[Coral-List] Large Scale Salinity Changes in the Oceans
Robert Rofen
rofen at prado.com
Tue Dec 23 19:58:40 EST 2003
from Robert Rofen <rofen at novalek.com>
In response to "Gregor Hodgson" <gregorh at ucla.edu>, Date: Sun, 21 Dec 2003,
Subject: [Coral-List] FW: [ReefCheck-list] Reef Fishes dying in huge
numbers, please note the following report. This has not only been reported
for oceans, but also has been seen in other saline waters, such as appears
to be the case this year for the hyper-saline Great Salt Lake, Utah, in
which this year a higher proportion of the Artemia brine shrimp "eggs"
(=cysts) than normal sank, rather than float. Apparently this was due to
the lowering of the salinity of the Lake water.
~~~NEW STUDY REPORTS LARGE-SCALE SALINITY CHANGES IN THE OCEANS
NSF PR 03-145 - December 17, 2003
Media contacts:Cheryl Dybas, NSF(703) 292-7734cdybas at nsf.gov
Shelley Dawicki, WHOI(508) 289-2270sdawicki at whoi.edu
Program contact:Elise Ralph, NSF(703) 292-8582eralph at nsf.gov
Saltier tropical oceans and fresher ocean waters near the poles further
signs of global climate change's impacts
Arlington, Va.Tropical ocean waters have become dramatically saltier over
the past 40 years, while oceans closer to Earths poles have become
fresher, scientists report in the December 18th issue of the journal
Nature. These large-scale, relatively rapid oceanic changes suggest that
recent climate changes, including global warming, may be altering the
fundamental planetary system that regulates evaporation and precipitation
and cycles fresh water around the globe.
The study was conducted by Ruth Curry of the Woods Hole Oceanographic
Institution (WHOI); Bob Dickson of the Centre for Environment, Fisheries,
and Aquaculture Science in Lowestoft, U.K.; and Igor Yashayaev of the
Bedford Institute of Oceanography in Dartmouth, Canada.
"This study is important because it provides direct evidence that the
global water cycle is intensifying," said Elise Ralph, associate director
of the National Science Foundation's (NSF) physical oceanography program,
which funded the research. "This is consistent with global warming
hypotheses that suggest ocean evaporation will increase as Earth's
temperature does. These issues are particularly important as pressure on
freshwater resources has become critical in many areas around the world."
An acceleration of Earth's global water cycle can potentially affect global
precipitation patterns that govern the distribution, severity and frequency
of droughts, floods and storms. It would also exacerbate global warming by
rapidly adding more water vaporitself a potent, heat-trapping greenhouse
gasto the atmosphere. And it could continue to freshen North Atlantic
Ocean waters to a point that could disrupt ocean circulation and trigger
further climate changes.
The oceans and atmosphere continually exchange fresh water. Evaporation
over warm, tropical and subtropical oceans transfers water vapor to the
atmosphere, which transports it toward both poles. At higher latitudes,
that water vapor precipitates as rain or snow and ultimately returns to the
oceans, which complete the cycle by circulating fresh water back toward the
equator. The process maintains a balanced distribution of water around our
planet.
The oceans contain 96 percent of the Earth's water, experience 86 percent
of planetary evaporation, and receive 78 percent of planetary
precipitation, and thus represent a key element of the global water cycle
for study, the scientists said. Because evaporation concentrates salt in
the surface ocean, increasing evaporation rates cause detectable spikes in
surface ocean salinity levels. In contrast, salinity decreases generally
reflect the addition of fresh water to the ocean through precipitation and
runoff from the continents.
Curry, Dickson, and Yashayaev analyzed a wealth of salinity measurements
collected over recent decades along a key region in the Atlantic Ocean,
from the tip of Greenland to the tip of South America. Their analysis
showed the properties of Atlantic water masses have been changingin some
cases radicallyover the five decades for which reliable and systematic
records of ocean measurements are available, the scientists report.
They observed that surface waters in tropical and subtropical Atlantic
Ocean regions became markedly saltier. Simultaneously, much of the water
column in the high latitudes of the North and South Atlantic became fresher.
This trend appears to have accelerated since 1990when 10 of the warmest
years since records began in 1861 have occurred. The scientists estimated
that net evaporation rates over the tropical Atlantic have increased by
five percent to ten percent over the past four decades.
These results indicate that fresh water has been lost from the low
latitudes and added at high latitudes, at a pace exceeding the ocean
circulation's ability to compensate, say the scientists. Taken together
with other recent studies revealing parallel salinity changes in the
Mediterranean, Pacific, and Indian Oceans, a growing body of evidence
suggests that the global hydrologic cycle has revved up in recent decades.
Among other possible climate impacts, an accelerated evaporation -
precipitation cycle would continue to freshen northern North Atlantic
waters. The North Atlantic is one of the few places on Earth where surface
waters become dense enough to sink to the abyss. The plunge of this great
mass of cold, salty water helps drive a global ocean circulation system,
often called the Ocean Conveyor. This Conveyor helps draw warm Gulf Stream
waters northward in the Atlantic, pumping heat into the northern regions
that significantly moderates wintertime air temperatures, especially in
Europe.
If the North Atlantic becomes too fresh, its waters would stop sinking and
the Conveyor could slow down. Analyses of ice cores, deep-sea sediment
cores, and other geologic evidence have clearly demonstrated the Conveyor
has abruptly slowed down or halted many times in Earth's history. That has
caused the North Atlantic region to cool significantly and brought
long-term drought conditions to other areas of the Northern Hemisphere over
time spans as short as years to decades.
Melting glaciers and Arctic sea ice, another consequence of global warming,
are other sources of additional fresh water to the North Atlantic. An
accelerated water cycle also appears to be increasing precipitation in
higher latitudes, contributing to the freshening of North Atlantic waters
and increasing the possibility of slowing the Conveyor.
A cooling of the North Atlantic region would slow the melting process,
curtail the influx of fresh water to the North Atlantic. The Conveyor would
again begin to circulate ocean waters. But global warming and an
accelerated water cycle would continue to bring fresh water to high
latitudespossibly enough to maintain a cap on the Conveyor even if the
Arctic melting ceased. Monitoring Earth's hydrological cycle is critical,
the scientists said, because of its potential near-term impacts on Earth's
climate.
The research was also supported by the Framework V Programme of the
European Community, the National Oceanic and Atmospheric Administration's
Consortium on the Ocean's Role in Climate, and the Ocean and Climate Change
Institute at the Woods Hole Oceanographic Institution.
-NSF-
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