PES is a process-oriented multidisciplinary project focused on the pockmarks, fluid migration and seepage recently discovered in the Estremadura Spur continental shelf (Portugal), and on their implications to the regional geology, to the evolution of this section of the margin and to their petroleum system, and their significance to the ecosystems. A field with more than 40 individual pockmarks, covering an area of at least 27 km2, was recently discovered and partially surveyed (Kim and shipboard scientific party, 2011; PACEMAKER project funded by the European Research Council). This data set was made available for this project. This field of pockmarks is located at the outer shelf of the Estremadura Spur, between 200 and 350 m water depth, with individual pockmarks up to 120 m in diameter and 10 m depth (Fig. 1). A preliminary processing of the backscatter data indicate that some pockmarks have a high acoustic seafloor reflectivity in their central part, most probably indicating the presence of methane-derived authigenic carbonate hardgrounds. While fluid flow is a widespread process in continental margins and sedimentary basins, this is the first record of fluid escape processes were not previously identified on the W Iberian margin. Gas seepage evidence in the Iberia margin has only been reported in estuarine environments such as the Ria de Vigo (Iglesias and GarciaGil, 2007), the Aveiro Estuary/lagoon (Duarte et al., 2007), and in the Gulf of Cadiz (Magalhães, 2007; Magalhães et al., 2012; Pinheiro et al., 2003). This pockmark field and underlying fluid generation and escape processes, which are the focus of this project, are thus the first fluid seepage system identified and reported from the W Portuguese margin, not yet investigated. Fluid seeps are highly dynamic systems characterized by strong coupling processes between the geosphere, biosphere, hydrosphere and atmosphere. As such, PES proposes a comprehensive and transdisciplinary investigation of the Estremadura Spur fluid seepage manifestations with the following main objectives:

(1) define the geographical distribution, types, geological setting and activity of the fluid seeps;
(2) understand the structural and the stratigraphic control of fluid migration and seepage;
(3) determine the composition of the emitted fluids and infer their source (microbial or thermogenic) possible depth of formation and processes occurring during their migration to the seafloor;
(4) infer the timing and processes that control the fluid expulsion at the seafloor;
(5) understand the controls and mechanisms of geochemical elements transport and breakdown of chemical compounds, diagenetically and by seep biota, to obtain a budget of elements cycling and export at the fluid seeps and better understand the coupling between geosphere and biosphere processes;
(6) characterize eventual chemosynthetic benthic ecosystems and evaluate their significance in this intermediate depth and the impact on the non-seepage ecosystem;
(7) infer the implications on the structure and petroleum geology of this margin (if the fluids expelled at seeps originated at depth, they may give important information on the underlying petroleum systems);
(8) evaluate the possible impacts of the fluid flow on the chemistry of the ocean and on the atmosphere, and help in assessing impacts of the input of greenhouse gases (e.g. methane) input of into the ocean/atmosphere;
(9) assess the potential of these seepage system on the formation of potential gas hydrates (under presentday and glacial conditions) and evaluate the regional dynamics of hydrates accumulation and destabilization.

The PES research team has a large experience with regards to fluid seepage systems, embracing geology, geophysics, geochemistry, ecosystem characterization and habitat mapping, and includes also key members of the European PEACEMAKER project. The proposed research objectives will be achieved, in a first stage, through the processing of the existing geophysical data where 4 pockmarks will be selected for detailed investigation during one research cruise. Detailed geophysical surveys will be acquired with swath-bathymetry, backscatter, seismics, sidescan sonar and water column acoustics. This will guide the direct seafloor observation with an ROV, capable of seawater analysis and sampling. The geophysical data and ROV observations will allow the characterization of the seepage system, at the seafloor and in depth, at a detailed (at structure) scale. Systematic sampling of sediments, authigenic carbonates, porewater fluids and gas, and macrofauna will follow using gravity, box and multicorer. Sediments and authigenic carbonates will be characterized for their grain size, mineralogy, geochemistry, C and O isotopes, pore water inorganic and organic geochemistry and seepage gas composition, so that the seepage activity will be characterized, allowing to infer the significance of the system to the regional geology and ecology.

CESAM members on this project

Ana Hilário
Researcher

Researcher

Clara F. Rodrigues
Researcher

Luciana Génio
Researcher

Luis Menezes Pinheiro
Researcher