Rodellas Valentí, Garcia-Orellana Jordi, Masqué Pere, Feldman Mor, Weinstein Yishai
Institut de Ciència i Tecnologia Ambientals and
Institut de Ciència i Tecnologia Ambientals and Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain;
Proc Natl Acad Sci U S A. 2015 Mar 31;112(13):3926-30. doi: 10.1073/pnas.1419049112. Epub 2015 Mar 16.
The Mediterranean Sea (MS) is a semienclosed basin that is considered one of the most oligotrophic seas in the world. In such an environment, inputs of allochthonous nutrients and micronutrients play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the MS, whereas the role of submarine groundwater discharge (SGD) has been largely ignored. However, given the large Mediterranean shore length relative to its surface area, SGD may be a major conveyor of dissolved compounds to the MS. Here, we used a (228)Ra mass balance to demonstrate that the total SGD contributes up to (0.3-4.8)⋅10(12) m(3) ⋅ y(-1) to the MS, which appears to be equal or larger by a factor of 16 to the riverine discharge. SGD is also a major source of dissolved inorganic nutrients to the MS, with median annual fluxes of 190⋅10(9), 0.7⋅10(9), and 110⋅10(9) mol for nitrogen, phosphorous, and silica, respectively, which are comparable to riverine and atmospheric inputs. This corroborates the profound implications that SGD may have for the biogeochemical cycles of the MS. Inputs of other dissolved compounds (e.g., iron, carbon) via SGD could also be significant and should be investigated.
地中海是一个半封闭的海域，被认为是世界上营养盐含量最低的海域之一。在这样的环境中，陆源营养物质和微量营养物质的输入对维持初级生产力起着重要作用。传统上，大气沉降和河流径流被认为是地中海营养物质的主要外部来源，而海底地下水排泄（SGD）的作用在很大程度上被忽视了。然而，鉴于地中海海岸线长度与其表面积之比很大，SGD可能是溶解化合物进入地中海的主要输送途径。在这里，我们利用镭-228质量平衡法证明，进入地中海的SGD总量高达（0.3 - 4.8）×10¹²立方米·年⁻¹，这似乎比河流径流量大16倍或与之相当。SGD也是地中海溶解无机营养物质的主要来源，氮、磷和硅的年通量中位数分别为190×10⁹、0.7×10⁹和110×10⁹摩尔，与河流和大气输入量相当。这证实了SGD可能对地中海生物地球化学循环产生深远影响。通过SGD输入的其他溶解化合物（如铁、碳）也可能很显著，值得进一步研究。
