The shallower oxygen-poor water masses of the ocean confine a majority of the microbial communities that can produce up to 90 % of oceanic N 2. This effective N 2yielding section encloses a suspended small-particle layer, inferred from particle backscattering (b bp) measurements. It is thus hypothesized that this layer (hereafter, the b bp-layer) is linked to microbial communities involved in N 2 yielding such as nitrate-reducing SAR11 as well as sulfur-oxidizing, anammox, and denitrifying bacteria-a hypothesis yet to be evaluated. Here, data collected by three BGC-Argo floats deployed in the Black Sea are used to investigate the origin of this b bp-layer. To this end, we evaluate how the key drivers of N 2-yielding bacteria dynamics impact the vertical distribution of b bp and the thickness of the b bp-layer. In conjunction with published data on N 2 excess, our results suggest that the b bp-layer is at least partially composed of the bacteria driving N 2 yielding for three main reasons: (1) strong correlations are recorded between b bp and nitrate; (2) the top location of the b bp-layer is driven by the ventilation of oxygen-rich subsurface waters, while its thickness is modulated by the amount of nitrate available to produce N 2 ; and (3) the maxima of both b bp and N 2 excess coincide at the same isopycnals where bacteria involved in N 2 yielding coexist. We thus advance that b bp and O 2 can be exploited as a combined proxy to delineate the N 2-yielding section of the Black Sea. This proxy can potentially contribute to refining delineation of the effective N 2-yielding section of oxygendeficient zones via data from the growing BGC-Argo float network.