Articles

Séminaire GM/LGO de Marco TERZARIOL (Géosciences Marines, Ifremer, Brest)

Methane Hydrate-Bearing Sediments: The Role of Fines

 

Methane hydrate-bearing sediments (MHBS) are relevant to the organic carbon cycle, seafloor instability, and as a potential energy resource. Sediment characteristics affect hydrate formation, gas migration, and potential recovery strategies. The first part of this presentation will focus on testing the Geotech properties of natural hydrate-bearing sediments. Finally, we combine the physics of granular materials with robust physical models to anticipate the pore habit of methane hydrates as a function of the sediment characteristics and depth. Results highlight the critical role of fines on sediments mechanical and flow properties, hydrate pore habit, and potential fluid migration.

Séminaire de Pascal Philippot (Géoscience Montpellier)

L’oxygénation de la Terre: point de non- retour global mais registre local

Séminaire GM/LGO de André DROXLER (Rice University, Houston, USA)

Centennial and extreme climate variability in the last 1500 years

from the Belize Central Shelf Lagoon (Central America):

successive droughts  and floods linked to the demise of the Mayan civilization

 

This study focuses on the last 1500 yr precipitation record archived in the mixed carbonate/siliciclastic sediments accumulated in the Belize Central Shelf Lagoon, part of the Yucatan Peninsula eastern continental margin, proximal to the land areas where the Mayan Civilization thrived and then abruptly collapsed. This study is mainly based upon the detailed analyses of marine sediment cores retrieved in 30 and 19 m of water depth from Elbow Caye Lagoon and English Caye Channel. The variations of elements such as Ti and K, and Ti/Al counts in these two cores have recorded, in the past 1500 years, the weathering rate variations of the adjacent Maya Mountain, defining alternating periods of high precipitation and droughts, linked to large climate fluctuations and extreme events highly influenced by the ITCZ latitudinal migration.
The CE 800-900 century just preceding the Medieval Climate Anomaly (MCA), characterized by unusually low Ti counts and Ti/Al, is interpreted to represent a time of low precipitation and resulting severe droughts in the Yucatan Peninsula, contemporaneous with the Mayan Terminal Classic Collapse. High Ti counts and Ti/Al, although highly variable, during the MCA (CE 900-1350) are interpreted as an unusually warm period characterized by two 100-to-250 years-long intervals of higher precipitation when the number of tropical cyclones peaked. These two intervals of high precipitation during the MCA are separated by a century (CE 1000 -1100) of severe droughts and low tropical storm frequency coinciding with the collapse of Chichen Itza (CE 1040-1100). The Little Ice Age (CE 1350-1850), several centuries during which Ti counts and Ti/Al reach minimum values, is characterized by systematic drier and colder climate conditions with low frequency of tropical cyclones. Two extreme Ti and K count minima might coincide with historical drought times and related Caribbean-wide famines in the year CE 1535 and the last third of the 18th century (CE 1765-1800).

Séminaire de Julia Ribeiro (Guangzhou Institute of Geochemistry, Chinese Academy of Sciences)

Cycling water within the deep Earth since subduction infancy

Séminaire GM/LGO de Paola MOFFA-SANCHEZ (Department of Geography, Durham University, UK)

Changes in the North Atlantic over the last 2000 years:

What can we learn from paleoceanographic records?

 

The climate of the last two millennia varied on decadal to centennial timescales which had important societal impacts. The cause of this climate variability is still debated, but changes in the North Atlantic circulation and specifically in the strength of the meridional circulation have repeatedly been proposed to have played an important role. In this seminar, I will review our current knowledge on the topic with particular focus on understanding past changes in the properties of the surface North Atlantic Current.

9 décembre 2019