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One of the most destructive tropical cyclones ever to strike the U.S., Hurricane Katrina made landfall along the Mississippi coast on 29th August 2005. The Mississippi-Alabama (MS-AL) barrier islands were subjected to storm breaching, area reduction, and vegetation loss caused by a number of parameters including salt spray, saltwater flooding, mechanical damage (e.g., ablation of bark from tree trunks), removal of plants and their soil substrate by scouring, burial under sand, and a 10-month, post-storm period of low rainfall. Repeated acquisitions of remotely-sensed data served as an essential tool in quantifying vegetated and total land area before and after the storm, and post-storm ecological community type and topographic elevation. Vegetated land area continued to decline on some islands in the first year following the storm. However, by November 2007, only 2.2 years after the storm, total vegetated land area had recovered to 72, 96, 77, 93, and 82%, and total subaerial land area to 97, 94, 33, 100, and 104%, of pre-Katrina values on Cat, W. Ship, E. Ship, Horn, and Petit Bois islands by natural re-growth and sediment accretion, respectively. Comparing ecological community-type maps that were developed from field and remotely-sensed data with LiDAR-derived digital elevation models determined that year 2010 ecological community type changed distinctively at the decimeter scale as mean surface elevation ranged from 0.1 m to 1.2 m. Storm-related changes in ecological community type included subtidal to supratidal sand flat, low marsh to wet or dry herbland, and woodland to wet herbland/shrubland.

A large body of chronologically well-constrained and detailed Quaternary data accumulated in the last decades from the coastal-shelf region of the northern Gulf of Mexico. Consequently, a preliminary synthesis of major aspects of the late Quaternary barrier and mainland coastal development on the northern Gulf of Mexico is timely. Several major factors account for the striking differences between barrier size and development styles in the three northern Gulf coast regions. Barriers are nearly continuous in the NW where they dominate by the greatest dimensions and continuity. Sand supply from shelf and mainland sources, continued at variable rates throughout six stages of the Last Eustatic Cycle (LEC). Differences in antecedent topography, in fluvial runoff volumes and relative sea level rise, including rapid overstepping-flooding events were critical in the regional distinctions. Leaving fewer and smaller relict fluvial delta behind, drowned shore and nearshore landforms on the shelf, only two large fluvial systems impacted the NE. The NW shelf and nearshore received abundant sediment supply from the Mississippi and lesser streams; indirectly by ravinement erosion of relict landforms and landward-directed cross-shelf sediment transfer. Sands originated mainly in relict deltas, fluvial, tidal channel, and inlet fill, as well as from submerged shore ridge remnants on the continental shelf. Shelf-margin deltas represented major secondary sources. Barrier formation categories and their respective importance in specific areas represent critical aspects of coastal development. The authorship of various formation concepts (e.g., Penck, Gilbert, McGee, Haage, Ganong, and Keilhack) often is still miscredited or remains unrecognized in the literature. Recognition of the stratigraphic and sedimentological diagnostic characteristics of the basic genetic barrier categories plays a key role in testing the validity of barrier evolution models. Closely-knit process-form relationships prevail between hydrodynamic (sea level change, storm, tidal current, overwash), sedimentary (shoal and island aggradation, rollover, and eolian accumulation) processes, and the resulting landform morphology. The most detailed accounts that deal with the development of the Alabama-Louisiana and Apalachicola barrier chains are particularly instructive. Almost all modern Gulf barriers with identifiable genetic background formed by shoal aggradation between 5.5 and 2.0 ka, during a marked deceleration in sea level rise. Concurrently, a sizable mainland strand plain complex extended the NE coastal plain. Tide- and storm-driven sediment transport to the large Mobile Bay ebb-delta, the focal role of composite east Dauphin Island in establishing the MS-LA island chain and the island-blocking role of Mississippi Delta advance were prime factors in a complex barrier history. Migration, paradoxically, may also occur by transgressive rollover concurrently with regressive landward progradation of island strand plains. Stream discharge and sand reworked from relict lithosomes on the shelf were insufficient in compensating for wave- and tide-related sediment loss. Gulf levels stayed below the present throughout the mid- and late Holocene.

Based on numerous publications and field work on the northern Gulf of Mexico coast, U.S. and other coastal areas, the present objective is to meet the need for an improved system of the definition and classification of barriers and their components. This topic includes morphological and functional interrelationships between beach ridges, barriers, and similar landforms. The term “beach ridge” was applied to a plethora of sub- and supratidal ridge types. In contrast, the presently proposed definition restricts the term to relict berm and foredune ridges, composed of sand or gravel and stabilized after isolation from shore zone of active processes. Barriers sustain paralic hydrology, sediment, biotic and nutrient condition in the coastal realm. In combination with adjacent lagoons and river deltas, these landforms represent physical barriers that lessen marine and related influences in brackish paralic-coastal environments. Benefiting from historic evolution of concepts and nomenclature, the task also involves the correction of misattributions rooted in early publications. Island, spit, and mainland barriers thus maintain lower salinities, reduce wave erosion, protect nutrient-rich paralic deposits and mitigate storm-induced inundation. “Fetch-limited lagoonal barrier islands” are considered valid barriers only in lagoons where they face inlet-transmitted full-marine conditions. “Mainland barriers” of several subcategories often are important sediment archives of past sea levels, hydroclimate, climate and tectonic-isostatic changes. They consist mostly of ridgeplains, at the start firmly attached or later migrated and welded to the mainland shore. In addition to local hydrodynamic and topographic influences, formation conditions may reflect overall paleogeographic conditions, including fluvial impact. In progradational (regressive) island settings, barriers consist mainly of strandplains that laterally may alternate with narrow spit-like sectors. They include only single, marine, respectively, lagoon-side shore ridges, with secondary dune fields sandwiched between them. Field observations and drillcore studies of microfossil- and sediment-based depositional facies suggest that most barrier islands originated by the often underestimated shoal-aggradation mode. Two additional genetic models are recognizable; a fourth remains hypothetical. Remotely-sensed images indicate that post-hurricane regeneration of the largest deltaic barrier chain in the Gulf of Mexico stalled in recent years. Late Pleistocene barriers significantly influenced present coastal landforms in two extensive regions. Dramatic changes in past decades indicate that sea-level rise and stormier future hydroclimate may likely accelerate the degradation of deltaic and non-deltaic barrier islands.

A bottomland flora that prevailed between ∼9900 and 6000 cal yr B.P. in a North Carolina stream valley may not reflect a regionally much wetter Atlantic climate, coeval with record drought in the Great Plains region and assumed dry Gulf coastal conditions. Such conditions were inferred for 6000 ± 1000 yr ago when the Bermuda High may have consistently occupied summer positions far to the NE. Arid episodes coeval with the Little River local wet interval are known from eolian sediments and pollen spectra in the Atlantic and the Gulf coastal plain. For multiple reasons, the regional extent, intensity, and duration of coastal aridity and alternating wet phases and the Bermuda High positions are not yet adequately constrained. The climate and edaphic causes for the steadily growing predominance of southern pines over hardwoods, achieved between ∼8900 and 4200 cal yr B.P. at different sites at different times are similarly still unresolved. New data from Shelby Lake, AL, reconfirms that no credible field or other proxy evidence exists for a previously postulated “catastrophic Gulf hurricane phase” in the late Holocene.

Luminescence dating of extensive dune fields and associated eolian sandsheets provided a chronology of recently recognized Pleistocene and early Holocene dry climate episodes in the currently humid warm temperate northern–northeastern Gulf of Mexico region. Scattered parabolic dunes and clusters of intersecting parabolic dunes, along with elongated shore-transverse and shore-parallel dunes, developed. These landforms occur in a 390-km-long and 2- to 3-km-wide, semicontinuous belt in southeast Alabama and northwestern Florida. Dune elevations reach ± 22 m. Sangamon coastal barrier sectors were the primary source of the eolian sand. Deflation was coeval with early Wisconsin to mid-Holocene marine low sea-levels and associated distant shorelines. Early Holocene dune dates were synchronous, with indications of a hypsithermal dry interval in southeast Louisiana, the Yucatan, and the south Atlantic seaboard. Overlapping with dry episodes in Yucatan and the High Plains, Texas dunes and Louisiana and Texas prairie mounds, especially in the southwest Texas coast still dominated by dry climate, suggests intervals of early to late Holocene drought. The dates provide the basis for identifying and correlating Wisconsin, early, and late Holocene climate phases between currently semiarid and humid, coastal and interior areas. They contribute to future studies, including interregional paleoclimate modeling. Although Pleistocene coastal eolian deposition coincided with glaciation in the northern interior and with cooler temperatures of a reduced Gulf of Mexico, Holocene aridity phases may have been related to major variations in the position of high-pressure cells, storm tracks, and branches of the jet stream, and even to prolonged La Niña conditions.

Thirty-five sand hills that form six scattered groups rise abruptly from the flat late Pleistocene coastal plain in southeastern Louisiana. New studies confirm their eolian origin. For the first time, several late Wisconsin to early Holocene episodes of arid climate conditions have been recognized and dated in this currently humid warm-temperate subtropical region. Periods of dune formation and reactivation (28,800 to 7900 yr B.P.) were determined by the thermoluminescence method. The onset of the current climate in this Gulf coastal region postdates early Holocene time. The textural and structural homogeneity of the ridge lithosomes, good sorting of their sand fraction, and the dominantly orange hues of the dune sediments contrast with the underlying yellowish–brown to light-brown sandy silts and the well-stratified, occasionally gravelly sands of the underlying alluvial Prairie Formation. Sharply defined, unconformable ridge bases; symmetrical, oval, occasionally parabolic mound shapes; and steep slopes confirm the dune origins. The dominant orientations of ridges and ridge chains clearly reflect paleowind directions. Age comparison with dunes of the lower Mississippi Valley, the northeastern–eastern Gulf of Mexico coast, and south Atlantic coastal areas confirms the existence of at least seasonally dry climate conditions from early Wisconsin to middle Holocene times. The onset of the modern humid-subtropical climate phase in this region thus dates back only to the middle Holocene.

Among numerous stream-valley terrace deposits of the Gulf and Atlantic coastal plains that occupy chronologically and spatially intermediate positions between the youngest coastwise (coast-parallel) Pleistocene surface and the present, active floodplain, those of the Tunica Hills seem to provide by far the best opportunity for radiometric dating. Earlier views on the age of the Little Bayou Sara creek alluvium, represented by a single, 8 to 10-m-thick unit, ranged between the last interglaciation and middle Holocene. Reexamination of these deposits in the Little Bayou Sara and adjacent valleys clearly suggests their Late Pleistocene (apparently Farmdalian Interstade) age. The majority of the 14 available dates from the Little Bayou Sara and Tunica Bayou valleys proved to be too young, due to postdepositinal contamination. Dates ranging between 33,720 and 25,965 yr B.P. came from samples thought to be uncontaminated. Plant and faunal elements with boreal affinities in the unique fossil assemblage appear to be relicts of a preceding, full-glacial period, as regarded by Brown (1938). The absence of colder climate taxa from the Wilcox Bluff flora on Bayou Sara is insufficient evidence for a suggested Sangamon Interglacial age of the flora, and the terrace stratigraphy holds no proof for that view either. Only a single, loess-mantled, constructional, Quaternary, valley-terrace surface is present in the area. A narrow, low, actively developing floodplain terrace along Little Bayou Sara, cut into the Pleistocene alluvial unit, is primarily erosional in origin and has no bearing on the age of that unit. The age of the Tunica Hills terrace unit may provide comparison for dating intermediate valley-terrace deposits in favorable coastal settings elsewhere.