Radiocarbon record of solar variability and Holocene climatic change in coastal southern California

EXTRACT (SEE PDF FOR FULL ABSTRACT): Pollen analysis and 5 radiocarbon dates for a 687-cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea level rise during the mid-Holocene, but after 4500 years BP, sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 years BP correlate global cooling events and (except the 3800-year BP event) with carbon-14 production anomalies. The coincidence of climate change and carbon-14 anomalies support a causal connection with solar variability, but regardless of the causal mechanism(s) the delta-carbon-14 curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

淤泥质潮滩地貌的遥感研究－以苏北辐射沙洲海岸为例

本文以具有典型特征的苏北淤泥质潮滩海岸作为研究区，利用1975-2003年间14景覆盖该地区的Landsat和SPOT卫星影像作为主要数据源，结合地面调查和验证工作，在遥感影像处理和地理信息系统分析技术的支持下，对区内潮滩、岸线、水边线和盐沼植被等进行遥感解译，分析苏北辐射沙脊群和沿岸地貌的空间分布特征和动态演变趋势。研究结果表明：苏北辐射沙脊群海域的潮汐水位过程的不同步现象普遍存在，限制了常规遥感数据在苏北潮滩地貌研究中的适用范围和解译精度；在人工判别的辅助下，多光谱遥感的非监督分类方法可以有效解译淤泥质潮滩的水边线；利用修改型土壤调整植被指数（MSAVI）可以较好地提取潮滩上的盐沼植被信息；苏北沿岸潮滩的快速淤长促进了盐沼植被带向海侧快速扩展，近年来持续的潮滩围垦工程则不断从陆侧侵占盐沼植被带，使盐沼植被带宽度减小乃至消失；在大规模人类活动和自然条件的共同影响下，苏北辐射沙脊群海岸的岸线发育趋于平直化，无序的潮滩围垦项目使得可垦滩地资源被过度消耗；1975～2002年间，研究区北部和南部沿岸的高潮滩整体上处于淤长状态，中部沿岸潮滩和离岸沙洲高潮滩则被大面积侵蚀；1999年以来，研究区内低潮滩部位开始形成有序排列的滩面地物，并表现出逐年大面积蔓延的趋势，可能是滩涂紫菜养殖区扩展的结果。

The Application Of Radioisotopes In The Study Of Estuarine Sedimentary Processes

The spatial and temporal distributions of some radionuclides in effluents originating from the British Nuclear Fuels Ltd (BNFL) reprocessing plant at Windscale, which are released into the Irish Sea, have been studied in sediments at 16 sites in the salt marsh region near Newbiggin on the Esk estuary Cumbria, England. The concentration of non-conservative radionuclides in surface sediments of the area cannot be described by a single parameter, but there is a high correlation with organic C, Cu, Al and the Si : Al ratio with particle size. The preservation of the historical record of the BNFL effluents in the Esk sediments is dependent on the hydrology of the area, as it effects such processes as accretion, erosion and remixing. From the 106Ru and 210Po concentrations and the 137Cs : 134Cs ratio in the sediment profiles with depth, we have identified these processes. Sedimentation rates at sites of accretion vary between 0·5 and 3 cm year−1. However, at some sites they appear to be much higher, approximately 6 cm year−1 in the top 10 cm, but they are not consistent throughout the depth profiles. This may be a true reflection of variable accretion related to sediment type, or one which is influenced by surficial mixing. Some cores showed evidence of continuous accretion but no significant radioactivity was detected at depths below 35–40 cm, indicating an overall sedimentation rate of approximately 1·5 cm year−1 for the 25–30-year period since BNFL effluents first entered the Irish Sea.

Sea-level changes in Iceland and the influence of the North Atlantic Oscillation during the last half millennium

We present a new, diatom-based sea-level reconstruction for Iceland spanning the last -500 years, and investigate the possible mechanisms driving the sea-level changes. A sea-level reconstruction from near the Icelandic low pressure system is important as it can improve understanding of ocean-atmosphere forcing on North Atlantic sea-level variability over multi-decadal to centennial timescales. Our reconstruction is from Viarhólmi salt marsh in Snæfellsnes in western Iceland, a site from where we previously obtained a 2000-yr record based upon less precise sea-level indicators (salt-marsh foraminifera). The 20th century part of our record is corroborated by tide-gauge data from Reykjavik. Overall, the new reconstruction shows ca0.6m rise of relative sea level during the last four centuries, of which ca0.2m occurred during the 20th century. Low-amplitude and high-frequency sea-level variability is super-imposed on the pre-industrial long-term rising trend of 0.65m per 1000 years. Most of the relative sea-level rise occurred in three distinct periods: AD 1620-1650, AD 1780-1850 and AD 1950-2000, with maximum rates of ~3±2mm/yr during the latter two of these periods. Maximum rates were achieved at the end of large shifts (from negative to positive) of the winter North Atlantic Oscillation (NAO) Index as reconstructed from proxy data. Instrumental data demonstrate that a strong and sustained positive NAO (a deep Icelandic Low) generates setup on the west coast of Iceland resulting in rising sea levels. There is no strong evidence that the periods of rapid sea-level rise were caused by ocean mass changes, glacial isostatic adjustment or regional steric change. We suggest that wind forcing plays an important role in causing regional-scale coastal sea-level variability in the North Atlantic, not only on (multi-)annual timescales, but also on multi-decadal to centennial timescales.

Matéria húmica de sapal: variações estruturais e complexação com o cobre

No presente trabalho foram estudadas as variações na composição, estrutura e comportamento das substâncias húmicas sedimentares (SHS), promovidas pela presença de duas espécies de plantas da família Chenopodiacea, presentes nos sapais da Ria de Aveiro: a Halimione portulacoides e a Arthrocnemum fruticosum. Para além das variações espaciais horizontais, foram investigadas as variações ao longo de um perfil de profundidades. Desta forma, para além da camada superficial (0-10 cm) de sedimentos com diferentes espécies de plantas e sem plantas, também foram investigadas camadas de sedimentos intermédia (20-25 cm) e profunda (45-50 cm). Para a extracção das SHS recorreu-se a uma pequena modificação do método proposto pela International Humic Substances Society (IHSS) para extracção e purificação de substâncias húmicas de solos. As SH extraídas foram caracterizadas através dos métodos espectroscópicos de absorção no ultravioleta visível, de fluorescência molecular síncrona, de absorção no infravermelho com transformadas de Fourier (FTIR) e de RMN 13C em estado sólido. Estas técnicas de caracterização foram complementadas pela análise elementar e termogravimetria. Em algumas amostras, foram ainda determinados o conteúdo em alguns metais por ICP-AES e o conteúdo funcional ácido por titulações potenciométricas. Após exaustiva caracterização das amostras de AH, procedeu-se ao estudo da sua capacidade de complexação com o cobre, recorrendo a titulações monitorizadas por fluorescência molecular síncrona. Os resultados revelaram que a colonização de sedimentos por plantas vasculares superiores conduz a uma alteração profunda no ambiente sedimentar e que esta é reflectida na diagénese das substâncias húmicas sedimentares, tendo-se observado variações a uma pequena escala espacial. O estudo deste tipo de variações nunca tinha sido efectuado em trabalhos anteriores. Nos ácidos fúlvicos detectaram-se diferenças na composição e estrutura das amostras correspondentes às camadas superiores de sedimentos, reflectindo a presença de diferentes colonizações vegetais. Relativamente aos ácidos húmicos, foi possível classificá-los em dois tipos distintos. Os AH do tipo I correspondem aos sedimentos superficiais e intermédios dos locais com plantas. Neste tipo de AH verificou-se uma incorporação de polissacarídeos e estruturas peptídicas, em estados de humificação pouco desenvolvidos. Os AH do tipo II correspondem aos sedimentos mais profundos de todos os locais e aos intermédios do local sem plantas e caracterizam-se por um maior grau de humificação e polimerização, um maior conteúdo aromático e de estruturas conjugadas e um maior conteúdo de grupos carboxílicos. Essas diferenças estruturais conduzem a diferentes comportamentos ácido/base e de complexação com o cobre. Assim, os AH do tipo I, que apresentam sinais espectroscópicos mais baixos associados a grupos carboxílicos e fenólicos, têm menor conteúdo de grupos funcionais ácidos e menor capacidade de complexação com o cobre quando se consideram ligandos característicos de unidades aromáticas conjugadas. Relativamente aos valores de log K dos complexos de AHS com o cobre, as amostras representativas da camada superficial dos sedimentos com plantas apresentaram valores superiores aos das restantes amostras de AH estudadas, cujos valores de log K são similares entre si. Atendendo aos resultados de análise elementar e espectroscópica, este facto pode estar associado à presença de compostos de azoto não peptídicos. Quanto a outros ligandos para o cobre, nomeadamente os representativos de estruturas peptídicas contendo o aminoácido triptofano e estruturas aromáticas simples, não foi possível obter resultados conclusivos. Dado que os ácidos húmicos do tipo I demonstraram um maior conteúdo peptídico e menor conteúdo aromático, o estudo destes ligandos torna-se importante para compreender melhor o efeito da presença de plantas nos sedimentos de sapal sobre o comportamento dos ácidos húmicos sedimentares como ligandos para o cobre. Refere-se ainda que foram detectadas certas especificidades na variação das características do sedimento e das substâncias húmicas com a profundidade nos diferentes locais estudados que não podem ser explicadas meramente com a presença de material vegetal oriundo de diferentes espécies de plantas, requerendo um conhecimento mais aprofundado das comunidades bentónicas e do ambiente físico-químico do sedimento.

Organic-walled dinoflagellate cysts in recent sediments from the Guadiana river estuary, South-East Portugal

Dissertação de Mestrado, Biologia Marinha, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, 2007

Microbial community composition and mercury cycling in sediments of tagus estuary

Tese de doutoramento, Farmácia (Toxicologia), Universidade de Lisboa, Faculdade de Farmácia, 2016

Limnological characteristics and zooplankton community structure of Mediterranean coastal lagoons undergoing restoration

Entre 1999 i 2003 es va desenvolupar un projecte Life de restauració a la maresma de La Pletera, afectada per un pla urbanització, i a la llacuna del Ter Vell, amb un elevat grau d'eutròfia (aiguamolls del Baix Ter, NE Península Ibèrica). L'objectiu d'aquesta tesi és establir el funcionament d'ambdós ecosistemes, analitzar-ne la problemàtica ambiental i avaluar els efectes de la restauració. A la maresma de la Pletera, es va analitzar el paper de la hidrologia en la composició i dinàmica dels nutrients i del zooplàncton en cinc llacunes, tres de les quals havien estat creades dins el projecte de restauració com a nous refugis per una espècie de peix amenaçada (Aphanius iberus). La hidrologia es va caracteritzar per un llarg període de confinament sense entrades d'aigua, interromput de manera irregular per inundacions puntuals. La dinàmica del nitrogen inorgànic es va relacionar amb les entrades d'aigua, mentre que la del fòsfor, del nitrogen total i de la matèria orgànica es va relacionar amb els processos d'acumulació i reciclatge intern durant el confinament. El zooplàncton es va analitzar mitjançant la combinació d'aproximacions taxonòmiques i de mides. L'estructura de mides de la comunitat es va veure més afectada per les interaccions tròfiques (depredació i competència) mentre que l'estructura taxonòmica va ser més sensible a factors abiòtics (nutrients). El ràpid creixement de la població A. iberus en les noves llacunes va suggerir que aquestes havien proporcionat l'hàbitat adequat per a l'espècie, almenys a curt termini. Les actuacions de restauració a la llacuna del Ter Vell es van centrar en la millora de la qualitat de l'aigua mitjançant (1) la construcció d'uns aiguamolls per depurar l'aigua d'entrada i (2) el dragat del sediment en diversos punts. Simultàniament a la restauració, però de forma independent, la gestió agrícola de l'aigua va reduir dràsticament el cabal d'entrada d'aigua dolça a la llacuna, provocant un canvi en el règim hídric. Es van analitzar els efectes a curt termini d'aquest canvi sobre la limnologia i el zooplàncton de la llacuna. Abans del canvi, la hidrologia era artificial ja que s'havia prolongat l'entrada d'aigua dolça d'acord amb la demanda agrícola, i per tant la llacuna presentava una elevada taxa de renovació de l'aigua i majors concentracions de nutrients. Després del canvi, la hidrologia va dependre més del clima, es van reduir les entrades d'aigua i es va allargar el període de confinament. La composició y dinàmica dels nutrients va tendir a assemblar-se a l'observada a les llacunes de la maresma, mentre que la comunitat del zooplàncton no ho va fer. L'estat ecològic de la llacuna va millorar després del canvi en el règim hídric.

An eclectic morphostratigraphic model for the sedimentary response to Holocene sea-level rise in northwest Europe

The improved empirical understanding of silt facies in Holocene coastal sequences provided by such as diatom, foraminifera, ostracode and testate amoebae analysis, combined with insights from quantitative stratigraphic and hydraulic simulations, has led to an inclusive, integrated model for the palaeogeomorphology, stratigraphy, lithofacies and biofacies of northwest European Holocene coastal lowlands in relation to sea-level behaviour. The model covers two general circumstances and is empirically supported by a range of field studies in the Holocene deposits of a number of British estuaries, particularly, the Severn. Where deposition was continuous over periods of centuries to millennia, and sea level fluctuated about a rising trend, the succession consists of repeated cycles of silt and peat lithofacies and biofacies in which series of transgressive overlaps (submergence sequences) alternate with series of regressive overlaps (emergence sequences) in association with the waxing and waning of tidal creek networks. Environmental and sea-level change are closely coupled, and equilibrium and secular pattern is of the kind represented ideally by a closed limit cycle. In the second circumstance, characteristic of unstable wetland shores and generally affecting smaller areas, coastal erosion ensures that episodes of deposition in the high intertidal zone last no more than a few centuries. The typical response is a series of regressive overlaps (emergence sequence) in erosively based high mudflat and salt-marsh silts that record, commonly as annual banding, exceptionally high deposition rates and a state of strong disequilibrium. Environmental change, including creek development, and sea-level movement are uncoupled. Only if deposition proceeds for a sufficiently long period, so that marshes mature, are equilibrium and close coupling regained. (C) 2002 Elsevier Science B.V. All rights reserved.

Holocene tidal palaeochannels, Severn Estuary Levels, UK: a search for granulometric and foraminiferal criteria

Holocene tidal palaoechannels, Severn Estuary Levels, UK: a search for granulometric and foraminiferal criteria. Proceedings of the Geologists' Association, 117, 329-344. Grain-size characteristics (by laser granulometry) and foraminiferal assemblages have been established for silts accumulated in five, dissimilar tidal palaeochannels of mid or late Holocene age in the Severn Estuary Levels, representative of muddy tidal systems. For purposes of general comparison, similar data were obtained from a representative active tidal inlet in the area, but all of these channels have been subject to human interference and are not relied upon as a model for environmental interpretation. Although the palaeochannel deposits differ substantially in their bedding characteristics and stratigraphical relationships from the level-bedded salt-marsh platform and mudflat deposits with which they are associated, and although the channel environment is distinctive morphologically and hydraulically, no critical textural differences could be found between the channel deposits and the associated facies. Similarly, no foraminiferal assemblages distinctive of a tidal channel were encountered. Instead, the assemblages compare with those from mudflats and salt-marsh platforms. It is concluded that the sides of the subfossil channels carried some vegetation, as was observed to be the case in the modern inlet. An alternative approach is necessary if concealed palaeochannel deposits are to be recognized in muddy systems from limited numbers of subsurface samples. Although the palaeochannels afforded no characteristic textural signature, they yield transverse grain-size patterns pointing to coastal movements during their evolution. Concave-up trends suggest outward coastal building, whereas convex-up ones point to marsh-edge retreat.

Seasonality of delta C-13 and C/N ratios in modern and mid-holocene sediments in the Severn Estuary levels, SW Britain

Bulk organic VC and C/N ratios from mid-Holocene salt-marsh deposits with sedimentary banding reveal subtle but significant differences between coarse- and fine-grained deposits. These are consistent with findings from seasonally sampled modern silts, and with the interpretation, on physical and palynological grounds, of the fine-grained and coarse-grained components as warm-season and cold-season deposits, respectively. The control is considered to be seasonal variations in the character of the organic matter supplied.

Autocyclic erosion in tidal marshes

A common mode whereby destruction of coastal lowlands occurs is frontal erosion. The edge cliffing, nonetheless, is also an inherent aspect of salt marsh development in many northwest European tidal marshes. Quite a few geomorphologists in the earlier half of the past century recognized such edge erosion as a definite repetitive stage within an autocyclic mode of marsh growth. A shift in research priorities during the past decades (primarily because of coastal management concerns, however) has resulted in an enhanced focus on sediment-flux measurement campaigns on salt marshes. This, somewhat "object-oriented" strategy hindered any further development of the once-established autocyclic growth concept, which virtually has gone into oblivion in recent times. This work makes an attempt to resurrect the notion of autocyclicity by employing its premises to address edge erosion in tidal marshes. Through a review of intertidal morphosedimentology the underlying framework for autocyclicity is envisaged. The phenomenon is demonstrated in the Holocene salt marsh plain of Moricambe basin in NW England that displays several distinct phases of marsh retreat in the form of abandoned clifflets. The suite of abandoned shorelines and terraces has been identified in detailed field mapping that followed analysis of topographic maps and aerial photographs. Vertical trends in marsh plain sediments are recorded in trenches for signs of past marsh front movements. The characteristic sea level history of the area offers an opportunity to differentiate the morphodynamic variability induced in the autocyclic growth of the marsh plain in scenarios of rising and falling sea level and the accompanied change in sediment budget. The ideas gathered are incorporated to construct a conceptual model that links temporal extent of marsh erosion to inner tidal flat sediment budget and sea level tendency. The review leads to recognition of the necessity of adopting an holistic approach in the morphodynamic investigations where marshes should be treated as a component within the "marsh-mudflat system" as each element apparently modulates evolution of the other, with an eventual linkage to subtidal channels. (C) 2009 Elsevier B.V. All rights reserved.

Onset of recent rapid sea-level rise in the western Atlantic Ocean

A high-resolution record of sea-level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2m thick salt-marsh peat sequence at Chezzetcook, Nova Scotia, Canada. Former mean tide level positions are reconstructed with a precision of +/- 0.055 in using a transfer function derived from distributions of modern salt-marsh foraminifera. Our age model for the core section older than 300 years is based on 19 AMS C-14 ages and takes into account the individual probability distributions of calibrated radiocarbon ages. The past 300 years is dated by pollen and the isotopes Pb-206, Pb-207, Pb-210, Cs-137 and Am-241. Between AD 1000 and AD 1800, relative sea level rose at a mean rate of 17cm per century. Apparent pre-industrial rises of sea level dated at AD 1500-1550 and AD 1700-1800 cannot be clearly distinguished when radiocarbon age errors are taken into account. Furthermore, they may be an artefact of fluctuations in atmospheric C-14 production. In the 19th century sea level rose at a mean rate of 1.6mm/yr. Between AD 1900 and AD 1920, sea-level rise accelerated to the modern mean rate of 3.2mm/yr. This acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming. (c) 2005 Elsevier Ltd. All rights reserved.

Remote sensing of tidal networks and their relation to vegetation

The study of the morphology of tidal networks and their relation to salt marsh vegetation is currently an active area of research, and a number of theories have been developed which require validation using extensive observations. Conventional methods of measuring networks and associated vegetation can be cumbersome and subjective. Recent advances in remote sensing techniques mean that these can now often reduce measurement effort whilst at the same time increasing measurement scale. The status of remote sensing of tidal networks and their relation to vegetation is reviewed. The measurement of network planforms and their associated variables is possible to sufficient resolution using digital aerial photography and airborne scanning laser altimetry (LiDAR), with LiDAR also being able to measure channel depths. A multi-level knowledge-based technique is described to extract networks from LiDAR in a semi-automated fashion. This allows objective and detailed geomorphological information on networks to be obtained over large areas of the inter-tidal zone. It is illustrated using LIDAR data of the River Ems, Germany, the Venice lagoon, and Carnforth Marsh, Morecambe Bay, UK. Examples of geomorphological variables of networks extracted from LiDAR data are given. Associated marsh vegetation can be classified into its component species using airborne hyperspectral and satellite multispectral data. Other potential applications of remote sensing for network studies include determining spatial relationships between networks and vegetation, measuring marsh platform vegetation roughness, in-channel velocities and sediment processes, studying salt pans, and for marsh restoration schemes.

Isolation of haloarchaea that grow at low salinities

Archaea, the third domain of life, were long thought to be limited to environmental extremes. However, the discovery of archaeal 16S rRNA gene sequences in water, sediment and soil samples has called into question the notion of Archaea as obligate extremophiles. Until now none of these novel Archaea has been brought into culture, a critical step for discovering their ecological roles. We have cultivated three novel halophilic Archaea (haloarchaea) genotypes from sediments in which the pore-water salinity was close to that of seawater. All previously reported haloarchaeal isolates are obligate extreme halophiles requiring at least 9% w/v NaCl for growth and are typically the dominant heterotrophic organisms in salt and soda lakes, salt deposits and salterns. Two of these three newly isolated genotypes have lower requirements for salt than previously cultured haloarchaea and are capable of slow growth at seawater salinity (2.5% w/v NaCl). Our data reveal the existence of Archaea that can grow in non-extreme conditions and of a diverse community of haloarchaea existing in coastal salt marsh sediments. Our findings suggest that the ecological range of these physiologically versatile prokaryotes is much wider than previously supposed.