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SUMMARY International Ocean Drilling Program (IODP) Expedition 341 recovered sediments from the south Alaska continental slope that preserves a well resolved and dated inclination record over most of the past ∼43 000 yr. The Site U1419 chronology is among the highest resolution in the world, constrained by 173 radiocarbon dates, providing the ability to study Palaeomagnetic Secular Variation (PSV) on centennial to millennial timescales. This record has an exceptionally expanded late Pleistocene sedimentary record with sedimentation rates commonly exceeding 100 cm kyr–1, while also preserving a lower resolution Holocene PSV record at the top. Natural and laboratory-induced magnetic remanences of U1419 u-channels from the 112-m-long spliced record were studied using stepwise AF demagnetization. Hysteresis loops were obtained on 95 and IRM acquisition curves on 9 discrete samples to facilitate magnetic domain state, coercivity and magnetic mineralogical determinations. Due to complexities related to lithology, magnetic mineralogy, and depositional and post-depositional processes, Site U1419 sediments are not suitable for palaeointensity studies and declination could not be robustly reconstructed. Progressive (titano-)magnetite dissolution with depth results in decreasing NRM intensity and signal-to-noise that is exacerbated at higher demagnetization steps. As a result, inclination measured after the 20 mT AF demagnetization step provides the most reliable directional record. Inclination appears to be well resolved with removal of just a few intervals influenced by depositional and/or sampling and coring deformation. The shipboard inclination stack from nearby IODP Site U1418, on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC, verifies centennial to millennial scale variations in inclination observed in U1419. Comparisons with other independently dated records from the NE Pacific and western North America suggest that these sites likely capture regional geomagnetic variability. As such, this new high-resolution and well-dated inclination record, especially robust between 15 and 30 cal kyr BP, offers new geomagnetic insights and a regional correlation tool to explore this generally understudied part of the world.
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Age model of sediment core SU92-18
Relative changes in geomagnetic field intensity over the last 280 kyears have been recovered from the study of three marine cores from the Açores area. One core was precisely dated by oxygen isotope study and the other two records were linked to it using light reflectance analysis which allowed precise correlation. Rock magnetic analysis shows that the main magnetic mineral is magnetite with a very homogeneous grain-size distribution in the pseudo-single domain range for the three cores. Changes in the amount of magnetite do not exceed a factor of 10. Therefore, these cores appear to be suitable for relative palaeointensity determinations. Two mineral magnetic components with periodicities of 23 and 18 kyears are present in the records of bulk magnetic parameters and natural remanent magnetisation (NRM), but the power at these frequencies is not significant at the 95% level for the normalised remanence records. For each core, normalisation of the NRM using different normalising parameters yields virtually identical results. Using saturation isothermal remanent magnetisation (SIRM) as the normalising parameter, the results of the three cores were then combined into a stacked curve. Squared coherence analysis between this stacked curve and bulk mineral-magnetic parameters reveals that the 18 kyear component is still present in the record, but that the power spectrum is barely above noise level at this frequency. Some of the features of this North Atlantic record are consistent with the main characteristics already documented in other sedimentary or volcanic records. For instance, distinct periods of low intensity are observed around 40, 120, and 190 kyears, and periods of high intensity at 50 and 80 kyears. Because of the uniformity of the mineral-magnetic characteristics of the three cores, we suggest that this record may be a suitable palaeointensity reference curve for the Central North Atlantic Ocean region.
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- Award ID(s):
- 0707551
- PAR ID:
- 10556409
- Publisher / Repository:
- PANGAEA
- Date Published:
- Edition / Version:
- 1
- Subject(s) / Keyword(s):
- DEPTH, sediment/rock Age model Isotopic event Piston corer Age model, Martinson et al (1987) SU92 Le Suroît
- Format(s):
- Medium: X Size: 30 data points Other: text/tab-separated-values
- Size(s):
- 30 data points
- Location:
- (Latitude:37.788333333333; Longitude:-27.231666666667); North Atlantic Ocean
- Right(s):
- Creative Commons Attribution 3.0 Unported
- Sponsoring Org:
- National Science Foundation
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