Monitoring absolute vertical land motions and absolute sea-level changes from GPS and tide gauges data over French Polynesia

In this study,we estimate the absolute vertical land motions at three tidal stations with collocated Global Navigation Satellite System(GNSS)receivers over French Polynesia during the period 2007-2020,and obtain,as ancillary results,estimates of the absolute changes in sea level at the same locations.To verify our processing approach to determining vertical motion,we first modeled vertical motion at the International GNSS Service(IGS)THTI station located in the capital island of Tahiti and compared our estimate with previous independent determinations,with a good agreement.We obtained the following estimates for the vertical land motions at the tide gauges:Tubuai island,Austral Archipelago-0.92±0.17 mm/yr,Vairao village,Tahiti Iti:-0.49±0.39 mm/yr,Rikitea,Gambier Archipelago-0.43±0.17 mm/yr.The absolute variations of the sea level are:Tubuai island,Austral Archipelago 5.25±0.60 mm/yr,Vairao village,Tahiti Iti:3.62±0.52 mm/yr,Rikitea,Gambier Archipelago 1.52±0.23 mm/yr.We discuss these absolute values in light of the values obtained from altimetric measurements and other means in French Polynesia.

Response of phytoplankton communities to environmental changes in the Bohai Sea in late summer (2011−2020)

Understanding the dynamics of phytoplankton communities in coastal zones is crucial for the management and conservation of coastal ecosystems.Previous research indicated that the phytoplankton community structure and dominant taxa in the Bohai Sea(BHS)have exhibited significant shifts from the 1990s to the early 2010s in response to environmental changes,especially the change in nutrient structure.This study comprehensively investigated the variations in net-collected phytoplankton(>76μm)community structure,diversity,and environmental factors in the BHS during the late summers of 2011-2020,aiming to understand the recent trend in phytoplankton community structure and to explore the interactions between the communities and the environment.During the study period,the nutrient status in the BHS was characterized by a decrease in dissolved inorganic nitrogen(DIN)concentration,an increase in dissolved inorganic phosphorus(DIP)concentration,and a return of the nitrogen-to-phosphorus(N/P)molar ratio(hereinafter referred to as N/P ratio)to the Redfield ratio since 2016.The eutrophication index(EI)in the BHS remained stable and was generally at a low level(<1).The Dia/Dino index fluctuated but did not show an obvious trend.Overall,the eutrophication,the imbalance in nutrient ratio,and the shift in phytoplankton community structure did not continue during the study period.The increased abundance of phytoplankton was strongly associated with elevated concentrations of DIN,as well as higher N/P and nitrogen-to-silicon(N/Si)ratios,whereas the greater diversity was strongly linked to higher concentrations of DIP.Diatoms and dinoflagellates showed significant differences in their interactions with the environment,and their relative dominance was related to water column depth and stratification intensity;their impacts on the phytoplankton community diversity were also significantly different.The variations of certain dominant species,i.e.,Skeletonema costatum,Paralia sulcata,and Tripos longipes,exhibited strong links to the changes in nutrient structure in the BHS.The findings of this study contribute to understanding the regional environmental changes and provide insights into the adaptive strategies of coastal ecosystems in response to environmental shifts and fluctuations.

Effects of Natural Processes on Sea Level Change along the West African Coastline

Coastal hazards induced by meteo-marine forcing are exacerbated by sea level change along the West African coastline. Changes in sea level are induced by ocean processes such as ocean heat content and river discharge. However, although these processes control largely change in sea level, they remain poorly understood. This study analyzes changes in ocean heat content, river discharge, and sea level and establishes an interconnection between these parameters using several statistical methods over the 1993-2021 period. Results showed a significant correlation between sea level and ocean heat content at 2000 m depth. The yearly minimum value appears in July from Cote d’Ivoire to Benin, whilst this value appears in June in Nigeria. The temporal variability of ocean heat content, river discharge and sea level along the West African coastline exhibits three or four periods interrupted by some breakpoints with unequal duration. The results indicate that the 1993-2000 period was dominated by an increasing ocean heat content along the coastline, while the period after the 2000s exhibits mostly a decreasing trend. Positive and negative trends characterized river discharge and sea level along this coastline. The result of multiple linear regression between sea level, river discharge and ocean heat content is a good approximation of sea level trend along the West African coastline. The results of this study could be used to predict future sea level trends along the coast.

Late Permian-Middle Triassic Sea Level Changes of Yangtze Platform

This paper first introduces procedures leading to the establishment of Late Permian-Middle Triassic sea level change curve of Yangtze platform. Bathymetric curves extracted from curve of habitat types are first transformed to sea level curves stage by stage. Comparison between curves of Yangtze and the world reveals that because the Late Permian marine sequences are lacking in most parts of the world, the Late Permian to Griesbachian curve of Yangtze may serve as an important reference for further revision of the world curve. The Early-Middle Triassic short-term changes of Yangtze are briefly concordant with those of Haq's world curve, whereas their long-term changes are discordant. The latter, however, is representative of the East Asian regions affected by the Indosinian orogeny. Basically the third cycles of Yangtze and the world are only pertly concordant, and even in concordant cases their concrete boundaries are not coincident. This indicater that sea level changes are not strictly synchronous over the world. It seems that the 1st and 2nd cycles (supercycles and megacycles) may be world-wide, but not the 3rd cycles.

Triassic Sequence Stratigraphy and Sea-Level Changes in Qomolongma Area, Southern Tibet, China: From Epicontinental Sea to Rift Basin

The Triassic in the Qomolongma area, southern Tibet, was deposited under an extensional tectonic setting from the Pangea supercontinent to continental rifting. From the Induan to Rhaetian, 12 depositional sequences (3rd order) have been recognized, which can be grouped into 5 sequence sets and in turn make up a well defined mesosequence (2nd order). Among the recognized marine transgressions, those at 250 Ma, 239 Ma, 231 Ma and 223 Ma respectively are particularly of significance and can be correlated widely across continents. The study shows that in Triassic the Qomolongma area experienced a sedimentary evolution from epicontinental sea to rift basin with the turning point at ca 228 Ma. During the early and middle epochs, the area was under epeiric sea, with carbonate ramp to mixed shoal environments predominant. In the late Carnian, the strong extension initiated listric faulting, thus resulting in rapid basement subsidence and the onset of a rift basin. From the late Norian to Rhaetian, it manifested as a rapid basin filling process in the area. Coupled with long term sea level fall, the excessive terrigenous influx led to the shift of environment from deep water prodelta to shore and finally to fluvial plain.

Tertiary Sea Level Changes and Sequence Stratigraphic Framework in East China Sea Shelf Basin

The East China Sea shelf basin is a key area for setting up the sea level changes of Cenozoic in the West Pacific. Based upon the characteristics of seismic reflection, the analysis of sequence stratigraphy and depositional system, the high resolution chronostratigraphic framework has been set up by using the data of micropaleontologic biozone fossils. The relative sea level change curve has been set up by combining analysis of paleoecology, genetic facies, specific sedimentary structures and on lap recognized from the seismic profiles with study of geochemical characteristics. There are 4 2nd order basin cycles showing the long term sea level changes, and 22 3rd order cycles showing short term ones with relative changing ranges of 0-150 m. Transgression and regression showing long term sea level changes bear asymmetric feature, which indicates that the speed of transgression is faster than that of regression. There are a lot of differences when compared with Haq ’s curve. The sequence stratigraphic framework has also been set up and 3 tectonic sequences, 7 supersequences and 19 sequences have been subdivided for Tertiary in the East China Sea shelf basin. On the basis of detailed analysis of genetic facies and log facies, 9 sedimentary systems, 20 depositional assemblages and many genetic facies have also been recognized and investigated. Based on the studies mentioned above, the favorable source and reservoir facies of gas and petroleum are indicated.

Late Quaternary diatom and sea level changes in estuarine plain of the Jiulong River

Four units and twenty-four zones of diatom have been discerned in the Borehole ZK5 in the estuarine plain of the Jiulong River, Fujian Province. Comprehensive analysis of these, together with microbiological assemblages and age determinations in some other boreholes, shows that during the Late Wurm Glacial, sea level of the study area rose and fell frequently, but had principally been in the environments of estuary-bay. This mainly resulted from the tectonic subouction. In this period 3 low sea levels occurred. at 18, 16 and 12 kaBP respectively. During Holocene, sea weter intruded massively and the sea level over the transgnaion maximum had been 5-10 m higher than that of the present.

Permian and Triassic Sequence Stratigraphy and Sea Level Changes of Eastern Yangtze Platform

The Permian and marine Triassic of eastern Yangtze platform, situated in eastern China, involve 19 orthosequences lasting about 2.7 Ma on average, which can be combined into five orthosequence sets ranging from 8 Ma to 12 Ma. Affected by the regional Dongwu and Indosinian movements, the sequence stratigraphic pattern and sea level changes in the Permian and Triassic of this region are distinctive and obviously different from most other regions in the world, but typical in the broad eastern Tethys and its neighboring areas. In this region not only did the continuous marine Permian and Triassic boundary sequences cause the orthosequence crossing the boundary belonging to type Ⅱ sequence but also the mesosequence including these stratigraphic intervals had its basal boundary in the upper Longlinian (Artinskian) (ca. 278 Ma), that is, the traditional Carboniferous and Permian boundary, and its top boundary moved from the Permian and Triassic boundary upward into the Anisian of Middle Triassic.

Sea-level changes controlled detrital sediment inputs to the Bicol Shelf in the western Philippine Sea since 150 ka

Detrital sediments derived from the Philippine Islands are one of the main sources of deep-sea sediments in the western Philippine Sea.However,systematic research on their characteristics and transport mechanisms are lacking.We used parametric end-member analysis to quantitatively partition the grain size of detrital sediments in core MD06-3052 from the Bicol Shelf in the western Philippine Sea;three endmembers EMI,EM2,and EM3,whose respective modes were at 2,10,and 45 μm,were separated.We also measured the Sr and Nd isotopic compositions of different size fractions(<4 and >20 μm) of the detrital sediments and the results showed that the detrital sediments mainly originate from the Philippine Islands.Components EMI and EM2 are transported to the Bicol Shelf mainly by surface and bottom currents from the islands,and component EM3 is delivered by gravity flow from the exposed shelf during low sea-level stands.The content of the total detrital fraction and the three end-members,as well as the mass accumulation rates(MARs) of the coarse detritus(EM2 and EM3),were considerably higher during glacial periods(40-14 ka and 150-130 ka) than during other intervals;the glacials corresponded to a low sea level,while the MAR of the fine detritus(EMI) did not increase remarkably during 40-14 ka.We therefore concluded that the input of coarse detritus to the Bicol Shelf from the islands was mainly controlled by sea-level change.Variations of the input of fine-grained detritus(EM1) was influenced not only by sea level but also by ocean currents and regional precipitation.Overall,our results help understand "source-to-sink" processes in the western Pacific marginal seas and their response to global change.

Evaluation of vertical crustal movements and sea level changes around Greenland from GPS and tide gauge observations

To better monitor the vertical crustal movements and sea level changes around Greenland,multiple data sources were used in this paper,including global positioning system(GPS),tide gauge,satellite gravimetry,satellite altimetry,glacial isostatic adjustment(GIA).First,the observations of more than 50 GPS stations from the international GNSS service(IGS)and Greenland network(GNET)in 2007–2018 were processed and the common mode error(CME)was eliminated with using the principal component analysis(PCA).The results show that all GPS stations show an uplift trend and the stations in southern Greenland have a higher vertical speed.Second,by deducting the influence of GIA,the impact of current Gr IS mass changes on GPS stations was analysed,and the GIA-corrected vertical velocity of the GPS is in good agreement with the vertical velocity obtained by gravity recovery and climate experiment(GRACE).Third,the absolute sea level change around Greenland at 4 gauge stations was obtained by combining relative sea level derived from tide gauge observations and crustal uplift rates derived from GPS observations,and was validated by sea level products of satellite altimetry.The results show that although the mass loss of Gr IS can cause considerable global sea level rise,eustatic movements along the coasts of Greenland are quite complex under different mechanisms of sea level changes.

Early Ordovician Sea Level Changes in South China and Their Worldwide Correlation

The sea level changes and their correlation from the latest Cambrian C. proavus zone to the Ordovician N. gracilis zone in South China are discussed on the basis of the Ordovician paleogeographic reconstruction in China. The study of sequence, biostratigraphy and ecostratigraphy suggests that at least 8 major regressive events, occurring in the following levels: basal H. simplex zone (RE1), near the base of C. intermedius zone (RE2), basal C. angulatus zone (RE3), near Mid/Upper G. quadriplicatus zone (RE4) and succeeding the first phase (RE4a) of RE4 at basal P. deltifer zone, Kiaerograptus/Brygograptus zonal boundary (RE5), end S.diversus-P.proteus A. Z.(RE6), end P. originalis zone (RE7) and Early H. teretiusculus or end P. serra zone (RE8), can be recognized in the cratonic plat- form and its shelf-slope tracts of the South China plate based on sequence change or disconformity and associated breaks in biological succession. Most of them can be traced in the other plates or continents.

Holocene sea level changes and coastline snitts in Zhejiang Province, China

In the present paper, the Holocene sea level changes and coastline shifts in Zhejiang, China are discussed, based on the ancient coastline evidence related with sea level changes and 21 14C dat-ings of shell, peat or mud and wood samples along the Zhejiang coast. The development of Zhejiang coastline during the Holocene period can be divided into four stages. A lot of data of historical period and modern times have shown that tracing coastline shifts back to its source, we have to consider tremendous effects of man's activities besides natural factors, such as elevation and subsidence of the earth crust, sea level changes, supply of sediment, and littoral hydrodynamics.

An Outline of Mesozoic to Paleogene SequenceStratigraphy and Sea－Level Changes in Northern Himalayas，Southern Xizang

In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequences and 6 super-sequence sets. During Mesozoic and Paleogene, several large sea - level falls occurred in the Eastern Neo-Tethys. Among the recognized sea- level falls, the important ones include those at the ages of 255 Ma, 215 Ma,177 Ma, 138 Ma, 103 Ma and 68 Ma .Those at 239 Ma, 215 Ma, 157 Ma,80 Ma, 50Ma and 36 Ma are also significant. The third-order Sequences and sea-level cycles Probably reflect mainly global sea - level fluctuations, while the higher rank cycles seem more closely related to the basin evolution of the Neo-Tethys. Based on the study, six major periods have been suggested for ths tectonic evolution of the Eastern Neo-Tethys and the plates, i. e. the Pangea Period (Pre-Triassic), continental rifting Period (Triassic to Early Jurassic ), inter-continental sea Period (Middle Jurassic ), continental divergence period (late Middle Jurassic to Early Cretaceous ), continental convergence period (Late Cretaceous ) and the continental collision Period (Paleogene ). These major Periods can be further subdivided into eight stages according to the basin evolution. In each of the periods and Stages, Sequences and their boundaries show clear characters related to the tectonic background. The study indicater that the initial breakup of the Pangea along the Indus- Yarlung may have taken Place around 239 Ma. The Late Bathonian to Early Callovian seems to have been a critical time in the evolution of the Neo-Tethys, with the turning Point around 158 Ma. The blocks split from the northern margin of the Gondwana continual did not obviously drift away from the Indian Plate until Callovian .The oceanic crust subduction in the Neo- Tethys may have Started at 113Ma, while the contraction of the ocean probably began at 107- 103 Ma. The initial contact of the Indian Plate with the Eurasian plate may have taken Place around 80 Ma, with strong uplifting and thrushng in Late Paleocene.

Nontidal sea level changes in Hiroshima Bay,Japan

Nontidal sea level changes generated in Hiroshima Bay of the Seto-Inland Sea in Japan are studied over various time scales, from the sub-tidal （2 d to 1 month） to inter-annual scales （〉2 years）. The total sea level variation produces a standard deviation （STD） of 12.5 cm. The inter-annual component of the sea level variation in Hiroshima Bay oscillates with a STD of 3.4 cm, forming a long-term trend of 4.9 mm/a. The STD of the sea level variation is 9.8 cm for the seasonal component （8 months to 2 years） and 4.7 cm for the intra-seasonal one （1 month to 8 months）. Significant sea level variations with a STD of 4.2 cm also occur in the sub-tidal range. Special attention is paid to the sub-tidal sea level changes. It is found that the upwelling and associated transient sea level changes generated along the north coast of Hiroshima Bay （opened southward） by the strong northerly wind, play a significant role in sub-tidal sea level changes. The transient sea level changes are over 10 cm in most cases when caused by typhoons that pass through the Pacific Ocean offthe Kii Peninsula, located at about 400 km east of Hiroshima Bay. Reasonable sea level changes are evaluated by the balance of pressure forces at the onshore and offshore boundary of the study domain.

Rates of Sea Level Changes—A Clarifying Note

The values of present to future rates in sea level changes vary in an almost chaotic way. In view of the urgent need to handle this question in a constructive way, we must anchor the issue in observational facts, physical laws and long-term scientific experience. Doing so, we can put a solid ultimate frame of any possible rise in sea level in the next centuries: viz. 10.0 mm/yr or 1.0 m per century. If this is the ultimate possible rate, the expected rate in the 21st century must be far less. The author’s proposition is +5 cm ± 15 cm by year 2100.

Permo-Carboniferous Sequence Stratigraphy and Sea Level Changes in North China Platform

Through a sequence stratigraphic research on the Permo-Carboniferous in North China, it is suggested that the boundary of the Carboniferous and the Permian may be better moved down to the bottom of the main workable coalbed which is overlain by the limestones containing Pseudoschwagerina zone. This study mainly deals with the Upper Carboniferous, the Lower Permian and the lower part of the Middle Permian coal bearing strata, which are 150-180 m thick totally and can be divided into 2 mesosequences, including 6 sequence sets and 19 sequences. The lithostratigraphic units are diachronous in North China. The upper two limestones of the Taiyuan Formation in the central part of the study area may be correlated with the bottom two limestones of the lower Taiyuan Formation in the southern part. The Shanxi Formation in the central and northern parts may be correlated with most of the Taiyuan Formation in the southern part. The Xiashihezi Formation in the northern part may be correlated with the upper part of Shanxi Formation in the central and southern parts. The Shangshihezi Formation in the northern part may be correlated with the Xiashihezi Formation in the southern part. The paleogeographical maps are compiled in a chrono stratigraphic framework. From the Late Carboniferous to the Early Permian, 3 cycles of sea level change and transgression regression occurred, and the major transgression took place in the Asselian. In the Late Carboniferous, the direction of transgression was from the east to the west, and in the Early Permian it was from the southeast and the southwest to the north. Three workable coalbed groups were formed in Asselian, early Sakmarian and late Sakmarian respectively. The TST coals developed under the bottom of the Asselian limestones are the best coals for coalbed meathane extracting. The Sakmarian coal beds were formed in HST. The coal beds of Lower Permian distribute southward along with the relative sea level falls and sediment progradation.

Estimating trends of the Mediterranean Sea level changes from tide gauge and satellite altimetry data (1993-2015)

The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of studies based on tide gauges observations and satellite altimetry measurements. This study focuses on trend estimates from 18 high-quality tide gauge stations along the Mediterranean Sea coast. The seasonal Mann-Kendall test was run at a 5% significance level for each of the 18 stations for the period of 1993-2015 (satellite altimetry era). The results of this test indicate that the trends for 17 stations were statistically significant and showed an increase (no significant trend was observed only at one station). The rates of sea level change for the 17 stations that exhibit significant trends, estimated using seasonal Sen's approach, range after correction for Vertical Land Motion (VLM) from 1.48 to 8.72 mm/a for the period 1993-2015. Furthermore, the magnitude of change at the location of each tide gauge station was estimated using the satellite altimetry measurements. Thus, the results obtained agree with those from the tide-gauge data analysis.

Mean Sea Level Changes near Weizhou Island from 1969 to 2010

Tidal data from Weizhou, Zhapo, and Shanwei stations between 1969 and 2010 and from five gauging stations in the western Pacific Ocean provided by PSMSL, and the global mean sea level data recorded between December 1992 and December 2010 by TOPEX and Jason satellites were compiled and analyzed. The results show that the perennial mean sea level near Weizhou Island is 211.7 cm(relative to the water gauge zero), and the relative mean sea level rising rate is 2.2 mm yr-1 from 1969 to 2010, which is consistent with the relative mean sea level rising rate recorded at other gauging stations in the western Pacific regions and with the global mean sea level rising rate. The absolute mean sea level rising rate at Weizhou Island is 3.0 mm yr-1 from 1993 to 2010, also conforming with the global mean sea level rising rate(3.1±0.4 mm yr-1) during the same time period. The highest annual tide level at Weizhou Island has a rising rate of 4.6 mm yr-1 and shows a 20-year quasi-periodic variation from 1966 to 2010. The primary cause of the mean sea level rising is global warming.

Organic Carbon Deposition on the Inner Shelf of the East China Sea Constrained by Sea Level and Climatic Changes Since the Last Deglaciation

The East China Sea(ECS),which is located in the transitional zone between land and ocean,is the main site for the burial of sedimentary organic carbon.Despite good constraints of the modern source to the sinking process of organic carbon,its fate in response to changes in climate and sea level since the last deglaciation remains poorly understood.We aim to fill this gap by presenting a high-resolution sedimentary record of core EC2005 to derive a better understanding of the evolution of the depositional environment and its control on the organic deposition since 17.3 kyr.Our results suggest that sedimentary organic carbon was deposited in a terrestrial environment before the seawater reached the study area around 13.1 kyr.This significant transition from a terrestrial environment to a marine environment is reflected by the decrease in TOC/TN and TOC/TS ratios,which is attributed to deglacial sea level rise.The sea level continued to rise until it reached its highstand at approximately 7.3 kyr when the mud depocenter was developed.Our results further indicate that the deposition of the sedimentary organic carbon could respond quickly to abrupt cold events,including the Heinrich stadial 1 and the Younger Dryas during the last deglaciation,as well as‘Bond events'during the Holocene.We propose that the rapid response of the organic deposition to those cold events in the northern hemisphere is linked to the East Asian winter monsoon.These new findings demonstrate that organic carbon deposition and burial on the inner shelf could effectively document sea level and climatic changes.

Modern sea level changes of the Eastern China Seas and their influences on coastal areas

The statistics of tidal gauging records showed that the mean sea level of the China Seas has risen for 14 cm in past 100 years. The annual mean sea levels of the Eastern China Seas have been rising at a speed of about 0.21 -0.23 cm/a since 1960. The annual mean sea levels of the Eastern China Seas in 1989 were 1.45 cm higher than that in 1988 on average.The sea level rise may cause the damage of the dynamical balance of the natural environments in the coastal area? and form or strengthen many coastal disasters, such as storm-tide catastrophic events, sea water invasion landward, soil salinization in coastal lowland and plains, and beach erosion retreat.