Early diagenesis of organic material in equatorial Pacific sediments: Stoichiometry and kinetics
Early diagenesis of organic material in equatorial Pacific sediments: Stoichiometry and kinetics
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DOI：
10.1016/0967-0645(96)00027-6
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发表时间：
1996-01-01
影响因子：
3
通讯作者：
Pope, RH
中科院分区：
文献类型：
--
作者：
Hammond, DE;McManus, J;Pope, RH
利用底栖培养箱和沉积物孔隙水剖面研究了赤道太平洋沉积物中有机质的早期成岩作用。在覆盖720 cml的通量室中进行的重复测量表明，单个站点的氧、TCO2、碱度、硝酸盐和二氧化硅通量的空间变异性不超过10-35%。相比之下，在单个站点覆盖70 cm(2)的复制岩心的氧扩散通量往往表现出更大的变化。1992年1月，沿赤道从西经103度到140度，以0.6-0.8 mmol m（-2）天（-1）的底栖动物耗氧量相当稳定。1992年11月，在赤道沿140度W方向的消耗大致对称，在2度S和2度N之间的消耗速率为0.6-0.8 mmol m(-2) day(-1)，在12度S和9度N的消耗速率下降到0.1-0.2 mmol m(-2) day（-1）。大多数剖面与假设反应速率随深度呈指数下降的模型拟合得很好，但在低纬度地区，假设分解有机物有两种不稳定组分，每种组分都以一级动力学衰变，并随深度呈指数下降的模型往往拟合得更好。两种拟合结果表明，至少70%的有机质降解发生在沉积物上部1 ~ 2 cm。在符合双分量模式的低纬度台站，70-90%的通量属于更不稳定的分量，其平均1/e穿透深度为0.4+/-0.1 cm。这些站点中较难熔成分的穿透深度为4.4+/-0.4 cm。根据沉积物混合速率估算，高纬度台站所有降解有机物的平均寿命为4 ~ 55年，而在符合双组分模型的台站，较不稳定组分的寿命为几周至几个月，较不稳定组分的寿命为40 ~ 300年。第三个碳部分存在于所有的站点，它要难熔得多。再矿化的O-2:CO2化学计量为-1.45+/-0.17，C:N比为8+/-1。这两个比例与沉积物捕集器和水系研究的结果一致，表明降解有机物中- ch2o -基团的碳约占70%，- ch2 -基团的碳约占30%。在两个邮轮中，底栖生物再矿化的C:P原子比率相差3倍，尽管两个邮轮的平均值（170+/-85）与在水柱中观察到的再矿化比率没有显著差异，但显示出实质性的时间变异性和碳的解耦。赤道太平洋上升流区的整体底栖生物呼吸速率至少为太平洋大陆边缘（坡+升）区整体呼吸速率的25%，强调了赤道太平洋沉积物作为底栖生物碳循环的主要场所的重要性。过去十年在赤道和西经140度附近确定的底栖生物碳再矿化率变化了2倍，考虑到大多数碳降解的寿命很短，这并不奇怪。碳再矿化速率的时间模式与海洋表面温度的时间模式相似，表明该地点的底栖生物碳氧化可能反映了相对较短时间尺度的水柱生产力。版权所有爱思唯尔科学有限公司
Benthic incubation chambers and sediment pore water profiles were used to study early diagenesis of organic matter in equatorial Pacific sediments. Replicate measurements with a flux chamber covering 720 cml indicated that the spatial variability of oxygen, TCO2, alkalinity, nitrate and silica fluxes at a single station did not exceed 10-35%. In contrast, diffusive fluxes of oxygen from replicate cores covering 70 cm(2) at a single station often showed greater variation.In January 1992, benthic oxygen consumption was fairly constant along the equator from 103 degrees W to 140 degrees W at 0.6-0.8 mmol m(-2) day(-1). In November 1992, consumption was roughly symmetrical across the equator along 140 degrees W, with rates of 0.6-0.8 mmol m(-2) day(-1) between 2 degrees S and 2 degrees N, declining to rates of 0.1-0.2 mmol m(-2) day(-1) at 12 degrees S and 9 degrees N. Pore water oxygen profiles were fit with a reaction-diffusion model equation to evaluate reaction kinetics. Most profiles were adequately fit with a model that assumed reaction rates declined exponentially with depth, but at low latitudes better fits often were obtained with a model that assumed decomposing organic matter has two labile components and that each decays with first-order kinetics and decreases exponentially with depth. Results of both fits indicate that at least 70% of the organic matter degradation occurs within the upper 1-2 cm of sediment. At the low-latitude stations fit with the two-component model, 70-90% of the flux is attributable to the more labile component which has an average 1/e penetration depth of 0.4+/-0.1 cm. The more refractory component at these stations has a penetration depth of 4.4+/-0.4 cm. From estimates of sediment mixing rates, the mean life of all degrading organic matter at the higher latitude stations is 4-55 years, while at the stations fit with the two-component model, the lifetime of the more labile fraction is weeks to months, and the lifetime of the less labile component is 40-300 years. A third carbon fraction exists at all stations that is far more refractory.The O-2:CO2 stoichiometry of remineralization is -1.45+/-0.17, and the C:N ratio is 8+/-1. Both ratios are in good agreement with those observed from sediment trap and hydrographic studies in the water column, and suggest that degrading organic matter has about 70% of its carbon in -CH2O- groups and 30% in -CH2- groups. The C:P atom ratios for benthic remineralization differ by a factor of 3 for the two cruises, showing substantial temporal variability and de-coupling from carbon, although the mean for the two cruises (170+/-85) is not significantly different than remineralization ratios observed in the water column. The aerally-integrated benthic respiration rate for the equatorial Pacific upwelling region is at least 25% of the integrated respiration rate for the continental margin (slope + rise) areas of the Pacific, emphasizing the importance of the equatorial Pacific sediments as a major site of benthic carbon recycling. Benthic carbon remineralization rates determined during the past decade near the equator and 140 degrees W have varied by a factor of 2, which is not surprising given the short lifetime of the majority of the carbon degrading. The temporal patterns of carbon remineralization rates resemble those of sea-surface temperature, suggesting that benthic carbon oxidation at this site may reflect water column productivity over relatively short timescales. Copyright (C) 1996 Elsevier Science Ltd.