[Vision2020] Journal of Climate, 2010:"Warming of Global Abyssal and Deep Southern Ocean Waters Between the 1990s and 2000s"

[Ted Moffett]

Journal of Climate article abstract from subject heading at bottom of post.
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http://www.noaanews.noaa.gov/stories2010/20100920_oceanwarming.html Scientists
Find 20 Years of Deep Water Warming Leading to Sea Level Rise
September 20, 2010

Scientists analyzing measurements taken in the deep ocean around the globe
over the past two decades find a warming trend that contributes to sea level
rise, especially around Antarctica.

Greenhouse gases in the atmosphere, such as carbon dioxide, cause heating of
the Earth. Over the past few decades, at least 80 percent of this heat
energy has gone into the ocean, warming it in the process.

"Previous studies have shown that the upper ocean is warming, but our
analysis determines how much additional heat the deep ocean is storing from
warming observed all the way to the ocean floor," said Sarah Purkey, an
oceanographer at the University of Washington and lead author of the study.

This study shows that the deep ocean - below about 3,300 feet - is taking up
about 16 percent of what the upper ocean is absorbing. The authors note that
there are several possible causes for this deep warming: a shift in Southern
Ocean winds, a change in the density of what is called Antarctic Bottom
Water, or how quickly that bottom water is formed near the Antarctic, where
it sinks to fill the deepest, coldest portions of the ocean around much of
the globe.

The scientists found the strongest deep warming around Antarctica, weakening
with distance from its source as it spreads around the globe. While the
temperature increases are small (about 0.03°C per decade in the deep
Southern Ocean, less elsewhere), the large volume of the ocean over which
they are found and the high capacity of water to absorb heat means that this
warming accounts for a huge amount of energy storage. If this deep ocean
heating were going into the atmosphere instead - a physical impossibility -
it would be warming at a rate of about 3°C (over 5°F) per decade.

"A warming Earth causes sea level rise in two ways," said Gregory Johnson, a
NOAA oceanographer at the Pacific Marine Environmental Laboratory in
Seattle, and the study's co-author. "The warming heats the ocean, causing it
to expand, and melts continental ice, adding water to the ocean. The
expansion and added water both cause the sea to encroach on the land."

Sea level has been rising at around 3 mm (1/8 of a inch) per year on average
since 1993, with about half of that caused by ocean thermal expansion and
the other half because of additional water added to the ocean, mostly from
melting continental ice. Purkey and Johnson note that deep warming of the
Southern Ocean accounts for about 1.2 mm (about 1/20th of an inch) per year
of the sea level rise around Antarctica in the past few decades.

The highly accurate deep-ocean temperature observations used in this study
come from ship-based instruments that measure conductivity through salinity,
temperature and depth. These measurements were taken on a series of
hydrographic surveys of the global ocean in the 1990s through the World
Ocean Circulation Experiment and in the 2000s in support of the Climate
Variability program. These surveys are now coordinated by the international
Global Ship-based Hydrographic Investigations Program.

The study, "Warming of Global Abyssal and Deep Southern Ocean Waters between
the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise
Budgets," authored by Sarah G. Purkey and Gregory C. Johnson, will be
published in an upcoming edition of the *Journal of Climate.*

*----------------------------------------------------*

http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1
Journal of Climate 2010 ; e-View
doi: 10.1175/2010JCLI3682.1

Warming of Global Abyssal and Deep Southern Ocean Waters Between the 1990s
and 2000s: Contributions to Global Heat and Sea Level Rise
Budgets*<http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#fn1>

*Sarah G. Purkey1,<http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#aff1>
2 <http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#aff2> and
Gregory C. Johnson2,<http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#aff2>
1 <http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#aff1><http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1#cor1>
*

1 School of Oceanography, University of Washington, Seattle WA 98195, USA

2 NOAA/Pacific Marine Environmental Laboratory, Seattle WA 98115, USA

  Abstract

We quantify abyssal global and deep Southern Ocean temperature trends
between the 1990s and 2000s to assess the role of recent warming of these
regions in global heat and sea level budgets. We compute warming rates with
uncertainties along 28 full-depth, high-quality, hydrographic sections that
have been occupied two or more times between 1980 and 2010. We divide the
global ocean into 32 basins defined by the topography and climatological
ocean bottom temperatures and estimate temperature trends in the 24 sampled
basins. The three southernmost basins show a strong statistically
significant abyssal warming trend, with that warming signal weakening to the
north in the central Pacific, western Atlantic, and eastern Indian Oceans.
Eastern Atlantic and western Indian Ocean basins show statistically
insignificant abyssal cooling trends. Excepting the Arctic Ocean and Nordic
seas, the rate of abyssal (below 4000 m) global ocean heat content change in
the 1990s and 2000s is equivalent to a heat flux of 0.027 (±0.009) W
m-2applied over the entire surface of the Earth. Deep (1000-4000 m)
warming
south of the Sub-Antarctic Front of the Antarctic Circumpolar Current adds
0.068 (±0.062) W m-2. The abyssal warming produces a 0.053 (±0.017) mm
yr-1increase in global average sea level and the deep warming south of
the
Sub-Antarctic Front adds another 0.093 (±0.081) mm yr-1. Thus warming in
these regions, ventilated primarily by Antarctic Bottom Water, accounts for
a statistically significant fraction of the present global energy and sea
level budgets.

Received: February 16, 2010; Revised: July 28, 2010; Revised: August 18,
2010

*Pacific Marine Environmental Laboratory Contribution Number 3524.
*Corresponding author address*: Gregory C. Johnson, NOAA/Pacific Marine
Environmental Laboratory, 7600 Sand Point Way N.E., Bldg 3, Seattle, WA
98115. E-mail: gregory.c.johnson at noaa.gov.
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Vision2020 Post: Ted Moffett
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