A pervasive link between Antarctic ice core and subarctic Pacific ...

Quaternary Science Reviews 29 (2010) 206–212
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Quaternary Science Reviews
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A pervasive link between Antarctic ice core and subarctic Pacific sediment records
over the past 800 kyrs
S.L. Jaccard a, *, E.D. Galbraith b , D.M. Sigman c , G.H. Haug a,d
a Geological Institute, ETH Zurich, Zurich, Switzerland
b Earth and Planetary Science, McGill University, Montreal, Canada
c Department of Geosciences, Princeton University, Princeton, NJ, USA
d Leibniz Center for Earth Surface and Climate Studies, Institute for Geosciences Potsdam University, 14476 Potsdam, Germany
article
info
abstract
Article history:
Received 23 January 2009
Received in revised form
24 August 2009
Accepted 11 October 2009
Recently developed XRF core-scanning methods permit paleoceanographic reconstructions on timescales
similar to those of ice-core records. We have investigated the distribution of biogenic barium (Ba/
Al), opal and carbonate (Ca/Al) in a sediment core retrieved from the abyssal subarctic Pacific (ODP 882,
50 N, 167 E, 3244 m) over an interval that spans the full length of the EPICA Dome C (EDC) ice-core
record. Ba/Al and biogenic opal show a strong resemblance to the EDC dD and CO 2 , with generally high
concentrations during interglacials and lower values during ice ages of the past 800 kyrs. The sedimentary
Ba/Al and biogenic opal are most easily interpreted as indicating a reduced sinking flux of
organic matter from the surface ocean during cold periods. The Ba/Al maxima during peak interglacials
are accompanied by transient Ca/Al peaks in these otherwise carbonate-devoid sediments, which are
best explained by a deepening of the calcite lysocline, presumably due to reduced storage of respired CO 2
in the deep North Pacific. For most of the ‘‘luke-warm’’ interglacials noted between 420 and 750 ka in
EDC, the Ba/Al peaks in ODP 882 are also lower, further strengthening the evidence for a simple physical
link between global climate and the biogeochemistry of the subarctic Pacific.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Air bubbles encapsulated in Antarctic ice reveal that past atmospheric
carbon dioxide concentrations (pCO 2 ) varied cyclically from
low values (w160–180 ppmv) during ice ages to higher values
(w280–300 ppmv) during interglacials over the past 800 kyrs (Lüthi
et al., 2008; Monnin et al., 2001; Petit et al.,1999; Siegenthaler et al.,
2005), exhibiting a strong stationary relationship with changes in
Antarctic air temperatures (Jouzel et al., 2007). While the transition
from warm to cold periods was generally progressive, temperature
and CO 2 increase during glacial terminations was relatively abrupt.
Since the deep ocean stores 25 times more CO 2 than the atmosphere
and surface ocean combined, it seems inescapable that changes in
the ocean carbon cycle played a significant role in modulating and
controlling past variations of atmospheric CO 2 , which in turn
amplified climate forcings to yield the large observed amplitude of
ice age cycles (e.g. Broecker, 1982; Sigman and Boyle, 2000). Abyssal
water is ventilated on a multi-centennial to millennial timescale, so
that a change in atmospheric CO 2 driven by factors other than
oceanic processes would be dampened. In addition, over thousands
* Corresponding author.
E-mail address: samuel.jaccard@erdw.ethz.ch (S.L. Jaccard).
of years, the deep ocean regulates the exchange of inorganic carbon
between the geological reservoir and the hydrosphere/atmosphere
system through its control of the burial of calcium carbonate on the
seafloor (Sigman and Boyle, 2000).
1.1. Efficiency of the biological pump and ocean-atmosphere
CO 2 exchange
The warm sunlit surface ocean layer is separated by a strong
temperature-driven density gradient (thermocline) from the cold
deep ocean, preventing rapid communication between the lowlatitude
ocean surface and the ocean interior. As a result, nutrients
transferred to the deep via the remineralization of sinking organic
matter are not readily returned to the photic zone, and phytoplankton
completely exhaust roughly 2/3 of global ocean surface
waters of available nutrients on a seasonal basis (Conkright et al.,
2002). In tropical and subtropical regions of the world ocean,
a large fraction of the nutrient resupply to the euphotic zone occurs
via Subantarctic Mode Water, which spreads throughout the entire
Southern Hemisphere and North Atlantic Ocean (e.g. Sarmiento
et al., 2004, 2007). The fact that nutrients are completely consumed
throughout the low-latitude surface ocean means that the biological
pump is at maximum efficiency there.
0277-3791/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.quascirev.2009.10.007

S.L. Jaccard et al. / Quaternary Science Reviews 29 (2010) 206–212 207
In contrast, dense waters are exposed at the surface of highlatitude
oceans, such as the subarctic Pacific (Gargett, 1991; Talley,
1995) and the Southern Ocean (Sarmiento et al., 2004), and are
returned to the subsurface before the available nutrients are fully
utilized by phytoplankton for carbon fixation (Sarmiento and
Toggweiler, 1984; Sigman and Boyle, 2000). The exposure of
nutrient-rich deep water at the surface fuels phytoplankton
growth, but simultaneously it allows CO 2 previously sequestered by
the biological pump to be released to the atmosphere. The uptake of
nutrients and CO 2 during formation of phytoplankton biomass
through photosynthesis and the eventual export of organic matter
subsequently lowers the pCO 2 of surface waters, causing the surface
layer to reabsorb a portion of the CO 2 that was initially released
from the upwelled water. However, any unused nutrients that are
physically pumped back into the ocean interior as ‘preformed’
nutrients represent a shortfall in the potential efficiency of the
biological pump (Sigman and Haug, 2003; Ito and Follows, 2005)
Thus, it is the ratio between export production and the ventilation
rate of CO 2 -rich subsurface waters (not the absolute rate of either
process alone) that controls the net exchange of CO 2 between the
atmosphere and the high-latitude surface ocean (Sarmiento and
Toggweiler, 1984). As a result, either increased export flux and/or
reduced communication between the subsurface ocean and the
atmosphere would contribute to sequester a larger proportion of
CO 2 in the ocean during ice ages, thereby contributing to reduce
atmospheric CO 2 concentrations (Stephens and Keeling, 2000;
Sarmiento and Toggweiler, 1984; Siegenthaler and Wenk, 1984;
Sigman and Boyle, 2000).
1.2. The subarctic NW Pacific – past and present
The subarctic Pacific is one of the three major high nutrient low
chlorophyll (HNLC) regions of the world ocean, characterized by
upwelling of nutrient-rich deep water into the euphotic zone due to
Ekman divergence (Gargett, 1991). Low ambient iron concentrations
limit complete utilization of available dissolved nutrients and
growth of large celled phytoplankton (Tsuda et al., 2003). Macronutrient
supply to the photic zone is moderated by the strength of
the permanent salinity-driven density gradient (halocline) that
dominates the region today. The presence of this low-salinity
surface layer prevents thorough convection; hence no deep water is
formed today in the open subarctic Pacific (Emile-Geay et al., 2003;
Warren, 1983). In addition, the relatively effective isolation of the
subtropical and subarctic gyres minimizes dilution of the high
nutrient water by nutrient-depleted waters from lower latitudes. In
spite of rather limited mixing between mid-depths and the surface
ocean, the modern subarctic Pacific still constitutes a source of
oceanic CO 2 to the atmosphere (Takahashi et al., 2002) despite the
anthropogenically-elevated atmospheric partial pressure of CO 2 .
Primary productivity is dominated by siliceous algae (diatoms) in
early summer and to a lesser degree by calcareous phytoplankton
early autumn when silicic acid concentrations have dropped.
Sediment trap observations have shown that total mass flux and
biogenic opal flux are highly correlated (Honda et al., 2002), suggesting
that opal is the main export vector for organic carbon
(Otosaka and Noriki, 2005). At station KNOT (44 N, 150 E), the
transfer efficiency of organic carbon (i.e. the ratio between organic
carbon flux to primary productivity) was estimated to be approx.
3% at 3000 m water depth, a value that is substantially higher than
observed elsewhere in the world ocean (Honda et al., 2002).
There seems to be a general consensus, that export production
in the NW subarctic Pacific was significantly lower during peak ice
ages when compared to interglacial periods (Brunelle et al., 2007;
Galbraith et al., 2008; Gebhardt et al., 2008; Kienast et al., 2004;
Jaccard et al., 2005, 2009; Narita et al., 2002; Shigemitsu et al.,
2007), suggesting that nutrient supply from below was reduced
during cold periods. A corollary to these observations is that the
physical transfer of deeply sequestered CO 2 to the surface ocean
through upwelling and turbulent mixing would have been reduced
during ice ages, thereby contributing to lower global atmospheric
CO 2 concentrations.
In this manuscript, we present new high-resolution measurements
from a sedimentary archive retrieved from the abyssal NW
subarctic Pacific Ocean. The time resolution achieved here rivals the
measurement density typical for Antarctic ice-core records. We
build upon previous observations (Galbraith et al., 2008; Jaccard
et al., 2005, 2009) by extending the Ba/Al, Ca/Al and biogenic opal
records back to 800 kyr to allow comparison with EPICA Dome C
(EDC) records. Our multi-proxy approach reveals that export
production and thus the nutrient supply to the surface is linked to
Antarctic dD and CO 2 records on millennial timescales, suggesting
a strong physical link between temperature in high southern latitudes
and the nutrient supply to the subarctic Pacific photic zone.
Our reconstructions further document the contribution the
subarctic Pacific made to modulate the partitioning of CO 2 between
the abyssal ocean and the atmosphere on glacial-interglacial
timescales.
2. Material, methods & proxies
2.1. Core material
ODP Site 882 is located in the subarctic NW Pacific (Detroit
Seamount, 50 21 0 N, 167 35 0 E; water depth 3244 m). The core
contains undisturbed diatomaceous ooze sequences with episodic
carbonate-rich intervals and scattered ash layers (Rea et al., 1993).
The astronomically calibrated stratigraphy for ODP Site 882 was
generated based on fine tuning of GRAPE (Gamma Ray Attenuation
Porosity Evaluator) density oscillations in the orbital precession
band to the summer insolation at 65 N(Tiedemann and Haug,
1995). In addition, benthic foraminiferal oxygen isotope records
from ODP Sites 882 and 883 (cross-correlated with magnetic
susceptibility) in intervals with CaCO 3 were used to corroborate the
tuned stratigraphy. The age model was linearly interpolated
between the selected tie-points. To derive the detailed age model
we then fine-tuned the ODP Site 882 Ba/Al record to the EDC dD
record (Jouzel et al., 2007) by visually matching common inflection
points and interpolating linearly between them (Galbraith et al.,
2008; Jaccard et al., 2005). This approach assumes a strict in-phase
relationship between EDC dD and ODP 882 Ba/Al records, which is
unlikely to be true, and therefore introduces some degree of
uncertainty. Bioturbation in these oxic sediments is in the order of
a few centimeters, smoothing the records slightly. Sedimentation
rates typically range between 5 and 10 cm*kyr 1 .
2.2. Analytical methods
Relative sedimentary elemental concentrations (Al, Ca, Ba) were
measured with an Aavatech profiling X-ray Fluorescence (XRF) core
scanner at Bremen University at a 1–3 cm (i.e. submillenial) resolution.
The calculations of normative Ba/Al and Ca/Al are based on
the assumption that the Al, Ba and Ca content of the terrigenous
material remained constant in space and time. Comparison
between discrete ICP-MS and coulometric determination of sedimentary
CaCO 3 and relative Ba/Al and Ca/Al counts, respectively,
has shown a highly significant statistical correlation (Jaccard et al.,
2009; Suppl. Fig.). Biogenic opal was quantified by alkaline
extraction of silica (Mortlock and Froelich, 1989) for the time
interval back to 150 kyr (Jaccard et al., 2009) and with help of the
density separation technique on carbonate- and organic carbon-

208
S.L. Jaccard et al. / Quaternary Science Reviews 29 (2010) 206–212
free sediments (Haug et al., 1995) for the rest of the investigated
interval. Replicate measurements indicate a general reproducibility
of about 3–5% depending on the sedimentary opal content.
2.3. Proxies
All proxies used to reconstruct past variability of export
production are subject to potential biases. A multi-proxy approach
may thus help to compensate for specific limitations associated
with individual proxies, assuming the proxy biases are independent
of each other. Biogenic (or excess) barite (bioBa) precipitates
from seawater, and its flux to the seafloor is correlated with integrated
export production (Goldberg and Arrhenius, 1958; Dymond
et al., 1992). Biogenic barite formation is thought to take place
through indirect biological mediation and abiotic precipitation
from supersaturated microenvironments within settling biogenic
particles (Ganeshram et al., 2003) and may therefore represent
a proxy for integrated organic carbon export from the photic zone
(Eagle et al., 2003; François et al., 1995). BioBa dissolves under
conditions of sulfate depletion by microbial sulfate reduction
(McManus et al., 1998; Paytan and Kastner, 1996), which is mainly
restricted to highly productive coastal areas and the equatorial
Pacific upwelling system. We note that in these highly productive
regimes, where sedimentation rates and organic carbon export
fluxes are significantly higher than in the subarctic Pacific, barite
dissolution has been observed under suboxic conditions,
precluding its application as a quantitative proxy to reconstruct
past changes in export production (McManus et al., 1998). Although
most of the ocean is undersaturated with respect to barite (Monnin
et al., 1999), a significant fraction of the bioBa produced in the
water-column is preserved in sediments under oxic/suboxic
conditions typical of pelagic environments (Dymond et al., 1992;
Paytan and Kastner, 1996; Paytan and Griffith, 2007). Approximately
30% of the barite precipitated during settling is preserved in
the sediment, whereas only 5 ky does not appear to hold at finer
temporal scales, such as during the last deglaciation (Galbraith
et al., 2007; Gebhardt et al., 2008; Kiefer et al., 2001; Sarnthein
et al., 2006). Ca/Al shows a bimodal distribution, with carbonatefree
sediments interrupted by apparent calcite preservation spikes
that occur at each glacial termination but also appear to persist into
roughly the first half of the following interglacial period. Ba/Al,
biogenic opal and Ca/Al show good correlations with Antarctic icecore
dD and CO 2 records (Fig. 2) both in terms of frequency and
(cps)
Ca/Al
(cps)
Ba/Al
200
150
100
50
0
b
2 4 6 8 10 12
ODP 882
MD2416
10
5.5
0
5.0 d
4.5
4.0
3.5
3.0
2.5
2.0
1.5
0 100 200 300 400 500 600 700 800
Age (kyr)
R el. NO utilizatio n
3
14 16 18
Fig. 1. Reconstructions of past changes in surface ocean fertility, calcium carbonate preservation in the sediment and nutrient dynamics at ODP site 882 across the past 800 kyrs.
(a) Residual (i.e. the fraction of the signal related to the degree of nitrate utilization by phytoplankton) bulk sediment d 15 N at site ODP 882 (black) and nearby core MD2416
(dark grey) (Galbraith et al., 2008). (b) Ca/Al (data smoothed by a five-point running mean), (c) biogenic opal, (d) Ba/Al (data smoothed by a five-point running mean). Grey bars are
indicative of glacial maxima. Marine Isotope Stages (MIS) are given in Arabic numerals.
a
c
-3
-2
-1
0
1
2
3
60
50
40
30
20
δ
1 5 N s
r e
(‰ vsAIR )
biogenic opal (wt%)

S.L. Jaccard et al. / Quaternary Science Reviews 29 (2010) 206–212 209
amplitude (Fig. 3) of the signal. Ba/Al and, to a lesser degree, Ca/Al
show a generally lower amplitude between 450 and 750 kyrs
during the ‘‘luke-warm’’ interglacials, MIS 13, 15 & 17 (Figs. 3 and 4).
In particular, interglacial maxima show significantly lower values
when compared to the past 450 kyr, the glacial baseline remaining
rather constant across the entire record (Fig. 2). We note, however,
that the correlation between ODP882 Ba/Al and EDC dD and CO2
was markedly weaker prior to 450kyr, for reasons that are currently
unclear. Further investigations will aim to clarify this issue.
4. Discussion
Reconstruction of past changes in organic carbon export is
uncertain, as each proxy has its own biases. Here we analyze two
different proxies, both of which yield a picture that is internally
consistent and supported by data from the literature (see above). It
is important to point out that the concentrations of both organic
carbon and chlorins (an algal biomarker) are higher in glacial age
sediments, in contrast to the bioBa and opal (Gebhardt et al., 2008;
Gorbarenko, 1996; Haug et al., 1995; Kiefer et al., 2001; Shigemitsu
et al., 2007). These organic phases might seem to be more direct
proxies of carbon export than the mineral proxies we present here.
However, the maximum chlorin concentrations observed in core
MD01-2416 (Gebhardt et al., 2008), gradually decrease downcore
with values up to 10 000 ng/g for TERM I to 20 mM)
(Pedersen and Ingram, 1995). We therefore assume here that the
less direct, but hopefully more robust mineral proxies are the most
accurate reflection of past changes in export production, with the
caveat that the causes of higher glacial concentrations of organic
components should be more thoroughly investigated.
Shigemitsu et al. (2007) recently presented a novel approach to
address past changes in the dust flux to the western subarctic
Pacific. Their results show that the eolain contribution to the
sediment was approximately twice as high during the past ice ages
when compared to interglacials. Preliminary results, based on 232 Th
MAR (Jaccard et al., 2009) seem to support their conclusion. As
a result, a portion of the Ba/Al signal is likely to reflect the enhanced
input of eolian material during glacial intervals. However, 230Thnormalized
flux reconstructions for TERM I (Jaccard et al., 2009)
clearly confirm that the last deglaciation was marked by a large
increase in the preserved flux of biogenic detritus, accompanying
the inferred decrease in dust supply.
Reconstructions of sea surface temperature from alkenones
(Haug, 1996), foraminiferal Mg/Ca (Gebhardt et al., 2008), and
foraminiferal transfer functions (Kiefer et al., 2001; Kiefer and
Kienast, 2005) all indicate that, even during the coldest times,
summertime SST never approached freezing in the vicinity of the
core site. This corroborates micropaleontological evidence that ODP
Site 882 is located well east of the maximum perennial sea-ice
extent over the Pleistocene (Climap Members, 1981) (Sancetta and
Silvestri, 1986). As a result, sea ice cover is unlikely to have represented
a major limitation on the spring/summer growing season
during glacial times. Rather, some other factor must have limited
phytoplankton growth during glacial times. The aeolian dust supply
(cps)
Ba/Al
D‰ ( vsSMOW )
δ
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
-360
-380
-400
-420
-440
T V
T IV
T VIII
T VII
TI T T III
T IX
II
T VI
b
d
a
c
200
150
100
50
0
300
280
260
240
220
200
180
160
Ca/Al (cps)
C O (ppmv )
2
-460
0 100 200 300 400 500 600 700 800
Age (kyr)
Fig. 2. (a) Ca/Al and (b) Ba/Al records from ODP site 882 compared to (c) EDC CO 2 (Lüthi et al., 2008) (Monnin et al., 2001) (Siegenthaler et al., 2005) and (d) the deuterium (dD)
(Jouzel et al., 2007) records during the past 800 kyrs. Glacial Terminations are indicated using Roman numerals in subscript.

210
S.L. Jaccard et al. / Quaternary Science Reviews 29 (2010) 206–212
1.5
Normalized Amplitude
1.0
0.5
CO 2
δD
Ba/Al
0
T I
T II
T III
T IV
T V
T VI
T VII
T VIII
T IX
Fig. 3. Interglacial-glacial CO 2 (dark grey), dD (light grey) and Ba/Al (red) amplitude for glacial terminations I-VII. Amplitude is (arbitrarily) defined as the difference between the
three consecutive highest interglacial values and the three consecutive lowest values preceding the onset of glacial terminations. The amplitude of each parameter has been
normalized to TERM 1 values.
of iron to the region was, if anything, higher during colder times
(Kienast et al., 2004; Shigemitsu et al., 2007). It is still possible that
some other physical change, such as a deeper summertime mixed
layer, led to greater light limitation during ice ages (e.g. Anderson
et al., 2002). Alternatively, reduced upwelling or vertical mixing
may have decreased the supply from below of both iron and the
major nutrients. In this case, the increased supply of iron from
above must have failed to compensate for the reduced supply from
below, leading to the net decrease in productivity. Nevertheless,
this situation should result in more complete major nutrient
consumption, because of the greater proportional importance of
the iron input from above. Indeed, subarctic northwest Pacific
sediment and diatom-bound d 15 N – a measure of the relative
utilization of dissolved nitrate (Altabet and François, 1994) – shows
a strong negative correlation with export production on >5ky
timescales (Brunelle et al., 2007; Galbraith et al., 2008; Nakatsuka
et al., 1995)(Fig. 1 panel (a)). This suggests that, during ice ages, the
relative amount of nitrate that was utilized by phytoplankton
increased, even though the absolute rate of nitrate consumption
decreased, which implies that the supply of nutrients to the
subarctic North Pacific was reduced during ice ages. The N isotope
data in themselves suggest that the efficiency of the subarctic
Pacific biological pump increased during ice ages, thereby
contributing to sequester a larger burden of remineralized carbon
into the abyssal ocean (Brunelle et al., 2007; Galbraith et al., 2008).
Enhanced glacial storage of metabolic carbon would have reduced
oxygenation of the abyssal ocean, consistent with other data, such
as authigenic Uranium content (Galbraith et al., 2007; Jaccard et al.,
2009; Shigemitsu et al., 2007). Similarly, d 15 N records from the
Antarctic Zone of the Southern Ocean indicate higher relative
nitrate utilization and yet reduced export production during peak
ice ages (François et al., 1997; Robinson et al., 2004; Robinson and
Sigman, 2008; Schneider-Mor et al., 2005), suggesting that either
a common physical mechanism modulated the nutrient supply of
both these polar regions in tandem (Sigman et al., 2004), or that
a physical change in the Southern Ocean controlled the subarctic
Pacific nutrient budget remotely.
Biogenic carbonate (Ca/Al), which was nearly or completely
absent in these cores throughout much of the glacial sediments,
suddenly appears in abundance at each glacial termination.
Although the increase in CaCO 3 concentration may reflect
enhanced local CaCO 3 export, the rapid increase suggests a rapid
deepening of the lysocline, driven by a decrease of DIC and/or
an increase in the alkalinity of bottom waters at times when
deeply sequestered CO 2 is released to (sub)surface waters. If
these intervals were solely deglacial, then they could be taken as
indicative of the global preservation event that one would
predict at the end of ice ages, when CO 2 is released from the
ocean to accumulate in the atmosphere and terrestrial biosphere
(e.g. Broecker and Peng, 1985; Marchitto et al., 2005). However,
high Ca/Al tends to persist into interglacials, suggesting that at
least in the early part of interglacials, the subarctic North Pacific
interior had a smaller burden of regenerated dissolved inorganic
carbon, due either to ventilation from the South and/or locally
interglacial-glacial δD ampl.
(‰ vs SMOW)
80
70
60
50
40
T III
T VII
T IV
T V
T IX
30 T VIII
20
T VI R = 0.92
10
30 40 50 60 70 80 90 100
interglacial- glacial CO 2
ampl. (ppmv)
T I
T II
interglacial-glacial δD ampl.
(‰ vs SMOW)
80
70
60
50
40
30
T VII
T III
T I
T VIII
T VI
T IV
T V
T II
T IX
20
R = 0.82
10
1.0 1.5 2.0 2.5 3.0 3.5
interglacial-glacial Ba/Al ampl .
interglacial-glacial CO 2
ampl.
(ppmv)
100
90
80
70
T VII
T IV
T V
T II
T III
T I
T IX
60
T
50
VIII
40
T R = 0.76
VI
30
1.0 1.5 2.0 2.5 3.0 3.5
interglacial-glacial Ba/Al ampl .
Fig. 4. Cross-plots illustrating the correlation between (a) dD and CO 2 amplitude; (b) dD and Ba/Al amplitude; (c) Ba/Al and CO 2 amplitude. Amplitude has been determined as the
difference between the three consecutive highest interglacial values and the three consecutive lowest values preceding the onset of glacial terminations. R represents the linear
correlation factor between variables. Glacial Terminations are indicated using Roman numerals in subscript.

S.L. Jaccard et al. / Quaternary Science Reviews 29 (2010) 206–212 211
by the Subarctic North Pacific (Jaccard et al., 2005; Gebhardt
et al., 2008).
The extended ODP 882 Ba/Al record shows reduced amplitude
of interglacial maxima during MIS 13–17, that is reminiscent of the
reduction in amplitude of the dD and CO 2 records (Fig. 2). Interglacial-glacial
amplitude variability in the EDC dD, CO 2 and ODP
882 Ba/Al records show strong correlations (Fig. 4), further
emphasizing that Antarctic air temperature, global atmospheric
CO 2 and subarctic Pacific export production are mechanistically
linked. The apparent implication is that whatever caused the luke
warm interglacials to be relatively cool was linked to marine
biogeochemistry in a roughly linear fashion. Presumably this
resulted from some combination of two things: (1) a straightforward
physical climate control of the marine ecosystem, likely
through modulation of the nutrient supply, or (2) to a straightforward
oceanic control on climate, such as through modulation of
atmospheric CO 2 . For example, given the significant dependency of
polar ocean water-column stability on the mean ocean temperature
(de Boer et al., 2007; Winton, 1997), upwelling of nutrient-rich
deep waters to the subarctic Pacific (and possibly to the Antarctic
Zone of the Southern Ocean) surface waters could have been
reduced as a direct result of ocean temperature. Wind-driven
mechanisms are also being considered as an explanation for the
reduced Antarctic and Subarctic North Pacific vertical exchange
during ice ages (Toggweiler et al., 2006). It remains to be seen
whether such mechanisms could similarly explain the ‘‘mid-way’’
state of North Pacific export production during the ‘‘luke-warm’’
interglacials.
5. Conclusion
Sedimentary measurements of Ba/Al from the NW subarctic
Pacific show a pervasive link to Antarctic ice-core dD (Jouzel et al.,
2007) and CO 2 records (Lüthi et al., 2008; Monnin et al., 2001; Petit
et al., 1999; Siegenthaler et al., 2005). The compelling decrease in
amplitude observed in EDC dD, CO 2 and ODP 882 Ba/Al during the
‘‘luke-warm’’ interglacials MIS 13, 15 & 17 adds further support for
the apparent climate/North Pacific biogeochemistry connection.
Our preferred interpretation is that the export flux from the surface
was significantly reduced during peak ice ages when compared to
warmer interglacial intervals, although the preservation of organic
carbon in the seafloor sediments was enhanced during glacials due
to some combination of low temperatures (Matsumoto, 2007), low
oxygen concentrations, and high clay concentrations. Increased
dust flux during glacial periods is likely to have further contributed
to low Ba/Al during these intervals. Sea surface temperature
reconstructions (Gebhardt et al., 2008; Haug, 1996; Kiefer et al.,
2001; Kiefer and Kienast, 2005) corroborated by micropaleontological
evidence (Sancetta and Silvestri, 1986) have shown that the
open subarctic Pacific was far from freezing during glacial maxima.
Sea ice cover is thus unlikely to have represented a major limitation
on the productive season during glacial times. The most reasonable
mechanism for reducing export productivity is a decrease in the
supply of nutrients from subsurface waters. Reconstruction of the
degree of nitrate utilization nitrate using the N isotopes (Brunelle
et al., 2007; Galbraith et al., 2008) suggests that the subarctic Pacific
biological pump was more efficient during ice ages. Thus, it may
have contributed significantly to increased deep ocean sequestration
of carbon during ice ages.
Acknowledgements
This research used samples provided by the Ocean Drilling
Program (ODP). ODP is sponsored by the U.S. National Science
Foundation (NSF) and participating countries under the
management of Joint Oceanographic Institutions (JOI), Inc. We
thank C. Murray-Wallace as well as two anonymous reviewers for
insightful and constructive comments.
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