Modelled glacial and non-glacial HCO3−, Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO2 concentrations and a potential proxy of continental chemical erosion, the marine Ge/Si ratio

Jones, Ian; Munhoven, Guy; Tranter, Martyn; Huybrechts, Philippe; Sharp, Martin

doi:10.1016/s0921-8181(02)00067-x

Cited by 42 publications

(36 citation statements)

References 36 publications

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“…Driving all oxidation by atmospheric O 2 would consume 5-14 × 10 11 mol O 2 /y, or 5-14 × 10 15 mol O 2 over 10 ky, less than 0.01-0.04% of the atmospheric reservoir of ∼4 × 10 19 mol O 2 and within the range of observed declines in pO 2 over the past 1 My (46). Similarly, proxies or models of total weathering fluxes to the oceans (36,47,48) may not capture modest increases in these sulfate fluxes because oxidative weathering is a small portion of the total global weathering flux.…”

Section: Discussionmentioning

confidence: 99%

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

Torres

Moosdorf

Hartmann

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

157

171

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Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO 2 , we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO 2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean-atmosphere CO 2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO 2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O 2 . Future work on glaciation-weathering-carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.weathering | carbon cycle | glaciation | oxidation | sulfide E pisodes of glaciation represent some of the most dramatic changes in the history of Earth's climate. Basic questions remain unanswered about why the planet has occasionally but not always supported glaciers, about why some glaciations have been more intense than others, and about how glaciers have shaped Earth's landscapes, chemical cycles, and climate. Before the Phanerozoic (i.e., before ∼540 Mya), several glaciations are thought to have approached complete or near-complete planetary ice cover ("Snowball Earth" events; ref. 1). In contrast, more recent glaciations, including the Quaternary glaciations of the last million years, have been characterized by oscillating climate with ice extent limited to high latitudes even during glacial maxima (2). The formation of ice cover has long been known to fundamentally alter Earth's environment, changing albedo (3), influencing atmospheric and ocean circulation (4), and reshaping landscapes (5). These diverse effects may contribute to planetary-scale feedbacks that influence the transition to and the evolution of glaciation.Chemical weathering influences the composition of the atmosphere by releasing ionic species from minerals that alter the alkalinity and redox condition of the ocean-atmosphere system. Weathering of silicate minerals produces alkalinity, removing carbon from the at...

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Section: Discussionmentioning

confidence: 99%

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

Torres

Moosdorf

Hartmann

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

157

171

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“…However, the presence of glaciers, drier atmospheric conditions and the exposure of continental shelves due to lower sea level would have increased the supply of carbonates to the ocean (Gibbs and Kump, 1994;Riebe et al, 2004), thereby increasing ocean alkalinity and further deepening the carbonate saturation horizon. This mechanism has been largely refuted as having a significant effect on the glacial-interglacial difference in the carbon budget (Brovkin et al, 2007;Foster and Vance, 2006;Jones et al, 2002) and can therefore be ignored.…”

Section: Reconciling Carbonate Chemistrymentioning

confidence: 99%

The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

et al. 2016

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Abstract. The ocean's ability to store large quantities of carbon, combined with the millennial longevity over which this reservoir is overturned, has implicated the ocean as a key driver of glacial-interglacial climates. However, the combination of processes that cause an accumulation of carbon within the ocean during glacial periods is still under debate. Here we present simulations of the Last Glacial Maximum (LGM) using the CSIRO Mk3L-COAL (Carbon-OceanAtmosphere-Land) earth system model to test the contribution of physical and biogeochemical processes to ocean carbon storage. For the LGM simulation, we find a significant global cooling of the surface ocean (3.2 • C) and the expansion of both minimum and maximum sea ice cover broadly consistent with proxy reconstructions. The glacial ocean stores an additional 267 Pg C in the deep ocean relative to the pre-industrial (PI) simulation due to stronger Antarctic Bottom Water formation. However, 889 Pg C is lost from the upper ocean via equilibration with a lower atmospheric CO 2 concentration and a global decrease in export production, causing a net loss of carbon relative to the PI ocean. The LGM deep ocean also experiences an oxygenation (> 100 mmol O 2 m −3 ) and deepening of the calcite saturation horizon (exceeds the ocean bottom) at odds with proxy reconstructions. With modifications to key biogeochemical processes, which include an increased export of organic matter due to a simulated release from iron limitation, a deepening of remineralisation and decreased inorganic carbon export driven by cooler temperatures, we find that the carbon content of the glacial ocean can be sufficiently increased (317 Pg C) to explain the reduction in atmospheric and terrestrial carbon at the LGM (194 ± 2 and 330 ± 400 Pg C, respectively). Assuming an LGM-PI difference of 95 ppm pCO 2 , we find that 55 ppm can be attributed to the biological pump, 28 ppm to circulation changes and the remaining 12 ppm to solubility. The biogeochemical modifications also improve model-proxy agreement in export production, carbonate chemistry and dissolved oxygen fields. Thus, we find strong evidence that variations in the oceanic biological pump exert a primary control on the climate.

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“…Some ocean box models of the PANDORA/CYCLOPS type were applied for glacial-interglacial transient simulations (e.g. Sigman et al, 1998;Jones et al, 2002). Especially for the latter type of models the terrestrial biosphere was so far ignored.…”

Section: Introductionmentioning

confidence: 99%

Simulating changes in the terrestrial biosphere during the last glacial/interglacial transition

Köhler

Fischer

2004

Global and Planetary Change

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The state of the terrestrial biosphere during the Holocene and the Last Glacial Maximum (LGM) was estimated from data bases and steady state simulations in former studies. Here, we use these previous estimates and run a simple globally averaged box model of the terrestrial carbon stocks driven by various paleorecords (temperature, pCO 2 , sea level) from the LGM across termination I to the Holocene to determine which forcing might be appropriate to explain observed changes in the biosphere. Former forcing strength of this type of model on recent climate changes is not transferable to our problem of glacial/interglacial variations. The modelled terrestrial carbon stock at the LGM is about 1600 PgC, 600 PgC less than in preindustrial times. The oceanic release of carbon during the last 20 kyr seems to be in phase with the atmospheric pCO 2 record, but four times larger than the pCO 2 increase due to the build-up of the terrestrial stocks. Calculated changes in oceanic δ 13 C correspond well with data and suggest not only a significant role of the biosphere on atmospheric δ 13 C during stable climate conditions such as the LGM or the Holocene, but also during the transition. A final identification of the relative importance of either climate change or CO 2 fertilization for fixation of carbon in the terrestrial biosphere is not yet possible.

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Modelled glacial and non-glacial HCO3−, Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO2 concentrations and a potential proxy of continental chemical erosion, the marine Ge/Si ratio

Cited by 42 publications

References 36 publications

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

The simulated climate of the Last Glacial Maximum and insights into the global marine carbon cycle

Simulating changes in the terrestrial biosphere during the last glacial/interglacial transition

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