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Perks, HM, Charles CD, Keeling RF.  2002.  Precessionally forced productivity variations across the equatorial Pacific. Paleoceanography. 17   10.1029/2000pa000603   AbstractWebsite

[1] Measurements of combustion oxygen demand (COD) in two sediment cores provide a record of paleoproductivity driven by surface-ocean dynamics in the equatorial eastern and western Pacific for the past 400,000 years. The COD time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods. The phase of this signal in the two cores is identical, to within chronological uncertainties, suggesting a common insolation forcing mechanism for the upper ocean across the equatorial Pacific. COD is also in phase with the precessionally forced component of global ice volume, as indicated by oxygen isotopes, and with atmospheric methane in the Vostok ice core. These relationships imply that the COD relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change.

Perks, HM, Keeling RF.  1998.  A 400 kyr record of combustion oxygen demand in the western equatorial Pacific: Evidence for a precessionally forced climate response. Paleoceanography. 13:63-69.   10.1029/97pa02892   AbstractWebsite

We have developed a combustion analysis technique for sediments which measures the amount of O-2 consumed by the reduced species. We have measured this quantity, which we call "combustion oxygen demand (COD)," on a carbonate-rich sediment core from the Ontong-Java Plateau in the western equatorial Pacific back to marine oxygen isotope stage 11. The precision of the COD technique is +/-6.3 mu mol O-2 g(-1), which corresponds to similar to+/-0.0076% wt C-org, assuming oxidation of organic carbon dominates the signal. The COD time series is characterized by values which are about twice as high during glacials as during interglacials, the largest shift occurring from 401 mu mol O-2 g(-1) in midstage 6 to 144 mu mol O-2 g(-1) at 5e, and is coherent with the oxygen isotope curve of Globigerinoides sacculifer in the same core at the Milankovitch frequencies of 100 and 41 kyr, Pronounced variations in the 19-23 kyr band suggest that the climate of the western equatorial Pacific is sensitive to precessional forcing, a response not apparent from other records obtained in this region.

Petrenko, VV, Severinghaus JP, Schaefer H, Smith AM, Kuhl T, Baggenstos D, Hua Q, Brook EJ, Rose P, Kulin R, Bauska T, Harth C, Buizert C, Orsi A, Emanuele G, Lee JE, Brailsford G, Keeling R, Weiss RF.  2016.  Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates. Geochimica et Cosmochimica Acta. 177:62-77.   10.1016/j.gca.2016.01.004   Abstract

Carbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from “old” carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26–19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high.