Rapid Sea Level Research Articles

Looking Back—Australia’s Sustainable Development and Climate Change Policy Agendas

In November 2022, a climate change performance index report released at the COP27 United Nations conference in Egypt, ranked Australia 55th on a list of 63 countries and country groupings in addressing the climate crisis. Australia is a leading development partner in the Pacific region; a region economically, environmentally, socially, and culturally impacted by climate change and global warming in the form of (e.g.,) rapid sea level rises, alarming shifts in marine ecosystems, and extreme weather events. How did Australia, a high-income country situated in the Pacific, become a nation that trails other developed countries in addressing climate change? Why has there been a lack of urgency for uptake of sustainable development policy and planning? A new Federal Government, elected in May 2022, has indicated willingness to meaningfully progress Australia’s interconnected climate change, wellbeing, and sustainability policy agendas, in which futures public health policy is inextricably linked. This change in government provides an important moment to review Australia’s sustainable-development climate change policy landscape over a 35-year period. By examining this landscape through a health lens, this paper can provide one of many critical perspectives tracing Australia’s slippage to the bottom of the global climate rankings today.

Microfacies types and distribution of epicontinental shale: A case study of the Wufeng–Longmaxi shale in southern Sichuan Basin, China

For black shales, laminae and bedding are hard to identify, grain size is difficult to measure, and trace fossils do not exist. Taking the Ordovician Wufeng – Silurian Longmaxi shale in southern Sichuan Basin, China, as an example, the types, characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections, argon-ion polishing field emission-scanning electron microscopy (FE-SEM), and kerogen microscopy. The epicontinental sea develops delta, tidal flat and shelf facies, with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies, the calcareous and clayey flats under intertidal flat facies, the calcareous and clayey shelfs under shallow shelf facies, the deep slope, deep plain and deep depression under deep shelf facies, and the overflow under gravity flow facies. Basinward, silty lamina decreases and clayey lamina increases, the grain size changes from coarse silt to fine mud, the silica content increases from about 20% to above 55%, the carbonate and clay minerals content decreases from above 40% to around 10%, and the kerogen type changes from type II2 to type II1 and type I. Provenance and topography dominate the types and distribution of shale microfacies. The underwater distributary channel, interdistributary bay, clayey flat, clayey shelf, and overflow microfacies are developed in areas with sufficient sediment supply. The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply. The deep shelf shale area is divided into deep slope, deep plain, and deep depression microfacies as a result of three breaks. The formation of epicontinental shale with different microfacies is closely related to the tectonic setting, paleoclimate, and sea level rise. The relatively active tectonic setting increases the supply of terrigenous clasts, forming muddy water fine-grained sediment. The warm and humid paleoclimate is conducive to the enrichment of organic matter. The rapid sea level rise is helpful to the widespread black shale.

Late Pleistocene to Holocene sedimentary history in the Pearl River Delta revealed by OSL and radiocarbon dating

A reliable chronology is essential to understand deltaic sedimentation processes in response to sea-level fluctuations and climatic changes. In the Pearl River Delta (PRD), high-resolution chronostratigraphy is still limited which hinders the detailed interpretation of sedimentary history. In this study, optically stimulated luminescence (OSL) dating and radiocarbon (14C) dating were applied to establish a chronological framework of core P5-4 (30 m depth) in the southern PRD. Fifteen OSL and four 14C samples produced ages ranging from c. 8 ka to 0.5 ka, and two older OSL samples produced minimum ages of 75 and 62 ka. 14C ages are generally older (up to c. 1 ka) than the corresponding OSL ages and the discrepancy increases with depth. The ages and sedimentary data of sixteen published cores have been compiled to correlate the regional stratigraphy and reconstruct the late Pleistocene to Holocene deltaic process. It is concluded that: (1) The bottom subaerially-exposed deposits of core P5-4 were dated to marine isotope stage (MIS) 5, which is consistent with similar OSL-based records in the PRD. The laterally correlation shows that a depositional hiatus during c. 70–8 ka prevailed in the PRD and may attribute to strong erosion due to weathering and fluvial scouring. (2) Due to the relatively high altitude of bedrock, the post-glacial marine deposition of the PRD started at c. 8 ka, postdating other megadeltas by at least 2–4 ka. During 8–0.5 ka, a three-stage sedimentary process that is common in the PRD occurred in P5-4, i.e., early-Holocene (8–6 ka) rapid accumulation rate (5.44 m/ka) associated with rapid sea level rise, followed by mid-Holocene (6–3 ka) decelerated sedimentation rate (1.17 m/ka) in response to reduced sediment supply and strong tidal forces and late-Holocene (3–0.5 ka) accelerated sedimentation rate (2.28 m/ka) due to enhanced human activity.

Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers based on lignin phenols and long-chain n-alkanes

Abstract. Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the Last Glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs and which changes in vegetation on land are associated with such warming. The Amur and Yukon rivers discharging into the Okhotsk and Bering seas, respectively, drain catchments that have been, or remain until today, covered by permafrost. Here we study two marine sediment cores recovered off the mouths of these rivers. We use lignin phenols as biomarkers, which are excellently suited for the reconstruction of terrestrial higher plant vegetation, and compare them with previously published lipid biomarker data. We find that in the Yukon basin, vegetation change and wetland expansion began already in the early deglaciation (ED; 14.6–19 ka). This timing is different from observed changes in the Okhotsk Sea reflecting input from the Amur basin, where wetland expansion and vegetation change occurred later in the Pre-Boreal (PB). In the two basins, angiosperm contribution and wetland extent all reached maxima during the PB, both decreasing and stabilizing after the PB. The permafrost of the Amur basin began to become remobilized in the PB. Retreat of sea ice coupled with increased sea surface temperatures in the Bering Sea during the ED might have promoted early permafrost mobilization. In modern Arctic river systems, lignin and n-alkanes are transported from land to the ocean via different pathways, i.e., surface runoff vs. erosion of deeper deposits, respectively. However, accumulation rates of lignin phenols and lipids are similar in our records, suggesting that under conditions of rapid sea level rise and shelf flooding, both types of terrestrial biomarkers are delivered by the same transport pathway. This finding suggests that the fate of terrigenous organic matter in the Arctic differs on both temporal and spatial scales.

Shelf inhabiting foraminifera as a tool for understanding late quaternary mass transport processes in the Northern Gulf of Eilat/Aqaba, Red Sea

Sedimentary systems on continental margins are sensitive to climate change and sea level fluctuations, especially in tectonically active areas as the Gulf of Eilat/Aqaba (GEA). During the Late Quaternary, in addition to the repetitive seismic activity along the Dead Sea Transform, drastic changes in sea level, temperature and salinity occurred in the marine environment resulting in changes of the faunal community. In this study, a newly established approach, using the depth distribution of foraminifera to identify displaced sediment units, is utilized to reconstruct the events, which occurred in this rapidly changing environment. A total of 11 units of displaced sediments and 3 temporally significant unconformities were identified based on foraminiferal assemblages and time constrained by radiocarbon dating. These were identified within two cores from the GEA northwestern slope at water depth of 300–400 m, covering up to 40 kyr BP. Two foraminiferal assemblages were identified corresponding with the changing salinity: 1) the ‘Holocene assemblage’ dominated by the stenohaline symbiont-bearing larger species Operculina ammonoides, Amphistegina papillosa and Amphistegina bicirculata; and 2) the ‘Glacial assemblage’ dominated by the hypersaline tolerant species Elphidium cf. limbatum, Elphidium jenseni and Peneroplis planatus. Both assemblages were found in deeper settings than their natural living habitat, indicating the presence of sediment transport down slope, and suggesting benthic foraminifera can serve as an indicator for sediment transport events. Unconformities were found to be associated with periods of rapid sea level changes and/or increased sedimentation rates, effecting sediment porosity and slope stability. Displaced shells of the ‘Holocene assemblage’ were dated to 12 kyr BP and believed to be the first recorded evidence for the post glacial re-settlement of this ecologically important group in the northern GEA.

Mangrove sediment erosion in the Sunda Shelf during meltwater pulses: Insights from biomarker records

Mangroves have received increasing attention in recent years for their high carbon storage capacity. The effects of sea-level change during the last glacial period on terrestrial deposition and coastal mangrove ecosystems were investigated using various organic lipid proxies in marine sediment cores from the Sunda Shelf in the southern South China Sea (SCS). The gradual reduction in the content of long-chain n-alkanes and n-alkanols, BIT index, and increasing δ13Corg trend from the last glacial to the Holocene indicated that the depocenter moved landward from the studied location during the deglacial sea-level rise. Remarkable peaks in the mangrove proxy (Taraxerol/n-C28 alcohol ratio) occurred during meltwater pulse (MWP) events in the Sunda Shelf area, associated with the drowning and destruction of mangroves that could not withstand the rapid sea-level rise. The decomposition of carbon-rich mangrove deposits may have contributed to atmospheric CO2 concentration during two strong MWP events in Sunda Shelf. Our results suggest the vulnerability of mangrove systems upon rapid sea level change with positive feedback for global warming.

Detrital zircons of the Devonian-Permian sandstones in the Qiangtang terrane, Tibet: Implication for Qiangtang rifting from Gondwana and uplift history of the Central Uplift

• New zircon ages of Devonian-Triassic deposits reveal sedimentary provenance change. • The breakup of the Qiangtang terrane from Gondwana occurred at about 288 Ma. • Primitive uplift of the Central Uplift occurred during the late Permian. • Closure of the Paleo-Tethys Ocean resulted in the uplift of the Central Uplift. This article reports new zircon U-Pb ages of the Devonian-Permian sedimentary rocks exposed in the central Qiangtang to reveal the change of sedimentary provenances through time. The age spectra of the Devonian and Carboniferous strata in the Qiangtang terrane are generally similar. They are typically characterized by two primary age populations at 520–700 Ma and 900–1000 Ma, indicating a Gondwana affinity. The Qiangtang terrane was part of the Gondwana supercontinent during a long period from the Ordovician to early Permian. The breakup time of the Qiangtang terrane from Gondwana is at ∼288 Ma, which is characterized by a drastic provenance change. The sedimentary evolution, together with detrital zircon ages also provides important perspectives on the uplift process of the Central Uplift in the Qiangtang terrane. Our data reveal that a primitive uplift of the Central Uplift occurred at the Late Permian. Although a continuous uplift has developed during the Early-earlier Middle Triassic, the Central Uplift was still an underwater environment due to rapid sea level rise. The final closure of the Paleo-Tethys Ocean and its branch gave rise to the uplift of the Central Uplift at the late Middle-earlier Late Triassic.

Amplification of regional tides in response to sea level

The study investigates the temporal change in tides under the background of rapid sea level rise, for a highly vulnerable coastal region. It highlights the existence of non-astronomic tidal variability at seasonal and secular time-scales in the Ganga-Brahmaputra-Meghna (GBM) delta, along with increasing low and high tidal levels. The observed variability in semi-diurnal tides was found to be coherent to the mean sea level changes. M2 tide can be a proxy for sea level changes as they show a direct relationship. Steric changes were introduced in the barotropic ADCIRC (ADvanced CIRCulation) model and the results proved that change in water depth modulates the energetics of the tidal wave thereby causing amplification. A regionally varying tidal response was noticed, such that the regions associated with the GBM delta showed maximum amplification. The factors that can cause tidal amplification are region-dependent and coastal geomorphology plays an important role in it. Tidal prediction based on changing sea level was able to capture the observed seasonal modulation of tides and increasing trend in low and high tidal levels. Incorporating the effect of changing tides can improve the accuracy of tidal predictions and will help advance studies regarding regional sea level change, coastal flooding and tide-surge interaction.

Time series analysis of the Caspian Sea shoreline in response to sea level fluctuation using remotely sensed data

The Caspian Sea (CS), biggest inland water worldwide has experienced around 3 m oscillation in sea level during the 20th century. These rapid sea level fluctuations have had a great impact on the coastal habitat around this sea. Therefore, this study is aimed to investigate the long-term changes of the western part of the Caspian Sea shoreline and Anzali lagoon and their dynamic responses to the sea level fluctuation using time series analysis of remotely sensed data over the 40-years. To this end, the long-term Caspian Sea shoreline and the area and perimeter of the Anzali Lagoon were extracted from the time series of Landsat satellite imagery (1975 till 2016) by using an automatic procedure including the combination of the Tasseled-Cap and texture filter methods. Afterwards, shoreline erosion/accretion rates were evaluated by using the Net Shoreline Movement (NSM) and End Point Rate (EPR) techniques. Finally, the sea level changes of the CS, were extracted through the multiple altimetry satellite data and the relationship between the relative sea level fluctuation and CS shoreline and Anzali lagoon area were studied. Results of the changes of shoreline positions over the study period (1975–2016) indicate that the whole coastal study area is subjected to accretion and erosion of 20.37 and -19.22 (m/year) respectively. There is balance between the whole EPR in all transects and periods between 1975 and 2016. This shows that when erosion happens in a region, accretion will be happened in another region, and this behavior is symmetrical. When the sea level decreased, the EPR values showed the accretion/seaward and vice versa. So, the shoreline movement has a strong nonlinear response to the sea level fluctuation with a coefficient of determination of −0.66. Also results show the strong response of the Anzali lagoon to the sea level fluctuation with a coefficient of determination of 0.78 for a nonlinear relationship between the changes of area of Anzali Lagoon and the CS fluctuation. This lagoon experienced the greatest and lowest values of its area on 2003 and 1985, respectively, which are matched with the high and low stands of the Caspian Sea Level.

Constraining rapid sea level change through radiometric dating of corals growing over a range in paleowater depths

Corals do not all grow near the sea surface. Different species favour different ranges in depth and can survive at different depths from 0 to 5 m to over 0–100 m. Fossil corals, as markers of sea level, are the preferred choice in radiometric dating. Timing and magnitude of sea-level variations are determined from the location and age of a set of in-situ coral samples, and mark the lower bound in sea level. In addition, they have to be assigned an uncertainty to define the upper bound in sea level. This is referred to as the paleowater depth (PWD) and creates a major ambiguity in estimating the appropriate span of habitable depth in sea level. This uncertainty also has an impact on constraining the timing and magnitude of rapid changes in sea level. However, there are approaches that may minimize PWD uncertainties. These include assessing sea level data for groups of coral, during relatively stable sea levels, rather than individually. If samples were recovered in multiple drill-cores, along a sea-bed transect, tighter PWD constraints may apply for samples, in each core, depending on the magnitude of the slope of the sea bed. This method is particularly useful in cases of rapid sea level change over shallow continental shelves when the shift in the shoreline, with sea level change, is large. In these circumstances, the presence of a shallow-water reef established up or down-slope is indicative of a rapid change in sea level.

A 1.5 Ma Marine Record of Volcanic Activity and Associated Landslides Offshore Martinique (Lesser Antilles): Sites U1397 and U1399 of IODP 340 Expedition

The products of eruptive and mass-wasting processes that built island arc volcanoes are better preserved in marine deposits than on land. Holes U1397A and U1399A drilled during IODP Expedition 340 provide a 1.5 Ma record of the volcanic history of Martinique. 14C dating and δ18O patterns are used to reconstitute the chronostratigraphy of tephra, volcaniclastic turbidites, and mass-wasting events (traced by debris avalanches, debrites, and duplication and deformation of pre-existing sediments), leading to a new volcanic history of Montagne Pelée and Pitons du Carbet volcanoes. The top 50 m of core U1397A provides a continuous high-resolution sedimentation record over the last ∼130 ka. The sedimentation record deeper than 50 m in core U1397A and in the whole core U1399A is discontinuous because of the numerous sliding and deformation events triggered by debris avalanches related to flank collapses. Three successive activity periods are identified since ∼190 ka: the “Old Pelée” until 50 ka, the “Grand Rivière” (50–20 ka), and the “Recent Pelée” (20 ka—present day). The first two periods have the highest volcanic deposition rates offshore but very little outcrop on land. The whole magmatic activity of Mt Pelée comprises silicic andesites, but mafic andesites were also emitted during the whole “Grand Rivière.” At ∼115 ka, a major flank collapse (“Le Prêcheur”) produced a debris avalanche and submarine landslide that affected sea floor sediments by erosion and deformation up to ∼70 km from the shore. The Pitons du Carbet volcano was active from 1.2 Ma to 260 ka with numerous large flank collapses at a mean rate of 1 event every 100 ka. The average deposition rate of tephra fall offshore is much less than that at Mt Pelée. Our data show that correlations between the timing of large landslides or emission of mafic magmas and rapid sea level rise or lowstands suggested by previous studies are not systematic. The reconstituted chronostratigraphy of cores U1397A and U1399A provides the framework necessary for further studies of the magma petrology and production rates and timing of the mechanisms triggering flank collapses and related submarine landslides of Mt Pelée and Pitons du Carbet.

Aerial surveys reveal biotic drivers of mangrove expansion along a Thai salt flat ecotone

Rapid sea level rise (SLR) could overwhelm the adaptive capacity of many mangrove forests. The conservation of functional mangrove ecosystems will rely on their expansion into upper intertidal areas, including salt marshes and salt flats, in advance of SLR. The development of new mangrove habitats could be accelerated by amplifying positive biotic interactions among herbaceous plants, macrofauna, and mangrove trees, such as trapping of hydrochorous propagules or site amelioration. It was investigated how biotic and abiotic factors influenced the expansion of mixed‐species mangrove stands along a mangrove‐salt flat ecotone. Multi‐temporal unmanned aerial vehicle (UAV) imagery (< 1 cm/pixel) was used to monitor seedlings of Avicennia alba, Bruguiera cylindrica, and Lumnitzera racemosa in three sample plots (0.7–0.9 ha) over 2 years. The aerial images were used to map mangrove crowns, sedges (Fimbristylis tetragona), substrate elevation, and microtopography. The spatial distribution of seedlings was modeled using point pattern processes; mixed‐effects models were used to analyze how environmental factors influenced seedling survival and growth. The spatio‐temporal patterns of mangrove regeneration revealed that sedges and macrofauna facilitated the regeneration of mangroves into higher‐elevated areas of low tree density. Sedges not only trapped seeds but also increased the likelihood of survival among seedlings of all species. Large‐sized propagules established in undulating microtopography created through the bioturbation of macrofauna. Herbaceous vegetation expanded the range of macrofauna in the absence of trees. Thus, the migration of mangroves into hypersaline retreat areas may be accelerated by enhancing the growth of herbaceous vegetation and promoting burrowing macrofauna.

A stepwise approach for identifying climate change induced socio-economic tipping points

Climate change may cause socio-economic tipping points (SETPs), where the state of a socio-economic system abruptly changes to a fundamentally different state. While their potential existence is recognized, a systematic method for policy-relevant research on SETPs is lacking. This study introduces a stepwise approach for identification of SETPs that supports decision making under uncertain climate and socio-economic conditions. The approach is demonstrated with a stylized case study on the collapse of house prices (a SETP) in a coastal city, due to increasing flood risk from sea level rise. We explore four dynamic adaptive management strategies under a wide range of possible futures. We find that under scenarios with very high and rapid sea level rise, tipping points in real estate prices occur if the market responds to sudden changes in perceived flood risk rather than gradually adjusting prices to changes in flood risk in a rational manner. Such SETPs can only be avoided with a proactive strategy and when flood protection measures are implemented rapidly. Our approach can guide future studies on SETPs and seeks to move the study of SETPs towards a concept that provides perspective of action for policy makers.

Chronostratigraphic and palaeogeographic interpretation of Nakdong deltaic sequences in the south-eastern Korean Peninsula

We investigated the chronostratigraphy of six boreholes in the Nakdong River delta area in South Korea based on optically stimulated luminescence (OSL) and 14C dating. The standardised growth curves (SGCs) produced from single and multiple boreholes performed well in determining low equivalent dose (De; < 40 Gy). 14C dates from shell and wood fragments were mostly representative of depositional time. Based on 14C and OSL ages, the lowermost fluvial sediments showed relatively low sediment accumulation rates (0.1–0.8 m/kyr−1) prior to 12 ka. A hiatal discontinuity ranging from 12 to a maximum of 50 ka resulted in a break in sedimentation between the Last Glacial Maximum and the Holocene. A thick fluvio-estuarine unit in the lower part indicated relatively high accumulation rates (3.3–9.4 m/kyr−1) from 12 to 9 ka, which corresponded to rapid sea level rise. In the middle part, decreased accumulation rates (1.7–5.5 m/kyr−1) from approximately 9 to 6 ka were interpreted as transgressive deepening. Lower accumulation rates (0.9–3.2 m/kyr−1) during the middle to late Holocene were caused by relative sea level fall and a horizontally extended sedimentation area. In the upper part, the highest sediment accumulation rates (3.5–8.3 m/kyr−1) and rapid delta progradation during the last 2.0 ka might have been caused by widespread human influence and monsoonal climatic change. Isochrons of 1-kyr scale were identified based on the lithologic boundary and age results for each borehole, which represent palaeoshoreline positions during the transgressive cycle and boundaries of considerable delta progradation.

Millennial-Scale Carbon Storage in Natural Pine Forests of the North Carolina Lower Coastal Plain: Effects of Artificial Drainage in a Time of Rapid Sea Level Rise

Coastal forested wetlands provide important ecosystem services along the southeastern region of the United States, but are threatened by anthropogenic and natural disturbances. Here, we examined the species composition, mortality, aboveground biomass, and carbon content of vegetation and soils in natural pine forests of the lower coastal plain in eastern North Carolina, USA. We compared a forest clearly in decline (termed “ghost forest”) adjacent to a roadside canal that had been installed as drainage for a road next to an adjacent forest subject to “natural” hydrology, unaltered by human modification (termed “healthy forest”). We also assessed how soil organic carbon (SOC) accumulation changed over time using 14C radiocarbon dating of wood sampled at different depths within the peat profile. Our results showed that the ghost forest had a higher tree density at 687 trees ha−1, and was dominated by swamp bays (Persea palustric), compared to the healthy forest, which had 265 trees ha−1 dominated by pond pine (Pinus serotina Michx). Overstory tree mortality of the ghost forest was nearly ten times greater than the healthy forest (p &lt; 0.05), which actually contributed to higher total aboveground biomass (55.9 ± 12.6 Mg C ha−1 vs. 27.9 ± 8.7 Mg ha−1 in healthy forest), as the dead standing tree biomass (snags) added to that of an encroaching woody shrub layer during ecosystem transition. Therefore, the total aboveground C content of the ghost forest, 33.98 ± 14.8 Mg C ha−1, was higher than the healthy forest, 24.7 ± 5.2 Mg C ha−1 (p &lt; 0.05). The total SOC stock down to a 2.3 m depth in the ghost forest was 824.1 ± 46.2 Mg C ha−1, while that of the healthy forest was 749.0 ± 170.5 Mg C ha−1 (p &gt; 0.05). Carbon dating of organic sediments indicated that, as the sample age approaches modern times (surface layer year 2015), the organic soil accumulation rate (1.11 to 1.13 mm year−1) is unable to keep pace with the estimated rate of recent sea level rise (2.1 to 2.4 mm year−1), suggesting a causative relationship with the ecosystem transition occurring at the site. Increasing hydrologic stress over recent decades appears to have been a major driver of ecosystem transition, that is, ghost forest formation and woody shrub encroachment, as indicated by the far higher overstory tree mortality adjacent to the drainage ditch, which allows the inland propagation of hydrologic/salinity forcing due to SLR and extreme storms. Our study documents C accumulation in a coastal wetland over the past two millennia, which is now threatened due to the recent increase in the rate of SLR exceeding the natural peat accumulation rate, causing an ecosystem transition with unknown consequences for the stored C; however, much of it will eventually be returned to the atmosphere. More studies are needed to determine the causes and consequences of coastal ecosystem transition to inform the modeling of future coastal wetland responses to environmental change and the estimation of regional terrestrial C stocks and flux.

The effects of non-Newtonian rheology in the upper mantle on relative sea level change and geodetic observables induced by glacial isostatic adjustment process

SUMMARY Studies of glacial isostatic adjustment (GIA) provide important constraints on the Earth's mantle viscosity. Most GIA models assume Newtonian viscosity through the mantle, but laboratory experimental studies of rock deformation, observational studies of seismic anisotropy, and modelling studies of mantle dynamics show that in the upper mantle non-Newtonian viscosity may be important. This study explores the non-Newtonian effects on the GIA induced variations in mantle stress and viscosity and on surface observables including vertical displacement, relative sea level (RSL) and gravity change. The recently updated and fully benchmarked software package CitcomSVE is used for GIA simulations. We adopt the ICE-6G ice deglaciation history, VM5a lower mantle and lithospheric viscosities, and a composite rheology that combines Newtonian and non-Newtonian viscosities for the upper mantle. Our results show that: (1) The mantle stress beneath glaciated regions increases significantly during deglaciation, leading to regionally reduced upper mantle viscosity by more than an order of magnitude. Such effects can be rather localized at the periphery of glaciated regions. However, non-Newtonian effects on far-field mantle viscosity are negligibly small. GIA induced stress is also significant in the lithosphere (∼30 MPa) and lower mantle (∼2 MPa). (2) The predicted RSL changes from non-Newtonian models display distinct features in comparison with the Newtonian model, including more rapid sea level falls associated with the rapid deglaciation at ∼14 000 yr ago followed by a more gradual sea level variation for sites near the centres of formerly glaciated regions, and an additional phase of sea level falls for the last ∼8000 yr for sites at the ice margins. Similar time-dependence associated with the deglaciation is also seen for rate of vertical displacement, suggesting a relatively slow present-day rates of vertical displacement and gravity change. These features can be explained by the non-Newtonian effects associated with a loading event which manifest a fast relaxation stage followed by a relative slow relaxation stage. Our results may provide GIA diagnoses for distinguishing non-Newtonian and Newtonian rheology.

Slowstands, stillstands and transgressions: Paleoshorelines and archaeology on Quadra Island, BC, Canada

On Quadra Island, west coast Canada, a series of marine terraces formed during a period of rapid marine regression from 200 m to 1 m above modern levels between ca. 14,500 and 12,000 years ago. Within this period of regional marine regression, evidence points to brief periods of sea level stillstand and even marine transgressions. It is hypothesized that during these anomalous periods, global meltwater events created a local signature on the Quadra Island sea level curve by slowing, halting and/or inversing the regional sea level regression trend. This is revealed through identification of high elevation paleoshorelines, landscape terracing and other stranded marine features from LiDAR Digital Elevation Models (DEMs) and subsurface investigation. These paleomarine terraces are believed to have developed during brief marine stillstands, slowstands and minor marine transgressions. Pauses or slowing periods of regression appear to result from global eustatic rise briefly matching or exceeding local isostatic and tectonic uplift. The ages of these terraces, based on local sea level history and radiocarbon dating of some of the raised marine features, match well to the ages of coral-based marine terraces sequences associated with periods of rapid global sea level rise. A number of early post glacial to earliest Holocene archaeological sites are associated with the Quadra marine terraces. These associations suggest an improved approach to location of early archaeological sites dating to times of rapid sea level change.

Laurentide Ice Saddle Mergers Drive Rapid Sea Level Drops During Glaciations

AbstractRecent glacial periods have included several periods of rapid sea level drop that are still not well understood. Here we show that rapid sea level drops can occur due to merger of two separate ice sheets without correspondingly rapid climate forcing. Using the Parallel Ice Sheet Model (PISM), we simulate glaciation of the Laurentide Ice Sheet (LIS) by gradually decreasing equilibrium‐line altitude (ELA). Merger of the extended Keewatin sector of the Laurentide Ice Sheet with Labrador sector of the Laurentide Ice Sheet south of Hudson Bay causes a positive feedback between increasing surface elevation and increasing surface mass balance in the merger region, leading to fast ice sheet growth. The simulated saddle merger of LIS lowers sea level by 20 m in less than 20 kyr with periods of sea level fall exceeding 2 m/kyr, similar to those observed in paleo‐sea level records.

An Ancient Meltwater Pulse Raised Sea Levels by 18 Meters

Meltwater pulse 1A, a period of rapid sea level rise after the last deglaciation, was powered by melting ice from North America and Scandinavia, according to new research.

Seismic characteristics and distributions of Quaternary mass transport deposits in the Qiongdongnan Basin, northern South China Sea

Mass transport deposits can cause marine geohazards and transport sediments to deep-water areas and act as hydrocarbon reservoirs and seals, which have been extensively examined throughout the last decade in the northern South China Sea. Based on 2D and newly acquired high-resolution 3D seismic data, as well as logging-while-drilling (LWD) data, we document the characteristics, distributions, sources, and triggering mechanisms of the Quaternary MTDs in the Qiongdongnan Basin (QDNB). Moreover, their impacts on deep-water channels, gas hydrate accumulation and marine geohazards are discussed. The results show that there are ten phases of Quaternary MTDs development in the study area. Among them, MTD3 covers the largest area, ~627 km2, while the smallest is MTD10 at ~89 km2. These MTDs are characterized by chaotic and translucent/transparent seismic facies and negative-phased seismic reflections on their seismic profiles. The transport directions of these MTDs mainly occur from the northwest to southeast, northeast to southwest, and southwest to northeast, with sources in the Northern Slope Area and Western Slope Area or Guangle Uplift Area. Based on an analysis of the tectono-sedimentary evolution of the QDNB, these Quaternary MTDs may have been triggered by an anomalously high sedimentation rate, increased slope gradient, fault reactivation, earthquakes, and sea level fluctuation. Among these processes, earthquakes and rapid sea level fluctuation could be the most critical triggering mechanisms. Furthermore, the MTDs primarily act as hydrocarbon seals in the study area, facilitating the accumulation in the shallow gas reservoirs and gas hydrates within the Quaternary strata. MTDs and related tsunamis are also major marine geohazards, which need in-depth integrated researches by multidisciplinary scientists.