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This paper presents a novel method to reconstruct sea-level change in coastal freshwater back-barrier marshes. Freshwater environments have long been considered to be unsuitable for the reconstruction of Holocene sea level changes as they provide limiting, rather than precise, sea-level index points. We recorded the stratigraphy of a small beach and back-barrier coastal Phragmites (reed) marsh at Hallsands, south Devon, southwest England, using hand-drilled cores and ground-penetrating radar, and collected five new sea-level index points from the base of a Holocene peat sequence to refine the regional Holocene relative sea-level curve. We demonstrate that the samples, despite their freshwater origin, yield accurate sea-level index points as determined from the quantifiable relationship between tide levels and groundwater. By means of water-table monitoring and groundwater modelling we show that the primary controls on the water table in the marsh are: (1) stratigraphy; (2)peat permeability; and (3) recharge rates in the back-barrier marsh. The five index points document relative sea-level positions between 7200 and 2400 cal yr BP. Three points are in good agreement with previously collected regional data from inter-tidal deposits and two points usefully fill gaps in the existing reconstruction. An amended Holocene relative sea-level curve for south Devon, based on 30 data points, is presented. We conclude that the combined approach of data collection and modelling used in this paper can be applied to similar coastal settings around the world and allows the collection of sea-level index points from locations not previously thought suitable for this purpose.

The flux of low-salinity Pacific Water (PW) through Bering Strait (BS) weights on the freshwater budget of the Arctic Ocean, which, in turn, impacts the Atlantic Meridional Overturning Circulation (AMOC). Through time, this PW flux has been tightly controlled by the bathymetry of the Strait (~ 50 m water depth at present), thus by sea-level (SL) changes and documented in several papers based on a large array of sedimentological and geochemical tracers. The present study aimed at reassessing the robustness of these tracers of the PW-flux, based on five surface samples collected along a south-north transect from BS to Chukchi Plateau, within the bathymetric range of the PW-mass dispersal. We also estimated their variation in relation to the post-glacial SL-rise in a sedimentary core (ARC4-R09), from the Chukchi shelf, spanning the last ~10 kyr. Potential indicators of PW-flux include sortable silt, clay minerals, and the particulate and exchangeable Nd-isotope composition of specific grain-size fractions. The results indicate that ɛNd-values in leachates, and to a lesser extent, the smectite abundance, both relating to volcanic rocks of the Bering Sea, are sensitive indicators of the PW-flux, whereas sortable silts and other clay minerals relative abundances are also influenced by other processes (e.g., west-east shelf currents, sea-ice rafting). The modern distributions of ɛNd-value and smectite abundance illustrate mixing between two endmembers: i) a northern Bering Sea endmember, characterized by ~14% of smectite (vs all clay minerals) and a ɛNd-value of the exchangeable fraction of ~ −2; ii) a Chukchi Sea endmember, characterized by ~8% of smectite and a ɛNd-value ranging from −7 to −8. The Holocene sedimentary record from the study core indicates a progressive increase in Bering Sea supplies through time, linked to an enhanced inflow of PW, which we associate with the deepening of the Strait due to the rising SL. Following a major reorganization of the Arctic Ocean circulation at ~8 ka BP, a steady increase in PW flux prevailed until ~4 cal. kyr BP. A tenuous but continuous positive trend towards modern eNd values followed during the late Holocene. The middle Holocene steep increase of warm, low salinity PW-flux through BS, led to important changes in the Arctic Ocean, in particular of its salinity budget. Assuming that the BS bathymetry is the main parameter governing the PW-flux towards the Arctic Ocean, a first-order estimate of PW-flux under a higher than modern SL can be made using the SL-elevation-ɛNd relationship of the major middle Holocene shift.

Refined records of Holocene sea level and coastal evolution are needed to forecast changes in the Anthropocene. Beach ridge strandplains and other prograded barriers preserve an exceptional (and relatively untapped) archive of past sea level within their stratigraphy. Extracting these records using high-resolution geophysics can unearth sea-level indicators with the potential to resolve small fluctuations over large spatial- and temporal-scales. Brooke et al. (2019) construct a sea-level curve from Cowley strandplain and performs interesting modelling/analyses; but does so based on the beach ridge topography. Unfortunately, this methodological approach contradicts a long-held understanding that it is not appropriate to use ridge morphology or sediment analysis from cores/augers/pits to indicate sea level. This sets a misleading precedent if perpetuated in future research and does so at a critical time when extracting sea-level reconstructions from prograded barriers is becoming more established. While the Brooke et al. (2019) curve appears to correlate with data from this region, it is not precisely clear how it was constructed. Particularly perplexing is the most recent half of the curve, starting with the peculiar location of the modern analogue below mean sea level. Simply adjusting the existing curve to zero on the y-axis removes it from the tenuous correlation. This comment paper uses the geophysical and topographic data published in Brooke et al. (2019), as well as the protocol referenced, to construct relative sea-level curves. The results accentuate the difference between the reconstructions from the berm stratigraphy and the ridge morphology. Furthermore, despite the cursory nature of this analysis and the complexity of this barrier's stratigraphy, the berm heights demonstrate remarkable correlation with the modelled sea-level curve for the region as well as the more traditional sea-level indicators. Ultimately, this glimpse provides insight on the possible extent of information that lies buried not just at Cowley and the ~30 prograded barriers around Australia, but at 300+ sites worldwide.

This paper presents the geological and morphological evolution of the prograded Cassino barrier during the middle and late Holocene. A special focus is given on the presentation and discussion of records of environmental changes that occurred during barrier progradation. The results demonstrated that variable rates of progradation were produced by environmental changes that affected the coastal sediment budget, such as changes in the wave climate. The total progradation of 18 km recorded for the Cassino barrier is probably the highest extension of progradation registered for a ridge plain associated with a coastal barrier. Sea-level changes during barrier progradation were accessed by the high difference between the degree of compaction of the foredune and backshore/foreshore deposits detected by the drilling system applied in this study and were confirmed by the limit of those deposits, which were also revealed by GPR records. During most of the time of barrier progradation, an overall sea-level fall of approximately 2 ± 1 m occurred. Six sets of relict foredune ridges were identified, and the limits between them were well marked by ridge truncations and the formation of transgressive dune sheets (TDS). Optically stimulated luminescence ages show that the TDS were formed under the driest climate conditions, with age periods very close to 3.8, 3.5, 1.9, 1.5, 0.22 and 0.09 ka ago, interspersed with ages of known wetter conditions in southern Brazil. The modern phases of TDS formation, with ages varying from 0.25 to 0.22 ka ago, were coincident with the time period of the younger pulse of the Little Ice Age (LIA), which was characterized by arid and cold conditions in southern South America. A comparison with prograded barriers located 350 to 600 km to the north suggests the existence of teleconnections, with phases of TDS and parabolic dunes that formed with a time interval of approximately 405 to 583 years.

Prograded barriers are depositional coastal landforms which preserve past shoreline locations and have been studied in order to understand the fundamental drivers of barrier formation. This paper reconstructs the Holocene history of the Seven Mile Beach, prograded barrier in Tasmania, Australia using optically stimulated luminescence (OSL) dating, ground penetrating radar (GPR), light detection and ranging (LiDAR) elevation models and sedimentological analyses. Shoreline progradation of the barrier commenced around 7300 years ago and continued to near present despite a ~ 3000 pause in deposition between 6700 and 3600 years ago indicative of substantial changes in sediment availability. GPR imaged subsurface structures contain a record of seaward dipping reflectors preserved as sediment supplied beaches and dunes leading to shoreline progradation. In the past 500 years a large transgressive dune has formed, built from reworked barrier sands, and now dominates the eastern portion of the barrier implying that shoreline progradation has ceased. This study reaffirms the notion that relict foredune ridges are strongly aligned with modal wave refraction patterns in planform and emphasises the importance of sediment delivery as a key driver of shoreline progradation through beachface and dune accretion. The substantial pause in shoreline progradation on this barrier system, as observed on others around the world, requires further explanation. Although changes in sediment delivery have been inferred, it may also be appropriate to reopen the debate on Holocene sea-level change in Tasmania.

This paper investigates the interplay between allocyclic controls and antecedent topography in the evolution of submerged coastal landforms, including a back-stepped delta. Using high-resolution tools, we examine the wave-dominated Thukela shelf, and define the major seismic units. Key features identified comprise incised valleys scoured into bedrock, that have overspilled to form lagoons at depths of 50 m. These are in turn overlain by two prograding and backstepped sandy delta systems at 40 m and 32 m depth respectively. The deltas interfinger with muddy prodelta deposits and are truncated by the Holocene ravinement, overlain by the contemporary prodelta of the Thukela River system. A bedrock high separates two physically separate strato-morphological zones; landward a sediment stripped, steep and shallow nearshore zone, and seaward a gentle zone downdip where the deltaic accumulations are sited. Delta development was favoured during sea-level stillstands at −40 m and −32 m respectively. The step-back of the deltas corresponds to sharp increases in the rate of sea-level rise associated with meltwater pulses. The overall gentle palaeo-bathymetric gradient has moderated erosion associated with rising sea level, preserving a sandy back-stepping delta and a draping mud clinoform. Submerged delta positioning relates to underlying incised valleys, suggesting a synchronous transgressive evolution of the drainage and the delta. Incised valley network positioning is further governed by Late Pliocene aged growth-faults in the basement rocks. The geological framework has acted as a recurring primary control to the geomorphic evolution of the area, partitioning accommodation for sediment accumulation and moderating the efficiency of ravinement.

Pockmark fields occur throughout northern North American temperate estuaries despite the absence of extensive thermogenic hydrocarbon deposits typically associated with pockmarks. In such settings, the origins of the gas and triggering mechanism(s) responsible for pockmark formation are not obvious. Nor is it known why pockmarks proliferate in this region but do not occur south of the glacial terminus in eastern North America. This paper tests two hypotheses addressing these knowledge gaps: 1) the region's unique sea-level history provided a terrestrial deposit that sourced the gas responsible for pockmark formation; and 2) the region's physiography controls pockmarks distribution. This study integrates over 2500 km of high-resolution swath bathymetry, Chirp seismic reflection profiles and vibracore data acquired in three estuarine pockmark fields in the Gulf of Maine and Bay of Fundy. Vibracores sampled a hydric paleosol lacking the organic-rich upper horizons, indicating that an organic-rich terrestrial deposit was eroded prior to pockmark formation. This observation suggests that the gas, which is presumably responsible for the formation of the pockmarks, originated in Holocene estuarine sediments (loss on ignition 3.5–10%), not terrestrial deposits that were subsequently drowned and buried by mud. The 7470 pockmarks identified in this study are non-randomly clustered. Pockmark size and distribution relate to Holocene sediment thickness (r2 = 0.60), basin morphology and glacial deposits. The irregular underlying topography that dictates Holocene sediment thickness may ultimately play a more important role in temperate estuarine pockmark distribution than drowned terrestrial deposits. These results give insight into the conditions necessary for pockmark formation in nearshore coastal environments.

17 pages, 11 figures, 1 table, Contourite depositional systems have been the focus of much recent research, but still relatively little is known about contourite erosive features and their associated processes. Based on multibeam bathymetry, side-scan imagery and different resolution seismic records, a detailed description and classification of the major erosive submarine valley features of the Contourite Depositional System of the Gulf of Cadiz middle slope is presented for the first time. Four types of erosive features have been differentiated, including contourite moats, contourite channels, marginal valleys and large isolated furrows, and interpreted in terms of their tectonic and oceanographic implications during the Quaternary. The study of the distribution and characteristics of erosive features is essential to better understand the present and past interaction of the Mediterranean Outflow Water (MOW) with the middle slope seafloor, and allows us to propose a new and more precise scheme for the MOW circulation patterns. This scheme includes a main along-slope circulation responsible for the excavation of the contourite moat and channels, and a secondary down-slope circulation responsible for the erosion of marginal valleys and isolated furrows. Three evolutionary stages have been observed in the development of the erosive system during the Quaternary, that can be related to changes in the distribution and splitting of the MOW as a consequence of the segmentation of the NE–SW diapiric ridges by neotectonic effects: 1) Early Pleistocene to Mid-Pleistocene: linear diapiric ridges; 2) Mid-Pleistocene to Late Pleistocene: diapiric reactivation and 3) Late Pleistocene to Holocene: main recent phase of diapiric ridges segmentation and rotation. This study provides important regional clues for establishing the evolution of the erosive features in relation with neotectonic effects, and represents a good example of the potential of erosive features as evidences for the reconstruction of the paleoceanography and recent tectonic changes, This work was supported by the projects FADO (PB94-1090-C03-03), TASYO (MAR-98-0209), GADES (REN2002-04117-C03-01/02/03) and CONTOURIBER (CTM 2008-06399-C04-01/MAR). In addition, our results are related to the Special Actions: REN2002-11669-E (MVSEIS Project) and REN2002-11668 (MOUNDFOURCE Project). The contribution by M. García to this paper was supported by a FSE fellowship from the Instituto Español de Oceanográfia (IEO) and a FPI fellowship from the Spanish Education Ministry in the Framework of the MARSIBAL Project (REN2001-3868-C03-03). This work has been partially carried out during a research stage of F. J. Hernández–Molina funded by the ‘Mobility Award' from the Spanish Ministry of Education and Science at NOCS (UK) (PR2006-0275) and Marine & Geophysical Division of the Argentine Hydrographic Institute (PR2007-0138)

Several fields of seafloor undulations from pro-deltaic wedges in the northern margin of Alboran Sea, Western Mediterranean Basin, are described in this paper. A series of elongated, subparallel bathymetric undulations are distinguished in the foreset-to-bottomsets regions of the Holocene pro-deltaic wedges related with the Guadalfeo and Verde–Seco rivers. Multibeam data, surficial sediment samples and high-resolution seismic profiles have been used in this study, and integrated in a Geographical Information System. Quantitative measurement of key morphometric parameters (wave-length, height, asymmetry, length and wave-form index) was performed on multibeam data and seismic profiles using the ArcGis software. Wave-form index and depth data were analysed statistically, and a cluster analysis was carried out in each area. According to these results, we infer that sea-floor undulations in the study areas are best explained by the influence of strong sediment flows normal to bathymetric contours, probably coupled with the effect of subsequent slow sediment deformation processes such as sediment creeps. The influence of bottom-current activity is considered less likely, as the position of river mouths and the very high slope gradients seems to be the key factors which control the development of these sea-floor undulations. The Alboran Sea sea-floor undulations are compared with those of other fields in shallow-water environments and the different processes of formation evaluated, Lobo received financial support to participate in the present research through the “Ramón y Cajal Program”, 2004 call. This study is a contribution to IGCP project 464: Continental Shelves during the Last Glacial Cycle

Paleosalinity estimates and rates of sedimentation inferred from core samples from the Hudson estuary for the interval between 6.4 and 1.3 ka indicate a possible role for the estuarine turbidity maximum (ETM) in influencing patterns of estuarine sedimentation at centennial to millennial time scales. Currently in the estuary, sedimentation is localized via sediment trapping particularly in the vicinity of the ETM, 13–26 km upstream from Battery Park (FBP) at the southern tip of Manhattan, in water depths greater than 4 m, and on the western side of the estuary. Data presented in this paper are from cores located within the segment of the estuary 29–50 km FBP. Age constraints are provided by C-14 dating. Paleoenvironmental interpretations are based upon paleosalinity estimates, grain size variability, and sedimentary structures. Paleosalinity was inferred on the basis of foraminiferal biofacies analysis and a new method for estimating summertime paleosalinity using oxygen isotope measurements in bivalve shell material. The isotopic analysis of a narrow size fraction (1.0– 1.7 mm) representing summer growth of a single bivalve species (Gemma gemma) reduces the uncertainty related to annual changes in temperature. Data from f45 km FBP indicate a gradual decrease in summertime paleosalinity between 6.4 and 2.0 ka from 25–20x to 15–10x (the latter is similar to present-day values). These results are consistent with the conclusion of an earlier low-resolution study. Sedimentation rates are generally low and are similar to the rate of sea-level rise in the Hudson River. Lowest sedimentation rates are noted in short ( 2.3 to f1.3 ka). We hypothesize that the observed pattern in sediment accumulation relates to a location for the ETM some 20 km upstream of its present position at 3 ka. Downstream migration of the ETM since 3 ka is ascribed to shoaling of the estuary, effectively squeezing the marine saltwater wedge in the same direction, and off marginal flats into the channel. Such shoaling would have enhanced the role of waves in mixing marine and fresher surface water, and reduced the effect of the ETM in

Relative sea-level curves for the mid- to late-Holocene have been proposed for eight different sectors along the Brazilian coast. This paper aims to review the data used to construct the curves proposed for two sectors, the Paranaguaand Cananeia regions in southeast Brazil. More specifically, we analyze the palaeo-sea-level indicators (vermetid tubes, shells, wood fragments and shell-midden deposits) related to (1) the sea-level maximum of the mid-Holocene and (2) the two secondary oscillations that would have occurred between 4100-3800 years B.P. and 3000-2700 years B.P. The sedimentary deposits of the coastal plain as well as vermetid datings suggest a mid-Holocene sea-level maximum between + 3.5 and + 4 m. The great majority of the indicators used to infer the secondary oscillations in previous studies were derived from shell middens. Besides being unreliable palaeo-sea-level indicators, these data also showed inconsistencies that undermine the existence of such oscillations. The plot of all the data derived from vermetid samples found along the Brazilian coast also indicate a rather smoother sea-level fall in the last 5100 years.

This paper defines the spatial trend in sea level around Australia at 3 timescales, namely at the time of the maximum of the last interglacial around 125,000 yr B.P., during the Holocene maximum between 5000 and 6000 yr B.P. and over the last 20 years. Last interglacial elevations range from −2 m around the Great Barrier Reef to +32 m in northeast Tasmania. Trend surface analysis shows that over 77% of the noise in these sea-level elevations can be accounted for by a pattern evidencing tectonic uplift towards the southern edge of the continent. Assuming a eustatic sea level at this time of +4 to 6 m, most of the east coast of New South Wales and the west coast of Western Australia can be considered tectonically stable, while the southern edge of the continent has risen by at least 5 m and the north-northeast corner has downwarped by at least 2 m. The spatial pattern of the Holocene maximum tentatively supports the continuation of this tectonic deformation. Sea level at this time reached 1.6 and 2.4 m above present high tide limits around the northern and southeastern coastlines of Australia respectively. This Holocene pattern is weak because much of the data is dominated by local variations reflecting differential loading of the continental shelf by water during the Holocene transgression. The Holocene trend surface does not support geophysical modelling implying a southern latitudinal downwarping of the crust produced by the melting of the Antarctic ice sheet and the loading of the ocean crust with meltwater. However, the spatial pattern of modern trends appears to contain a remnant Holocene signal fitting this isostatic model rather than the long term pattern of tectonic flexure since the last interglacial. Sea level is presently rising at a rate of 1.75 mm yr−1 in northern Australia compared to only 0.75 mm yr−1 in Tasmania. These results imply that isostatic factors, as well as previously identified climatic variables, may be controlling present-day variations in the rate of change of sea levels around the Australian continent.