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Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter. Ammonia and urea are released into the water by excretion from plankton. Nitrogen sources are removed from the euphotic zone by the downward movement of the organic matter. This can occur from sinking of phytoplankton, vertical mixing, or ...
Biological productivity (photosynthesis) in marine ecosystems is often limited by the bioavailability of nitrogen. [6]The amount of bioavailable nitrogen (nitrate (NO 3 −), nitrite (NO 2 −), and ammonium (NH 4 +)) depends on the inputs from nitrogen fixation and losses from denitrification and anammox as dinitrogen gas (N 2), a compound only accessible to nitrogen-fixing bacteria.
There is also evidence for shifts in the production of key intermediary volatile products, some of which have marked greenhouse effects (e.g., N 2 O and CH 4, reviewed by Breitburg in 2018, [15] due to the increase in global temperature, ocean stratification and deoxygenation, driving as much as 25 to 50% of nitrogen loss from the ocean to the ...
In general, nitrogen tends to be a limiting ocean nutrient, but in HNLC regions it is never significantly depleted. [1] [2] Instead, these regions tend to be limited by low concentrations of metabolizable iron. [1] Iron is a critical phytoplankton micronutrient necessary for enzyme catalysis and electron transport. [3] [4]
Deep ocean water contains the largest reservoir of nitrogen available to hydrothermal vents, with around 0.59 mM of dissolved nitrogen gas. [24] [25] Ammonium is the dominant species of dissolved inorganic nitrogen, and can be produced by water mass mixing below hydrothermal vents and discharged in vent fluids. [25]
Ocean iron fertilization is an example of a geoengineering technique that involves intentional introduction of iron-rich deposits into oceans, and is aimed to enhance biological productivity of organisms in ocean waters in order to increase carbon dioxide (CO 2) uptake from the atmosphere, possibly resulting in mitigating its global warming effects.
Once iron enters the ocean, it can be distributed throughout the water column through ocean mixing and through recycling on the cellular level. [54] In the arctic, sea ice plays a major role in the store and distribution of iron in the ocean, depleting oceanic iron as it freezes in the winter and releasing it back into the water when thawing ...
Upwelling recycles iron and causes higher deep water iron concentrations. On average there is 0.07±0.04 nmol Fe kg −1 at the surface (<200 m) and 0.76±0.25 nmol Fe kg −1 at depth (>500 m). [21] Therefore, upwelling zones contain more iron than other areas of the surface oceans. Soluble iron in ferrous form is bioavailable for utilization ...