Climate in Earth History Studies in Geophysics (1982) / Chapter Skim
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4 The Carbon Cycle--Controls on Atmosphere CO2 and Climate in the Geologic Past
4 The Carbon Cycle--Controls on Atmosphere CO2 and Climate in the Geologic Past
Pages 55-67
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From page 55... ...
, will spread to the others through a series of feedback mechanisms. The marine sedimentary record—changes in lithology, chemistry, stable isotopic composition, and the biotic constituents of pelagic sediments—is a monitor of changes in ocean chemistry, and through consideration of the feedback mechanism one can deduce possible variations in global climate.
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From page 56... ...
in buffering changes in pCO2 and consequent changes in climate. The discus ion deals first with the extent of possible excursions in atmospheric PCO2 and their causes, the operation of the geologic carbon cycle, and the feedback mechanisms that appear to help damp pCO2 f uch~ations (i.e., long- and short-term buffers)
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From page 57... ...
. Decreased fertility could 57 drastically affect the rate of burial of marine organic matter and the ability of the ocean system to absorb "excess" atmospheric CO..
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From page 58... ...
The operation of the carc~nrr cycle is one of the most important in this regard as it ultimately controls levels of oxygen and carbm~ dioxide in the atmosphere. The carbon cycle is responsive to changes in climate and oceanography and is cmrpled to nutrients cycles if climate is influenced by varying levels of atmospheric CO,, for example, controls on atmospheric pCO3 levels are therefore important to understand This understanding must include adequate knowledge of COz sources and source strengths, the allowable excursions of pCO2 levels within the limitations imposed on the operation of global carbon cycle by nutrient availability, net productivity and burial of organic carbon, carbonate sedimentation and dissolution, weathering rates and reactions (Figures 4 1 and 4 2)
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From page 59... ...
Burial of terrestrial organic matter in marine sediments is also important. Evidence suggests that, at present, relatively little land-derived organic mat+er reaches the deep sea beyond the shelf (e.g., Hunt, 1970; Sackett, 1964; Sackett and Thompson, 1963; Sackett et al., 1965 Rogers and Koons, 1969)
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From page 60... ...
. Carbon Isoto pes in Pelagic Carbonates as Constraints on Carbon Cycling Consideranon of tbe possible past excursions of atmospheric CO2 has I een made by examining constraints on changes in ocean chemistry imposed by dhe composinon of marine chemical sediments—main y evaporites and carbonates— through time and by examining ohanges in tbe carbon isotopic composition (li 13C values)
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From page 61... ...
evidence of increased dissolution of carbonate in the deep sea and possible decreases in the rate of accumulation in deep-sea sediments; (2) changes in the s 13C values of total carbon in the oceanic reservoir as ref ected in analyses of pelagic carbonate bu k samples, or preferably both benthic and planktonic organisms, through the time interval in question; (3)
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From page 62... ...
. The accumulation rates of carbonate in the deep sea were also at a low point in the early Paleocene, as were those of organic carbon.
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From page 63... ...
, and a decrease in deep-sea carbonate accumulation rates, as well as an elevated b13C gradient and more positive &13C values. Deep-sea accumulation rates of organic carbon remained low, as in the Oligocene, but were high around the continental margins and began to increase in the deep sea in the Late Miocene.
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From page 64... ...
Stable stratification related to salinitv contrasts between surface and deep waters may have been one mechanism for the development of poorly oxygenated deep waters (Ryan and Cita, 1977 Rotb, 1978; Thiersten and Berger, 1978; Arthur and Nadand, 1979) ; some of the most saline deep vvater may have been derived from periodic spillage from the evaporatic northern South Atlanbc and from epicontinental and shelf seas in low lantudes.
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From page 65... ...
More definite reconstructions of the relationship between changes in atmospheric CON, ocean chemistry, and climate will depend on collecting and analyzing large amounts of data on accumulation rates of organic matter and carbonate in marine sediments through time, on the bulk chemistry of sediment, and on the carbon isotopic composition of organic rnatter and carbonate. Time series of such data, in conjunedon with those of isotopic paleotemperatures and faunal studies, will aid in examining the interrelationships of climate and ocean chemistry and will allow better estimation of leads and lags in the system.
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From page 66... ...
and some Pale cone palentemperatures and carbon isotope variations in the Atlantic Ocean, in Initial Reports of the Deep Sea Drilling Pro ject 43, U.S Government Printing Office, Washington, D.C., pp.
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From page 67... ...
. Cretaceous nannoplankton biostratigraphy and oceanography of the northwestern Atlantic Ocean, in initial Peports oJ the Deep Sea Drilling Project 44, U S
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