0
mm/year
Sea level rise in
north Carolina,
100 B.C.–950
0.6
mm/year
Sea level rise in
north Carolina,
950–1400
2. 1
mm/year
Sea level rise in
north Carolina,
1880–1920
Marsh sediment analysis reveals
fastest sea level rise in 2,000 years
Core samples show rapid increase starting in 19th century
successive sediment layers. Radioisotope dating showed that the sediments
recorded 2,100 years of sea level history,
the researchers report online June 20 in
the Proceedings of the National Academy
of Sciences.
“We know what sea level has done,
in a broad sense, going back 20,000
years,” Miller says. But detailed records
of what’s happened over the past 2,000
years have been spotty, he says.
The cores show that sea level at
the North Carolina sites was largely
unchanged from 100 B.C. until A.D. 950.
Then sea level under went a four-century
rise averaging 0.6 millimeters per year.
After another 500 years of stability, sea
level began its most recent advance after
1865. Since then, it has been climbing an
average of 2. 1 millimeters annually. And
at least for the last 80 years, Horton says,
“the fit with North Carolina tide gauge
data is one-to-one: It’s perfect.”
The results validate the use of general
equations relating past temperatures
with sea level changes to predict sea level
rise as the climate continues to warm,
says Aslak Grinsted of the University of
Copenhagen’s Centre for Ice and Climate.
“What’s great about this new record is
that it’s really high resolution and continuous,” Grinsted says, “and quite consistent with records all around the world.” s
Sea level has risen an average
of 2. 1 millimeters a year along
the North Carolina coast since
the late 19th century.
By Janet Raloff
Sea levels began rising precipitously in
the late 19th century and have since tripled the rate of climb seen at any time in
at least two millennia, a detailed analysis of North Carolina marsh sediments
reveals.
“This clearly shows the recent trend
is not part of a natural cycle,” says Ken
Miller of Rutgers University in Piscat-away, N.J., who was not associated with
the analysis.
Andrew Kemp of the University of
Pennsylvania and his colleagues spent
five years plumbing salt marsh sediments that had remained largely undisturbed for thousands of years. Kemp,
now at Yale, and his team drilled cores
at two sites, unearthing the microscopic
remains of single-celled shelled organisms known as foraminifera.
Foraminifera vary in their salt tolerance. So as the sea level changed over
millennia, so did the mix of species living at any given site, explains coauthor
Benjamin Horton of the University of
Pennsylvania. Knowing the modern-day
distribution of foraminifera at various
water depths along the modern-day
coast, the researchers could infer past
sea levels at the two core sites from
the abundance of different species in
Ice melt boosts Earth’s waistline
melting ice has changed the shape
of the earth, making it more bulgy at
the equator. Satellite measurements
between 1975 and 2009 show an
unexplained change starting in the
mid-1990s. Researchers at the University of Colorado at Boulder have
now combined those measurements
with data from the gravity-sensing
GRACe satellites and report that ice
melting off Greenland and Antarctica
is to blame. Solid ice near the poles
has transformed into liquid water distributed around the planet, the team
reports in an upcoming Geophysical
Research Letters. — Alexandra Witze
Mangroves absorbed quakes
Buried remnants of mangrove
swamps help soak up the shock of
earthquakes, protecting island coasts
from damage. A new analysis of a
site in the French Antilles suggests
that these soft deposits protect the
stiffer overlying soil from deforming.
The effect is similar to that provided
by rubber dampening systems for
buildings in earthquake-prone areas,
French researchers report in the
June Bulletin of the Seismological
Society of America. — Devin Powell
Earth’s early core
long ago, something happened
deep inside the earth. new studies
of ancient rocks reveal how strong
the earth’s magnetic field was as its
liquid core began to cool and solidify.
About 2 billion years ago, the difference between the north and south
magnetic poles became surprisingly
weaker, scientists led by Aleksey
Smirnov of michigan Technological
University in Houghton report in an
upcoming Physics of the Earth and
Planetary Interiors. — Alexandra Witze
www.sciencenews.org
July 16, 2011 | SCIENCE NEWS | 13
