How much nitrogen and light noble gases are recycled in modern subduction zones is unclear. Fumaroles act as a means for passive degassing in arcs. They receive variable contributions of volatiles from arc magmas, themselves sourced from the mantle wedge. The gas compositions reflect the extent of volatile enrichment in sub-arc mantle sources and constrain slab dehydration. However, contributions from atmospheric components in fumaroles are unavoidable. For N₂, neon and argon, the atmospheric components are challenging to discern from slab-derived components. Here, we report ¹⁵N¹⁵N measurements from eight fumaroles and seven bubbling springs, along the Central American arc. Our new ¹⁵N¹⁵N data are coupled with noble gases measurements and show that air-derived components in volcanic gas discharges can easily be underestimated, in both fumaroles and springs, using conventional stable isotope or noble gases methods. We show that, in the absence of ¹⁵N¹⁵N data, previously used tracers for air (e.g., ${\delta }^{15}$N, N₂/Ar, N₂/He, among others) may lead to erroneous conclusions regarding the origin of volatiles in mixed gases. In contrast, ¹⁵N¹⁵N data provide quantitative constraints on the nature and contributions of both atmospheric and magmatic components. Most springs are heavily dominated by air-derived N₂, while fumaroles show substantial contributions of volcanic endmembers. Based on the fumarole data, we show that magma sources beneath the central American arc are enriched in all volatiles relative to ³He, by two to three orders of magnitude compared to the MORB source. We use new ¹⁵N¹⁵N data to obtain source N₂/³He, ³He/³⁶Ar and ³He/²²Ne ratios which we then use to compute volcanic N₂, Ar and Ne degassing fluxes. Using this approach, we show that outgassing fluxes appear to match subduction fluxes in the Central America subduction zone. We determine an N₂ outgassing flux of between $4.0\times {10}^8$ and $1.0\times {10}^9$ mol N₂/y, comparable to the subduction flux of $5.7\times {10}^8$ mol N₂/yr determined previously. We obtain a similar conclusion for ²²Ne and ³⁶Ar. Overall, the volatile fluxes in the central American subduction zone no longer seem to require net transfer of N₂, Ar, and Ne, to the deep mantle.

在现代俯冲带中回收了多少氮气和轻质惰性气体尚不清楚。喷气孔作为电弧被动脱气的一种手段。它们从弧形岩浆中接收到挥发物的可变贡献，这些岩浆本身来自地幔楔。气体成分反映了亚弧地幔源中挥发性物质的富集程度并限制了板片脱水。然而，喷气孔中大气成分的贡献是不可避免的。对于 N ₂、氖气和氩气，大气成分很难与平板衍生成分区分开来。在这里，我们报告了沿中美洲弧线的八个喷气孔和七个冒泡弹簧的¹⁵ N ¹⁵ N 测量值。我们的新¹⁵ N ¹⁵N 数据与惰性气体测量值相结合，表明使用传统的稳定同位素或惰性气体方法很容易低估火山气体排放中的空气衍生成分，无论是在喷气孔还是泉水。我们表明，在没有¹⁵ N ¹⁵ N 数据的情况下，以前使用的空气示踪剂（例如，${\delta }^{15}$N、N ₂ /Ar、N ₂ /He 等）可能会导致关于混合气体中挥发物来源的错误结论。相比之下，¹⁵ N ¹⁵ N 数据提供了对大气和岩浆成分的性质和贡献的定量限制。大多数泉水主要以空气衍生的 N _{2 为主}，而喷气孔则显示出火山端元的重要贡献。根据喷气孔数据，我们表明中美洲弧下方的岩浆源相对于³ He富含所有挥发物，与 MORB 源相比高出两到三个数量级。我们使用新的¹⁵ N ¹⁵ N 数据来获得源 N ₂/ ³ He、³ He/ ³⁶ Ar 和³ He/ ²² Ne 比率，然后我们使用它们来计算火山 N ₂、Ar 和 Ne 脱气通量。使用这种方法，我们表明除气通量似乎与中美洲俯冲带的俯冲通量相匹配。我们确定了之间的 N ₂除气通量$4.0\times {10}^8$ 和 $1.0\times {10}^9$mol N ₂ /y，与俯冲通量相当$5.7\times {10}^8$mol N ₂ /yr 先前确定。我们对²² Ne 和³⁶ Ar得到了类似的结论。总体而言，中美洲俯冲带的挥发性通量似乎不再需要 N ₂、Ar 和 Ne 向深部地幔的净转移。