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<DIV class=instapaper_title><FONT size=4>How an ocean went into hiding in
Australia</FONT></DIV>
<DIV>by <A href="http://www.newscientist.com/search?rbauthors=Michael+Marshall"
s_oc="null">Michael Marshall</A></DIV>
<DIV>20 August 2013 </DIV>
<DIV><A
href="http://www.newscientist.com/article/dn24080?cmpid=NLC%7CNSNS%7C2013-2208-GLOBAL&utm_medium=NLC&utm_source=NSNS">http://www.newscientist.com/article/dn24080?cmpid=NLC%7CNSNS%7C2013-2208-GLOBAL&utm_medium=NLC&utm_source=NSNS</A>&</DIV><!-- pgtop -->
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<P class=infuse>A chunk of the oceans took a wrong turn in 2011. Instead of
going from sky to rain, into rivers, and then back into the oceans in the usual
water cycle, it got stuck in Australia, caught up in record-breaking floods and
rivers that run backwards into the continent. So much water got lost down under
that global sea levels fell and stayed low for more than a year.</P>
<P class=infuse><A href="http://www.cgd.ucar.edu/cas/Staff/Fasullo/"
s_oc="null">John Fasullo of the National Center for Atmospheric Research</A> in
Boulder, Colorado, noticed something amiss while looking at trends in global sea
levels. They had been rising steadily by about 3 millimetres every year, but in
the second half of 2010, they suddenly plummeted. By early 2011, they had
dropped by 7 mm, the biggest drop since satellite measurements began in
1992.</P>
<P class=infuse>The reversal lasted until late 2011. Not many people noticed: at
the time, the world was preoccupied with massive floods in Australia. Fasullo
wondered whether the two events might be linked. If more water than usual was
evaporating from the oceans and falling on Australia, that might help to explain
both the floods and sea level drop.</P>
<P class=infuse>Satellite data showed that more water was stored on land in 2011
than in previous years, most of it in Australia, South America and South-East
Asia (<A href="http://dx.doi.org/10.1029/2012GL053055"
s_oc="null"><I>Geophysical Research Letters</I>, doi.org/nhk</A>). An early
explanation was a strong La Niņa, which funnelled warm, moist air towards
Australia. But La Niņa events happen every few years and regularly make it rain
in Australia, says Fasullo. "Why don't we see massive sea level drops after all
La Niņas?"</P>
<H3 class=crosshead>Triple whammy</H3>
<P class=infuse>Re-examining weather records revealed two other factors. The
Indian Ocean was much warmer in the east than in the west, pushing yet more
warm, moist air towards Australia. This had not happened for 20 years. At the
same time, a band of winds circling Antarctica shifted to the south, boosting
the effect still further (<A href="http://dx.doi.org/10.1002/grl.50834"
s_oc="null"><I>Geophysical Research Letters</I>, doi.org/ngx</A>).</P>
<P class=infuse>The rare combination of events led to unusually heavy Australian
rainfall, says Fasullo. But why did the water stay out of the oceans for so
long? Extra rainfall on land should get washed back out to sea by rivers within
a few months.</P>
<P class=infuse>It turns out that Australia has an uncanny ability to trap water
for long periods. River channels are sparse in the west, so rainwater tends to
sit in the sandy soil. And in the east, many of the channels run into a
low-lying desert basin at the centre of the continent rather than out to sea.
With heavy rains, the basin fills up to become <A
href="http://dx.doi.org/10.1016/j.jhydrol.2011.08.008" s_oc="null">Kati
Thanda-Lake Eyre</A>; fish eggs lying dormant in the soil hatch, and an
ecosystem briefly comes to life. "It's an instant inland sea," says Fasullo.</P>
<P class=infuse>The unusual weather and geology offer a convincing explanation
for the sudden drop in sea levels, says <A
href="http://www.csiro.au/Organisation-Structure/Divisions/Marine--Atmospheric-Research/JohnChurch.aspx"
s_oc="null">John Church of CSIRO Marine and Atmospheric Research</A> in Hobart,
Tasmania. But his colleague <A
href="http://www.cmar.csiro.au/sealevel/sl_about_us.html#zhang"
s_oc="null">Xuebin Zhang</A> says questions remain. He calculates that the extra
water on land accounts for about 3.75 mm of the 7 mm fall in sea levels.</P>
<P class=infuse>Similarly heavy rain fell on Australia in 1973-74, but sea-level
records from then are not detailed enough to draw conclusions, and the three
climate systems might not align again for decades.</P>
<P class=infuse><I>This article appeared in print under the headline "Australia:
where oceans go to hide"</I></P>
<DIV class="artbx bxbg">
<H3 id=bxdn24080B1>Sheer weight of water</H3>
<P>When the seas rose at the end of the last ice age, all hell broke loose.
According to a new analysis, the extra weight of liquid water deformed the
seabed, causing vast submarine landslides and tsunamis, perhaps even releasing
extra greenhouse gases. Today's rising seas could have similar effects, but
probably not for centuries.</P>
<P><A href="http://dx.doi.org/10.1016/j.marpetgeo.2008.02.008"
s_oc="null">Underwater landslides</A> were more common <A
href="http://dx.doi.org/10.1016/j.margeo.2008.09.009" s_oc="null">in the first
5000 years after the last ice age</A> than they are today. During that time, sea
levels rose by 120 metres as melting ice sheets poured their cargo into the
ocean.</P>
<P><A href="http://geology.usgs.gov/postdoc/profiles/brothers/"
s_oc="null">Daniel Brothers</A> of the US Geological Survey in Woods Hole,
Massachusetts, and his colleagues estimated how much stress the extra weight
would have placed on the seabed. They found that faults were more likely to
rupture along the Amazon and North Carolina coasts, triggering landslides (<A
href="http://dx.doi.org/10.1130/G34410.1" s_oc="null"><I>Geology</I>,
doi.org/nhq</A>).</P>
<P>Submarine earthquakes and landslides can cause tsunamis, so these monster
waves may have been more common as sea levels rose. The changes <A
href="http://dx.doi.org/10.1016/j.quascirev.2006.12.011" s_oc="null">might also
have released methane</A>, which is stored beneath the seabed in icy crystals
called <A
href="http://www.newscientist.com/article/mg21729074.200-fuel-of-the-future-how-fiery-ice-could-power-asia.html"
s_oc="null">clathrates</A>. Methane is a potent greenhouse gas, so <A
href="http://dx.doi.org/10.1098/rsta.2010.0065" s_oc="null">would have helped to
warm the climate</A>.</P>
<P><A href="http://www.ucl.ac.uk/rdr/people/simon-day" s_oc="null">Simon Day of
University College London</A> broadly agrees with the findings. He adds that we
are unlikely to experience <A
href="http://www.newscientist.com/article/mg19025531.300-climate-change-tearing-the-earth-apart.html"
s_oc="null">similar convulsions</A>. It would take about 10 metres of sea level
rise to affect the number of underwater landslides. Most <A
href="http://www.newscientist.com/article/mg21829180.200-sea-level-rise-drowning-in-numbers.html"
s_oc="null">predictions for this century</A> are for a rise of about 1
metre.</P></DIV></DIV></DIV></DIV></FONT></BODY></HTML>