Open AccessObservations of wave‐generated vortex ripples on the North Carolina continental shelf
Author(s) -
Ardhuin Fabrice,
Drake T. G.,
Herbers T. H. C.
Publication year - 2002
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2001jc000986
Subject(s) - geology , ripple , continental shelf , vortex , wavelength , drag , oceanography , seismology , geomorphology , meteorology , physics , mechanics , optics , quantum mechanics , voltage
Sand ripples with wavelengths between 0.5 and 3 m were observed on the bottom across the U.S. east coast continental shelf off North Carolina during three side‐scan sonar surveys in September and December 1999. Ripples were present in about 75% of the survey images, in particular, in regions with coarser sediments. Analysis of surficial sediment samples shows that median grain diameters range from 0.1 to 4.7 mm with large variations on the inner shelf over distances <1 km. The observed ripple properties are consistent with wave‐generated vortex ripples. Analysis of concurrent wave observations indicates that the ripple crests were aligned perpendicular to the average direction of near‐bottom wave‐induced motions during preceding events that were sufficiently energetic to mobilize surficial sediments. Furthermore, the ripple wavelengths proportionality to near‐bottom wave orbital excursions is consistent with wave‐formed vortex ripples. These findings support the hypothesis that the observed strong attenuation of waves across the shelf resulted from form drag over large vortex ripples.