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Article ; Online: Dependence of the duration of geomagnetic polarity reversals on site latitude.

Clement, Bradford M

2004 Volume 428, Issue 6983, Page(s) 637–640

Abstract: An important constraint on the processes governing the geodynamo--the flow in the outer core responsible for generating Earth's magnetic field--is the duration of geomagnetic polarity reversals; that is, how long it takes for Earth's magnetic field to ... ...

Abstract	An important constraint on the processes governing the geodynamo--the flow in the outer core responsible for generating Earth's magnetic field--is the duration of geomagnetic polarity reversals; that is, how long it takes for Earth's magnetic field to reverse. It is generally accepted that Earth's magnetic field strength drops to low levels during polarity reversals, and the field direction progresses through a 180 degrees change while the field is weak. The time it takes for this process to happen, however, remains uncertain, with estimates ranging from a few thousand up to 28,000 years. Here I present an analysis of the available sediment records of the four most recent polarity reversals. These records yield an average estimate of about 7,000 years for the time it takes for the directional change to occur. The variation about this mean duration is not random, but instead varies with site latitude, with shorter durations observed at low-latitude sites, and longer durations observed at mid- to high-latitude sites. Such variation of duration with site latitude is predicted by simple geometrical reversal models, in which non-dipole fields are allowed to persist while the axial dipole decays through zero and then builds in the opposite direction, and provides a constraint on numerical dynamo models.
Language	English
Publishing date	2004-04-08
Publishing country	England
Document type	Journal Article
ZDB-ID	120714-3
ISSN	1476-4687 ; 0028-0836
ISSN (online)	1476-4687
ISSN	0028-0836
DOI	10.1038/nature02459
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Book ; Online: Magnetostratigraphy of DSDP Leg 94 sediments, supplementary data to: Clement, Bradford M; Robinson, Frank (1987): The magnetostratigraphy of Leg 94 sediments. In: Ruddiman, WF; Kidd, RB; Thomas, E; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 94, 635-650

Clement, Bradford M / Robinson, Frank

1987

Abstract: The primary objective of DSDP Leg 94 was to obtain continuous paleoclimatic records along a roughly north-south transect in the North Atlantic. The magnetostratigraphy of 21 holes at 6 sites cored with the hydraulic piston corer and extended-core-barrel ... ...

Abstract	The primary objective of DSDP Leg 94 was to obtain continuous paleoclimatic records along a roughly north-south transect in the North Atlantic. The magnetostratigraphy of 21 holes at 6 sites cored with the hydraulic piston corer and extended-core-barrel corer is presented here and establishes an independent chronology for these sediments. Nearly complete records were obtained for the last 2.5 m.y.; in addition, deeper drilling at three sites to satisfy tectonic and paleoceanographic objectives produced older sections suitable for magnetostratigraphic study, allowing first-order correlations of the polarity sequences with calcareous and siliceous micro fossil events. The sections with high sediment accumulation rates yielded very detailed records of polarity history and allowed three short normal-polarity zones within the Matuyama Chronozone to be detected, in addition to the Jaramillo and Olduvai subchronozones. A short reversed-polarity zone also occurs, within the upper intervals of the Gauss Chronozone. These short zones are present in multiple holes, ruling out the possibility that they might be of local origin. Correlation of these short zones with radiometrically dated polarity zones in igneous rocks strongly supports the interpretation of these polarity zones as records of true geomagnetic polarity chrons.
Language	English
Dates of publication	1987-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.2973/dsdp.proc.94.112.1987
DOI	10.1594/PANGAEA.788554
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Conference proceedings ; Online: Magnetostratigraphy of ODP Sites 114-703 and 114-703, supplementary data to: Hailwood, Ernie A; Clement, Bradford M (1991): Magnetostratigraphy of Sites 703 and 704, Meteor Rise, southeastern South Atlantic. In: Ciesielski, PF; Kristoffersen, Y; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 114, 367-386

Hailwood, Ernie A / Clement, Bradford M

1991

Abstract: ODP Sites 703 and 704 were drilled near the crest of the Meteor Rise in the southeastern part of the South Atlantic in order to explore the role of this aseismic rise as a barrier to the flow of deep water between the Antarctic and South Atlantic during ... ...

Abstract	ODP Sites 703 and 704 were drilled near the crest of the Meteor Rise in the southeastern part of the South Atlantic in order to explore the role of this aseismic rise as a barrier to the flow of deep water between the Antarctic and South Atlantic during the early evolution of the South Atlantic and to investigate the subsequent subsidence and paleoceanographic evolution of this area. A combination of shipboard whole-core paleomagnetic determinations on all archive core halves and post-cruise paleomagnetic analyses of some 440 discrete samples from the two sites has allowed definition of the sequence of geomagnetic polarity reversals that occurred during deposition of much of this sedimentary sequence. The magnetostratigraphic record for Sift 703 extends from the middle Eocene to the early Miocene and that for Site 704 from the early Miocene to the Pleistocene. The correlation of this record to the standard geomagnetic polarity time scale of Berggren et al. (1985, doi:10.1130/0016-7606(1985)96<1407:CG>2.0.CO;2) is generally good for the Oligocene and late Miocene to Pleistocene, but is poorer for the early and middle Miocene. The combined magnetostratigraphic record for these two sites will facilitate the development and chronometric calibration of refined high-latitude biostratigraphic zonations. Furthermore, it provides an important basis for defining the periodicity of the late Neogene stable isotope and carbonate fluctuations observed in these cores and relating these changes to the paleoclimatic and paleoceanographic driving forces.
Language	English
Dates of publication	1991-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Conference proceedings ; Online
Note	This dataset is supplement to doi:10.2973/odp.proc.sr.114.186.1991
DOI	10.1594/PANGAEA.754616
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Conference proceedings ; Online: Magnetostratigraphy of ODP Sites 114-699 and 114-700, supplementary data to: Hailwood, Ernie A; Clement, Bradford M (1991): Magnetostratigraphy of sites 699 and 700, East Georgia Basin. In: Ciesielski, PF; Kristoffersen, Y; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 114, 337-357

Hailwood, Ernie A / Clement, Bradford M

1991

Abstract: ODP Sites 699 and 700 were drilled within the East Georgia Basin primarily to explore the paleoceanographic and sedimentary history of this region during the early stages of separation of South America from Africa and Antarctica. Determination of the ... ...

Abstract	ODP Sites 699 and 700 were drilled within the East Georgia Basin primarily to explore the paleoceanographic and sedimentary history of this region during the early stages of separation of South America from Africa and Antarctica. Determination of the timing of the various events represented in the sedimentary record of these sites requires the establishment of a high-resolution stratigraphic framework. This was achieved through combined magnetostratigraphic/biostratigraphic studies of the sediments recovered from Holes 699A and 700B. The magnetostratigraphic data are presented in this paper. They are based on a combination of shipboard whole-core paleomagnetic determinations made at 10-cm intervals on all archive core halves and involving AF demagnetization in fields of 5 and/or 9 mT together with shipboard and post-cruise incremental AF demagnetization analyses of some 450 discrete samples. A generally continuous magnetostratigraphic record has been obtained for the Pliocene-Pleistocene and Oligocene sequences recovered from Hole 699A. A record of the Brunhes, Matuyama, and late Gauss Chrons has been identified in the Pleistocene to late Pliocene age sediments cored in the upper 30-m section of this hole. However, interpretation of the magnetostratigraphic record observed for the Pliocene sediments in the interval from 30 to 70 mbsf is complicated by the possible presence of hiatuses. A well-defined sequence of normal and reverse polarity magnetozones was identified for the Oligocene sequence of Hole 699A in the interval from 85 to 219 mbsf. Although there are few biostratigraphic datums for this interval, the observed polarity sequence shows a good correlation with geomagnetic polarity Chrons C6CR to C11R. As a result of poor core recovery, the magnetostratigraphic sequence for the early Oligocene to early Eocene age sediments from 243 to 468 mbsf in Hole 699A is discontinuous. However, available biostratigraphic datums allow the identification of Chrons C13N and C13R in the depth interval from 270 to 306 mbsf and the Chron sequence C20R to C22R in the interval from 397 to 465 mbsf. The sedimentary sequence recovered from Hole 700B extends from the middle Eocene through to the Coniacian or Turonian stages. The magnetostratigraphic record for the Eocene part of this sequence is fragmentary, but chronal assignments can be made for certain isolated parts of the section. In contrast, a well-defined succession of magnetozones established for the Paleocene to Late Cretaceous age part of the section correlates well with the polarity time scale between Chrons C26R and C34N. Biostratigraphic (nannofossil) data indicate that a hiatus may be present at the Cretaceous/Tertiary boundary. However, the magnetostratigraphic data indicate the probable presence of a reverse polarity magnetozone at this level, which can be correlated with the reverse interval (Chron C29R) known to span the Cretaceous/Tertiary boundary. The record of the preceding Chron C30N is anomalously short at this site. These data indicate that sedimentation may have been continuous across the Cretaceous/Tertiary boundary and that the hiatus is located instead within late Maestrichtian age Chron C30N.
Language	English
Dates of publication	1991-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Conference proceedings ; Online
Note	This dataset is supplement to doi:10.2973/odp.proc.sr.114.155.1991
DOI	10.1594/PANGAEA.734978
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Conference proceedings ; Online: Magnetostratigraphy of ODP sites 114-701 and 114-702, supplementary data to: Clement, Bradford M; Hailwood, Ernie A (1991): Magnetostratigraphy of sediments from sites 701 and 702. In: Ciesielski, PF; Kristoffersen, Y; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 114, 359-366

Clement, Bradford M / Hailwood, Ernie A

1991

Abstract: During Leg 114 of the Ocean Drilling Program 12 holes were drilled at seven sites in the subantarctic South Atlantic Ocean. A major objective of this cruise was to document the development of the deep-water passageway that formed as the Meteor and Islas ... ...

Abstract	During Leg 114 of the Ocean Drilling Program 12 holes were drilled at seven sites in the subantarctic South Atlantic Ocean. A major objective of this cruise was to document the development of the deep-water passageway that formed as the Meteor and Islas Orcadas rises rifted and spread apart. We report here the results of a magnetostratigraphic study of the sediments recovered at Site 701, a deep-water site located within the gateway, and Site 702, a shallow-water site located near the crest of the Islas Orcadas Rise. The sequence of Pliocene-Pleistocene reversals observed at Site 701 is readily correlated with the Brunhes Chron through Chron C3A. Although correlation is more difficult in the older sections at Site 701 because of coring gaps and the lack of tight biostratigraphic control, it is possible to correlate the late Miocene sequence of reversals with Chrons C4A and C5. The polarity sequence observed in the very weakly magnetized middle to upper Eocene nannofossil chalks recovered from Hole 702B is correlated with Chrons C18 through C21. The correlation of the polarity sequences at these two sites provides a temporal framework for these sediments and makes it possible to calibrate southern high-latitude biostratigraphic datums to the geomagnetic polarity time scale.
Language	English
Dates of publication	1991-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Conference proceedings ; Online
Note	This dataset is supplement to doi:10.2973/odp.proc.sr.114.156.1991
DOI	10.1594/PANGAEA.734996
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: (Table 1) Ages of planktonic foraminiferal datums at Leg 94 Sites, supplementary data to: Weaver, Philip PE; Clement, Bradford M (1987): Magnetobiostratigraphy of planktonic foraminiferal datums: Deep Sea Drilling Project Leg 94, North Atlantic. In: Ruddiman, WF; Kidd, RB; Thomas, E; et al. (eds.), Initial Reports of the Deep Sea Drilling Project (U.S. Govt. Printing Office), 94, 815-829

Weaver, Philip PE / Clement, Bradford M

1987

Abstract: The six Leg 94 sites have produced a unique data set from a north-south transect of sites, all with good paleomagnetic records, and all but one with above-average accumulation rates. We show that it is necessary to have high accumulation rates to obtain ... ...

Abstract	The six Leg 94 sites have produced a unique data set from a north-south transect of sites, all with good paleomagnetic records, and all but one with above-average accumulation rates. We show that it is necessary to have high accumulation rates to obtain good quality magnetobiostratigraphies, and that it is difficult to correlate geological sequences over distances of several hundred kilometers without independent age control. Using the paleomagnetically derived ages for species ranges, we show several examples of diachronic first and last appearance datums between the core sites. This has enabled us to test the existing zonal schemes for the Pliocene-Pleistocene and to identify new zonal markers.
Language	English
Dates of publication	1987-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.2973/dsdp.proc.94.120.1987
DOI	10.1594/PANGAEA.788559
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Synchroneity of Pliocene planktonic foraminiferal datums in the North Atlantic, supplementary data to: Weaver, Philip PE; Clement, Bradford M (1986): Synchroneity of Pliocene planktonic foraminiferal datums in the North Atlantic. Marine Micropaleontology, 10(4), 295-307

Weaver, Philip PE / Clement, Bradford M

1986

Abstract: Leg 94 of the Deep Sea Drilling Project has provided a unique set of paleomagnetically dated cores, taken along a N-S transect in the North Atlantic. High deposition rates in the sediments, combined with the palaeomagnetic ages, have enabled existing ... ...

Abstract	Leg 94 of the Deep Sea Drilling Project has provided a unique set of paleomagnetically dated cores, taken along a N-S transect in the North Atlantic. High deposition rates in the sediments, combined with the palaeomagnetic ages, have enabled existing planktonic foraminiferal zonations to be tested and a new zonation for the mid- to high latitudes to be erected. The PL zonation of Berggren (1973, 1977) is shown to be adequate as far north as 41?N, although both the LAD's of Globigerina nepenthes and Globorotalia margaritae occur earlier than in tropical regions. North of 41?N these two species have very diachronous LAD's, even though they are common during their range in the northern sites. The new zonation for the mid to high latitude North Atlantic is based on the FAD of G. margaritae, FAD of G. puncticulata, LAD of G. cf. crassula, LAD of N. atlantica, FAD of G. inflata and FAD of sinistrally coiled encrusted N. pachyderma.
Language	English
Dates of publication	1986-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1016/0377-8398(86)90033-2
DOI	10.1594/PANGAEA.684353
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Strontium isotope record of Miocene sediments from DSDP Hole 94-608, supplementary data to: Miller, Kenneth G; Feigenson, Mark D; Wright, James D; Clement, Bradford M (1991): Miocene isotope reference section, Deep Sea Drilling Project Site 608: an evaluation of isotope and biostratigraphic resolution. Paleoceanography, 6(1), 33-52

Miller, Kenneth G / Clement, Bradford M / Feigenson, Mark D / Wright, James D

1991

Abstract: We developed an isotope (87Sr/86Sr, delta18O) reference section for the uppermost Oligocene to lower upper Miocene (ca. 25-8 Ma) at Site 608 in the northeastern North Atlantic. This site contains the least ambiguous magnetostratigraphic record of Miocene ...

Abstract	We developed an isotope (87Sr/86Sr, delta18O) reference section for the uppermost Oligocene to lower upper Miocene (ca. 25-8 Ma) at Site 608 in the northeastern North Atlantic. This site contains the least ambiguous magnetostratigraphic record of Miocene polarity changes available, providing direct correlations to the Geomagnetic Polarity Time Scale (GPTS). We integrate biostratigraphic, magnetostratigraphic, Sr isotope, and stable isotope data to provide a reference section for Miocene isotope fluctuations. The direct correlation of isotopes and biostratigraphy to the Geomagnetic Polarity Time Scale (GPTS) provides relatively precise age estimates. We use these age estimates to evaluate the timing of first and last occurrences of planktonic foraminifera, and conclude that many of these are synchronous within a 0.5 m.y. resolution between subtropical Site 563 (33?N) and high-latitude Site 608 (43?N). In addition, we use this chronology to estimate the ages of previously established Miocene oxygen isotope Zones Mi 1 through Mi 7 and to compare the Sr isotope record at Site 608 with previously published 87Sr/86Sr records. We approximate latest Oligocene to early late Miocene (25-8 Ma) Sr isotope changes with two linear regressions. The rate of increase of 87Sr/86Sr was high from the latest Oligocene (~25 Ma) to earliest middle Miocene (~15 Ma), with an estimated rate of 0.000059/m.y. Our ability to reproduce Sr isotope measurements is +/-0.000030 or better, yielding a stratigraphic resolution of as good as +/-0.5 m.y. for this interval. The rate of change was much lower from about 15 to 8 Ma (on average, 0.000013/m.y.), yielding Sr isotope stratigraphic resolution of worse than +/-2.3 m.y. The causes of the late Eocene to Miocene 87Sr/86Sr increases are not known. We speculate that a moderate 87Sr/86Sr increase (0.000030/m.y) which occurred during the late Eocene-latest Oligocene can be explained by intermittent glaciations and deglaciations of the Antarctic continent. These pulse-like changes in the input of glacial weathering products yield what appears to be a monotonic, linear increase. The increase in the frequency of glaciations during the latest Oligocene-early Miocene can explain the higher rate of change of 87Sr/86Sr at this time. We speculate that by the middle Miocene, the development of a permanent east Antarctica ice sheet resulted in decreased input of glacial weathering products and a lower rate of 87Sr/86Sr change.
Language	English
Dates of publication	1991-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1029/90PA01941
DOI	10.1594/PANGAEA.727187
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Stable isotope record and calcium carbonate concentrations of Late Pliocene sediments of the North Atlantic, supplementary data to: Raymo, Maureen E; Ruddiman, William F; Backman, Jan; Clement, Bradford M; Martinson, Douglas G (1989): Late Pliocene variation in northern hemisphere ice sheets and North Atlantic deep water circulation. Paleoceanography, 4(4), 413-446

Raymo, Maureen E / Backman, Jan / Clement, Bradford M / Martinson, Douglas G / Ruddiman, William F

1989

Abstract: High-resolution records of delta18O, delta13O, and percent CaCO3 from the late Pliocene North Atlantic (Deep Sea Drilling Project sites 607 and 609) are presented and oxygen isotope stages are formalized back to stage 116 at 2.73 Ma. From 2.8 to 1.6 Ma, ... ...

Abstract	High-resolution records of delta18O, delta13O, and percent CaCO3 from the late Pliocene North Atlantic (Deep Sea Drilling Project sites 607 and 609) are presented and oxygen isotope stages are formalized back to stage 116 at 2.73 Ma. From 2.8 to 1.6 Ma, the interval studied, variations in these records were dominated by the 41-kyr component of orbital obliquity. Significant variation at the orbital frequencies of eccentricity (96-kyr) and precession (23-kyr) are observed in the delta18O record between 1.6 and 2.1 Ma, but not before. Prior to 2.4 Ma (stage 100), delta18O variations suggest ice sheet growth 1/4 to 1/2 as large as late Pleistocene ice volumes; however, these events are below the threshold needed to result in extensive ice-rafting to the open North Atlantic Ocean. After 2.4 Ma, ice sheets appear to be, on average, 1/2 as large as those of the late Pleistocene. The delta18O record indicates that some glacial suppression of North Atlantic Deep Water occurred both before and after 2.4 Ma and that glacial-interglacial transfers of 12C between the continents and oceans appear to have been larger in the late Pliocene relative to the late Pleistocene. In addition, the strong 23-kyr power observed in delta18O between 2.75 and 2.10 Ma suggests that deep-sea circulation (or changes in biomass) is controlled, in part, by climatic variations unrelated to ice sheets.
Language	English
Dates of publication	1989-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1029/PA004i004p00413
DOI	10.1594/PANGAEA.701337
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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Book ; Online: Stable isotope record, calcium carbonate conentrations, and sea surface temperture reconstructions of sediment cores from the North Atlantic, supplementary data to: Ruddiman, William F; Raymo, Maureen E; Martinson, Douglas G; Clement, Bradford M; Backman, Jan (1989): Pleistocene evolution: northern hemisphere ice sheets and North Atlantic Ocean. Paleoceanography, 4(4), 353-412

Ruddiman, William F / Backman, Jan / Clement, Bradford M / Martinson, Douglas G / Raymo, Maureen E

1989

Abstract: We analyze five high-resolution time series spanning the last 1.65 m.y.: benthic foraminiferal delta18O and delta13O, percent CaCO3, and estimated sea surface temperature (SST) at North Atlantic Deep Sea Drilling Project site 607 and percent CaCO3 at ... ...

Abstract	We analyze five high-resolution time series spanning the last 1.65 m.y.: benthic foraminiferal delta18O and delta13O, percent CaCO3, and estimated sea surface temperature (SST) at North Atlantic Deep Sea Drilling Project site 607 and percent CaCO3 at site 609. Each record is a multicore composite verified for continuity by splicing among multiple holes. These climatic indices portray changes in northern hemisphere ice sheet size and in North Atlantic surface and deep circulation. By tuning obliquity and precession components in the delta18O record to orbital variations, we have devised a time scale (TP607) for the entire Pleistocene that agrees in age with all K/Ar-dated magnetic reversals to within 1.5%. The Brunhes time scale is taken from Imbrie et al. [1984], except for differences near the stage 17/16 transition (0.70 to 0.64 Ma). All indicators show a similar evolution from the Matuyama to the Brunhes chrons: orbital eccentricity and precession responses increased in amplitude; those at orbital obliquity decreased. The change in dominance from obliquity to eccentricity occurred over several hundred thousand years, with fastest changes around 0.7 to 0.6 Ma. The coherent, in-phase responses of delta18O, delta13O, CaCO3 and SST at these rhythms indicate that northern hemisphere ice volume changes have controlled most of the North Atlantic surface-ocean and deep-ocean responses for the last 1.6 m.y. The delta13O, percent CaCO3, and SST records at site 607 also show prominent changes at low frequencies, including a prominent long-wavelength oscillation toward glacial conditions that is centered between 0.9 and 0.6 Ma. These changes appear to be associated neither with orbital forcing nor with changes in ice volume.
Language	English
Dates of publication	1989-9999
Size	Online-Ressource
Publisher	PANGAEA - Data Publisher for Earth & Environmental Science
Publishing place	Bremen/Bremerhaven
Document type	Book ; Online
Note	This dataset is supplement to doi:10.1029/PA004i004p00353
DOI	10.1594/PANGAEA.701229
Database	Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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