Life in the world’s oceans depends upon and is sustained by iron and phytoplankton

Oceans, especially those areas far from land, biologically modifies, optimizes, and recycles iron that begins as dust in the wind.

In spite of this potent biological evolutionary enhancement of iron contained in dust, high and rising CO2 has depleted dust falling in the oceans by 60%!

Just as plants at the base of the food chain on land need the rain to fall, ocean plants need the dust to fall.

A new research report published in the journal Nature Geoscience describes extensive in situ observations of bacterial iron conversion and recycling that is controlled by biological activity in the mesopelagic zone—the twilight zone where light does not penetrate. The study compared the nature and behaviour of raw and recycled iron from both the Southern Ocean and the Mediterranean Sea.

Ocean iron ecosystem – click to enlarge

Lead author Dr. Matthieu Bressac noted the research found that iron recycled from organic sources dissolves up to 100 times more efficiently in cold Subantarctic water, that is the most distant ocean from sources of dust, than the iron in dust blown from the desert in warmer Mediterranean waters, that are under a constant dust fall from the Sahara and North Africa.

“Iron is critical for phytoplankton at the base of the marine food chain and therefore for the productivity of life in the ocean,” Dr. Bressac said.

“Where iron is scarce, as it is in much of the Southern Ocean, the ocean is more like a desert, with less marine life.”

Life Finds A Way

The paper describes how ocean science suffers from a limited understanding of how iron dissolved in the ocean is distributed in deep layers such as the mesopelagic zone. This deep zone just beneath the productive sunlit top of the ocean is a major reservoir of iron for the surface ocean. The study combined observations with biogeochemical models, highlighting the roles of organic iron, that in the active life driven (biogenic) cycles with the freshly arriving windblown (lithogenic) iron.

Ocean Pastures Are Tended By Tiny Zooplankton Farmers. Every night these tiny creatures are in the surface pastures tending and feeding their plankton blooms By the time the sun rises they are hundreds of meters below, in the dark digesting and sending a vast amount of the days harvested carbon into the dark abyss as ‘plankton pies’ – click to read more

They found that the efficiency of iron nourishing and sustaining ocean pastures is significantly higher when the living system recycles iron as opposed to when the iron is fresh mineral dust. Co-author IMAS Professor Philip Boyd said better understanding marine iron distribution and utility is important to inform models and predictions of likely changes in ocean chemistry and productivity as the climate changes.

Indeed as the world is becoming dramatically less and less dusty due to global greening and the ocean pastures and their phytoplankton and entire food chain are suffering from the loss of mineral dust. A lesson can be learned from the Southern Ocean, most dust-free of all oceans, there the living ocean has adapted and evolved to make the most of what iron is available.

“By controlling the productivity of marine life, dissolved iron is critical to the carbon cycle, where atmospheric CO2 is absorbed by phytoplankton and sequestered.

“Our simulations reveal that the combined effect of lithogenic particles and ocean dynamics is responsible for a major redistribution (recycling) of dissolved iron in the first 1000 metres of the water column, not only in regions close to deserts but also at a global scale.

“As the climate changes these effects are likely to be accentuated, with significant repercussions for ocean productivity and the effectiveness of the carbon cycle,” Professor Boyd said.

How much carbon sinks

In the scientific history regarding the role of the iron carbon link in ocean pasture ecology has seen a persistent debate has gone on between the pure chemical oceanographers and the plankton ecologists. The simple-minded chemists have insisted that the most simple chemical equations ruled how iron behaved in the ocean. Their estimates were that each atom of iron could only be responsible for the capture of about 1000 atoms of carbon.  Some vigorously eschewed their ocean ecologist peers informed understandings that biological enhancement of the potency of iron was the rule. Now that 1000X is shown to have been a very very conservative number.

In this new report, the authors show that there is a 1,000-fold range in the dissolved available iron replenishment (recycling) rate when the system is biologically in need of iron, such as their Southern Ocean data sites. This finding highlights that the multifaceted effects of particle composition and dynamics on mesopelagic iron recycling need to be considered in global biogeochemical models to better explain the large spatial variability seen that is due to vital iron nutrient recycling.

Dust is down by 60%

More grass growing due to high and rising CO2 is good news for the Earth very bad news for the Oceans. A multi-national team has just published a study titled “Greening of the Earth and its Drivers“ in the journal Nature Climate Change showing significant global greening of Earth’s vegetated lands using data from NASA satellites over the past 33 years. – click to read more

The authors conclude by saying: Our findings suggest that the predicted changes in dust inputs by alteration of the biogenic/lithogenic composition of the sinking particle assemblage, may impact the replenishment of the subsurface iron inventory and vertical supply of iron not only in dusty regions, but also across the global ocean.

This alteration, across many oceanic provinces, of iron biological recycling, may, in return, have profound effects, aka collapse, of the C sequestration efficiency of the biological pump. They reference their cataclysmic concern to a paper by Mahowald, N. M. & Luo, C. A less dusty future? Geophys. Res. Lett. 30, 1903 (2003).  In that paper those authors show that the collapse of dust is upwards of 60% due to anthropogenic impacts.