A pseudo-Thellier relative palaeointensity record, and rock magnetic and geochemical parameters in relation to climate during the last 276 kyr in theAzores region

In the pseudo-Thellier method for relative palaeointensity determinations ( Tauxe et al. 1995) the slope of the NRM intensity left after AF demagnetiza tion versus ARM intensity gained at the same peak field is used as a palaeo intensity measure. We tested this method on a marine core from the Azores, spanning the last 276 kyr. We compared the pseudo-Thellier palaeointensity record with the conventional record obtained earlier by Lehman et al. (1996 ), who normalized NRM by SIRM. The two records show similar features: inten sity lows with deviating palaeomagnetic directions at 40-45 ka and at 180-1 90 ka. The first interval is associated with the Laschamps excursion, while the 180-190 ka low represents the Iceland Basin excursion (Channell et al. 1997). The pseudo-Thellier method, in combination with a jackknife resampl ing scheme, provides error estimates on the palaeointensity. Spectral analysis of the rock magnetic parameters and the palaeointensity e stimates shows orbitally forced periods, particularly 23 kyr for climatic p recession. This suggests that palaeointensity is still slightly contaminate d by climate. Fuzzy c-means cluster analysis of rock magnetic and geochemic al parameters yields a seven-cluster model of predominantly calcareous clus ters and detrital clusters. The clusters show a strong correlation with cli mate, for example samples from detrital clusters predominantly appear durin g rapid warming. Although both the pseudo-Thellier palaeointensity m(a) and fuzzy clusters show climatic influences, we have not been able to find an unambiguous connection between the clusters and m(a).