Wetlands in the Mississippi River deltaic plain are deteriorating 1 in part because levees and control structures starve them of sediment [2][3][4] . In spring 2011 a record-breaking flood brought discharge on the lower Mississippi River to dangerous levels, forcing managers to divert up to 3,500 m 3 s −1 of water to the Atchafalaya River Basin 5 . Here we use fieldcalibrated satellite data to quantify differences in inundation and sediment-plume patterns between the Mississippi and Atchafalaya River. We assess the impact of these extreme outflows on wetland sedimentation, and use in situ data collected during the historic flood to characterize the Mississippi plume's hydrodynamics and suspended sediment. We show that a focused, high-momentum jet emerged from the leveed Mississippi, and delivered sediment far offshore. In contrast, the plume from the Atchafalaya was more diffuse; diverted water inundated a large area, and sediment was trapped within the coastal current. The largest sedimentation, of up to several centimetres, occurred in the Atchafalaya Basin despite the larger sediment load carried by the Mississippi. Sediment accumulation was lowest along the shoreline between the two river sources. We conclude that river-mouth hydrodynamics and wetland sedimentation patterns are mechanistically linked, providing results that are relevant for plans to restore deltaic wetlands using artificial diversions 2-4,6-8 .Protecting and expanding coastal wetlands is vital for ecosystem services of the Mississippi River Delta 9-12 , and harnessing natural processes of wetland building using the Mississippi River and its sediments is an essential component of restoration plans [2][3][4] . The only portion of the delta experiencing significant expansion of coastal wetland at present is at the mouth of the Atchafalaya River (Fig. 1a), where a higher mineral (that is, non-organic) sediment concentration 3 and hydrodynamic factors 8 allow sufficient sediment deposition 6 to outpace subsidence and sea-level rise 13 . The recently released 2012 Coastal Master Plan 14 proposes river diversions and channel realignment to divert sediment and fresh water from the Mississippi River and Atchafalaya River into adjacent basins, to reconnect the river to delta wetlands. Successful design and implementation of such measures require an understanding of diverted sediment movement and deposition, especially during high-water events when the potential sediment load is greatest.The Mississippi River flood of spring 2011 was one of the largest on record 5,15 . Both the Mississippi River and Atchafalaya River

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Discoveries from multibeam bathymetry and geochemical surveys performed off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water (<150 m water depth). Based on a detailed morpho‐bathymetric study we identify the seabed morphologies produced by hydrothermal fluid emission activity. We recognize five giant depressions (length >250 m) that host pockmarks, mounds, small cones, and active fluid vents, which are interpreted as complex fluid‐escape features developed both through vigorous‐explosive events and steady seepage. Their spatial distribution suggests that the NE‐SW trending faults bounding the Ponza‐Zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids. Moreover, we performed a detailed geochemical study to investigate the source of the hydrothermal fluids. The geochemical signature of the collected fluids provides information of active CO2‐dominated degassing with a significant contribution of mantle volatiles, with measured 3He/4He values > 3.0 Ra that are similar to those recorded at Stromboli and Panarea volcanoes. The hydrothermal system produces volatiles that may originate from residual magma batches, similar to the Pleistocene trachytes cropping out in the SE sector of Ponza Island that were probably intruded in the shallow crustal levels and never erupted. The discovery of the Zannone hydrothermal field updates the record of active hydrothermal areas of the Mediterranean Sea. Moreover, the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the Mediterranean Sea.

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