Metals + seawater = life?
Photo credit: Ryan Tabata
Tons of metals enter the oceans every day, but it's normally more subtle than this...
For over 2 months, Kīlauea's Lower East Rift Zone Eruption in 2018 poured fresh lava into the Pacific Ocean. Within seconds, cold seawater hardened the surface of the lava to rock, bottling up enormous pressures until it exploded, launching elements like iron, manganese, and cobalt into the surrounding ocean.
Inputs like this have been going on since our planet's formation, creating an early Earth rich in metals at the time when life first evolved. The usefulness of these elements in primordial biochemistry is evident in metalloenzymes: metal-protein mash-ups that have unique abilities to catalyze photosynthesis, fix nitrogen, and make DNA.
Today, metals are trace constituents of seawater, sometimes less than 1 part per trillion. Marine life works hard to conserve and recycle these scarce resources, In some regions, however, these adaptations are not enough and the size of the ecosystem is "limited" by the low levels of metals.
Structure of photosystem II with the Mn4CaO5 water oxidation cluster shown. Credit: DOE/LBNL
This was demonstrated by the iron fertilization experiments of the 1990s and 2000s, where researchers poured iron sulfate into patches of the Equatorial and Subarctic Pacific Ocean and the Southern Ocean around Antarctica.
False color map of satellite chlorophyll show a horseshoe-shaped patch of high chlorophyll following the addition of iron in the SOIREE experiment in the Southern Ocean (Credit: Wesberry et al. 2013, Deep Sea Research II)
A greening of the ocean followed, as previously-limited phytoplankton were now able to grow at maximum speed. Eventually, their predators, zooplankton arrived and ate the new crop of phytoplankton and the ocean returned to its background state. Still, these experiments show demonstrate that ocean life we know today - be it phytoplankton, or fish, or corals - would not be there without an adequate supply of iron and other metals.
So how much iron is enough for a healthy ocean? How much cobalt? How much manganese? What processes provide these metals? How can this change in the past of the future? These are questions we seek to answer.
In the Hawco Lab, we examine the (usually) invisible processes that deliver essential elements to the ecosystems that need them most, and how life in the oceans have evolved to cope with widespread scarcity of metal micronutrients.