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Polar Oceanography Maury Project 2017 John Woods NASA Goddard Space Flight Center 18 July 2017 2016 Update from Walt Meier, NASA Goddard
Polar Oceanography
Maury Project 2017
John Woods
NASA Goddard Space Flight Center
18 July 2017
2016 Update from Walt Meier, NASA Goddard
Resources
http://climate.nasa.gov/
http://www.arctic.noaa.gov/reportcard/
Resources
http://www.meted.ucar.edu
http://nsidc.org/cryosphere
Geography of the polar regionsAn ocean
surrounded by land
Ice-covered land
surrounded by an
ocean
http://www.ngdc.noaa.gov/mgg/fliers/00mgg04.html
Geography of the polar regions
Perry-Casteneda Library Map Collection, National Geographic, 1983. From http://nsidc.org
Where is the Arctic?
10°C July isotherm
Treeline
Maximum ice extent
Arctic Circle
Arctic Freshwater
34 psu
31 psu
25 psu
Kolyma
Lena
Yenisey
Mackenzie
Ob
River input: 3500 km3/yr
Bering Strait: 1800 km3/yr
River inflow makes the
Arctic the freshest major
ocean
30 psu
Geography of the polar regions
Perry-Casteneda Library Map Collection, National Geographic, 1983. From http://nsidc.org
The Antarctic
Antarctic
Convergence
or
Antarctic Polar
Frontal Zone
Why is it so cold?
and ice
Northern Hemisphere winter solstice
Albedo
effect
Why is it so cold?
Rnet = SW¯´ 1-a( )+ LW¯-LW ( )
SW = shortwave (solar) radiation
LW = longwave (upward = earth emitted radiation)
α = albedo (fraction of incident solar radiation reflected by a surface)
Rnet is negative at poles, so heat is lost from the polar region
The high albedo is a critical factor in this
Net Radiative Flux Balance
Poles disperse heat
Net radiative gain
Net
radiative
loss
Net
radiative
loss
How cold is cold?
– North Pole
• Summer Average: -2 °C
• Winter Average: -32 °C
– South Pole
• Summer Average: -25 °C
• Winter Average: -70 °C
Why is it colder at the South
Pole?
Arctic Precipitation
Low precipitation
over Arctic Ocean
because sea ice
cover acts like a cap,
preventing exchange
of moisture from
ocean to atmosphere
Antarctic Precipitation
mm
The interior of Antarctica qualifies as a
desert
Heavy snow in some regions near coast,
especially the Antarctic Peninsula
50 mm = 2 inches
Geography and Weather Summary:Poles Apart
• Ocean enclosed by land
• Fresh ocean isolated from world’s oceans
• Ice sheet primarily on Greenland only, smaller and lower elevation
• Cold
• Dry
• Indigenous communities
• Smaller icebergs, mainly in Greenland area
• Land surrounded by ocean
• Ocean well connected to most major oceans
• Ice sheet covers most of Antarctic continent
• Colder
• Drier
• No permanent human residents
• Many large tabular “state-sized” icebergs
Arctic Antarctic
Both are important in global circulation and climate, but in
different ways
Varieties of sea iceGrease Pancake
First YearMulti-Year
Varieties of sea iceLeads Leads
Melt pondsRidges
Sea ice, salinity, brine
Ocean water
S = 30 psu
First-Year ice
S = 6 psu
Multi-year ice
S = 3 psu
Upper ocean
Salt Melt water
Deep water
formation
Dense water sinks
Arctic Ocean surface currents
Polar ocean currents
Arctic Ocean
Bathymetry
Vertically exaggerated
Arctic water masses
Lomonosov Ridge
Deep water circulation
Antarctic water masses
Antarctic Bottom Water (AABW): -2.0ºC, S=34.75, very dense
Thermohaline circulation
From NOAA Paleoclimatology Program; http://www.ncdc.noaa.gov/paleo/abrupt/story2.html
First: Definitions
• Concentration = fraction of
square covered by cheese
• Area = total area of cheese within
the square
• Extent = total area of square
(including holes), as long as there
aren’t too many holes
Annual sea ice cycle
From NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
Annual Sea Ice Extent Cycle
0
2
4
6
8
10
12
14
16
18
20
J F M A M J J A S O N D
Exte
nt (1
06 k
m2)
Arctic
Antarctic
Data from NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
1981 – 2010 Average
Seasonal Cycle – A Different Look
0
2
4
6
8
10
12
14
16
18
20
J F M A M J J A S O N D
Exte
nt (1
06 k
m2)
Arctic
Antarctic
Data from NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
1981 – 2010 Average
Arctic winter sea ice, 2015-2016
NASA Scientific Visualization Studio, https://svs.gsfc.nasa.gov
Minimum Extent, 1979 - 2016
0
1
2
3
4
5
6
7
8
1979 1983 1987 1991 1995 1999 2003 2007 2011 2015
Exte
nt (1
06 k
m2)
Arctic (Sep)
-83,100 km2 yr-1
-13.4 % decade-1
Antarctic (Feb)
+12,900 km2 yr-1
+4.5 % decade-1
Data from NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
Arctic losing >3 Marylands per year
Concentration Trends, Minimum
From NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
Maximum Extent
13
14
15
16
17
18
19
20
21
1979 1983 1987 1991 1995 1999 2003 2007 2011 2015
Exte
nt
(10
6 k
m2)
Arctic (Mar)
-43,300 km2 yr-1
-2.8 % decade-1
Antarctic (Sep)
+22,600 km2 yr-1
+1.2 % decade-1
Data from NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
Concentration Trends, Maximum
From NSIDC Sea Ice Index, http://nsidc.org/data/seaice_index/
Why is Antarctic sea ice
increasing?• Changes in atmospheric
circulation – stronger
circumpolar winds links
to Antarctic Oscillation
(possibly due to ozone
hole)
• Changes in snow cover:
more snow insulates ice
and adds to thickness
• Colder, less dense
surface waters due to ice
shelf melt
• Tropical tele-
connections?
• Natural variability?Figure from Stammerjohn et al., J. Geophysical Research, 2008
Recap – Extent trends
• Arctic sea ice is decreasing rapidly, especially during summer– Arctic clearly responding to
warming, though atmospheric circulation patterns and other factors play some role
• Antarctic sea ice is increasing relatively slowly– Specific mechanism(s) not nailed
down, many possible contributors
– Antarctic sea ice likely to start declining in the future
• What’s missing?
The third dimension: thickness!
CryoSat-2 thickness• ESA satellite, launched 2010
• Radar altimeter
• Emits radar signal and times the return
signal
• NASA operated ICESat, laser altimeter,
2003-2009
Snow thickness
Freeboard
Ice Draft
Sea ice
thickness
Snow
Sea ice
Water
Surface
elevation
Water
level
Laser altimeter
Auger,
thermistor
Electromagnetic
induction
Radar altimeter
Upward-looking
sonar
Coming soon to
an orbit near you:
• Launch scheduled Fall 2018
• Laser altimeter
• 6-beams
• 10,000 pulses per second
Operation IceBridge
2009 – 2019
Fill in gap between ICESat and ICESat-2
Calibration of satellite data
Flights at least yearly to Arctic and
Antarctic
Currently in Thule, Greenland for first ever
summer melt campaign
Photos by Nathan Kurtz, NASA Goddard
Photo by Nathan Kurtz, NASA Goddard
Arctic sea ice thinning
Figures from Kwok and Cunningham, Phil. Trans. Royal Society, 2015
Data from upward looking sonar (from submarines) and satellite altimeters
Sea ice age: a long-term proxy for thickness
Animation by NOAA; sea ice age data from NASA, courtesy Mark Tschudi, Univ. Colorado
Ice Age movie here, download from:https://www.climate.gov/news-features/videos/old-ice-arctic-vanishingly-rare
Younger,
thinner ice
is weaker –
more easily
broken up
and pushed
around by
winds
April 23, 2016
Alaska
Barrow
MODIS true-color image
NASA WorldView
Younger,
thinner ice
is weaker –
more easily
broken up
and pushed
around by
winds
May 20, 2016
Alaska
Barrow
MODIS true-color image
NASA WorldView
Younger,
thinner ice is
weaker –
more easily
broken up and
pushed
around by
winds
Small floes
melt faster
July 1, 2016
Alaska
Barrow
MODIS true-color image
NASA WorldView
Recap - Thickness
• In the Arctic, the oldest and thickest ice types are being lost– Arctic is becoming a more
seasonal ice cover
• Antarctic thickness data limited, but likely little change since Antarctic is largely a seasonal ice cover
• “Arctic sea ice is the new Antarctic sea ice”
Climate impacts of changing
Arctic sea ice
Why does the loss of summer sea ice
matter?
With sea ice <40% of incoming
energy absorbed
Without sea ice >90% of incoming
energy absorbed
The change from sea ice to ice-free ocean is the largest
surface contrast on earth as far as solar energy is concerned
Albedo – how much of the sun’s energy gets absorbed
Sea ice albedo feedback
Temperature
Ice melt
Albedo
Energy absorption
Heat An ice-free Arctic in
summer by 2050?
Arctic Amplification: a warmer autumn and
winter
• Heat absorbed
– 2º C over upper 10 m of ocean
= 2.8 x 1020 Joules of energy
= 26 years of U.S. energy
consumption (at 2007 levels)
(courtesy J. Francis, Rutgers Univ.)
• Temperatures:
– Ocean absorbs more of sun’s
energy during summer than
sea ice
– Ocean heat keeps atmosphere
warm into the fall
– “Arctic Amplification”
SST data provided by Univ. Washington Polar Science Center
Air temperature data from NOAA NCEP; Serreze, et al., 2008
Autumn air temperature
anomalies,
(2003-2007) minus
(1979-2007)
Arctic Amplification: a warmer, wetter
Arctic• Temperatures:
– Ocean absorbs more of
sun’s energy during
summer than sea ice
– Ocean heat keeps
atmosphere warm into the
fall
– “Arctic Amplification”
• Water vapor:
– Less sea ice means more
transfer of moister to the
atmosphere
– More water vapor during the
autumm
Serreze, et al., 2008 and Serreze et al., 2012
Data from NOAA NCEP (top) and NASA MERRA (bottom)
Autumn air temperature
anomalies,
(2003-2007) minus (1979-
2007)
September water vapor
anomalies,
(2003-2007) minus (1979-
2007)
Hot Arctic-Cold Continents Hot Arctic-Cold Continents
Added Ocean Heat Storage and Heat Flux from New
Sea Ice Free Areas
Works against the stability of the Polar Vortex
50Thanks to Jim Overland, NOAA PMEL for image
Changes in Arctic sea ice affecting global
climate?
• Sea ice loss and Arctic
warming lead to:
– Weakened jet stream
– More north-south flow
• Extreme events more
likely, e.g.,
– Heat waves, drought
– Flooding
• Idea is still somewhat
controversial in the
community
– More data needed
– Some effect expected
Francis and Vavrus, Geophys. Res. Letters, 2012
New
Old
What happens in the Arctic
doesn’t stay in the Arctic
Recap: Sea ice impacts
• Loss of sea ice results in greater absorption of solar energy by ocean– Sea ice-albedo feedback
• Arctic amplification observed in reanalysis fields– Contributor to Arctic temperature
increases that are 2-3 times the global average
• Impacts are expected outside of the Arctic and may already be happening
Ice Caps, Glaciers, and Ice Sheets
Land ice definitions
• Glacier – slow moving river of ice formed from compacted layers of snow
• Ice cap – smaller masses of ice, not constrained by topography (cover mountain tops); may feed several glaciers
• Ice sheet – large, continental mass of ice formed from compacted layers of snow. Greenland and Antarctica.
• Ice shelf – floating platform of ice extending from a glacier or ice sheet
• Iceberg – a floating mass of ice that has broken off of an ice shelf or glacier
Land ice implications
• Freshwater storage – about 70% of earth’s
freshwater is locked up in glaciers and ice
sheets
• Melt regions influence ocean salinity
• Major source of future sea level rise
Sea level rise
From University of Colorado Sea Level Research Group; http://sealevel.colorado.edu
~80 mm SLR since 1992
Sea level rise
From Environmental Protection Agency and NOAA
~200 mm SLR since 1880
Contributors to SLR
http://ejap.org/environmental-issues-in-asia/climate-change-in-asia.html
IPCC sea level projections
Up to 1.2 m SLR by 2100
Emission scenario is a source
of uncertainty: how much CO2
will we emit over this century?
Ice sheet response is also a
major uncertainty:
• we don’t fully understand
the physics of how ice
sheets respond to warming
• there have already been
surprises on how fast ice
sheets may be able to lose
mass
High emission (RCP 8.5)
Low emission (RCP 2.6)
IPCC AR5 projection, from http://realclimate.org
Ice sheet contribution to SLR
Ice sheet mass balance intercomparison exercise; http://imbie.org
Ice shelves
• Ice sheets “drain” via ice shelves
• Ice shelves act as a buttress, holding back the ice sheet
• When ice shelves retreat, the ice behind them flows faster
• Warmer ocean waters playing key role in the ice shelf losses
National Cathedral in Washington, DC; image from tudorhistory.org
Ice shelvesJakobshavn Glacier, Greenland
Original image from NASA
Photo by Terry Haran, NSIDC
Thanks!
