This document summarizes research validating that growth bands seen in deep sea black corals from the Gulf of Mexico and Southeastern United States are annual. The researchers used several methods to examine the corals including visual counts of growth bands under a scanning electron microscope, measuring iodine and backscattered electron concentrations along the corals, and radiocarbon dating. They concluded that iodine and visual counts are suitable for determining coral growth rates and lifespans, and that iodine measurements can provide a less subjective dating method than visual counts. Ongoing work aims to better understand variability in radiocarbon reservoir ages recorded by the corals.

1.
Validating Annual Growth Bands of Deep Sea Black Corals from the
Gulf of Mexico and Southeastern United States
Leslye Mohon (lmohon@neo.tamu.edu)1, E. Brendan Roark1, Renald Guillemetter2, Nancy Prouty3, Steve Ross4
Deep-­‐sea
black
corals
have
the
poten2al
to
be
u2lized
as
a
proxy
record
of
historical
and
biogeochemical
changes
in
worlds
oceans
(Williams
et
al.
2006).
These
black
corals
(Leiopathes
sp.)
grow
in
a
tree
like
fashion
by
deposi2ng
poten2al
annual
growth
bands.
By
valida2ng
that
growth
bands
are
in
fact
annual,
the
ages
and
growth
rates
of
black
corals
from
the
Gulf
of
Mexico
and
Southeastern
United
Stated
(SEUS)
can
be
determined.
Iodine
concentra2on
in
black
corals
also
have
the
poten2al
to
be
used
as
a
new
da2ng
method
to
determine
the
lifespan
and
growth
rates
of
black
corals.
When
the
iodine
chronology
is
combined
with
radiocarbon
measurements,
con2nuous
records
of
ocean
ven2la2on
changes
are
possible.
Introduc)on
Visual
Counts
• Scanning
electron
microscope
(SEM)
was
used
to
develop
images
(900x)
that
shows
growth
bands.
Iodine
and
BSE
Counts
• The
number
of
backscaPer
electrons
(BSE)
reaching
the
detector
is
propor2onal
to
the
mean
atomic
number
of
the
sample.
• Iodine
and
BSE
were
measured
along
radial
transects
using
the
SEM
at
1
µm
spot
intervals.
Figure
2.
Prouty
et
al.,
(2011)
analyzed
black
corals
(GOM-­‐JSL04-­‐4734-­‐BC1)
by
o b s e r v i n g
s c a n n i n g
e l e c t r o n
microscope
(SEM)
40x
images
and
counted
an
average
age
of
576
bands
c o m p a r e d
t o
t h e
c a l c u l a t e d
radiocarbon
derived
life
span
of
670
±40
yrs.
The
USGS
Terrestrial,
Marine,
and
Freshwater
Environments-­‐Outer
Con2nental
Shelf
Ecosystem
Program
and
USGS
Coastal
and
Marine
Geology
Program
and
a
grant
to
EBR
from
The
Norman
Hackerman
Advanced
Research
Program
supported
this
work.
Acknowledgments
§ Confident
that
the
growth
bands
in
black
corals
are
indeed
annual.
§ Iodine
and
visual
counts
along
with
BSE
are
suitable
methods
to
calculate
growth
rates
and
life
spans
of
black
corals
§ Ongoing
research
will
replicate
and
validate
reservoir
ages
to
account
for
the
variability
in
ocean
circula2on.
Conclusions
Figure
4.
This
is
an
SEM
image
of
a
black
coral
with
iodine
and
BSE
counts
overlaid
on
top.
This
shows
that
Iodine
along
with
BSE
match
the
visual
growth
bands.
When
conduc2ng
visual
counts,
different
observers
will
have
different
defini2on
of
what
is
a
growth
band
so
iodine
may
serve
as
a
less
subjec2ve
da2ng
method.
Figure
6.
The
top
panel
represents
an
en2re
radial
transect
of
iodine
and
BSE
data.
The
boPom
panel
represents
clearly
defined
iodine
and
BSE
peaks
ader
a
threshold
of
1000
was
implemented
over
a
1
mm
distance.
This
was
to
remove
the
base
line
noise
associated
with
the
darker
parts
of
the
SEM
image
in
order
to
more
easily
iden2fy
the
iodine
and
BSE
peaks.
Study
Site
and
Samples
Figure
7.
Iodine
can
be
u2lized
as
an
independent
chronology
which
allows
for
the
calcula2on
of
radiocarbon
reservoir
ages.
This
con2nuous
high
resolu2on
600
year
record
of
reservoir
ages
from
Viosca
Knoll
in
the
Gulf
of
Mexico
shows
a
high
degree
of
variability.
Reservoir
ages
calculated
from
modern
(Wagner
et
al.,
2009)
and
fossil
mid-­‐Holocene
(Druffel
et
al.,
2008)
tropical
(surface)
corals
are
included
for
comparison.
Possible
explana2ons
for
the
variability
in
reservoir
ages:
• Strong
and
weak
Yucatan
current,
which
turns
on
and
off
the
regional
upwelling
associated
with
gyre
forma2on
in
the
Gulf
of
Mexico
(Fig.
8).
• Proximity
to
the
Mississippi
river
and
associated
changes
in
discharge
could
influence
reservoir
ages.
• Falling
atmospheric
∆14C
values
can
result
in
transient
lower
reservoir
ages
(Druffel
et
al.
2008).
• 250
µm
by
250
µm
• Magnified
by
900x
• SEM
and
PIXIE
analyses
Figure
3.
Nowak
et
al.,
(2009)
examined
the
concentra2on
of
different
elements
in
black
corals.
They
found
that
higher
iodine
concentra2ons
appear
to
be
closely
associated
with
growth
bands
iden2fied
in
SEM
images.
A
SEM
and
micro-­‐Par2cle
induced
x-­‐ray
Emission
( u -­‐ P I X I E )
w a s
u s e d
a t
9 0 0 x
magnifica2on.
Figure
1.
Map
of
two
loca2ons
where
the
black
corals
were
collected.
In
the
Gulf
of
Mexico
the
corals
came
from
the
Viosca
Knoll
or
the
Desoto
canyon.
There
are
three
banks
that
make
up
the
Southeastern
United
States
(SEUS):
Savannah
Bank,
Stetson
Bank,
and
Jacksonville
Bank.
Valida)ng
Annual
Growth
Bands
Data
&
Methods
Figure
5.
The
comparison
of
four
methods
of
obtaining
the
life
span
and
growth
rates
of
black
corals
is
presented.
These
results
show
that
the
ages
and
growth
rate
es)mates
using
iodine
peaks
closely
match
the
radiocarbon
results
and
validates
that
the
these
bands
and
peaks
in
iodine
are
indeed
annual
chronometers.
GOM-JSL04-4734-BC1
1
Department
of
Geography,
Texas
A&M
University,
College
Sta2on,
TX
77840
2Department
of
Geology
and
Geophysics,
Electron
Microbe
Lab,
Texas
A&M
University,
College
Sta2on,
TX
77840
3US
Geological
Survey,
400
Natural
Bridges
Drive
Santa
Cruz,
CA
95060
4Center
for
Marine
Science,
University
of
North
Carolina
at
Wilmington,
Wilmington,
NC
28409
Figure
8.
When
the
Yucatan
current
is
strong,
it
invades
the
Gulf
of
Mexico
forming
a
loop
current
and
mesoscale
gyres.
This
process0
increases
upwelling
which
in
turn
increases
reservoir
ages.
When
the
Yucatan
current
is
weak
it
turns
sharply
into
the
Florida
Straights
and
no
gyres
or
upwelling
occurs
in
the
Gulf
of
Mexico
decreasing
the
reservoir
ages
recorded
in
the
black
corals
(Druffel
et
al.
2008).
Druffel,
E.
R.
M.,
L.
F.
Robinson,
S.
Griffin,
R.
B.
Halley,
J.
R.
Southon
&
J.
F.
Adkins
(2008)
Low
reservoir
ages
for
the
surface
ocean
from
mid-­‐Holocene
Florida
corals.
Paleoceanography,
23,
PA2209.
Nowak,
D.,
M.
Florek,
W.
Kwiatek,
J.
Lekki,
P.
Chevallier,
A.
Hacura,
R.
Wrzalik,
B.
Ben-­‐Nissan,
R.
Van
Grieken,
A.
Kuczumow
(2009).
Morphology
and
the
Chemical
Make-­‐Up
of
the
Inorganic
Components
of
Black
Corals.
Materials
Science
and
Engineering,
29,
1029-­‐1038.
Williams,
B.,
M.
J.
Risk,
S.
W.
Ross
&
K.
J.
Sulak
(2006)
Deep-­‐water
an2patharians:
Proxies
of
environmental
change.
Geology,
34,
773-­‐776
References
Measured 14C age – IntCal09 Atm 14C age (yrs. BP –Iodine age model) = 14C reservoir age
Background
Valida)ng
Annual
Growth
Bands