Sediment size fractionation and focusing in the equatorial Pacific: Effect on <sup>230</sup>Th normalization and paleoflux measurements

Lyle, Mitchell W; Marcantonio, Franco; Moore, Willard S.; Murray, Richard W; Huh, Chih-An; Finney, Bruce P.; Murray, David; Mix, Alan C

doi:10.1002/2014pa002616

Cited by 17 publications

(20 citation statements)

References 56 publications

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“…Although questions have been raised concerning the assumptions inherent in this method, these questions have been addressed using a variety of approaches (R. F. Anderson et al, ; Costa & McManus, ; Francois et al, ; Mitchell & Huthnance, ; Singh et al, ), so we conclude that the method provides reliable estimates of the preserved fluxes of sedimentary constituents corrected for sediment focusing. Furthermore, our application of 230 Th xs ‐normalized accumulation rates is limited to proxies in the fine fraction of the sediments, which is not sensitive to the reported fractionation of the coarse (carbonate) fraction during sediment redistribution (Lyle et al, ).…”

Section: Methodsmentioning

confidence: 99%

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Anderson

Sachs

Fleisher

et al. 2019

Global Biogeochemical Cycles

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Enhanced ocean carbon storage during the Pleistocene ice ages lowered atmospheric CO2 concentrations by 80 to 100 ppm relative to interglacial levels. Leading hypotheses to explain this phenomenon invoke a greater efficiency of the ocean's biological pump, in which case carbon storage in the deep sea would have been accompanied by a corresponding reduction in dissolved oxygen. We exploit the sensitivity of organic matter preservation in marine sediments to bottom water oxygen concentration to constrain the level of dissolved oxygen in the deep central equatorial Pacific Ocean during the last glacial period (18,000–28,000 years BP) to have been within the range of 20–50 μmol/kg, much less than the modern value of ~168 μmol/kg. We further demonstrate that reduced oxygen levels characterized the water column below a depth of ~1,000 m. Converting the ice age oxygen level to an equivalent concentration of respiratory CO2, and extrapolating globally, we estimate that deep‐sea CO2 storage during the last ice age exceeded modern values by as much as 850 Pg C, sufficient to balance the loss of carbon from the atmosphere (~200 Pg C) and from the terrestrial biosphere (~300–600 Pg C). In addition, recognizing the enhanced preservation of organic matter in ice age sediments of the deep Pacific Ocean helps reconcile previously unexplained inconsistencies among different geochemical and micropaleontological proxy records used to assess past changes in biological productivity of the ocean.

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Section: Methodsmentioning

confidence: 99%

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Anderson

Sachs

Fleisher

et al. 2019

Global Biogeochemical Cycles

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“…The advantages of 230 Th normalization are (1) quantification of absolute particle fluxes, (2) elimination of dilution effects, (3) insensitivity to small errors in age model (about 1%/kyr), and (4) correction for lateral sediment inputs (e.g., focusing and winnowing). Although 230 Th normalization has been a topic of considerable debate in the equatorial Pacific [ Lyle et al , , , ; Francois et al , ; Marcantonio et al , ], the applicability of this technique has been justified in extensive detail [ Mollenhauer et al , , ; McGee et al , ; Costa and McManus , ], including across the equatorial Pacific [ Pichat et al , ; Anderson et al , , ; Kienast et al , ; McGee et al , , , Winckler et al , , ] and particularly at the Line Islands [ Costa et al , ; Jacobel et al ., , ].…”

Section: Methodsmentioning

confidence: 99%

Productivity patterns in the equatorial Pacific over the last 30,000 years

Costa

Jacobel

McManus

et al. 2017

Global Biogeochemical Cycles

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The equatorial Pacific traverses a number of productivity regimes, from the highly productive coastal upwelling along Peru to the near gyre-like productivity lows along the international dateline, making it an ideal target for investigating how biogeochemical systems respond to changing oceanographic conditions over time. However, conflicting reconstructions of productivity during periods of rapid climate change, like the last deglaciation, render the spatiotemporal response of equatorial Pacific productivity ambiguous. In this study, surface productivity since the last glacial period (30,000 years ago) is reconstructed from seven cores near the Line Islands, central equatorial Pacific, and integrated with productivity records from across the equatorial Pacific. Three coherent deglacial patterns in productivity are identified: (1) a monotonic glacial-Holocene increase in productivity, primarily along the Equator, associated with increasing nutrient concentrations over time; (2) a deglacial peak in productivity~15,000 years ago due to transient entrainment of nutrient rich southern-sourced deep waters; and (3) possible precessional cycles in productivity in the eastern equatorial Pacific that may be related to Intertropical Convergence Zone migration and potential interactions with El Niño-Southern Oscillation dynamics. These findings suggest that productivity was generally lower during the glacial period, a trend observed zonally across the equatorial Pacific, while deglacial peaks in productivity may be prominent only in the east.

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“…Dilution of CaCO 3 by bio-SiO 2 deposition appears to be relatively common in the middle and late Miocene (Holbourn et al, 2014;Lyle and Baldauf, 2015). For the most part, CaCO 3 burial was high since the end of the Miocene Climate Optimum, except within the late Miocene carbonate crash, 11-8 Ma (Lyle et al, 1995;Roth et al, 2000;Lyle and Baldauf, 2015). Poorest CaCO 3 preservation occurred at about 9.7 Ma.…”

Section: Disentangling Production Versus Dissolutionmentioning

confidence: 96%

Late Miocene to Holocene high-resolution eastern equatorial Pacific carbonate records: stratigraphy linked by dissolution and paleoproductivity

et al. 2019

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Abstract. Coherent variation in CaCO3 burial is a feature of the Cenozoic eastern equatorial Pacific. Nevertheless, there has been a long-standing ambiguity in whether changes in CaCO3 dissolution or changes in equatorial primary production might cause the variability. Since productivity and dissolution leave distinctive regional signals, a regional synthesis of data using updated age models and high-resolution stratigraphic correlation is an important constraint to distinguish between dissolution and production as factors that cause low CaCO3. Furthermore, the new chronostratigraphy is an important foundation for future paleoceanographic studies. The ability to distinguish between primary production and dissolution is also important to establish a regional carbonate compensation depth (CCD). We report late Miocene to Holocene time series of XRF-derived (X-ray fluorescence) bulk sediment composition and mass accumulation rates (MARs) from eastern equatorial Pacific Integrated Ocean Drilling Program (IODP) sites U1335, U1337, and U1338 and Ocean Drilling Program (ODP) site 849, and we also report bulk-density-derived CaCO3 MARs at ODP sites 848, 850, and 851. We use physical properties, XRF bulk chemical scans, and images along with available chronostratigraphy to intercorrelate records in depth space. We then apply a new equatorial Pacific age model to create correlated age records for the last 8 Myr with resolutions of 1–2 kyr. Large magnitude changes in CaCO3 and bio-SiO2 (biogenic opal) MARs occurred within that time period but clay deposition has remained relatively constant, indicating that changes in Fe deposition from dust is only a secondary feedback to equatorial productivity. Because clay deposition is relatively constant, ratios of CaCO3 % or biogenic SiO2 % to clay emulate changes in biogenic MAR. We define five major Pliocene–Pleistocene low CaCO3 % (PPLC) intervals since 5.3 Ma. Two were caused primarily by high bio-SiO2 burial that diluted CaCO3 (PPLC-2, 1685–2135 ka, and PPLC-5, 4465–4737 ka), while three were caused by enhanced dissolution of CaCO3 (PPLC-1, 51–402 ka, PPLC-3, 2248–2684 ka, and PPLC-4, 2915–4093 ka). Regional patterns of CaCO3 % minima can distinguish between low CaCO3 caused by high diatom bio-SiO2 dilution versus lows caused by high CaCO3 dissolution. CaCO3 dissolution can be confirmed through scanning XRF measurements of Ba. High diatom production causes lowest CaCO3 % within the equatorial high productivity zone, while higher dissolution causes lowest CaCO3 percent at higher latitudes where CaCO3 production is lower. The two diatom production intervals, PPLC-2 and PPLC-5, have different geographic footprints from each other because of regional changes in eastern Pacific nutrient storage after the closure of the Central American Seaway. Because of the regional variability in carbonate production and sedimentation, the carbonate compensation depth (CCD) approach is only useful to examine large changes in CaCO3 dissolution.

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Sediment size fractionation and focusing in the equatorial Pacific: Effect on ²³⁰Th normalization and paleoflux measurements

Cited by 17 publications

References 56 publications

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Productivity patterns in the equatorial Pacific over the last 30,000 years

Late Miocene to Holocene high-resolution eastern equatorial Pacific carbonate records: stratigraphy linked by dissolution and paleoproductivity

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Sediment size fractionation and focusing in the equatorial Pacific: Effect on 230Th normalization and paleoflux measurements

Cited by 17 publications

References 56 publications

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

Productivity patterns in the equatorial Pacific over the last 30,000 years

Late Miocene to Holocene high-resolution eastern equatorial Pacific carbonate records: stratigraphy linked by dissolution and paleoproductivity

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Sediment size fractionation and focusing in the equatorial Pacific: Effect on ²³⁰Th normalization and paleoflux measurements