Iron is the single most important element in our world’s oceans and to you and I.
It empowers efficient photosynthesis and without it ocean pasture plant life cannot make sufficient food to feed their world, nor would they make the 4 out of 5 breaths of oxygen that keep you alive.
But iron is heavy and in the oceans it sinks like an anchor and would be lost to the abyss save for the cleverness of Mother Nature.
She evolved ocean life’s ability to fight to keep every atom of iron from sinking in the most perfect recycling system ever created!
Iron, limits the growth of green plants, aka primary production, in much of the world’s ocean. It arrives in the ocean primarily in the form of tiny particles of iron rich mineral dust whether as sediment washed in by rivers or dust that blows in the wind. But deep ocean hydrothermal vents, ‘hot springs’, gushing ‘black smokers’, also are an important source of ocean iron.
Once in the ocean iron empowers ocean pasture photosynthesis by the phytoplankton. Nature has ordained that iron more precious than gold is so vital that photosynthesis is barely able to take place without it, but with iron atoms sitting on the tips of the photosynthetic antennae ocean photosynthesis soars to unimaginable rates and efficiencies. A new paper in Nature Geoscience reveals more about iron.
Iron will boost or limit the growth of plankton depending on its presence which only needs to be in infinitesimal amounts measured in parts per trillion. Thirty years ago the late great John Martin (a chemical oceanographer) showed that the oceans default iron concentration is only about 3 parts per trillion, when iron rich dust arrives and the concentration rises to 30 parts per trillion the ocean blooms. It is iron that controls the ‘bloom and bust’ cycle of ocean ecosystems.
In July 1988, during at a lecture at the Woods Hole Oceanographic Institution, oceanographer John Martin stood up and said in his best Dr. Strangelove accent, “Give me a half tanker of iron, and I will give you an ice age.”
Martin’s Iron hypothesis has spawned a decades long fascinating scientific study of ocean pastures.
Hard as Iron
Iron is a tough element and it is chemically challenged in nature. As soon as iron is exposed to oxygen,whether in air or water, it ‘rusts’ and forms a tough iron oxide. There its reactivity might end save for the force of living Nature that can change that rust once again and again and again into dissolved bioavailable iron and even when the iron naturally aggregates into heavy sinking particles, aka anchors, Nature immediately re-dissolves and recycles it to keep this most precious element of all available to sustain ocean life.
Iron rarely persists in dissolved forms. Although dissolved iron ought not to sink in the water in which it is dissolved, it forms and binds to particles making them heavy so that they sink rapidly. However, writing in Nature Geoscience 20 Feb. 2017, Fitzsimmons et. al. report dissolved iron instead persists and can remain in hydrothermal plumes that stretch halfway across the Pacific Ocean.
The authors state this shows that a natural mechanism exists that keeps iron from sinking via particulate forms. This iron phenomenon dramatically illustrates the way Nature keeps it most precious iron available for the all important life force of the oceans, its ocean pastures and their photosynthetic plankton.
Black Smokers help fuel ocean life and ocean science
Hydrothermal vents are a rare but precious source of iron to the ocean. Their plumes transport dissolved metals and disperse them across ocean basins. The world’s largest hydrothermal plume from the South East Pacific Rise (SEPR) shares its dissolved iron and other metals westwards more than 4,000 km (note image at top of this post.) Such long-range transport of dissolved iron from hydrothermal vents has proven to challenge prevailing ocean science dogma.
Iron has been assumed to precipitate out of the hot hydrothermal, black smoker, plumes and end up entirely as mineral deposits surrounding the smoker vents. However, nanometer-sized minerals and organic molecules, ligands, that bind iron have long been observed to comprise an important fraction of iron found in seawater. The fact that there is a natural iron scavenging and recycling facet of Nature is a simple explanation that readily accounts for the pervasive occurrence of iron, albeit at low concentrations everywhere in the world’s oceans.
The largest of these dissolved iron fractions — known as colloids — are so small and low density that they have a sinking rate that is inconsequential compared to ocean motion and mixing. The authors estimate such iron colloids might only sink 1.5 m per year! Even less, much less, as they become part of a living derived biomass.
Strikingly, the research reports that the speed of descent of iron near or far from the black smoker vent was indistinguishably similar. To explain these findings, Fitzsimmons et al. argue that comparatively rapid and reversible exchanges with the drifting particles must be responsible for the slow sinking rate of dissolved iron.
Life finds a way
Dissolved iron persists due to it being actively conserved by the life force of the oceans which had to evolve a way to keep it’s incredibly precious but heavy iron. Bacteria are surely responsible for some of the iron recycling processes but the physical chemical ocean science boffins of this team have yet to describe the process with the simplicity of a chemist as opposed to the acknowledged biologists ‘life found a way’ standard explanation. Fitzsimmons et al. make a compelling case that dissolved iron persists in a deep ocean hydrothermal plume by recycling exchanges with biological processes. Whatever the processes driving these exchanges, they are surely manifest throughout the world’s seven seas.
Parts of this post derive from Heriot Watt Univ. and Scripps Inst. press releases as well as a review by William Homoky.