营养物增加和碳酸盐沉积物溶解，并导致南大洋表面环极深水上升流的碱度增加。我们使用来自东南印度洋中脊和南大西洋深海开普盆地的岩心来表明，在现在被环极深水沐浴的地区，碳酸盐溶解在冰川阶段得到了增强。这表明南大洋深部碳酸根离子浓度在冰期低于间冰期，而不是极地碱度模型所表明的较高[Broecker 和 Peng，1989]。我们的观察表明，南大洋 CaCO3 保存的变化与 NADW 相对通量的变化是一致的，这表明南大洋碳酸盐化学与深水环流的变化密切相关。冰川溶解增强的模式与南大洋营养贫乏水（NADW）供应的减少以及深水团中营养物质的增加是一致的。东南印度洋中脊（3200-3800 m）以及凯尔盖朗高原和南太平洋相对较浅的岩心（<3000 m）的碳酸盐质量积累率在冰川期显着降低，约减少了 50%。冰川期间碳酸盐质量积累率降低和溶解增强可能部分归因于CaCO3:Corg通量比的降低，这是提高南大洋表层水碱度的另一种机制。极性碱度模型假设表面碱度下有机碳与碳酸盐生成的比率是恒定的。即使南大洋的总体生产力保持不变，CaCO3:Corg 比率的下降也会导致冰期期间南大洋表层水域的碱度增加和 pCO2 减少。这种生态驱动的表面碱度变化可能会增强深水介导的碱度变化，并放大 pCO2 的快速变化。
Recent geochemical models invoke ocean alkalinity changes, particularly in the surface Southern Ocean, to explain glacial age pCO2 reduction. In such models, alkalinity increases in glacial periods are driven by reductions in North Atlantic Deep Water (NADW) supply, which lead to increases in deep-water nutrients and dissolution of carbonate sediments, and to increased alkalinity of Circumpolar Deep Water upwelling in the surface Southern Ocean. We use cores from the Southeast Indian Ridge and from the deep Cape Basin in the South Atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by Circumpolar Deep Water. This suggests that deep Southern Ocean carbonate ion concentrations were lower in glacial stages than in interglacials, rather than higher as suggested by the polar alkalinity model [Broecker and Peng, 1989]. Our observations show that changes in Southern Ocean CaCO3 preservation are coherent with changes in the relative flux of NADW, suggesting that Southern Ocean carbonate chemistry is closely linked to changes in deepwater circulation. The pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient-depleted water (NADW) to the Southern Ocean and with an increase of nutrients in deep water masses. Carbonate mass accumulation rates on the Southeast Indian Ridge (3200–3800 m), and in relatively shallow cores (<3000 m) from the Kerguelen Plateau and the South Pacific were significantly reduced during glacial stages, by about 50%. The reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in CaCO3:Corg flux ratios, acting as another mechanism which would raise the alkalinity of Southern Ocean surface waters. The polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant. Even if overall productivity in the Southern Ocean were held constant, a decrease in the CaCO3:Corg ratio would result in increased alkalinity and reduced pCO2 in Southern Ocean surface waters during glacials. This ecologically driven surface alkalinity change may enhance deepwater-mediated changes in alkalinity, and amplify rapid changes in pCO2.