Earth Orbital Parameters Research Articles

Holocene glacier variability: three case studies using an intermediate-complexity climate model

Synthetic glacier length records are generated for the Holocene epoch using a process-based glacier model coupled to the intermediate-complexity climate model ECBilt. The glacier model consists of a mass-balance component and an ice-flow component. The climate model is forced by the insolation change due to variations in the Earth's orbital parameters. We consider three glaciers, ranging from maritime to continental. At Nigardsbreen (southern Norway), the simulated long-term trend in the annual mass-balance is primarily determined by summer temperature, with a smaller contribution from winter precipitation. In the early Holocene, summers were warmer and winters wetter than today in the ECBilt simulation. Both signals seems consistent with proxy data. The simulated glacier length shows a phase of rapid expansion during the mid-Holocene, followed by more gradual growth. At Rhonegletscher (the Swiss Alps), ECBilt simulates warmer and wetter summers in the early Holocene. The temperature signal seemns realistic, but proxy data and earlier modelling results are not conclusive with respect to the precipitation signal. The implied glacier length shows a maximum extent at 3-5 kyr BP, which seems unlikely. This suggests that the simulated precipitation response is not realistic. The simulated early-Holocene climate at Abramov glacier (Kirghizia) is characterized by high summer precipitation, associated with a northward extension of the Asian monsoon. The precipitation signal reaches its maximum around 6 kyr BP, which is consistent with the timing of the maximum in lake-level data. The simulated glacier length shows a pronounced postglacial maximum at the time of maximum monsoon intensity. There is considerable centennial-timescale variability in the simulated glacier length records. These length variations are generated by internal climatic variability. They are typically asynchronous among the three different glaciers. ECBilt has reasonable skill in simulating the relative importance of temperature and precipitation as well as the seasonality of the forcing, although the overall level of variability is underestimated. Length variations are shown to behave as a lagged moving-average process, with a glacier-specific memory.

Last Glacial Maximum over China: Sensitivities of climate to paleovegetation and Tibetan ice sheet

With the boundary conditions appropriate for the Last Glacial Maximum (LGM), including ice sheets, sea surface temperatures, sea‐ice distribution, atmospheric CO2 concentration, the Earth's orbital parameters, topography, and coastline, the atmospheric general circulation model of the Institute of Atmospheric Physics (IAP‐AGCM) computes colder and drier conditions than for present day. Global annual‐average surface temperature decreased by 5.3°C, and terrestrial precipitation was down by 29%. It is shown that IAP‐AGCM LGM simulation compares favorably to results from other AGCMs, and/but generally shows a weak terrestrial cooling when compared to paleoclimatic reconstructions in tropics. The 21 ka (ka: thousands of years ago) vegetation reconstruction is introduced into the model to study the regional climate response to the changes in vegetation and associated soil characteristics over China. The additional cooling due to these two changes reduces, to a certain degree, the model‐data discrepancies. In addition, under the precondition of continental ice existing over part of the Tibetan Plateau at the LGM, the authors examine the regional climate response to the continental ice. It follows that the glacial‐age environment over the Tibetan Plateau is a very important factor for 21 ka climate simulation in East Asia.

Pleistocene warming stages in Southern West Siberia: soils, environment, and climate evolution

A comparison of Neopleistocene soils in complete loess-soil sequences in southern West Siberia has shown a distinct trend in the evolution of soil formation and climate during warming stages. The Late Neopleistocene climate changes differed in amplitude and frequency from those in the Early and Middle Neopleistocene, when the territory of southern Siberia was dominated by a temperate warm and humid climate. The amplitude and frequency of climatic fluctuations changed significantly after the Kazantsevo interglacial. Warming stages at that time were much shorter, colder, and more arid. Early Neopleistocene soils are represented by Meadow and Meadow-Chernozem soils, formed upon heavy clay sediments in semi-hydromorphic conditions under wet meadow vegetation. They show intense humus accumulation, gleying features, R 2O 3 enrichment and lessivage. In the Middle Neopleistocene, Chernozem soils with double humic profiles and Grey Forest–Chernozem poligenetic soils formed on porous loess-like sediments. In the Late Neopleistocene, Chernozems and Grey Forest soils have reduced weakly differentiated profiles and humus horizons, which are half as thick relative to the soils of the previous stages. Correlation of the Neopleistocene loess-soil sequences in West Siberia with the oxygen isotope record from deep oceanic sediments shows that climate change in mid-latitude regions is in line with the global change controlled by Earth's orbital parameters. Climate change occurs in 100 kyr cycles that correspond to major glacial–interglacial alternation.

High frequency variations of the Earth's orbital parameters and climate change

Besides the low frequency variations, the Earth's orbital elements also exhibit variabilities at shorter time scales. This study investigates the quantitative impact of these high frequency orbitally induced insolation variations on climatic variables such as surface temperature as well as the dynamical change in vegetation. Moreover it aims to assess the extent to which these different factors (high frequency insolation variations and subsequent vegetation changes) may compete with the changes in solar activity. To this end, we have carried out a series of transient climate simulations over the last 1000 years using a climate model of intermediate complexity.

Interhemispheric space–time attributes of the Dansgaard–Oeschger oscillations between 100 and 0 ka

The persistence, stability and interhemispheric phasing of the Dansgaard–Oeschger (DO) climate oscillation over the last glacial period (0–100 ka) has been evaluated in oxygen isotope records of three polar ice cores (GRIP, GISP2, and Byrd Station) and a midlatitude deep-sea core from the North Atlantic Ocean (MD95-2042). The results show that DO oscillations in atmospheric conditions occurred in both northern and southern polar ice records, although in the southern records the oscillations had at most only ca. one-tenth the power of those in the north. The DO oscillations first appeared during Marine Isotope Stage (MIS) 4, and the average spectral power of the northern hemisphere DO oscillations increased markedly during MIS 3 (30–38 ka). The DO mode in the GISP2 record is confined to the frequency band 1/(1.59 kyr) to 1/(1.37 kyr), but in the GRIP record, the mode exhibits strong frequency splitting over a band that is wider by ca. 50%. Time-frequency analysis shows that in GRIP the DO mode undergoes a frequency modulation that is phase-locked with the Earth's obliquity cycle; this modulation does not appear in nearby GISP2. In the North Atlantic marine record, DO oscillations behaved somewhat differently, appearing sporadically during MIS 5 and 4. The planktonic DO oscillations increased in spectral power during MIS 3, leading peak power in the GISP2 record by ca. 3 kyr. DO oscillations were relatively stable in all five records during MIS 3; they could not be detected unequivocally in any of the records during the Holocene (0–11 ka). At other times, the DO mode in all of the records was amplitude-modulated by Earth's orbital parameters. Finally, interhemispheric phasing of DO oscillations over 10–90 ka was assessed between the Byrd Station and GISP2 records, and between the benthic and planktonic records of Core MD95-2042. Coherency studies reveal an apparent time lead of Byrd DO oscillations over GISP2 by 384±70 yr (2 σ level), and of the North Atlantic benthic over planktonic DO oscillations by 208±33 yr. This apparent time lead of the southern over the northern temperature proxies is likely the consequence of the distinctive harmonic shapes affecting the northern (rectangular) vs. southern (triangular) DO oscillations; the actual northern–southern relationship, as suggested by modelling and other recent data studies, is most probably in simple antiphase (cross phase of 180°).

Global climate models: past, present, and future.

Global climate is a result of the complex interactions between the atmosphere, cryosphere (ice), hydrosphere (oceans), lithosphere (land), and biosphere (life), fueled by the nonuniform spatial distribution of incoming solar radiation. We know from climate reconstructions using recorders such as ice cores, ocean and lake sediment cores, tree rings, corals, cave deposits, and ground water that the Earth's climate has seen major changes over its history. An analysis of the temperature variations patched together from all these data reveals that climate change occurs in cycles with characteristic periods, for example 200 million, 100,000, or 4–7 years. For some of these cycles, particular mechanisms have been identified, for example forcing by changes in the Earth's orbital parameters or internal oscillations of the coupled ocean-atmosphere system. However, major uncertainties remain in our understanding of the interplay of the components of the climate system. Paleoclimate reconstructions, in particular from ice cores (1) also have shown that climate can change (e.g., ΔT = 5°C) over extremely short periods of time such as a few years. Over the last century, humans have altered the Earth's surface and the composition of its atmosphere to the extent that these factors measurably affect current climate conditions. There is concern that perhaps during one human generation we will gradually change climate conditions or even trigger a rapid and much more dramatic shift. We might be “poking an angry beast” (2).

Wavelet analysis of relative geomagnetic paleointensity at ODP Site 983

Abstract We performed spectral analysis of the record of relative geomagnetic paleointensity obtained at ODP Site 983, covering the time interval 0–1.1 Ma. The results confirm the presence of significant power at frequencies corresponding to the earth orbital parameters (eccentricity, obliquity, precession). The construction of the evolutionary spectrum allowed us to establish the non-stationarity of the signal at those frequencies. The subsequent use of wavelet techniques made it possible to demarcate the time intervals over which orbital frequencies are present in the record. For those intervals, the paleointensity record shows some coherency with the isothermal remanent magnetization, normalizer of the natural remanent magnetization, and the ratio anhysteretic remanent magnetization/k. These results suggest that the orbital frequencies embedded in the paleointensity record are the expression of lithologic variations, and probably not a characteristic of the geodynamo itself. Extracting (filtering) these wavelet components from the Site 983 paleointensity record indicates, however, that this secondary overprint is of sufficiently low level that it has a minor effect on the overall character of the record.

Response of mollusk assemblages from the Luochuan loess section to orbital forcing since the last 250 ka

This note presents a new result of terrestrial mollusk study from the Luochuan loess section since the last 250 ka. A total of 213 samples, taken at intervals of 10 cm in the S0-L3 portion, were analyzed for fossil mollusks. Generally, 150–600 individuals were counted in each sample. According to the distribution of mollusk fossil assemblages in the loess section, 11 mollusk fossil zones have been recognized, representing different climatic and ecological conditions. Three main ecological groups were identified according to the temperature and moisture requirements of each taxon. The cold-aridiphilous group shows maxima at about 240–220, 190–182, 150–140 and 74–66 ka BP. The thermo-humidiphilous set has high abundances for at least 6 times in the section at about 246–240, 220–216, 170–158, 92–86, 60–44 and 10 kaBP. Our results show that variations in mollusk ecological groups are related with changes in the Earth orbital parameters at the 41 and 20 ka frequencies. Maxima in thermo-humidiphilous taxa are in phase with accretion intervals of obliquity (41 ka period), reflecting the East Asian summer monsoon with 41 ka period in controlling variations in terrestrial mollusk ecological groups. In addition, maxima in thermohumidiphilous taxa appearing at about 246–240, 220–216, 60 and 10 kaBP, are consistent with procession (20 ka period) maxima, indicating that the procession period also plays an important role in adjusting the ecological pattern of mollusk groups.

Lithological expression of Milankovitch cyclicity in carbonate-dominated, pelagic, Barremian deposits in central Italy

In continuous sedimentary sequences, cyclostratigraphy can provide good time control on the duration of stratigraphic stages and palaeomagnetic chrons. This approach has been applied to the Barremian pelagic marl-limestone alternations of the Umbria-Marche Basin. Two criteria have been used: variations in the thickness and carbonate content of limestones and the vertical distribution of intercalated black marls. Marl–limestone alternations are organized in bundles of generally four or five couplets. The cyclicity expressed by the vertical stacking of couplets and bundles has been interpreted as the sedimentary expression of the Earth's orbital parameters, specifically the precession of the equinoxes and the eccentricity.This breakdown of the Barremian Stage into astroclimatic cycles allows the calibration of the duration of the stage and of the magnetic chrons M-3 to M-0. The lower and upper stratigraphic boundaries of the Barremian Stage are picked at the base of the M-3 and M-0 chrons, respectively. The duration of the Barremian Stage is estimated at 5.13±0.34Myr by adding up contained cycles. The duration of related magnetic chrons varies considerably from 0.43 to 2.3Myr.

Comparison of cosmogenic radionuclide production and geomagnetic field intensity over the last 200 000 years

The production rate of cosmogenic radionuclides such as 10Be or 14C is known to vary as a function of the geomagnetic field intensity. It should, therefore, be possible to extract a record of palaeofield intensity from the deposition record of these radionuclides in marine or terrestrial sediments and ice cores. Field intensity variations, however, are not the only factor that has influenced the cosmogenic radionuclide records. In the case of 14C, variations of the global carbon cycle, caused by reorganization of the ocean circulation patterns from the last glacial to the present interglacial, are superimposed. 10Be is not affected by these variations because it is not part of the carbon cycle, but its deposition rates in marine sediments vary as a function of lateral sediment redistribution and boundary scavenging intensity. A global stacked record of 10Be deposition rates, corrected for sediment redistribution by normalizing to 230Thex, was shown to remove most of the disturbances, and provides a record of 10Be production rate variations over the last 200 000 years, which translates into geomagnetic field intensity variations. This dataset is compared with palaeofield intensities reconstructed from marine sediments by palaeomagnetic methods, from variations in atmospheric 14C/12C derived from independent calibrations of 14C ages, such as U/Th dating and tree ring chronology, and from 36Cl and 10Be fluxes in polar ice cores. Potential influences of the Earth’s orbital parameters and insufficient correction for orbitally triggered climate variations on the palaeointensity reconstructions are assessed. It is argued that the palaeointensity records derived from marine sediments are not significantly affected by these factors.

The ice age cycle and the deglaciations: an application of nonlinear regression modelling

We have applied the nonlinear regression technique known as additivity and variance stabilisation (AVAS) to time series which reflect Earth's climate over the last 600 ka. AVAS estimates a smooth, nonlinear transform for each variable, under the assumption of an additive model. The Earth's orbital parameters and insolation variations have been used as regression variables. Analysis of the contribution of each variable shows that the deglaciations are characterised by periods of increasing obliquity and perihelion approaching the vernal equinox, but not by any systematic change in eccentricity. The magnitude of insolation changes also plays no role. By approximating the transforms we can obtain a future prediction, with a glacial maximum at 60 ka AP, and a subsequent obliquity and precession forced deglaciation.

Chronology, causes and progression of the Messinian salinity crisis

The Messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years (1–3). Earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated Mediterranean basin that had been repeatedly isolated from the Atlantic Ocean1,2, but elucidation of the causes of the isolation — whether driven largely by glacio-eustatic or tectonic processes — have been hampered by the absence of an accurate time frame. Here we present an astronomically calibrated chronology for the Mediterranean Messinian age based on an integrated high-resolution stratigraphy and ‘tuning’ of sedimentary cycle patterns to variations in the Earth's orbital parameters. We show that the onset of the Messinian salinity crisis is synchronous over the entire Mediterranean basin, dated at 5.96 ± 0.02 million years ago. Isolation from the Atlantic Ocean was established between 5.59 and 5.33 million years ago, causing a large fall in Mediterranean water level followed by erosion (5.59–5.50 million years ago) and deposition (5.50–5.33 million years ago) of non-marine sediments in a large ‘Lago Mare’ (Lake Sea) basin. Cyclic evaporite deposition is almost entirely related to circum-Mediterranean climate changes driven by changes in the Earth's precession, and not to obliquity-induced glacio-eustatic sea-level changes. We argue in favour of a dominantly tectonic origin for the Messinian salinity crisis, although its exact timing may well have been controlled by the ∼400-kyr component of the Earth's eccentricity cycle.

Orbital controls on the El Niño/Southern Oscillation and the tropical climate

The global synchroneity of glacial‐interglacial events is one of the major problems in understanding the link between Milankovitch forcing and the climate of the late Quaternary. In this study we isolate a part of the climate system, the tropical Pacific, and test its sensitivity to changes in solar forcing associated with changes in the Earth's orbital parameters. We use a simplified coupled ocean‐atmosphere model that is run for the past 150,000 years and forced with Milankovitch changes in the solar insolation. This system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant. The mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the El Niño/Southern Oscillation (ENSO). Changes in the ENSO behavior result in a mean tropical climate change. The hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to Milankovitch forcing.

Global changes in intensity of the Earth's magnetic field during the past 800 kyr

Recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the Earth's past magnetic field at numerous field sites. The compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the Earth's geodynamo itself. A previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1, with the geomagnetic origin of the signal supported by an independent analysis of 10Be production made on different cores2. The persistence of long-term features in the Earth's magnetic intensity or the existence of long-term periodic changes cannot, however, be resolved in this relatively short time span. Here we present the integration of 33 records of relative palaeointensity3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19 into a composite curve spanning the past 800 kyr. We find that the intensity of the Earth's dipole field has experienced large-amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction, reflecting the emergence of non-dipole components. No stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the Earth's orbital parameters have a direct and strong influence on the geodynamo.

A review of the Milankovitch climatic beat: template for Plio–Pleistocene sea-level changes and sequence stratigraphy

The Milankovitch theory of climate change predicts that global ice volume, and hence sea-level changes, were controlled by long-term quasi-periodic variations in the earth's orbital parameters (obliquity, precession and eccentricity). δ 18O records from deep-sea cores are a proxy for sea-level changes and have an orbitally tuned chronology covering the last 5 Ma. The sea-level signal in δ 18O data from east equatorial Pacific core V19-30 is well calibrated with sea-level data from coral terraces on Huon Peninsula, New Guinea, over the last 140 ka, and with less certainty back to 340 ka. Over the last 140 ka, the sea-level contribution to benthic glacial–interglacial isotopic variation is about 1.2–1.3‰ or 0.011‰ m −1, and for core V19-30 the glacial-age temperature contribution from deep ocean cooling of 1.7°C is 0.4‰. Independent constraints on Late Pliocene sea-level changes interpreted from shallow marine continental margin records indicate that the sea-level δ 18O calibration may not have been the same over the last 2.6 Ma, and the temperature correction is unlikely to have been the same in all glacial periods and all ocean settings. Nevertheless, the astronomically tuned isotopic records from deep-sea cores provide an accurate chronology and approximate the magnitudes of sea-level changes over the last 2.6 Ma, against which the facies architecture of stratigraphic sequences can be analysed and the concepts of sequence stratigraphy properly evaluated.

Simulated influence of carbon dioxide, orbital forcing and ice sheets on the climate of the Last Glacial Maximum

A coupled atmosphere–ocean–sea-ice model is used to investigate the climate of the Last Glacial Maximum (∼21,000 years ago) and the relative climate-forcing effects of atmosphere CO2, the Earth's orbital parameters and ice-sheet albedo. Tropical temperatures are found to be ∼2.2 °C less than today's—slightly colder than indicated by the CLIMAP palaeoclimate reconstruction. This result is consistent with a low to medium climate sensitivity to radiative perturbations. Temperatures are colder still in the northern North Atlantic region, owing to a weakening and shallowing of the thermohaline circulation. A sensitivity analysis suggests that changes in ocean circulation since the Last Glacial Maximum have not contributed directly to the global-mean temperature change since that time.

Modelling global terrestrial vegetation–climate interaction

By coupling an atmospheric general circulation model asynchronously with an equilibrium vegetation model, manifold equilibrium solutions of the atmosphere–biosphere system have been explored. It is found that under present–day conditions of the Earth's orbital parameters and sea–surface temperatures, two stable equilibria of vegetation patterns are possible: one corresponding to present–day sparse vegetation in the Sahel, the second solution yielding savannah which extends far into the south–western part of the Sahara. A similar picture is obtained for conditions during the last glacial maximum (21 000 years before present (BP)). For the mid–Holocene (6000 years BP), however, the model finds only one solution: the green Sahara. We suggest that this intransitive behaviour of the atmosphere–biosphere is related to a westward shift of the Hadley–Walker circulation. A conceptual model of atmosphere–vegetation dynamics is used to interpret the bifurcation as well as its change in terms of stability theory.

A warm future in the past

To understand the impact of a future Earth which may be warmer than now, geologists look to records of warmer times in the past - often the last interglacial period, around 120,000 years ago. But a better match to today's conditions might be found in a period around 400,000 years ago, an earlier interglacial known as stage 11, when Earth's orbital parameters were closer to those of the present day. Stage 11 was an unusual period, with severe climate change and, at its peak, exceptionally warm temperatures.

Discussion of the results from solar astrolabes

In this work we investigate on the sta- bility of the results from solar observations obtained with the modied astrolabes of the Observatoire de la C^ ote d'Azur/France, of the Observat orio Abrah~ ao de Moraes/IAG/USP-Brazil and of the Observat orio Nacional/Brazil. The mass of data is comprised of 6273 observations of both solar limbs, from 1974 to 1992, and is analyzed to determine the origin of the fundamental ref- erence system and the Earth's orbital parameters. The so- lution stability was veried by checking against any large variation upon the individual weights, as well as for dier- ent sub samples of the whole set of observations. The re- sults were also shown invariant to changes in the adopted model, such as adding unknowns to the refraction algo- rithm, to the time variation of the obliquity (including the nutation constant) and to the azimuthal anomalies of the refraction. In our analysis we obtain a standard devi- ation of 0: 6 for the combination of the observations with no bias on its distribution. It is also indicated that the Sun observations at astrolabes do not require any further atmosphere modelling complexity.

Eccentricity forcing of Pliocene–Early Pleistocene climate revealed in a marine oxygen-isotope record

Milankovitch theory—that climate is controlled by variations in the Earth's orbital parameters—has gained wide acceptance for its ability to account for two climate cycles: a 23-kyr cycle that is phase-locked to the precession-driven insolation cycle, and a 41-kyr cycle that is phase-locked to the obliquity-driven insolation cycle1–6. But, explaining the observed ∼100-kyr climate cycle in terms of Milankovitch theory—especially for the Late Pleistocene ice-age cycle—remains controversial in spite of a strong correlation with the ∼100-kyr cycle in the Earth's orbital eccentricity5. One problem is that eccentricity affects insolation mainly by modulating the precession cycle; its direct contribution to radiation change is too small (<0.1%) to effect the observed climate change directly5,7. Another is the absence of a Late Pleistocene ice-volume cycle in oxygen-isotope records to match the ∼404-kyr component of the eccentricity cycle5,8. Here we examine an oxygen-isotope record spanning the interval 1.2 to 5.2 million years ago, before the Late Pleistocene ice-age regime. We find 404-kyr and ∼100-kyr climate cycles which are coherent with eccentricity and which have amplitudes that are similar to the coexisting 23-kyr cycle. Analysis of these low-frequency cycles suggests that they originate through an asymmetrical response mechanism that preferentially introduces variance into the climate system from the warmer portions of the eccentricity-modulated precession cycle. Our data thus support eccentricity's role in the origin of low-frequency oxygen-isotope cycles before the Late Pleistocene ice age.