CaCO<sub>3</sub> size distribution: A paleocarbonate ion proxy?

Broecker, Wallace S.; Clark, Elizabeth

doi:10.1029/1999pa900016

Cited by 86 publications

(76 citation statements)

References 15 publications

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“…Proxy measures have been developed for past changes in ambient carbonate ion concentrations. One, based on analysis of foraminiferal size fractions [ Broecker and Clark , 1999] suggests an ∼11 μmol kg −1 decline in deep‐sea CO 3 2− concentration over the last 8 kyr [ Broecker et al , 1999, 2001]. Another, based on planktonic foraminifer abundance indicates only slightly higher (<5 μmol kg −1 ) deep Pacific CO 3 2− at the LGM compared to present [ Anderson and Archer , 2002].…”

Section: Methodsmentioning

confidence: 99%

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum

et al. 2003

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[1] We examine the effect on atmospheric CO 2 of the occurrence of increased shallow water carbonate deposition and regrowth of the terrestrial biosphere following the last glacial. We find that contrary to recent speculations that changes in terrestrial carbon storage were primarily responsible for the observed $20 ppmv late Holocene CO 2 rise, a more likely explanation is coral reef buildup and other forms of shallow water carbonate deposition during this time. The importance of a responsive terrestrial carbon reservoir may instead be as a negative feedback restricting the rate of CO 2 rise possible in the early stages of the deglacial transition. This separation in time of the primary impacts of regrowth of the terrestrial biosphere and increased shallow water carbonate deposition explains the occurrence of an early Holocene carbonate preservation event observed in deep-sea sediments. We demonstrate that their combined influence is also consistent with available proxy estimates of deep ocean carbonate ion concentration changes over the last 21 kyr. Accounting for the processes that act on the carbonate chemistry of the ocean as a whole then allows us to place strong constraints on the nature of the remaining processes that must be operating at the deglacial transition. By subtracting the net CO 2 effect of coral reef buildup and terrestrial biosphere regrowth from recent high-resolution ice core data, we highlight two periods, from 17.0 to 13.8 kyr and 12.3 to 11.2 kyr BP characterized by sustained rapid rates of CO 2 increase (>12 ppmv kyr À1 ). Because these periods are coincident with Southern Hemisphere ''deglaciation,'' we argue that changes in the biogeochemical properties of the Southern Ocean surface are the most likely cause.

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Section: Methodsmentioning

confidence: 99%

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum

et al. 2003

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“…Despite the similarities in terms of applicability for this kind of study, the two locations do have some notable differences. Bottom waters on the Ontong‐Java Plateau are undersaturated at depths well shallower than 3000 m, while the saturation horizon on the Ceara Rise is not reached until a depth of over 4000 m. Sediments on the Ontong‐Java Plateau show increases in several dissolution indices [ Broecker et al , 1999; Broecker and Clark , 1999a, 1999b; McCorkle et al , 1995; Lohmann , 1995] at depths shallower even than 2000 m; similar indices on the Ceara Rise do not show strong dissolution signatures until 4000 m or deeper [ Broecker and Clark , 2003]. Additionally, calcite content in the two locations is markedly different: the shallowest sediments on the Ceara rise are only about 65% calcite; by a depth of 4700 m (and a bottom‐water saturation of about 0.85), that has dropped to about 40%.…”

Section: Lysoclinementioning

confidence: 99%

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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“…The coarse fraction is a possible indicator of dissolution: carbonate dissolution commonly leads to fragmentation of foraminiferal tests, which decreases the coarse size fraction of bulk sediment (e.g. Berger et al, 1982;Broecker and Clark, 1999).…”

Section: Weight Percent Coarse Fractionmentioning

confidence: 99%

Ecological and evolutionary response of Tethyan planktonic foraminifera to the middle Eocene climatic optimum (MECO) from the Alano section (NE Italy)

Luciani

Giusberti

Agnini

et al. 2010

Palaeogeography, Palaeoclimatology, Palaeoecology

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a b s t r a c t a r t i c l e i n f oThe enigmatic middle Eocene climatic optimum (MECO) is a transient (∼ 500 kyr) warming event that significantly interrupted at ∼ 40 Ma the long-term cooling through the middle and late Eocene, eventually resulting in establishment of permanent Antarctic ice-sheet. This event is still poorly known and data on the biotic response are so far scarce. Here we present a detailed planktonic foraminiferal analysis of the MECO interval from a marginal basin of the central-western Tethys (Alano section, northeastern Italy). The expanded and continuous Alano section provides an excellent record of this event and offers an appealing opportunity to better understand the role of climate upon calcareous plankton evolution. A sapropel-like interval, characterized by excursions in both the carbon and oxygen bulk-carbonate isotope records, represents the lithological expression of the post-MECO event in the study area and follows the δ 18 O negative shift, interpreted as representing the MECO warming. High-resolution quantitative analysis performed on both N38 μm and N 63 μm fractions reveals pronounced and complex changes in planktonic foraminiferal assemblages indicating a strong environmental perturbation that parallels the variations of the stable isotope curves corresponding to the MECO and post-MECO intervals. These changes consist primarily in a marked increase in abundance of the relatively eutrophic subbotinids and of the small, low-oxygen tolerant Streptochilus, Chiloguembelina and Pseudohastigerina. At the same time, the arrival of the abundant opportunist eutrophic Jenkinsina and Pseudoglobigerinella bolivariana, typical species of very high-productivity areas, also occurs. The pronounced shift from oligotrophic to more eutrophic, opportunist, low-oxygen tolerant planktonic foraminiferal assemblages suggests increased nutrient input and surface ocean productivity in response to the environmental perturbation associated with the MECO. Particularly critical environmental conditions have been reached during the deposition of the sapropel-like beds as testified by the presence of common giant and/or odd morphotypes. This is interpreted as evidence of transient alteration in the ocean chemistry. The enhanced surface water productivity inferred by planktonic foraminiferal assemblages at the onset of the event should have resulted in heavier δ 13 C values. The recorded lightening of the carbon stable isotope preceding the maximum warmth therefore represents a robust indication that it derives principally by a conspicuous increase of pCO 2 . The increased productivity of surface waters, also supported by geochemical data, may have acted as mechanism for pCO 2 reduction and returned the climate system to the general Eocene cooling trend. The oxygen-depleted deep waters and the organic carbon burial following the peak of the MECO event represent the local response to the MECO warming and suggest that high sequestration of organic matter, if representing a widespread response to this event, m...

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CaCO₃ size distribution: A paleocarbonate ion proxy?

Cited by 86 publications

References 15 publications

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum

Respiration, dissolution, and the lysocline

Ecological and evolutionary response of Tethyan planktonic foraminifera to the middle Eocene climatic optimum (MECO) from the Alano section (NE Italy)

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CaCO3 size distribution: A paleocarbonate ion proxy?

Cited by 86 publications

References 15 publications

Implications of coral reef buildup for the controls on atmospheric CO2since the Last Glacial Maximum

Implications of coral reef buildup for the controls on atmospheric CO2since the Last Glacial Maximum

Respiration, dissolution, and the lysocline

Ecological and evolutionary response of Tethyan planktonic foraminifera to the middle Eocene climatic optimum (MECO) from the Alano section (NE Italy)

Contact Info

Product

Resources

About

CaCO₃ size distribution: A paleocarbonate ion proxy?

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum

Implications of coral reef buildup for the controls on atmospheric CO₂since the Last Glacial Maximum