James Morison of the University of Washington has been studying Arctic sea ice for decades and runs an annual expedition to the North Pole to drop instruments through the ice into the ocean below. Here he lays out one scenario for the forces driving recent dramatic changes in summer sea ice on the Arctic Ocean. Read more from Morison on Arctic change here: http://j.mp/dotmorison And more on sea ice in a warming climate here: http://j.mp/DotArcIce Here's the Web home for the North Pole Environmental Observatory: http://psc.apl.washington.edu/northpole/

1. A
Highly
Specula/ve
Discussion
of
Bathymetry-­‐Ocean
Controls
on
Ice
Extent
Jamie
Morison
8/29/2012
Acknowledgments:
Florence
FeMerer
for
the
MASIE
image
in
kmz
format,
Son
Ngheim
for
first
poin/ng
out
the
idea.

2. Claim:
At
minimum
ice
extent,
the
ice
edge
mainly
corresponds
the
deep-­‐
water
/
shallow-­‐water
boundary
(e.g.,
500
m
isobath.
The
sense
of
bathymetry-­‐ocean
controls
on
ice
edge
posi/on
come
in
two
flavors.
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry

3. Ice
Survives
in
the
Shallower
Region:
The
prime
example
is
the
East
Greenland
shelf,
which
almost
always
has
a
sea
ice
cover
and
where
the
the
ice
edge
almost
always
lies
along
the
500
m
isobath.
The
reason
for
this
is
that
Arc/c
Surface
Water
near
the
freezing
point
flows
out
of
the
Arc/c
Ocean
over
the
East
Greenland
con/nental
slope
and
thermodynamically
buffers
the
oulowing
sea
ice
against
the
effects
of
the
atmosphere.
The
front
associated
with
the
East
Greenland
Current
lies
roughly
over
the
shelf
break,
and
any
ice
that
dri]s
east
across
this
front
encounters
much
warmer
water
of
the
Greenland
Sea
cyclonic
gyre
circula/on
and
rapidly
melts.
We
saw
this
up
close
in
the
MIZEX
cruises
of
the
early
1980s
and
it
looks
like
it
s/ll
happens
today.
Greenland
Sea
Gyre
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry

4. Ice
Survives
in
the
Deeper
Region:
This
is
shown
along
most
of
the
Eurasian
con/nental
shelf
break.
Here
the
inflow
of
warm
Atlan/c
Water
via
the
Barents
Sea
Branch
and
Eurasian
runoff
input
heat
to
the
ocean
over
the
shelf.
This
and
the
fact
that
radia/ve
hea/ng
is
trapped
in
the
shallow
water
provides
a
thermodynamic
environment
that
is
rela/vely
hos/le
to
the
overlying
sea
ice
compared
to
deeper
water
off
the
shelf,
which
has
the
chance
to
develop
a
freezing
point
mixed
layer
and
even
a
cold
halocline
that
provide
an
ice
bath
buffer
for
the
sea
ice.
Consequently
the
ice
disappears
first
off
the
con/nental
shelves
and
only
disappears
from
the
deep
water
areas
if
there
is
a
major
disturbance
in
the
upper
ocean.
The
examples
of
this
are
where
we
are
seeing
important
ice
losses.
War
m
Ba
rent
s
Sea
Bra
nch
Greenland
Sea
Gyre
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry

5. Example
1
off
the
Laptev
Sea:
The
ice
edge
has
retreated
away
from
the
Laptev
Sea
shelf
break
and
we
even
see
reduced
ice
out
over
the
eastern
Amundsen
Basin.
This
is
specula/ve,
but
over
the
past
couple
of
decades
cyclonic
circula/on
aligned
along
the
Russian
shelf
break
has
tended
to
shi]
Eurasian
runoff
eastward
to
Canada
Basin,
which
tends
to
weaken
the
cold
halocline
layer
that
insulates
sea
ice
from
Atlan/c
Water
heat
in
the
Eurasian
Basin.
Hence
ice
disappears
more
easily
over
deep
water.
War
m
Ba
rent
s
Sea
Bra
nch
Greenland
Sea
Gyre
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry

6. Example
2,
Beaufort
Sea:
As
recently
as
a
couple
of
years
ago,
major
chunks
of
the
ice
edge
would
align
with
the
Beaufort
shelf
break.
This
year’s
storm
event
separated
the
ice
into
two
divergent
chunks,
one
ice
edge
moving
north
and
one
south.
The
southern
por/ons
melted
most
quickly
over
the
shallowest
regions
of
the
Chukchi
shelf,
likely
for
the
reasons
men/oned
earlier
with
respect
to
the
typical
“ice-­‐remains-­‐over-­‐deep-­‐
water”
case.
It
is
noteworthy
that
some
of
this
ice
remains
over
the
deeper
parts
of
the
shelf
associated
with
the
bathymetry
around
Herald
Canyon
(unfortunately
the
google
bathymetry
doesn’t
resolve
this
bathymetry).
War
m
Ba
rent
s
Sea
Bra
nch
Greenland
Sea
Gyre
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry

7. Implica/ons
for
Future
Ice
Extent:
I
think
that
in
the
past
even
under
warm
atmospheric
condi/ons,
the
ocean
has
provided
refuge
areas
for
summer
sea
ice.
Major
reduc/ons
of
ice
extent
into
these
refuge
areas
s/ll
require
special
circumstances.
For
the
sake
of
argument,
I’ll
speculate
that
we
won’t
have
an
ice
free
Arc/c
Ocean
un/l
winter
freezing
is
radically
decreased
or
the
Arc/c
Ocean
circula/on
changes
significantly.
As
long
as
freezing
occurs
in
the
winter,
the
ocean
will
tend
to
build
up
a
buffer
that
can
see
major
areas
of
sea
ice
through
the
summer.
Substan/al
increases
in
ocean
heat
fluxes
through
Fram
and
Bering
straits
could
change
this.
More
subtle,
if
changes
in
atmospheric
circula/on
cause
changes
in
upper
ocean
circula/on,
structure,
and
mixing
that
allow
more
ocean
heat
to
get
to
the
ice
(e.g.,
weakening
of
the
cold
halocline)
the
ocean
might
lose
this
buffering
capacity
and
summer
sea
ice
will
mostly
disappear.
MASIE
Ice
Extent
for
Aug
28,
2012
Overlaid
in
Semi-­‐transparent
White
on
Google
Bathymetry