Benthic phosphorus regeneration, net primary production, and ocean anoxia: A model of the coupled marine biogeochemical cycles of carbon and phosphorus

Abstract

We examine the relationships between ocean ventilation, primary production, water column anoxia, and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon (C) and phosphorus (P). The elemental cycles are coupled via the Redfield C/P ratio of marine phytoplankton and the C/P ratio of organic matter preserved in marine sediments. The model assumes that on geologic timescales, net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone. The model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water‐sediment interface. Evidence from marine and lacustrine settings, modern and ancient, demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia‐dysoxia expands. Steady state simulations show that a reduction in the rate of thermohaline circulation, or a decrease of the oxygen content of downwelling water masses, intensifies water column anoxia‐dysoxia and at the same time increases surface water productivity. The first effect reflects the declining supply of oxygen to the deeper parts of the ocean. The second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides. Sedimentary burial of organic carbon and authigenic calcium phosphate mineral (francolite), on the other hand, is promoted by reduced ocean ventilation. According to the model, global‐scale anoxia‐dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system. Consequently, higher rates of primary production and organic carbon burial can be achieved, even when the continental supply of reactive phosphorus to the oceans remains unchanged.

Redfield revisited: 2. What regulates the oxygen content of the atmosphere?

“…Mass-balance approaches demonstrate that crustal overturn only buffers oxygen over hundreds of millions of years [Van Cappellen and Ingall, 1996]. By enhancing phosphorus input through amplifying rock weathering and suppressing phosphorus output through preferential recycling from sediments, different organisms increase the amount of phosphorus in circulation in the Earth system, while other nitrogen-fixing organisms help maintain nitrogen at equivalent, biologically available levels to phosphate.…”

“…On the basis of data relating primary production to sedimentation rate [Miiller and Suess, 1979] and sedimentation rate to organic carbon burial [Henrichs and Reeburgh, 1987], organic carbon burial is assumed to be a quadratic function of new production, given by (3) and independent of ocean anoxia. The nonlinearity implies that increases in new production occur primarily in the shelf environments where a greater fraction of production is preserved than in the deep ocean [Van Cappellen and Ingall, 1994]. A sensitivity study in which the power relating organic carbon burial to changes in new production was altered over the range 1-3 revealed that this does not have a great impact on the final steady state of oxygen [Lenton, 1998b].…”

Marine redox variations and nitrogen cycle of the early Cambrian southern margin of the Yangtze Platform, South China: Evidence from nitrogen and organic carbon isotopes

“…Owing to the high energy demand of breaking the molecular nitrogen bond, N 2 -fixation can only occur when fixed-N (nitrate and ammonia) concentrations are low, and nutrient phosphorus is in excess supply (Tyrrell, 1999). This means that fixed-N (nitrate and ammonia) in the surface water most likely had been consumed by intense denitrification and/or anammox processes (Junium and Arthur, 2007;Luo et al, 2011) while phosphorus was efficiently recycled under anoxic conditions (Ingall et al, 1993;Van Cappellen and Ingall, 1994). In the early Cambrian, increasing weathering sulfate flux into the ocean (Feng et al, 2014;Jin et al, 2014) and high TOC (Fig.…”

Environmental Impacts—Marine Biogeochemistry

“…Sedimentation rates of organic matter vary spatially, especially in the archipelagos because of the fractured topography (Winterhalter et al 1981) and temporally because of the seasonality of plankton growth and senescence (Bianchi et al 2002). Anoxia which is common in the Baltic Sea can favour burial of organic matter but diminish the burial of P because the formation of Fe-oxyhydroxides that bind PO 4 is inhibited (Van Cappellen and Ingall 1994;Ingall et al 1993;Mort et al 2010;Jilbert et al 2011). In the Baltic Sea, Edlund and Carman (2001) reported higher organic C:P ratios for anoxic than for oxic sites and Jilbert et al (2011) suggested increasing rates of P mineralisation in more reduced conditions.…”