- Integrated Ocean Drilling Program Expedition 341 recovered sediment cores from Site U1418 in the Gulf of Alaska dating to the Pleistocene (~0-0.3 Ma). - Calcareous nannofossils were examined from 44 samples to reconstruct paleoenvironmental conditions. Abundances shifted around 100 ka from dominance by Gephyrocapsa to Coccolithus, likely related to changes in sea surface temperature or nutrients. - Glacial periods like the Last Glacial Maximum (Stage 2) and penultimate glaciation (Stage 6) saw more Gephyrocapsa, while Coccolithus abundances were highest near the end of the last glacial

1. Calcareous
Nannofossil
Assemblages
from
the
Northern
Gulf
of
Alaska
and
Late
Pleistocene
Environmental
Change
Inva
Braha1and
Leah
LeVay2
1ibraha@tamu.edu
,
Department
of
Geology
and
Geophysics,
Texas
A&M
University,
College
StaIon,
TX
77843—3115;
2levay@iodp.tamu.edu
InternaIonal
Ocean
Discovery
Program,
College
StaIon,77845
IntroducIon/Background
ScienIfic
ObjecIves
Future
Work
Results
Abstract
Discussion/Conclusions
References
Acknowledgments
Integrated
Ocean
Drilling
Program
(IODP)
Site
U1418
recovered
an
expanded
Middle
to
Late
Pleistocene
deep
water
sedimentary
sequence
in
the
Gulf
of
Alaska.
The
purpose
of
this
project
is
to
reconstruct
paleoenviromental
sea
surface
condiIons
using
calcerous
nannofossil
from
the
Late
Pleistocene
(~
0-­‐0.3
Ma).
Smear
slides
were
prepared
from
site
U1418
core
samples,
and
a
Zeiss
Axioskop
microscope
at
1000×
magnificaIon
was
used
to
calculate
relaIve
abundances
of
nannofossil
species.
Principal
component
analysis
was
used
to
examine
the
variance
in
the
assemblage
and
relate
it
to
changes
in
paleoceanographic
condiIons.
IniIal
results
show
a
shid
between
a
fossil
assemblage
dominated
by
the
genus
Gephyrocapsa
to
one
dominated
by
Coccolithus
at
~
100
ka.
This
major
alteraIon
of
the
assemblage
is
likely
related
to
a
change
in
surface
water
temperature,
nutrient
availability,
or
both.
Ø Integrated
Ocean
Drilling
Program
(IODP)
ExpediIon
341
recovered
deep
water
sedimentary
records
from
the
Southern
Alaska
Margin.
Site
U1418
was
drilled
on
the
Surveyor
Fan
in
the
Gulf
of
Alaska.
Ø BiostraIgraphy
and
magnetostraIgraphy
data
indicate
a
Pleistocene
age
for
the
secIon
cored
at
Site
U1418
(~
0-­‐0.3
Ma).
Ø Site
U1418
was
drilled
in
3703
m
of
water
and
penetrated
to
~950
m
below
seafloor
(mbsf).
Figure
1.
The
Gulf
of
Alaska
region
(located
in
the
subarcIc
northeast
Pacific
Ocean
):
geography
and
locaIon
of
previous
DSDP
and
ODP
drilling
locaIons
(see
inset)
and
ExpediIon
341
drilling
sites
(from
Jaeger
et
al.,
2014).
Figure
2.
Site
U1418
is
located
between
AleuEan
Trench
channel
and
Bering
channel
at
the
base
of
the
conEnental
shelf
break
(from
Jaeger
et
al.,
2014)
Site
U1418
Lat:
58˚56.60ʹ′
N
Long:
144˚29.56ʹ′
W
Water
depth:
948.7
m
Age:
Pleistocene
to
Holocene
Ø The
objecIve
of
this
research
is
to
reconstruct
paleoenviromental
sea
surface
condiIons
using
calcareous
nannofossils
from
the
Late
Pleistocene.
Ø Determine
glacial
and
interglacial
cyclicity
recorded
in
the
cores
by
comparing
the
nannofossil
data
from
Site
U1418
with
the
global
benthic
oxygen
isotope
record
of
Lisiecki
and
Raymo
(2005).
Ø A
total
of
44
samples
for
this
project
were
collected
from
cores
recovered
during
IODP
ExpediIon
341,
Southern
Alaska
Margin
Tectonics,
Climate
&
SedimentaIon.
Ø We
prepared
smear
slides
for
examinaIon
of
calcareous
nannofossils
using
standard
techniques
(Bown
and
Young,
1998).
Ø We
examined
samples
using
a
Zeiss
Axioskop
and
a
Zeiss
Axioscope
.A1
microscope
(Fig.
3)
at
1000×
magnificaIon.
Up
to
100
specimens
were
counted
per
slide
to
calculate
relaIve
abundances
of
nannofossil
species.
Ø
Photomicrographs
were
taken
using
a
Spot
camera
(Fig.
3).
Ø The
abundances
of
Gephyrocapsa
and
Coccolithus
are
inversely
related
throughout
much
of
the
record,
suggesIng
that
they
are
responding
in
opposite
ways
to
changes
in
sea-­‐
surface
condiIons.
Since
both
prefer
colder
waters
(e.g.,
Winter
et
al.,
2004),
these
variaIons
may
be
due
to
changes
in
nutrient
availability,
as
G.
muellerae
prefers
eutrophic
condiIons
(e.g.,
Winter
et
al.,
1994;
Boeckel
et
al.,
2006).
Ø Based
on
the
correlaIon
of
the
calcareous
nannofossil
assemblage
data
and
Site
U1418
age
model
to
the
global
oxygen
Isotope
stack
based
on
on
benthic
foraminifera,
we
interpret
that
Geophyrocapsa
is
more
abundant
during
the
last
glacial
maximum
(Marine
Isotope
Stage
2)
and
penulImate
glaciaIon
(Stage
6),
whereas
Coccolithus
pelagicus
and
Cruciplacolithus
have
their
highest
abundances
near
the
end
of
the
last
glacial
cycle
(Marine
Isotope
Stages
3
and
4).
Ø InteresIngly,
very
warm
interglacial
Stage
5
also
has
high
abundances
of
Gephyrocapsa
and
low
abundances
of
Coccolithus,
similar
to
glacial
Stage
6.
More
work
is
needed
to
understand
the
mechanisms
driving
the
variaIons
in
abundance
of
these
taxa.
Ø The
total
abundance
of
nannofossils
decreases
and
is
more
variable
below
100
mbsf
(Fig.
4)
Ø High
abundances
of
Gephyrocapsa
and
low
abundances
of
Coccolithus
occur
from
~100-­‐250
mbsf
(Fig
4)
Ø
Cruciplacolithus
decreases
below
100
mbsf
(Fig.
4)
Ø Reworked
specimens
are
consistently
present
above
50
mbsf,
with
intermipent
pulses
below
that
depth
(Fig.
4)
Ø Figure
5
shows
the
nannofossil
assemblage
data
compared
to
the
Lisiecki
and
Raymo
(2005)
benthic
oxygen
isotope
stack
using
the
Site
U1418
age
model
to
see
illustrate
the
influence
of
glacial/interglacial
variability
on
the
nannofossil
abundances.
Boeckel,
B.,
Baumann,
K.-­‐H.,
Henrich,
R.,
and
Kinkel,
H.,
2006.
Coccolith
distribuIon
paperns
in
South
AtlanIc
and
Southern
Ocean
surface
sediments
in
relaIon
to
environmental
gradients.
Deep-­‐Sea
Research
I,
1073-­‐1099.
Bown,
P.R.
&
Young,
J.R.
1998.
Techniques.
In:
P.R.
Bown
(Ed.).
Calcareous
Nannofossil
Biostra8graphy.
Kluwer
Academie,
London:
16–28.
Jaeger,
J.M.,
Gulick,
S.P.S.,
LeVay,
L.J.,
Asahi,
H.,
Bahlburg,
H.,
Belanger,
C.L.,
Berbel,
G.B.B.,
Childress,
L.B.,
Cowan,
E.A.,
Drab,
L.,
Forwick,
M.,
Fukumura,
A.,
Ge,
S.,
Gupta,
S.M.,
Kioka,
A.,
Konno,
S.,
März,
C.E.,
Matsuzaki,
K.M.,
McClymont,
E.L.,
Mix,
A.C.,
Moy,
C.M.,
Müller,
J.,
Nakamura,
A.,
Ojima,
T.,
Ridgway,
K.D.,
Rodrigues
Ribeiro,
F.,
Romero,
O.E.,
Slagle,
A.L.,Stoner,
J.S.,
St-­‐Onge,
G.,
Suto,
I.,
Walczak,
M.H.,
and
Worthington,
L.L.,
2014.
Site
U1418.
In
Jaeger,
J.M.,
Gulick,
S.P.S.,
LeVay,
L.J.,
and
the
ExpediIon
341
ScienIsts,
Proc.
IODP,
341:
College
StaIon,
TX
(Integrated
Ocean
Drilling
Program).
doi:10.2204/iodp.proc.341.104.2014
Lisiecki,
L.E.,
and
Raymo,
M.E.,
2005,
A
Pliocene-­‐Pleistocene
stack
of
57
globally
distributed
benthic
d18O
records.
Paleoceanography,
20:PA1003.
Winter,
A.,
Jordan,
R.W.,
and
Roth,
P.H.,
1994.
Biogeography
of
living
coccolithophores
in
oceanic
waters.
In:
Winter,
A.
and
Siesser,
W.G.
(Eds),
Coccolithophores.
Cambridge
University
Press,
Cambridge,
pp.
161-­‐177.
This
project
uses
samples
and
data
provided
by
the
Integrated
Ocean
Drilling
Program.
Funding
for
this
research
comes
from
an
IODP
Post-­‐ExpediIon
Award
to
Leah
LeVay.
This
project
has
been
supported
by
laboratory
equipment
at
IODP
at
Texas
A&M
University.
Special
thank
you
to
Dr.
Leah
LeVay
and
Dr.
Denise
Kulhanek
for
assisIng
and
guiding
me
in
this
project.
Gephyrocapsa
sp.
U1418C-­‐2H-­‐3,
116-­‐120
cm
Coccolithus
pelagicus
U1418C-­‐2H-­‐3,
16-­‐20
cm
Re8culofenstrata
sp.
(reworked)
U1418D-­‐2H-­‐5,
116-­‐120
cm
Gephyrocapsa
muellerae
U1418C-­‐2H-­‐3,
116-­‐120
cm
Figure
6.
Photomicrographs
of
calcareous
nannofossil
taken
from
different
samples.
Pictures
taken
using
a
Spot
camera
on
a
Zeiss
Axioscope.
Figure
4.
VariaIons
in
the
total
abundance
of
nannofossils
and
percentage
abundance
of
different
species
downhole,
ploped
against
the
lithology
of
Site
U1418.
Ø Future
work
will
include
addiIonal
analyses
and
comparison
to
other
paleoclimaIc
proxies
to
beper
understand
the
Late
Pleistocene
paleoceanography
and
paleoclimate
of
the
region.
Methods
Cruciplacolithus
sp.
U1418C-­‐2H-­‐3,
116-­‐120
cm
Re8culofenstrata
sp.
(reworked)
U1418D-­‐4H-­‐5,
36-­‐40
cm
Re8culofenstrata
sp.
(reworked)
U1418D-­‐2H-­‐5,
116-­‐120
cm
Toweius
sp.
(reworked)
U1418C-­‐2H-­‐3,
116-­‐120
cm
Figure
3.
Zeiss
Axioscope
.A1
microscope
and
Spot
camera
used
for
this
study.
Figure
5.
Benthic
oxygen
isotope
stack
(Lisiecki
and
Raymo,
2005)
(black)
ploped
together
with
percent
abundance
Gephyrocapsa
(blue),
Coccolithus
(red),
and
Cruciplacolithus
(green)
according
to
the
Site
U1418
age
model.
Marine
isotope
stages
are
indicated
at
the
top
and
gray
rectangles
highlight
cold
(glacial)
stages.
Depth(mbsfHoleU1418D)
Site U1418
300
275
250
225
200
175
150
125
100
75
50
25
0
I
II
4
3
2
1
Lith.
unit
Graphic
lithology
Volcanic
grain
abundance
0 20 40 60 80 100120
Total Nannofossils
(counts)
0 20 40 60 80 100
Gephyrocapsa
muellerae >3 µm
0 20 40 60 80 100
Gephyrocapsa
muellerae <3 µm
0 20 40 60 80 100
Coccolithus
(total)
0 20 40 60 80 100
Reworked
nannofossils
0 20 40 60 80 100
Cruciplacolithus
(total)
0 20 40 60 80 100
Gephyrocapsa
(total)
Depth(ccsfSiteU1418)