Sea Level Rise Flooding may Have Some Marine Ecosystem Benefits

Due to climate change, sea levels are expected to rise and flood large low-lying areas in many regions of the world. The big question is how we should cope? Should we built dykes or let the sea in?

The choice is not easy, but we have to make it. If we build dykes, we can keep the land dry. But it is a costly and sometimes risky choice. According to biologists at University of Southern Denmark, it is worth considering letting the seawater take over. The results might be more beneficial than trying to keep the water out, they suggest.

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Many Atolls may be Uninhabitable by Mid Century

Sea-level rise and wave-driven flooding will negatively impact freshwater resources on many low-lying atoll islands in such a way that many could be uninhabitable in just a few decades. According to a new study published in Science Advances, scientists found that such flooding not only will impact terrestrial infrastructure and habitats, but, more importantly, it will also make the limited freshwater resources non-potable and, therefore, directly threaten the sustainability of human populations.

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Reconstructing Sea Level Rise and Fall Since the NeoProterozoic

Reconstructing first-order changes in sea level during the Phanerozoic and Neoproterozoic using strontium isotopes

Authors:

van der Meer et al

Abstract:

The eustatic sea-level curves published in the seventies and eighties have supported scientific advances in the Earth Sciences and the emergence of sequence-stratigraphy as an important hydrocarbon exploration tool. However, validity of reconstructions of eustatic sea level based on sequence stratigraphic correlations has remained controversial. Proposed sea level curves differ because of site-to-site changes in local tectonics, depositional rates, and long-wavelength dynamic topography resulting from mantle convection. In particular, the overall amplitude of global Phanerozoic long-term sea level is poorly constrained and has been estimated to vary between ~ 400 m above present-day sea level to ~ 50 m below present-day sea level. To improve estimates of past sea level, we explore an alternative methodology to estimate global sea level change. We utilise the Phanerozoic-Neoproterozoic 87Sr/86Sr record, which at first order represents the mix of inputs from continental weathering and from mantle input by volcanism. By compensating for weathering with estimates of runoff from a 3D climate model (GEOCLIMtec), a corrected 87Sr/86Sr record can be obtained that solely reflects the contribution of strontium from mantle sources. At first order, the flux of strontium from the mantle through time is due to increases and decreases in the production of oceanic crust through time. Therefore, the changing levels of mantle-derived strontium can be used as a proxy for the production of oceanic lithosphere. By applying linear oceanic plate age distributions, we compute sea level and continental flooded area curves. We find that our curves are generally within the range of previous curves built on classical approaches. A Phanerozoic first order cyclicity of ~ 250 Myr is observed that may extend into the Neoproterozoic. The low frequency (i.e., on the order of 10 to 100 My) sea level curve that we propose, while open for improvement, may be used as baseline for refined sequence-stratigraphic studies at a global and basin scale.

Marine Biota was Brought into Songliao Lake by Marine Incursions During the Late Cretaceous

Late Cretaceous marine fossils and seawater incursion events in the Songliao Basin, NE China

Authors:

Xi et al

Abstract:

The Songliao Basin is the largest non-marine oil-bearing basin in China. Because of the absence of substantial evidence, the hypothesis of seawater incursion events into the Songliao Basin remains controversial. The presence of marine fossils could provide direct proof to support this supposition. Here, we report new discoveries of foraminifera, calcareous nannofossils, brackish dinoflagellates, and other marine and brackish-water fossils to support the suggestion of seawater incursion events in the Songliao Basin. Relatively abundant benthic and planktonic foraminifera, calcareous nannofossils, marine and brackish-water dinoflagellates, fish, and bivalves have been discovered in Members 1 and 2 of the Nenjiang Formation, a few foraminifera and brackish-water dinoflagellates have been found in the lower Qingshankou Formation, and just a few brackish-water bivalves have been found in the uppermost Qingshankou Fm. Based on the presence of marine molecular fossils and other evidence, we suggest that relatively large seawater incursion events occurred during the sedimentation of the lower Nenjiang Fm., relatively smaller seawater incursions occurred during the deposition of the lower Qingshankou Fm., and possibly a very small seawater incursion occurred during the sedimentation of the uppermost Qingshankou Fm. These seawater incursion events in the Songliao Basin were controlled by regional tectonic activity, evolution of the palaeo Songliao Lake, and global sea level change. These periodic seawater incursions brought marine biota into the palaeo Songliao Lake.

At the end of the Pleistocene Ice Age, Antarctica had a Massive Ice-Shelf Collapse

In a new study that provides clues about how Antarctica's nation-sized Ross Ice Shelf might respond to a warming climate, U.S. and Japanese oceanographers have shown that a 100,000-square-mile section of the ice shelf broke apart within 1,500 years during a warming period after the last ice age.

The Ross Ice Shelf is the world's largest ice shelf, a vast floating extension of the West Antarctic Ice Sheet that is about the size of France. But at the end of the last ice age, it extended much farther north and covered the entire Ross Sea.

A study in this week's Proceedings of the National Academy of Sciences details how the ice shelf shrank during a period of climate warming following the ice age. The paper was co-authored by Rice University oceanographer John Anderson, postdoctoral research associate Lauren Simkins, graduate student Lindsay Prothro and colleagues at the University of Tokyo.

"At the height of the last ice age, we know that the sheet of ice covering the Antarctic continent was larger and thicker than it is today," said Anderson, Rice's Maurice Ewing Professor of Oceanography and professor of Earth science. "This continent-enveloping ice sheet extended all the way to the continental shelf, and in western Antarctica it filled the entire Ross Sea basin."

While people typically think of continents as landmasses that rise above the sea, the margins of all continents, including Antarctica, extend well beyond their shores to include continental shelves, subsea aprons that are far more shallow than the deep ocean abysses that mark the continental boundary.

In western Antarctica, the Ross Sea is characterized by a continental shelf that extends nearly 1,000 miles from the coast and is as much as 3,500 feet deep. Anderson said the geologic record shows that as recently as 18,000 years ago the entire Ross basin was filled with ice that was so thick and heavy it was grounded on the seafloor all the way to the edge of the continental shelf.

"We found that about 10,000 years ago, this thick, grounded ice sheet broke apart in dramatic fashion," Anderson said. "The evidence shows that an armada of icebergs -- each at least twice as tall as the Empire State Building -- was pushed out en masse. We know this because this part of the Ross Sea is about 550 meters (1,804 feet) deep, and the icebergs were so large and so tightly packed that they gouged huge furrows into the seafloor as they moved north."

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In the Face of Global Warming, Pacific Islanders Look to Emigrate

On the frontline of climate change, many people in low-lying Pacific islands say they will consider migrating if droughts, floods or rises in sea level worsen, a study showed on Wednesday at United Nations talks.

Even so, very few of the islanders surveyed in Kiribati, Tuvalu and Nauru have the money needed to move, the report by the U.N. University and the European Union said.

"Pacific islanders are facing the brunt of climate change impacts and are increasingly finding themselves with few options," Tuvalu's Prime Minister Enele Sosene Sopoaga said, commenting on the report.

The first survey of its kind, it said more than 70 percent of households surveyed in Kiribati and Tuvalu and 35 percent of those in Nauru, said family members would be willing to move if the impact of climate change worsened.

It said that 1.3 percent of people in Kiribati, 10 percent of those in Nauru and 15 percent of those in Tuvalu had moved internationally in the period 2005-15. It did not give comparisons with previous decades.

The researchers projected that international migration would increase sharply by 2055 from all three island states. Storms and "king tides" are likely to worsen. Sea levels have risen about 20 centimetres (8 inches) in the past century.

It said only 26 percent of the 6,852 people surveyed in the three nations reckoned they had enough money to migrate - average monthly earnings are just $12 per capita.

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What are the Upper Limits of Sea Level Rise Caused by the Antarctic Icesheet Melting

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations

Authors:

Ritz et al

Abstract:

Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions the centennial to millennial contribution could be several metres. Physically plausible projections are challenging9: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections11 rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B, although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments9 (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

New, Contrarian Study Claims Antarctic Driven Sea Level Rise Will be Slower Than Expected

A new study by scientists in the UK and France has found that Antarctic ice sheet collapse will have serious consequences for sea level rise over the next two hundred years, though not as much as some have suggested.

This study, published today in the journal Nature, uses an ice-sheet model to predict the consequences of unstable retreat of the ice, which recent studies suggest has begun in West Antarctica. Scientists, led by Catherine Ritz from Université Grenoble Alpes in France and Tamsin Edwards from The Open University, predict that the contribution is most likely to be 10 cm of sea-level rise this century under a mid to high climate scenario, but is extremely unlikely to be higher than 30 cm. When combined with other contributions, that's a significant challenge for adapting to future sea level rise. But it's also far lower than some previous estimates, which were as high as one metre from Antarctica alone.

The study's central estimate raises the Intergovernmental Panel on Climate Change (IPCC) central prediction of 60 cm global sea-level rise by just a few centimetres under the mid to high scenario they used. But the UK and France team's method allowed them to assess the likelihood of sea-level rise from substantial parts of the ice sheet collapsing, which the IPCC could not due to a lack of evidence. They predict there is a one in twenty chance that Antarctic collapse could contribute more than 30 cm sea-level rise by the end of the century and more than 72 cm by 2200. This does not rule out larger contributions on longer time scales.

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Mangrove Forests are Critically Endangered by Sea Level Rise in the Indo-Pacific Region

Mangrove forests around the Indo-Pacific region could be submerged by 2070, international research published today says. Even with relatively low sea-level rises, many mangrove forests had a poor outlook said Professor Catherine Lovelock, a University of Queensland ecologist.

"Mangrove forests are particularly vulnerable," she said.

"Mangroves are predicted to be submerged in parts of Thailand, Sumatra, Java, Papua New Guinea and the Solomon Islands."

However the outlook in other parts of the world was more positive.

"Our modelling shows mangroves are likely to persist in east Africa, the Bay of Bengal, eastern Borneo and north-western Australia - areas where there are relatively large tidal ranges and/or higher sediment supply," said Professor Lovelock, who works in UQ's School of Biological Sciences and the Global Change Institute.

"Even in other areas though, the good news is that through accretion of sediment and maintenance of wetland soils, mangrove forests do have the capacity to avoid inundation and keep pace with sea-level rise."

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Global Warming Commits the World to Long Term Sea Level Rise Even if Held to 2 C

The multi-millennial Antarctic commitment to future sea-level rise

Authors:

Golledge et al

Abstract:

Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century1. If anthropogenic emissions continue unchecked, the warming increase may reach 8–10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change3. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6–3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

Which American Cities Face Sea Level Rise in the Long Term

Carbon choices determine US cities committed to futures below sea level

Authors:

Strauss et al

Abstract:

Anthropogenic carbon emissions lock in long-term sea-level rise that greatly exceeds projections for this century, posing profound challenges for coastal development and cultural legacies. Analysis based on previously published relationships linking emissions to warming and warming to rise indicates that unabated carbon emissions up to the year 2100 would commit an eventual global sea-level rise of 4.3–9.9 m. Based on detailed topographic and population data, local high tide lines, and regional long-term sea-level commitment for different carbon emissions and ice sheet stability scenarios, we compute the current population living on endangered land at municipal, state, and national levels within the United States. For unabated climate change, we find that land that is home to more than 20 million people is implicated and is widely distributed among different states and coasts. The total area includes 1,185–1,825 municipalities where land that is home to more than half of the current population would be affected, among them at least 21 cities exceeding 100,000 residents. Under aggressive carbon cuts, more than half of these municipalities would avoid this commitment if the West Antarctic Ice Sheet remains stable. Similarly, more than half of the US population-weighted area under threat could be spared. We provide lists of implicated cities and state populations for different emissions scenarios and with and without a certain collapse of the West Antarctic Ice Sheet. Although past anthropogenic emissions already have caused sea-level commitment that will force coastal cities to adapt, future emissions will determine which areas we can continue to occupy or may have to abandon.

Sea Level Fluctuation Ceased Globally 6k Years Ago, Resumed Rising 100 to 150 Years Ago

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

Authors:

Lambeck et al

Abstract:

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet’s dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ice margins has provided new constraints on the fluctuation of ice volume in this interval. Key results are: (i) a rapid final fall in global sea level of ∼40 m in less than 2,000 y at the onset of the glacial maximum ∼30,000 y before present (30 ka BP); (ii) a slow fall to −134 m from 29 to 21 ka BP with a maximum grounded ice volume of ∼52 × 106 km3 greater than today; (iii) after an initial short duration rapid rise and a short interval of near-constant sea level, the main phase of deglaciation occurred from ∼16.5 ka BP to ∼8.2 ka BP at an average rate of rise of 12 m⋅ka−1 punctuated by periods of greater, particularly at 14.5–14.0 ka BP at ≥40 mm⋅y−1 (MWP-1A), and lesser, from 12.5 to 11.5 ka BP (Younger Dryas), rates; (iv) no evidence for a global MWP-1B event at ∼11.3 ka BP; and (v) a progressive decrease in the rate of rise from 8.2 ka to ∼2.5 ka BP, after which ocean volumes remained nearly constant until the renewed sea-level rise at 100–150 y ago, with no evidence of oscillations exceeding ∼15–20 cm in time intervals ≥200 y from 6 to 0.15 ka BP.

Searching for Archaeological Sites Underwater

A specialist group of European researchers are studying the remains of prehistoric human settlements which are now submerged beneath our coastal seas. Some of these drowned sites are tens of thousands of years old. From the progressive discovery and analysis of these prehistoric remains, a new scientific field has emerged, combining the expertise from many disciplines including archaeology, oceanography and the geosciences. The new field is called Continental Shelf Prehistoric Research.

This rapidly evolving research field is the focus of a new European Marine Board (EMB) position paper titled 'Land Beneath the Waves: Submerged Landscapes and Sea-Level Change.' The paper describes how during the successive ice ages of the last 1 million years, the sea level dropped at times by up to 120m, and the exposed area of the continental shelf added 40% to the land area of Europe; a terrain occupied by vegetation, fauna, and people. Consequently, many of the remains and artefacts of Europe's prehistory are now underwater. Considering that pre-humans inhabited the Black Sea coast 1.8 million years ago, the coast of northern Spain over 1 million years ago and; the coast of Britain at least 0.8 million years ago, the drowned land includes some of the earliest routes from Africa into Europe, and the areas where people survived during the multiple Ice Ages.

More than 2,500 submerged prehistoric artefact assemblages, ranging in age from 5,000 to 300,000 years, have been found in the coastal waters and open sea basins around Europe. Only a few have been properly mapped by divers, or assessed for preservation or excavation. These remains contain information on ancient seafaring, and the social structures and exploitation technologies of coastal resources before the introduction of agriculture some 10,000 years ago. To understand how prehistoric people responded to changing sea level, researchers combine examinations of these deposits with palaeoclimate models, reconstructions of ice-cap and sea level curves, and sophisticated survey and excavation techniques.

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Sea Level Rose as Much as *5* Meters per Century During Pleistocene Interglacials

Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study.

An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.

The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.

Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: "The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.

"Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century."

Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change. He says: "For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat."

"This happened within 400 years for 68 per cent of all 120 cases considered, and within 1100 years for 95 per cent. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries."

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Pacific Island Nations Looking to Procure Land Elsewhere to Survive Inundation by Rising Seas

The president of the Pacific island state of Kiribati favors buying more land abroad after a purchase in Fiji, to secure both food supplies and perhaps a future home if rising sea levels swamp low-lying atolls.

Anote Tong, in Norway on a stopover to view melting Arctic ice pushing up sea levels before he attends a U.N. climate summit in New York on Tuesday, said he wanted to lay conditions for "migration with dignity" from the islands.

Kiribati, a nation of 100,000 people scattered over 32 Pacific atolls, completed a deal with Fiji this year to buy 6,000 acres (2,400 hectares) of forest land for A$9.3 million ($8.3 million) on the island of Vanua Levu, he said.

"With sea level rise, the value of land will go up," Tong predicted in a weekend interview, nursing a cold from a visit to the Arctic archipelago of Svalbard. "I am not going to relocate my people, but someone else might" in coming decades.

"Some people have suggested 'why not (buy more land in) Australia and New Zealand, they are selling land to the Chinese?'," he said. "My view is 'yes' ... property poses the least risk" compared to other investments.

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inundation 

The Dark Snow of Greenland

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How Salt Marshes Respond to Sea Level Rise

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Louisiana Only has a Holey Sock, no Boot

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Antarctic Sea Level Rise Faster Than Rest of World due to Glacial Melt, Water Freshening

A new study of satellite data from the last 19 years reveals that fresh water from melting glaciers has caused the sea-level around the coast of Antarctica to rise by 2cm more than the global average of 6cm.

Researchers at the University of Southampton detected the rapid rise in sea-level by studying satellite scans of a region that spans more than a million square kilometres.

The melting of the Antarctic ice sheet and the thinning of floating ice shelves has contributed an excess of around 350 gigatonnes of freshwater to the surrounding ocean. This has led to a reduction in the salinity of the surrounding oceans that has been corroborated by ship-based studies of the water.

"Freshwater is less dense than salt water and so in regions where an excess of freshwater has accumulated we expect a localised rise in sea level," says Craig Rye, lead author of the paper that has been published in the journal Nature Geoscience.

In addition to satellite observations, the researchers also conducted computer simulations of the effect of melting glaciers on the Antarctic Ocean. The results of the simulation closely mirrored the real-world picture presented by the satellite data.

"The computer model supports our theory that the sea-level rise we see in our satellite data is almost entirely caused by freshening (a reduction in the salinity of the water) from the melting of the ice sheet and its fringing ice shelves," says Craig.

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Antarctica Could Contribute up to 37 cm (14 in) to Sea Level Rise

The results reproduce Antarctica's recent contribution to sea level rise as observed by satellites in the last two decades and show that the ice continent could become the largest contributor to sea level rise much sooner than previously thought.

"If greenhouse gases continue to rise as before, ice discharge from Antarctica could raise the global ocean by an additional 1 to 37 centimeters in this century already," says lead author Anders Levermann. "Now this is a big range – which is exactly why we call it a risk: Science needs to be clear about the uncertainty, so that decision makers at the coast and in coastal megacities like Shanghai or New York can consider the potential implications in their planning processes," says Levermann.

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