Recent Field Work Investigates a Modern Analog to Explore Volcanic Carbon’s Role in Ancient Environments
A French research team is investigating volcanic carbon’s role in fueling biomass in the Dziani Dzaha crater lake located in the Comoros Archipelago, a small volcanic hotspot chain in the Indian Ocean between Madagascar and Mozambique. The alluring emerald Dziani Dzaha on Petite Terre, one of France’s Mayotte islands, may prove to be a gem to Deep Carbon Observatory (DCO) scientists seeking to understand Earth’s early life. It may also have implications for the existence of significant deep carbon "bioenergy factories" in Earth’s history.
Dziani Dzaha presents a very unusual combination of characteristics making it a likely analog for some hydrocarbon-bearing lacustrine rocks of economic importance and possibly certain Precambrian environments, including expanding rift valleys and basins. A dense population of prokaryotes and cyanobacteria dominates the Dziani Dzaha ecosystem—giving it a permanently green color. Its waters are saline (twice the ocean salinity), alkaline (pH = 9), extremely rich in dissolved inorganic carbon (100 times the amount in seawater), and anoxic below one-meter depth. It also precipitates microbialites, which are organo-sedimentary deposits that accrete as a result of a lake-bottom microbial community, forming the locus for mineral precipitation.
In April 2014, a French research expedition, led by Magali Ader of the Institut de Physique du Globe de Paris, made its first of four planned field expeditions to the Dziani Dzaha lake to begin characterizing the physical chemistry and biology of the lake during different seasons. Its scientists performed on-site measurements of the water chemistry and microorganisms’ metabolic activity. They also sampled gases, waters at various depths, and procured a 1.8-meter-long sediment core for subsurface biodiversity, chemical, mineralogical, and isotopic analyses. DCO support is being provided to partially cover the cost of 14C analyses of the dissolved inorganic carbon and biomass, and of detrital remains of terrestrial plants found at various levels in the core. These analyses will test the hypothesis that the biomass feeds directly on volcanic CO2 and provide an approximate model age for the core.
The research team hypothesizes that the ecosystem’s characteristics are strongly controlled by its geological setting. On its eastern border, the lake is separated from the nearby Indian Ocean by only the crater wall. It is thus highly probable that the lake chemistry is influenced by a combination of seawater percolating through the volcanic crater walls, CO2-rich gases of probable magmatic origin bubbling through the water, and hydrothermal fluids. The expedition and research goals are threefold: 1) to better characterize the geochemistry and biology of this unique ecosystem and its analogies to past environments; 2) to understand the driving factors responsible for its stability; and 3) to identify the mineralogical, chemical, and isotopic signatures recorded in the sedimentary products of this environment to better identify similar ones in the ancient sedimentary record.
Magali Ader, Professor, Institut de Physique du Globe de Paris (IPGP), Expedition Principal Investigator
Eric Fouilland, Researcher, CNRS, Université Montpellier II
Emilie Le Floc’k, Research Engineer, CNRS, Université Montpellier II
Patrice Got, Dr, Research Engineer, CNRS, Université Montpellier II
Cécile Bernard, Professor. Museum d’Histoire Naturelle
Dider Jézéquel, Assistant Professor, Université Paris Diderot
Gérard Sarazin, Profesor Emeritus, Université Paris Diderot
Pierre Cadeau, PhD student, Université Paris Diderot
Also strongly involved but not present in the field:
Christophe Leboulanger, Researcher, IRD, Université Montpellier II, Expedition co-PI
Marc Bouvy, Researcher, IRD, Université Montpellier II
Hélène Agogué, Researcher, CNRS, Université La Rochelle
Emmanuelle Gérard, Research Engineer, CNRS, IPGP
Carine Chaduteau, Ingener, IPGP
Nelly Assayag, Ingener, CNRS, IPGP
Patrick Alberic, Professor, Université d’Orléans
Gwenael Abril, Researcher, CNRS, Université de Bordeaux I
Marc Benedetti, Professor, University Paris Diderot
Pierre Cartigny, Researcher, CNRS, IPGP
Primary Project Funding
French Agence Nationale de la Recherche (ANR DZIANI)
Institut de Recherche pour le Développement (IRD)
Institut de Physique du Globe de Paris (IPGP)
Université Montpellier II
Centre National de la Recherche Scientifique (CNRS)
The video and photos were produced with DCO funding by
Sébastien Turay from the company "Sur une Île."