Deceleration Of Sea-level Rise Research Articles

Holocene evolution and signature of environmental change of the Burullus lagoon (Nile Delta) deciphered from a long sediment record

This study presents high-resolution multi-proxy analyses of a well-dated sediment core (BR-1, 19.20 m long) retrieved from the Nile Delta, aiming to reconstruct the Holocene evolution of the Burullus lagoon. In particular, we focus on the morphodynamical processes, sediment provenances and related hydro-climatic changes. The Holocene strata of the lagoon coast comprise Early-Holocene marine transgressive facies and the Mid-Late Holocene retrogressive deltaic facies. Although BR-1 shows no river-channel facies, two peaks of magnetic susceptibility (MS) at ca. 8.0–7.0 ka (also associated with a high sedimentation rate of 50 mm/yr) and 3.5–2.0 ka evoke phases of greater morphodynamic influence of palaeo-Nile branches on the lagoon's development. Both dated peat layers (ca. 13 m and 8 m below MSL) and lagoon muds intercalated in BR-1, together with previously-dated peat strata were benchmarked relatively to MSL for the reconstruction of relative Holocene sea level in the study area. Our results show considerable land lowering on the Burullus coast indicated by a sea-level elevation, ca. 4–1 m lower than the one reconstructed along adjacent coastlines where less land subsidence occurred. The lagoon system began to form after ca. 6.0 ka in response to deceleration in sea-level rise and, being a shallower water body, both macrofauna (Cerastoderma glaucum etc.) and ostracods (Cyprideis torosa) of brackish-water nature emerged. In addition, geochemical data from BR-1 provide insights into environmental change in association with basin-wide hydro-climate fluctuations. Concomitant peaks in Fe/Al, Ti/Al and Cr/Al ratios (mafic origin), together with higher Zr/Al and Hf/Al ratios (felsic origin) before ca. 8.0 ka suggest sediment provenances derived from the White and the Blue Nile during the main African Humid Period (AHP). Since then, Ti/Al kept slightly ascending core-upwards with two pulses at 7.8–7.3 ka and 3.5–2.0 ka, which was asynchronous to Zr/Al and Hf/Al. This corroborates more sediments of basaltic origin transported to the delta coast after the main AHP due to southerly shift in the position of the ITCZ. The two periods of Ti/Al pulse are consistent with the MS peaks in BR-1, suggesting that palaeo-Nile branches remained active during 8.0–7.0 ka and 3.0–2.0 ka nearby.

Influence of antecedent geology on the Holocene formation and evolution of Horn Island, Mississippi, USA

Horn Island, one of the two most stable barriers along the Mississippi-Alabama chain (Cat, East and West Ship, Horn, West Petit Bois, Petit Bois, and Dauphin), provides critical habitat, helps regulate estuarine conditions in the Mississippi Sound, and reduces wave energy and storm surge before they reach the mainland shore. However, important details of the formation and evolution of the island in response to sea-level rise, storms, and antecedent geology remain unclear. This study integrates 2200 km of high-resolution geophysical data, 35 sediment cores, and 18 radiocarbon ages to better understand the geologic history of the island. Incised valleys of the Biloxi and Pascagoula Rivers underlie Horn Island and played a profound role in the evolution of the system. Within the incised valleys, sandy paleochannel deposits represent potential sediment sources during island development. Scour associated with wave and tidal ravinement processes liberated sand from the paleochannels and along with numerous other sizable sand sources on the shelf contributed to the formation and continued maintenance of Horn Island. Based on radiocarbon ages, transgressive ephemeral islands/shoals with no preserved shoreface existed at least 8000 cal yr BP and were frequently overwashed when sea-level rise rates were ~ 4–5 mm/yr. Approximately 5000 cal yr BP, coinciding with a deceleration in sea-level rise to about 1.4 mm/yr and attendant increased sand supply, radiocarbon ages associated with Horn Island's barrier complex and lower shoreface indicate a period of island stabilization. Seismic and sediment core data show a long history of westward lateral migration by longshore currents through tidal ravinement and inlet fill. Subsurface sand packages associated with tidal inlet fill and paleochannels are available for ravinement and may be important sand sources for Horn Island to maintain subaerial exposure with the expected accelerated future sea-level rise.

Coastal barriers, northern Gulf - Last Eustatic Cycle; genetic categories and development contrasts. A review

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.

Global mean sea level rise during the recent warming hiatus from satellite-based data

ABSTRACTSatellite remote sensing has provided an unprecedented opportunity to understand the spatio-temporal change of the Earth’s climate system. In this study, we take advantage of the oceanographic satellite-based data to examine the global mean sea level rise, with a focus on a transitional episode (1994–2003) referred to as the onset of recent global warming hiatus. We remove the signals accounted for the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, and solar radiation using an Empirical Orthogonal Function and multivariate regression analysis. The trend estimates over the period 1993–2015 are significantly improved in accordance with the reduction of uncertainty by half. Our results associate the observed deceleration of sea level rise during the onset with the climate oscillations. It strengthens a conclusion deduced by an alternative approach using modelling, whilst highlights the robustness of combining satellite-based datasets and climate indices in a reliable statistical estimation.

Holocene floodplain evolution in the Shiribeshi-Toshibetsu River lowland, northern Japan

The influence of sea-level and climate changes on the evolution of coastal floodplains is an important problem in fluvial geomorphology and geology. However, few studies have constructed detailed chronologies of floodplain evolution, and the influence of sea-level and climate changes at submillennial time scales is not clear. This study investigated the Holocene evolution of the floodplain in the Shiribeshi-Toshibetsu River lowland, Hokkaido, northern Japan, based on 13 auger cores, 15 radiocarbon ages, and 2 cross sections made using existing columnar sections. In the study area, peat beds 3–6m thick in the uppermost Holocene sediments are underlain by fluvial sediment that mainly consists of sand beds resulting from crevassing or progradational avulsion. Age–elevation plots of the bases of these peat beds suggest that fluvial aggradation was continuous until peat formation began, which in turn suggests that peat beds began to form with the cessation of fluvial deposition. The chronology of floodplain sediments based on radiocarbon ages indicates that peatlands began to develop locally before ca. 6500calBP and became moderately widespread before 5600calBP. Peatlands then became more extensive after two periods of rapid expansion during ca. 5300–5000 and 4100–3900calBP. Comparison with sea-level and regional climate changes suggests that the initiation of these peat beds before 5600calBP was associated with the deceleration of sea-level rise at ca. 7000calBP. The two later periods of peatland expansion may have been strongly influenced by reduced fluvial activity due to decreased precipitation from a weakened East Asian summer monsoon. This interpretation suggests that floodplain evolution was controlled by sea-level and climate changes and that the response to climate change occurred at submillennial time scales. A comparison with the Ishikari lowland on Hokkaido showed that the two floodplains have slightly different histories, possibly because of differences in internal characteristics of the fluvial systems such as the number and size of tributary rivers, water discharge, and sediment supply, although their responses to sea-level and climate changes were similar. The fluvial response to sea-level and climate changes revealed in this study has implications for studies of the Holocene evolution of other coastal floodplains.

Stepwise post-glacial transgression in the Rhône Delta area as revealed by high-resolution core data

Integrated sedimentological and micropalaeontological (benthic foraminifers and ostracods) analyses of two continuous cores (40m and 50m long, respectively) recovered in the lower delta plain of modern Petit Rhône Delta, along with data from the previously studied Core SF, enable detailed reconstruction of the late Pleistocene–Holocene palaeoenvironmental evolution of the Rhône Delta system. Through identification of nine microfossil assemblages and with the aid of 28 radiocarbon dates, a high-resolution picture of stratigraphic architecture is offered for the first time for the entire post-glacial succession. Above late Pleistocene fluvial-channel gravels, a retrograding pattern of swamp and estuarine/bay deposits (lower transgressive systems tract — TST) is overlain by vertically stacked, late transgressive nearshore deposits (upper TST). This succession reflects the progressive landward migration of the palaeoshoreline driven by the rapid post-glacial sea-level rise, which took place in the study area between ca. 12 and 7cal ky BP. The following deceleration in sea-level rise (highstand phase) induced the onset of deltaic sedimentation, as evidenced by superposition of middle–late Holocene prodelta, delta-front and delta-plain deposits within the cored succession. At distal location the occurrence, within prodelta deposits, of a distinctive microfossil assemblage dominated by opportunistic benthic foraminifer Valvulineria bradyana marks the onset of the Rhône Delta mud-belt around 4cal ky BP. Identification and lateral tracking of six separate flooding surfaces within the TST enable the characterization of five short-term (millennial to sub millennial-scale) depositional cycles with distinctive transgressive–regressive internal architecture (T–R 1–5). The lower, transgressive portions of cycles 1–3 (11.8–9.8cal ky BP) mark abrupt shifts from freshwater to increasingly mixed, brackish-marine environments under conditions of rapid sea-level rise. In contrast, the upper, ‘regressive’ portions represent the filling of newly formed accommodation space via extensive crevasse to bay-head delta processes. Cycles 4 and 5 (9.8–8.2cal ky BP) and the uppermost transgressive deposit below the maximum flooding surface document three distinct landward shifts of the shoreline that took place under conditions of rapidly increasing sea-level rise. The vertical stacking of these millennial-scale cycles is interpreted to reflect the stratigraphic response to stepwise sea-level rise during the early Holocene. The youngest flooding surface may represent the sea-level signature of the 8.2ka climate event.

Evidence for Holocene Marine Transgression and Shoreline Progradation Due to Barrier Development in Iskele, Bay of Izmir, Turkey

This study addresses the paleogeographic coastal evolution of the coastal plain in the environs of Iskele, Turkey. Eight sediment cores were collected along a north–south and east–west transect and analyzed to determine whether the coastal environment had changed in the recent past. The results illustrate that the coastal environment consisted of a transgressive systems tract, ending approximately 6000 BP and represented by marine transgression, flooding of incised river channels, and marsh development, followed by a high stand systems tract. Five major environmental facies were identified: terrestrial, wetland, lagoon, foreshore, and upper shoreface. The high stand systems tract was characterized by the development of a beach-barrier consecutive series of longshore transport-derived sandbars. These sandbars contributed to the creation and eventual isolation and terrestrial infilling of nearshore lagoons and wetlands. Sea-level indicators indicate rapid sea-level rise reaching a peak approximately 6000 YBP, followed by deceleration of sea-level rise and resulting shoreline progradation. The construction of a causeway connecting Karantina Island to the mainland approximately 2400 years ago has accelerated the process of progradation east of the causeway by decreasing the wave energy. Sediment that would have previously been transported further east is now deposited in the zone immediately east of the causeway.

Basin-scale reconstruction of the geological context of human settlement: an example from the lower Mississippi Valley, USA

Large river valleys integrate hydroclimatic change differently than smaller ones. Whereas sedimentary deposits in smaller valleys serve to record temporally short-lived and/or low-amplitude hydrological and geomorphic responses, larger valleys are relatively insensitive to changes at these scales. However, because of their size, larger valleys archive sedimentary records of longer-term, geographically extensive flooding and climate-related landscape evolution. Recent work in the Upper Tensas Basin of the lower Mississippi River Valley, USA, demonstrates the utility of analyzing sediments from a large, geomorphically and fluvially complex river basin as a proxy for significant climatic and landscape changes and their relation to human history. A ∼6000 year sedimentary archive is used to explore the interplay between climate change, landscape evolution, and human responses to changing environmental parameters. Once the Mississippi River basin stabilized following glacial retreat and deceleration of sea-level rise, the history of the river and its inhabitants was dominated by long periods of landscape stability punctuated by episodes of significant landform alteration. Modifications of the landscape are correlated with intervals of rapid climate change recorded in globally distributed multiproxy data sets. Periods of significant landscape instability and fluvial re-adjustment are recorded for the periods ca 4800–3800, 3000–2500, and 1000–800 cal BP. These punctuations in the history of the lower Mississippi Valley are related to periods of major cultural transformation and suggest climate change plays a significant role in the long-term history of human occupation in this river valley. This research demonstrates how geoarcheology can provide information on human–environmental relationships and long-term landscape histories at temporal and spatial scales relevant to understanding cultural responses to climate change.

Coastal evolution and Holocene ostracods in Melides lagoon (SW Portugal)

A multidisciplinary study covering sedimentology (texture, carbonate and organic matter content, clay mineralogy), geochemistry (major, minor and trace elements, isotopes), palaeoecolgy (ostracods) and isotopic dating ( 14C) has been carried out on two long cores (MB-40.0 m and MIGM-34.0 m) retrieved from the barrier and the alluvial plain margining the Melides lagoon (south-western coast of Portugal). The interpretation of the whole data set allowed the establishment of an evolutionary model for this lowland since the Late Glacial. This model includes four stages. It starts with a fluvial terrestrial environment, replaced by an estuarine to fully marine one (circa 9500 cal BP), due to the rapid rise in sea level recorded during the first phase of the Holocene transgression. The deceleration of sea level rise favoured the emplacement of a sandy barrier (circa 5900 cal BP) that promoted the differentiation of a coastal lagoon which has been progressively filled with fluvial sediments. The ostracod fauna in both locations includes 38 species of littoral to sublittoral/phytal marine forms (mainly Urocythereis britannica, Carinocythereis whitei, Loxoconcha rhomboidea, Pontocythere elongata, Semicytherura sella, Semicytherura acuta, Basslerites cf. berchoni, Hiltermannicythere emaciata) and brackish water forms ( Cyprideis torosa, Loxoconcha elliptica), which clearly characterize the signature of both the marine and lagoonal episodes, respectively.

Braarudosphaera -rich sediments in the Turonian of the Bohemian Cretaceous Basin, Czech Republic

Braarudosphaera -rich sediments occur in the Turonian (nannofossil zones CC13 and UC9a) epicontinental marine sediments of the Bohemian Cretaceous Basin. This phenomenon is linked to the input of terrigenous material during deceleration of sea-level rise, or stillstand in sea level, which possibly both triggered the Braarudosphaera bigelowii bloom and reduced the diversity of the nannoplankton assemblages. The occurrence of Marthasterites furcatus and Lithastrinus septenarius probably reflects depositional conditions that were suitable for their preservation. Hence, the resultant limitations to their use as local zonal markers in the Bohemian Cretaceous Basin are discussed. The influence of the Tethyan Bioprovince is documented by the coincident first occurrences of L. septenarius and M. furcatus. The presence of the high-latitude species Thiersteinia ecclesiastica indicates penetration of Boreal biota into this depositional area within the Turonian.

Worldwide Initiation of Holocene Marine Deltas by Deceleration of Sea-Level Rise

Radiocarbon-dated deltaic sequences of Holocene age from different parts of the world began to accumulate within a restricted time range, from about 8500 to 6500 years ago. Evaluation of major delta processes indicates that deceleration in sea-level rise was the key factor in Holocene delta formation. Within many deltas, there is as much as a 2000-year age range between basal deposits in seaward and landward cores. This age difference records the progressive landward migration of near mean sea-level depositional environments during the lower to mid-Holocene. Establishment of a chronostratigraphic framework for Holocene delta development provides a fundamental global baseline for distinguishing sea-level change from vertical land motion by tectonism and isostasy, and for evaluating rates of future marine incursion into low-lying deltas.

Deceleration of Sea-Level Rise at 8000-7000 Years B.P. as the Dominant Factor in Progradation of Holocene Marine Deltas: ABSTRACT

Deceleration of Sea-Level Rise at 8000-7000 Years B.P. as the Dominant Factor in Progradation of Holocene Marine Deltas: ABSTRACT

Sea level and initiation of Predynastic culture in the Nile delta

PREDYNASTIC occupation of the Nile valley and delta, dating back to at least 5000 BC, has been attributed by most archaeologists to environmental factors, primarily regional climate change and fluctuating Nile flood stages1–5. Here we propose instead that initiation of farming settlements in the Nile delta was closely related to eustatic sea level. We present geological analyses of late Quaternary subsurface sections throughout the delta which reveal that the deceleration in sea-level rise that occurred at about 6500–5500 BC was a prime factor in the accumulation of Nile silt, and the creation of the widespread and fertile delta plain. As rising sea level reduced the gradient of the river course, a system of meandering Nile distributaries evolved, with increased overbank deposition burying the former (early Holocene), partially vegetated sandy plain. The broadening, seasonally flooded, fecund plain, with its increasing plant cover, provided a setting that was conducive to evolving agricultural activity and was therefore instrumental in the development of Predynastic communities in the Nile delta.

Lily Bank, Bahamas: History of an Active Oolite Sand Shoal

ABSTRACT Study of the response of an active oolite sand shoal (Lily Bank), located along the northeastern margin of Little Bahama Bank, to its physical environment and the Holocene sea-level rise has provided a developmental sequence from initial formation to present maintenance for this marine sand belt. Lily Bank is oriented parallel to the bank margin and is independent of underlying bedrock topography. It has developed immediately bankward of two large, intrareef bank-margin reentrants which allow a relatively unrestricted flow of tidal and storm-generated currents on and off the bank top. Subsequent to the initial sea-level rise over the bank approximately 5,700 yr BP, these reentrants funnelled bankward-directed flow which resulted in two zones of bedforms: (1) an outer zone of linear, p rallel-to-flow sand ridges (200-500-m spacing, 3-4 km long, 2-3 m in height) oriented in a radiating pattern away from the reentrant throats; (2) an inner belt of sand waves oriented transverse to flow (90-300-m spacing, 1-2 m in height). These now-relict bedforms developed approximately 4,000 yr BP. As sea level continued to rise, bankward flow velocities decreased as the reentrant channeling effect decreased. The linear sand ridges, which require a higher flow velocity for development and maintenance, became less active and eventually were stabilized by marine grasses. The adjacent sand-wave field developed rapidly during the deceleration in sea-level rise which occurred around 3,500 yr BP. A portion of this sand-wave field continues to migrate slowly into the shelf lagoon in response o the dominant bankward energy flux and maintains itself in pace with the slowed sea-level rise. The present geometry and sand-transport regime on the oolite shoal appear to result from interplay between storm-generated and tidal currents. Storm-generated currents have developed channels which cross the sand body and terminate in flood- or ebb-oriented spillover-lobes. Between the lobes are wide, flood-dominated zones with flood oriented sand waves protected from ebb-tidal flow by topographically higher shield areas covered with symmetrical sand waves. During storms, the shield areas are flattened and sand is transported bankward onto the shelf lagoon when the dominant energy flux is in that direction. Tidal currents reestablish the shield areas during poststorm recovery. Tidal bar belts oriented perpendicular to bank margins, and marine sand belts, parallel to bank margins, are not necessarily mutually exclusive, and occur together along this same bank edge. The now inactive linear sand ridges seaward of Lily Bank may be analogous to active tidal bar belts found elsewhere in the Bahamas today. Paleoenvironmental ramifications are that, despite differences in sand-body and sedimentary structures, both types of sand body may exist along the same bank margin. The tidal bar field is located near the bank edge and the marine sand belt is adjacent to it but farther bankward. Because reentrants within the bank margin are common, they have played an important role in localizing oolite shoals which then may serve as foundations for future island development, perhaps during a later sea-level fluctuation. Some of the large Pleistocene islands in the Bahamas may be situated upon reentrant-controlled oolitic sand shoals.