P Fluxes and Prokaryotic Cycling at Benthic Boundary Layer in the Deep Southeastern Mediterranean Sea

Guy Sisma-Ventura, Barak Herut, Jacob Silverman, Timor Katz, Maxim Rubin-Blum, Eyal Rahav

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Article numbere2020JG006110
JournalJournal of Geophysical Research: Biogeosciences
Issue number4
StatePublished - Apr 2021
Externally publishedYes

Bibliographical note

Funding Information:
The authors would like to thank Dar Golomb for producing the illustration in Figure 1 , Hila Frank, and Dina Kolker for their help in sampling and analyses, and the R.V captain and crew for help at sea. This work was partly by the National Monitoring Program of Israel's Mediterranean waters and by the Israel Scientific Foundation (grant # 913/19 to M.R‐B) and by the Ministry of Science and Technology (MOST) (grant # 001126 to G.S‐V, M.R‐B and E.R). The authors declare that they have no known conflicts of interests that could have appeared to influence the work reported in this paper. Bat‐Galim

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.


  • DOP
  • East Mediterranean Sea
  • P flux
  • PO
  • deep-sea sediments
  • prokaryotic production

ASJC Scopus subject areas

  • Soil Science
  • Forestry
  • Water Science and Technology
  • Paleontology
  • Atmospheric Science
  • Aquatic Science
  • Ecology


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