The Holocene preservation history of equatorial Pacific sediments

Oxburgh, Rachel

doi:10.1029/97pa02607

Cited by 20 publications

(20 citation statements)

References 33 publications

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“…Dissolution at or above the sediment‐water interface has long been shown to produce a trend of older bulk carbonate age with water depth (Broecker et al, ). We see this same trend in bulk radiocarbon age (Figure a), consistent with the previous studies on the Ontong‐Java Plateau (Broecker et al, , ), and with a body of literature arguing that a substantial portion of carbonate dissolution must occur at the sediment‐water interface (Broecker et al, ; Hales & Emerson, ; Martin et al, ; Oxburgh, ; Oxburgh & Broecker, ).…”

Section: Discussionsupporting

confidence: 90%

“…With a known value of R nc at the Ontong‐Java Plateau of 0.2 g·cm −2 ·kyr −1 (Oxburgh, ) and measured values of f f and

f_{{CaCO}_{3}}

, equations and can be used to calculate the steady‐state preservation flux of coccoliths and foraminifera (Figure d).…”

Section: Resultsmentioning

confidence: 99%

“…The radiocarbon age of bulk carbonate in surface sediments has helped to elucidate some of the mechanistic controls on dissolution. At many locations, surface sediments show increasing radiocarbon ages with water depth, implying that a significant portion of dissolution occurs at or above the sediment‐water interface (Broecker et al, , ; Oxburgh & Broecker, ; Oxburgh, ; Martin et al, ). Barker et al () also documented radiocarbon age offsets between planktic foraminiferal species and also between whole foraminiferal tests and their fragments.…”

Section: Introductionmentioning

confidence: 99%

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Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Subhas¹,

McCorkle

Quizon

et al. 2019

Paleoceanog and Paleoclimatol

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Dissolution of calcite in deep ocean sediments, which is required to balance global marine CaCO 3 production and burial fluxes, is still a poorly understood process. In order to assess the mechanisms of dissolution in sediments, we analyzed four multicore tops taken along a depth transect on the Ontong-Java Plateau. These cores were taken directly on the equator, and span water column calcite saturation states from ∼0.93 to ∼0.74, allowing us to assess the effect of dissolution on carbonate sediment composition. The top 2 cm of each multicore was sectioned and sieved to separate coccolith from foraminiferal calcite, and the %CaCO 3 , 13 C, Δ 14 C, and Mg/Ca were evaluated. The mass ratio of coccoliths to foraminifera increases by a factor of 3 as a function of water depth, reflecting the preferential dissolution of foraminifera. Carbon isotope ( 13 C and Δ 14 C) data suggest that most dissolution takes place at the sediment-water interface and primarily affects foraminifera. Mg/Ca analyses indicate that the Mg content of the entire foraminiferal assemblage decreases as a function of dissolution. In contrast, coccolith dissolution takes place within the sediments, rather than at the interface. Together these two processes cause coccoliths to be up to 1,000 radiocarbon years younger than foraminifera from the same depth horizon. Despite this within-sediment coccolith dissolution flux, sediments below the calcite saturation horizon remain enriched in coccolith calcite. Combined with global seafloor hypsometry and calcium carbonate content, this enrichment suggests that globally, coccoliths may outweigh foraminifera in deep ocean sediments by a factor of 1.8.

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Section: Discussionsupporting

confidence: 90%

“…With a known value of R nc at the Ontong‐Java Plateau of 0.2 g·cm −2 ·kyr −1 (Oxburgh, ) and measured values of f f and

f_{{CaCO}_{3}}

, equations and can be used to calculate the steady‐state preservation flux of coccoliths and foraminifera (Figure d).…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Subhas¹,

McCorkle

Quizon

et al. 2019

Paleoceanog and Paleoclimatol

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“…The model is steady state. Several authors have questioned whether or not the mixed layer, which likely has a mean age of a few thousand years, can be considered in steady state, especially at the Ontong‐Java Plateau [ Archer , 1996a, 1996b; Oxburgh , 1998; Matsumoto et al , 2001]. This is a much larger issue than I can hope to address in this paper, and I will not attempt to.…”

Section: Lysoclinementioning

confidence: 91%

Respiration, dissolution, and the lysocline

Hales

2003

Paleoceanography

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[1] Here I synthesize the results of several types of measurements of organic carbon respiration and calcium carbonate dissolution rates in pelagic seafloor sediments. Measurements of pore water oxygen demonstrate that most of the respiration takes place very near the sediment-water interface, with a scale depth of a few millimeters. The remainder of the oxic respiration occurs much deeper in the sediments, with a scale depth of several centimeters. All measures of respiration from locations as disparate as the tropical Pacific and Atlantic, and the subtropical North Atlantic agree that pelagic seafloor rates of oxic respiration of organic carbon are relatively independent of depth and location, with the exception of sediments beneath the Pacific eastern equatorial upwelling zone. Calcite dissolution in seafloor sediments requires forcing by respiration-produced CO 2 , and rates are consistent with a first-order dependence on pore water undersaturation, solubility as determined by Mucci [1983] at atmospheric pressure, and locally variable mass-specific dissolution rate constants. Respiration-driven calcite dissolution fluxes predicted by this combination of respiration and dissolution rate expressions are significantly lower than many previous estimates. Comparison of dissolution fluxes in the oligotrophic open ocean measured by other researchers with benthic chamber incubation techniques with those predicted by this combination of rate expressions is, within stated uncertainties, in agreement in all but one case, questioning the need for complicated mechanisms such as surface buffering or authigenic precipitation to explain seafloor calcite diagenesis. Applying these kinetics to a simple one-dimensional, steady state model of the bulk calcite content and sediment accumulation rates of the sediment mixed layer yields results consistent with observations of the seafloor lysocline, the region of transition from high calcite to lowcalcite sediments, on the Ceara Rise in the western tropical North Atlantic and the Ontong-Java Plateau in the western equatorial Pacific. Scenarios ignoring dissolution driven by respiration-produced CO 2 in pore waters and using the high-order dependence on undersaturation and very large dissolution rate constants implied by some earlier laboratory studies do not simulate these observations. While the scheme represented here does, in fact, imply a strong shift in the locus of carbonate dissolution toward the sediment water interface as bottomwater saturation decreases, as implied by the observations of Martin et al. [2000], no simple combination of sediment transport coefficients and reaction kinetics can reproduce the observation of increasing 14 C age as dissolution progresses. These results emphasize the importance of accurate knowledge of the kinetics of respiration and dissolution to interpretation of either the present-day or paleolysocline.

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“…Instead, she posited that dissolution occurred while the grains rested on the sea floor, before they were mixed into the sediment. In this case, an increase in the core-top 14 C age with water depth would be expected, because the input of CaCO 3 to the sediment would correspondingly decrease (Oxburgh 1998).…”

Section: Figurementioning

confidence: 99%

Wally's Quest to Understand the Ocean's CaCO₃ Cycle

2009

Annu. Rev. Mar. Sci.

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Aspects of the production and dissolution of CaCO 3 hard parts dominate the literature regarding contemporary marine chemistry and paleoceanography. During my long career I have contributed more than 200 papers related to this subject. In this prefatory article in the first volume of the Annual Review of Marine Science, I recount what I consider to be the highlights of my attempts to understand the cycle of CaCO 3 in today's ocean and in oceans of the past. These studies began in the Bahamas in the early 1960s and then quickly graduated to the world ocean. Although much of my research has involved stable and radioisotopes contained in shells and coral directed toward reconstruction of the late Quaternary operation of the earth system, in this review I concentrate on carbonate chemistry and, in particular, the compensation in the deep sea for the overproduction of CaCO 3 by marine organisms.1

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The Holocene preservation history of equatorial Pacific sediments

Cited by 20 publications

References 33 publications

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Respiration, dissolution, and the lysocline

Wally's Quest to Understand the Ocean's CaCO₃ Cycle

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The Holocene preservation history of equatorial Pacific sediments

Cited by 20 publications

References 33 publications

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Respiration, dissolution, and the lysocline

Wally's Quest to Understand the Ocean's CaCO3 Cycle

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Product

Resources

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Wally's Quest to Understand the Ocean's CaCO₃ Cycle