An ancient reef found in the Pacific may provide clues to what will happen to coral when sea temperatures rise.
A team of researchers from Australia and New Zealand have discovered a huge 9,000-year-old reef surprisingly far south. Lord Howe Island is 600km east of the Australian mainland and has a small modern coral reef - the furthest south in the world.
The ancient reef however is nearly 30 times as large as the modern reef. The scientists, headed by Colin Woodroffe from the University of Wollongong in Australia and researchers from Geoscience Australia, discovered a large ridge about 30m under water in the Tasman Sea. They have published their work in Geophysical Research Letters.
The team suspected it might be an ancient reef. The size and shape of the ridge can be mapped using a type of sonar called multi-beam echo sounding. The researchers could not be sure it was coral until they had taken samples.
The modern reef appears in red, the ancient one in orange
Drilling for samples in the Tasman Sea is very dependent on weather and the seas can be rough - it involves lowering a submersible drill from a boat. The samples confirmed that it was indeed coral and radiocarbon dating confirmed its age.
Other similar ancient reefs - called relict reefs - have been discovered before, but none as far south as this. The team think that this reef died when it was flooded as a result of sea levels rising about 7,000 years ago, but the modern temperature at these latitudes also limits coral growth, which is why the relict reef is so much bigger than the modern reef.
Now that sea temperatures are rising, however, reefs may start to grow bigger at higher latitudes.
The relict reef doesn't have an extensive modern reef attached to it but it does have some individual corals which are newer - from the last 2,000 years. This suggests that there is a suitable habitat for corals which might grow into a larger reef when temperatures rise further.
In the Northern Hemisphere both Florida and Bermuda have small reefs, though they are at the northern limits for coral life. It is possible that large relict reefs might also be found in those northern waters. Like the Tasman Sea relict reef, these might be able to support new growth.
Rising sea temperatures are dangerous for coral reefs at hotter tropical latitudes but they may mean we see new reef growth at the far southern, and northern, limits of current reefs. Links :
AFP : Ancient Australian reef raises hopes for coral as seas warm
From NASA Goddart Multimedia On August 29, 2005, Hurricane Katrina made landfall along the Gulf Coast. Five years later, NASA revisits the storm with a short video that shows Katrina as captured by satellites. Before and during the hurricane's landfall, NASA provided data gathered from a series of Earth observing satellites to help predict Katrina's path and intensity. In its aftermath, NASA satellites also helped identify areas hardest hit.
BARBARA KLEIN: This is SCIENCE IN THE NEWS in VOA Special English. I’m Barbara Klein.
BOB DOUGHTY: And I’m Bob Doughty. Today we remember Hurricane Katrina and tell about the science of severe ocean storms.
BARBARA KLEIN: Many Americans are observing the fifth anniversary of one of the nation’s worst natural disasters. Hurricane Katrina reached the state of Louisiana on the morning of August twenty-ninth, two thousand five. It was the costliest hurricane in American history, and one of the deadliest.
Radio and television programs, concerts and films are recalling the storm and its effects on the nation. Literary readings and religious observances also are marking the event. Hurricane Katrina struck hardest in Louisiana, Mississippi and Alabama. Death and destruction from the hurricane and its effects extended along the Gulf Coast. More than one thousand eight hundred people were killed.
BOB DOUGHTY: The storm formed over the Bahamas on August twenty-third, two thousand five. The next day, it grew strong enough for scientists to call it a tropical storm. Then it moved toward the United States. It first reached land in south Florida on August twenty-fifth.
At that time, the National Hurricane Center said the winds were at a top continuing speed of more than one hundred thirty kilometers per hour. Experts identified the storm as a hurricane. They named it Katrina, and rated it as the least severe type of hurricane. Still, it caused flooding and killed people in Florida.
BARBARA KLEIN: Hurricane Katrina weakened again after striking Florida. Later it moved to the Gulf of Mexico. The Gulf’s warm waters helped it gain strength. At one point, the storm’s winds were blowing at more than two hundred sixty-eight kilometers per hour. Experts increased its rating to the most severe hurricane.
Time passed, and the winds again weakened. Then Hurricane Katrina reached land in Louisiana. Its speed had fallen to about two hundred kilometers per hour when it struck near New Orleans. But the wind was strong enough to pick up trees, vehicles and buildings. It threw them into the air like toys. Walls of water flooded over the land. Intense rain fell. Then Hurricane Katrina struck land again, this time at the border of Mississippi and Louisiana. Again, there was loss of life and terrible destruction.
BOB DOUGHTY: Severe ocean storms in the northern part of the world usually develop in late summer or early autumn near the equator. Scientists call them cyclones when they develop over the Indian Ocean. When they happen over the northwestern Pacific Ocean, the storms are typhoons. And in the eastern Pacific and the Atlantic Ocean they are called hurricanes. Ocean storms develop when the air temperature in one area is different from the temperature nearby. Warmer air rises, while cooler air falls. These movements create a difference in the pressure of the atmosphere.
BARBARA KLEIN: If the pressure changes over a large area, winds start to blow in a huge circle. High pressure air is pulled toward a low pressure center. Thick clouds form and heavy rains fall as the storm gains speed and moves over the ocean waters. Storms can get stronger as they move over warm ocean waters.
The strongest, fastest winds of a hurricane blow in the area known as the eyewall. It surrounds the center, or eye, of the storm. The eye itself is calm by comparison. Wind speeds in severe ocean storms can reach more than two hundred fifty kilometers an hour. Up to fifty centimeters of rain can fall. Some storms have produced more than one hundred fifty centimeters of rain.
These storms also cause high waves and ocean surges. A surge is a continuous movement of water that may reach as high as six meters or more. The water strikes low coastal areas. Surges are commonly responsible for about ninety percent of all deaths from ocean storms.
BOB DOUGHTY: The National Hurricane Center in Miami, Florida, keeps watch on severe storms. It works closely with public officials and with radio and television stations to keep people informed. Experts believe this early warning system has helped reduce deaths from ocean storms in recent years. But sometimes people cannot or will not flee the path of a storm. That is what happened in many places in New Orleans.
BARBARA KLEIN: Weather scientists use computer programs to create models that show where a storm might go. The programs combine information such as temperatures, wind speed, atmospheric pressure and the amount of water in the atmosphere. Scientists collect the information with satellites, weather balloons and devices floating in the world's oceans. They also collect information from ships and passenger flights and from government planes. These planes fly into and around storms. The crews drop instruments attached to parachutes. The instruments report temperature, pressure, wind speed and other conditions.
BOB DOUGHTY: Scientists use the Saffir-Simpson Hurricane Scale to measure the intensity of storms based on wind speed. It provides an idea of the amount of coastal flooding and property damage that might be expected. The scale is divided into five groups or categories. The mildest hurricane is called category one. It has winds of about one hundred twenty to one hundred fifty kilometers an hour. This storm can damage trees and lightweight structures. It can also cause flooding.
Wind speeds in a category two hurricane can reach close to one hundred eighty kilometers an hour. These storms are often powerful enough to break windows or blow the roofs off houses. Winds between about one hundred eighty and two hundred fifty kilometers an hour represent categories three and four. An even more powerful storm is a category five hurricane.
BARBARA KLEIN: The National Oceanic and Atmospheric Administration said Hurricane Katrina was a strong category three hurricane when it hit land in Louisiana. But researchers say other forces than its wind speed helped cause Katrina’s extensive destruction. NOAA scientists say Katrina’s air pressure was very low. The lower the air pressure, the stronger the storm. And Katrina was also an unusually wide storm.
Katrina’s most damaging power, however, came from the water it brought. The storm surge was estimated at more than six meters, and may have been as high as nine meters.
BOB DOUGHTY: All this water poured into Lake Pontchartrain on the north side of New Orleans. It also flooded into the Mississippi River to the south. New Orleans was built below sea level. The city is surrounded by levees made of earth and walls made of concrete.
The water and wind pressure from Katrina broke through the flood dams and destroyed many areas of New Orleans. The surge washed away large areas of the coastal cities of Biloxi and Gulfport, Mississippi. There was also heavy damage in Alabama.
BARBARA KLEIN: Some scientists believe climate change affects major storms. Some say the warming of Earth’s atmosphere is already making the storms worse. Other scientists have published studies that disagree.
Earlier this year, a special World Meteorological Organization committee reported on severe storms. The committee’s work appeared in the journal Nature Geoscience. Ten scientists took part. The experts represented both sides of the debate about global warming. They reached no clear answer about whether global warming had already intensified storms. Still, the committee made some predictions.
BOB DOUGHTY: They said global warming might cause more powerful ocean storms in the future. They said the overall strength of storms measured by wind speed might increase two to eleven percent by the year twenty-one hundred. And there might be an increase in the number of the most severe storms. But there might be fewer weak and moderate storms.
The current Atlantic Ocean hurricane season began in June. Weather experts say fewer severe storms than usual have struck since then. Experts had predicted above-normal numbers of storms during the season, which continues through November.
Or download MP3 (Right-click or option-click and save link)
Links :
MSNBC Hurricane tracker : interactive mashup built by Stamen using Bing Maps. Use the app to track recent events and see exactly where the storm has been and where its going
Webb Chiles was the first American to round Cape Horn solo. He is the author of five books, has circumnavigated by sail four times, and has set numerous world records.
The Island of California (Map, circa 1650) refers to a long-held European misconception, dating from the 16th century, that California was not part of mainland North America but rather a large island separated from the continent by a strait now known instead as the Gulf of California.
One of the most famous cartographic errors in history, it was propagated on many maps during the seventeenth and eighteenth centuries, despite contradictory evidence from various explorers.
How accurate are nautical charts? How much faith can be placed in them?
The Australian Hydrographic Service proposes a valuable guide which any skipper or navigator of a sailing vessel should be aware with.
Unfortunately, the answer is quite complex – far more complex than simply saying one chart is accurate whilst another is not.
However, having the necessary skills should be essential for any mariner venturing into unfamiliar waters.
All charts, whether paper or electronic, contain data which varies in quality due to the age and accuracy of individual surveys. In general, remote areas away from shipping routes tend to be less well surveyed, and less frequently, while areas of high commercial traffic are re-surveyed frequently to very high levels of accuracy, particularly where under-keel clearances are small.
It is quite accurate to consider a chart as a jigsaw of individual surveys pieced together to form a single image. These surveys vary in age and quality, particularly due to changes in technology.
However, one fundamental truth remains – a hydrographic surveyor can typically only physically see a very small percentage of their survey area – the parts which rise above the sea surface; for the remainder they must have confidence in their systems and long-standing practices to accurately and confidently chart the seabed.
Because priority for surveying is given to the major shipping routes, an essential skill for mariners venturing into unfamiliar waters away from these routes is the ability to interpret the various quality indicators that are, or should be, on every chart.
These are the best guides available to mariners, whether on commercial vessels or cruising yachts, to help them decide how much confidence should be had in past and current surveyors and the technology available to them when surveying the different areas of each chart.
Indeed, a prudent mariner should be wary of any chart that does not show these indicators, irrespective of whether it is a traditional paper chart, a Raster Nautical Chart or one of the new Electronic Navigational Charts.
Finally, if in doubt, post a lookout, make your approach in daylight and good conditions, or go somewhere else – there is no such thing as a good grounding.
Links :
MySailing : All you've ever wanted to ask the hydrographic-service
Mariners may be putting their lives at risk by relying on electronic navigation charts that are not up-to-date, says the Australian Hydrographic Service (AHS).
The AHS’s director of charting services, Mike Prince said last week an outdated chart could have been the cause of the yachting tragedy last year that claimed the lives of two experienced sailors.
Veteran skipper Andrew Short, 48, and navigator Sally Gordon, 47, both of Sydney died after they were swept from the deck of PWC Shockwave after the yacht struck Flinders Islet off the New South Wales South Coast in October.
The 26-metre multimillion-dollar yacht broke up after the crash, which occurred about 3am as it was about to make the return journey in a 169-kilometre race from Sydney.
“A CYC (Cruising Yacht Club) report (read Navigation Systems Reliability chapter p.26 to P.31) to said they were using an electronic chart at the time of the crash and there is speculation that there could have been a problem with it,” Mr Prince said.
A yacht race inquiry in January heard some of the boat’s crew before the tragic race had observed errors on the chart plotter in Sydney Harbour and at Hamilton Island in Queensland.
The AHS is working with Yachting Australia and maritime services around the country to raise awareness of the limitations of the commercial charts used within chart plotters and software systems.
Mr Prince estimated that one million Australian boaties used unofficial electronic charts. ‘‘Sailors should use the charts to support navigation, not totally rely on them,’’ he said.
In another case, Timothy O'Neill, 39, died after his motorboat doing 25 knots crashed into a seawall at the mouth of the Brisbane River in 2007. The boat’s electronic charts had not been updated to show the seawall had been built on reclaimed land. (see Maritime Safety Queensland SeaScape p. 4 saying the accident was partly to blame due to an over-reliance on an outdated GPS system / Office of the State Coroner - Findings of Inquest) In 2008, a $1.7m yacht Asolare hit a reef 200 nautical miles east of Cairns and two crew members who had been clinging to the boat’s hull were winched to safety by rescue helicopter. “The skipper said the reef wasn’t on his electronic chart but it was on the paper chart so he obviously hadn’t updated it,” he said.
The AHS publishes fortnightly updates new and altered information that could affect safety at sea on the Australian Notice to Mariners. It is up to mariners to apply the updates to their charts.
“If people don’t update them they could be ignorant of hazards or dangers that could affect their safety,” he said.
Makers of commercial electronic charts are not legally required to regularly update their charts because they are marked “not for navigation” or “aid to navigation only”.
These unofficial charts might only be updated every few years.
The modern reef appears in red, the ancient one in orange
