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The nitrogen cycle is as important in the ocean as it is on land. While the overall cycle is similar in both cases, there are different players and modes of transfer for nitrogen in the ocean. [81] Nitrogen enters the ocean through precipitation, runoff, or as N 2 from the atmosphere.
Aeolian dust is a critical part of the iron cycle by transporting iron particulates from the Earth's land via the atmosphere to the ocean. [ 23 ] Volcanic eruptions are also a key contributor to the terrestrial iron cycle, releasing iron-rich dust into the atmosphere in either a large burst or in smaller spurts over time. [ 24 ]
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.
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 ...
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]
Open ocean areas with no oxygen have grown more than 1.7 million square miles in the last 50 years, and coastal waters have seen a tenfold increase in low-oxygen areas in the same time. [34] Measurement of dissolved oxygen in coastal and open ocean waters for the past 50 years has revealed a marked decline in oxygen content.
[33] [34] [35] A decrease in ocean oxygen levels affects how productive the ocean is, how nutrients and carbon move around, and how marine habitats function. [36] [37] As the oceans become warmer this increases the loss of oxygen in the oceans. This is because the warmer temperatures increase ocean stratification. The reason for this lies in ...