Paleo-sea Level Research Articles

Sedimentological evidence of Late Pleistocene Shorelines in Oman

As the climate crisis intensifies, estimating sea-level rise will become increasingly relevant, in particular assessing changes in the relative sea level in different regions. One key to comprehending global sea-level changes is the study of past sea-level highstands. Many regional studies help refine the reconstruction of paleo sea levels globally. Thus far, the Middle East remains understudied.This paper presents evidence for Quaternary sea-level variations along the shores of the western Indian Ocean. Eight coastal outcrops along the northern and eastern coasts of Oman are presented in detail. The sedimentological evidence for sea-level highstands varies within the study area. However, in relation to recent sea-level conditions, all of these marine and beach deposits are now found well above the environments where such formations would typically form. Dating the timing of sea-level highstands remains a challenging task within the study area. In different studies, attempts to 14C date samples from that area were unsuccessful, as the time of sediment deposition lies beyond the dating limit of 14C, precluding a Holocene formation of these sediments. Thus, the sediments are regarded as deposits formed during Pleistocene sea-level highstands, presumably during MIS 5e. For some sections, optically stimulated luminescence dating could provide a solution, as igneous source rocks supply quartz and feldspar. This paper aims to localise eight sea-level related outcrops along the Omani coast and depict their potential for future work, which should include dating and elevation measurements. Through this, our work contributes to the ongoing effort to globally identify records of sea-level changes, as well as providing insights into the regional setting in Oman.

Sources and pathways of carbon and nitrogen of macrophytes and sediments using stable isotopes in Al-Kharrar Lagoon, eastern Red Sea coast, Saudi Arabia.

Elemental ratios (δ13C, δ15N and C/N) and carbon and nitrogen concentrations in macrophytes, sediments and sponges of the hypersaline Al-Kharrar Lagoon (KL), central eastern Red Sea coast, were measured to distinguish their sources, pathways and see how they have been influenced by biogeochemical processes and terrestrial inputs. The mangroves and halophytes showed the most depleted δ13C values of -27.07±0.2 ‰ and -28.34±0.4 ‰, respectively, indicating their preferential 12C uptake, similar to C3-photosynthetic plants, except for the halophytes Atriplex sp. and Suaeda vermiculata which showed δ13C of -14.31±0.6 ‰, similar to C4-plants. Macroalgae were divided into A and B groups based on their δ13C values. The δ13C of macroalgae A averaged -15.41±0.4 ‰, whereas macroalgae B and seagrasses showed values of -7.41±0.8 ‰ and -7.98 ‰, suggesting uptake of HCO3- as a source for CO2 during photosynthesis. The δ13C of sponges was -10.7±0.3 ‰, suggesting that macroalgae and seagrasses are their main favoured diets. Substrates of all these taxa showed δ13C of -15.52±0.8 ‰, suggesting the KL is at present a macroalgae-dominated lagoon. The δ15N in taxa/sediments averaged 1.68 ‰, suggesting that atmospheric N2-fixation is the main source of nitrogen in/around the lagoon. The heaviest δ15N (10.58 ‰) in halophytes growing in algal mats and sabkha is possibly due to denitrification and ammonia evaporation. The macrophytes in the KL showed high C %, N %, and C/N ratios, but this is not indicated in their substrates due possibly to a rapid turnover of dense, hypersaline waters carrying most of the detached organic materials out into the Red Sea. The δ13C allowed separation of subaerial from aquatic macrophytes, a proxy that could be used when interpreting paleo-sea level or paleoclimatic changes from the coastal marine sediments.

Understanding paleo-earthquakes in the Kuril Trench based on Late-Holocene tsunami deposits in the distal region from wave sources, northern Hidaka, Hokkaido, Japan.

Geological evidence, such as tsunami deposits, is crucial for studying the largest rupture zone of the Kuril Trench in Hokkaido, Japan, due to its poor historical record. Although 17th-century tsunami deposits are widely distributed across Hokkaido, the presence of multiple wave sources during that period, including the collapse of Mt. Komagatake, complicates the correlation with their wave sources. Understanding the regional distribution of these tsunami deposits can provide valuable data to estimate the magnitude of megathrust earthquakes in the Kuril Trench. The northern part of Hidaka, Hokkaido, where tsunamis from multiple wave sources are expected to overlap, is distant from the Kuril Trench. To clarify the depositional history of tsunami deposits in such distal areas, evaluating the influence of the depositional environments on the event layer preservation becomes even more critical. We conducted field surveys in Kabari, located in the northern Hidaka region, identifying three sand layers from the 10th to the 17th century and two layers dating beyond 2.3 thousand years ago. The depositional ages of most sand layers potentially correlate with tsunami deposits resulting from the Kuril Trench earthquakes. Utilizing reconstructed paleo-sea level data, we estimated that most sand layers reached approximately 2 m in height. However, it is noteworthy that the latest sand layer from the 17th century exhibited an unusual distribution, more than 3 m in height. This suggests a different wave source as the Mt. Komagatake collapse. The discovery of multiple sand layers and their distributions is crucial to constraining the maximum magnitude of giant earthquakes in the Kuril Trench and understanding the volcanic tsunami events related to Mt. Komagatake.

Coastal Evolution of Satingpra Peninsula, Songkhla Province: Implications for Understanding Songkla Lagoon Formation

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to wind-driven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it’s essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. HIGHLIGHTS OSL ages, based on average dose model at the Northern Satingpra Peninsula were 1.04 - 3.27 ka. The old sand ridges of the Satingpra Peninsula prograde northward after mid Holocene sea level highstand. Paleo sea level based on wind-wave sediments contact was 1.4 m lower than present day at 1.46 ka. GRAPHICAL ABSTRACT

Holocene southwest Greenland ice sheet behavior constrained by sea-level modeling

The melting of the Greenland ice sheet (GrIS) is a major contributor to past and future global sea-level rise. Understanding the response of the GrIS to times in the past when temperatures were as warm or warmer than today offers insights into its current and future response to climate change. In the southwest sector, the GrIS retreated inland beyond its current margin during the (at least regionally) warmer-than-present mid-Holocene, before it readvanced to the historical maximum position during the Little Ice Age. This was then followed by a slight retreat to its current position. To investigate the timing and magnitude of southwest GrIS retreat and readvance in response to Holocene warmth, we model the response of the solid Earth and local relative sea level (RSL) to past ice sheet change. We test a suite of eleven ice sheet scenarios that are based on ICE-6G_C but are modified in the timing and magnitude of ice retreat and readvance and pair them with four different viscoelastic Earth structures. We compare model predictions to observations of paleo sea level, present-day sea-level change, and present-day vertical land motion (VLM) around Nuuk, Greenland. We find that the modeled timing and magnitude of the Holocene retreat and readvance have a significant impact on modern sea-level change and VLM in Nuuk. Models that assume a readvance approaching the southwest GrIS’ historical maximum between 2 and 1 ka are most consistent with observations. The RSL response, however, is less sensitive to the timing of the minimum GrIS extent. Nonetheless, better data-model fits are generally obtained when the minimum ice sheet extent is reached between 5 and 3 ka, within the tested range of 6-3 ka. Comparing this timing to local and regional records of temperature and ice-sheet change suggest that the evolution of the southwestern GrIS presented here was in-phase with the likely evolution of southwestern GrIS mass balance through the Holocene. Our results have implications for future ice sheet modeling studies targeting southwestern Greenland by providing additional constraints and strengthening existing ones. Moreover, this work provides a deeper understanding of the interactions between the climate and the cryosphere and thus of future ice sheet change.

Paleo sea-level indicators and proxies from Greenland in the GAPSLIP database and comparison with modelled sea level from the PaleoMIST ice-sheet reconstruction

One of the most common ways to assess ice-sheet reconstructions of the past is to evaluate how they impact changes in sea level through glacial isostatic adjustment. PaleoMIST 1.0, a preliminary reconstruction of topography and ice sheets during the past 80 000 years, was created without a rigorous comparison with past sea-level indicators and proxies in Greenland. The basal shear stress values for the Greenland ice sheet were deduced from the present day ice-sheet configuration, which were used for the entire 80 000 years without modification. The margin chronology was based on previous reconstructions and interpolation between them. As a result, it was not known if the Greenland component was representative of its ice-sheet history. In this study, I compile sea–level proxy data into the Global Archive of Paleo Sea Level Indicators and Proxies (GAPSLIP) database and use them to evaluate the PaleoMIST 1.0 reconstruction. The Last Glacial Maximum (c.20 000 years before present) contribution to sea level in PaleoMIST 1.0 is about 3.5 m, intermediate of other reconstructions of the Greenland ice sheet. The results of the data-model comparison show that PaleoMIST requires a larger pre-Holocene ice volume than it currently has to match the sea-level highstands observed around Greenland, especially in southern Greenland. Some of this mismatch is likely because of the crude 2500 year time step used in the margin reconstruction and the limited Last Glacial Maximum extent. Much of the mismatch can also be mitigated if different Earth model structures, particularly a thinner lithosphere, are assumed. Additional ice in Greenland would contribute to increasing the 3–5 m mismatch between the modelled far-field sea level at the Last Glacial Maximum and proxies in PaleoMIST 1.0.

Holocene vertical velocity fields in the Calabrian Arc (southern Italy): New insights from uplifted sea-level markers in the Crotone Peninsula

The study of fossil coastlines is one of the most widely used methods to unravel the vertical movements of the Earth's solid surface. All along the coast of the Calabrian Subduction Arc, well preserved Pleistocene marine terrace sequences document a protracted uplift history. Although Pleistocene vertical movements have been extensively explored, the Holocene history is not well understood. Numerous uplifted coastlines of the Holocene period have been studied along the Tyrrhenian side of Calabria, but the Ionian coastal sector is considerably under-studied. Our new data from the coast of the Crotone Peninsula fill this crucial data-gap. AMS 14C dating of seventeen sea level markers, elevated above the current mean sea level, show ages between 2300 and 7000 Cal. Yr BP. The elevation of the markers was corrected for the paleo sea level using the most updated GIA models ICE-6G (VM5a) and ICE-7G (VM7). We found that a coastline dated to 7 ka shows uplift rates of 0.8 mm/yr, consistent with late Pleistocene uplift rates (≈0.8 mm/yr). In contrast, a 2.3 ka coastline was uplifted by only 1 m, resulting in lower uplift rates of ≈0.5 mm/yr. However, there are clues that the abandonment of this younger coastline may have occurred with a rapid uplift pulse. Reconstructing the past vertical movements of the Crotone Peninsula reveals an unsteady uplift history. At some times fast uplift rates are required, while for other periods, lasting as long as 3–4 kyr, the uplift rate is slower or zero. An uplift history consisting of periods of accelerated uplift, or even coseismic pulses, would also explain the difference in uplift rates between short term (<5 ka) and long term (>5 ka) markers through a metric we have defined as uplift rate sensitivity. Understanding the details of this uplift history has social relevance. The co-seismic uplift hypothesis requires further investigation but if confirmed would likely affect the seismic and tsunami hazard of the Crotone Peninsula. Similarly, the unsteady uplift rate would cause a risk given the current rapid rate of global sea level rise. Periods of sustained vertical stability would increase the risk of flooding even in areas characterized by long-term uplift and thus considered safe.

How can past sea level be evaluated from traces of anthropogenic layers in ancient saltpans?

Footprints of human activities identified in the sedimentary sequence of submerged historical saltpans can reveal the history of the site and can indicate the relative sea level during its operational period. Saltpans are man-made constructions used continuously for salt production in the Mediterranean at least for the last 2000 years. The east Adriatic coast contains many such submerged remains, preserved and well-dated by historical archives. Sedimentological, microfossil and geochemical analyses of the sediments from cores drilled in the saltwork area at Brbinj, Dugi Otok, Croatia, enable the reconstruction of various past environmental conditions. The current study aims to: a) identify the anthropogenic unit in the sedimentary sequence deposited over time, b) determine its age, and c) use it as past sea-level limiting points. Basal units made of terra rossa soil materials were identified in the sedimentary records. These layers are located -120 ±7 cm below mean sea level next to the separation wall and -125 ±7 cm and -135 ±7 cm, respectively, in the inner pools, most likely representing a man-made pavement. The terra rossa layer is overlaid by a unit rich in faunal remains dominated by euryhaline foraminifera and ostracod species such as Ammonia veneta and Cyprideis torosa, representing the saltworks unit. The flooding of the saltpans by the rising sea is manifested by the deposition of an upper sedimentary unit dominated by remains of marine species. The base and the top of the saltwork unit are dated by Optically Stimulated Luminescence to 1040±50 CE and to 1390±30 CE, respectively. The study presents a new approach for obtaining footprints of human activities in ancient, submerged saltpans, by identifying and dating the indicative anthropogenic layers and using these for the reconstruction of paleo sea-level. The described method can be applied all around the Mediterranean.

The Fish Tanks of the Mediterranean Sea

Roman fish tanks are found in various coastal regions of the Mediterranean, although the vast majority is found on the Tyrrhenian coast of Italy. In this work, a database was developed with information on 62 fish tanks along the Mediterranean coasts to document and compare their features and characteristics. The analysis of the developed database from the Mediterranean fish tanks has shown that, among the 62 fish tanks, ~56% were cut into the rock, indicating that this type of construction was the most popular at that time and probably had advantages over the others. Fish tanks as sea level indicators can provide accurate data on the sea level 2000 years ago. Well-preserved installations with prominent architectural features have a crucial role in determining the paleo sea level. The architectural elements that are mostly used in fish tanks for paleo sea level reconstructions are the crepido, cataractae and channels. Besides the scientific importance of the fish tanks as sea level markers, they also have great cultural and historical significance. Fish tanks can be promoted as heritage monuments and scholarly models to strengthen awareness about climate change, sea level rise and its consequences.

Robbins Island: The index site for regional Last Interglacial sea level, wave climate and the subtropical ridge around Bass Strait, Australia

A unique index-record of Last Interglacial (Marine Isotope Stage 5e MIS5e) relative sea level (RSL) and wave climate history in South-east Australia is presented from Robbins Island, in western Bass Strait. This is applied to interpret the wider MIS5e coastal evidence around Bass Strait. At Robbins Island, the combination of low wave and wind energy, a tide-modified regime and a sand supply resulted in the shoreline progradation throughout MIS5e. This preserved a time-series of paleo-sea level across a 7 km wide strandplain (Remarkable Banks). After a highstand, MIS5e RSL attained a stillstand of +5.75 ± 0.5 m above modern mean sea level during 126 to ∼119 ka BP. The MIS5e RSL interpretation is underpinned by modern analogues and hydrodynamic modelling of waves, tides and currents. A high resolution LiDAR Digital Elevation Model (DEM) supported by morpho-sedimentary studies, ground-penetration radar (GPR) surveys and a geochronology based upon Optically Stimulated Luminescence (OSL) methods were used to define the proxy RSL record. The observed RSL history was compared to modelled RSL history that accounted for the theoretical fall in RSL (regression) throughout MIS5e, due to the Glacio-Isostatic Adjustment (GIA) forcing.

Development of Pag-asa Reefs, West Philippine Sea: Role of Relative Sea Level Change and Wave Exposure

Atoll reefs are associated with subsiding regions. In the West Philippine Sea, the Kalayaan Island Group is an emergent feature of the region’s atoll reefs. In this study, we established the long-term rate of subsidence in the Pag-asa Atoll Reefs by indicators of sea level positions on the seafloor and in Pag-asa Island. For submerged indicators of paleo-sea levels, a multibeam bathymetry with a 5-m resolution was used as the primary data source. Four pairs of submerged terraces and scarps, interpreted as former coral reef flats and reef fronts, respectively, were mapped. The terraces, PARa-d, from shallowest to deepest, occur at depth ranges of 7–10, 36–45, 82–90, and 115–120 m. The step-like morphology of the slopes off Pag-asa is likely due to the backstepping of reefs during the overall rise of sea level from the Last Glacial Maximum (LGM). Terraces PARa-d are interpreted as records of reef re-establishments during the stillstand periods following meltwater pulse event (MWP)-1C, MWP-1B, MWP-1A, and MWP-2B/2A. There is no clear morphological indicator of coral terraces that can be attributed to the LGM period. Variation in the widths and depths of the terraces between the leeward and windward sides of the island is also observed. Greater wave exposure appears favorable for coral reef terrace growth in Pag-asa, except for deeper terraces. The possible absence of the deepest terrace on the north side and an LGM terrace is attributed to possible thinner coral reef accretion due to the combination of cooler waters and possible swifter winds prior to 14 kyr. Correlation of the terrace depths and beach rock elevations as Pag-asa with the paleo-sea level of correlative stillstand events indicate long-term subsidence of 1.2 mm/yr between 15–12 kyr that declined to 0.3 mm/yr between 12 kyr to present. With sea level rise due to global warming and continuing subsidence, Pag-asa Island is threatened by coastal erosion, more frequent inundation, and groundwater salinization that needs to be addressed through proper adaptation practices.

Insight into contrasting patterns of sedimentation from shelf edge to base-of-slope on the Mozambique-Zambezi margin (17°30′S-20°S) during the last 40 ka

The pattern of sediment dispersal and the location of sediment depocentres on continental margins can be very complex in both space and time. We aim at investigating how significantly external and internal factors, such as river runoff, bottom current and sliding can deviate the sediment dispersal from a simplistic fully sea-level controlled spreading. In this study we examined the sedimentation at two transects across the Mozambique-Zambezi slope between 17°20S-20°S, where multibeam bathymetry, sub-bottom profiler data and sediment cores were acquired. The period investigated spans the last 40 cal ka BP with a focus on the contrast between the last glacial (lowstand) and the Holocene (highstand) periods. Results show contrasting patterns of sediment dispersal, deposition and preservation. Sea level fluctuation remains the main forcing and most of the sediment from the Zambezi River settled on the inner shelf since the last sea level rise. However, we found that two major depocentres have developed on the upper slope during the Holocene consequent to the interaction of bottom currents with seabed morphologies at the shelf edge and at the upper slope. Early Holocene sliding in the north-east and in the south-west upper slope is a secondary but yet major factor of sediment transfer to the deep domain. Identified preconditioning factors for sliding on the slope are related to lowstand sediment loading and fluid circulation on the upper slope, and erosion at the base of slope of a plastered drift. Triggering must be related to margin wide mechanisms such as changes in hydrostatic pressure and reorganisation of sediment dispersal, subsequent to the post-glacial sea level rise, or maybe a period of regional seismicity. Climatic conditions in the Zambezi River watershed during the Bolling-Allerod and Younger Dryas periods are recorded and imprinted on the upper slope in the form of a detrital rich layer and a prominent slope-wide high-amplitude reflector. All over the continental slope, plastering of sediment deposits by bottom currents is pervasive and shows a morphological continuum from erosional scours at the base of slope to sediment waves on the upper slope and a possible interaction between along and across slope transport processes. We conclude that, in addition to sea level, the interplay of external and internal factors such as oceanic circulation and sliding, together with margin morphology, lead to the development of unexpected depocentres on the continental slopes. Thus, the study of modern marine analogues is crucial to avoid misleading interpretation of fossil deposits in terms of paleo sea level and more generally of paleo-environmental conditions.

Sediment Transport Modeling Based on Geological Data for Holocene Coastal Evolution: Wave Source Estimation of Sandy Layers on the Coast of Hidaka, Hokkaido, Japan

AbstractSediment transport modeling (STM) is a potentially effective tool for estimating the magnitude of tsunamis and earthquakes without historical records. However, the application of STM to prehistorical tsunamis is challenging because of multiple uncertainties in topography and roughness. Along the coast of Hidaka, Hokkaido, Japan, there is potential to conduct STM even in the absence of historical records because comprehensive geological data for the coastal evolution during the Holocene are available here. The tsunami deposits in Hokkaido indicate the presence of events on a larger scale than historical tsunamis; in particular, the seventeenth‐century tsunami had multiple potential wave sources other than a Kuril Trench earthquake, inhibiting its magnitude estimation. In this study, we applied STM to paleotsunamis for the coast of Hidaka, where comprehensive geological data are available, although the wave source is unknown. The modeling parameters—paleotopography, roughness, grain size, initial sand source, sea level, and beach ridge height—were estimated using data obtained from geological surveys and sensitivity tests. The modeling of a tsunami induced by a Kuril Trench earthquake reproduced the sediment distributions and sedimentary structures of the observed sand layers better than that of extreme storms and volcanic tsunamis. Because the conventional fault model is reasonably suitable in the western area from the Kuril Trench, a much wider rupture zone is less likely. Parameters such as sand source area, roughness, ridge height, and paleo sea level are important for geologists and modelers when applying STM to paleotsunamis.

Mid- to Late Holocene sealevel changes at Abrolhos Archipelago and Bank, southwestern Atlantic, Brazil

This study presents spatiotemporal paleo-sea-level reconstructions from Abrolhos archipelago and Abrolhos Bank, and fill in a coastline gap of 500 km where no precise paleo-sea level reconstruction exists. The reconstructions are based on sedimentary, biological and geomorphological evidences. The data indicates sea-levels up to 2.9 m higher than the current one between the Mid- to Late Holocene, in agreement with the empirical sea-level envelope and with predictions of geophysical sea-level models for the Brazilian coast. The data suggests that there was little, if any, hydroisostatic compensation across 55 km of the continental shelf in the study area, between the archipelago and the mainland coast, given that similar elevations of the post-glacial sea-level maximum exist in both places.

Late-Holocene sea levels from vermetids and barnacles at Ponta do Papagaio, 27° 50′S latitude and a comparison with other sectors of southern Brazil

The height difference between paleo-vermetids and present homologous bioconstructions remains as the best Mid- to Late-Holocene paleo-sea level indicator on the Brazilian coast. The vertical range of the vermetid bioconstructions and, consequently, their precision as a sea-level indicator, varies from ±0.1 to ±1.0 m according to local conditions such as wave energy exposure and tidal range. However, live vermetid bioconstructions are scarce or do not occur at several places south of 23°S latitude, which has led to the use of other bioconstructions (e.g. Phragmatopoma caudata) as a homologous reference level, adding uncertainties to the paleo-sea level reconstructions. At the Southeast Brazilian coast, from 25° 30′ S to 28° 37′ S latitude, the precision varies from ±0.5 to ±1.0 m. At the Ponta do Papagaio headland, at 27°50′38″- 44″ S latitude, the occurrence of the subfossil barnacle Tetraclita stalactifera included in the remains of Holocene vermetids (Petaloconchus varians (d'Orbigny, 1839)) bioconstructions allowed the authors to adopt the living fringe of this barnacle species as a homologous reference level and thereby improve the accuracy of paleo-sea level reconstructions (error margin of only ± 0.5 to ± 0.3 m). The paleo-sea level obtained at Ponta do Papagaio by this method varied between +2.4 and 0.8 m. The resultant relative sea-level curve is included in the empiric sea-level envelop previously determined for the Brazilian coast, south of 28°S latitude, and matches with the far-field eustatic sea-level models. It is also similar to other curves defined for Southern Brazil regions such as Laguna-Imbituba (Santa Marta Cape surroundings, 85-40 km to South from Ponta do Papagaio), São Francisco do Sul (180 km North) and Paraná (220–260 km North). However, the height of 2.4 ± 0.3 m at 4 ky BP at Ponta do Papagaio is similar to the two cited regions to the North, but higher than the one at Laguna-Imbituba for the same period. This difference may not be significant, as it is within the ±1.0 m error margin adopted in the inference of the paleo-sea level at Laguna-Imbituba. If it is significant, it can be attributed to a local lowering of relative sea-level by thermosteric and dynamic effects of the Santa Marta Cape coastal upwelling strengthening at the epoch of maximum sea-level. This work also suggests further quantification of the living vertical distribution of vermetids and other species used as reference species (e.g. Tetraclita stalactifera, Phragmatopoma caudata), under different bedrock morphology, wave exposure and oceanographic conditions, as a necessary way to improve the precision of paleo-sea level reconstructions.

Reply to comment by Harald Böhnel and Alejandro Rodríguez-Trejo on García et al. (2021) ‘Semicontinuous paleomagnetic record of the last 1 Ma from radiometrically dated igneous rocks (Trans-Mexican Volcanic Belt and surrounding areas)’

This work presents a few comments on the paper “Relative sea-level curve during the Holocene in Rio de Janeiro, Southeastern Brazil: A review of the indicators - RSL, altimetric and geochronological data”. Surprisingly the authors omitted in this review a former discussion on the interpretation of paleo-sea level indicator and paleo-sea level reconstructions on the Rio de Janeiro coast that questions their results. Therefore, at this present work we resume the previous discussion. We conclude that although at the commented paper the altitudes of the paleo-sea level indicators were determined precisely, they did not consider the vertical distance between a given a paleo-sea level indicator and its current homologous one, and thus do not indicate paleo-sea levels.

Comments on Castro et al. (2021) “Relative sea-level curve during the Holocene in Rio de Janeiro, Southeastern Brazil: A review of the indicators - RSL, altimetric and geochronological data”

This work presents a few comments on the paper “Relative sea-level curve during the Holocene in Rio de Janeiro, Southeastern Brazil: A review of the indicators - RSL, altimetric and geochronological data”. Surprisingly the authors omitted in this review a former discussion on the interpretation of paleo-sea level indicator and paleo-sea level reconstructions on the Rio de Janeiro coast that questions their results. Therefore, at this present work we resume the previous discussion. We conclude that although at the commented paper the altitudes of the paleo-sea level indicators were determined precisely, they did not consider the vertical distance between a given a paleo-sea level indicator and its current homologous one, and thus do not indicate paleo-sea levels.

Paleo-sea levels, Late-Holocene evolution, and a new interpretation of the boulders at the Rocas Atoll, southwestern Equatorial Atlantic

Rocas Atoll is a remote place and the only atoll in the southwestern Atlantic Ocean. This study presents new paleo-sea level reconstructions and a new interpretation on former ones. The new data indicate that sea level was higher at the Late-Holocene than it is at present and that the hydrodynamic factors overlap with sea-level changes, precluding more precise paleo-sea level reconstructions. According to previous works, the Rocas Atoll presents one of the most conspicuous paleo-sea level indicators, represented by reef remains. But, in this paper, these supposedly reef remains are reinterpreted as algal-reef boulders detached from the atoll reef-front by high-wave energy events and deposited over the reef rim, where they remain detached or are cemented and, sometimes, mushroom shaped. It is considered that the bigger boulders may have been deposited in their current position by the cumulative effects of past energetic wave events. Furthermore, the use of beachrocks as paleo-sea level indicators in former studies is discussed, leading to the conclusion that they actually indicate beach progradation and lateral accretion resulting from a positive sand budget. Finally, a schematic morphological evolution of the atoll during the Late-Holocene is proposed. At the atoll, leveling with RTK and imagery with laser scanner were collected, and eleven radiocarbon ages were measured by accelerator mass spectrometry (AMS).

The influence of rock uplift rate on the formation and preservation of individual marine terraces during multiple sea-level stands

AbstractMarine terraces are a cornerstone for the study of paleo sea level and crustal deformation. Commonly, individual erosive marine terraces are attributed to unique sea-level high stands based on the reasoning that marine platforms could only be significantly widened at the beginning of an interglacial. However, this logic implies that wave erosion is insignificant at other times. We postulate that the erosion potential at a given bedrock elevation datum is proportional to the total duration of sea-level occupation at that datum. The total duration of sea-level occupation depends strongly on rock uplift rate. Certain rock uplift rates may promote the generation and preservation of particular terraces while others prevent them. For example, at rock uplift of ~1.2 mm/yr, the Marine Isotope Stage (MIS) 5e (ca. 120 ka) high stand reoccupies the elevation of the MIS 6d–e mid-stand, favoring creation of a wider terrace than at higher or lower rock uplift rates. Thus, misidentification of terraces can occur if each terrace in a sequence is assumed to form uniquely at successive interglacial high stands and to reflect their relative elevations. Developing a graphical proxy for the entire erosion potential of sea-level history allows us to address creation and preservation biases at different rock uplift rates.

Age attribution to a karst system using river long profile analysis (Hyblean Plateau, Sicily, Italy)

In steady-state tectonic-climate systems, the fluvio-karst processes attain a stable base level, whether it be local or global. In contrast, in an uplifting region, relative base-level changes force river incision processes and a concurrent lowering of the karst water-table. Even at local scales (e.g., single fault-controlled valley), combined tectonically- and climatically-driven base-level drops induce geomorphic and hydrogeological disequilibrium. Thus, the karst system develops vertically and the water-table lowers trying to attain the new local base level. Conversely, the paleo-karst network dries, and becomes abandoned as a hanging relic with aligned karst morphologies. They are exhumed by the entrenchment of the fluvial network, as base-level fall related knickpoints migrate upstream. We propose a geomorphic approach to build fluvio-karst age models, based upon the analysis of river long-profiles. This approach is complementary to altimetric correlation between karst horizons and coastal paleo-sea level markers. Our approach is useful for an inland study area that is far from the marine terraced coast or where active faulting cuts off the coastal area from the inland landscape. We tested the approach in the eastern sector of the Hyblean Plateau (Sicily, Italy), where a carbonate sequence experienced Middle-Late Pleistocene tectonic uplift combined with active faulting. Specifically, we investigated the Cassibile River basin, at the footwall of the active Cassibile-Noto Fault. By reconstructing river paleo-long profiles we fixed time-space reference lines, connecting the abandoned and hanging fluvio-karst levels to the correlative marine strandlines carved along the fault-controlled coastal landscape.