Modeling the impact of iron and phosphorus limitations on nitrogen fixation in the Atlantic Ocean
Modeling the impact of iron and phosphorus limitations on nitrogen fixation in the Atlantic Ocean
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DOI：
10.5194/bg-4-455-2007
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发表时间：
2007-01-01
期刊：
影响因子：
4.9
通讯作者：
Hood, R. R.
中科院分区：
文献类型：
--
作者：
Coles, V. J.;Hood, R. R.
本研究的首要目标是模拟地下N*（感，格鲁伯和萨米恩托，1997年; GS 97）异常模式在北大西洋，并确定全流域的N-2固定率，需要这样做。我们提出的结果从一个新的大西洋实施耦合的物理-地球化学模型，其中包括一个明确的，动态的表示N-2固定与光，氮，磷和铁的限制，和可变的化学计量比。该模型能够再现氮，磷和铁的浓度变异一阶。后者是通过将铁沉积直接纳入模型的碎屑铁隔间来实现的，这使模型能够重现非洲西海岸附近溶解铁浓度的急剧近地表梯度和最近观测研究中观察到的深层溶解铁浓度。该模型可以重现大尺度的N* 异常模式，但需要相对较高的表面固氮率（10 ° N-30 ° N为1.8 × 10（12）摩尔N年（-1），25 ° S-65 ° N为3.4 × 10（12）摩尔N年（-1））。在该模型中，表面固氮速率模式不与N* 的亚表面梯度共位。相反，固定氮平流远离其源之前，产生地下N* 异常。磷矿化率（相对于氮）的变化线性地决定了表面固氮率，因为它们改变了磷限制的程度，这是模型中大西洋的主要限制。磷矿化率必须增加约2倍（相对于氮），以产生地下N* 异常，是可比的观测。我们的结论是，大西洋（和全球）的N-2固定率估计值可能需要向上修正，这将有助于解决Codispoti et al.（2001）和Codispoti（2007）提出的全球氮收支失衡问题。
The overarching goal of this study is to simulate subsurface N* (sensu, Gruber and Sarmiento, 1997; GS97) anomaly patterns in the North Atlantic Ocean and determine the basin wide rates of N-2-fixation that are required to do so. We present results from a new Atlantic implementation of a coupled physical-biogeochemical model that includes an explicit, dynamic representation of N-2-fixation with light, nitrogen, phosphorus and iron limitations, and variable stoichiometric ratios. The model is able to reproduce nitrogen, phosphorus and iron concentration variability to first order. The latter is achieved by incorporating iron deposition directly into the model's detrital iron compartment which allows the model to reproduce sharp near surface gradients in dissolved iron concentration off the west coast of Africa and deep dissolved iron concentrations that have been observed in recent observational studies. The model can reproduce the large scale N* anomaly patterns but requires relatively high rates of surface nitrogen fixation to do so (1.8 x 10(12) moles N yr(-1) from 10 degrees N-30 degrees N, 3.4x10(12) moles N yr(-1) from 25 degrees S-65 degrees N). In the model the surface nitrogen fixation rate patterns are not co-located with subsurface gradients in N*. Rather, the fixed nitrogen is advected away from its source prior to generating a subsurface N* anomaly. Changes in the phosphorus remineralization rate (relative to nitrogen) linearly determine the surface nitrogen fixation rate because they change the degree of phosphorus limitation, which is the dominant limitation in the Atlantic in the model. Phosphorus remineralization rate must be increased by about a factor of 2 (relative to nitrogen) in order to generate subsurface N* anomalies that are comparable to the observations. We conclude that N-2-fixation rate estimates for the Atlantic (and globally) may need to be revised upward, which will help resolve imbalances in the global nitrogen budget suggested by Codispoti et al. (2001) and Codispoti (2007).