Nitrate uptake and diffusive nitrate supply in the Central Atlantic
Nitrate uptake and diffusive nitrate supply in the Central Atlantic
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大西洋中部的硝酸盐吸收和扩散硝酸盐供应
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
M. Merino
中科院分区：
文献类型：
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作者：
D. Planas;S. Agustí;C. M. Duarte;T. Granata;M. Merino
研究了大西洋中部温跃层中硝酸盐扩散供应速率的纬度变化(35°~28°N)及其与之相关的硝酸盐和铵吸收速率的变化。计算的扩散硝酸盐通量呈现明显的纬向梯度，南大西洋副热带环流的硝酸盐供应最低(0.00037μmolm−3 d−1)，赤道至15°N之间的硝酸盐供应最高(2 3.5μmolm−3 d−1)，大部分站点的硝酸盐吸收速率在高光照下受到抑制。样带南端的硝态氮和氨氮吸收速率最低(分别为3和10umol m−3d−1)，向赤道方向增加(分别约为20和55μ−m 3d−1)，其中氨氮的增加幅度远大于硝态氮的吸收。F值在赤道以南最高(≈0.4)，样带南端最低(≈0.0 3)。根据基于O2的测量计算，表层水域溶解无机氮的总吸收速率与总初级生产力之间的斜率(4.72±1.54)略低于预期的C/N比6.6，但并不显著。硝酸盐的平均摄取率与中大西洋生物层中硝酸盐的平均估计扩散供应量没有显著差异。然而，随着扩散硝酸盐通量到生物层的⅓功率的增加，硝酸盐吸收速率也随之增加。结果，在硝酸盐供应最低的站点，硝酸盐的吸收远远超过了生物层的硝酸盐通量(最高可达100倍)。过量硝酸盐吸收平均为0.6 5±0.2 4mmolN3m−2 d−1(范围0.0 5~1.9mmolN3m−2 d−1)，这必须通过大气沉降和其他扰动事件提供。这种过量的硝酸盐吸收与最不具生产力的地区的扩散供应相比相对较大，在这些地区，外部硝酸盐投入推动了新的生产。相反，在高扩散通量足以维持高硝酸盐摄取率的情况下，这些硝酸盐来源的重要性要小得多。
The latitudinal variation (35° to 28°N) in the rate of diffusive nitrate supply across the thermocline and the associated variation in the uptake rate of nitrate and ammonium in the Central Atlantic was studied. The calculated diffusive nitrate flux showed a sharp latitudinal gradient, with the lowest nitrate supply (0.00037 μmol m−3 d−1) in the South Atlantic subtropical gyre and the highest values (23.5 μmol m−3 d−1) between the Equator and 15°N. The uptake rate of nitrate was inhibited at high irradiance at most stations. Both nitrate and ammonium uptake rates were lowest (about 3 and 10 umol m−3 d−1, respectively) at the southern end of the transect and increased (about 20 and 55 μmol m−3 d−1, respectively) towards the Equator, with this increase being much greater for ammonium than for nitrate uptake. The f‐ratio was highest (≈0.4) just south of the Equator and lowest (≈0.03) at the southern end of the transect. The slope between total uptake rate of dissolved inorganic nitrogen and gross primary production, calculated from O2 ‐based measurements, in surface waters (4.72 ± 1.54) was somewhat lower, but not significantly so, than the expected C/N ratio of 6.6. The average uptake rate of nitrate did not differ significantly from the average estimated diffusive supply of nitrate to the biogenic layer over the Central Atlantic. However, the nitrate uptake rate increased as the ⅓ power of the diffusive nitrate flux to the biogenic layer. As a result, nitrate uptake far exceeded (by up to 100‐fold) the nitrate flux to the biogenic layer in the stations where the supply of nitrate was lowest. The excess nitrate uptake averaged 0.65 ± 0.24 mmol NO3 m−2 d−1 (range, 0.05–1.9 mmol NO3 m−2 d−1), which must be supplied through atmospheric deposition and other perturbation events. This excess nitrate uptake is relatively large compared to the diffusive supply in the most unproductive areas, where external nitrate inputs fuel the new production. In contrast, these sources of nitrate are far less significant where high diffusive fluxes suffice to maintain high nitrate uptake rates.