Isostatic Response Research Articles

Isostatic Control of Axial Rivers and Large Drainage Basins on Passive Margins

AbstractMore than half of the world's large rivers flow towards the ocean crossing passive continental margins. Here using an analytical solution and numerical models, we demonstrate that on passive margins, river basins may be integrated by major margin‐parallel channels, which form as a flexural isostatic response of the lithosphere to mechanical/erosional unloading along the margin. We analyzed the downstream courses of large rivers flowing across the passive margins and find that the majority of them (31 of 36) have major margin‐parallel channels. Occurrences of these channels are generally consistent with the model predictions, although the exact locations and geometry of these rivers may also be controlled/changed by other factors. Our results suggest that the lithosphere strength has an important control on the geometry of large river systems on passive margins, linking the evolution and routing of the Earth's freshwater systems to its deep interior dynamics.

Geoarchaeological Evidence for the Decline of the Medieval City of Qalhat, Oman

The medieval city of Qalhat was an important trade town along the sea routes in the Indian Ocean. The reasons for the decline of the city are unclear, as the archaeological evidence is inconclusive. Geological field work was conducted and a digital elevation model analysed to test the hypothesis that the city was destroyed by an earthquake. The study area is located along the passive continental margin of the Arabian Plate. The coast shows a set of Pleistocene marine terraces. These landforms are in indication of lithosphere uplift. Faulted terrace fill deposits and deviating fluvial streams indicate rather recent lithosphere deformation. Processes responsible for the deformation are seen as subduction related forebulge uplift, serpentinite diapirism as well as isostatic response to karstification of limestone. We conclude that earthquake activity along the most prominent structural element, the Qalhat Fault, is a plausible reason for the decline of the medieval city.

Deformation in response to landscape evolution during glacial cycles on the U.S. Atlantic passive margin

Elevations of Pleistocene highstand formations that lie across the South Carolina and northern Georgia coastal plain lie well above those of reconstructed past sea levels. This discrepancy has been attributed to some combination of tectonics, glacial isostatic adjustment, and/or deviations in estimated ocean volumes derived from the marine δ18O record. To reconcile these anomalous elevations, we combine a landscape evolution model with models of coupled ice sheet, sea level and solid Earth deformation along the southern U.S. Atlantic passive margin to estimate erosion, deposition and corresponding isostatic response since Marine Isotope Stage (MIS) 11 (∼410 ka). We find that along-shore changes in modeled paleo-shoreline elevations are similar to measured elevations along 100s of kilometers. Up to 10 m of shoreline uplift since MIS 11 may be attributed to isostatic feedback in response to sediment redistribution.

The sea cliff at Dwasieden: soft-sediment deformation structures triggered by glacial isostatic adjustment in front of the advancing Scandinavian Ice Sheet

Abstract. Isostatic response of the Earth's crust as a consequence of the fluctuating extent of ice-sheet masses was accompanied by earthquakes probably due to local reactivation of pre-existing faults. Our study of a glacilacustrine and glacifluvial succession exposed on Rügen Island (SW Baltic Sea) indicates that some of the soft-sediment deformation structures within the succession must have formed shortly before the front of the Pleistocene Scandinavian Ice Sheet reached the study area (during the Last Glacial Maximum), thus during a stage of ice advance. Based on analysis of the textural and structural features of the soft-sediment deformation structures, the deformed layers under investigation are interpreted as seismites which formed as a result of seismically induced liquefaction and fluidisation.

The Role of Lithospheric Flexure in the Landscape Evolution of the Wilkes Subglacial Basin and Transantarctic Mountains, East Antarctica

AbstractReconstructions of the bedrock topography of Antarctica since the Eocene‐Oligocene Boundary (approximately 34 Ma) provide important constraints for modeling Antarctic ice sheet evolution. This is particularly important in regions where the bedrock lies below sea level, since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change. Here we use 3‐D flexural modeling to reconstruct the evolution of the topography of the Wilkes Subglacial Basin (WSB) and Transantarctic Mountains (TAM) in East Antarctica. We estimate the spatial distribution of glacial erosion beneath the East Antarctic Ice Sheet, and restore this material to the topography, which is also adjusted for associated flexural isostatic responses. We independently constrain our post‐34 Ma erosion estimates using offshore sediment stratigraphy interpretations. Our reconstructions provide a better‐defined topographic boundary condition for modeling early East Antarctic Ice Sheet history. We show that the majority of glacial erosion and landscape evolution occurred prior to 14 Ma, which we interpret to reflect more dynamic and erosive early ice sheet behavior. In addition, we use closely spaced 2‐D flexural models to test previously proposed hypotheses for a flexural origin of the TAM and WSB. The pre‐34 Ma topography shows lateral variations along the length of the TAM and WSB that cannot be explained by uniform flexure along the front of the TAM. We show that some of these variations may be explained by additional flexural uplift along the south‐western flank of the WSB and the Rennick Graben in northern Victoria Land.

The importance of lateral Earth structure for North American glacial isostatic adjustment

The isostatic response of the Earth to past mass exchange between ice sheets and oceans, so-called glacial isostatic adjustment (GIA), is an important geodynamic process in North America. Modelling GIA observables provides one of the few direct methods for estimating Earth viscosity structure. We investigate here the requirement for anomalously high mantle viscosities to fit the relative sea level (RSL) data along the Atlantic and Gulf coasts of North America found in recent GIA studies. We demonstrate that this requirement is primarily related to the modelled geometry and evolution of the peripheral bulge of the Laurentide ice sheet. We show that a 3D Earth model with a global average viscosity in the upper mantle of 0.3×1021 Pas and 3×1022 Pas in the lower mantle, which is consistent with both the Richmond Gulf (Hudson Bay) relaxation time and several recent global analyses, is able to produce a much improved fit to the Gulf and Atlantic coast RSL data relative to the 1D Earth model results when no lateral structure is applied. Therefore, we conclude that realistic implementations of lateral structure can explain the markedly different viscosity inferences obtained using 1D GIA models and RSL data from different regions of North America. A necessary caveat is that there are significant differences among the computed RSL curves corresponding to the three different realisations of lateral structure considered here, demonstrating significant uncertainty associated with this model input.

Post-rift stratigraphic architectures along the African margin of the Equatorial Atlantic: Part I the influence of extension obliquity

We investigated the variability of the first-order crustal structure and early post-rift stratigraphy of six segments of the African Equatorial Atlantic margin using sub-surface data (seismic and wells). Extension obliquity of the segments varies from 0° for the West Ivory Coast and Ghana transform segments to 30° for the Togo-Benin oblique segment and 75° for the East Ivory Coast normally divergent segment. The Sierra Leone and Liberia segments underwent probably deformation during both the early Jurassic rifting of the Central Atlantic and the early Cretaceous rifting of the Equatorial Atlantic with contrasted divergence obliquities. For segments that underwent a single rifting, we show that, the higher the obliquity, the wider the crustal thinning domain. This has a major influence on the first-order geometry of all the post-rift horizons, including the present-day slope: the lower the obliquity, the larger the differential subsidence across the margin and the steeper the present-day slopes of post-rift horizons. This also has a major influence on the flexural isostatic response of the lithosphere to thermal- and erosion/sedimentation- driven (un)loads during the early post-rift. Narrow (transform) segments underwent higher flexural (and/or thermal) uplifts in the proximal domain than wider divergent segments. Along the same margin, divergent segments therefore may preserve early post-rift deposits in their proximal domains, whereas they are not preserved on nearby transform segments.

New relative sea-level insights into the isostatic history of the Western Mediterranean

A recent suite of Relative Sea-Level (RSL) data for the past 12 ka BP has provided new insights into the sea-level histories of the western Mediterranean region. Our analysis of the chronostratigraphic context of sea-level indicators from Spain (Catalonia, the Balearic Islands and the Gulf of Valencia), France (Corsica Island) and Italy (Sardinia Island) has yielded 162 new sea-level index and limiting points. These data have considerably enhanced previous RSL compilations, in addition to improving the quality of spatio-temporal sea-level reconstructions and our capacity to estimate isostatic-related vertical motions in the western Mediterranean basin. The glacial and hydro-isostatic adjustment (GIA) pattern elucidated by the new database shows discrepancy with respect to those predicted by the available GIA models. In particular, the new results underscore a non-coherent isostatic response of the central portion of the western Mediterranean, with the Balearic Islands manifesting significant departures from the sea-level histories of Corsica, Sardinia and, more generally, along most of the western Mediterranean coast. Our results are a crucial contribution to defining both the pattern and the magnitude of the isostatic signal along the western Mediterranean coast. In fact, vertical isostatic motions represent a key to better assess any possible post-industrial acceleration in sea-level rise and to define future scenarios of coastal inundation in the context of global change.

Resolving the contributing factors to Mississippi Delta subsidence: Past and Present

AbstractTo date, quantification of individual components that contribute to shallow and deep‐seated subsidence in passive margin deltas worldwide has proven problematic. A new, regional gridded chronostratigraphic dataset for the Lower Mississippi Delta region, derived from 80,928 well reports across the northern Gulf of Mexico (GOM), has bridged the disparity between geodetic mean rates measuring total land surface subsidence across annual‐to‐decadal timescales and the deep‐seated stratigraphic subsidence rates that record isostatic response over timescales of >104 years. Through a quantitative assessment of gridded chronostratigraphic surfaces, sections, and subsidence rates extending from the Middle Pleistocene (0.58 Ma) to the Late Pliocene (3.85 Ma), we identify both temporal and spatial variability in deep‐seated subsidence across the northern GOM. Targeted deep‐seated subsidence data extracted across prior GOM Holocene sea‐level sample locations have revealed more than an order of magnitude greater rates of isostatic compensation in the Mississippi depocentre versus similar GOM sea‐level control sites in Florida and Alabama, casting doubt on efforts towards a representative Holocene sea‐level curve. Spatial variability in subsidence was also assessed locally in both the strike and dip directions to assess the contributions of growth faults. Fault throw displacement magnitude was discovered to decrease with depth, accounting for less than half of the total deep‐seated subsidence record of the Middle Pleistocene. Temporal subsidence complexities were also revealed including a direct, inverse logarithmic relationship between subsidence rate and time indicating variable subsidence component controls across different timescales. Despite the spatial and temporal complexities, this dataset serves as the first regional baseline for deep‐seated subsidence rates across the northern GOM.

Tectonic geomorphology: An interdisciplinary study of the interaction among tectonic climatic and surface processes

Tectonic geomorphology is a fast-developing interdisciplinary research field. Different from traditional geomorphology, tectonic geomorphology strongly shifts to quantify the geomorphic processes. The central tenet in tectonic geomorphology is to clarify the interactions among tectonic, climatic, and surface processes, and to provide quantitative descriptions of climate, topography, hydrology, physical and chemical erosion, deposition and rock deformation and their relationships in tectonically active settings. In this review, we first introduce major scientific questions and central concepts, the techniques and methods commonly used in this field, especially the major game-changing dating techniques (e.g., cosmogenic nuclide dating and low-temperature thermochronology) and remote sensing or surveying methods (e.g., LiDAR). Then we present some case studies in the past three decades showing lines of evidence that the interaction among tectonic, climatic, and surface processes can occur in a wide range of temporal and spatial scales, ranging from hours to million-year in time, and from single fault to orogenic belt in space. We also synthesize important progresses in this field toward a better understanding of the topographic evolution of orogenic belts: (1) Tectonic, climatic and surface processes collaborate to shape the landscape such that tectonic activities alone do not necessarily lead to topographic growth. For instance, when erosion and tectonic accretion are in equilibrium, topographic steady state is reached, with no surface uplifting despite on-going tectonic activity. (2) Sedimentary records in range-front basins, such as the increase of deposition rate, or the occurrence of conglomerates, were often used as proxies of tectonic uplift of mountain ranges in early studies. However, sedimentary sequence should be a collective product of tectonic, climatic, and surface processes. These commonly-used proxies for tectonic activity can also be due to climate changes, instead. (3) Tectonics plays a key and leading role in the coupling of tectonic-climatic-surface process; climatic and surface processes influence but do not drive tectonics. (4) Isostatic response to erosion will lead to the rebound of mountain peaks, but the overall effect of erosion is to lower the mean elevation. Thus, uplift due to isostatic rebound is a secondary component of tectonics. Lastly, we outline in brief a list of outstanding scientific questions remaining to be answered in the field.

The Role of the 2008 Mw 7.9 Wenchuan Earthquake in Topographic Evolution: Seismically Induced Landslides and the Associated Isostatic Response

AbstractThe widely held notion about the relationship between reverse‐faulting earthquakes and mountain building has been challenged by recent studies suggesting a net coseismic lowering of surface height due to the 2008 Mw 7.9 Wenchuan earthquake. We calculate the long‐term isostatic response to the removal of coseismic landslide mass produced by the 2008 Wenchuan earthquake, using re‐estimated coseismic landslide volumes. The total isostatic response volume is associated with the input landslide volumes and ranges from ~1.0 to 2.7 km3, which did not change much with the varied input value of the effective elastic thickness (Te); however, the rebound distribution changes with Te. Consequently, the net uplift volume will be ~1.2–2.9 km3, taking into account the total landslide volume of 2.8 + 0.9/−0.7 km3 and the coseismic uplift of 2.6 ± 1.2 km3. The isostatic response due to Wenchuan earthquake is ~0.3 m but may vary from 0.15 to 0.6 m (input minimum and maximum landslide volumes from the combined scaling parameters, respectively) in the central Longmen Shan. We also find that the average net uplift is ~0.11–0.26 m, which resulted from the imbalance between earthquake‐caused uplift and the isostasy within the landslide region due to the Wenchuan earthquake. The total isostasy could reach ~550–1,300 m during the past 10–15 Ma, in the corridor bounding the coseismic surface ruptures. Our findings reveal that the evolution of local topography in the Longmen Shan region is inevitably related to the repeated tectonic events, especially the strong earthquakes similar to the 2008 Wenchuan earthquake.

Evidence from seismites for glacio-isostatically induced crustal faulting in front of an advancing land-ice mass (Rügen Island, SW Baltic Sea)

It is hitherto commonly thought that earthquakes triggered by geologically rapid changes in the pressure caused by the fluctuating extent of thick land-ice masses occur exclusively during ice retreat. Our study of deformed sediment layers within an undeformed glaciolacustrine and glaciofluvial succession exposed in a coastal cliff on Rügen Island, south-western Baltic Sea, challenges this widespread idea. Based on their structural and deformational features, the layers under investigation are interpreted as seismites which formed as a result of seismically-induced liquefaction. The stratigraphic context aided by optically stimulated luminescence (OSL) dating indicate that the documented seismites must have formed shortly before the front of the Pleistocene Scandinavian Ice Sheet reached the study area during the Last Glacial Maximum, thus during a stage of ice advance. This implies that the flexural isostatic response of the Earth's crust as a consequence of the ice load during ice advance was accompanied by earthquakes probably due to local re-activation of pre-existing faults. The crustal response to an increasing ice load was consequently less gradual than previous studies about glaciation-related tectonics suggest.

Evolution of the central West Greenland margin and the Nuussuaq Basin: Localised basin uplift along a stable continental margin proposed from thermochronological data

AbstractThe Late Cenozoic is typically considered a time of widespread episodic tectonic uplift along the West Greenland continental margin (36–2 Ma), similar to other margins across the North Atlantic, such as Norway, East Greenland and the UK. The present study re‐examines and remodels onshore thermochronological data from central West Greenland and the Cretaceous Nuussuaq Basin, utilising a Bayesian modelling approach and new concepts related to radiation damage within apatite. These new thermal histories indicate that slow‐protracted cooling has occurred across the southern extent of the margin during the Mesozoic and Cenozoic, whereas those from within the Nuussuaq Basin display reheating through the Late Cretaceous/Palaeogene and cooling to present. Results suggest that no significant Late Cenozoic uplift has occurred along the southern margin, while cooling in the Nuussuaq Basin is consistent with events outlined in the basin's stratigraphy and implies uplift during volcanism and an isostatic response to the unroofing of the lithosphere has elevated the modern topography. These results imply significant tectonism in the region ceased by ~45 Ma, yet have wider implications regarding how low temperature thermochronology data are treated and our understanding of the postrift evolution of passive margins.

Erosion-driven vertical motions of the circum Arctic: Comparative analysis of modern topography

Deep and complex geodynamic processes, including the effects of plumes, heat, plate tectonics, and local tectonics control the Earth’s surface. In the Arctic these deep processes are masked by extensive glaciations and associated or roughly synchronous erosion. In this study we aim to reveal these hidden geodynamic processes by modeling erosion backward in time by numerically restoring eroded material and calculating the flexural isostatic response repeatedly iteratively until eroded features are filled. This method estimates erosion recorded in the modern topography and models the influence of that erosion. Although the obvious topographic response to erosion is a lowering of the elevation, our coupled erosion-isostatic response method results in dramatic vertical motions leading to km-scale uplift in fjord carved areas of Scandinavia, Greenland, and Canadian Arctic Archipelago and supporting ancient orogenic belts of northern Siberia and northern Alaska to stay at high elevation. Sensitivity testing confirms the utility of our method over a range of effective elastic plate thicknesses as well as for laterally varying elastic thickness. Comparison of modelling results with observed gravity anomalies shows that our method is valid for both glacial and fluvial affected landscapes but more importantly links surface and deep Earth dynamics. Combined analysis of the gravity anomalies and model results also explains erosion as one of the main mechanisms responsible for gravity signal for tectonically inactive regions and illustrates the interaction of short wavelength erosional processes and large scale, regional processes like active orogenesis and dynamic topography.

Directly dating postglacial Greenlandic land-surface emergence at high resolution using in situ10Be

AbstractPostglacial emergence curves are used to infer mantle rheology, delimit ice extent, and test models of the solid Earth response to changing ice and water loads. Such curves are rarely produced by direct dating of land emergence; rather, most rely on the presence of radiocarbon-datable organic material and inferences made between the age of sedimentary deposits and landforms indicative of former sea level. Here, we demonstrate a new approach,10Be dating, to determine rates of postglacial land emergence in two different settings. In southern Greenland (Narsarsuaq/Igaliku), we date directly the exposure, as relative sea level fell, of gravel beaches and rocky outcrops allowing determination of rapid, post–Younger Dryas emergence. In western Greenland (Kangerlussuaq), we constrain Holocene isostatic response by dating the sequential stripping of terrace sediment driven by land-surface uplift, relative sea-level fall, and resulting fluvial incision. The technique we employ provides high temporal and elevation resolution important for quantifying rapid emergence immediately after deglaciation and less rapid uplift during the middle Holocene.10Be-constrained emergence curves can improve knowledge of relative sea-level change by dating land emergence along rocky coasts, at elevations and locations where radiocarbon-datable sediments are not present, and without the lag time needed for organic material to accumulate.

Resolution test of GOCE satellite data applied to density anomalies at crustal and upper mantle levels.

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission was devised by the European Space Agency to study the Earth’s gravity field with an unprecedented accuracy using gravity gradient data. The goal of this study is to analyze the resolution in terms of size, burial depth and density contrast of anomalous bodies related to geological structures that can be identified from GOCE data. A parametric study is performed by calculating the gravity gradients associated with rectangular prisms with fixed aspect ratio of 9:3:1 and varying the size, burial depth, and density contrast, selecting those structures showing amplitudes and wavelength variations comparable to the accuracy of GOCE data. Results show that the minimum size for crustal anomalies to be resolved for the vertical component of the gravity gradient is 22.5x7.5x2.5km for a Δρ=500kg/m 3 , burial depth of 0km, and at computation height of 255km. To generate a sufficient signal in amplitude and wavelength in all the components, the size of the anomalous body is 270x90x30km. For a body with Δρ=50kg/m 3 and 0km burial depth a minimum size of 41.4x13.8x4.6km is required for the vertical component at a computation height of 255km. In addition, the application to the 3D case of a passive continental margin which broadly resembles the crustal structure of the NW-Iberia shows that the signal of all gravity gradient components is dominated by the crustal thinning associated with the passive continental margins and the corresponding isostatic response.

Nonlinear inversion of isostatic residual gravity data from Montage Basin, northern Gulf of California

The flexural isostatic response to surface loads is used to estimate the crustal thickness in northwestern Mexico and Southwestern USA. This estimate is used to compute an isostatic regional gravity, which, subtracted from Bouguer gravity anomalies, led to the isostatic residual gravity anomaly at Montage Basin. This basin is located between the southern portion of the Mexicali Valley and the northern Gulf of California, it roughly has an extension of [Formula: see text] wide, and it shows a gravity minimum reaching approximately [Formula: see text]. Montage Basin is within the extensional province of the Gulf of California, where rifting is currently an ongoing geologic process, and deep exploratory wells drilled by Petróleos Mexicanos have shown that the basin accommodates thick sedimentary sequences greater than 5 km. The interpretation of the isostatic residual gravity anomaly is considered as a nonlinear inverse problem, constrained using density as a function of depth derived from Gardner’s equation applied to dual time [Formula: see text]-logs, assuming isostatic equilibrium and considering the basin as a subsurface load that is compensated at depth by a mass of unknown shape and density. The outcome of the inverse problem suggests that Montage Basin accommodates as much as 7.5 km thick sedimentary sequences and a compensating mass at a minimum depth of 13 km.

Vertical tectonic movements and sedimentary filling of basins during syn-rift and post-rift stages of lithosphere development

One-dimensional numerical modeling of isostatic response of lithosphere to thermal uplift of its bottom (active rifting) and interconnected formally independent thinning of the crust has been fulfilled. Evolution curves of vertical movements and interfaces displacements velocities have been examined. Depending on the introduced index of thinning of the crust velocity n =0,1¸3 spectrum of surface expression has been segregated: from the arc rift via annectent forms ( n =0,8¸1,5) to deep water depressions. In relation to a set of problems of paleo-tectonic reconstructions of sedimentary basins modeling of vertical movements accompanied by sedimentation was conducted. Situations have been examined when syn-rift sedimentation and dipping are much less than post-rift ones. Possibilities of establishment of conditions and evolution of continental and marine sedimentation within the limits of different regimes of riftogenesis have been investigated. In order to overcome limitations specific to methods of modern back-stripping an expanded variant of direct modeling has been tested based on the principle of «free sedimentation», taking into account facial vertical heterogeneity of the section and stratigraphic unconformities. In the model which explains formation of the Permian-Triassic sedimentary column of the Ebro depression (Iberia) paleo-geographic features of sedimentation are replicated: it was the continental one in the Permian and early Triassic with transition to marine in the end of Middle Triassic, uncertainty of stratigraphic unconformities of the Late Permian is also revealed. Accordingly, the complicated character of active riftogenesis consisting of two stages is predicted; for the second (Late Permian) variation of regime as three phases with different indices of thinning the crust is provided. Sedimentation and dipping of southeastern part of DDD which is characterized by abnormally high thicknesses of Carboniferous deposits are replicated at first approximation within the limits of a model including riftogenic dipping in the Late Devonian and the post-rift thermal one in the Carboniferous. The obtained changes of the sea depths are correlated with formational subdivisions of the Carboniferous cover and the intensity of coal accumulation.

Does slab-window opening cause uplift of the overriding plate? A case study from the Gulf of California

Complete subduction of an oceanic plate results in slab-window opening. A key uncertainty in this process is whether the higher heat flux and asthenospheric upwelling conventionally associated with slab-window opening generate a detectable topographic signature in the overriding plate. We focus on the Baja California Peninsula, which incorporates the western margin of the Gulf of California rift. The topography and tectonics of the rift flank along the peninsula are strongly bimodal. North of the Puertecitos accommodation zone, the primary drainage divide attains a mean elevation of ca. 1600m above sea level (asl), above an asthenospheric slab-window opened by Pacific-Farallon spreading ridge subduction along this section of the trench at ca. 17–15Ma. To the south, mean topography decreases abruptly to ca. 800m asl (excluding the structurally distinct Los Cabos block at the southern tip of the peninsula), above fragments of the oceanic Farallon slab which stalled following slab tear-off at ca. 15–14Ma. Along the peninsula, a low-relief surface established atop Miocene subduction-related volcaniclastic units has been incised by a west-draining canyon network in response to uplift. These canyons exhibit cut-and-fill relationships with widespread post-subduction lavas. Here, we utilise LANDSAT and digital elevation model (DEM) data, integrated with previously published K-Ar and 40Ar/39Ar lava crystallisation ages, to constrain the onset of rift flank uplift to ca. 9–5Ma later than slab-window formation in the north and ca. 11–10Ma later in the south. These greatly exceed response time estimates of ca. 2Ma or less for uplift triggered by slab-window opening. Instead, uplift timing of the high-elevation northern region is consistent with lower-lithospheric erosion driven by rift-related convective upwelling. To the south, stalled slab fragments likely inhibited convective return flow, preventing lithospheric erosion and limiting uplift to the isostatic response to crustal unloading during rifting.

Tide gauge observations in Antarctica (1958–2014) and recent ice loss

AbstractSeveral historical sea level time series from Antarctic tide gauges, available from the Permanent Service for Mean Sea Level, are analysed. Two sea level curves, obtained by averaging data from the Antarctic Peninsula and West Antarctica, for 1958–2014, show trends of (2.0±0.1) and (1.8±0.2) mm yr-1, respectively. By empirical mode decomposition, cyclic and non-cyclic components of sea level change were separated. A periodicity of 4–5 years was confirmed and attributed to the effects of the Antarctic Circumpolar Wave. The non-cyclic components were found to show a ‘levelling off’ of ≈ 1 mm yr-1 since c. 2000, which cannot be attributed to the isostatic response to Holocene ice melting. Using assessed mass balance data from the West Antarctic Ice Sheet and the Antarctic Peninsula, we studied the response to current ice loss in the region and found that the levelling off could be partly explained by accelerated melting during the last approximately two decades. This may represent the first evidence of sea level fingerprints of glacial melting in Antarctica.