Ninth international conference on - Marum

86
Abstracts of posters
Engineered bubble plumes and the study of natural marine seepage
– a natural bubble-driven buoyancy flow
I. Leifer 1,2 H. Jeuthe 3 , S. H. Gjøsund 4 , V. Johansen 4
1 Marine Sciences Institute, University of California, Santa Barbara, CA, 93106, US.
ira.leifer@bubbleology.com.
2 Institute for Crustal Studies, University of California, Santa Barbara, CA, 93106.
3 Norwegian College of Fishery Science, University of Tromsø, NO-9073 Tromsø, Norway.
4 SINTEF Fisheries and Aquaculture, NO-7465 Trondheim, Norway.
Bubble plume upwelling flows were studied in the marine environment through dye releases into engineered
plumes and natural marine seep plumes. For engineered plumes, these experiments measured the water-column
averaged upwelling flows, , for a wide range of flows and depths. From , the local upwelling flow,
Vup(z), where z is depth, was calculated and agreed well with published relationships between Vup(z) and flow, Q,
Vup~Q^ 0.23 , for plumes strong enough to penetrate the near surface thermally stratified layer.
These data were used to interpret observations at a natural marine seep, where the upwelling flow was decreased
towards the sea surface instead of increase as observed for the engineered plumes. Data showed a significantly
colder and more saline upwelling flow of water being lifted towards the sea surface. The increased density
difference between this upwelling fluid and the surrounding fluid most likely caused flow deceleration.
Comparison of dimensions of the engineered and seep bubble-plumes and Vup estimated a total seep flow of
similar magnitude as direct flux measurements. However, application fo the results of this study to observations
of a blowout predicted a flux many orders of magnitude too large, indicating that other processes likely are
important for large transient emissions.
Blind submarine valleys in the gulf of Cadiz: Fluid flow geological structures
R. León 1 , T. Medialdea 1 , L. Somoza 1 , J. T. Vazquez 2 and F. J. Gonzalez 1
1 Marine Geology Dv., Geological Survey of Spain IGME, Rios Rosas 23, 28003 Madrid, Spain
2 Instituto Español de Oceanografía IEO, Fuengirola, 29640 Málaga, Spain
During Tasyo, Mounforce and MVSEIS cruises, blind valleys have been defined as geological structures related
to seabed fluid flow in the Gulf of Cadiz. Blind valleys are located in the Central Sector of Tasyo Field where
several minor channels, pockmarks, mudvolcanoes and HDAC are present. Blind valleys (Fig 1) are giant
elongated collapses, from 3 to 10 km long, without open extremes. These valleys start and finish by pockmarks
or sub-circular collapsed structures, thus constitute whole structure of collapse generate by fluid flow. They are
located along normal and strike slip faults, clearly distinguished on seismic and multibeam data aligned along
NE-SW and NW-SE. Seismic profiles show as blind valleys have diapire structures below and the faults, which
control the blind valley structure, work as fluid path ways.
The geological study of the crater-like structures of fluid flow in the Gulf of Cadiz allows establishing an
evolutionary model for generation of blind valleys constituted by three stages: i) initial stage ii) progress stage,
and c) mature stage. Initial stage is defined by the presence of single depression structures resulting from fluid
flow, locally jointed. Single structures are mainly conic and U-shaped aligned along focused fluid flow pathways
defined by normal and strike-slip faults. In the progress stage, pockmarks and collapses trend to alienate along
the principal direction of faulting, generating elongated asymmetric pockmarks by the growing up and union
with the neighbours. Finally, in mature stage, fluid path-ways controlled by faults are wide-extend affected by
collapse and pockmark processes. Fluid path-ways configure a huge elongated areas fully collapsed by the
absence of mass below the seafloor due the ejection of fluids and sediments. The distinctive morphological type
is the blind valley. Blind valleys present singular processes and structures such as: collapses in the extremes of
the valleys, slumps around the flank, an irregular floor due to presence of carbonate mounds, mudvolcanoes,
minor collapses or pockmarks.
The evolution and consequent growth by merging with other lineal collapses produce blind submarine valleys of
nearly 10 km long. Presently these blind valleys work in the Tasyo Field as furrows along which MOW is
channelized. Even though blind submarine valleys can behave as channels of undercurrents they are deep-rooted
with faults and fluid path ways and their origin is related to a gravitational collapse due to fluid flow.