Origin of millennial-scale climate signals in the subtropical North Atlantic
Abstract
In this study, I am testing the hypothesis that millennial-scale climate signals in the northwestern subtropical Atlantic are linked to external driving factors such as the harmonics of precession. The test is based on the observation that the precession period is not stationary through time. For example, between 900 and 340 Ka the time interval between successive precession minima (or maxima) ranges primarily from 17 kyr to 21 kyr with discrete intervals lasting up to ~30 kyr (spectral power centered on the 23 kyr and 19 kyr periodicities). After 340 Ka, however, precession minima (or maxima) consistently occur at longer intervals, between 21 kyr and 25 kyr (spectral power focused at the 23 kyr period). If in proxy records millennial-scale variations reflect the harmonics of precession, I expect that the millennial-scale periodicity associated with the 19 kyr precession period (e.g., the 4.8 kyr peak) loses power as the primary orbital peak loses power at 340 Ka. First order tests of this idea can be made using published planktic foraminiferal δ18O records from ODP Site 1059 (Hagen and Keigwin, 2002; Oppo et al., 2001) in the northwestern subtropical Atlantic spanning Marine Isotope Stages 2-6 (~20-150 Ka) and Site 1058 spanning MIS 12-22 (~450-900 Ka, Weirauch et al., 2008). After filtering the records to remove the 100 kyr cycle, the older time slice contains both precession peaks (23 and 19 kyr). Significant (95% confidence interval) suborbital peaks occur at 12 kyr, 5.7 kyr and 5.0 kyr, which are close to the periodicities of the expected harmonics. The younger time slice shows only one precession peak centered at ~23 kyr and significant (95% confidence interval) sub-orbital peaks at 11.2 kyr, and 5 kyr. Only the 11.2 kyr peak agrees with the expected period of the second harmonic of the 23 kyr precession peak. We are currently generating high resolution planktic foraminiferal stable isotope records in this region to span MIS 7, which, together with data from MIS 9 (Billups et al. in press) will complete a ~1.4 myr long record of suborbital climate proxy variability that will allow us to fully resolve changes in precession variations and potentially related suborbital periodicities.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP43A1803B
- Keywords:
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- 4910 PALEOCEANOGRAPHY / Astronomical forcing;
- 4934 PALEOCEANOGRAPHY / Insolation forcing;
- 4999 PALEOCEANOGRAPHY / General or miscellaneous