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  • 1
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    On the structure and origin of major glaciation cycles 2. The 100,000‐year cycle
    American Geophysical Union (AGU) ; 1993
    In:  Paleoceanography Vol. 8, No. 6 ( 1993-12), p. 699-735
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 8, No. 6 ( 1993-12), p. 699-735
    Abstract: Climate over the past million years has been dominated by glaciation cycles with periods near 23,000, 41,000, and 100,000 years. In a linear version of the Milankovitch theory, the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity. But the 100,000‐year radiation cycle (arising from eccentricity variation) is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing. We present phase observations showing that the geographic progression of local responses over the 100,000‐year cycle is similar to the progression in the other two cycles, implying that a similar set of internal climatic mechanisms operates in all three. But the phase sequence in the 100,000‐year cycle requires a source of climatic inertia having a time constant (∼15,000 years) much larger than the other cycles (∼5,000 years). Our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source. When these ice sheets, forced by precession and obliquity, exceed a critical size, they cease responding as linear Milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses. In our model, the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity‐driven modulations in the 23,000‐year sea level cycle. During an interval when sea level is forced upward from a major low stand by a Milankovitch response acting either alone or in combination with an internally driven, higher‐frequency process, ice sheets grounded on continental shelves become unstable, mass wasting accelerates, and the resulting deglaciation sets the phase of one wave in the train of 100,000‐year oscillations. Whether a glacier or ice sheet influences the climate depends very much on the scale…. The interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger, thereby gradually increasing its radius of influence. Johannes Oerlemans [1991, p. 155]
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/93PA02751
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1993
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  • 2
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    On the Structure and Origin of Major Glaciation Cycles 1. Linear Responses to Milankovitch Forcing
    American Geophysical Union (AGU) ; 1992
    In:  Paleoceanography Vol. 7, No. 6 ( 1992-12), p. 701-738
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 7, No. 6 ( 1992-12), p. 701-738
    Abstract: Time series of ocean properties provide a measure of global ice volume and monitor key features of the wind‐driven and density‐driven circulations over the past 400,000 years. Cycles with periods near 23,000, 41,000, and 100,000 years dominate this climatic narrative. When the narrative is examined in a geographic array of time series, the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles. We argue that the 23,000‐ and 41,000‐year cycles of glaciation are continuous, linear responses to orbitally driven changes in the Arctic radiation budget; and we use the phase progression in each climatic cycle to identify the main pathways along which the initial, local responses to radiation are propagated by the atmosphere and ocean. Early in this progression, deep waters of the Southern Ocean appear to act as a carbon trap. To stimulate new observations and modeling efforts, we offer a process model that gives a synoptic view of climate at the four end‐member states needed to describe the system's evolution, and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems. “Solutions to problems involving systems of such complexity are not born full grown like Athena from the head of Zeus. Rather they evolve slowly, in stages, each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step.” —Victor P. Starr
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/92PA02253
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1992
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  • 3
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    Erratum: Modelling the global climate response to orbital forcing and atmospheric carbon dioxide changes
    Springer Science and Business Media LLC ; 1984
    In:  Nature Vol. 312, No. 5996 ( 1984-12), p. 786-786
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 312, No. 5996 ( 1984-12), p. 786-786
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/312786b0
    RVK:
    TA 1000
    RVK:
    UA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 1984
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  • 4
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    Correction to “Paleoceanography and the diachrony of radiolarian events in the eastern equatorial Pacific”
    American Geophysical Union (AGU) ; 1993
    In:  Paleoceanography Vol. 8, No. 6 ( 1993-12), p. 875-875
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 8, No. 6 ( 1993-12), p. 875-875
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/93PA03148
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1993
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  • 5
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    Paleoceanography and the diachrony of radiolarian events in the eastern equatorial Pacific
    American Geophysical Union (AGU) ; 1993
    In:  Paleoceanography Vol. 8, No. 5 ( 1993-10), p. 567-586
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 8, No. 5 ( 1993-10), p. 567-586
    Abstract: The development of an orbitally tuned time scale for the ODP leg 138 sites provides biostratigraphers a very high resolution chronostratigraphic framework. With this framework we are better able to define which of the first and last appearances of species appear to be synchronous. In addition, the geographic distribution of sites provides the means with which the detailed spatial patterns of invasion of new species and the extinction of older species can be mapped. These maps not only provide information on the process of evolution, migration, and extinction, they can also be related to water mass distributions and near‐surface circulation of the ocean. Of 39 radiolarian events studied at 11 sites in the eastern equatorial Pacific, 28 were found to have a minimum range in their estimated age that exceeded 0.15 m.y. The temporal pattern of first and last appearances of these diachronous events have coherent spatial patterns that indicate shifts in the areas of high oceanographic gradients over the past 10 Ma. These changes in the locations of high gradient regions suggest that the South Equatorial Current (SEC) was north of its present position prior to approximately 7 Ma. There was a southward shift in the northern boundary of this current between approximately 6 and 7 Ma, and the development of a relatively strong gradient between the northeastern and northwestern sites. Between approximately 3.7 and 3.4 Ma, there was a very slight northward shift in the northern boundary of the SEC and the steep gradients between the northeastern and northwestern sites may have disappeared. This change is thought to be associated with the closing of the Isthmus of Panama. The temporal‐spatial patterns of diachronous events younger than 3.4 Ma are consistent with patterns of circulation in the modern ocean.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/93PA01328
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1993
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  • 6
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    Revised Technique for Preparing Quantitative Radiolarian Slides from Deep-Sea Sediments
    JSTOR ; 1986
    In:  Micropaleontology Vol. 32, No. 2 ( 1986), p. 182-
    Details
    In: Micropaleontology, JSTOR, Vol. 32, No. 2 ( 1986), p. 182-
    Type of Medium: Online Resource
    ISSN: 0026-2803
    URL: Article
    DOI: 10.2307/1485631
    RVK:
    TE 1000
    Language: Unknown
    Publisher: JSTOR
    Publication Date: 1986
    detail.hit.zdb_id: 415738-2
    detail.hit.zdb_id: 2175613-2
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  • 7
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    Aliasing of the geologic record and the search for long‐period Milankovitch cycles
    American Geophysical Union (AGU) ; 1988
    In:  Paleoceanography Vol. 3, No. 5 ( 1988-10), p. 613-619
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 3, No. 5 ( 1988-10), p. 613-619
    Abstract: Aliasing of a time series shifts high‐frequency variance into lower frequencies. It is caused by sampling at an interval too broad to resolve true high‐frequency signals. This effect is well understood in classical time series analysis, where sample intervals are known and constant, but in a geologic context, where sample intervals may vary, aliasing remains poorly known. We address here the aliasing problem relevant to the search for orbital variations recorded in sedimentary sections. Our example is aliasing of the 23,000‐year period orbital precession rhythm which is common in late Quaternary paleoclimatic records. We illustrate three cases of aliasing. First, we sample precession at a constant interval of 25,000 years. This is a typical target for many “high‐resolution” studies of Neogene sections. This sampling interval translates precessional variance into predictable spectral peaks near 400 ka and 100 ka, which could be mistaken for the longer‐period eccentricity rhythms. Second, random variations in the sampling interval around the 25,000‐year target spread the aliased variance over a range of frequencies. This induces either unpredictable long‐period spectral peaks or, in the extreme, a white noise spectrum. In the third case, variations of the sampling interval are autocorrelated. This simulates a section with long‐period variations in sedimentation rate sampled at constant depth intervals. Here the single aliased peaks of case 1 are split into two or more peaks of slightly higher and lower frequencies. In all three cases, for long enough time series, the total variance recorded is the same. We compare these numerical experiments to a Miocene oxygen isotope record from Deep Sea Drilling Project site 577, sampled at ∼25,000‐year intervals. With these data it is impossible to tell whether the long‐period variations are due to the direct effects of eccentricity or the aliased effects of precession. In theory it should be possible to test for eccentricity signals at low resolution by randomizing the sampling intervals. In practice, however, it is only through high‐density sampling that we can define intervals well enough to assess the effects of aliasing.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/PA003i005p00613
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1988
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  • 8
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    Paleoceanography of the eastern equatorial Pacific during the Pliocene: A High‐Resolution Radiolarian Study
    American Geophysical Union (AGU) ; 1989
    In:  Paleoceanography Vol. 4, No. 1 ( 1989-02), p. 57-73
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 4, No. 1 ( 1989-02), p. 57-73
    Abstract: Pliocene sediments from hydraulic piston cores of Deep Sea Drilling Project sites 572 and 573 in the eastern equatorial Pacific provide material for a high‐resolution stratigraphic and paleoceanographic study during a period of time from 2.4 to 3.7 Ma. Radiolarian stratigraphy of these two sites reveals two major faunal events. The older event involves the gradual disappearance of five species and the appearance of three equatorial surface‐dwelling radiolarian species and occurs at the Gauss/Gilbert paleomagnetic reversal boundary which is coincident with the time of the closing of the Isthmus of Panama around 3.5 Ma [Berggren and Hollister, 1974; Keigwin, 1978, 1982a, b]. The younger event involves a disappearance and appearance of two mainly Subarctic species and occurs at 2.9 Ma, prior to the onset of northern hemisphere glaciation as dated in North Atlantic sections. Analysis of quantitative radiolarian data for extant species divides the Pliocene fauna into two assemblages which are composed of radiolarian species that are abundant in the surface sediments of central and eastern equatorial regions. From the time series variations of these fauna, the variability of these factors has remained constant over the time interval at the eastern site but underwent a stepwise decrease at the western site. Paleotemperature transfer function techniques provided quantitative comparisons between Pliocene and Pleistocene paleooceanographic variability. At the more western site, a shift in paleotemperature estimates occurred. Using the modern day observation that the slope of the thermocline is related to the magnitude of westward wind stress, this change corresponds to an increase in wind stress. This event has been dated at about 2.8 Ma and may represent an important oceanic and atmospheric precursor to the major onset of northern hemisphere glaciation at 2.4 Ma. From the modern relationship between seasonal differences in temperatures at each site the Pliocene gradient in seasonally has been compared with the Pleistocene (and modern) gradients. Relative to the Pleistocene, seasonal differences in temperature were the same for the more eastern site but lower at the western site. The Pliocene gradient in seasonally was thus located farther east toward the South American continent than during the Pleistocene. No influence of the final closure of the Isthmus of Panama is seen in the extant radiolarian data for sites 572 and 573 during the time interval from 2.4 Ma to 3.7 Ma.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/PA004i001p00057
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1989
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  • 9
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    Carbon 13 in Pacific Deep and Intermediate Waters, 0‐370 ka: Implications for Ocean Circulation and Pleistocene CO 2
    American Geophysical Union (AGU) ; 1991
    In:  Paleoceanography Vol. 6, No. 2 ( 1991-04), p. 205-226
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 6, No. 2 ( 1991-04), p. 205-226
    Abstract: Stable isotopes in benthic foraminifera from Pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages. The carbon isotope differences between ∼1400 and ∼3200 m depth in the eastern Pacific are consistently greater in glacial than interglacial maxima over the last ∼370 kyr. This phenomenon of “bottom heavy” glacial nutrient distributions, which Boyle proposed as a cause of Pleistocene CO 2 change, occurs primarily in the 1/100 and 1/41 kyr −1 “Milankovitch” orbital frequency bands but appears to lack a coherent 1/23 kyr −1 band related to orbital precession. Averaged over oxygen‐isotope stages, glacial δ 13 C gradients from ∼1400 to ∼3200 m depth are 0.1‰ greater than interglacial gradients. The range of extreme shifts is somewhat larger, 0.2 to 0.5‰. In both cases, these changes in Pacific δ 13 C distributions are much smaller than observed in shorter records from the North Atlantic. This may be too small to be a dominant cause of atmospheric pCO 2 change, unless current models underestimate the sensitivity of pCO 2 to nutrient redistributions. This dampening of Pacific relative to Atlantic δ 13 C depth gradient favors a North Atlantic origin of the phenomenon, although local variations of Pacific intermediate water masses can not be excluded at present.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/90PA02303
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1991
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  • 10
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    Late Pleistocene Continental Climate and Oceanic Variability Recorded in Northwest Pacific Sediments
    American Geophysical Union (AGU) ; 1991
    In:  Paleoceanography Vol. 6, No. 3 ( 1991-06), p. 349-370
    Details
    In: Paleoceanography, American Geophysical Union (AGU), Vol. 6, No. 3 ( 1991-06), p. 349-370
    Abstract: Core V21‐146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the past 530,000 years. Downcore variations of δ 18 O from benthic foraminiferal calcite were correlated to the SPECMAP record to provide an age model for late Pleistocene paleoclimatic and paleoceanographic variation. Fluxes of CaCO 3 and eolian material have been determined by combining information about linear sedimentation rates, bulk densities and component percentages. The mass accumulation rate (MAR) of CaCO 3 varies from 58 to 1435 mg(cm² kyr) −1 and exhibits the Pacific Ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record. However, the pattern of CaCO 3 accumulation appears to shift during the mid‐Brunhes so that prior to 350,000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods. The flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess‐soil stratigraphy in China. Dust fluxes range from 43 to 718 mg(cm² kyr) −1 and are greater by a factor of about 4 during glacial times. Cross‐spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100, 41, and 19 kyr. Eolian grain sizes, generally used as a proxy record of wind intensity, range from 8.4ф (2.9 µm) to 6.2ф (13.6 µm). A change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower‐frequency and higher‐amplitude fluctuations than the younger portion. Power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25–35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities. The phase relationship for eccentricity between the eolian grain size and δ 18 O records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions.
    Type of Medium: Online Resource
    ISSN: 0883-8305 , 1944-9186
    URL: Article
    DOI: 10.1029/91PA00559
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1991
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