Studies show deep ocean iron has changed little over the last 76 million years leaving only the diminishing iron from failing dust in the wind to influence and explain changing and collapsing ocean pasture productivity and ecology.
Ocean student boffins at the Woods Hole Oceanographic Institution (WHOI) have published a paper that shows over the span of tens of millions of years that the deep ocean geology is a large unchanging source of dissolved iron in the central Pacific Ocean. This finding illustrates the role of ever so slow but steady deep ocean source of iron that makes it to the sunlit surface waters where that iron, along with other sources of iron, plays a critical role in sustaining ocean pasture life. The work clearly reveals just how critical the declining iron from dust in the wind from fossil fuel age CO2 impacts is to ocean ecology. It’s only wind born iron that is diminishing in lock step with declining ocean primary productivity. Read more about the catastrophe for the ocean that is accompanying global greening.
The new results fit well with long-standing reports that iron from dust in the wind is the primary driving factor in present day ocean pasture ecology as pioneered by the late great ocean scientist John Martin. Martin also was the champion of dust in the wind being a major factor in the waxing and waning of ice ages and this new 76 million year data set seems to perfectly confirm Martins ice age dust hypotheses.
“Our study is a long-term view–over the past 76 million years–of where iron has been coming from in the central Pacific,” says Tristan Horner, a postdoctoral fellow in the Marine Chemistry and Geochemistry Department at WHOI and lead author of the paper to be published February 3, 2015, in Proceedings of the National Academy of Sciences.
Vast regions of the worlds oceans are rich in other nutrients, but are lacking vital iron–a most critical element for marine life. Iron is what empowers photosynthesis to kick into ‘high gear’ and sustain the growth of phytoplankton, tiny drifting ocean plants that form the base of the ocean food chain. Phytoplankton is the ‘grass of ocean pastures’ feeding all of ocean life and they play a most important role, far greater than trees for example, in the Earth’s climate by regulating atmospheric CO2.
In addition to producing the majority of planet’s oxygen, phytoplankton living at the ocean’s surface and act to repurpose CO2 –a heat-trapping ‘greenhouse gas’. Through photosynthesis, phytoplankton take carbon from the air to grow and reproduce. Billions of tonnes of CO2 have naturally been parked in ocean pastures as standing biomass, more sinks into the ocean abyss where it is more permanently sequestered for millenia to eons of time.
“In basic terms, iron is so important because it helps control climate,” says Sune Nielsen, a WHOI geologist and coauthor. “We need to understand where iron in the ocean is coming from in order to truly understand the role of iron in the marine carbon cycle.”
The scientific community has long know that a great deal of the ocean’s iron comes from atmospheric dust that is blown on the wind from dry lands ashore. Smaller local inputs of iron also arrive in the oceans from eroded sediments carried by rivers and streams along continental margins. The amount of iron contributed by the unchanging deep ocean rocks of the Earth’s crust has been scarcely studied and very imprecisely known. This work contributes to the understanding of the steady state deep source iron although its unchanging nature over such long time frames makes it far less pertinent to present day radically and rapidly changing ocean ecology.
Deep iron in a soluble form has been known to pour into the oceans in from abysmal hydrothermal vent sites, including those well-studied such sites along continental margins, but it was believed such iron remained in these localized spots and didn’t contribute much to the overall iron content of the ocean as the ocean waters near the vents is very low in oxygen.
“According to conventional wisdom, as soon as these iron-rich fluids hit seawater with higher oxygen concentrations, the iron would just dump (precipitate) out and never really go anywhere,” explains Nielsen.
However, Horner says, “That is not the case, at least in the central Pacific Ocean. We found that much of the dissolved iron in that region originated from hydrothermal vents and sediments thousands of meters below the sea surface. And we found that the iron from these deep sources can be transported long distances.”
To conduct their research, the researchers analyzed a small marine sediment collection, part of what is known as ferromanganese crust, taken from a spot far from any hydrothermal vent sites in the central Pacific Ocean. The old archived sample was collected from the flank of the Karin Ridge, a seamount located in the central Pacific, in the 1980s by coauthor Jim Hein of the U.S. Geological Survey (USGS) in Santa Cruz, from a dredge along the seafloor.
The student team utilized mass spectroscopy to analyze the sample for long-term changes in seawater isotopic chemistry recorded in the growth layers of the ferromanganese crust, which forms very slowly. Drilling cross sections in the sample allowed scientists to look through “sections of time” to analyze variations in the composition of iron isotopes–stable natural isotopes iron-56 and iron-54–in order to track the origins of iron.
“The ratio of iron isotopes vary among the different iron sources–atmospheric dust, hydrothermal vents, and dissolved sediments– and are actually quite distinct, like fingerprints. We were able to measure those ratios in the growth layers of our sample, which tells us about where the iron came from and how the different iron sources have waxed and waned over time,” Horner says.
“This study is exciting in that it applies some of the recently developed metal isotope capabilities to parse the different sources of scarce iron in seawater going back through time, and builds on the emerging story about the importance of hydrothermal vents to the inventory of iron in the sea,” adds Mak Saito, a biogeochemist at WHOI and one of the coauthors of the study.