Present and near-future global sea-level changes

Values between 1.0 and 1.5 mm/yr, often quoted in the literature for the present-day rate of eustatic sea-level rise, have been obtained in many cases by averaging records of tide-gauge stations, after having omitted areas of glacio-isostatic or tectonic uplift, though including areas of subsidence. This approach results in an overestimation of the sea-level rise, which is increased by the fact that, for geological reasons and human-induced factors, subsidence is expected to occur more frequently than uplift in oceanic and coastal areas.In the absence of absolutely stable areas in the world, a new approach is proposed, which shows that on the Atlantic coasts of Europe, when land movements are removed, the sea-level rise during the last century has been only 4–6 cm, i.e. two to three times smaller than the estimation claimed by most authors. This value is consitent with current computations of the recent effects on sea level of the thermal expansion of the ocean water (2–5 cm) and of the melting of small glaciers (1.4–5 cm).Estimations of possible sea-level changes during the next century diverge with different authors, varying from a sea-level drop of 7 cm to a sea-level rise of over 3.5 m. There are some problems however with the assumptions made and some feedback phenomena have not yet been taken into account. In addition, the relationship between the atmospheric CO₂ content, temperature and sea level is far from being demonstrated for the recent past.     

Effective sea-level rise and deltas: Causes of change and human dimension implications

An assessment is made of contemporary effective sea-level rise (ESLR) for a sample of 40 deltas distributed worldwide. For any delta, ESLR is a net rate, defined by the combination of eustatic sea-level rise, the natural gross rate of fluvial sediment deposition and subsidence, and accelerated subsidence due to groundwater and hydrocarbon extraction. ESLR is estimated under present conditions using a digital data set of delta boundaries and a simple model of delta dynamics. The deltas in this study represent all major climate zones, levels of population density, and degrees of economic development. Collectively, the sampled deltas serve as the endpoint for river basins draining 30% of the Earth's landmass, and 42% of global terrestrial runoff. Nearly 300 million people inhabit these deltas. For the contemporary baseline, ESLR estimates range from 0.5 to 12.5 mm yr^− 1. Decreased accretion of fluvial sediment resulting from upstream siltation of artificial impoundments and consumptive losses of runoff from irrigation are the primary determinants of ESLR in nearly 70% of the deltas. Approximately 20% of the deltas show accelerated subsidence, while only 12% show eustatic sea-level rise as the predominant effect. Extrapolating contemporary rates of ESLR through 2050 reveals that 8.7 million people and 28,000 km² of deltaic area in the sample set of deltas could suffer from enhanced inundation and increased coastal erosion. The population and area inundated rise significantly when considering increased flood risk due to storm surge. This study finds that direct anthropogenic effects determine ESLR in the majority of deltas studied, with a relatively less important role for eustatic sea-level rise. Serious challenges to human occupancy of deltaic regions worldwide are thus conveyed by factors which to date have been studied less comprehensively than the climate change–sea-level rise question.     

Geocentric sea-level trend estimates from GPS analyses at relevant tide gauges world-wide

The problem of correcting the tide gauge records for the vertical land motion upon which the gauges are settled has only been partially solved. At best, the analyses so far have included model corrections for one of the many processes that can affect the land stability, namely the Glacial-Isostatic Adjustment (GIA). An alternative approach is to measure (rather than to model) the rates of vertical land motion at the tide gauges by means of space geodesy. A dedicated GPS processing strategy is implemented to correct the tide gauges records, and thus to obtain a GPS-corrected set of ‘absolute’ or geocentric sea-level trends. The results show a reduced dispersion of the estimated sea-level trends after application of the GPS corrections. They reveal that the reference frame implementation is now achieved within the millimetre accuracy on a weekly basis. Regardless of the application, whether local or global, we have shown that GPS data analysis has reached the maturity to provide useful information to separate land motion from oceanic processes recorded by the tide gauges or to correct these latter. For comparison purposes, we computed the global average of sea-level change according to Douglas [Douglas, B.C., 2001. Sea level change in the era of the recording tide gauge. Int. Geophys. Ser., 75, pp. 37–64.] rules, whose estimate is 1.84 ± 0.35 mm/yr after correction for the GIA effect [Peltier, W.R., 2001. Global glacial isostatic adjustment and modern instrumental records of relative sea level history. Int. Geophys. Ser., 75, pp. 65–95.]. We obtain a value of 1.31 ± 0.30 mm/yr, a value which appears to resolve the ‘sea level enigma’ [Munk, W., 2002. Twentieth century sea level: an enigma. Proc. Natl. Acad. Sci. U.S.A., 99(10), pp. 6550–6555].     

Sea level budget over 2003–2008: A reevaluation from GRACE space gravimetry,satellite altimetry and Argo

From the IPCC 4th Assessment Report published in 2007, ocean thermal expansion contributed by ～ 50% to the 3.1 mm/yr observed global mean sea level rise during the 1993–2003 decade, the remaining rate of rise being essentially explained by shrinking of land ice. Recently published results suggest that since about 2003, ocean thermal expansion change, based on the newly deployed Argo system, is showing a plateau while sea level is still rising, although at a reduced rate (～ 2.5 mm/yr). Using space gravimetry observations from GRACE, we show that recent years sea level rise can be mostly explained by an increase of the mass of the oceans. Estimating GRACE-based ice sheet mass balance and using published estimates for glaciers melting, we further show that ocean mass increase since 2003 results by about half from an enhanced contribution of the polar ice sheets – compared to the previous decade – and half from mountain glaciers melting. Taking also into account the small GRACE-based contribution from continental waters (< 0.2 mm/yr), we find a total ocean mass contribution of ～ 2 mm/yr over 2003–2008. Such a value represents ～ 80% of the altimetry-based rate of sea level rise over that period. We next estimate the steric sea level (i.e., ocean thermal expansion plus salinity effects) contribution from: (1) the difference between altimetry-based sea level and ocean mass change and (2) Argo data. Inferred steric sea level rate from (1) (～ 0.3 mm/yr over 2003–2008) agrees well with the Argo-based value also estimated here (0.37 mm/yr over 2004–2008). Furthermore, the sea level budget approach presented in this study allows us to constrain independent estimates of the Glacial Isostatic Adjustment (GIA) correction applied to GRACE-based ocean and ice sheet mass changes, as well as of glaciers melting. Values for the GIA correction and glacier contribution needed to close the sea level budget and explain GRACE-based mass estimates over the recent years agree well with totally independent determinations.     

Trends of sea level variations in the South China Sea from merged altimetry data

In this study, more than 13 yr of merged altimetry sea level anomalies (SLA) data were used to analyze the trends of sea level variations in the South China Sea (SCS). The result shows that the mean sea level over the SCS has a rise rate of 11.3 mm/yr during 1993–2000 and a fall rate of 11.8 mm/yr during 2001–2005. The geographical distribution of the sea level variations over the SCS is asymmetric with a pronounced variation existing in the deep water. The trends of thermosteric sea level variations were also examined using Ishii data and MITgcm assimilation data. The result indicates that the thermal change of the upper layer of the SCS has a significant contribution to the sea level variations. Heat budget analysis suggests that heat advection may be a key factor influencing the thermal change. Apart from thermal contribution, the effect of water exchange on the sea level variations was also studied.     

Land water storage contribution to sea level from GRACE geoid data over 2003–2006

Seasonal and inter-annual change in land water storage (expressed in terms of water volume change) over 27 large river basins worldwide are estimated from monthly GRACE geoids solutions computed at GFZ from February 2003 to February 2006. The largest annual water volume change is found in the Amazon basin, followed by the Parana, Ob, Orinoco, Tocantins, Niger, Congo, Ganges, Mekong, and Brahmaputra. In terms of trend over the 3-year period, positive and negative values are observed but in a number of cases computed trends are at the noise level. However significant negative trends are found in the Amazon, Ganges, Mississippi, Nile, Parana, and Zambezi basins, indicating water mass loss over that period. Positive trends (water mass gain) are marginally significant. We have computed the land water contribution to sea level change. On average over the 3-year time span, we find that the net effect is positive (net loss of water in terrestrial reservoirs), on the order of 0.19 +/− 0.06 mm/yr. If sustained over a longer time span than considered here, such a value may become comparable to the ice sheets contribution to sea level rise.     

Sea level forcing in the Mediterranean Sea between 1960 and 2000

Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975.     

Growth patterns of the last ice age coral terraces at Huon Peninsula

At Huon Peninsula, Papua New Guinea, prolific coral growth during the last-glacial was episodic and in response to a series of sea-level rises. The resultant step-like coral terraces are currently situated from 20 m up to 140 m above sea-level due to continuous tectonic uplift of the Peninsula. The sea-level rises were in response to periodic partial disintegration of Northern Hemisphere ice sheets associated with severe climate swings and occurred within decadal timescales. The relatively rapid 15 m to 35 m rise in sea-levels exposed new head-room for corals to colonize. The resulting terrace structures contain individual corals that do not appear to have grown sequentially in time and with elevation. Additionally, following the peak, sea level fell relatively slowly over several thousand years and corals grew and filled in the flanks of the terrace such that younger corals now occupy lower elevations. We have labeled these structures “pack-up” reefs. This is in contrast to coral terraces formed during major sea-level rises from glacial to interglacial or glacial to interstadial transitions where the rate of sea level rise is commensurate with coral growth rates and corals can keep up with sea-level rise by growing on top of each other in a time orderly sequence. Deriving sea-level information from pack-up terraces is difficult and is likely to be ambiguous. The periodic fluctuations in climate were associated with atmospheric radiocarbon swings that seem to have varied smoothly with time. The same corals that show a scatter in stratigraphic temporal ordering appear regularly distributed in time and with radiocarbon content attesting to the veracity of the age measurements and at the same time confirm the disordered distribution of corals in “pack-up” type reefs.     

The Greenland ice sheet and greenhouse warming

Increased melting on glaciers and ice sheets and rising sea level are often mentioned as important aspects of the anticipated greenhouse warming of the earth's atmosphere. This paper deals with the sensitivity of Greenland's ice mass budget and presents a tentative projection of the Greenland component of future sea level rise for the next few hundred years. To do this, the ‘Villach II temperature scenario’ is prescribed,output from a comprehensive mass balance model is used to drive a high-resolution 3-D thermomechanic model of the ice sheet.The mass balance model consists of two parts: the accumulation part is based on presently observed values and is forced by changes in mean anr tempeerature. The ablation model is based on the degree-day method and accounts for daily and annual temperature cycle, a different degree-day factor for ice and snow melting and superimposed ice formation. Under present-day climatic conditions, the following total mass balance results (in ice equivalent per years): 599.3 × 10⁹ m³ of accumulation, 281.7 × 10⁹m³ of runoff assuming a balanced budget, 317.6 × 10⁹m³ of iceberg calving. A 1K uniform warming is then calculated to increase the runoff by 119.5 × 10⁹ m³. Since accumulation also increases by 32 × 10⁹ m³, this leads to reduction of the total mass balance by 887.5 × 10⁹ m³ of ice, corresponding to a sea level rise of 0.22 mm/yr. For temperature increase larger than 2.7 K, runoff, exceeds accumulation, and if ice sheet dynamics were to remain unchanged, this would add an extra amount of 0.8 mmyr to the worl's oceans.Imposing the Villach II scenario (warming up to 4.23 K) and accumulating mass balance changes forward in time (static response) would then result in a global sea level rise of 7.1 cm by 2100 AD, but this figure may go up to as much as 40 cm per century in case the warming is doubled. In a subsequent dynamic model involving the ice flow, the ice sheet is found to produce a counteracting effect by dynamically producing steeper slopes at the margin, thereby reducing the area over which runoff can take place. This effect is particularly apparent in the northeastern part of the ice sheet, and is also more pronounced for the smaller temperature perturbations. Nevertheless, all these experiments certainly highlight the vulnerability of the Greenland ice sheet with respect to a climatic warming.     

Potential impacts of human-induced land cover change on East Asia monsoon

As one major performance of anthropogenic activities, human-induced land use and land cover changes in East Asia have been one of the largest regions in the world. In the past 3000 years, more than 60% of the region has been affected by conversion of various categories of natural vegetation into farmland, conversion of grassland into semidesert and widespread land degradation. Such human-induced land cover changes result in significant changes of surface dynamic parameters, such as albedo, surface roughness, leaf area index and fractional vegetation coverage, etc.The results of a pair of numerical experiments in this paper have shown that by altering the complex exchanges of water and energy from surface to atmosphere, the changes in land cover have brought about significant changes to the East Asian monsoon. These include weakening of the summer monsoon and enhancement of winter monsoon over the region and a commensurate increase in anomalous northerly flow. These changes result in the reduction of all components of surface water balance such as precipitation, runoff, and soil water content. The consequent diminution of northward and inland moisture transfer may be a significant factor in explaining the decreasing of atmospheric and soil humidity and thus the trend in aridification observed in many parts of the region, particularly over Northern China during last 3000 years.The variation of East Asia monsoon presented here is the result of land cover changes only. It is very likely that the anthropogenic modification of monsoon system would have been occurred in the long history of civilization.     

Reef-island topography and the vulnerability of atolls to sea-level rise

Low-lying reef islands on the rim of atolls are perceived as particularly vulnerable to the impacts of sea-level rise. Three effects are inferred: erosion of the shoreline, inundation of low-lying areas, and saline intrusion into the freshwater lens. Regional reconstruction of sea-level trends, supplementing the short observational instrumental record, indicates that monthly mean sea level is rising in the eastern Indian and western Pacific Oceans. This paper reviews the morphology and substrate characteristics of reef islands on Indo-Pacific atolls, and summarises their topography. On most atolls across this region, there is an oceanward ridge built by waves to a height of around 3 m above MSL; in a few cases these are topped by wind-blown dunes. The prominence of these ridges, together with radiocarbon dating and multi-temporal studies of shoreline position, indicate net accretion rather than long-term erosion on most of these oceanward shores. Less prominent lagoonward ridges occur, but their morphology and continuity are atoll-specific, being a function of the processes operating in each lagoon. Low-lying central areas are a feature of many islands, often locally excavated for production of taro. These lower-lying areas are already subject to inundation, which seems certain to increase as the sea rises. Tropical storms play an important role in the geomorphology of reef islands in those regions where they are experienced. Topographical differences, as well as features such as emergence of the reef flat and the stability of the substrate, mean that islands differ in terms of their susceptibility to sea-level rise. Further assessment of variations in shoreline vulnerability based on topography and substrate could form the basis for enhancing the natural resilience of these islands.     

Stepwise decreases of the Huanghe (Yellow River) sediment load (1950–2005): Impacts of climate change and human activities

The sediment load delivered from the Huanghe (Yellow River) to the sea has decreased sharply to 0.15 × 10⁹ metric tons per year (0.15 Gt/yr) between 2000 and 2005, and now represents only 14% of the widely cited estimate of 1.08 Gt/yr. The river seems to be reverting to the pristine levels characteristic of the middle Holocene, prior to human intervention. Datasets from 1950 to 2005 from four key gauging stations in the main stream reveal distinct stepwise decreases in sediment load, which are attributed to both natural and anthropogenic impacts over the past 56 yr. Completions of two reservoirs, Liujiaxia (1968) and Longyangxia (1985), in the upper reaches of the river and their joint operations have resulted in stepwise decreases in sediment load coming from the upper reaches. Effective soil conservation practices in the middle reaches since the late 1970s, combined with the operation of the Sanmenxia and Xiaolangdi reservoirs, have also caused stepwise decreases in sediment load at Huayuankou in the middle reaches, but the decrease differs from that observed in the upper reaches. Decrease in precipitation is responsible for 30% of the decrease in sediment load at Huayuankou, while the remaining 70% is ascribed to human activities in the river basin, of which soil conservation practices contribute 40% to the total decrease. Sediment retention within reservoirs accounts for 20% of the total sediment load decrease, although there was notable sediment retention within the Xiaolangdi reservoir from 2000 to 2005. The remaining 10% of the decrease in sediment load is a result of the operation of reservoirs in the upper reaches. In the lower reaches, 20% of the sediment passing Huayuankou has been lost as a result of channel deposition and water abstraction. Soil conservation practices and the operation of reservoirs have lowered the content of coarser sediment (D > 0.05 mm) at Huayuankou, and reduced channel deposition in the lower reaches. In contrast, sediment loss owing to water abstraction in the lower reaches has increased considerably as water consumption for agricultural needs has increased. Therefore, the combined effects of climate change and human activities in the upper, middle, and lower reaches have resulted in stepwise decreases in the sediment load delivered from the Huanghe to the sea. The Huanghe provides an excellent example of the altered river systems impacted by climate change and extensive human activities over the past 56 yr. Further dramatic decreases in sediment load and water discharge in the Huanghe will trigger profound geological, morphological, ecological, and biogeochemical responses in the estuary, delta, and coastal sea.     

Time Variation In Hydrology and Gravity

In view of the pivotal role that continental water storage plays in the Earth’s water, energy and biogeochemical cycles, the temporal and spatial variations of water storage for large areas are presently not known with satisfactory accuracy. Estimates of the seasonal storage change vary between less than 50 mm water equivalent in areas with uniform climatic conditions to 450 mm water equivalent in tropical river basins with a strong seasonality of the climate. Due to the lack of adequate ground-based measurements of water storage changes, the evapotranspiration rate, which depends on the actual climatic and environmental conditions, is only an approximation for large areas until now, or it is based on the assumption that storage changes level out for long time periods. Furthermore, the partitioning of the water storage changes among different storage components is insufficiently known for large scales. The direct measurement of water storage changes for large areas by satellite-based gravity field measurements is thus of uttermost importance in the field of hydrology in order to close the water balance at different scales in space and time, and to validate and improve the predictive capacity of large-scale hydrological models. Due to the high spatial variability of hydrological processes temporal and spatial resolutions beyond that of GRACE are essential for a spatial differentiation in evapotranspiration and water storage partitioning.     

Simulations of water resource environmental changes in China during the last 20 000 years by a regional climate model

We utilize a regional climate model with detailed land surface processes (RegCM2) to simulate East Asian monsoon climates at 0 ka, 6 ka and 21 ka BP, and evaluate the changes in hydrology process, including vapor transportation, precipitation, evapotranspiration and runoff in the eastern and western China during these periods. Results indicate that the Tibetan Plateau climate presents a wet–cold status during the LGM while it exhibits a wet–warm climate at 6 ka BP. The LGM wetter climate over the Tibetan Plateau mainly results from the increased vapor inflow through its south boundary, while the increase in the vapor import over the Tibetan Plateau at 6 ka BP mostly sources from its west boundary. The increase in the LGM runoff over the Tibetan Plateau is mainly caused by the decrease in evapotranspiration, while the increase in runoff at the 6 ka BP mainly by the enhanced precipitation. Eastern China (including southern China) presents a dry status during the LGM, which precipitation and runoff decreases significantly due largely to weakened Asian summer monsoon that results in the decreased vapor inflow through the south boundary of eastern China. The variation pattern in the hydrological cycle in eastern China is contrary to that in western China during the LGM. The increase in precipitation and runoff at 6 ka BP in eastern China is tightly related to the strong Asian summer monsoon that leads to increased vapor import through the south boundary. Long term decrease trend in precipitation and runoff in northern China since the last 20 000 years may be attributed to the steady increase in vapor export through the east boundary as a result of the changes of East Asian monsoon and the adjustments of local atmospheric circulations in this area.     

Ecological and morphological response of brackish tidal marshland to the next century of sea level rise: Westham Island, British Columbia

In response to climatic warming, eustatic sea level has been predicted to rise by about 50 cm in the next century. While feedbacks between vegetation growth and sediment deposition tend to allow marshes to maintain their morphology under a constant rate of sea level rise, recent observations of marsh deterioration suggest that changes in the rate of sea level rise may induce loss of economically and ecologically important marshland. We have developed a three dimensional model of tidal marsh evolution that couples vegetation growth and sediment transport processes including bed accretion and wave erosion. We use the model to simulate the response of marshes and tidal flats along the Fraser River Delta, British Columbia to 100 yr forecasts of sea level change. Under low sea level-rise scenarios, the delta and its marshes prograde slightly, consistent with historical measurements. While accretionary processes greatly mediate the response to increased rates of sea level rise, vegetation zones transgress landward under median and high sea level rise rate scenarios. In these scenarios, low marsh erosion and constriction of high marsh vegetation against a dyke at its landward edge result in a 15–35% loss of marshland in the next century. Several important behavioral changes take place after 2050, suggesting that predictions based on field observations and short term model experiments may not adequately characterize (and sometimes underestimate) long-term change. In particular, the replacement of highly productive high marsh vegetation by less productive low marsh vegetation results in continued reduction of the system's total biomass productivity, even as the rate of loss of vegetated area begins to decline.     

Modelling the impacts of environmental changes on hydrological regimes in the Hei River Watershed, China

This study aimed to disclose impacts of environment changes on hydrologic regimes in the Hei River Watershed, Shaanxi Province in China. We investigated the effects of the man-made landscape (Jingpen Reservoir) on the rainstorm–flood processes using a proposed Kinematic Wave model, simulated impacts of land use and cover changes on surface runoff generation and river flow characteristics at monthly, seasonal, and annual scales through designed scenarios of different combinations of land use and cover and climate conditions on basis of the SWAT model, evaluated the climate change and human activities effects on water balance from 1954 to 2001. Through these investigations, the following results were achieved. Firstly, it showed that the man-made landscape (the Jingpen Reservoir) had altered the rainstorm–flood process, the flood wave damped right after it flowed out the Jingpen Reservoir. Secondly, changes of land use and cover led to river flow redistribution, soil moisture and recharge fluctuations. Evapotranspiration increased 12.9%, river flow discharge decreased 17.7%, runoff generation process accelerated 1.31 times in 2000 than in 1986, and water resources of the total watershed decreased 7.7% in 2000 compared to the land use and cover scenario in 1986. Finally, the interaction between climate change and human activities led to the total water resource decreased by 10.6% in 2000 compared to that in 1986 in the Hei River Watershed.     

Tree-ring record of hillslope erosion and valley floor dynamics: Landscape responses to climate variation during the last 400 yr in the Colorado Plateau, northeastern Arizona

Dendrogeomorphologic approaches were used to study hillslope erosion and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, U.S.A. Root exposure in pinyon pines indicated hillslope erosion averaged 1.9 mm/yr over the last 400 yr, but erosion has been highly episodic. Negative increment growth anomalies in hillslope trees are interpreted as the consequence of rapid aerial exposure of roots by erosion. During the last 300 yr, two of three major episodes of these growth anomalies occurred after abrupt transitions from prolonged, multi-year droughts to sustained, lengthy periods of above-average precipitation. The most recent episode of these growth anomalies began within a few years after 1905 and was associated with the largest precipitation shift (drought to wet interval) in the last 400 yr. In contrast to trees on eroding hillslopes, increment growth of trees in more geomorphically stable landscape positions closely tracked the regional precipitation signal. Two major alluvial fills on the adjacent valley floor are also linked to the abrupt changes in precipitation regimes and the associated increases in delivery of runoff and sediments from slopes. The clay-cemented sandstones weather rapidly; rapid weathering and sediment production make slopes highly responsive to decadal precipitation changes. Significant vegetation declines on slopes during extreme drought make hillslope soils more prone to erosion if heavy precipitation follows soon thereafter.     

Elevated marine terraces from Eleuthera (Bahamas) and Bermuda: sedimentological,petrographic and geochronological evidence for important deglaciation events during the middle Pleistocene

Sedimentological, petrographic and geochronological (uranium series and amino acid racemization dating) study of middle Pleistocene deposits from the archipelagos of Bermuda and The Bahamas revealed the occurrence of marine terraces of possible stage 11 age at +2, +7 and over 20 m above mean sea level. Considering the tectonic stability of the investigated regions, these elevated deposits likely correspond to three discrete, higher than present sea levels during this time period, which is regarded by many as the warmest interglacial of the late Quaternary. It follows that warmer than present climatic conditions might profoundly modify water distribution between the cryosphere and the oceans. The punctuated nature of our stratigraphy further suggests that future deglaciation might not be a smooth process, but could be marked by rapid ice-sheet breakdown leading to abrupt, meter-scale sea-level rises. Given the long period of warm climate and stable sea level of the past few thousands of years and CO₂ loading of the atmosphere, the probability of a rapid eustatic rise must be seriously considered.     

Late Weichselian fluvial evolution on the southern Kara Sea Shelf, North Siberia

Glaciations had a profound impact on the global sea-level and particularly on the Arctic environments. One of the key questions related to this topic is, how did the discharge of the Siberian Ob and Yenisei rivers interact with a proximal ice sheet? In order to answer this question high-resolution (1–12 kHz), shallow-penetration seismic profiles were collected on the passive continental margin of the Kara Sea Shelf to study the paleo-drainage pattern of the Ob and Yenisei rivers. Both rivers incised into the recent shelf, leaving filled and unfilled river channels and river canyons/valleys connecting to a complex paleo-drainage network.These channels have been subaerially formed during a regressive phase of the global sea-level during the Last Glacial Maximum. Beyond recent shelf depths of 120 m particle transport is manifested in submarine channel–levee complexes acting as conveyor for fluvial-derived fines. In the NE area, uniform draping sediments are observed. Major morphology determining factors are (1) sea-level fluctuations and (2) LGM ice sheet influence. Most individual channels show geometries typical for meandering rivers and appear to be an order of magnitude larger than recent channel profiles of gauge stations on land.The Yenisei paleo-channels have larger dimensions than the Ob examples and could be originated by additional water release during the melt of LGM Putoran ice masses.Asymmetrical submarine channel–levee complexes with channel depths of 60 m and more developed, in some places bordered by glacially dominated morphology, implying deflection by the LGM ice masses. A total of more than 12,000 km of acoustic profiles reveal no evidence for an ice-dammed lake of greater areal extent postulated by several workers. Furthermore, the existence of the channel–levee complexes is indicative of unhindered sediment flow to the north. Channels situated on the shelf above 120-m water depth exhibit no phases of ponding and or infill during sea-level lowstand. These findings denote the non-existence of an ice sheet on large areas of the Kara Sea shelf.     

Chronology of the Holocene transgression at the North Siberian margin

To establish a chronology of the Holocene transgression in Arctic Siberia, a total of 14 sediment cores from the Laptev Sea continental slope and shelf were studied covering the water depth range between 983 and 21 m. The age models of the cores were derived from 119 radiocarbon datings, which were all analyzed on marine biogenic calcite (mainly bivalve shells). The oldest shell sample was found at the slope and dates back to about 15.3 cal. ka, indicating that the time interval investigated starts prior to the onset of the meltwater pulse 1A (14.2 cal. ka) when global sea-level rose dramatically. The inundation history was reconstructed mainly on the basis of major changes in average sedimentation rates (ASR), but also other sedimentological parameters were incorporated. A diachronous reduction in ASR from the outer to the inner shelf region is recognized, which was related to the southward migration of the coastline as the primary sediment source. We estimate that the flooding of the 50-, 43-, and 31-m isobaths was completed by approximately 11.1, 9.8, and 8.9 cal. ka, and that Holocene sea-level highstand was approached near 5 cal. ka. Between these time intervals, sea level in the Laptev Sea rose by 5.4, 13.3, and 7.9 mm/year, respectively.