[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.


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 Earth’s 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 vapor—itself a potent, heat-trapping greenhouse 
gas—to 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 
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 changing—in some 
cases radically—over 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 1990—when 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 
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 
latitudes—possibly 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 
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.
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