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Nitrogen enters the ocean through precipitation, runoff, or as N 2 from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N 2 so it must undergo nitrogen fixation which is performed predominantly by cyanobacteria. [82] Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 ...
Whales feed at deeper levels in the ocean where krill is found, but return regularly to the surface to breathe. There whales defecate a liquid rich in nitrogen and iron. Instead of sinking, the liquid stays at the surface where phytoplankton consume it. In the Gulf of Maine, the whale pump provides more nitrogen than the rivers.
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]
The iron oxides were denser than water and fell to the ocean floor forming banded iron formations (BIF). [19] Over time, rising oxygen levels removed increasing amounts of iron from the ocean. BIFs have been a key source of iron ore in modern times. [20] [21]
There are three different iron dependent proteins, molybdenum-dependent, vanadium-dependent, and iron-only, with all three nitrogenase protein variations containing an iron protein component. Molybdenum-dependent nitrogenase is the most commonly present nitrogenase. [33] The different types of nitrogenase can be determined by the specific iron ...
Another cause of concern is the sheer amount of urea needed to capture the same amount of carbon as eq. iron fertilization. The nitrogen to iron ratio in a typical algae cell is 16:0.0001, meaning that for every iron atom added to the ocean a substantial larger amount of carbon is captured compared to adding one atom of nitrogen. [35]
Iron is also stored as a pigment called hemosiderin, which is an ill-defined deposit of protein and iron, created by macrophages where excess iron is present, either locally or systemically, e.g., among people with iron overload due to frequent blood cell destruction and the necessary transfusions their condition calls for. If systemic iron ...
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.