[1] We present a new common stratigraphic timescale for the North Greenland Ice Core Project (NGRIP) and GRIP ice cores. The timescale covers the period 7.9–14.8 kyr before present and includes the Bolling, Allerod, Younger Dryas, and early Holocene periods. We use a combination of new and previously published data, the most prominent being new high-resolution Continuous Flow Analysis (CFA) impurity records from the NGRIP ice core. Several investigators have identified and counted annual layers using a multiparameter approach, and the maximum counting error is estimated to be up to 2% in the Holocene part and about 3% for the older parts. These counting error estimates reflect the number of annual layers that were hard to interpret, but not a possible bias in the set of rules used for annual layer identification. As the GRIP and NGRIP ice cores are not optimal for annual layer counting in the middle and late Holocene, the timescale is tied to a prominent volcanic event inside the 8.2 kyr cold event, recently dated in the DYE-3 ice core to 8236 years before A. D. 2000 (b2k) with a maximum counting error of 47 years. The new timescale dates the Younger Dryas-Preboreal transition to 11,703 b2k, which is 100–150 years older than according to the present GRIP and NGRIP timescales. The age of the transition matches the GISP2 timescale within a few years, but viewed over the entire 7.9–14.8 kyr section, there are significant differences between the new timescale and the GISP2 timescale. The transition from the glacial into the Bolling interstadial is dated to 14,692 b2k. The presented timescale is a part of a new Greenland ice core chronology common to the DYE-3, GRIP, and NGRIP ice cores, named the Greenland Ice Core Chronology 2005 (GICC05). The annual layer thicknesses are observed to be log-normally distributed with good approximation, and compared to the early Holocene, the mean accumulation rates in the Younger Dryas and Bolling periods are found to be 47 ± 2% and 88 ± 2%, respectively.

/pdf/a-new-greenland-ice-core-chronology-for-the-last-glacial-3dndo2ft0g.pdf

A new Greenland ice core chronology for the last glacial termination

Surrogate time series

A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China

https://boris.unibe.ch/62575/1/1-s2.0-S0277379114003485-main.pdf

A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

https://www.manfredmudelsee.com/publ/pdf/redfit.pdf

REDFIT: estimating red-noise spectra directly from unevenly spaced paleoclimatic time series

The 3-km-long Greenland Ice Sheet Project 2 (GISP2) ice core presents a 100,000 +- year detailed oxygen isotope profile covering almost a full glacial-interglacial cycle. Measuranents of isotopic fluctuations in snow, frost, and atmospheric water vapor samples collected during summer field seasons (up to 20%0) are compatible with the large and abrupt 80/160 changes observed in accumulated tim. Snow pit 1580 profiles from the GISP2 summit area, however, show rapid smoothing of the 180/160 signal near the surface. Beyond about 2-m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate. The longer climate fluctuations also have regional and often global significance. In the older part of the record, corresponding to marine isotope stages (MIS) 5a to 5d, the effect of orbital climate forcing via the 19- and 23-kyr precession cycles and the 41-kyr obliquity cycle is obvious. From the end ofMIS 5a, at about 75,000 years B.P., till the end of the glacial at the Younger Dryas-Preboreal transition, at 11,650 years B.P., the O180/160 record shows frequent, rapid switches between intermediate interstadial and low stadial values. Fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1.5 kyr, a broad peak at 4.0 kyr, and additional shorter periods. Detailed comparison of the GISP2 180/160 record with the Vostok, Antarctica, 15D record; Pacific Ocean foraminiferal 180/160; Grande Pile, France, tree pollen; and insolation indicates that a counterpart to many of the rapid 180/160 fluctuations of GISP2 can be found in the other records, and that the GISP2 isotopic changes clearly are the local expression of climate changes of worldwide extent. Correlation of events on the independent GISP2 and SPECMAP time scales for the interval 10,000-50,000 years B.P. shows excellent chronometric agreement, except possibly for the event labeled 3.1. The glacial to interglacial transition evidently started simultaneously in the Arctic and the Antarctic, but its development and its expression in Greenland isotopes was later suppressed by the influence of meltwater, especially from the Barents Sea ice sheet, on deep water formation and ocean circulation. Meltwaters from different ice sheets bordering the North Atlantic also influenced ocean circulation during the Bolling-Allerod interstadial complex and the Younger Dryas and led to a distinct development of European climate and Greenland 180/160 values. The Holocene interval with long-term stable mean isotopic values contains several fluauations with periods from years to millennia. Dominant is a 6.3-year oscillation with amplitude up to 3 to 4%0. Periodicities of 11 and 210 years, also found in the solar-modulated records of the cosmogenic isotopes 1oBe and 14C, suggest solar processes as the cause of these cycles. Depression of180/160 values (cooling) by volcanic eruptions is observed in stacked GISP21580 records, but the effect is small and not likely to trigger major climate changes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JC00880

M. Stuiver

Papers

Oxygen 18/16 variability in Greenland snow and ice with 10 -3- to 105-year time resolution