Assessment of nonlinear trends and seasonal variations in global sea level using singular spectrum analysis and wavelet multiresolution analysis

The main purpose of this paper is to apply the singular spectrum analysis (SSA), based on the phase space, and the wavelet multiresolution analysis (WMA), based on the frequency space, to the weekly time series of global sea level anomaly (GSLA) derived from satellite altimetry data over 1993–2013, in order to assess its nonlinear trends and its seasonal signals. The SSA results show that the GSLA time series is mainly dominated by a nonlinear trend explaining 89.89 % of the total GSLA variability, followed by annual and semi-annual signals with an explained variance of 9.15 and 0.32 %, respectively. For the annual signal, both methods give similar results. Its amplitude is less than 14 mm with an average of about 11 mm, and its minimum and maximum occur in April and October, respectively. The calculation of sea level trend, by both methods, is direct without removing the seasonal signals from the original GSLA time series as the most commonly used in the literature. The global sea level trend obtained from the WMA is about 2.52 ± 0.01 mm/year which is in good agreement with 2.94 ± 0.05 mm/year estimated from the SSA. Furthermore, the SSA method is most suitable for seasonal adjustment, and the WMA method is more useful for providing the different rates of sea level rise. Indeed, the WMA reveals that the global sea level has risen with the rate of 3.43 ± 0.01 mm/year from January/1993 to January/1998, 0.66 ± 0.01 mm/year from February/1998 to May/2000, 5.71 ± 0.03 mm/year from June/2000 to October/2003, and 1.57 ± 0.01 mm/year since January/2004.     

Trends in global and regional sea level from satellite altimetry within the framework of auto-SSA

The sea level change is a crucial indicator of our climate. The spatial sampling offered by satellite altimetry and its continuity during the last 18 years are major assets to provide an improved vision of the sea level changes. In this paper, we analyze the University of Colorado database of sea level time series to determine the trends for 18 large ocean regions by means of the automatic trend extraction approach in the framework of the singular spectrum analysis technique. Our global sea level trend estimate of 3.19 mm/year for the period from 1993 to 2010 is comparable with the 3.20-mm/year sea level rise since 1993 calculated by AVISO Altimetry. However, the trends from the different ocean regions show dissimilar patterns. The major contributions to the global sea level rise during 1993–2010 are from the Indian Ocean (3.78?±?0.08 mm/year).     

中国东海海平面变化多尺度周期分析与预测

海平面变化规律尤其是对海平面变化周期和上升趋势的研究,已成为国内外科学界研究的热点问题.使用1992-2009年海平面卫星测高仪数据资料,运用小波变换方法对中国东海海平面变化的周平均数据信号进行多尺度周期分析,并通过Winters指数平滑法对未来海平面变化进行预测,结果显示:①1992-2009年东海海平面呈现波动上升...     

Pre-salt to salt stratigraphic architecture in a rift basin: insights from a basin-scale study of the Gulf of Suez (Egypt)

We propose a basin-scale (～300 × 100 km) study of the pre-salt to salt sedimentary fill from the Suez rift based on outcrop and subsurface data. This study is a new synthesis of existing and newly acquired data using an integrated approach with (1) basin-scale synthesis of the structural framework, (2) stratigraphic architecture characterization of the entire Suez rift using sequence stratigraphy concepts, (3) lithologic maps reconstruction and interpretation, (4) isopach/depocenter maps interpolation to quantify sedimentary volumes, and (5) quantification of the sediment supply, mean carbonate and evaporite accumulation rates, and their integration into the rift dynamic. The Gulf of Suez is ca. 300-km-long and up to 80-km-wide rift structure, resulting from the late Oligocene to early Miocene rifting of the African and Arabian plates. The stratigraphic architecture has recorded five main stages of rift evolution, from rift initiation to finally tectonic quiescence characterized by salt deposits. Rift initiation (ca. 1–4 Myr duration): the Suez rift was initiated at the end of the Oligocene along the NNW-SSE trend of the Red Sea with evidences of active volcanism. Continental to lacustrine deposits only occurred in isolated depocenters. Sediment supply was relatively low. Rift widening (ca. 3 Myr duration): the rift propagated from south to north (Aquitanian), with first marine incursions from the Mediterranean Sea. The rift was subdivided into numerous depocenters controlled by active faults. Sedimentation was characterized by small carbonate platforms and associated sabkha deposits to the south and shallow open marine condition to the north with mixed sedimentation organized into an overall transgressive trend. Rift climax (ca. 5 Myr duration): the rift was then flooded during Burdigalian times recording the connection between the Mediterranean Sea and the Red Sea. The faults were gradually connected and reliefs on the rift shoulders were high as evidenced by a strong increase of the uplift/subsidence rates and sediment supply. Three main depocenters were then individualized across the rift and correspond to the Darag, Central, and Southern basins. Sedimentation was characterized by very large Gilbert-type deltas along the eastern margin and associated submarine fans and turbidite systems along the basin axis. Isolated carbonate platforms and reefs mainly occurred in the Southern basin and along tilted block crests. Late syn-rift to rift narrowing (ca. 4 Myr duration): during the Langhian, the basin recorded several falls of relative sea level and bathymetry in the rift axis was progressively reduced. The former reliefs induced during the rift climax were quickly destroyed as evidenced by the drastic drop in sediment supply. Stratigraphic reconstruction indicates that the Central basin was restricted during lowstand period; meanwhile, open marine conditions prevailed to the north and south of the Suez rift. The Central basin, Zaafarana, and Morgan accommodation zones thus acted as a major divide between the Mediterranean Sea and the Red Sea. During Serravalian times, the Suez rift also recorded several disconnections between the Mediterranean and Red seas as evidenced by massive evaporites in major fault-controlled depocenters. The Suez rift was occasionally characterized by N–S paleogeographic gradient with restricted setting to the north and open marine setting to the south (Red Sea). Tectonic quiescence to latest syn-rift (ca. 7 Myr duration): the Tortonian was then characterized by the deposition of very thick salt series (>1000 m) which recorded a period of maximum restriction for the Suez rift. The basin was still subdivided into several sub-basins bounded by major faults. The basin with a N-S paleogeographic gradient was totally and permanently disconnected from the Mediterranean Sea and connected to open marine condition via the Red Sea. The Messinian was also characterized by a thick salt series, but the evaporite typology and sedimentary systems distribution suggest a more humid climate than during Tortonian times. Pre-salt to salt transition was not sharp and lasted for ca. 4 Myr (Langhian-Serravalian). It was initiated as the result of the combined effect of (1) climatic changes with aridization and low water input from the catchments and (2) rift dynamic induced by plate tectonic reorganization that controlled the interplay between sea level and accommodation zones constituting sills.     

Messinian events in the Black Sea

Past hydrological interactions between the Mediterranean Sea and Black Sea are poorly resolved due to complications in establishing a high‐resolution time frame for the Black Sea. We present a new greigite‐based magnetostratigraphic age model for the Mio‐Pliocene deposits of DSDP Hole 380/380A, drilled in the southwestern Black Sea. This age model is complemented by ⁴⁰Ar/³⁹Ar dating of a volcanic ash layer, allowing a direct correlation of Black Sea deposits to the Messinian salinity crisis (MSC) interval of the Mediterranean Sea. Proxy records divide these DSDP deposits into four intervals: (i) Pre‐MSC marine conditions (6.1–6.0 Ma); (ii) highstand, fresh to brackish water conditions (~6.0–5.6 Ma); (iii) lowstand, fresh‐water environment (5.6–5.4 Ma) and (iv) highstand, fresh‐water conditions (5.4–post 5.0 Ma). Our results indicate the Black Sea was a major fresh‐water source during gypsum precipitation in the Mediterranean Sea. The introduction of Lago Mare fauna during the final stage of the MSC coincides with a sea‐level rise in the Black Sea. Across the Mio‐Pliocene boundary, sea‐level and salinity in the Black Sea did not change significantly.     

Stochastic analyses of maximum daily rainfall series recorded at two stations across the Mediterranean Sea

Independence, stationarity, homogeneity, trend, and periodicity tests are applied on 48-year-long complete and 79-year-long incomplete maximum daily rainfall series recorded at Alexandria, Egypt, and on 61-year-long maximum daily rainfall series recorded at Antalya, Turkey, which are located at the southeastern and northeastern shores of the Mediterranean Sea. The results indicate no significant trend and no periodicity in mean, and both series are independent and homogeneous. Linear regression trend test applied to the 10 % highest part of the Alexandria series indicated a significant increasing trend. Next, frequency analysis is applied on each of these series by the probability distributions of Gumbel, general extreme-values, three-parameter log-normal, Pearson-3, log-Pearson-3, log-logistic, generalized Pareto, and Wakeby. The distributions, except for the generalized Pareto and Wakeby, pass the χ ² and Kolmogorov–Smirnov goodness-of-fit tests at 90 % probability. By visual inspection of the plots of histograms together with the probability density functions, and by the results of the χ ², Kolmogorov–Smirnov, and probability plot correlation coefficient tests, the general extreme-value distribution whose parameters are computed by the method of probability-weighted moments is deemed to be suitable for these two maximum daily rainfall series.     

Geomorphology and drainage network of Ras Banas Peninsula, Egyptian Red Sea coast: a model of coastal threshold

Ras Banas Peninsula is a large triangular tract of land jutting out into the Red Sea. It extends about 40 km eastward out of the general trend of the Red Sea coast of Egypt, covering an area of about 600 km². Three sandy spits are jutting out from the main body of the peninsula into the Red Sea, possibly representing relics of structural trends, two of which are located at the western part and the third one is extending from the eastern edge forming a further seaward extension of the main body. A series of isometric and contour maps of the whole area under investigation are provided in digitized visual form of geomorphologic features, landforms and slope configuration. According to difference in relief, the study area can be subdivided into three topographic divisions, namely coastal plain (<50 m), medium-height land (50–150 m) and hinterland (>150 m). Drainage and lineament maps of the drainage networks were prepared from the topographic map and satellite images of the area. The prepared lineament map shows four main trends that control the configuration of the drainage system in the study area. These trends are Aqaba trend (NE–SW to NNE–SSW), Red Sea trend (NW–SE to NNW–SSE), Nubian trend (N–S), and Tethyan trend (E–W). It is clear that the structural trends, lithology and general slope are the main controls of developing parallel and dendritic drainage patterns in the area. Both geomorphology and drainage system configuration have great influences on the land use and natural hazards affecting the peninsula especially torrential floods and sea level fluctuations.     

Localisation and temporal variability of groundwater discharge into the Dead Sea using thermal satellite data

The semi-arid region of the Dead Sea heavily relies on groundwater resources. This dependence is exacerbated by both population growth and agricultural activities and demands a sustainable groundwater management. Yet, information on groundwater discharge as one main component for a sustainable management varies significantly in this area. Moreover, discharge locations, volume and temporal variability are still only partly known. A multi-temporal thermal satellite approach is applied to localise and semi-quantitatively assess groundwater discharge along the entire coastline. The authors use 100 Landsat ETM + band 6.2 data, spanning the years between 2000 and 2011. In the first instance, raw data are transformed to sea surface temperature (SST). To account for groundwater intermittency and to provide a seasonally independent data set ?T (maximum SST range) per-pixel within biennial periods is calculated subsequently. Groundwater affected areas (GAA) are characterised by ?T < 8.5 °C. Unaffected areas exhibit values >10 °C. This allows the exact identification of 37 discharge locations (clusters) along the entire Dead Sea coast, which spatially correspond to available in situ discharge observations. Tracking the GAA extents as a direct indicator of groundwater discharge volume over time reveals (1) a temporal variability correspondence between GAA extents and recharge amounts, (2) the reported rigid ratios of discharge volumes between different spring areas not to be valid for all years considering the total discharge, (3) a certain variability in discharge locations as a consequence of the Dead Sea level drop, and finally (4) the assumed flushing effect of old Dead Sea brines from the sedimentary body to have occurred at least during the two series of 2000–2001 and 2010–2011.     

Storm surges in the Singapore Strait due to winds in the South China Sea

Among the semi-enclosed basins of the world ocean, the South China Sea (SCS) is unique in its configuration as it lies under the main southwest-northeast pathway of the seasonal monsoons. The northeast (NE) monsoon (November–February) and southwest (SW) monsoon (June–August) dominate the large-scale sea level dynamics of the SCS. Sunda Shelf at the southwest part of SCS tends to amplify Sea Level Anomalies (SLAs) generated by winds over the sea. The entire region, bounded by Gulf of Thailand on the north, Karimata Strait on the south, east cost of Peninsular Malaysia on the west, and break of Sunda Shelf on the east, could experience positive or negative SLAs depending on the wind direction and speed. Strong sea level surges during NE monsoon, if coincide with spring tide, usually lead to coastal floods in the region. To understand the phenomena, we analyzed the wind-driven sea level anomalies focusing on Singapore Strait (SS), laying at the most southwest point of the region. An analysis of Tanjong Pagar tide gauge data in the SS, as well as satellite altimetry and reanalyzed wind in the region, reveals that the wind over central part of SCS is arguably the most important factor determining the observed variability of SLAs at hourly to monthly scales. Climatological SLAs in SS are found to be positive, and of the order of 30 cm during NE monsoon, but negative, and of the order of 20 cm during SW monsoon. The largest anomalies are associated with intensified winds during NE monsoon, with historical highs exceeding 50 cm. At the hourly and daily time-scales, SLA magnitude is correlated with the NE wind speed over central part of SCS with an average time lag of 36–42 h. An exact solution is derived by approximating the elongated SCS shape with one-dimensional two-step channel. The solution is utilized to derive simple model connecting SLAs in SS with the wind speeds over central part of SCS. Due to delay of sea level anomaly in SS with respect to the remote source at SCS, the simplified solutions could be used for storm surge forecast, with a lead time exceeding 1 day.     

Holocene seasonal sea‐surface temperature variations in the southern Adriatic Sea inferred from a multiproxy approach

Holocene cooling events have been reconstructed for the southern Adriatic Sea (central Mediterranean) by means of analyses of organic walled dinoflagellate cysts, planktonic foraminifera, oxygen isotopes, calcareous nanoplankton, alkenones and pollen from a sediment core. Two cooling events have been detected, during which sea‐surface temperatures (SSTs) were ca. 2°C lower. Unravelling the SST signal into dominant seasonal components suggests maximum winter cooling of 2°C at around 6.0 ka, whereas the cooling at ca. 3.0 ka might be the result of a spring temperature cooling of 2–3°C. The events, lasting several hundred years, are apparently synchronous with those in the Aegean Sea, where they have been related to known cooling events from the Greenland ice‐core record. A distinct interruption in Adriatic Sea sapropel S1 is not clearly accompanied by a local drop in winter temperatures, but seems to be forced by ventilation, which probably occurred earlier in the Aegean Sea and was subsequently transmitted to the Adriatic Sea. Copyright © 2003 John Wiley & Sons, Ltd.     

Study on potential tsunami by earthquake in subduction zone of Sulawesi Sea

Indonesia is one country in the world featuring a complex tectonic structure. This condition makes earthquakes often occur in many areas of this country and as an earthquake rages beneath the sea, it will potentially trigger tsunami. One of the areas in Indonesia with a high seismic activity is Sulawesi region particularly in the Sulawesi Sea subduction zone, making it important to carry out a study on the potential tsunami at this location. The purpose of this study was to analyze the existing huge potential energy in Sulawesi Sea subduction zone and to identify tsunami modeling likely to occur based on the potential energy of the region. The approach used in assessing the tsunami disaster was the calculation of the potential energy of an earthquake and tsunami modeling based on the potential energy. The method used in this research was the least squares method for the calculation of potential energy, and near-field tsunami modeling with the assistance of TUNAMI-N2 COD. The research finding has shown that the Sulawesi Sea subduction zone has potential energy of 1.35469?×?10²³ erg, equivalent to an earthquake with a magnitude of 7.6 Mw. The tsunami modeling made shown the average wave propagation reaching ashore within 12.3 min with a height varying between 0.1 and >?3 m. The tsunami modeling also indicated that there are seven sub-districts in Buol District, Central Sulawesi, which is affected by a significant tsunami.     

Spatiotemporal variations of extreme sea levels around the South China Sea: assessing the influence of tropical cyclones,monsoons and major climate modes

With sea levels projected to rise as a result of climate change, it is imperative to understand not only long-term average trends, but also the spatial and temporal patterns of extreme sea level. In this study, we use a comprehensive set of 30 tide gauges spanning 1954–2014 to characterize the spatial and temporal variations of extreme sea level around the low-lying and densely populated margins of the South China Sea. We also explore the long-term evolution of extreme sea level by applying a dynamic linear model for the generalized extreme value distribution (DLM-GEV), which can be used for assessing the changes in extreme sea levels with time. Our results show that the sea-level maxima distributions range from ~?90 to 400 cm and occur seasonally across the South China Sea. In general, the sea-level maxima at northern tide gauges are approximately 25–30% higher than those in the south and are highest in summer as tropical cyclone-induced surges dominate the northern signal. In contrast, the smaller signal in the south is dominated by monsoonal winds in the winter. The trends of extreme high percentiles of sea-level values are broadly consistent with the changes in mean sea level. The DLM-GEV model characterizes the interannual variability of extreme sea level, and hence, the 50-year return levels at most tide gauges. We find small but statistically significant correlations between extreme sea level and both the Pacific Decadal Oscillation and El Niño/Southern Oscillation. Our study provides new insight into the dynamic relationships between extreme sea level, mean sea level and the tidal cycle in the South China Sea, which can contribute to preparing for coastal risks at multi-decadal timescales.

     

Tracing submarine groundwater discharge flux in Tolo Harbor,Hong Kong (China)

Submarine groundwater discharge (SGD) is an important pathway for groundwater and associated chemicals to discharge to the sea. Groundwater levels monitored along a transect perpendicular to the shoreline are used to calculate SGD flux from the nearshore aquifer to Tolo Harbor, Hong Kong (China). The calculated SGD flux—recharge/discharge measured with Darcy’s Law methods—agrees well with estimates based on geo-tracer techniques and seepage meter in Tolo Harbor during previous studies. The estimated freshwater SGD is 1.69–2.0 m²/d at the study site and 0.3?±?0.04 cm/d for the whole of Tolo Harbor, which is comparable to the river discharge (0.25?±?0.07 cm/d) and precipitation (0.45?±?0.15 cm/d). The tide-driven SGD in the intertidal zone is 13.98–17.59 m²/d at the study site and 2.42?±?0.56 cm/d for the whole of Tolo Harbor. The SGD occurring in the subtidal zone and the bottom of Tolo Harbor is 3.12?±?4.63 cm/d. Fresh SGD accounts for ~5% of the total SGD, while the rest (~95%) is contributed by saline SGD driven by various forces. About 96% of the tide-driven SGD in the intertidal zone occurs in the ebbing tide period because the head difference between the groundwater level and sea level is great during this period. Tide-driven SGD in the spring tide is ~1.2 times that during neap tide. The tidal fluctuation amplitude and tide-driven SGD in the intertidal zone are positively correlated to each other; thus, a spring neap variation of the tide-driven SGD is observed.     

The origin of the Dead Sea rift

The Dead Sea rift is considered to be a plate boundary of the transform type. Several key questions regarding its structure and evolution are: Does sea floor spreading activity propagate from the Red Sea into the Dead Sea rift? Did rifting activity start simultaneously along the entire length of the Dead Sea rift, or did it propagate from several centres? Why did the initial propagation of the Red Sea into the Gulf of Suez stop and an opening of the Gulf of Elat start?

Using crustal structure data from north Africa and the eastern Mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half-space, the regional stress field in this region was calculated. Using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust. By application of a strain-dependent visco-elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization, corresponding to the high value of the damage parameter i.e. fault zones.

Mathematical simulation of the plate motion and faulting process suggests that the Dead Sea rift was created as a result of a simultaneous propagation of two different transforms. One propagated from the Red Sea through the Gulf of Elat to the north. The other transform started at the collision zone in Turkey and propagated to the south.     

On causes and impacts of land subsidence in Bandung Basin, Indonesia

The Bandung Basin is a large intra-montane basin surrounded by volcanic highlands, in western Java, Indonesia, inhabited by more than seven million people. The basin, an area of about 2,300 km², is a highland plateau at approximately 650–700 m above sea level and is surrounded by up to 2,400 m high Late Tertiary and Quaternary volcanic terrain. Based on the results of nine GPS surveys conducted since 2000 up to 2011, it was shown that several locations in the Bandung Basin have experienced land subsidence, with an average rate of about ?8 cm/year and can go up to about ?23 cm/year in certain locations. A hypothesis has been proposed by several studies that land subsidence observed in several locations in the Bandung Basin has been caused mainly by excessive groundwater extraction. It is found that there is a strong correlation between the rates of groundwater level lowering with the GPS-derived rates of land subsidence in several locations in Bandung Basin. The GPS results in this study detected significant subsidence in the textile industry area, where very large volumes of groundwater are usually extracted. The impact of land subsidence in Bandung can be seen in several forms, mainly in the cracking and damage of houses, buildings and infrastructure. Land subsidence also aggravates the flooding in Bandung Basin, which has brought huge economic losses and deteriorated the quality of life and environment in the affected areas.     

关于矿床学创新问题的探讨

2003年1月4日至2月15日期间,在5种不同情况下对南极海冰进行了调查研究。包括:(1)基于走航观测的威德尔海至普利茨湾之间海冰分布研究;(2)基于航空拍摄的普利茨湾海冰分布研究;(3)纳拉海峡固定冰和上浮雪厚度钻孔测量以及冰心钻取;(4)中山站附近融化冰的分布研究以及(5)中山站附近海冰早期冻结过程观测研究。结果表明,威德尔海至普利茨湾之间走航观测得到的海冰全部密集度为14.4%,大部分冰(99.7%~99.8%)属于一年冰,观测到冰的厚度在15~150 cm。沿观测航线上海冰最大密集度(80%)出现在威德尔海,从59°56 S到69°22 S以及从040°41 W到076°23 E的区域分布着广阔的水域。这一结果验证了Silvia的海冰漂移理论。普利茨湾沿岸海冰受制于沿岸地形、拉斯曼丘陵以及搁浅冰山的影响,其密集度呈现较大的空间变化。钻孔测量显示,纳拉海峡固定冰平均厚度为169.5 cm。风吹雪的重分布以及日照强度差异是导致纳拉海峡固定冰厚度差异的主要因素。观测表明,中山站附近海冰早期冻结遵循Lange的海冰早期冻结过程“饼状循环”最初的两个阶段。     

Tectonic indentation in the central Alboran Sea (westernmost Mediterranean)

The Alboran Sea constitutes a Neogene–Quaternary basin of the Betic–Rif Cordillera, which has been deformed since the Late Miocene during the collision between the Eurasian and African plates in the westernmost Mediterranean. NNE–SSW sinistral and WNW–ESE dextral conjugate fault sets forming a 75° angle surround a rigid basement spur of the African plate, and are the origin of most of the shallow seismicity of the central Alboran Sea. Northward, the faults decrease their transcurrent slip, becoming normal close to the tip point, while NNW–SSE normal and sparse ENE–WSW reverse to transcurrent faults are developed. The uplifting of the Alboran Ridge ENE–WSW antiform above a detachment level was favoured by the crustal layering. Despite the recent anticlockwise rotation of the Eurasian–African convergence trend in the westernmost Mediterranean, these recent deformations—consistent with indenter tectonics characterised by a N164°E trend of maximum compression—entail the highest seismic hazard of the Alboran Sea.     

L'évolution séculaire des températures de surface de la mer Méditerranée (1856–2000)

The mean sea surface temperature anomalies (SSTA) of the Mediterranean Sea during the past 150 years (1856–2000) are analysed. The first empirical orthogonal function (EOF) of the covariance matrix of the SSTA explains more than 45% of the variance, suggesting that the temporal variation of the Mediterranean Sea is largely in phase over the whole basin. The mean variability of Mediterranean SSTA from 1856 to 2000 superposes a main irregular oscillation (period of 60–70 years and mean amplitude of 0.4–0.5 °C) and a weak long-term positive trend (equivalent to an increase of +0.1 °C per century). The last warm phase, which is strongest in the western basin, is not warmer than the decade 1935–1945 or the ending part of the 1960s. The mean temporal evolution of the North Hemisphere is close to the variation of the Mediterranean Sea, except that the long-term increase is more intense in the North Hemisphere. To cite this article: V. Moron, C. R. Geoscience 335 (2003).     

Past methane release events and environmental conditions at the upper continental slope of the South China Sea: constraints by seep carbonates

Authigenic carbonates and seep biota are archives of seepage history and record paleo-environmental conditions at seep sites. We obtained the timing of past methane release events at the northeastern slope of the South China Sea based on U/Th dating of seep carbonates and seep bivalve fragments from three sites located at 22°02′–22°09′N, 118°43′–118°52′E (water depths from 473 to 785 m). Also, we were able to reconstruct the paleo-bottom water temperatures by calculating the equilibrium temperature using the ages, the corresponding past δ¹⁸O of seawater (δ¹⁸O_sw) and the δ¹⁸O of the selected samples formed in contact with bottom seawater with negligible deep fluid influence. A criterion consists of mineralogy, redox-sensitive trace elements and U/Th-isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid. Our results show that all methane release events occurred between 11.5 ± 0.2 and 144.5 ± 12.7 ka, when sea level was about 62–104 m lower than today. Enhanced methane release during low sea-level stands seems to be modulated by reduced hydrostatic pressure, increased incision of canyons and increased sediment loads. The calculated past bottom water temperature at one site (Site 3; water depth: 767–771 m) during low sea-level stands 11.5 and 65 ka ago ranges from 3.3 to 4.0 °C, i.e., 1.3 to 2.2 °C colder than at present. The reliability of δ¹⁸O of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of ¹⁸O-enriched fluids that might be emitted from gas hydrate and/or clay dehydration. Our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the South China Sea.     

Caspian Sea level prediction using satellite altimetry by artificial neural networks

The demand for accurate predictions of sea level fluctuations in coastal management and ship navigation activities is increasing. To meet such demand, accessible high-quality data and proper modeling process are critically required. This study focuses on developing and validating a neural methodology applicable to the short-term forecast of the Caspian Sea level. The input and output data sets used contain two time series obtained from Topex/Poseidon and Jason-1 satellite altimetry missions from 1993 to 2008. The forecast is performed by multilayer perceptron network, radial basis function, and generalized regression neural networks. Several tests of different artificial neural network (ANN) architectures and learning algorithms are carried out as alternative methods to the conventional models to assess their applicability for estimating Caspian Sea level anomalies. The results derived from the ANN are compared with observed sea level values and with the forecasts calculated by a routine autoregressive moving average (ARMA) model. Different ANNs satisfactorily provide reliable results for the short-term prediction of Caspian Sea level anomalies. The root mean square errors of the differences between observations and predictions from artificial intelligence approaches can be significantly reduced by about 50 % compared with ARMA techniques.