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

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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