A new Holocene sea-level record for Singapore

Relative sea-level (RSL) records from far-field regions distal from ice sheets remain poorly understood, particularly in the early Holocene. Here, we extended the Holocene RSL data from Singapore by producing early Holocene sea-level index points (SLIPs) and limiting dates from a new ~40 m sediment core. We merged new and published RSL data to construct a standardized Singapore RSL database consisting of 88 SLIPs and limiting data. In the early Holocene, RSL rose rapidly from −21.0 to −0.7 m from ~9500 to 7000 cal. yrs. BP. Thereafter, the rate of RSL rise decelerated, reaching a mid-Holocene highstand of 4.0 ± 4.5 m at 5100 cal. yrs. BP, before falling to its present level. There is no evidence of any inflections in RSL when the full uncertainty of SLIPs is considered. When combined with other standardized data from the Malay-Thai Peninsula, our results also show substantial misfits between regional RSL reconstructions and glacial isostatic adjustment (GIA) model predictions in the rate of early Holocene RSL rise, the timing of the mid-Holocene highstand and the nature of late-Holocene RSL fall towards the present. It is presently unknown whether these misfits are caused by regional processes, such as subsidence of the continental shelf, or inaccurate parameters used in the GIA model

Hydrology signal from GRACE gravity data in the Nelson River basin, Canada: a comparison of two approaches

Abstract The Gravity Recovery and Climate Experiment (GRACE) satellite mission measures the combined gravity signal of several overlapping processes. A common approach to separate the hydrological signal in previous ice-covered regions is to apply numerical models to simulate the glacial isostatic adjustment (GIA) signals related to the vanished ice load and then remove them from the observed GRACE data. However, the results of this method are strongly affected by the uncertainties of the ice and viscosity models of GIA. To avoid this, Wang et al. (Nat Geosci 6(1):38–42, 2013. https://doi.org/10.1038/NGEO1652; Geodesy Geodyn 6(4):267–273, 2015) followed the theory of Wahr et al. (Geophys Res Lett 22(8):977–980, 1995) and isolated water storage changes from GRACE in North America and Scandinavia with the help of Global Positioning System (GPS) data. Lambert et al. (Postglacial rebound and total water storage variations in the Nelson River drainage basin: a gravity GPS Study, Geological Survey of Canada Open File, 7317, 2013a, Geophys Res Lett 40(23):6118–6122, https://doi.org/10.1002/2013GL057973, 2013b) did a similar study for the Nelson River basin in North America but applying GPS and absolute gravity measurements. However, the results of the two studies in the Nelson River basin differ largely, especially for the magnitude of the hydrology signal which differs about 35%. Through detailed comparison and analysis of the input data, data post-processing techniques, methods and results of these two works, we find that the different GRACE data post-processing techniques may lead to this difference. Also the GRACE input has a larger effect on the hydrology signal amplitude than the GPS input in the Nelson River basin due to the relatively small uplift signal in this region. Meanwhile, the influence of the value of $$\alpha$$ α , which represents the ratio between GIA-induced uplift rate and GIA-induced gravity-rate-of-change (before the correction for surface uplift), is more obvious in areas with high vertical uplift, but is smaller in the Nelson River basin. From Gaussian filtering of simulated data, we found that the magnitude of the peak gravity signal value can decrease significantly after Gaussian filtering with large average radius filter, but the effect in the Nelson River basin is rather small. More work is needed to understand the effect of amplitude restoration in the post-processing of GRACE g-dot signal. However, it is encouraging to find that both the methodologies of Wang et al. (2013, 2015) and Lambert et al. (2013a, b) can produce very similar results if their inputs are the same. This means that their methodologies can be applied to study the hydrology in other areas that are also affected by GIA provided that the effects of post-processing of their inputs are under control

Coastal GIA processes revealed by the early to middle Holocene sea-level history of east China

In order to examine relative sea-level responses to the postglacial ice-volume change and the glacio-hydro isostatic adjustments (GIA), this study investigated the inner part of the Hangzhou Bay, east China, a tectonically relatively stable far-field location, and reconstructed the early to middle Holocene sea-level history. This investigation has established the elevational relationship between modern saltmarsh-mudflat and tidal levels based on diatom analysis for sea-level indicative meaning estimates, produced 17 high-quality sea-level index points, and simulated GIA processes for the study site. These results reveal that the relative sea level rose from −38.3 ± 1.6 m in c. 10,000 cal a BP to the present height by c. 7000 cal. a BP, and the average rate of sea-level rise decreased gradually from 19.6 ± 2.6 mm/a to 2.3 ± 1.5 mm/a during the 3000 years. This period of sea-level history was punctuated by two episodes of accelerated rise around 8200 and 7500 cal a BP. The relative sea level rose to 0.8 ± 1.4 m above msl by c. 6500 cal. a BP, followed by a gradual fall back to the present height at 4500 cal a BP, implying a different response to the potential additional ice melting between 7000 and 4000 cal a BP. A comparison of the sea-level histories between the inner and outer Hangzhou Bay indicates the coastal levering effect due to the marine inundation of the continental shelves. A further comparison between sea-level data from China and Malay Peninsula reveals different GIA effects between the Cathaysia-Yangtze Blocks and the Sundaland Block.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThis research is funded jointly by Guangdong Academy of Sciences (2016GDASRC-0209), National Natural Science Foundation of China (41771024), Natural Science Foundation of Guangdong Province (2017A030311020) and Research Grant Council of Hong Kong (HKU17311816). Li, T is funded by the Singapore Ministry of Education Academic Research Fund MOE2018-T2-1-030, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centres of Excellence initiative. This paper is a contribution to IGCP Project 639 ‘Sea Level Change from Minutes to Millennia’, PALSEA2 (Palaeo-Constraints on Sea- Level Rise) and Earth Observatory of Singapore contribution 277

A re-evaluation of Holocene relative sea-level change along the Fujian coast, southeastern China

The southeastern China coast is a region of special interest in the study of past and present relative sea-level change, given its distal location from giant ice sheets (far-field regions). During the past decades, a large number of biological, geological, and archaeological sea-level indicators have been retrieved from the Fujian coastal region which allows for recalibration and recalculation of sea-level index points (SLIPs). This study constructs a database of Holocene relative sea-level (RSL) observations for the Fujian coast, southeastern China. The database contains 59 quality-controlled SLIPs which show that RSL for the Fujian coast did not exceed present (0 m) during the Holocene, except potentially during 7.5–5.5 cal. kyr BP and 1.8–0.7 cal. kyr BP. Rates of RSL change were highest during the early Holocene and have decreased over time, due to the diminishing response of the Earth's mantle to glacial isostatic adjustment (GIA) and reduction of meltwater input. A series of sea-level oscillations were recorded in our SLIPs-based reconstructions which might correspond to global climate warming or cooling events. We assessed the spatial variability of RSL histories and compared these with the ICE-6G_C and ANU-ICE GIA model predictions. Substantial misfits between GIA predictions and regional RSL reconstructions were recognized: (1) the deceleration of the early-Holocene sea-level rise ended about one millennia earlier in the ICE-6G_C model than in the SLIPs-based reconstructions; (2) GIA model predictions show a mid-Holocene sea-level highstand of 1–3 m which is absent from our SLIPs-based reconstructions; and (3) all GIA model predicted a gradual RSL fall to 0 m since the middle Holocene, while our reconstruction displays significant RSL oscillations. It is presently unknown whether these misfits are caused by uncertainties in regional tectonic movement estimation or parameters used in the GIA models. Future applications of spatiotemporal statistical techniques are required to better quantify the gradient of the isostatic contribution and to provide improved context for the assessment of the ongoing acceleration of sea-level rise.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThis work was financially supported by the National Natural Science Foundation of China (Grant No. 42076207 to Fengling Yu); the Funda- mental Research Funds for the Central Universities of Xiamen University (Grant No. 20720190096 to Fengling Yu); the China Postdoctoral Sci- ence Foundation (Grant No. 2021M691862 to Nannan Li); the Singapore Ministry of Education Academic Research Fund MOE2019-T3-1-004 and MOE-T2EP50120-0007, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centers of Excellence initiative (to Tanghua Li)

Holocene environmental evolution and relative sea-level change in the Oka estuary (Urdaibai Biosphere Reserve, northern Spain)

The Holocene environmental evolution in coastal areas, including deltas and estuaries, is vital to understanding coastal dynamics and how they may change in the future. Here, we studied the Holocene environmental evolution of the Oka estuary (Urdaibai Biosphere Reserve, northern Spain) from sedimentary cores that were 11–49 m long. We applied a multi-proxy approach of benthic foraminifera and grain size, and a temporal framework of radiocarbon dates to reconstruct paleoenvironments. The benthic foraminifera assemblages varied from near-marine (allochthonous and autochthonous hyaline species such as Lobatula lobatula, Rosalina irregularis, Ammonia tepida and Haynesina germanica) to brackish intertidal (autochthonous hyaline species such as A. tepida and H. germanica) to salt-marsh (autochthonous agglutinated species Trochammina inflata and Entzia macrescens) environments. Grain size analysis supported the foraminiferal assemblages and the sedimentary sequences were sand-dominated in near-marine intertidal environments and mud-dominated in the brackish intertidal and salt-marsh environments. The chronology was constrained by thirty four radiocarbon dates from plant macrofossils, marine shells and wood fragments. Our paleoenvironmental reconstructions were used to produce an updated local Holocene relative sea-level (RSL) record based on new data, revised reconstructions, and age recalibration of previous research. Marine limiting dates showed that RSL changed from above −20.4 ± 0.2 m at ∼9100 cal. yrs. BP to above −4.2 ± 0.2 m at ∼6700 cal. yrs. BP. In the late Holocene, sea-level index points (SLIPs) reconstructed the RSL position from −2.7 ± 1.2 m at ∼4900 cal. yrs. BP to −1.4 ± 1.2 m at ∼1500 cal. yrs. BP. Estimates of rates of RSL change from the Errors-in-Variables Integrated Gaussian Process (EIV-IGP) model show RSL gradually rose at 0.3 ± 2.1 mm yr−1 in the late Holocene. There was a progressive shallowing of the estuary as rates of RSL rise reduced during the Holocene. Between ∼9000 and 7000-6000 cal. yrs. BP pre-Holocene fluvial gravels (Lowstand Systems Tract) were replaced by both sandy marine and brackish intertidal sediments (Transgressive Systems Tract). After ∼7000-6000 cal. yrs. BP salt-marsh sediments deposited (Highstand Systems Tract). The sequence was overlain by anthropogenic deposits derived from agricultural, dredging and dumping activities since the 18th century (Anthropogenic Systems Tract). The Holocene environmental evolution and relative sea-level change of Oka is broadly consistent with previous studies in northern Spain, although it places the onset of the Highstand Systems Tract ∼2000 years earlier.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThis research was funded through the years by the projects UNESCO04/05, UNESCO06/08, Harea-Coastal Geology Group (Basque Government, IT332-07, IT365-10, IT767-13, IT976-16 and IT1616-22), TANYA (MICINN, CGL2009-08840), K-Egokitzen II (Basque Govern- ment, Climate Change: Impact and Adaptation, Etortek 2010), Antro- picosta (MINECO, CGL2013-41083-P), Antropicosta-2 (RTI2018- 095678-B-C21, MCIN/AEI/10.13039/501100011033 and ERDF A way of making Europe and European Union) and UFI11/09 (UPV/EHU). BPH and TL are supported by the Singapore Ministry of Education Academic Research Fund MOE2019-T3-1-004 and MOE-T2EP50120-0007, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centers of Excellence initiative

Glacial isostatic adjustment: physical models and observational constraints

By far the most prescient insights into the interior structure of the planet have been provided on the basis of elastic wave seismology. Analysis of the travel times of shear or compression wave phases excited by individual earthquakes, or through analysis of the elastic gravitational free oscillations that individual earthquakes of sufficiently large magnitude may excite, has been the central focus of Earth physics research for more than a century. Unfortunately, data provide no information that is directly relevant to understanding the solid state ‘flow’ of the polycrystalline outer ‘mantle’ shell of the planet that is involved in the thermally driven convective circulation that is responsible for powering the ‘drift’ of the continents and which controls the rate of planetary cooling on long timescales. For this reason, there has been an increasing focus on the understanding of physical phenomenology that is unambiguously associated with mantle flow processes that are distinct from those directly associated with the convective circulation itself. This paper reviews the past many decades of work that has been invested in understanding the most important of such processes, namely that which has come to be referred to as ‘glacial isostatic adjustment’ (GIA). This process concerns the response of the planet to the loading and unloading of the high latitude continents by the massive accumulations of glacial ice that have occurred with almost metronomic regularity over the most recent million years of Earth history. Forced by the impact of gravitational n-body effects on the geometry of Earth’s orbit around the Sun through the impact upon the terrestrial regime of received solar insolation, these surface mass loads on the continents have left indelible records of their occurrence in the ‘Earth system’ consisting of the oceans, continents, and the great polar ice sheets on Greenland and Antarctica themselves. Although this ice-age phenomenology has been clearly recognized since early in the last century, it was for over 50 years considered to be no more than an interesting curiosity, the understanding of which remained on the periphery of the theoretical physics of the Earth. This was the case in part because no globally applicable theory was available that could be applied to rigorously interpret the observations. Equally important to understanding the scientific lethargy that held back the understanding of this phenomenon involving mantle flow processes was the lack of appreciation of the wide range of observations that were in fact related to GIA physics. This paper is devoted to a review of the global theories of the GIA process that have since been developed as a means of interpreting the extensive variety of observations that are now recognized as being involved in the response of the planet to the loading and unloading of its surface by glacial ice. The paper will also provide examples of the further analyses of Earth physics and climate related processes that applications of the modern theoretical structures have enabled.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionTanghua Li is supported by the Singapore Ministry of Education Academic Research Fund MOE2019-T3- 1-004 and MOE2018-T2-1-030, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centers of Excellence initiative. This work comprises Earth Observatory of Singapore Contribution No. 428. Jesse Velay-Vitow is supported by NSERC Grant CGSD3—547034—2020 as well as by the Walter C Sumner Mmeorial Foundation

Past, present and future sea-level change in the Russian Arctic

Accurate projection of future sea-level change in the Russian Arctic is important for navigation, coastal infrastructure, and has implications for changes in ocean circulation, ecosystems, and coastal erosion (Lamoureux et al., 2015). Accurate sea-level projection relies on an understanding of the mechanisms driving its complex evolution, which must be founded on an understanding of its history (Horton et al., 2018).Ministry of Education (MOE)The authors acknowledge funding from Singapore Ministry of Education Academic Research Fund MOE2018-T2-1-030. This work is Earth Observatory of Singapore contribution 314

Eddy Current Inversion Models for Estimating Dimensions of Defects in Multilayered Structures

In eddy current nondestructive evaluation, one of the principal challenges is to determine the dimensions of defects in multilayered structures from the measured signals. It is a typical inverse problem which is generally considered to be nonlinear and ill-posed. In the paper, two effective approaches have been proposed to estimate the defect dimensions. The first one is a partial least squares (PLS) regression method. The second one is a kernel partial least squares (KPLS) regression method. The experimental research is carried out. In experiments, the eddy current signals responding to magnetic field changes are detected by a giant magnetoresistive (GMR) sensor and preprocessed for noise elimination using a wavelet packet analysis (WPA) method. Then, the proposed two approaches are used to construct the inversion models of defect dimension estimation. Finally, the estimation results are analyzed. The performance comparison between the proposed two approaches and the artificial neural network (ANN) method is presented. The comparison results demonstrate the feasibility and validity of the proposed two methods. Between them, the KPLS regression method gives a better prediction performance than the PLS regression method at present

LM17.3 - a globalvertical land motion model of glacial isostatic adjustment.

Additional models (W12, Whitehouse et al. 2012, and IJ05_R2, Ivins et al. 2013, for Antarctica; ANU-ICE, Lambeck et al. 2017, and NAIce, Gowan et al. 2016, for North America) were tested in the development of the model but not used in the end. Little ice age is not included nor any ice mass change during the last 100 years. The eustatic sea-level equivalent at last glacial maximum amounts to 113.8 m for all ice sheets and glaciers together. Because we use an ice model that has not been tuned to fit global constraints, it may highlight areas which cannot match commonly used GIA observations. However, we note that the earth model used in our calculations is different to the earth model used in the development of some regional ice models, e.g. HUY3, ANU-ICE, IJ04_Patagonia (see respective references), thus some differences can be related to this. The LM17.3 model was introduced in Jäggi et al. (2019), and its DDK5-filtered geoid and water heights can be found in the EGSIEM plotter (http://plot.egsiem.eu/index.php?p=timeseries). The GIA model uses material compressibility and includes time-dependent coastlines and rotational feedback. The vertical land motion can be used/tested in sea-level investigations and projections. Work towards a model that incorporates 3D earth structure, and an updated ice model, is ongoing

Influence of 3D earth structure on glacial isostatic adjustment in the Russian Arctic

Analyses of glacial isostatic adjustment (GIA) and deglacial relative sea-level (RSL) change in the Russian Arctic deliver important insights into the Earth's viscosity structure and the deglaciation history of the Eurasian ice sheet complex. Here, we validate the 1D GIA models ICE-6G_C (VM5a) and ICE-7G_NA (VM7) and select new 3D GIA models in the Russian Arctic against a quality-controlled deglacial RSL database of >500 sea-level data points from 24 regions. Both 1D models correspond to the RSL data along the southern coast of the Barents Sea and Franz Josef Land from ∼11 ka BP to present but show notable misfits (>50 m at 10 ka BP) with the White Sea data. We find 3D model predictions of deglacial RSL resolve most of the misfits with the observed data for the White Sea while retaining comparable fits in other regions of the Russian Arctic. Our results further reveal: (a) RSL in the western Russian Arctic is sensitive to elastic lithosphere with lateral thickness variation and 3D viscosity structure in the upper mantle; and (b) RSL in the whole Russian Arctic is less sensitive to 3D viscosity structure in the lower mantle compared to the upper mantle. The 3D models reveal a compromise in the upper mantle between the background viscosity and scaling factor to best fit the RSL data, which needs to be considered in future 3D GIA studies.Ministry of Education (MOE)National Research Foundation (NRF)Published versionTanghua Li, Timothy A. Shaw, and Benjamin P. Horton are supported by the Singapore Ministry of Education Academic Research Fund MOE2019 -T3-1-004, MOE2018-T2-1-030 and MOE-T2EP50120-0007, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centers of Excellence initia- tive. The research of W. Richard Peltier at Toronto is supported by NSERC discov- ery Grant A9627. The work of Alisa Baranskaya was supported by the Russian Science Foundation Grant 22-77-10,031; she used equipment and facilities obtained within the State Budget Theme АААА- А16-116032810055-0. The FE calcula- tion was performed with the ABAQUS package from Hibbitt, Karlsson and Sorensen Inc. This research is conducted in part using the research computing facilities and/or advisory services offered by Information Technology Services, the University of Hong Kong. The authors acknowledge HOLSEA and PALSEA, working groups of the International Union for Quaternary Sciences (INQUA) and Past Global Changes (PAGES), which in turn received support from the Swiss Academy of Sciences and the Chinese Academy of Sciences. This article is a contribution to International Geoscience Program (IGCP) Project 639, “Sea-Level Changes from Minutes to Millennia.” We express our gratitude to Muhammad Hadi Ikhsan for support with the graphics. This work is Earth Observatory of Singapore contribution 435