Magnetotactic bacterial production in response to Middle Eocene Climatic Optimum (MECO) in the Neo-Tethys Ocean

Monday, 15 December 2014
Jairo F Savian1, Luigi Jovane2, Fabrizio Frontalini3, Ricardo Trindade2, Rodolfo Coccioni4, Steven M Bohaty5, Paul A Wilson5, Fabio Florindo6, Andrew P Roberts7, Rita Catanzariti8 and Francesco Iacoviello2, (1)Federal University of Rio Grande do Sul - UFRGS, Department of Geology, Porto Alegre, Brazil, (2)USP University of Sao Paulo, São Paulo, Brazil, (3)University of Urbino, Dipartimento di Scienze della Terra, della Vita e dell'Ambiente, Urbino, Italy, (4)Università degli Studi di Urbino “Carlo Bo”, Urbino, Italy, (5)University of Southampton, Southampton, United Kingdom, (6)National Institute of Geophysics and Volcanology, Rome, Italy, (7)Australian National University, Canberra, Australia, (8)Istituto di Geoscienze e Georisorse CNR, Pisa, Italy
The Middle Eocene Climatic Optimum (MECO) at ~40 Ma is a warming event characterized in the deep Southern, Atlantic, Pacific and Indian Oceans by a distinct negative δ18O excursion over 500 kyr. In this work we report results of high-resolution paleontological, geochemical, and environmental magnetic investigations of the Monte Cagnero (MCA) section (Central Italy), which can be correlated on the basis of magneto- and biostratigraphic results to the MECO event. In the MCA section, an interval with a relative increase in eutrophic nannofossil taxa spans the culmination of the MECO warming and its aftermath and coincides with a positive carbon isotope excursion, and a peak in magnetite and hematite/goethite concentration. Our results suggest that magnetite peak reflects the appearance of putative magnetofossils, while the hematite/goethite apex is attributed to an enhanced detrital mineral contribution, likely as aeolian dust transported from the continent adjacent to the Neo-Tethys Ocean during a drier, more seasonal climate during the peak MECO warming. Based on our new data record, the MECO warming peak and its immediate aftermath are interpreted as a period of high primary productivity. Sea-surface iron fertilization is inferred to have stimulated high phytoplankton productivity, increasing organic carbon export to the seafloor and promoting enhanced biomineralization of magnetotactic bacteria, which are preserved as putative magnetofossils during the warmest periods of the MECO event in the MCA section.