Bottom scour observed under Hurricane Ivan

Abstract

[1] Observations that extensive bottom scour along the outer continental shelf under Hurricane Ivan resulted in the displacement of more than 100 million cubic meters of sediment from a 35 Â 15 km region directly under the storm's path are presented. Sediment resuspension was accomplished by the extreme waves generated by Ivan and transported by strong near-bottom wind-driven currents. The sediment transport was primarily westward along the shelf, but also contained a significant offshore component, suggesting sediment was transported toward the Mississippi Delta and that it may have accumulated near the shelf break and on the upper continental slope. The maximum observed scour of about 32 and 36 cm took place at two locations approximately 17 km apart along the 60 m isobath over which the maximum wind stress occurred.

Phylogeography of the marine interstitial nemertean Ototyphlonemertes parmula (Nemertea, Hoplonemertea) reveals cryptic diversity and high dispersal potential

“…Metapopulation dynamics may especially be important on subtropical coasts, where hurricanes can scour bottom sediment to substantial depths (Teague et al 2006), and local populations of Ototyphlonemertes have been observed to undergo extinction or near-extinction following hurricanes (Norenburg, pers obs). However, the conditions under which recurrent extinction and recolonization could result in reduced (rather than increased) structuring between populations are rather limited based on theoretical considerations (Wade and McCauley 1988;Barton and Whitlock 1997) and are unlikely to apply in our case.…”

Observed Oceanic Response over the Upper Continental Slope and Outer Shelf during Hurricane Ivan*

“…Aside from obvious leaks, some pipe-section 7, a comprehensive wave discussion is provided lines were reported to have moved about 915 m while in section 8, and a summary and conclusions are given others were buried under 9 m of mud and could not be in section 9. (Powell et al 1998) tered the Gulf of Mexico on a northwest trajectory and and the Donelan et al (2004) drag coefficient formulaintensified to category 5. On September 16 around 0000 tion, in which the drag coefficient peaks at 0.0028 for UTC, as a category-4 storm, Ivan veered to the east and wind speeds greater than 33 m s-.The maximum wind passed directly over 14 ADCPs deployed in the Missis-stress was about 9.5 Pa at R and 7.5 Pa at 1.5R, respecsippi Bight in support of SEED ( Fig.…”

Wave-Dominated Coasts

“…On some coasts, the break in slope may not be evident but conceptually there is merit in distinguishing between an inner zone where there is frequent and measurable reworking of form in response to changing wave conditions and an outer zone where the time frame of measurable change and sediment accumulation increases from decades and centuries to perhaps thousands of years near the outer boundary. At the outer edge of the shoreface, sediment inputs may come in the form of the nearly continuous accumulation of fine sediments settling out of suspension and infrequent, episodic injections associated with extreme events such as hurricanes (Hayes, 1967;Teague et al, 2006).…”

“…While there have been a number of field measurements of near bottom-water motion and the effect of storms on mobilization of sediments and bedform development using instrumented tripods (e.g., Wright et al, 1994;Li and Amos, 1999;Teague et al, 2006), the timescale of morphological response is longer than these measurements and so morphological evolution of the lower shoreface and the relationship to dynamic controls are generally inferred from a combination of short-term mea surements of dynamics and longer-term evidence, such as from sedimentary cores (Cowell et al, 1999). Since morphological change in the upper shore face and foreshore takes place much more rapidly, there is much better understanding of it.…”