Characterizing the North Pacific Biological Pump in Glacial-Interglacial Cycles and Its Role in Carbon Sequestration

Tianjia Liu1 and Jerry F. McManus1,2 1Department of Earth and Environmental Sciences, Columbia University, New York, NY 2Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY

The Biological Pump

JdFR Biological Pump

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Through photosynthesis and gas exchange, the surface ocean sequesters, or removes, CO2 from the atmosphere, and its biological pump subsequently buries the carbon in the deep ocean. The calcium carbonate shells of foraminifera record and reflect the oxygen and carbon isotope fractionation of the water column as a function of time. While δ18O is a proxy for ice volume and ocean temperature (glacial-interglacial cycles), δ13C is a proxy for marine productivity. Organisms preferentially utilize the lighter 12C for photosynthesis, leaving behind relatively 13C-enriched surface waters (photosynthesis is limited by sunlight). In contrast, respiration reintroduces 12C, and produces 13C-depleted water, especially in the deep ocean, where photosynthesis is absent. Because the North Pacific deep water solely originates from other sources, namely the Southern Ocean and the Atlantic, and the coring location Juan de Fuca Ridge is relatively not subject to much upwelling, its deep ocean is a prime location for carbon sequestration and storage.

1. How does the strength of the biological pump, and therefore, biological productivity, change with respect to glacial-interglacial cycles?

2. Does the North Pacific foraminifera record at Juan de Fuca Ridge show that surface ocean is more 13C-enriched (photosynthesis-dominated) and deep ocean, 13C-depleted (respiration-dominated)?

Benthic foraminifera Uvigerina peregrina

Planktonic Foraminifera Neogloboquadrina pachyderma

1. AT-26-19-05 piston core (Juan de Fuca Ridge) North Pacific deep-sea sediments were sampled, processed, and washed.

2. Uvigerina peregrina and N. pachyderma were picked from coarse fractions by using a microscope and fine paintbrush.

3. The picked foraminifera were loaded into carousels for δ18O an δ13C analysis in the mass spectrometer.

Sampling

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Future Work

Figure 3. CO2 is

removed from the atmosphere in photosynthesis, enriching surface waters in 13C. Respiration and calcium carbonate formation depletes the ocean by releasing 12C into surrounding waters. The δ13C relative profile with respect to depth in the ocean is shown on the left.

Figure 5. The δ18O an δ13C are plotted for Uvigerina and NpL. The δ18O of Uvigerina is used as an age-depth model to identify interglacial-glacial cycles (marine isotope stages, MIS 1-13 are tentatively identified on the δ18O Uvigerina plot). The δ13C of Uvigerina (benthic) and NpL (planktonic) indicates relative productivity of the deep water and surface water, respectively, based on the respective habitats of the foraminifera. However, factors can complicate the interpretation of δ13C and biological productivity. For example, the circulation of the deep water may be relatively stagnant at a given time, and an unusually low productivity would be concluded for Uvigerina. During a glacial, the entire ocean negatively shifts ~0.3 ‰ δ13C from terrestrial carbon input. Even if this difference is taken into account, it is difficult to characterize and pinpoint the shift during the glacial. Taking the difference in δ13C of Uvigerina and NpL not only eliminates these potential errors of absolute productivity for either surface or deep ocean but also characterizes the relative strength of the biological pump with respect to each glacial and interglacial.

Figure 4. The strength of the biological pump is characterized by the δ13C of Uvigerina – NpL, with the plot of d18O of Uvigerina as a reference for time. The biological pump seems to follow glacial-interglacial cycles. Generally, glacials have a relatively strong biological pump, while interglacials have a relatively weak biological pump.

Photosynthesis enriches the surface water in 13C, while respiration causes the deep water to be depleted in 13C. This difference in δ13C is a perfect proxy for characterizing the strength of the biological pump, which is relatively strong during glacials and weak during interglacials.

What, if any, is the connection between volcanic activity and the biological pump, with respect climate changes in the North Pacific?

Funding for this research assistantship was provided by the Earth Institute and NSF. Special thanks to Kassandra Costa, Kelly Luis, Anna LoPresti, and Christy Jenkins for their help, dedication, and work on the SeaVOICE project.

(tl2581@columbia.edu) (jmcmanus@ldeo.columbia.edu)

Figure 1. As seen in the Vostok ice core record, atmospheric CO2 varied repeatedly in past ice age cycles, with low CO2 during glacials and high CO2 during interglacials. Glacial-interglacial cycles are driven by changes in solar insolation (Milankovitch cycles) (Petit et al., 1999).

References Petit, J.R. et al. (1999). Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica. Nature, 399 (429-436).

Lisieski, L. E. and Raymo, M. E. (2005). A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records. Paleoceanography, 20 (PA1003).

Juan de Fuca Ridge Site Map

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Figure 2. Tectonically spreading, Juan de Fuca Ridge is an active underwater volcanic mountain range in the North Pacific off the coast of Washington state, as Shown on the right. The location of JdFR piston cores (PC) are shown on the left. 05PC (circled in red), farthest from the Juan de Fuca Ridge (red band), was analyzed for this study.

Source: NOAA

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