Holocene Sea-level Change Research Articles

Holocene sea-level change and evolution of a mixed coral reef and mangrove system at Iriomote Island, southwest Japan

Exposed fossil microatolls and core samples from a coral reef and a mangrove forest at the Yutsun River mouth, Iriomote Island, southwest Japan, reveal the internal structure and temporal changes in the sedimentary processes of a mixed reef–mangrove system. Evidence from the core samples and fossil microatolls suggests sea level reached its present position before 5100 cal yr B.P., and a relative sea-level highstand of 1.1–1.2 m above the present sea level occurred from 5100 to 3600 cal yr B.P. This was followed by a gradual fall in relative sea level. The tectonically corrected sea-level curve indicates a stable sea level after 5100 cal yr BP., with a sea-level highstand of up to 0.4 m between 5100 and 3600 cal yr B.P.A nearshore reef dominated by massive Porites and arborescent Acropora initially developed at 6500–3900 cal yr B.P. Reef development was potentially terminated by relative sea-level fall and sediment discharge from the Yutsun River that affected the backreef environment. An offshore coral reef reached present-day sea level by 1000 cal yr B.P., forming a wave break that enabled the foundation of mangrove forest on the fringing reef after ∼1000 cal yr B.P. The reef development was significantly delayed compared with other coral reefs in the region with similar medium-to high-energy conditions, but it provided a calm environment in the backreef area that allowed the development of mangroves. These features demonstrate the chronology and causal relationship between coral reef and mangrove development under the influence of Holocene sea-level change and river discharge.

Holocene Indian Ocean sea level, Antarctic melting history and past Tsunami deposits inferred using sea level reconstructions from the Sri Lankan, Southeastern Indian and Maldivian coasts

Holocene sea level change in the northern Indian Ocean was studied using geochemical and geophysical approaches. Molluscs were sub-sampled for radiocarbon dating from sediment cores retrieved from a south Sri Lankan coastal lagoon. They were then combined with previously published sediment core radiocarbon ages from the same lagoon. We observe a ∼20-fold reduction in sedimentation rates at around 4 ka, attributed to a decrease in the rate of sea level rise. Previously reported radiocarbon ages based on total organic matter in the lagoon show remarkable agreement with our new dates suggesting stable and homogeneous sedimentation during the last 8 ka. Comparison of down core age trends of both data sets reveal that sediments are older than coeval molluscs, except for the horizons adjacent to the paleo Tsunami layers, indicating fresh and younger sediments are provided during Tsunami events, which could become a new proxy for identifying paleo Tsunamis. Compilation of previously reported sea level indicators from Sri Lanka, Southeastern India and the Maldives, together with predicted sea level obtained from a glacio-hydro-isostatic adjustment model (GIA), suggest that 3–4 m of global sea level equivalent ice sheet melting occurred during the Mid Holocene due to the retreat of the Antarctic and/or Greenland ice sheets. Previous works suggests late Holocene (ca. 4 ka) climate anomalies in both the low and high latitudes. We suggest the low latitude climate anomaly, transmitted via atmosphere to the high latitude during the late Holocene, seems to have induced changes in polar ice sheets.

Late Holocene sea level change along the coast of Fethiye Gulf in southwestern Turkey

AbstractIn the Fethiye Gulf on the southwest coast of Turkey, several submerged archaeological sites provide useful data about relative sea level changes since the Byzantine period. The current elevations of contemporary archaeological structures were measured to determine the amount of relative sea level change. The archaeological sea level markers in this seismically active region provide new data about the amount and period of relative sea level rise. Taking into consideration the time of the last use of the structures, instead of their time of construction, three different rates of vertical land movement of 2.18 ± 0.3, 2.96 ± 0.3, and 3.29 ± 0.5 mm/yr were estimated. These data indicate that tectonic activity differs from region to region, most likely related to local normal faults in the gulf. Recent earthquakes have confirmed active seismicity in this area. These results demonstrate that the changing sea levels in the Fethiye Gulf have been strongly influenced by vertical tectonic movement over the last 1,400 years. Results also contribute to studies of future coastal changes in the Fethiye Gulf and its surroundings.

Late Holocene sea-level changes in eastern Québec and potential drivers

Late Holocene sea-level changes can be reconstructed from salt-marsh sediments with decimetre-scale precision and decadal-scale resolution. These records of relative sea-level changes comprise the net sea-level contributions from mechanisms that act across local, regional and global scales. Recent efforts help to constrain the relative significance of these mechanisms that include sediment dynamics and isostasy, which cause relative sea-level changes via vertical land motion, ocean-atmosphere processes that influence regional-scale ocean mass redistribution, and ocean-cryosphere and steric interactions that drive global scale ocean-volume changes. There remains a paucity of high-resolution Late Holocene sea-level data from eastern Canada. This precludes an interrogation of the mechanisms that define sea-level changes over recent centuries and millennia in a region sensitive to oceanic (Atlantic Multidecadal Variability, Atlantic Meridional Overturning Circulation), atmospheric (North Atlantic Oscillation, Arctic Oscillation) and cryospheric (ice-mass balance) changes. We present new relative sea-level data that span the past three millennia from Baie des Chaleurs in the Gulf of St. Lawrence generated using salt-marsh foraminifera supported with plant macrofossil analyses. The accompanying chronology is based on radiocarbon and radionuclide analyses, which are independently verified using trace metal and microcharcoal records. Relative sea level has risen at a mean rate of 0.93 ± 1.25 mm yr−1 over the past ∼1500 years. Residual structure within the reconstruction (‘internal variability’) has contributed up to an additional 0.61 ± 0.46 mm yr−1 of short-lived RSL rise prior to 1800 CE. Following a sea-level low stand during the Little Ice Age, acceleration in relative sea-level rise is identified between 1800 and 1900 CE within the estimates of internal variability and from 1950 CE to present in both the secular and residual trends. Phases of relative sea-level changes in the Gulf of St. Lawrence are concomitant with periods of glacier mass loss following the Little Ice Age, phase periods of the North Atlantic Oscillation and the Atlantic Meridional Overturning Circulation and Northern Hemisphere warming. Quantifying the individual effects of these different mechanisms is important for understanding how ocean-atmosphere processes redistribute ocean-mass upon larger scale background ocean-volume changes.

The geological origin of the Umm Al-Binni Lake within the Ahwar of Southern Mesopotamia, Iraq

The Umm Al-Binni Lake is one of the well-known lakes within the Ahwar of southern Mesopotamia in Iraq. It is located about 45 km north of the confluence of the Tigris and Euphrates rivers. The Umm Al-Binni Lake has been postulated as a-meteorite-impact crater, particularly by geo-archeologists, based on indices such as shape, size, depth, and the presence of a perceived lake-rim structure. However, no unambiguous evidence of such an impact has been put forward to date though. The lake measures 3.4 km in diameter, and it has a polygonal shape, with a maximum depth of 3 m. The age of the alleged crater was estimated to be less than 5000 years (or earlier than 3000 BC), based on the reported deposition rates of the Tigris–Euphrates delta sediments as a result of the Holocene sea-level changes of the Arabian Gulf during that time around the Umm Al-Binni Lake area. In the current study, using geophysical data and remote-sensing techniques investigates the origin of the Umm Al-Binni Lake. The results of magnetic and gravity analyses showed that the Ahwar area of southern Mesopotamia, including the Umm Al-Binni Lake, was subjected to the differential subsidence of the basement faulted blocks, as the distribution of the lakes is mostly controlled by such basement tectonic zones of weakness. Satellite imagery also showed some evidence of anthropogenic activity that contributed to the shaping of the southern sector of the Lake rim, which locally displays an angular shape. None of the latter evidence could support any meteorite-impact origin for the Umm Al-Binni Lake.

The Variable Influences of Sea Level, Sedimentation and Exposure on Holocene Reef Development over a Cross-Shelf Transect, Central Great Barrier Reef

Coral reefs globally are impacted by natural and anthropogenic stressors that are compounded by climate change. Understanding past reef responses to natural stressors (cyclones, sea-level change, freshwater inputs, and sedimentation) can provide important insights to further understand recent (within the past century) trends in coral cover and diversity. Here we use a compilation of recently published data to investigate the Holocene development of five fringing reefs that are located on a cross-shelf transect on the central Great Barrier Reef, and that are exposed to varying degrees of natural and anthropogenic sedimentation, storm exposure, and Holocene sea-level change. Forty-two reef cores collected using a combination of manual percussion coring and hydraulic drilling techniques, were analysed and dated using uranium-thorium methods. The chronostratigraphic records of reef development established using 105 recently published radiometric ages and seven new uranium-thorium ages from the reef cores and fossil microatolls preserved across the reef flats were compared to investigate cross-shelf variations in reef development. This is the first study to conduct an internal investigation of reef framework across an inshore–offshore gradient to examine the varying levels of influence of sedimentation, sea level and cyclones. Our observations from the central Great Barrier Reef show that reefs furthest offshore from the mainland coast were typically initiated earliest after the post-glacial marine transgression. Reef flat size, morphology, and growth style varied according to constraints placed on reef development by the composition, depth, shape, and relief of the underlying substrate. We establish that terrigenous sedimentation had a marked effect on the development of inshore reefs closest to the mainland (within 10 km of the mainland coast). Periods of relatively high terrigenous sedimentation correspond with enhanced reef accretion rates, and also resulted in a superior record of palaeo-ecological coral composition (i.e., better preservation) at inshore sites. In contrast, mid-Holocene cyclones played a seemingly more important role in the development of reefs >10 km from the mainland; although cyclones clearly affect reefs closer inshore, their geomorphology is affected by a range of controlling factors. Insights provided by these five Holocene reef chronostratigraphies provide useful baseline understanding of reef condition and growth along a cross-shelf transect where the reefs are exposed to variable stressors.

Reply to: Punctuated transgression (?): Comment on Oliver, T.S.N., Donaldson, P., Sharples, C., Roach, M., and Woodroffe, C.D. “Punctuated progradation of the Seven Mile Beach Holocene barrier system, southeastern Tasmania”

Our interpretation of the depositional history of the prograded barrier at Seven Mile Beach in Tasmania, described in Oliver et al. (2017a), was based on the morphology of ridges apparent in the LiDAR-based digital elevation data and a sample of 14 optically-stimulated luminescence (OSL) ages. Dougherty (2018) has identified gaps in the chronology and speculated that progradation may have occurred as sea level fell from a mid-Holocene highstand inappropriately applying sea-level curves from mainland Australia. Despite a highstand being inferred by early research in Tasmania, glacio-isostatic modelling and recent sea-level studies adopted a prevailing view that excluded a highstand. Our observations led us to question this prevailing view and to suggest that it might be appropriate to reopen the debate on Holocene sea-level change in Tasmania. We welcome the renewed interest in the chronology and sea-level history of this prograded barrier, and look forward to further clarification based on new evidence. The site may have the potential to become one of the more continuous and better-constrained sea-level records in southern Australia.

The mode and timing of windward reef-island accretion in relation with Holocene sea-level change: A case study from Takapoto Atoll, French Polynesia

Takapoto Atoll (northern Tuamotu Islands, French Polynesia, Central Pacific) was selected as a test area to clarify the conditions of atoll island accretion in relation to mid- to late-Holocene sea-level changes. Surveys were conducted along two distinct cross-island profiles, on the windward coast of the atoll. In addition, the stratigraphy of an ocean-facing islet was described from an excavation in order to reconstruct the successive island accretionary stages.At both sites, the basement of the atoll-rims consists of conglomerate pavements on which lie shingle ridges, reaching 4 m in elevation. Stratigraphic analysis of the excavated ridge reveals alternation of gravelly sand-supported to gravel-dominated sediments. The chronology of island accretion is based on dating of 41 U/Th surface and excavated coral specimens. Ridge initiation occurred from about 1000 yr BP when sea level was close to its present position, shingle deposits progressively prograded from the lagoon margins oceanwards and were partially cemented at their bases. Cementation may have increased the resistance of the islets to erosion. As a result, some island lands accumulated and have persisted over the last millennium. The modern gross island morphology was acquired during the last 500 years. This model can be considered to be of regional value for the northern Tuamotu islands, adjusted for local thermal subsidence, hydroisostasy and/or lithospheric flexure.Compared to some other Indo-Pacific reef islands, island initiation at Takapoto appears to be have been delayed by 2 to 4 millennia, probably in response to retardation in the reef catching-up with mid-Holocene sea level. Dating of individual coarse-grained coral clasts allowed the major wave-surge events that have hit Takapoto to be identified for the last millennium. The use of gravels results in the identification of a greater number of medium-energy surge impacts, when compared with megaclast-based records. The frequency of storm events identified is consistent with that derived from historical observations; severe storms have a very low frequency of occurrence – one to two events per century on average.

Holocene sea-level history of the northern coast of South China Sea

This study has collected and analyzed seven sediment cores from the Pearl River delta, from which 16 new and high-quality sea-level index points are generated using a new approach. This study has also re-checked and re-calibrated the previously published sea-level data from China's southeast coast with corrections made for tectonic subsidence and sediment compaction factors. These sea-level data indicate a rise of relative sea level from −49.3 ± 0.8 m to the present height between 10,500 and 7000 cal. a BP. This sea-level history is similar to those recorded from other far-field locations and ice-volume equivalent sea-level models. The early to early-middle Holocene sea-level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16.4 ± 6.1 mm/a at 10,500 cal. a BP to 33.0 ± 7.1 mm/a at 9500 cal. a BP. This phase was followed by a period of rapid decrease in the rate of sea-level rise to 8.8 ± 1.9 mm/a at 8500 cal. a BP and 1.7 ± 1.3 mm/a at 7500 cal. a BP. During the past 7000 years, the relative sea level in the study area changed very little. This new and complete history of Holocene sea-level change supports the following findings: (1) no obvious higher-than-present sea-level highstand in the Holocene is found from the northern South China Sea; (2) certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area; (3) meltwater pulse 1b likely exists spanning into the early Holocene; (4) there are significant misfit between sea-level data and glacial isostatic adjustment models, and a revision to the existing ice melting history for the early Holocene is possibly needed.

Holocene sea-level change and coastal landscape evolution in the southern Gulf of Carpentaria, Australia

A revised Holocene sea-level history for the southern Gulf of Carpentaria is presented based on new data from the South Wellesley Archipelago and age recalibration of previous research. Results confirm that rising sea levels during the most recent post-glacial marine transgression breached the Arafura Sill ca. 11,700 cal. yr BP. Sea levels continued to rise to ca. –30 m by 10,000 cal. yr BP, leading to full marine conditions. By 7700 cal. yr BP, sea-level reached present mean sea-level (PMSL) and continued to rise to an elevation of between 1.5 m and 2 m above PMSL. Sea level remained ca. + 1.5 between 7000 and 4000 cal. yr BP, followed by rapid regression to within ± 0.5 m of PMSL by ca. 3500 cal. yr BP. When placed into a wider regional context results from this study show that coastal landscape evolution in the tropical north of Australia was not only dependent on sea-level change but also show a direct correlation with Holocene climate variability. Specifically, the formation and preservation of beach-rock deposits, intertidal successions, beach and chenier ridge systems hold valuable sea-level and Holocene climate proxies that can contribute to the growing research into lower latitude Holocene sea-level and climate histories.

CORRIGENDUM: Holocene sea-level change derived from microbial mats

Correction| January 01, 2018 CORRIGENDUM: Holocene sea-level change derived from microbial mats Daniel Livsey; Daniel Livsey Search for other works by this author on: GSW Google Scholar Alexander R. Simms Alexander R. Simms Search for other works by this author on: GSW Google Scholar Author and Article Information Daniel Livsey Alexander R. Simms Publisher: Geological Society of America First Online: 21 Dec 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2017 Geological Society of America Geology (2018) 46 (1): 86. https://doi.org/10.1130/G34387E.1 Article history First Online: 21 Dec 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Daniel Livsey, Alexander R. Simms; CORRIGENDUM: Holocene sea-level change derived from microbial mats. Geology 2018;; 46 (1): 86. doi: https://doi.org/10.1130/G34387E.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Geology, v. 41, p. 971–974, http://doi.org/10.1130/G34387.1 A sign error in the radiocarbon reservoir effect used in the calibration of the buried microbial mat 14C ages requires a correction to Table DR1 and to Figure 4 of the text. 14C ages presented in the corrected Table DR1 and in Figure 4 were calibrated using the same methods presented in the original manuscript, and utilized the calibration curves in CALIB 7.1 (Reimer et al., 2013). The change in the calibrated median ages ranges from 166 yr to 297 yr and does not affect the findings of... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lagoon-barrier system response to recent climate conditions and sea level rise, Mozambique, Africa

Transitioning lagoon-barrier systems and coastal transgressive dunes offer the valuable opportunity to correlate their formation and interactions with seasonal dry and wet climate conditions, stepped relative sea-level rise of ∼3.5 m, and sediment supply at various scales. This manuscript examines the Holocene sea level changes and recent climate conditions and controls on a 150 m-high coastal barrier system in Mozambique, southeastern Africa. The methodological approach was based on the use of 7 kyr B.P. relative sea-level curve; 37 years of wind records from 1979 to 2016; 52 years of rainfall records from 1960 to 2012; and 56 years of average recorded temperatures from 1960 to 2016. Local dunefield migrations were monitored and the sand transport rate was measured from 2016 to 2017. The combined effects of the relative sea-level rise and sediment supply indicate the formation of the lagoon-barrier system in southern Mozambique. While the recent dry and wet climate conditions suggest that they might be a controlling factor on the generation of transgressive dunefields that migrate landward. This migration is reflected on the sand transport rate of 1.4 kg m−1 s−1, which is controlled by winds from the SSW, the S and the SSE quadrants. The active parabolic dunes monitored, indicated a SE-NW migration rate of 22.5 m yr−1, which rapidly buries lakes and lagoons systems. The formation of different geomorphological features on the transgressive paleodunes and modern dunes reflect their exposure to prevailing S, SSE, SE, E and N winds, the annual rainfall of 1600 mm yr−1, and the absence of rain for 7 months yr−1. The stepped Holocene sea-level changes combined with high sediment supply and persistent acting of seasonal dry and wet climatic conditions led on the sedimentation and definition of transgressive dunefields morphology in southern Mozambique coast.

The Stone Tidal Fish Weirs of the Molène Archipelago, Iroise Sea, Brittany, Western France: a long‐term tradition with early megalithic origins

This reports on a project that combined evidence gleaned from aerial photographs, place-names, interviews, topography, LIDAR data, and sonar bathymetry to locate stone tidal fish weirs in the Mol`ene Archipelago. The results were verified by diver and pedestrian visual surveys. Models of Holocene sea-level change allowed a group of possibly Late Mesolithic–Early Neolithic weirs to be recognized, with a second group broadly dated to the later Neolithic–Early Bronze Age. The construction of these long megalithic structures is compared to the funerary monuments for which the Mol`ene Archipelago is well known, in terms of technique, cost, and societal organization.

Revisiting late Holocene sea-level change from the Gilbert Islands, Kiribati, west-central Pacific Ocean

AbstractNew coral microatoll data allow presenting an updated late Holocene sea-level curve for the Gilbert Islands of Kiribati. Examination of build-up elevation and spatial distribution of microatolls, along with radiocarbon age data from coral samples, suggest an approximately 1 m sea-level high stand, possibly lasting from ~3500 to 1900 cal yr BP. Our sea-level curve, which is similar to the one reported from the Marshall Islands, is a baseline to reconstruct the evolution of reef flats and reef islands. In addition, it provides important contextual data to infer human settlement on islands in the west-central Pacific.

Evidence for Holocene sea level and climate change from Almenara marsh (western Mediterranean)

AbstractIn the Almenara marsh (western Mediterranean), four cores were analyzed to establish the relationship between the marsh record of the Almenara marshlands and the environmental factors responsible for its evolution during the Holocene. One hundred and eighty-six samples were collected for sedimentologic and paleontological study: 63 for biomarker analysis; 5 for amino acid racemization (AAR) dating; and 5 for 14C dating. Litho and biofacies analyses identified distinct paleoenvironments, with the presence of a marsh environment alternating with inputs of alluvial material and marine sediments. Biomarkers indicated the constant presence of terrestrial (herbaceous) plants, together with a variable development of aquatic macrophytes. During the Holocene transgression, the Almenara marsh was occupied by oligohaline marsh facies with an oscillating water level and peat formation, which was established at the bottom of the record at 7570 cal yr BP and persisted until 3100±780 yr (AAR). Maximum surface flooding occurred at 5480 cal yr BP, registered 450m from the current coastline. At least three peat beds (dated with 14C dating and AAR) correlated with Bond (episode 5900 cal yr BP) and Wanner (episodes 4800–4500 and 3300–3500 cal yr BP) cycles and thus correspond to a regional model that affected the Northern Hemisphere.

Late Holocene sea-level changes in Tarama Island, the Ryukyus, Japan

Late Holocene sea-level changes in Tarama Island, the Ryukyus, Japan

完新世後期海面変動と湾口砂嘴・波食棚・古環境との関係 ―千葉県坂川低地の例―

完新世後期海面変動と湾口砂嘴・波食棚・古環境との関係 ―千葉県坂川低地の例―

전라북도 곰소만 일대의 전통 소금(자염) 생산 기록으로 본 현세 후기 해수면 변동

우리나라의 전통적인 소금은 바닷물을 끓여 증발시켜 얻는 자염이다. 부안과 고창 일대의 곰소만에서는 바닷물을 농축시킨 함수를 얻기 위해서 섯구덩을 만드는데, 이때 섯구덩의 위치는 갯벌 최상부의 사리(대조) 때에만 바닷물이 들어오는 가장 육지쪽 장소를 선택하게 된다. 고문헌 기록을 근거로 고창군 심원면 사등마을의 검당포(검당마을) 일대의 섯구덩의 위치가 역사시대 동안 변하였다는 것을 파악하였다. 1900년대 초기에는 검당마을 바로 앞에 섯구덩을 만들었다. 500년 전후 시기에는 백제 때의 제방인 김제 벽골제, 익산 황등제, 정읍 눌제의 위치와 기능을 근거로 섯구덩의 위치가 1900년대 초기의 위치와 거의 유사하였을 것으로 추정하였다. 1500년 전후 시기에는 조선 초기의 신증동국여지승람(1530)의 기록을 근거로 섯구덩의 위치가 바다쪽으로 약 800 m 정도 들어간 곳으로 옮겨졌으며, 1800년대 이후에는 택리지(1751)와 지방지도의 고부군 지도(1872) 등의 기록을 근거로 섯구덩 위치가 다시 검당마을 바로 앞으로 이동한 것으로 보았다. 이렇게 1500년대와 1800년대 이후에 섯구덩 위치가 차이를 보이는데, 이는 해수면 높이의 변화가 있었음을 시사하는 것이다. 역사 기록에 의해 추론한 해수면 변화는 지역적이나 전지구적 해수면 변동 양상과 거의 일치한다.

Late Holocene sea-level changes and paleoclimate recorded in Lake Lungué, southern Mozambique

We report on late Holocene paleoenvironmental and sea-level changes in southern Mozambique, based on analysis of diatom stratigraphy, mineral magnetic susceptibility, Saturation Isothermal Remnant Magnetization (SIRM) and organic carbon content in a sediment core from Lake Lungué, located ca. 30km north of Xai Xai City in the Limpopo River floodplain. Eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age-depth model. High content of brackish-marine taxa, especially Diploneis suborbicularis and Navicula yarrensis, suggests that the Lake Lungué basin was part of the Indian Ocean coastal zone between ca. 740 and 910CE, suggesting higher relative sea-level during this phase. A similar diatom distribution in older parts of the sequence, of unknown age, indicates that the site was connected to the Indian Ocean also at some stage prior to 740CE. Between ca. 910 and 1130CE the basin was under a combined effect of sporadic marine water influx and Limpopo River actions. A freshwater lake was established sometime between 1130 and 1360CE, when the basin became less affected by marine influences due to lower sea-levels. Instead, the lake system was more influenced by Limpopo River meandering dynamics and flooding events, and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources. During this phase, high abundance of freshwater planktonic species, i.e. Aulacoseira granulata and A. ambigua, indicates high lake levels and wetter conditions dated to ca. 1360–1560CE. From 1560CE until present, the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels, reported by a decline in freshwater planktonic taxa and increase in brackish taxa, e.g. Amphora robusta.

Intertidal foraminifera and stable isotope geochemistry from world's largest mangrove, Sundarbans: Assessing a multiproxy approach for studying changes in sea-level

Recent changes in sea level have appeared as a major threat to the existence of coastal habitats like mangroves and to the biodiversity characterizing such habitats. In this study benthic foraminifer analysis along with carbon isotopes (δ13C‰) and ratio between organic Carbon and Nitrogen (C/N) were analyzed from five intertidal stations in Sundarbans, the world's largest mangrove ecosystem to test the efficiency of these signatures toward tracking relative rise in sea level. The stability of these signatures with respect to gap of twenty months across varying elevations of the targeted stations has been tested. Benthic foraminifer abundance ranged from 0 to 118 individuals per 10 g and the assemblage was found to be mostly dominated by agglutinated species. The δ13C‰ values (−26.6 to −23.8) reflected that the origin of carbon is majorly from vascular land plants in some inputs from estuarine phytoplankton that are known to characterize tidal water of Sundarbans. The values of C/N (0.48–1.43) represented a microbially degraded total organic carbon (TOC) pool and thus were not a suitable proxy. Out of three signatures, δ13C‰ showed a strong co-relation with elevation and thus could be used as a reliable proxy to track relative sea level rise in mangrove environments.