Sea levels rising in parts of Indian Ocean, according to new study

Rising sea levels in parts of the Indian Ocean appear to be at least partly the result of rising greenhouse emissions. -  University of Colorado
Rising sea levels in parts of the Indian Ocean appear to be at least partly the result of rising greenhouse emissions. – University of Colorado

Newly detected rising sea levels in parts of the Indian Ocean, including the coastlines of the Bay of Bengal, the Arabian Sea, Sri Lanka, Sumatra and Java, appear to be at least partly a result of human-induced increases of atmospheric greenhouse gases, says a study led by the University of Colorado at Boulder.

The study, which combined sea surface measurements going back to the 1960s and satellite observations, indicates anthropogenic climate warming likely is amplifying regional sea rise changes in parts of the Indian Ocean, threatening inhabitants of some coastal areas and islands, said CU-Boulder Associate Professor Weiqing Han, lead study author. The sea level rise — which may aggravate monsoon flooding in Bangladesh and India — could have far-reaching impacts on both future regional and global climate.

The key player in the process is the Indo-Pacific warm pool, an enormous, bathtub-shaped area of the tropical oceans stretching from the east coast of Africa west to the International Date Line in the Pacific. The warm pool has heated by about 1 degree Fahrenheit, or 0.5 degrees Celsius, in the past 50 years, primarily caused by human-generated increases of greenhouse gases, said Han.

“Our results from this study imply that if future anthropogenic warming effects in the Indo-Pacific warm pool dominate natural variability, mid-ocean islands such as the Mascarenhas Archipelago, coasts of Indonesia, Sumatra and the north Indian Ocean may experience significantly more sea level rise than the global average,” said Han of CU-Boulder’s atmospheric and oceanic sciences department.

A paper on the subject was published in this week’s issue of Nature Geoscience. Co-authors included Balaji Rajagopalan, Xiao-Wei Quan, Jih-wang Wang and Laurie Trenary of CU-Boulder, Gerald Meehl, John Fasullo, Aixue Hu, William Large and Stephen Yeager of the National Center for Atmospheric Research in Boulder, Jialin Lin of Ohio State University, and Alan Walcraft and Toshiaki Shinoda of the Naval Research Laboratory in Mississippi.

While a number of areas in the Indian Ocean region are showing sea level rise, the study also indicated the Seychelles Islands and Zanzibar off Tanzania’s coastline show the largest sea level drop. Global sea level patterns are not geographically uniform, and sea rise in some areas correlate with sea level fall in other areas, said NCAR’s Meehl.

The Indian Ocean is the world’s third largest ocean and makes up about 20 percent of the water on Earth’s surface. The ocean is bounded on the west by East Africa, on the north by India, on the east by Indochina and Australia, and on the south by the Southern Ocean off the coast of Antarctica.

The patterns of sea level change are driven by the combined enhancement of two primary atmospheric wind patterns known as the Hadley circulation and the Walker circulation. The Hadley circulation in the Indian Ocean is dominated by air currents rising above strongly heated tropical waters near the equator and flowing poleward, then sinking to the ocean in the subtropics and causing surface air to flow back toward the equator.

The Indian Ocean’s Walker circulation causes air to rise and flow westward at upper levels, sink to the surface and then flow eastward back toward the Indo-Pacific warm pool. “The combined enhancement of the Hadley and Walker circulation form a distinct surface wind pattern that drives specific sea level patterns,” said Han.

The international research team used several different sophisticated ocean and climate models for the study, including the Parallel Ocean Program — the ocean component of NCAR’s widely used Community Climate System Model. In addition, the team used a wind-driven, linear ocean model for the study.

“Our new results show that human-caused changes of atmospheric and oceanic circulation over the Indian Ocean region — which have not been studied previously — are the major cause for the regional variability of sea level change,” wrote the authors in Nature Geoscience.

Han said that based on all-season data records, there is no significant sea level rise around the Maldives. But when the team looked at winter season data only, the Maldives show significant sea level rise, a cause for concern. The smallest Asian country, the Maldives is made up of more than 1,000 islands — about 200 of which are inhabited by about 300,000 people — and are on average only about five feet above sea level.

The complex circulation patterns in the Indian Ocean may also affect precipitation by forcing even more atmospheric air down to the surface in Indian Ocean subtropical regions than normal, Han speculated. “This may favor a weakening of atmospheric convection in the subtropics, which may increase rainfall in the eastern tropical regions of the Indian Ocean and increase drought in the western equatorial Indian Ocean region, including east Africa,” Han said.

The new study indicates that in order to document sea level change on a global scale, researchers also need to know the specifics of regional sea level changes that will be important for coastal and island regions, said NCAR’s Hu. Along the coasts of the northern Indian Ocean, seas have risen by an average of about 0.5 inches, or 13 millimeters, per decade.

“It is important for us to understand the regional changes of the sea level, which will have effects on coastal and island regions,” said Hu.

Research challenges models of sea level change during ice-age cycles

<IMG SRC="/Images/114125549.jpg" WIDTH="299" HEIGHT="200" BORDER="0" ALT="Theories about the rates of ice accumulation and melting during the Quaternary Period — the time interval ranging from 2.6 million years ago to the present — may need to be revised, thanks to research findings published by a University of Iowa researcher and his colleagues in the February 12 issue of the journal Science.”>
Theories about the rates of ice accumulation and melting during the Quaternary Period — the time interval ranging from 2.6 million years ago to the present — may need to be revised, thanks to research findings published by a University of Iowa researcher and his colleagues in the February 12 issue of the journal Science.

Theories about the rates of ice accumulation and melting during the Quaternary Period — the time interval ranging from 2.6 million years ago to the present — may need to be revised, thanks to research findings published by a University of Iowa researcher and his colleagues in the 12 February issue of the journal Science.

Jeffrey Dorale, assistant professor of geoscience in the UI College of Liberal Arts and Sciences, writes that global sea level and Earth’s climate are closely linked. Data he and colleagues collected on speleothem encrustations (see photo right), a type of mineral deposit, in coastal caves on the Mediterranean island of Mallorca indicate that sea level was about one meter above present-day levels around 81,000 years ago. The finding challenges other data that indicate sea level was as low as 30 meters — the ice equivalent of four Greenland ice sheets — below present-day levels.

He said the sea level high stand of 81,000 years ago was preceded by rapid ice melting, on the order of 20 meters of sea level change per thousand years and the sea level drop following the high water mark, accompanied by ice formation, was equally rapid.

“Twenty meters per thousand years equates to one meter of sea level change in a 50-year period,” Dorale said. “Today, over one-third of the world’s population lives within 60 miles of the coastline. Many of these areas are low-lying and would be significantly altered — devastated — by a meter of sea level rise. Our findings demonstrate that changes of this magnitude can happen naturally on the timescale of a human lifetime. Sea level change is a very big deal.”

Dorale also noted that although their findings disagree with some sea level estimates, such as those from Barbados and New Guinea that come from ancient coral reefs, they are in agreement with data gathered from other sites such as the Bahamas, the U.S. Atlantic coastal plain, Bermuda, the Cayman Islands and California.

“There has been a long-standing debate on this issue, but our data is pretty robust,” he said. “The key to our research is two-fold. First, the speleothem approach we employed is novel and extremely precise compared to other methods of sea-level reconstruction. Second, Mallorca appears to be particularly well suited to the task, because neither tectonics nor isostasy — geological forces of crustal motion — over-complicate the record. It’s really close to the ideal scenario. It’s also a heck of a nice place to do fieldwork.”

Dorale’s colleagues include Bogdan Onac of the University of South Florida, Tampa; Joan Fornos, Joaquin Gines and Angel Gines, all of the Universitat de les Illes Balears, Mallorca, Spain; Paola Tuccimei of the University of Rome III, Italy; and UI associate professor of geoscience David Peate.

The research was supported by the National Science Foundation in a grant to Dorale and Onac.

The sea level has been rising and falling over the last 2,500 years

Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,' explains Dr. Dorit Sivan, who supervised the research.
The Templar palace in Acre, seen here, is one of the sites where this study was carried out. -  Amir Yurman, Director of the Leon Recanati Institute for Maritime Studies Maritime Workshop at the University of Haifa;
Courtesy of the University of Haifa
Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,’ explains Dr. Dorit Sivan, who supervised the research.
The Templar palace in Acre, seen here, is one of the sites where this study was carried out. – Amir Yurman, Director of the Leon Recanati Institute for Maritime Studies Maritime Workshop at the University of Haifa;
Courtesy of the University of Haifa

“Rising and falling sea levels over relatively short periods do not indicate long-term trends. An assessment of hundreds and thousands of years shows that what seems an irregular phenomenon today is in fact nothing new,” explains Dr. Dorit Sivan, who supervised the research.*

The sea level in Israel has been rising and falling over the past 2,500 years, with a one-meter difference between the highest and lowest levels, most of the time below the present-day level. This has been shown in a new study supervised by Dr. Dorit Sivan, Head of the Department of Maritime Civilizations at the University of Haifa. “Rises and falls in sea level over relatively short periods do not testify to a long-term trend. It is early yet to conclude from the short-term increases in sea level that this is a set course that will not take a change in direction,” explains Dr. Sivan.

The rising sea level is one of the phenomena that have most influence on humankind: the rising sea not only floods the littoral regions but also causes underground water salinization, flooded effluents, accelerated coastal destruction, and other damage.

According to Dr. Sivan, the changing sea level can be attributed to three main causes: the global cause – the volume of water in the ocean, which mirrors the mass of ice sheets and is related to global warming or cooling; the regional cause – vertical movement of the earth’s surface, which is usually related to the pressure placed on the surface by the ice; and the local cause – vertical tectonic activity. Seeing as Israel is not close to former ice caps and the tectonic activity along the Mediterranean coast is negligible over these periods, it can be concluded that drastic changes in Israel’s sea levels are mainly related to changes in the volume of water.

In the present study, in light of earlier studies, research student Ayelet Toker and Dr. Sivan, set out to examine Israel’s sea level over the past 2,500 years, based on data deduced from many coastal archaeological findings. They made a careful selection of findings that have been reliably and accurately dated, and first focused on findings that were excavated by the Antiquities Authority in Acre of the Crusader period. These revealed that the sea level during the Crusader period – just 800 years ago – was some 50-90 centimeters lower than the present sea level. Findings from the same period at Caesarea and Atlit reinforced this conclusion. When additional sites were examined from periods before and after the Crusader period, it was revealed that there have been significant fluctuations in sea level: During the Hellenistic period, the sea level was about 1.6 meters lower than its present level; during the Roman era the level was almost similar to today’s; the level began to drop again during the ancient Muslim period, and continued dropping to reach the same level as it was during the Crusader period; but within about 500 years it rose again, and reached some 25 centimeters lower than today’s level at the beginning of the 18th century.

“Over the past century, we have witnessed the sea level in Israel fluctuating with almost 19 centimeters between the highest and lowest levels. Over the past 50 years Israel’s mean sea level rise is 5.5 centimeters, but there have also been periods when it rose by 10 centimeters over 10 years. That said, even acute ups and downs over short periods do not testify to long-term trends. An observation of the sea levels over hundreds and thousands of years shows that what seems a phenomenon today is as a matter of fact “nothing new under the sun”, Dr. Sivan concludes.

Sea level is rising along US Atlantic coast, say environmental scientists

Professor Ben Horton (University of Pennsylvania)
collects salt marsh sediment in North Carolina. -  University of Pennsylvania
Professor Ben Horton (University of Pennsylvania)
collects salt marsh sediment in North Carolina. – University of Pennsylvania

An international team of environmental scientists led by the University of Pennsylvania has shown that sea-level rise along the Atlantic Coast of the United States was 2 millimeters faster in the 20th century than at any time in the past 4,000 years.

Sea-level rise prior to the 20th century is attributed to coastal subsidence. Put simply, land is being lost to subsidence as the earth continues to rise in response to the removal of the huge weight of ice sheets during the last glacial period. Using sediment cores from the U.S. Atlantic coast, researchers found significant spatial variations in land movement, with the mid-Atlantic coastlines of New Jersey, Delaware and Maryland subsiding twice as much as areas to the north and south. Coastal subsidence enhances sea-level rise, which leads to shoreline erosion and loss of wetlands and threatens coastal populations.

Researchers corrected relative sea-level data from tide gauges using the coastal-subsidence values. Results clearly show that the 20th-century rate of sea-level rise is 2 millimeters higher than the background rate of the past 4,000 years. Furthermore, the magnitude of the sea-level rise increases in a southerly direction from Maine to South Carolina. This is the first demonstrated evidence of this phenomenon from observational data alone. Researchers believe this may be related to the melting of the Greenland Ice Sheet and ocean thermal expansion.

“There is universal agreement that sea level will rise as a result of global warming but by how much, when and where it will have the most effect is unclear,” said Ben Horton, assistant professor in the Department of Earth and Environmental Science at Penn. “Such information is vital to governments, commerce and the general public. An essential prerequisite for accurate prediction is understanding how sea level has responded to past climate changes and how these were influenced by geological events such as land movements.”

The study provides the first accurate dataset for sea-level rise for the U.S. Atlantic coast, identifying regional differences that arise from variations in subsidence and demonstrate the possible effects of ice-sheet melting and thermal expansion for sea level rise.

New Antarctic seabed sonar images reveal clues to sea-level rise

British Antarctic Survey ship RRS James Clark Ross is equipped with sonar technology to map the seabed. -  British Antarctic Survey
British Antarctic Survey ship RRS James Clark Ross is equipped with sonar technology to map the seabed. – British Antarctic Survey

Motorway-sized troughs and channels carved into Antarctica’s continental shelves by glaciers thousands of years ago could help scientists to predict future sea-level rise according to a report in the journal Geology this month (May).

Using sonar technology from onboard ships, scientists from British Antarctic Survey (BAS) and the German Alfred Wegener Institute (AWI) captured the most extensive, continuous set of images of the seafloor around the Amundsen Sea embayment ever taken. This region is a major drain point of the West Antarctic Ice Sheet (WAIS) and considered by some scientists to be the most likely site for the initiation of major ice sheet collapse.

The sonar images reveal an ‘imprint’ of the Antarctic ice sheet as it was at the end of the last ice age around 10 thousand years ago. The extent of ice covering the continent was much larger than it is today. The seabed troughs and channels that are now exposed provide new clues about the speed and flow of the ice sheet. They indicate that the controlling mechanisms that move ice towards the coast and into the sea are more complex than previously thought.

Lead author Rob Larter from British Antarctic Survey said, “One of the greatest uncertainties for predicting future sea-level rise is Antarctica’s likely contribution. It is very important for scientists and our society to understand fully how polar ice flows into the sea. Indeed, this issue was highlighted in 2007 by the Intergovernmental Panel on Climate Change (IPCC). Our research tells us more about how the ice sheet responded to warming at the end of the last ice age, and how processes at the ice sheet bed controlled its flow. This is a big step toward understanding of how the ice sheets are likely to respond to future warming.

Ebb and flow of the sea drives world’s big extinction events


If you are curious about Earth’s periodic mass extinction events such as the sudden demise of the dinosaurs 65 million years ago, you might consider crashing asteroids and sky-darkening super volcanoes as culprits.



But a new study, published online today (June 15, 2008) in the journal Nature, suggests that it is the ocean, and in particular the epic ebbs and flows of sea level and sediment over the course of geologic time, that is the primary cause of the world’s periodic mass extinctions during the past 500[sc1] million years.



“The expansions and contractions of those environments have pretty profound effects on life on Earth,” says Shanan Peters, a University of Wisconsin-Madison assistant professor of geology and geophysics and the author of the new Nature report.



In short, according to Peters, changes in ocean environments related to sea level exert a driving influence on rates of extinction, which animals and plants survive or vanish, and generally determine the composition of life in the oceans.



Since the advent of life on Earth 3.5 billion years ago, scientists think there may have been as many as 23 mass extinction events, many involving simple forms of life such as single-celled microorganisms. During the past 540 million years, there have been five well-documented mass extinctions, primarily of marine plants and animals, with as many as 75-95 percent of species lost.



For the most part, scientists have been unable to pin down the causes of such dramatic events. In the case of the demise of the dinosaurs, scientists have a smoking gun, an impact crater that suggests dinosaurs were wiped out as the result of a large asteroid crashing into the planet. But the causes of other mass extinction events have been murky, at best.



“Paleontologists have been chipping away at the causes of mass extinctions for almost 60 years [sc2], ” explains Peters, whose work was supported by the National Science Foundation. “Impacts, for the most part, aren’t associated with most extinctions. There have also been studies of volcanism, and some eruptions correspond to extinction, but many do not.”


Arnold I. Miller, a paleobiologist and professor of geology at the University of Cincinnati, says the new study is striking because it establishes a clear relationship between the tempo of mass extinction events and changes in sea level and sediment: “Over the years, researchers have become fairly dismissive of the idea that marine mass extinctions like the great extinction of the Late Permian might be linked to sea-level declines, even though these declines are known to have occurred many times throughout the history of life. The clear relationship this study documents will motivate many to rethink their previous views.”



Peters measured two principal types of marine shelf environments preserved in the rock record, one where sediments are derived from erosion of land and the other composed primarily of calcium carbonate, which is produced in-place by shelled organisms and by chemical processes. “The physical differences between (these two types) of marine environments have important biological consequences,” Peters explains, noting differences in sediment stability, temperature, and the availability of nutrients and sunlight.



In the course of hundreds of millions of years, the world’s oceans have expanded and contracted in response to the shifting of the Earth’s tectonic plates and to changes in climate. There were periods of the planet’s history when vast areas of the continents were flooded by shallow seas, such as the shark- and mosasaur-infested seaway that neatly split North America during the age of the dinosaurs.



As those epicontinental seas drained, animals such as mosasaurs and giant sharks went extinct, and conditions on the marine shelves where life exhibited its greatest diversity in the form of things like clams and snails changed as well.



The new Wisconsin study, Peters says, does not preclude other influences on extinction such as physical events like volcanic eruptions or killer asteroids, or biological influences such as disease and competition among species. But what it does do, he argues, is provide a common link to mass extinction events over a significant stretch of Earth history.



“The major mass extinctions tend to be treated in isolation (by scientists),” Peters says. “This work links them and smaller events in terms of a forcing mechanism, and it also tells us something about who survives and who doesn’t across these boundaries. These results argue for a substantial fraction of change in extinction rates being controlled by just one environmental parameter.”



  1. The study starts in the Ordovician
  2. 100 years would refer to larger-scale changes in faunal composition

Glacier Melt Impact on Sea-Level is Underestimated


Global sea level has been climbing steadily over the past 80 years-and the contribution from melting ice has been more substantial than previously estimated, according to new research in Science Express.



The missing factor in earlier calculations: how much of the Earth’s water is impounded in artificial reservoirs, say Benjamin Chao and colleagues at National Central University in Chung-Li, Taiwan.


The total rise in sea level over the past century is due mostly to ocean water expanding in volume as it warms up, and ice melt from mountain glaciers and Greenland and Antarctic ice sheets. Subtracting the effect of thermal expansion from the observed rate of sea level rise should give a reasonable estimate of the rate of ice melting, the researchers say, but the equation leaves out the amount of water locked up in reservoirs.



They estimate that trapping the reservoir waters has artificially dropped sea levels by 30 millimeters over the past half-century. Add that water back in, they say, and the contribution of ice melt must be higher than previously thought.



The paper was published in the 13 March issue of Science Express (“Impact of Artificial Reservoir Water Impoundment on Global Sea Level”). The Web site provides electronic publication of selected Science papers in advance of print; some editorial changes may occur between the online version and the final printed version.