Origin of millennial-scale climate instabilities in the subtropical Atlantic Ocean
Abstract
We have generated a high resolution (~250-500 year) planktonic foraminiferal stable isotope record (Globigerinoides ruber white, senso lato) spanning Marine Isotope Stages (MIS) 6 through 8 in the northwestern subtropical Atlantic (Ocean Drilling Program Leg 172 Site 1059). The record fills a gap in an about 1.3 million year long time series of millennial-scale surface ocean hydrography in this region. We test the hypothesis that sub-orbital climate signals are linked to a response to precession forcing in tropical latitudes. Power spectra provide evidence for an increase in the length of half precession cycles as the 19 kyr precession period disappears from the insolation forcing at about 320 Ka in first order support of the hypothesis. In the time series, half precession (and quarter precession cycles when present) are evident as double (and quadruple) peaks within the given precession framework. However, in the time series there is no match between the amplitude modulation of the precession signal and its harmonics. During the time interval between 340-0 Ka (MIS 9-1) when the temporal resolution is high (250 year time step), the power spectra also contain significant peaks in the Dansgaard-Oeschger band (~1-8-1.5 kyr). Comparison of filter output with the time series, however, illustrates that there are only few instances where these types of variations are distinct in the foraminiferal δ18O record. We conclude that the evolution of half precession cycles over the time interval is largely consistent with a response to low latitude insolation, such as introduced by insolation maxima at the equinoxes and solstices (e.g., Short et al., 1991). Our analysis also shows that quarter precession cycles are present in the time series, at least intermittently, but we cannot uniquely tie them to changes in the primary precession signal. Our study highlights the importance of evaluating variations in the original time series to guide interpretations of significant peaks in power spectra.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP21A1884B
- Keywords:
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- 4900 PALEOCEANOGRAPHY;
- 4901 PALEOCEANOGRAPHY Abrupt/rapid climate change;
- 4934 PALEOCEANOGRAPHY Insolation forcing