Marum

The main aim of the MODAL project is to carry out hazard and hazard analyses associated to sediment deformations in submarine environments prone to earthquakes, fluid activities and landslides. The study zone -the Nice Slope (France) - is nested in heavily populated areas, highly exposed to geohazards. The major challenging scientific question in this project concerns the coupling between fluids and sediment deformation in submarine environments. Historically, the study area is sadly famous for the 1979 catastrophic submarine landslide which results in several casualties and infrastructural damage. Geotechnical and geophysical investigations carried out in late 2007 to the East of the 1979 landslide scar provide evidence for the possible occurrence of a new important sedimentary collapse and submarine landslide. Geophysical data acquired in the area show the presence of several seafloor morphological steps rooted to shallow sub-surface seismic reflections. Moreover, in situ piezocone measurements demonstrate the presence of several shear zones at the border of the shelf break at different depth below the seafloor. Both geophysical and geotechnical data suggest the start-up of a progressive failure mechanism and reveal the possible occurrence of future submarine landslide. The MODAL project is built according to a typical scheme for hazard and risk analysis going from the understanding of underlying physical processes (causal, predisposition and triggering factors) through the detection of revealing factors (thanks to geophysical mapping and imaging, in situ measurements and monitoring) and hazard assessment (calculation of probability of a given danger to occur during a given time period). More specifically, we propose to monitor the displacement rate field of the sediment and measure the fluid pressure to assess the probability of the slope failure, in response to gravity sliding, earthquake loading or excess pore pressure associated with rainfalls on the Nice region. The study site has been actively studied during the last decade within the framework of national and/or European projects. We have already an important set of geotechnical, geological and geophysical data which facilitate the application and validation of the proposed schemes. The MODAL project will be conducted within the framework of fundamental research, technological developments and practical field applications.

Over periods of hundreds of millions of years, Earth's surface is recycled via the fragmentation of continents to form new oceans and elsewhere the sinking of oceanic plates into the mantle beneath. The breakup of continents involves progressive stretching and thinning prior to final breakup and the formation of new oceanic crust from molten rock that rises from below, flanked by continental margins comprised of thinned continental crust. There is a range of continental margin types, varying from those where the underlying mantle starts to melt very early in the process and very large volumes are added to the crust, to those "magma-poor" margins where there is little evidence for such melting until the very end of the process. At these magma-poor margins, which are common globally, it has been found that the crust can thin to nothing and mantle rocks can be exposed at the seabed, where they react with seawater in a process called serpentinisation. This serpentinisation plays an important role in exchange of chemicals between the Earth's interior and the ocean, and may be particularly intense around geological faults. While the final stages of thinning of the continental crust have been studied extensively over the past three decades, the transition from exposing mantle at the seabed through to forming new oceanic crust by the eruption of molten rock has been less well studied. Even designing such a study can be challenging because it is often unclear how wide this transition is. Also, because such mantle exposure has also been found in the middle of the oceans, this transition may be more complicated than often assumed. Our project will use a novel combination of geophysical techniques to study this final stage of continental breakup at a magma-poor continental margin southwest of the UK. There, crust that seems from all available data to be "normal" oceanic crust lies within about 150 km of crust confirmed by drilling to be continental. A region of serpentinised mantle, now overlain by up to around 1 km of mud, lies in between. For the first time in such a location, we will use electromagnetic waves, generated from a towed source, to measure the electrical resistivity of the crust and serpentinised mantle. Electromagnetic waves are strongly attenuated by seawater, so the source must be powerful and must be towed close to the seabed. We will use a combination of towed sensors, that are most sensitive to structures just below the seabed, and seabed detectors that can measure tiny fluctuations in electrical and magnetic fields at distances of up to tens of kilometres from our source, and thus allow us to probe deeper. We will also use some of the same seabed receivers to detect sound waves travelling through the crust from a source towed close to the ship, and to detect lower-frequency electromagnetic waves that are generated by natural sources and penetrate deeper into the Earth. The data that we collect will allow us, via the use of powerful computer programmes, to construct models of the variation of both sound speed and electrical resistivity in the crust and in the upper few tens of kilometres of the mantle beneath. These parameters provide a powerful combination because they are sensitive in different ways to the nature of the rocks. The electrical resistivity is particularly sensitive to the presence of water, and also of a mineral called magnetite that can be formed during the process of serpentinisation. The sound velocity is less sensitive to the presence of water but can be more sensitive to variations in the minerals present. From our models, we expect to be able to distinguish the continental crust and mantle, the oceanic crust and mantle, and the nature of the materials in between. We will then link these observations to computer models of the physical and chemical processes occurring as continents break apart. Thus we will find out how the formation of new oceanic crust actually starts.

Analyses of marine sediments allow reconstructions of climatic processes. From these the most critical are short-term climate transitions, which have large impact on time scales relevant to society e.g. decadal to millennial variations such as the Dansgaard–Oeschger events D-O and changes the Earth's natural climate cycles e.g. the Middle Pleistocene transition MPT. Such variations are recorded in both North Atlantic NA and North Pacific NP and can be linked globally Lund and Mix, 1998. By reconstructing their patterns and interactions, climate models can be validated against an independent archive and model simulations can better identify man-induced climatic variability. The assumption of our strategy is that these records can show variations in Primary Productivity PP, Sea Surface Temperature SST and salinity that can be synchronized in both oceans, and SST and PP in the NP a region where other proxies have preservation problems, e.g. alkanones and foraminifera can be reconstructed using diatom based Transfer Functions TFs, Lopes et al, 2014, Lopes and Ventura, 2014. By identifying the extension and lead/lag effects of these climate events in both NP and NA, we can investigate which climate regulation processes was in action e.g. oceanic circulation and /or atmospheric alterations due to continental ice variations, fig. 1. The NA has been widely studied fig. 2, Kucera et al. 2005 as it is the center of the Deep Water Formation the engine of oceanic circulation and climate regulator and data from marine sediments that record D-O and MPT in this area, are available free of charge at http://www.pangaea.de, fig 3. The NP role in climate variations is less understood, although tightly connected to NA through atmospheric waves and upwelling of deep water originated in the NA e.g. Mix et al., 1999. However, to fully understand past climate in a global perspective, even if focusing in the north hemisphere, studies from the NP need to be included in global models. Recent studies show correlations between marine records from the NP and the ice records from Greenland e.g. Pretorius and Mix, 2014. This work shows possible links related with changes in North America ice, the opening of the Bering Strait or even a freshwater input to the NA. The variation of D-O events from the NA also affects the patterns of Asian Monsoons that are recorded in the Sea of Japan Tada, 2004. Understanding the impact of D-O variability on monsoon variations is extremely important because of their impact on the Asian populations. Lopes et al. 2014 showed that for the Northeast NE Pacific, more CO2 has been withdrawn by the biological pump diatoms into the deep ocean sediments since the last Glacial Maximum LGM warming due to changes in the NP atmospheric and oceanic circulation. These studies are just examples of how reconstructions based on marine sediments proxies can help to simulate how future climate variations can affect the Earth's natural balance. The fact that D-O cycles are recorded in marine sediments from the east and west NP allows the possibility to check for synchronicity and thus the path of transmission oceanic and/or atmospheric. The setback is that although being a key area to understand climate variability, long marine records were rare in the NP. However, three IODP Expeditions: Exp. 323 Bering Sea Paleoceanography in 2009, Exp. 341 Southern Alaska Margin and Exp. 346 Asian Monsoon in 2013 have now recovered the necessary material. These expeditions combined a large team of multi proxy experts involved in this project. In addition any sample needed is available for free. Two previous FCT projects Panocean: PTDC/AAC-CLI/112189/2009 and EVAL:EXPL/AGG-GLO/1067/2012 show that it is possible to apply the methodology, strategy and team collaborations proposed here. Lopes et al. 2014 and Lopes and Ventura 2014 develop TFs that can be applied to the new long cores recovered in the mentioned IODP Expeditions. Therefore, this project will apply a multi-disciplinary approach to understand the oceanic and atmospheric links between the NP and the NA, and verify how they can affect or be affected by climate variations. In order to achieve this goal we propose to study marine sediments from the NP fig. 4 because it lacks significant information about climate variations that are largely studied in the NA although it should record the same specific climate variations. We will focus on D-O cycles in records that spam the past 50 ky in both NA and NP and also the timing of the change in the dominant Earth's natural glacial cyclicity, the MPT ± 1.2 Ma. The different proxies proposed will be studied by these project collaborators but also through the IODP expeditions established collaborations Table 1. Spectral analysis, cross-correlations, multivariate analysis and spatial correlations will be applied to all proxies and to all the proposed cores. As análises dos sedimentos marinhos permitem reconstruções climáticas. As transições climáticas "curtas" e as alterações dos ciclos climáticos naturais da Terra têm impacto sobre escalas de tempo relevantes para a sociedade e.g. variações milenares, como os eventos Dansgaard-Oeschger DO e a Transição do Pliocénico Médio MPT. Estas são registadas, tanto no Atlântico Norte NA como no Pacífico Norte NP e podem ser ligadas a nível global Lund e Mix, 1998. Ao reconstruir os seus padrões e interacções, os modelos climáticos podem ser validados contra um arquivo e modelo independente que podem identificar melhor a variabilidade climática induzida pelo homem. A nossa estratégia é que estes apresentam variações na produtividade primária PP, na temperatura da superfície do mar SST e salinidade que podem ser sincronizados em ambos os oceanos, e estes podem ser reconstruído no NP onde outros proxies têm problemas de preservação como por exemplo, alcanonas e foraminíferos usando Funções de Transferência TFs de diatomáceas Lopes et al, 2014, Lopes e Ventura, 2014. Ao identificar a extensão e o "lead / lag" desses eventos climáticos, tanto no NP e NA, podemos investigar quais os processos de regulação do clima em ação e.g. circulação oceânica e / ou alterações atmosféricas, devido às variações de gelo continentais, fig. 1. O NA tem sido amplamente estudado fig. 2, Kucera et al., 2005, uma vez que é o centro da formação de águas profundas o motor da circulação oceânica e regulador do clima e os dados de sedimentos marinhos desta área, estão disponíveis gratuitamente em http://www.pangaea.de, fig 3. O papel do NP em variações climáticas é menos compreendido, embora ligado ao NA através de ondas atmosféricas e ressurgência de águas Mix et al.1998. No entanto, para entender o clima do passado, numa perspectiva global, mesmo focando o hemisfério norte, os estudos do NP precisam ser incluídos em modelos globais. Estudos recentes mostram correlações entre registos marinhos do NP e os registos de gelo da Gronelândia eg Pretorius e Mix, 2014. Este trabalho mostra links possíveis relacionados com as mudanças no gelo da América do Norte, com a abertura do Estreito de Bering ou até mesmo com uma entrada de água doce para o NA. A variação de eventos do NA também afecta os padrões de monções asiáticas, que são registadas no Mar do Japão Tada, 2004. Compreender o impacto da variabilidade destas variações é importante devido ao seu impacto sobre as populações asiáticas. Lopes et al. 2014 mostraram que para o Nordeste NE do Pacífico, mais CO2 foi sugado pela bomba biológica diatomáceas e incorporado nos sedimentos oceânicos profundos durante o aquecimento desde o último máximo glacial LGM devido a mudanças na circulação atmosférica e oceânica. Estes estudos são apenas alguns exemplos de como as reconstruções com base em sedimentos marinhos podem ajudar a simular como futuras variações climáticas podem afectar o equilíbrio natural da Terra. O fato de que os ciclos são registados em sedimentos marinhos do este e oeste NP permite a possibilidade de verificar a existência de sincronicidade e, assim, o caminho da transmissão oceânica e / ou atmosférica. O revés é que apesar de ser uma área-chave para compreender a variabilidade do clima, os registos marinhos longos eram raros no NP. No entanto, três expedições IODP EXP. 323 Bering Sea Paleoceanography em 2009, Exp. 341 Southern Alaska Margin e Exp. 346 Monsoon asiático em 2013 recuperaram o material necessário para colmatar esta falha. Estas expedições combinam equipas de especialistas multidisciplinares envolvidos neste projecto. Além disso, qualquer amostra necessária está disponível gratuitamente. Dois projectos FCT anteriores Panocean: PTDC / AAC-CLI / 112189/2009 e EVAL: EXPL / AGG-GLO / 1067/2012, mostram que é possível aplicar a metodologia, estratégia e colaborações da equipa aqui proposta. Lopes et al. 2014 e Lopes e Ventura 2014 desenvolveram TFs que podem ser aplicados aos cores recuperados nas expedições mencionadas. Portanto, este projecto irá aplicar uma abordagem multidisciplinar para investigar as ligações oceânicas e atmosféricas entre o NP e o NA, e verificar como elas podem afectar ou ser afectado por variações climáticas. Para atingir este objectivo, propomos estudar os sedimentos marinhos do NP fig. 4 porque falta informação significativa sobre as variações climáticas que são em grande parte estudadas no NA embora registe as mesmas variações climáticas específicas. Iremos concentrar-nos em ciclos milenares DO dos últimos 50 ky em ambos NA e NP e também o momento da mudança de ciclicidade glacial natural da Terra, o MPT ± 1,2 Ma. Proxies diferentes serão estudados por colaboradores do projecto, mas também através das colaborações estabelecidas nas expedições IODP Tabela 1. Análise espectral, correlações cruzadas, análise multivariada e correlações espaciais serão aplicada a todos os proxies e cores proposto