The Scientist
I grew up in the USA.
My interest in science was probably sparked by my mum,
who was a science teacher. Typical family activities included mucking
around in tide pools, collecting water from nearby ponds and looking
for bugs with a microscope, and expeditions with rock hammers
to look for fossils and not-so-precious stones.
I studied physics at Harvard University before
doing my PhD in physical oceanography at the Woods Hole Oceanographic
Institution and Massachussetts Institute of Technology in the
USA. I chose physical
oceanography because it seemed like a good way to combine my fascination
with how things worked (the domain of physics) and my preference
for working "in the field" rather than in a lab. After finishing my degree, I saw an advertisement for a job
with the CSIRO in Tasmania and thought it might be an interesting
change for a few years.
Twelve years later, we are still here, and my kids play
cricket instead of baseball.
Steve Rintoul's
collaboration is with artist Peter
James Smith.
The Research
As a physical oceanographer, I am interested
in ocean currents - where the water goes and why.
In particular, I study how ocean currents affect the Earth's
climate. Sea water can store lots of heat due to its large heat capacity
(the upper few metres of the ocean can store as much heat as the
entire atmosphere).
Ocean currents transport heat from one part of the ocean
to another. The release of heat from the ocean to
the overlying atmosphere influences the temperature and rainfall
patterns, or climate, that we experience on land.
The particular focus
of my research is on the Southern Ocean, the waters that surround
the Antarctic continent. The Southern Ocean is famous for being
the home of the strongest winds and largest waves on the planet. Ships generally try to avoid these inhospitable
regions and so we have few observations of the ocean currents
there.
The strong winds also drive the largest current
in the world ocean, called the Antarctic Circumpolar Current.
The Circumpolar Current carries about 150 million cubic
metres per second from west to east around Antarctica (this is
about 150 times the flow of all the world's rivers combined -
equivalent to 500 billion cans of soft drink per second).
The importance of the current is not so much its size,
but the fact that it connects the ocean basins.
For example, a patch of warm water formed in the Atlantic
today can be carried downstream by the current to influence the
climate of Australia a few years later (see image 3).
The Southern Ocean is also important to the Earth's
climate because water sinks from the sea surface into the deep
ocean in this region. The sinking waters carry oxygen into the deep sea: if there was no sinking of dense water
in the high latitudes, the deep ocean would have very little oxygen
and the deep biology and chemistry of the sea would be very different. In other regions of the Southern
Ocean, water rises to the surface.
Ocean currents connect the regions of sinking and upwelling. The resulting complex, three-dimensional
circulation pattern carries heat from one part of the globe to
another, and so influences the Earth's climate.
The water sinking in the Southern Ocean also
carries carbon dioxide into the ocean. Carbon dioxide is released into the atmosphere
by burning fossil fuels like oil and coal and by land clearing. Once in the atmosphere, carbon dioxide
acts as a "greenhouse" gas that traps heat and tends
to make the Earth warm up.
About half of the carbon dioxide released into the atmosphere
remains in the atmosphere, contributing to greenhouse warming;
the rest is absorbed by the oceans or by plants on land.
Most of the carbon dioxide absorbed by the oceans is accumulating
in the southern oceans, where water sinking from the surface is
carrying the carbon down to the deep sea (see image 4).
Image 5 shows a "Southern Ocean oceanographer's
view of the world." Antarctica is in the centre. Each of the ocean basins is shown as a
spoke or wedge radiating out from the centre. The coloured arrows show the flow of water of different
density and temperature.
Water sinks from the sea surface to the deep ocean only
in the northernmost Atlantic and at a few locations near the coast
of Antarctica. Lighter, warmer water flows towards these
regions to replace the sinking water. To close the loop, some of the dense water is converted back
to lighter water in the Southern Ocean.
The big red arrow looping around Antarctica represents
the Circumpolar Current.
By carrying water between the ocean basins, the Circumpolar
Current plays a key role in this global "conveyor belt"
circulation. The
conveyor belt, in turn, strongly influences our climate (see
image 5).
One
important way in which the high latitude oceans differ from those
at lower latitudes is that they are partially covered by sea ice.
Sea water will freeze if it gets cold enough (temperatures
less than -2 degrees C). Each winter, enough sea ice forms around
Antarctica to double the area of the continent. Even in summer, sea ice remains around
many parts of Anarctica.
The sea ice provides important habitat for Antarctic animals. The sea ice is also important for the climate system. Snow and ice are bright and reflect light,
so the more ice, the more of the sun's energy gets reflected back
into space rather than being absorbed by the earth. (see image 6).
Sea ice also influences the ocean.
When sea water freezes, the salt is left behind, increasing
the salinity of the water beneath the ice.
Sea water gets heavier as its salinity increases and as
it gets colder. Cooling by the atmosphere and salt released
from sea ice together make the water near Antarctica so dense
that it can sink from the sea surface to the deep ocean.
The combination of conditions needed to make
surface waters dense enough to sink 4 or 5 km to the sea floor
are only found in a handful of spots on the Earth. One of those locations is near the Mertz
Glacier on the Antarctic coast, more or less south of Tasmania. The satellite picture shows the distribution
and movement of sea ice.
The Mertz Glacier can also be seen extending out from the
coast. Dark areas near the coast show open water.
The open water (called a "polynya") is kept free
of ice by very strong winds blowing off the continent.
The combination of strong winds, cold temperatures, and
rapid formation and export of ice make the polynya a very effective
producer of cold, dense, oxygen-rich water (see image 7).
Our work involves studying each of these aspects
of the Southern Ocean. We use ships, moored and drifting buoys, and satellites to
measure the ocean currents.
We also use computers to simulate the ocean circulation. The goal is to improve our understanding of how the Earth's
climate works, so that we can do a better job of predicting what
kind of climate we will experience in the future.
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