At what rate are ISA particles adsorbed onto marine snow and thereby removed from the euphotic zone?
We don’t have a rate per-se. What we can say is given that iron gets recycled naturally, some will go to the depths and become part of the sediments.
Precipitation of Fe(III) chloride by rain induces a colloid in seawater. It is worth noting that such colloidal precipitates become dissolved by the dissolution of phytoplankton excretes, converting them into an efficient, consumable nutrient.
We envisage the ISA method delivering iron to the troposphere for many years until the surface temperatures become normalized. So, iron lost from the ocean surface will be replaced by a semi-permanent immersion process for as long as ISA dispersion remains in operation.
Your claim that iron is the most limiting nutrient can be challenged, as many would say that is phosphorus or even reactive nitrogen.
For our most preferred ISA plume emission region, the Southern Ocean, iron is clearly the most limiting nutrient. This ocean region is very rich in phosphate and nitrate macronutrients.
ISA would additionally reactivate vertical ocean currents, increasing the upwelling of deep water rich in macronutrients.
In ocean regions with lower macronutrient content, zooplankton can increase the uplift of nutrients from the deep, feeding their phytoplankton food through their diurnal movement up and down of up to 1000 m.
In 1.4 doesn’t most oxidation of phytoplankton litter take place in the upper water column, perhaps just in the top 300m?
Phytoplankton litter is oxidised within the whole food chain that consumes it. This includes faeces and bodies of zooplankton, which fall much faster and deeper than the original litter itself. Because most phytoplankton end up digested, most of their remnants become oxidised in the deep ocean.
During its cycling through the food chain, a proportion of the digested phytoplankton organic carbon, estimated in the one-digit percentage range, gets changed into dissolved and undissolved refractory organic substances, such as humid acids.
In “By assimilation”, it is my understanding that dissolution of silicate rocks reacts with or absorbs H2CO3, it does not produce it.
Silicate rocks produce alkalinity by transforming calcium silicate with water and CO2 (as carbonic acid) to calcium hydrogen-carbonate and silica, or more silica-rich silicates. The water-soluble hydrogen-carbonate generated is then transported to the ocean by water run-off, including ground water, melt water, springs and rivers.
The ocean crust aquifer is probably the most potent alkalinity source, even surpassing continental weathering, because it is produced largely from alkaline-reacting olivine and serpentine minerals. These sub-ocean rocks are additionally ‘weathered’ by carbonic acid, producing hydrogen-carbonate. The high temperatures that are present in ocean crust aquifers generate this reaction of olivine with ocean bottom water, which is driven through crevices in huge quantities by strong convection currents. (These quantities are comparable to the run off into the oceans of all the world’s rivers.) Serpentine, magnetite and also hydrogen is produced in great quantities. By abiotic and biotic activities within this creviced crust aquifer, this reducing reaction changes sulfates to sulphides, nitrates to ammonium and hydrogen carbonates to organic carbons, such as humic acids. This generates a sufficient mass of alkalinity to neutralize a roughly equivalent amount of carbonic acid in the ocean bottom water, which derives from the phytoplankton dependent food chain.
Doesn’t acid assimilation by phytoplankton just convert acidic CO2 into neutral biomass and oxygen, rather than leaving an alkaline surplus?
When assimilation converts acid hydrogen-carbonate to organic carbon that is still a pH rise, so we consider it as generating alkalinity.
(Interestingly, to keep their internal pH constant, some algae such as coccolithophores use their assimilation-derived alkalinity to create calcium carbonate shells.)
In 3.2 shouldn’t ‘suboxic’ be ‘hypoxic’?
Here’s our understanding of the language terms designating different oxygen concentrations within oxygen-depleted redox milieu:
- Oxic: Water containing enough oxygen for there to be no nitrate or manganese(IV)-reducing tendency.
- Suboxic: Water low enough in oxygen that microbes use the oxidants nitrate, manganese(IV), or iron(III) to consume reductants.
- Anoxic: Any CO2, carbonic acid, or sulfate-reducing water milieu.
- We understand the term hypoxic as used to describe metabolic states.