Preface The expedition ARK XIX/3 with the German icebreaking RV ...

and speeds exceeded 50 cm s -1 on all diurnal tidal cycles 2-3 days either side of
spring tides (pers. comm. M White). The maximum mean daily currents occurred at
diurnal spring tides and the minimum at neap tides. Similar observations have been
recorded to the north of the Galway mound by Pingree and LeCann (1989, 1990). Full
analysis of this and other datasets is on-going.
A. 4.3.6 Influence of hydrodynamics on sedimentary processes: "Belgica mounds"
and "Moira mounds"
Foubert, A., Wheeler, A.
The "Moira mounds" are identified in the "Belgica mound" Province (Fig. A4.1-1) and
were first imaged on 100 and 410 kHz sidescan sonar (Wheeler et al., 2000). These
are small mounds up to 5-10 m high and 15 to 40 m across. The mounds include
isolated examples although most occur in swarms or clusters (Wheeler et al., subm.).
The "Moira mounds" located to the east of "Thérèse mound" were investigated using
the ROV "Victor 6000" (Olu-Le Roy et al., 2002). These video dives and sidescan
sonar images showed that the "Moira mounds" occur in areas of active sediment
transport on rippled sand sheets in areas of sediment wave development (Wheeler et
al., subm.). A rippled sand facies with occasional dropstones and isolated coral
patches is present in between the mounds. The flanks of the mounds are
characterised by patches of live coral coverage in a rippled sand facies. Towards the
centre of the mounds the coral framework becomes denser (Wheeler et al., subm.).
The "Moira mounds" are confined to the present-day seabed surface with no seismic
evidence for buried components. This implies that the "Moira mounds" are probably a
recent feature (?Holocene).
The use of the multibeam echosounder SIMRAD EM2000 mounted on the ROV
"Victor 6000" made it possible to map the "Moira mounds" by producing a very highresolution
microbathymetric grid with a pixel size corresponding to 20 cm. All the data
were recorded and processed in Qinsy (Fig. A4.3.6-1). The microbathymetric grid
helps a lot by interpreting the hydrodynamic setting of the "Moira mounds".
Sandwaves up to 50 cm high and with a wavelength of 15 to 20 m, are visualised and
seem to be aligned E-W. They demonstrate the presence of strong northerly-directed
benthic bottom currents.
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