The origin of the 1500-year climate cycles in Holocene North-Atlantic records
Maxime DebretViviane Bout‐RoumazeillesF. GroussetM. DesmetJerry F McManusNicolas MasséiDavid SebagJean‐Robert PetitYoann CopardAlain Trentesaux
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Abstract. Since the first suggestion of 1500-year cycles in the advance and retreat of glaciers (Denton and Karlen, 1973), many studies have uncovered evidence of repeated climate oscillations of 2500, 1500, and 1000 years. During last glacial period, natural climate cycles of 1500 years appear to be persistent (Bond and Lotti, 1995) and remarkably regular (Mayewski et al., 1997; Rahmstorf, 2003), yet the origin of this pacing during the Holocene remains a mystery (Rahmstorf, 2003), making it one of the outstanding puzzles of climate variability. Solar variability is often considered likely to be responsible for such cyclicities, but the evidence for solar forcing is difficult to evaluate within available data series due to the shortcomings of conventional time-series analyses. However, the wavelets analysis method is appropriate when considering non-stationary variability. Here we show by the use of wavelets analysis that it is possible to distinguish solar forcing of 1000- and 2500- year oscillations from oceanic forcing of 1500-year cycles. Using this method, the relative contribution of solar-related and ocean-related climate influences can be distinguished throughout the 10 000 Holocene intervals since the last ice age. These results reveal that the mysteriously regular 1,500-year climate cycles are linked with the oceanic circulation and not with variations in solar output as previously argued (Bond et al., 2001). In this light, previously studied marine sediment (Bianchi and McCave, 1999; Giraudeau et al., 2000), ice core (O'Brien et al., 1995) and dust records (Jackson et al., 2005) can be seen to contain the evidence of combined forcing mechanisms, whose relative influences varied during the course of the Holocene. Circum-Atlantic climate records cannot be explained by solar forcing, but require changes in ocean circulation, as suggested previously (Broecker et al., 2001; McManus et al., 1999).Keywords:
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The Greenland Ice Sheet Project 2 (GISP2) ice core dust profile in glacial (Wisconsinan) ice from Central Greenland has been measured using Laser‐Light Scattering (LLS) from ice. This data exhibits considerable high frequency variability. By applying appropriate running averages to the data, certain regularities emerge. Thus, for example, when the data was smoothed with rectangular 4 and 5 year running averages, ∼11 year dust modulations of considerable amplitude were revealed. In this paper, we show how further smoothing of the data causes very large, longer period dust modulations centered at ∼91 years in a Gaussian distribution to emerge. We believe that this corresponds to the 80–90 year modulation of the 11 year sunspot cycle first suggested by Gleissberg. We also show how adjacent 11 year dust periods can combine in a unique way to generate a 22 year (Hale) period of dust modulation. The way this occurs is similar to that by which a 22 year modulation of the measured terrestrial neutron flux is generated from two 11 year periods. Taken together with our observation of a ∼200 year (Suess) dust modulation period, these observations strengthen our claim that the dust modulations we measured in GISP2 ice are solar induced and suggest a mechanism for their production.
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Abstract. During the Mid-Pleistocene Transition (MPT), ca. 1250–800 kya, the Earth’s glacial cycles changed from 41 ky to 100 ky periodicity. The emergence of this longer ice-age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume in interglacial periods. Since there is no known change in external orbital forcing across the MPT, it is generally agreed that the cause of this transition is internal to the earth system. Resolving the climate–carbon cycle–cryosphere dynamics processes responsible for the MPT remains a major challenge in ice core and climate science. To address this challenge, the international ice core community has prioritized recovery of an ice core record spanning the MPT interval. The results from such ‘oldest ice’ projects are still several years away. Our objective here it to make an advanced prediction of atmospheric CO2 out to 1.5 my. Our prediction utilizes existing records of atmospheric carbon dioxide (CO2) from Antarctic ice cores spanning the past 800 ky along with the existing benthic water stable isotope (ẟ18O) record from marine sediment cores. Our predictions assume that the relationship between CO2 and benthic ẟ18O over the past 800 thousand years can be extended over the last one and a half million years. The implied null hypothesis is that there has been no fundamental change in the global climate–carbon cycle–cryosphere feedback systems across the MPT. We find that our predicted CO2 record is significantly lower during glacial intervals than the existing blue-ice and boron isotope-based estimates of CO2 that pre-date the continuous 800 ky CO2 record. Our predicted glacial CO2 concentrations are ~9 ppm below glacial CO2 concentrations observed in blue ice data at ca. 1 mya and ~19 ppm below glacial CO2 concentrations reconstructed from boron isotopic data over ca ~1.1–1.25 mya. These results support rejection of our null hypothesis and provide quantitative evidence of a fundamental shift in the global climate–carbon cycle–cryosphere feedback systems across the MPT. However, the definitive test of the various theories explaining the MPT will be comparison of our predicted records with the forthcoming oldest ice core records.
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We have re‐examined the dust record from the GISP2 ice core retrieved from central Greenland and found that the background dust concentration is modulated with a period of 11 years all the way back to ice from at least 100,000 yrs BP. The only known, relevant, naturally occurring phenomenon with such a period is the well‐known solar cycle. We believe that the background modulation we observe is related to the solar cycle and discuss this hypothesis.
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Ice cores are known to yield information about astronomical phenomena as well as information about past climate. We report time series analyses of annually resolved nitrate variations in an ice core, drilled at the Dome Fuji station in East Antarctica, corresponding to the period from CE 1610 to 1904. Our analyses revealed clear evidence of ~11, ~22, and ~90 year periodicities, comparable to the respective periodicities of the well-known Schwabe, Hale, and Gleissberg solar cycles. Our results show for the first time that nitrate concentrations in an ice core can be used as a proxy for past solar activity on decadal to multidecadal time scales. Furthermore, 11-year and 22-year periodicities were detected in nitrate variations even during the Maunder Minimum (1645-1715), when sunspots were almost absent. This discovery may support cyclic behavior of the solar dynamo during the grand solar minimum.
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A number of recent reports have interpreted paleoproxy data to describe the state of the tropical Pacific, especially changes in the behavior of the El Niño‐Southern Oscillation (ENSO), over the Holocene. These interpretations are often contradictory, especially for the eastern tropical Pacific and adjacent areas of South America. Here we suggest a picture of the mid‐Holocene tropical Pacific region which reconciles the data. ENSO variability was present throughout the Holocene but underwent a steady increase from the mid‐Holocene to the present. In the mid‐Holocene, extreme warm El Niño events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial Pacific and largely arid coastal regions as in the present climate. This picture emerges from an experiment in which a simple numerical model of the coupled ocean‐atmosphere system in the tropical Pacific was driven by orbital forcing. We suggest that the observed behavior of the tropical Pacific climate over the mid‐ to late Holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics, which dominates extratropical influences.
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Two cores of mid-Holocene raised-bog deposits from the Netherlands were 14 C wiggle-match dated at high precision. Changes in local moisture conditions were inferred from the changing species composition of consecutive series of macrofossil samples. Several wet-shifts were inferred, and these were often coeval with major rises in the Δ 14 C archive (probably caused by major declines in solar activity). The use of Δ 14 C as a proxy for changes in solar activity is validated. This paper adds to the increasing body of evidence that solar variability forced climatic changes during the Holocene.
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During the Mid-Pleistocene Transition (MPT), ca. 1250–800 kya, the Earth’s glacial cycles changed from 41 ky to 100 ky periodicity. The emergence of this longer ice-age periodicity was accompanied by higher global ice volume in glacial periods and lower global ice volume in interglacial periods. Since there is no known change in external orbital forcing across the MPT, it is generally agreed that the cause of this transition is internal to the earth system. Resolving the climate–carbon cycle–cryosphere dynamics processes responsible for the MPT remains a major challenge in ice core and climate science. To address this challenge, the international ice core community has prioritized recovery of an ice core record spanning the MPT interval. The results from such ‘oldest ice’ projects are still several years away. Our objective here it to make an advanced prediction of atmospheric CO2 out to 1.5 my. Our prediction utilizes existing records of atmospheric carbon dioxide (CO2) from Antarctic ice cores spanning the past 800 ky along with the existing benthic water stable isotope (áº18O) record from marine sediment cores. Our predictions assume that the relationship between CO2 and benthic áº18O over the past 800 thousand years can be extended over the last one and a half million years. The implied null hypothesis is that there has been no fundamental change in the global climate–carbon cycle–cryosphere feedback systems across the MPT. We find that our predicted CO2 record is significantly lower during glacial intervals than the existing blue-ice and boron isotope-based estimates of CO2 that pre-date the continuous 800 ky CO2 record. Our predicted glacial CO2 concentrations are ~9 ppm below glacial CO2 concentrations observed in blue ice data at ca. 1 mya and ~19 ppm below glacial CO2 concentrations reconstructed from boron isotopic data over ca ~1.1–1.25 mya. These results support rejection of our null hypothesis and provide quantitative evidence of a fundamental shift in the global climate–carbon cycle–cryosphere feedback systems across the MPT. However, the definitive test of the various theories explaining the MPT will be comparison of our predicted records with the forthcoming oldest ice core records.
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