The role of prokaryotic microbial productivity in P cycling in the benthic boundary layer (BBL) of deep‐sea sediments (350–1,900 m bottom depths) was studied in the P‐impoverished southeastern Mediterranean Sea (SEMS) using sediment cores and incubation reactors. Our results show that orthophosphate (PO₄) benthic fluxes were negative (consumption) at a rate of −11.0 ± 3.3 µmolem⁻²d⁻¹, while the dissolved organic phosphate (DOP) flux was positive (production) at rate of 4.5 ± 1.6 µmolem⁻²d⁻¹. Therefore, the SEMS sedimentary BBL acts as an active net sink for P, similar to other impoverished subtropical oceanic gyres, yet at much shallower water depths and much closer to the terrestrial margin. Considering the water column integrated P mass, and the sedimentary net removal fluxes of P, we calculated a turnover time of ∼90 years for the bottom water in the SEMS, which is similar to the deep water residence time in this basin. Apart abiotic removal of PO₄ under oxic conditions (e.g., co‐precipitation with iron, forming iron‐phosphate minerals), prokaryotic microbial utilization played an important role in generating DOP through aerobic respiration in the BBL, resulting in a net release of DOP. Our study demonstrates that microbial communities in the BBL play an important role in regulating P concentrations, fluxes and forms in the energy‐starved environment of the SEMS seabed. These results may contribute to our understanding of water column P dynamics in the low nutrient low chlorophyll basins.

中文翻译：

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东地中海深部底栖边界层的磷通量与原核循环

在深海沉积物底栖生物边界层（BBL）（350-1,900 m底部深度）的P循环中，原核微生物生产力在P贫化的东南地中海（SEMS）中使用沉积物核心和孵化反应器进行了研究。我们的结果表明，正磷酸盐（PO ₄）底流通量为负（消耗），速率为-11.0±3.3 µmolem ^-2 d ^-1，而溶解的有机磷酸盐（DOP）通量为正值（生产），速率为4.5± 1.6 µmolem ^-2 d ^-1。因此，与其他贫困的亚热带海洋环流相似，SEMS沉积BBL充当了P的活动净汇，但水深更浅且距离陆地边缘更近。考虑到水柱的P积分质量和P的沉积净去除通量，我们计算出SEMS底部水的周转时间约为90年，这与该盆地深水停留时间相似。除非生物性去除PO ₄在有氧条件下（例如与铁共沉淀，形成磷酸铁矿物质），原核微生物利用在BBL的有氧呼吸产生DOP中起着重要作用，从而导致DOP的净释放。我们的研究表明，BBL中的微生物群落在调节SEMS海床能源匮乏的环境中的P浓度，通量和形式方面起着重要作用。这些结果可能有助于我们了解低营养低叶绿素盆地中水柱P的动态。