Ideas and perspectives: Sea-level change, anaerobic methane oxidation, and the glacial–interglacial phosphorus cycle

[摘要] The oceanic phosphorus cycle describes how phosphorusmoves through the ocean, accumulates with the sediments on the seafloor, andparticipates in biogeochemical reactions. We propose a new two-reservoirscenario of the glacial–interglacial phosphorus cycle. It relies ondiagenesis in methane hydrate-bearing sediments to mobilize sedimentaryphosphorus and transfer it to the oceanic reservoir during times whenfalling sea level lowers the hydrostatic pressure on the seafloor anddestabilizes methane hydrates. The stock of solid phase phosphorusmobilizable by this process is of the same order of magnitude as thedissolved phosphate inventory of the current oceanic reservoir. Thepotential additional flux of phosphate during the glacial period is of thesame order of magnitude as pre-agricultural, riverine dissolved phosphatefluxes to the ocean. Throughout the cycle, primary production assimilatesphosphorus and inorganic carbon into biomass, which, upon settling andburial, returns phosphorus to the sedimentary reservoir. Primary productionalso lowers the partial pressure of  CO 2 in the surface ocean,potentially drawing down  CO 2 from the atmosphere. Concurrent with thisslow “biological pump”, but operating in the opposite direction, a “physicalpump” brings metabolic CO 2 -enriched waters from deep-ocean basins tothe upper ocean. The two pumps compete, but the direction of the CO 2  flux at the air–sea interface depends on the nutrient content of the deepwaters. Because of the transfer of reactive phosphorus to the sedimentaryreservoir throughout a glaciation cycle, low-phosphorus and high- CO 2 deepwaters reign at the beginning of a deglaciation, resulting in rapid transferof  CO 2 to the atmosphere. The new scenario provides another element tothe suite of processes that may have contributed to the rapidglacial–interglacial climate transitions documented in paleo-records.

[学科分类] 大气科学