During the 2005 hurricane season, the storm surge and wave field associated with Hurricanes Katrina and Rita eroded 527 km 2 of wetlands within the Louisiana coastal plain. Low salinity wetlands were preferentially eroded, while higher salinity wetlands remained robust and largely unchanged. Here we highlight geotechnical differences between the soil profiles of high and low salinity regimes, which are controlled by vegetation and result in differential erosion. In low salinity wetlands, a weak zone (shear strength 500–1450 Pa) was observed ∼30 cm below the marsh surface, coinciding with the base of rooting. High salinity wetlands had no such zone (shear strengths > 4500 Pa) and contained deeper rooting. Storm waves during Hurricane Katrina produced shear stresses between 425–3600 Pa, sufficient to cause widespread erosion of the low salinity wetlands. Vegetation in low salinity marshes is subject to shallower rooting and is susceptible to erosion during large magnitude storms; these conditions may be exacerbated by low inorganic sediment content and high nutrient inputs. The dramatic difference in resiliency of fresh versus more saline marshes suggests that the introduction of freshwater to marshes as part of restoration efforts may therefore weaken existing wetlands rendering them vulnerable to hurricanes.

9Submarine and fluvial channels exhibit qualitatively similar geomorphic patterns, 10 yet produce very different stratigraphic records. We reconcile these seemingly 11 contradictory observations by focusing on the channel-belt scale and quantifying the 12 time-integrated stratigraphic record of the belt as a function of (1) the geometric scale and 13 (2) the trajectory of the geomorphic channel, applying the concept of stratigraphic 14 mobility. By comparing 297 submarine and fluvial channel belts from a range of tectonic 15 settings and time intervals, we identify channel kinematics (trajectory) rather than 16 channel morphology (scale) as the first order control on stratigraphic architecture and 17show that seemingly similar channel forms (in terms of scaling) have the potential to 18 produce markedly different stratigraphy. Submarine channel-belt architecture is 19 dominated by vertical accretion (aggradational channel fill deposits), in contrast to fluvial 20 systems that are dominated by lateral accretion (point bar deposits). This difference is 21 best described with the channel-belt aspect ratio, which is 9 for submarine systems and

Changes in sediment supply and caliber during the last ~130 ka have resulted in a complex architectural evolution of the Y channel system on the western Niger Delta slope. This evolution consists of four phases, each with documented or inferred changes in sediment supply. Phase 1 flows created wide (1,000 m), low-sinuosity (1.1) channel forms with lateral migration and little to no aggradation. During Phase 2, the Y channel system began to aggrade, creating more narrow (300 m) and sinuous (1.4) channel forms with many meander cutoffs. This system was abandoned at ~ 130 ka, perhaps related to rapid relative sea-level rise during MIS (Marine Isotope Stage) 5. Phase 3 flows were mud-rich and deposited sediment on the outer bends of the channel form, resulting in the narrowing (to 250 m), straightening (to a sinuosity of 1.22), and aggradation of the Y channel system. Renewed influx of sand into the Y channel system occurred with Phase 4 at ~ 50 ka, during MIS 3 sea-level fall. The onset of Phase 4 is marked by the initiation of the Y′ tributary channel, which re-established sand deposition in the Y channel system. Flows entering the Y channel from the Y′ channel were underfit, resulting in inner levee deposition that is most prevalent on outer banks, acting to further straighten (1.21) and narrow (to 200 m wide) the Y channel. The inner levees accumulated quickly as the flows sought equilibrium, with deposition rates > 200 cm/ky. Marked by the presence of the last sand bed, abandonment occurred at ~19 ka in the Y channel and ~15 ka in the Y′ channel and is likely related to progressive abandonment due to shelf-edge delta avulsion and/or progressive sea level rise associated with Melt Water Pulse 1-A. The muddy, 5-meter-thick Holocene layer has thickness variations that mimic those seen in the sandy part of Phase 4, suggesting that dilute, muddy flows continue to affect the modern Y channel system. This unique dataset allows us to unequivocally link changes in submarine channel architecture to variations in sediment supply and caliber. Changes in the updip sediment routing system (i.e. the channel "plumbing") are shown to have profound implications for submarine channel architecture and reservoir connectivity.

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15Near-seafloor core and seismic-reflection data from the western Niger Delta continental 16 slope document the facies, architecture, and evolution of submarine channel and intraslope 17 submarine fan deposits. The submarine channel enters an 8 km long x 8 km wide intraslope 18 basin, where more than 100 m of deposits form an intraslope submarine fan. Lobe deposits in the 19 intraslope submarine fan show no significant downslope trend in sand presence or grain size, 20 indicating that flows were bypassing sediment through the basin. This unique dataset indicates 21 that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by 22 traditional lobe facies models, and that thickness patterns in intraslope submarine fans do not 23 necessarily correlate with sand presence and/or quality. 24Core and radiocarbon age data indicate that sand beds progressively stack southward 25 during the late Pleistocene, resulting in the compensation of at least two lobe elements. The 26 youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km 27 long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds 28Jobe et al. -Bed compensation on an intraslope submarine fan, Nigeria 2 forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 29 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location 30