Raise Sea Level Research Articles

Melting ice sheets 400,000 yr ago raised sea level by 13 m: Past analogue for future trends

Marine Isotope Stage (MIS) 11 was possibly the longest (∼423,000–362,000 yr ago) and warmest interglacial of the entire Quaternary Period. This resulted from a special arrangement of Earth's orbital parameters-similar to the present interglacial (MIS 1)-suggesting that MIS 11 provides an analogue for future natural climate forcing and sea levels. Although precise documentation of MIS 11 sea level history is, therefore, crucial – especially considering additional impetus from anthropogenic warming – the maximum MIS 11 sea level remains highly contentious. Estimates from onshore indicators have ranged from below present sea level to about +20m, resulting from uncertainties in reliability of sea level indicators, estimates of their subsequent displacement by vertical crustal motion and in dating. We used a clear and unambiguous sea level indicator (interface between subtidal and intertidal deposits) in well exposed, regressive raised shoreline deposits along South Africa's southern coast. The coast is stable in terms of tectonic setting and falls within a zone of low predicted glacio-isostatic adjustment (GIA) and low sensitivity for plausible model parameters. The sea level indicators were directly dated using thermally transferred optically stimulated luminescence (TT-OSL), which gave a mean age of ∼390ka, corresponding with MIS 11. We determined a precise maximum elevation of +14m for the MIS 11 sea level indicator, which corrected for minor crustal uplift and GIA yielded a eustatic sea level of +13m ±2m. The complete MIS 11 transgressive/regressive shoreline succession is preserved and the wave-cut platform extends 950m inland from the present shoreline, indicating a prolonged highstand. We have also documented sea level fluctuations during MIS 11, including an earlier (lower) highstand close to present sea level, which may explain the lower elevation range of some previous estimates. At one locality, MIS 11 deposits form a sea cliff against which MIS 5e sediments (at an elevation of +6.2m) abut. The +13m MIS 11 sea level tallies with total melting of the Greenland and West Antarctica ice sheets, regarded as most susceptible to melting. Our data predict notably higher sea levels in the future, regardless of anthropogenic influence on climate.

Grounding-line retreat of the West Antarctic Ice Sheet from inner Pine Island Bay

Ice loss from the marine-based, potentially unstable West Antarctic Ice Sheet (WAIS) contributes to current sea-level rise and may raise sea level by ≤3.3 m or even ≤5 m in the future. Over the past few decades, glaciers draining the WAIS into the Amundsen Sea Embayment (ASE) have shown accelerated ice flow, rapid thinning, and fast retreat of the grounding line (GL). However, the long-term context of this ice loss is poorly constrained, limiting our ability to accurately predict future WAIS behavior. Here we present a new chronology for WAIS retreat from the inner continental shelf of the eastern ASE, based on radiocarbon dates from three marine sediment cores. The ages document a retreat of the GL to within ∼100 km of its modern position before ca. 10,000 calibrated (cal.) yr B.P. This early deglaciation is consistent with ages for GL retreat from the western ASE. Our new data demonstrate that, in contrast to the Ross Sea, WAIS retreat from the ASE shelf was largely complete by the start of the Holocene. Our results further suggest either slow GL retreat from the inner ASE shelf throughout the Holocene, or that any episodes of fast GL retreat must have been short-lived. Thus, today’s rapid retreat may be exceptional during the Holocene and may originate in recent changes in regional climate, ocean circulation, or ice-sheet dynamics.

The Potential for an Impending Sea-Level Rise

Sea level rise has become one of the most discussed topics regarding climate change. In the past the sea level has been known to rise several meters during interglacial periods. The rapid spread of human populations and new technological innovations have led to an outpouring of carbon dioxide over the centuries causing the global mean temperature to rise by 0.8°C. This slight increase in temperature has raised sea level from thermal expansion of the ocean and is having a dramatic effect on the cryosphere. Retreating glaciers continue to contribute to the current rate of sea level rise but the potential for the Greenland and Antarctic ice sheets to melt from increasing global temperatures could raise the ocean by more than 1 m this century. Low-lying developing countries such as Bangladesh and Vietnam are the most vulnerable to a rise in sea level due to lack of infrastructure, high population densities, and geographic locations situated on a delta. In the developed world, Australia and Italy are at risk areas due to large populations found along the coast in both countries. If the rate of mass loss from glaciers and ice sheets continue a future sea level rise is imminent.

Visualising the spatial extent of predicted coastal zone inundation due to sea level rise in south-west Western Australia

Visualising coastal zone inundation is crucial for both a quick assessment of coastal vulnerability and a full understanding of possible implications to population, infrastructure and environment. This study presents a simple but effective method of assessing the spatial extent of coastal zone inundation due to predicted sea level rise using commonly available elevation and image data as well as GIS software. The method is based on the geometrical principle of matching the raised sea level with the corresponding elevation contour line on land. Results for a test area along the south-west coast of Western Australia (∼200 km of coast line) show that a sea level rise of less than 0.5 m over the 21st century will have only minor impact but will become important when added to an extreme sea level event (e.g. storm surge). Both century-scale (∼0.5 m) based on tide gauge records and larger (>few metres) longer-term sea level rise predictions based on the melt of ice covered areas show essentially the same areas that are most vulnerable. Furthermore, the effectiveness of the method is demonstrated by the detection of areas that can be protected by relatively small flood protective structures at river and estuary entrances, thus providing valuable information for policy makers and local councils.

Antarctic Ice's Future Still Mired in Its Murky Past

As shrinking ice sheets raise sea level, estimates of how quickly the frozen continent is losing and gaining ice remain slippery.

Possible impact of rising sea levels on vector-borne infectious diseases

BackgroundVector-borne infectious diseases are a significant cause of human and animal mortality and morbidity. Modeling studies predict that changes in climate that accompany global warming will alter the transmission risk of many vector-borne infectious diseases in different parts of the world. Global warming will also raise sea levels, which will lead to an increase in saline and brackish water bodies in coastal areas. The potential impact of rising sea levels, as opposed to climate change, on the prevalence of vector-borne infectious diseases has hitherto been unrecognised.Presentation of the hypothesisMosquito species possessing salinity-tolerant larvae and pupae, and capable of transmitting arboviruses and parasites are found in many parts of the world. An expansion of brackish and saline water bodies in coastal areas, associated with rising sea levels, can increase densities of salinity-tolerant vector mosquitoes and lead to the adaptation of freshwater vectors to breed in brackish and saline waters. The breeding of non-mosquito vectors may also be influenced by salinity changes in coastal habitats. Higher vector densities can increase transmission of vector-borne infectious diseases in coastal localities, which can then spread to other areas.Testing the hypothesisThe demonstration of increases in vector populations and disease prevalence that is related to an expansion of brackish/saline water bodies in coastal areas will provide the necessary supportive evidence. However the implementation of specific vector and disease control measures to counter the threat will confound the expected findings.Implications of the hypothesisRising sea levels can act synergistically with climate change and then interact in a complex manner with other environmental and socio-economic factors to generate a greater potential for the transmission of vector-borne infectious diseases. The resulting health impacts are likely to be particularly significant in resource-poor countries in the tropics and semi-tropics. Some measures to meet this threat are outlined.

Dynamics and mass balance of four large East Antarctic outlet glaciers

AbstractThe East Antarctic ice sheet (EAIS) is Earth’s largest reservoir of fresh water and has the potential to raise sea level by ~50 m. A significant amount of the ice sheet’s mass is discharged by outlet glaciers draining through the Transantarctic Mountains, the balance characteristics of which are largely unknown. Here the mass balance is estimated for four glaciers draining ice from the EAIS through the Transantarctic Mountains into the Ross Sea embayment: David, Mulock, Byrd and Nimrod glaciers. Remote-sensing observations are used to map changes in ice flow and surface elevation, and ultimately to compute the mass balance of each glacier using the input–output method and three separate estimates for accumulation rate. Results computed using this method indicate small positive balances for David (2.41±1.31 Gt a–1), Mulock (1.91±0.84 Gt a–1) and Nimrod (0.88±0.39 Gt a–1) glaciers, and a large positive imbalance for Byrd Glacier (21.67±4.04 Gt a–1). This large imbalance for Byrd Glacier is inconsistent with other observations, and is likely due to an overestimation of accumulation rates across large regions of the interior catchment.

Effect of sea-level rise on piping plover ( Charadrius melodus) breeding habitat

Climate change is raising sea levels, threatening many low-lying coastal areas and associated wildlife. We assessed the threat of sea-level rise (SLR) to the breeding habitat of the federally threatened piping plover on the barrier islands of Suffolk County, New York. We determined the extent of habitat change over the next 100 years under several SLR estimates, as well as the interactive effects of coastal development and storm surge. We found that if plover habitat cannot migrate, SLR is likely to reduce breeding areas. However, if habitat is able to migrate upslope and inland, breeding areas could actually increase with SLR. Unfortunately, this potential habitat gain is stymied by human development, which we found to reduce migrating habitat by 5–12%, depending on SLR estimates. We also found that the spatial configuration of developed areas mattered more than intensity of development in blocking the migration of potential habitat area. Our results raise concern over the likelihood of increased conflict between plover habitat protection and human recreation as habitat is likely to become a larger proportion of the barrier islands in the future. Finally, our results highlight risk from the synergism between SLR and coastal storms, as we estimate that a large hurricane could flood up to 95% of plover habitat. To assure the future of plover habitat on these barrier islands, management needs to promote natural overwash and habitat migration, while minimizing development adjacent to future breeding habitat.

High-latitude diversification within Eurasian least shrews and Alaska tiny shrews (Soricidae)

A novel shrew was discovered recently in Alaska and described based on morphological characters as Sorex yukonicus. This species is closely allied to Sorex minutissimus, a widespread shrew ranging through Eurasia. Together their distribution spans Beringia, a large Pleistocene nonglaciated area that connected Asia and North America. Beringia was repeatedly divided due to raised sea levels during Pleistocene interglacials and subsequently reconnected during glacials. We tested predictions related to the influence of large-scale geologic events on genetic variability through a phylogeographic analysis of both species of shrew using evidence from 3 independent genetic loci. We found low genetic divergence between S. minutissimus and S. yukonicus across continents. However, major phylogeographic breaks were found for Eurasian and Maritime Northeast Asia populations. Neither species is reciprocally monophyletic for any of the loci examined. Coalescence times for all pairwise population comparisons within both species fall within the Wisconsinan–Weichselian glacial (,130 thousand years ago), and significant population expansion estimates date to the Holocene suggesting that divergence between these taxa is minimal and may not warrant recognition of 2 distinct species. Phylogeographic relationships and sequence divergence estimates place populations of North American S. yukonicus and Siberian S. minutissimus as most closely related, and together they are sister to European S. minutissimus. We conclude that populations east and west of the Bering Strait represent a single Holarctic species, S. minutissimus. Temporal changes in range based on ecological niche predictions and a comparative assessment of other codistributed taxa provide a preliminary view of potential Last Glacial Maximum refugia in northern Asia. DOI: 10.1644/09-MAMM-A-402.1.

Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier

An acceleration of ice-mass loss has been observed near the margin of the Greenland ice sheet, partly as a result of faster ice motion. Observations by GPS receivers reveal high seasonal variability in ice motion, with summer motion up to 220% higher than winter background levels. The Greenland ice sheet contains enough water to raise sea levels by 7 m. However, its present mass balance and future contribution to sea level rise is poorly understood1. Accelerated mass loss has been observed near the ice sheet margin, partly as a result of faster ice motion2,3,4. Surface melt waters can reach the base of the ice sheet and enhance basal ice motion5,6. However, the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time. Here we present ice motion data obtained with global positioning system receivers located along a ∼35 km transect at the western margin of the Greenland ice sheet throughout a summer melt season. Our measurements reveal substantial increases in ice velocity during summer, up to 220% above winter background values. These speed-up events migrate up the glacier over the course of the summer. The relationship between melt and ice motion varies both at each site throughout the melt season and between sites. We suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers.

Improving Constraints on Paleo Ice Sheets in the Amundsen Sea Embayment: Amundsen Sea Embayment: Tectonic and Climatic Evolution; Granada, Spain, 9 September 2009

Geoscientists working on the Amundsen Sea Embayment (ASE) of West Antarctica met at a workshop during the First Antarctic Climate Evolution Symposium to discuss recent advances from, and future priorities for, work in this region. The ASE is the most rapidly changing sector of the West Antarctic Ice Sheet (WAIS) and contains enough ice to raise sea level by 1.2 meters. Ice sheet modeling studies suggest that this sector of the WAIS is potentially unstable.Considerable efforts have been made through several national Antarctic programs to acquire new data on the geological structure, subglacial topography, bathymetry, and glacial history of this remote region. These data are important for establishing boundary conditions for ice sheet modeling, for providing constraints on past ice sheet changes that can be used to test models, and for putting recent changes into a longer‐term context.

A tidal depositional model for the Carolina sand (Pliocene, Talparo Formation) of central Trinidad

A BSTRACT. — The Pliocene geological history of Trinidad’s Northern Basin is little known. The need for such knowledge is pressing; some rock units cropping out there yield hydrocarbons offshore in the Gulf of Paria, but the environments in which they were deposited have yet to be deciphered. As a first step towards unravelling this geohistory, this study examines the sedimentology of the Carolina sand, a small and informal member of the Pliocene Talparo Formation. From plan view the lenticular Carolina sand is concluded to comprise a tidal sand ridge that built up almost to sea level. This interpretation is supported by abundant sedimentary structures indicative of tidal influence (herringbone cross-bedding, mud couplets, clay drapes). Drape and ripple orientations show northward transport that is concluded to be indicative of ebb tide currents. For most of the succession, sediments alternate between two lithofacies (tabular cross-bedded sands with clay drapes, and interlaminated sands and silts). Comparison with tidal flats suggests these lithofacies indicate rapid cycling between different water depths. The depth changes are suggested to be related to outflow from the paleo-Orinoco River, which, like the present day Orinoco, is suggested to have raised sea levels around Trinidad during the annual rainy season. The cross-bedded sands were deposited as deeper-water megaripples on the tidal ridge surface during the rainy season, the interlaminated sands and silts under intertidal conditions when sea levels fell during the dry season. The Carolina sand was probably deposited during one of the eustatic sea level highstands hitherto noted farther east, in the offshore Columbus Basin. K EYWORDS. — tidal sand ridge , Orinoco , clay drapes , herringbone cross-bedding , mud couplets

What Happens When an Ice Sheet Melts?

Abstract The great ice sheets covering Antarctica and Greenland have enough frozen water locked in them to raise the global sea level by some 70 metres. The West Antarctic Ice Sheet may be inherently unstable and if it collapses the universal belief is that it would raise sea levels by 5–6 metres globally. But that estimate is wrong. What happens to sea levels when an ice sheet melts is complex and surprising. In some places, even, levels can go down. Jonathan Bamber explains.

Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet

Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.

Obliquity-paced Pliocene West Antarctic ice sheet oscillations

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch ( approximately 5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, approximately 40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to approximately 3 degrees C warmer than today and atmospheric CO(2) concentration was as high as approximately 400 p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO(2).

West Antarctic Ice Sheet collapse – the fall and rise of a paradigm

It is now almost 30 years since John Mercer (1978) first presented the idea that climate change could eventually cause a rapid deglaciation, or “collapse,” of a large part of the West Antarctic ice sheet (WAIS), raising world sea levels by 5 m and causing untold economic and social impacts. This idea, apparently simple and scientifically plausible, created a vision of the future, sufficiently alarming that it became a paradigm for a generation of researchers and provided an icon for the green movement. Through the 1990s, however, a lack of observational evidence for ongoing retreat in WAIS and improved understanding of the complex dynamics of ice streams meant that estimates of likelihood of collapse seemed to be diminishing. In the last few years, however, satellite studies over the relatively inaccessible Amundsen Sea sector of West Antarctica have shown clear evidence of ice sheet retreat showing all the features that might have been predicted for emergent collapse. These studies are re-invigorating the paradigm, albeit in a modified form, and debate about the future stability of WAIS. Since much of WAIS appears to be unchanging, it may, no longer be reasonable to suggest there is an imminent threat of a 5-m rise in sea level resulting from complete collapse of the West Antarctic ice sheet, but there is strong evidence that the Amundsen Sea embayment is changing rapidly. This area alone, contains the potential to raise sea level by around ~1.5 m, but more importantly it seems likely that it could, alter rapidly enough, to make a significant addition to the rate of sea-level rise over coming two centuries. Furthermore, a plausible connection between contemporary climate change and the fate of the ice sheet appears to be developing. The return of the paradigm presents a dilemma for policy-makers, and establishes a renewed set of priorities for the glaciological community. In particular, we must establish whether the hypothesized instability in WAIS is real, or simply an oversimplification resulting from inadequate understanding of the feedbacks that allow ice sheets to achieve equilibrium: and whether there is any likelihood that contemporary climate change could initiate collapse.

The physics of ice sheets

The great ice sheets in Antarctica and Greenland are vast deposits of frozen freshwaterthat contain enough to raise sea level by approximately 70 m if they were to completelymelt. Because of the potentially catastrophic impact that ice sheets can have, it isimportant that we understand how ice sheets have responded to past climate changes andwill respond to present climate changes, so that we can predict the effect global warmingwill have on sea level rise in the coming centuries. The purpose of this article is tointroduce students to some of the basic concepts of glaciology, the physical variables thatcontrol the evolution of ice sheets, and how changes in these parameters may affect thelong-term evolution of ice sheets.

A discussion of the potential impacts of climate change on the shorelines of the Northeastern USA

An increase in the rate of sea-level rise and potential changes in storminess represent important components of global climate change that will likely affect the extensive coasts of the Northeastern USA. Raising sea level not only increases the likelihood of coastal flooding, but changes the template for waves and tides to sculpt the coast, which can lead to land loss orders of magnitude greater than that from direct inundation alone. There is little question that sea-level rise, and in particular an increased rate of rise, will result in permanent losses of coastal land. However, quantitative predictions of these future coastal change remains difficult due in part to the complexity of coastal systems and the influence of infrequent storm events, and is further confounded by coastal science’s insufficient understanding of the behavior of coastal systems over decadal timescales. Recently, dramatic improvements in technology have greatly improved our capabilities to investigate and characterize processes and sedimentary deposits in the coastal zone, allowing us, for the first time, to address some of the over-arching problems involved in shoreline change. Despite advances in many areas of coastal geology, our fundamental understanding of shoreline change has been limited by a lack of a broad and integrated scientific focus, a lack of resources, and a lack of willingness on the part of policymakers who make crucial decisions about human activity along the coast to support basic research in this area. Although quantitative predictions remain constrained, there remains little doubt that the predicted climates changes will have profound effects upon the Northeastern coast.

West Antarctic ice sheet change since the Last Glacial Period

The potential for rapid deglaciation, or collapse, of the 2‐million‐square‐kilometer West Antarctic Ice Sheet (WAIS) in response to climate change is one of the most serious environmental threats facing mankind. The WAIS is a marine ice sheet with large parts of its ice grounded below sea level. Complete collapse would result in a global sea level rise of approximately 5 meters, with immense social, economic, and ecological consequences.While most experts consider such a collapse unlikely within the next few centuries, the Amundsen Sea sector has been identified as the most likely site for initiation of collapse, and it alone contains the potential to raise sea level by approximately 1.5 meters [Vaughan, 2007]. This would result in devastating flooding in many low‐lying cities (e.g., New Orleans, London), agricultural areas (e.g., Netherlands, Bangladesh) and atolls (e.g., Maldives).

Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets

After a century of polar exploration, the past decade of satellite measurements has painted an altogether new picture of how Earth's ice sheets are changing. As global temperatures have risen, so have rates of snowfall, ice melting, and glacier flow. Although the balance between these opposing processes has varied considerably on a regional scale, data show that Antarctica and Greenland are each losing mass overall. Our best estimate of their combined imbalance is about 125 gigatons per year of ice, enough to raise sea level by 0.35 millimeters per year. This is only a modest contribution to the present rate of sea-level rise of 3.0 millimeters per year. However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade. In both continents, there are suspected triggers for the accelerated ice discharge-surface and ocean warming, respectively-and, over the course of the 21st century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models.