The DZIANI project objectives are twofold:

·      To provide new evidence of the importance of local mechanisms leading to positive d13Ccarb excursions from an integrated study investigating the biodiversity, the microbiology and the biogeochemistry of the Dziani Dzaha ecosystem. 

·       To characterize the specific chemical, mineralogical and isotopic signatures in sediment and microbialites of this ecosystem, in order to be able (i) to estimate its temporal stability by a multiproxy study of sediments cores and (ii) to identify the occurrence of similar ecosystems in the past Earth’s history. The temporal stability of the microbial ecosystem of Dziani Dzaha Lake, if proved, will reinforce its relevancy as an actual analog of ancient marine systems.

(i) Achieving the first objective will provide the first state of the art multidisciplinary description of a completely new type of Precambrian ocean analog. This will allow us to elaborate conceptual models to best understand the lake functioning and to formulate testable hypotheses. This will in turn allow us to envisage the possibility that such ecosystems may have been common during the 2.2-20 Ga time period, thus explaining its abundance of regionally controlled positive d13Ccarb excursions. This could transform our understanding of d13Ccarb significance and hence of the evolution of the biogeochemical carbon cycle and its consequent modifications of the oxygen cycle at 2.2-2.0 Ga. A mathematical modeling of the lake Dziani Dzaha ecosystem and of its extrapolation to Precambrian times will be considered as further development of this project.

(ii) chieving the second objective will constitute a multiproxy tool-box for future studies aiming at identifying similar ecosystems in the rock record. To date proxies are hardly used in combination, but because each proxy taken individually provides some level of constraint on only one aspect of the paleoenvironment, most paleoenvironmental interpretations remain ambiguous. Multiproxy characterizations of modern analogs therefore are one of the bottlenecks for paleoenvironmental reconstructions.

The DZIANI project is expected to provide both new insights into the paleoenvironmental conditions and biogeochemical cycle having given rise to one of the major features of the carbon isotope secular variations, the prominent positive excursions at 2.2-2.0 Ga, and a new tool box to search for similar paleoenvironments from the rock record.

Moreover, our preliminary studies showed that the Dziani Dzaha Lake is a rare example of a very high productive and stable ecosystem in an extreme environment (section 2.2). Its fully integrated characterization will also be very useful to assess its potential as a model for industrial bioenergetic methane or biomass production, as proposed in the IEED GreenStars Investissement d’Avenir (MIWACO project to be started in 2013, leader C. Leboulanger). 

The novelty and timeliness of the project lies in the recently discovered unique ecosystem and biogeochemistry of lake Dziani Dzaha and in its astonishing resemblance to the major two positive d13Ccarb excursions in the Earth history. The wide interdisciplinarity of the project ranging from molecular diversity, microbiology, biogeochemistry, and paleooceanography is also quite unique at the French, European and International levels. Due to its broad significance to the understanding of early Earth evolution, the results of the entire project have a great potential to deliver very high impact publications.

Didier Jezequel and Laurent (our host in Mayotte) working on the assembly of the coring platform

                                                                                                                                                                                                                        The coring platform on the lake.

Didier Jezequel with the core on the platform

The sampling of sediment with the coring system

                                                                                                                                                                                                    The collection of the sediment from the coring system.

All photos on this page : S. TURAY / Sur une île  ; (c) DCO 2014