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  1. Evaluating the fate of freshwater lenses on atoll islands after eustatic sea-level rise and cyclone-driven inundation: A modelling approach

    NASA Astrophysics Data System (ADS)

    Terry, James P.; Chui, Ting Fong May


    Dispersed human populations inhabiting remote atolls across the tropical Pacific Ocean are reliant on the viability of thin freshwater lenses (FWLs) contained within the island coralline sediments for their survival. Yet FWLs are uniquely fragile and easily damaged by saline intrusion. Eustatic sea-level rise (SLR) and sea flooding generated by intense tropical cyclones therefore pose special perils for continued existence on atolls. In this work, mathematical modelling is used to examine the effects on an atoll freshwater lens of various projected long-term SLR scenarios (10, 20, and 40 cm). A cyclone-driven wave washover event is then simulated in order to observe the responses and recovery of the FWL, subsequent to the SLR scenarios imposed. A key attribute of our model design is the inclusion of a topographic depression containing a low-lying fresh swamp in the atoll islet interior (which is often ignored), where seawater accumulates during inundation. Results indicate that a 40 cm SLR produces a major impact: the FWL decreases in thickness by approximately 50%, develops a brackish centre and contracts to a shrunken 'doughnut' morphology. Following cyclone inundation, observed salinity profiles are illuminating. Steep salinity gradients show how a strong saline plume forms at shallow depths, but also reveal the existence of an undisturbed fresh horizon beneath the salt plume under both present conditions and the modest 10 cm SLR scenario. Within the preserved fresh horizon, salt concentrations are maintained below 1.5 g/L (i.e. within usable limits) for at least a year. In contrast, the diminished freshwater lenses that exist after 20 and 40 cm SLR then exhibit far less resilience to saline damage over comparable post-cyclone timeframes. The findings point towards Pacific atolls becoming increasingly uninhabitable long before their complete submergence by sea-level rise, owing to irrecoverable groundwater salinisation seriously reducing the availability of

  2. Generalized Cauchy model of sea level fluctuations with long-range dependence

    NASA Astrophysics Data System (ADS)

    Li, Ming; Li, Jia-Yue


    This article suggests the contributions with two highlights. One is to propose a novel model of sea level fluctuations (sea level for short), which is called the generalized Cauchy (GC) process. It provides a new outlook for the description of local and global behaviors of sea level from a view of fractal in that the fractal dimension D that measures the local behavior of sea level and the Hurst parameter H which characterizes the global behavior of sea level are independent of each other. The other is to show that sea level appears multi-fractal in both spatial and time. Such a meaning of multi-fractal is new in the sense that a pair of fractal parameters (D, H) of sea level is varying with measurement sites and time. This research exhibits that the ranges of D and H of sea level, in general, are 1 ≤ D < 2 and 0 . 5 < H < 1, respectively but D is independent of H. With respect to the global behavior of sea level, we shall show that H > 0 . 96 for all data records at all measurement sites, implying that strong LRD may be a general phenomenon of sea level. On the other side, regarding with the local behavior, we will reveal that there appears D = 1 or D ≈ 1 for data records at a few stations and at some time, but D > 0 . 96 at most stations and at most time, meaning that sea level may appear highly local irregularity more frequently than weak local one.

  3. The anatomy of recent large sea level fluctuations in the Mediterranean Sea

    NASA Astrophysics Data System (ADS)

    Landerer, Felix W.; Volkov, Denis L.


    Abstract During the boreal winter months of 2009/2010 and 2010/2011, Mediterranean mean <span class="hlt">sea</span> <span class="hlt">level</span> rose 10 cm above the average monthly climatological values. The non-seasonal anomalies were observed in sea surface height (from altimetry), as well as ocean mass (from gravimetry), indicating they were mostly of barotropic nature. These relatively rapid basin-wide <span class="hlt">fluctuations</span> occurred over time scales of 1-5 months. Here we use observations and re-analysis data to attribute the non-seasonal <span class="hlt">sea</span> <span class="hlt">level</span> and ocean mass <span class="hlt">fluctuations</span> in the Mediterranean Sea to concurrent wind stress anomalies over the adjacent subtropical Northeast Atlantic Ocean, just west of the Strait of Gibraltar, and extending into the strait itself. The observed Mediterranean <span class="hlt">sea</span> <span class="hlt">level</span> <span class="hlt">fluctuations</span> are strongly anti-correlated with the monthly North-Atlantic-Oscillation (NAO) index.</p> </li> <li> <p><span>Reconstruction of Caspian <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span>: Radiocarbon dating coastal and bottom deposits</span></p> <p>SciTech Connect</p> <p>Karpytchev, Yu.A. )</p> <p>1993-01-01</p> <p>Owing to the large basin area of the Caspian Sea, <span class="hlt">fluctuations</span> in its level reflect climatic changes in the northern hemisphere. To reconstruct these <span class="hlt">fluctuations</span>, they collected mollusk shells, plant debris, carbonates and organic matter samples for [sup 14]C dating from deposits of ancient salt marshes, depressions and bars formed during significant <span class="hlt">sea-level</span> decline they studied the impact of eolian sedimentation via parallel dating of carbonates and other materials. The data demonstrate that <span class="hlt">sea</span> <span class="hlt">level</span> rises during periods of cooling and falls during warming periods; this is true for both long-term (2--2.5 ka) and short-term climatic changes.</p> </li> <li> <p><span>A "chaos" of Phanerozoic <span class="hlt">eustatic</span> curves</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Ruban, Dmitry A.</p> <p>2016-04-01</p> <p>The knowledge of eustasy has changed during the past two decades. Although there is not any single global <span class="hlt">sea-level</span> curve for the entire Phanerozoic, new curves have been proposed for all periods. For some geological time intervals, there are two and more alternative reconstructions, from which it is difficult to choose. A significant problem is the available <span class="hlt">eustatic</span> curves are justified along different geological time scales (sometimes without proper explanations), which permits to correlate <span class="hlt">eustatic</span> events with the possible error of 1-3 Ma. This degree of error permits to judge about only substage- or stage-order global <span class="hlt">sea-level</span> changes. Close attention to two geological time slices, namely the late Cambrian (Epoch 3‒Furongian) and the Late Cretaceous, implies that only a few <span class="hlt">eustatic</span> events (6 events in the case of the late Cambrian and 9 events in the case of the Late Cretaceous) appear on all available alternative curves for these periods, and different (even opposite) trends of <span class="hlt">eustatic</span> <span class="hlt">fluctuations</span> are shown on these curves. This reveals significant uncertainty in our knowledge of eustasy that restricts our ability to decipher factors responsible for regional transgressions and regressions and relative <span class="hlt">sea-level</span> changes. A big problem is also inadequate awareness of the geological research community of the new <span class="hlt">eustatic</span> developments. Generally, the situation with the development and the use of the Phanerozoic <span class="hlt">eustatic</span> reconstructions seems to be ;chaotic;. The example of the shoreline shifts in Northern Africa during the Late Cretaceous demonstrates the far-going consequences of this situation. The practical recommendations to avoid this ;chaos; are proposed. Particularly, these claim for good awareness of all <span class="hlt">eustatic</span> developments, their critical discussion, and clear explanation of the employed geological time scale.</p> </li> <li> <p><span>Pleistocene <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> and human evolution on the southern coastal plain of South Africa</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Compton, John S.</p> <p>2011-03-01</p> <p>Humans evolved in Africa, but where and how remain unclear. Here it is proposed that the southern coastal plain (SCP) of South Africa may have served as a geographical point of origin through periodic expansion and contraction (isolation) in response to glacial/interglacial changes in <span class="hlt">sea</span> <span class="hlt">level</span> and climate. During Pleistocene interglacial highstands when <span class="hlt">sea</span> <span class="hlt">level</span> was above -75 m human populations were isolated for periods of 360-3400 25-yr generations on the SCP by the rugged mountains of the Cape Fold Belt, climate and vegetation barriers. The SCP expands five-fold as <span class="hlt">sea</span> <span class="hlt">level</span> falls from -75 to -120 m during glacial maxima to form a continuous, unobstructed coastal plain accessible to the interior. An expanded and wet glacial SCP may have served as a refuge to humans and large migratory herds and resulted in the mixing of previously isolated groups. The expansive glacial SCP habitat abruptly contracts, by as much as one-third in 300 yr, during the rapid rise in <span class="hlt">sea</span> <span class="hlt">level</span> associated with glacial terminations. Rapid flooding may have increased population density and competition on the SCP to select for humans who expanded their diet to include marine resources or hunted large animals. Successful adaptations developed on an isolated SCP are predicted to widely disperse during glacial terminations when the SCP rapidly contracts or during the initial opening of the SCP in the transition to glacial maxima. The hypothesis that periodic expansion and contraction of the SCP, as well as the coastal plain of North Africa, contributed to the stepwise origin of our species over the last 800 thousand years (kyr) is evaluated by comparing the archeological, DNA and <span class="hlt">sea-level</span> records. These records generally support the hypothesis, but more complete and well dated records are required to resolve the extent to which <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> influenced the complex history of human evolution.</p> </li> <li> <p><span>Global <span class="hlt">sea</span> <span class="hlt">level</span> <span class="hlt">fluctuations</span> and uncertainties through a Wilson cycle based on ocean basin volume reconstructions</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Wright, Nicky; Seton, Maria; Williams, Simon E.; Dietmar Müller, R.</p> <p>2017-04-01</p> <p>Variations in the volume of ocean basins is the main driving force for (long-wavelength) changes in <span class="hlt">eustatic</span> <span class="hlt">sea</span> <span class="hlt">level</span> in an ice-free world, i.e. most of the Mesozoic and Cenozoic. The volume of ocean basins is largely dependent on changes in the seafloor spreading history, which can be reconstructed based on an age-depth relationship for oceanic crust and an underlying global plate kinematic model. Ocean basin volume reconstructions need to include: (1) a predicted history of back-arc basin formation, including where geological evidence exists for the opening and closing of back-arc basins within a single Wilson cycle, (2) the emplacement and subsidence of oceanic plateaus (LIPs), (3) variations in sediment thickness through time, and (4) a reconstruction of the depth of continental margins and fragments. Unfortunately, due to subduction of oceanic crust, we must rely on synthetically modelled ocean crust for much of Earth's history, for which it is impossible to ground truth the history of LIPs and sediment thickness. In order to improve reconstructions of <span class="hlt">sea</span> <span class="hlt">level</span> on geologic time scales and assess the uncertainty in deriving the volume of ocean basins based on a global plate kinematic model, we investigate the influence of these poorly constrained features (e.g. LIPs, back-arc basins, sediment thickness, passive margins) on ocean basin volume since 230 Ma (i.e. throughout an entire Wilson cycle). We assess the characteristics for each feature at present-day and during well-constrained times during the Cenozoic, and create suites of alternative paleobathymetry grids which incorporate varying degrees of each feature's influence. Further, we derive a global <span class="hlt">sea</span> <span class="hlt">level</span> curve based only on the reconstruction of ocean basin volume (i.e. excluding effects such as dynamic topography and glaciation), and present the influence of each component and their uncertainties through time. We find that by incorporating reasonable predictions for these components during times</p> </li> <li> <p><span>Relative <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> since deglaciation in western North America</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Shugar, D. H.; Walker, I. J.; Lian, O. B.; Eamer, J.; Neudorf, C. M.</p> <p>2013-12-01</p> <p>We synthesize the state of knowledge regarding post-glacial <span class="hlt">sea-level</span> changes on the Pacific coast of North America based on more than 2,000 radiocarbon dates from Oregon to Alaska. Relative <span class="hlt">sea-level</span> (RSL) history over the late Quaternary is complex owing to regional differences in crustal deformation (neotectonics), changes in global ocean volumes (eustasy) and the depression and rebound of the Earth's crust in response to ice sheets on land (isostasy). The RSL history is further complicated by the diachronous timing of the Last Glacial Maximum (LGM) and subsequent ice retreat across the region. For instance, the LGM ranged in timing from as early as 25 ka (14C years) BP in south-central Alaska, to between 15-14 ka BP at its southernmost extent in southwest BC and northern Washington. During this time, the Cordilleran Ice Sheet depressed the crust over which it formed and, as the ice thinned and retreated, the sea rapidly transgressed isostatically depressed lowland areas. Early-postglacial RSL highstands within the region range from ~25 masl in Cook Inlet, Alaska, to approximately 200 masl at fjord head locations such as Kitimat and in the Lower Mainland of southern BC. As the crust rebounded, RSL dropped. In contrast to the BC mainland, <span class="hlt">sea</span> <span class="hlt">levels</span> at the LGM were 150 m lower than present in Haida Gwaii on BC's north coast, due to an isostatic forebulge raising the land. Forebulge collapse led to a rise in relative <span class="hlt">sea</span> <span class="hlt">level</span>, up to about 15-18 masl by 9.5 ka BP. Spatial and temporal gaps exist in our understanding of post-glacial <span class="hlt">sea-level</span> change and landscape evolution along the Pacific coast as data constraining RSL <span class="hlt">fluctuations</span> around the LGM are limited (e.g. south-central Alaska). Similarly, we lack understanding of post-glacial <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> on BC's central coast. We present an overview of the differences in RSL patterns from Oregon to south-central Alaska and discuss the geophysical foundations for them, as well as present new data filling data</p> </li> <li> <p><span>Early Pleistocene <span class="hlt">sea</span> <span class="hlt">level</span> and millennial-scale climate <span class="hlt">fluctuations</span>: a view from the tropical Pacific</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Alix Jakob, Kim; Friedrich, Oliver; Pross, Jörg</p> <p>2015-04-01</p> <p>This project aims at deciphering the rate of <span class="hlt">sea</span> <span class="hlt">level</span> variability and its effect on millennial-scale climate <span class="hlt">fluctuations</span> during the final phase of the intensification of northern hemisphere glaciation (NHG). Millennial-scale climate <span class="hlt">fluctuations</span> appear to have changed significantly at glacial-interglacial time scales during the late Pliocene and Pleistocene. Thereby, millennial-scale climate <span class="hlt">fluctuations</span> under a warmer climate during late Pliocene and early Pleistocene show markedly lower ampitudes compared to the <span class="hlt">fluctuations</span> of the late Pleistocene. Numerous Pleistocene proxy records (e.g. McManus et al., 1999) suggest that this difference can be explained by an ice-volume/<span class="hlt">sea-level</span> threshold that amplifies millennial-scale climate <span class="hlt">fluctuations</span> and was not reached prior to the Mid-Pleistocene Transition (MPT). However, new records question the existence of this threshold (Bolton et al., 2010) and indicate that either the amplification of millennial-scale climate <span class="hlt">fluctuations</span> before the MPT required a higher ice-volume threshold than in the late Pleistocene, that ice-volume had no significant effect on the amplitude of climate <span class="hlt">fluctuations</span>, and/or the available <span class="hlt">sea</span> <span class="hlt">level</span> estimates for the early Pleistocene are inaccurate. For identifying the mechanisms underlying the dynamics of early Pleistocene ice sheets, material from the tropical Pacific Ocean (ODP Site 849) is studied over a time interval from 2.6 to 2.4 Ma (marine isotope stages 104 to 96). In summary, the main deliverables are (1) the establishment of a precise δ18O chemostratigraphy using the benthic foraminifera Cibicidoides wuellerstorfi by tuning the δ18O dataset to the LR04 benthic isotope stack (Lisiecki & Raymo, 2005), and (2) providing high-resolution (˜700 years) Mg/Ca and δ18O datasets using the benthic foraminifera Oridorsalis umbonatus and the planktonic foraminifera Globigerinoides ruber. This combined geochemical approach will be used to address the following research questions: (1</p> </li> <li> <p><span>Interannual <span class="hlt">fluctuations</span> of the global mean <span class="hlt">sea</span> <span class="hlt">level</span> during the altimetry era</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Dieng, H.; Munier, S.; Henry, O.; Palanisamy, H.; Meyssignac, B.; Cazenave, A. A.</p> <p>2012-12-01</p> <p>The detrended global mean <span class="hlt">sea</span> <span class="hlt">level</span> (GMSL) displays significant year-to-year <span class="hlt">fluctuations</span> of 2-3 mm amplitude, as revealed by satellite altimetry over the past 2 decades. In particular, the detrended GMSL shows positive anomalies during El Nino and negative anomalies during La Nina. Previous studies (Llovel et al, 2011, Boening et al., 2012, Cazenave et al., 2012) have shown that these ENSO-related anomalies are mostly caused by ocean mass variations linked to changes of the global water cycle, with precipitation excess (deficit ) over the oceans (land) during El Nino, and inversely during La Nina. Here, we study the respective contributions of the mass and steric contributions to the interannual GMSL <span class="hlt">fluctuations</span> over the whole altimetry period (since 1993); We find that over this time span, interannual GMSL <span class="hlt">fluctuations</span> are in general poorly correlated to the steric component while ocean mass variations explain most of the observed year to year oscillations, even apart from ENSO events . These ocean mass oscillations appear inversely correlated to the total land water storage oscillation. However over the oceanic domain, interannual mass changes are not uniformly distributed but mostly confined in the tropical Pacific and Indian oceans. We also find that at some periods (in particular during the 2010/2011 La Nina event), the steric <span class="hlt">sea</span> <span class="hlt">level</span> contribution has to be accounted for, in addition to the mass term, to fully explain the observed GMSL anomaly.</p> </li> <li> <p><span><span class="hlt">Sea-level</span> <span class="hlt">fluctuations</span> show Ocean Circulation controls Atlantic Multidecadal Variability</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>McCarthy, Gerard; Haigh, Ivan; Hirschi, Joel; Grist, Jeremy; Smeed, David</p> <p>2015-04-01</p> <p>We present observational evidence that ocean circulation controls the decadal evolution of heat content and consequently sea-surface temperatures (SST) in the North Atlantic. One of the most prominent modes of Atlantic variability is the Atlantic multidecadal oscillation (AMO) observed in SSTs. Positive (negative) phases of the AMO are associated with warmer (cooler) SSTs. Positive phases of the AMO have been linked with decadal climate <span class="hlt">fluctuations</span> including increased summer precipitation in Europe; increased northern hemisphere land temperatures, fewer droughts in the Sahel region of Africa and increased Atlantic hurricane activity. It is widely believed that the Atlantic circulation controls the phases of the AMO by controlling the decadal changes in heat content in the North Atlantic. However, due to the lack of ocean circulation observations, this link has not been previously proven. We present a new interpretation of the <span class="hlt">sea-level</span> gradient along to the east coast of the United States to derive a measure of ocean circulation spanning decadal timescales. We use this to estimate heat content changes that we validate against direct estimates of heat content. We use the longevity of the tide gauge record to show that circulation, as interpreted in <span class="hlt">sea-level</span> gradient changes, drives the major transitions in the AMO since the 1920's. We show that the North Atlantic Oscillation is highly correlated with this <span class="hlt">sea-level</span> gradient, indicating that the atmosphere drives the circulation changes. The circulation changes are essentially integrated by the ocean in the form of ocean heat content and returned to the atmosphere as the AMO. An additional consequence of our interpretation is that recently reported accelerations in <span class="hlt">sea-level</span> rise along the US east coast are consistent with a declining AMO that has been predicted by a number of authors.</p> </li> <li> <p><span>Orbital forced <span class="hlt">sea</span> <span class="hlt">level</span> <span class="hlt">fluctuations</span> during the Middle Eocene (ODP site 1172, East Tasman Plateau)</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Warnaar, J.; Stickley, C.; Jovane, L.; Roehl, U.; Brinkhuis, H.; Visscher, H.</p> <p>2004-12-01</p> <p>Ocean Drilling Program leg 189 was undertaken to test and refine the hypothesis (by Kennett et al., 1975), that the reconfiguration of continents around Antarctica (e.g.: the opening of the Tasmanian Gateway and Drake passage) led to the onset of the Antarctic Circumpolar Current that, in turn, would cause thermal isolation and hence cooling of Antarctica. This would possibly even cause global cooling, as suggested by the 33.3 Ma Oi1 event. The cores of leg 189, site 1172 on the eastern side of the Tasmanian Gateway provided a nearly complete succession of Eocene and Oligocene sediments. Cyclostratigraphic analysis based on XRF derived Ca and Fe records indicates distinct Milankovitch cyclicity between 40 and 36 Ma. (Röhl et al, in press). In the core-section representing magnetochron 18n-1n, the Ca record shows precession cycles in combination with obliquity, suggested to reflect <span class="hlt">sea</span> <span class="hlt">level</span> <span class="hlt">fluctuations</span> (Röhl et al, in press). New datasets include microfossil data (organic-walled dinoflagellate cysts, pollen/spores and diatoms), loss-on-ignition measurements, magnetic data (environmental magnetics - ARM). Here, we aim to further investigate the proposed relationship between astronomical forcing and <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span>. Additionally, we aim to obtain insight in the palaeoecology of the distinct endemic circum-Antarctic late Middle to Late Eocene dinoflagellate cyst assemblages. Results corroborate the concept that the cyclicity recorded by Ca and Fe measurements is the result of <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span>. This implies that during late Middle Eocene times, astronomical forcing has modulated <span class="hlt">sea</span> <span class="hlt">level</span> - most likely through Antarctic ice buildup and meltdown. In turn, this would indicate the presence of significant, though probably modest, ice masses already ~40 Ma ago, well before the onset of the Antarctic Circumpolar Current. Kennett, J. P., R. E. Houtz, et al. (1975). Development of the circum-Antarctic current. Science 186: 144-147. Röhl, U.; H. Brinkhuis, C</p> </li> <li> <p><span>Global <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> during the Last Interglaciation (MIS 5e)</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Hearty, Paul J.; Hollin, John T.; Neumann, A. Conrad; O'Leary, Michael J.; McCulloch, Malcolm</p> <p>2007-09-01</p> <p>The geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of <span class="hlt">sea</span> <span class="hlt">level</span> during the peak of the Last Interglaciation (Marine Isotope Stage (MIS) 5e, assumed average duration between 130±2 and 119±2 ka). Because <span class="hlt">sea</span> <span class="hlt">level</span> was higher than present, deposits are emergent, exposed, and widespread on many stable coastlines. Correlation with MIS 5e is facilitated by similar morphostratigraphic relationships, a low degree of diagenesis, uranium-thorium (U/Th) ages, and a global set of amino-acid racemization (AAR) data. This study integrates information from a large number of sites from tectonically stable areas including Bermuda, Bahamas, and Western Australia, and some that have experienced minor uplift (˜2.5 m/100 ka), including selected sites from the Mediterranean and Hawaii. Significant <span class="hlt">fluctuations</span> during the highstand are evident at many MIS 5e sites, revealed from morphological, stratigraphic, and sedimentological evidence. Rounded and flat-topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story. Despite predictions of much different <span class="hlt">sea-level</span> histories in Bermuda, the Bahamas, and Western Australia due to glacio- and hydro-isostatic effects, the rocks from these sites reveal a nearly identical record during the Last Interglaciation. The Last Interglacial highstand is characterized by several defined <span class="hlt">sea-level</span> intervals (SLIs) that include: (SLI#1) post-glacial (MIS 6/5e Termination II) rise to above present before 130 ka; (SLI#2) stability at +2 to +3 m for the initial several thousand years (˜130 to ˜125 ka) during which fringing reefs were established and terrace morphology was imprinted along the coastlines; (SLI#3) a brief fall to near or below present around 125 ka; (SLI#4) a secondary rise to and through ˜+3-4 m (˜124 to ˜122 ka); followed by (SLI#5) a brief period of instability (˜120 ka) characterized by a rapid rise to between +6 to +9 m during</p> </li> <li> <p><span>Humboldt Bay Vertical Reference System Working Group: unraveling tectonic and <span class="hlt">eustatic</span> factors of <span class="hlt">sea</span> <span class="hlt">level</span> rise in northern California, Humboldt Bay</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Williams, T. B.; Anderson, J. K.; Burgette, R. J.; Gilkerson, W.; Hemphill-Haley, M.; Leroy, T. H.; Patton, J. R.; Southwick, E.; Stallman, J.; Weldon, R. J.</p> <p>2012-12-01</p> <p><span class="hlt">Sea-level</span> rise is a critical factor in managing estuarine ecosystems, maintaining public infrastructure, and mitigating geologic hazards along north coastal California. The coastal region between Fort Bragg, California and Vancouver Island experiences ongoing land-level changes due to Cascadia subduction zone tectonics. These tectonic land-level changes sufficiently modify relative <span class="hlt">sea</span> <span class="hlt">level</span> such that <span class="hlt">sea-level</span> rise cannot be accurately estimated without determining the tectonic contribution. We use tide gages and precise level-loop surveys to observe modern land and water surface elevations around Humboldt Bay. These modern data, combined with historic survey data, will be used to deconfound the various factors contributing to relative <span class="hlt">sea</span> <span class="hlt">level</span> change. Independent analysis of existing NOAA tide gages and EarthScope CGPS stations indicate 2.5 mm/yr of land subsidence near Humboldt Bay and 2 mm/yr of land uplift in Crescent City. Presuming the bulk of the strain accumulation is due to the southern portion of the Cascadia subduction zone, these data suggest Humboldt Bay is west of the locked zone, not to the east as previously reported by several researchers.</p> </li> <li> <p><span>Effects of Pleistocene <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> on mangrove population dynamics: a lesson from Sonneratia alba.</span></p> <p>PubMed</p> <p>Yang, Yuchen; Li, Jianfang; Yang, Shuhuan; Li, Xinnian; Fang, Lu; Zhong, Cairong; Duke, Norman C; Zhou, Renchao; Shi, Suhua</p> <p>2017-01-18</p> <p>A large-scale systematical investigation of the influence of Pleistocene climate oscillation on mangrove population dynamics could enrich our knowledge about the evolutionary history during times of historical climate change, which in turn may provide important information for their conservation. In this study, phylogeography of a mangrove tree Sonneratia alba was studied by sequencing three chloroplast fragments and seven nuclear genes. A low level of genetic diversity at the population level was detected across its range, especially at the range margins, which was mainly attributed to the steep <span class="hlt">sea-level</span> drop and associated climate <span class="hlt">fluctuations</span> during the Pleistocene glacial periods. Extremely small effective population size (Ne) was inferred in populations from both eastern and western Malay Peninsula (44 and 396, respectively), mirroring the fragility of mangrove plants and their paucity of robustness against future climate perturbations and human activity. Two major genetic lineages of high divergence were identified in the two mangrove biodiversity centres: the Indo-Malesia and Australasia regions. The estimated splitting time between these two lineages was 3.153 million year ago (MYA), suggesting a role for pre-Pleistocene events in shaping the major diversity patterns of mangrove species. Within the Indo-Malesia region, a subdivision was implicated between the South China Sea (SCS) and the remaining area with a divergence time of 1.874 MYA, corresponding to glacial vicariance when the emerged Sunda Shelf halted genetic exchange between the western and eastern coasts of the Malay Peninsula during Pleistocene <span class="hlt">sea-level</span> drops. Notably, genetic admixture was observed in populations at the boundary regions, especially in the two populations near the Malacca Strait, indicating secondary contact between divergent lineages during interglacial periods. These interregional genetic exchanges provided ample opportunity for the re-use of standing genetic variation</p> </li> <li> <p><span>Millennial/submillennial-scale <span class="hlt">sea-level</span> <span class="hlt">fluctuations</span> in western Mediterranean during the second highstand of MIS 5e</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Dabrio, C. J.; Zazo, C.; Cabero, A.; Goy, J. L.; Bardají, T.; Hillaire-Marcel, C.; González-Delgado, J. A.; Lario, J.; Silva, P. G.; Borja, F.; García-Blázquez, A. M.</p> <p>2011-02-01</p> <p>This paper investigates a series of small-scale, short-lived <span class="hlt">fluctuations</span> of <span class="hlt">sea</span> <span class="hlt">level</span> registered in a prograding barrier spit that grew during the MIS 5e. This interglacial includes three highstands ( Zazo et al., 2003) and we focus on the second highstand, of assumed duration ˜10 ± 2 ka, given that U-Th ages do not provide more accurate data. Geometry and 3D architecture of beach facies, and thin-section petrography were used to investigate eight exposed offlapping subunits separated by seven conspicuous erosion surfaces, all interpreted as the result of repeated small-scale <span class="hlt">fluctuations</span> of <span class="hlt">sea</span> <span class="hlt">level</span>. Each subunit records a relatively rapid rise of <span class="hlt">sea</span> <span class="hlt">level</span> that generated a gravelly shoreface with algal bioherms and a sandy uppermost shoreface and foreshore where most sand accumulated. A second range of still smaller-scaled oscillations of <span class="hlt">sea</span> <span class="hlt">level</span> has been deduced in this phase of <span class="hlt">sea-level</span> <span class="hlt">fluctuation</span> from lateral and vertical shifts of the foreshore-plunge-step-uppermost shoreface facies. Eventually, progradation with gently falling <span class="hlt">sea</span> <span class="hlt">level</span> took place and foreshore deposits underwent successive vadose cementation and subaerial dissolution, owing to relatively prolonged exposure. Later recovery of <span class="hlt">sea</span> <span class="hlt">level</span> re-established the highstand with <span class="hlt">sea</span> <span class="hlt">level</span> at approximately the same elevation, and there began deposition of a new subunit. The minimum <span class="hlt">sea-level</span> variation (fall and subsequent rise) required to generate the observed features is 4 m. The time span available for the whole succession of events, and comparison with the Holocene prograding beach ridge complex in the nearby Roquetas (Almería) were used to calculate the periodicity of events. A millennial-suborbital time scale is suggested for <span class="hlt">fluctuations</span> separating subunits and a decadal scale for the minor oscillations inside each subunit.</p> </li> <li> <p><span>Paleo-surfaces of glacio-<span class="hlt">eustatically</span> forced aggradational successions in the coastal area of Rome: Assessing interplay between tectonics and <span class="hlt">sea-level</span> during the last ten interglacials</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Marra, Fabrizio; Florindo, Fabio; Anzidei, Marco; Sepe, Vincenzo</p> <p>2016-09-01</p> <p>Recently acquired geochronological and stratigraphic data provide new information on the sedimentary successions deposited by the Paleo-Tiber River in the coastal and near-coastal area of Rome in consequence of the glacio-<span class="hlt">eustatic</span> changes, allowing to better define their inner geometry and palaeogeographic spatial distribution. In the present work we use this revised sedimentary dataset to provide a geochronologically constrained and tectonically adjusted record of paleo <span class="hlt">sea-level</span> indicators. Aimed at this scope, we review literature data acquired in the last 35 years and using the new geochronological constraints we pinpoint the coastal-to-fluvial terraces of MIS 5 and MIS 7, mapping their relic surfaces in an area of 30 km along the coast north and south of the Tiber River mouth, and 20 km inland of the fluvial valleys of Tiber and Aniene rivers. The geometry of these paleo-surfaces provides constraints on the relative elevation of the <span class="hlt">sea-level</span> during the last interglacials and on the uplift rates in this region during the last 200 ka. In particular, we recognize the previously undetected terraces of MIS 5.3 and MIS 5.1 interstadials, and we assess their spatial relationship with respect to MIS 5.5, providing important information on <span class="hlt">sea-level</span> oscillations during this time span. Comparison with <span class="hlt">sea-level</span> indicators provided by previous aggradational successions deposited during past interglacials spanning MIS 9 through MIS 21 in the coastal area of Rome, also allows us to reconstruct the tectonic history and investigate its relationships with the Middle-Pleistocene volcanic activity of the Roman Comagmatic Region along the Tyrrhenian Sea margin of Italy in the last 900 ka.</p> </li> <li> <p><span>An algorithm based on <span class="hlt">sea</span> <span class="hlt">level</span> pressure <span class="hlt">fluctuations</span> to identify major Baltic inflow events</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Schimanke, Semjon; Dieterich, Christian; Markus Meier, H. E.</p> <p>2014-05-01</p> <p>The Baltic Sea is one of world largest brackish water areas with an estuarine like circulation. It is connected to the world ocean through the narrow Danish straits limiting the exchange of water masses. The deep water of the Baltic Sea is mainly renewed by so called major Baltic inflows which are an important feature to sustain the sensitive steady state of the Baltic Sea. We introduce an algorithm to identify atmospheric variability favourable for major Baltic inflows. The algorithm is based on <span class="hlt">sea</span> <span class="hlt">level</span> pressure fields as the only parameter. Characteristic <span class="hlt">sea</span> <span class="hlt">level</span> pressure pattern <span class="hlt">fluctuations</span> include a precursory phase of 30 days and 10 days of inflow period. The algorithm identifies successfully the majority of observed major Baltic inflows between 1961--2010. In addition, the algorithm finds some occurrences which cannot be related to observed inflows. In these cases with favourable atmospheric conditions inflows were precluded by contemporaneously existing saline water masses or strong freshwater supply. No event is registered during the stagnation period 1983-1993 indicating that the lack of inflows is a consequence of missing favourable atmospheric variability. The only striking inflow which is not identified by the algorithm is the event in January 2003. We demonstrate that this is due to the special evolution of <span class="hlt">sea</span> <span class="hlt">level</span> pressure fields which are not comparable with any other event. Finally, the algorithm is applied to an ensemble of scenario simulations. The result indicates that the number of atmospheric events favourable for major Baltic inflows increases slightly in all scenarios. Possible explanations as for instance more frequent atmospheric blockings or changes in the NAO will be discussed.</p> </li> <li> <p><span>Temporal scaling behavior of <span class="hlt">sea-level</span> change in Hong Kong - Multifractal temporally weighted detrended <span class="hlt">fluctuation</span> analysis</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Zhang, Yuanzhi; Ge, Erjia</p> <p>2013-01-01</p> <p>The rise in global <span class="hlt">sea</span> <span class="hlt">levels</span> has been recognized by many scientists as an important global research issue. The process of <span class="hlt">sea-level</span> change has demonstrated a complex scaling behavior in space and time. Large numbers of tide gauge stations have been built to measure <span class="hlt">sea-level</span> change in the North Pacific Ocean, Indian Ocean, North Atlantic Ocean, and Antarctic Ocean. Extensive studies have been devoted to exploring <span class="hlt">sea-level</span> variation in Asia concerning the Bohai Gulf (China), the Yellow Sea (China), the Mekong Delta (Thailand), and Singapore. Hong Kong, however, a mega city with a population of over 7 million situated in the mouth of the Pear River Estuary in the west and the South China Sea in the east, has yet to be studied, particularly in terms of the temporal scaling behavior of <span class="hlt">sea-level</span> change. This article presents an approach to studying the temporal scaling behavior of <span class="hlt">sea-level</span> change over multiple time scales by analyzing the time series of <span class="hlt">sea-level</span> change in Tai Po Kou, Tsim Bei Tsui, and Quarry Bay from the periods of 1964-2010, 1974-2010, and 1986-2010, respectively. The detection of long-range correlation and multi-fractality of <span class="hlt">sea-level</span> change seeks answers to the following questions: (1) Is the current <span class="hlt">sea-level</span> rise associated with and responsible for the next rise over time? (2) Does the <span class="hlt">sea-level</span> rise have specific temporal patterns manifested by multi-scaling behaviors? and (3) Is the <span class="hlt">sea-level</span> rise is temporally heterogeneous in the different parts of Hong Kong? Multi-fractal temporally weighted de-trended <span class="hlt">fluctuation</span> analysis (MF-TWDFA), an extension of multi-fractal de-trended <span class="hlt">fluctuation</span> analysis (MF-DFA), has been applied in this study to identify long-range correlation and multi-scaling behavior of the <span class="hlt">sea-level</span> rise in Hong Kong. The experimental results show that the <span class="hlt">sea-level</span> rise is long-range correlated and multi-fractal. The temporal patterns are heterogeneous over space. This finding implies that mechanisms associated with the</p> </li> <li> <p><span>Bay sedimentation as controlled by regional crustal behaviour, local tectonics and <span class="hlt">eustatic</span> <span class="hlt">sea-level</span> changes: Coquimbo Formation (Miocene Pliocene), Bay of Tongoy, central Chile</span></p> <p>NASA Astrophysics Data System (ADS)</p> <p>Le Roux, J. P.; Olivares, Danisa M.; Nielsen, Sven N.; Smith, Norman D.; Middleton, Heather; Fenner, Juliane; Ishman, Scott E.</p> <p>2006-02-01</p> <p>The north-facing Bay of Tongoy in central Chile is flanked by topographic highs in the west and east. During the Miocene and Pliocene, the bay extended inland at least 30 km farther south than a present. It was filled with muds, sands, coquinas and gravel during a series of transgressions and regressions related to regional and local tectonic movements combined with global <span class="hlt">sea-level</span> variations. 87Sr/ 86Sr and microfossil dating indicates transgressions between 11.9-11.2 Ma, 10.1-9.5 Ma, 9.0-7.3 Ma, 6.3-5.3 Ma, 4.3-2.2 Ma and 1.7-1.4 Ma. The regional tectonic behaviour of the crust shows general uplifting from 10.5 Ma to 6.9 Ma, associated with subduction of the Juan Fernández Ridge (JFR) beneath this part of the continent. Subsidence followed between 6.9 and 2.1 Ma, in the wake of the southeastward-migrating JFR. The subsequent subduction of an oceanic plateau similar to the JFR caused rapid uplift that led to the final emergence of the bay above <span class="hlt">sea</span> <span class="hlt">level</span>. The Puerto Aldea normal fault along the western limit of the study area was reactivated during the regional uplift and subsidence events, with reverse faulting occurring during the latter phase. Sporadic fault reactivation probably triggered the rapid changes in water depth reflected in the recorded vertical succession of facies.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li>«</li> <li>1</li> <li>2</li> <li class="active"><span>3</span></li> <li>4</li> <li>5</li> <li>»</li> </ul> </div> </div> </div> </div> </div> <div id="sidebar"> <div id="sidebar-bgtop"></div> <div id="sidebar-content"> <ul> <li> <h2>I nostri siti</h2> <p><b>Il web delle imprese di pulizie Lecco:</b></p> <ul> <li><a href=""></a></li> <li><a href=""></a></li> <li><a href=""></a></li> <li><a href=""></a></li> <li><a href=""></a></li> </ul> </li> <li> <h2>Dove Siamo a Lecco</h2> <p> <b>piazza 20 settembre, 2 <br/>23900 LECCO (LC)</b> <br/> <br/> Altre sedi : <br/> <br/> <b>CERNUSCO LOMBARDONE <br/>via G.Lurani Cernuschi 3</b> <br/> <br/> <b>CAPRIATE SAN GERVASIO <br/>Via Bergamo, 48</b> <br/> <br/> <b>BERGAMO - Via Statuto</b> <br/> <br/> <img src="images/logo-numeroverde4.jpg" alt="numero verde Il Giglio"/> <br/> <br/> Per maggiori informazioni<br/> vai alla sezione <a href="contatti.html"><b>Contatti</b></a> <br/> <br/> oppure visita il sito: <a href=""><b></b></a> </p> </li> </ul> </div> <div id="sidebar-bgbtm"></div> </div> </div> <div id="footer"> <p>© 2010. 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