Chemistry of eastern tropical Atlantic porewater

Distributions of pore water O2, NO-2, NO-3, NH+4, Si(OH)4, PO[3-]4, Mn[2+], F-, and T.A. were determined at 15 stations in the eastern equatorial Atlantic. While overall profile characteristics are consistent with previous models of organic matter diagenesis, profile shapes suggest that a deep reaction layer, rich in organic C, is also present at many sites. While it is unlikely that the oxidation of organic C in this layer has had a major effect on the ocean C cycle, pore water profile shapes are significantly altered. Despite exposure to seawater SO[2-]4 concentrations for > 1000 years, decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes. These results suggest major differences in organic carbon decomposition and preservation under oxic/suboxic and anoxic conditions.
Present-day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern Pacific. Preliminary estimates suggest that the benthic respiration in the eastern 1/3 of the North Atlantic south of 20°N may alone account for >20% of the total deep North Atlantic respiration. Combining these results with estimates of organic C burial and deep water-column decomposition suggests that this region is a major location of organic C input into the deep sea.

在赤道大西洋东部的15个观测站位中，测定了孔隙水（pore water）中氧气（O₂）、亚硝酸盐（NO₂⁻）、硝酸盐（NO₃⁻）、铵根离子（NH₄⁺）、硅酸（Si(OH)₄）、磷酸盐（PO₄³⁻）、锰离子（Mn²⁺）、氟离子（F⁻）与总碱度（T.A.）的分布特征。尽管整体剖面特征与前人提出的有机质成岩作用模型相一致，但剖面形态显示，多数站位还存在富含有机碳的深层反应层。尽管该层内有机碳的氧化过程不太可能对海洋碳循环造成显著影响，但孔隙水的剖面形态已发生显著改变。尽管该层与海水硫酸盐（SO₄²⁻）的接触时长已超过1000年，但其中有机质的分解似乎仅局限于有氧与亚有氧过程。上述研究结果表明，在有氧/亚有氧与无氧环境下，有机碳的分解与保存过程存在显著差异。
现代底栖通量在东边界沿岸上升流区附近达到峰值，其量级与东太平洋已报道的相关研究数值相近。初步估算结果显示，北纬20°以南北大西洋东部三分之一海域的底栖呼吸作用，即可贡献北大西洋深层总呼吸量的20%以上。将上述研究结果与有机碳埋藏及深水柱有机质分解的估算值相结合，表明该区域是有机碳输入深海的关键区域。