Iceberg-Rafted Debris data from South Atlantic for study of Antarctic Ice Sheet stability over last ~500 kyrs

This database contains the data resulting from a study of Antarctic Ice Sheet history, over the last ~500 thousand years. Iceberg-rafted debris (IRD), considered as an indicator of the presence of a continental ice sheet in the source area, is counted and analyzed in relation to the other components of the studied size fraction. The study materials are derived from two cores raised from a deep-water marine site in the southeastern Atlantic Ocean: the piston core TN057-6-PC4 and the associated drill core from the Ocean Drilling Program (ODP) Leg 177 Site 1090 (177-1090). Because the top portion of the 177-1090 drill core was apparently disturbed by the drilling, the piston core TN057-6-PC4 has been used to represent the most recent part of the record. The site is located at ~43 deg S, 9 deg E, about 2/3 of the way from the Antarctic coast to South Africa. The location from which both cores were raised is on the southern slope of the Agulhas Ridge, on the northern edge of the Agulhas Basin, in the southeastern Atlantic Ocean. The initial cleaning and preparation of samples from these cores was carried out by Kathryn Venz and David Hodell (UF). The methods used here to examine the IRD are those described by Allen and Warnke (1991, doi:10.2973/odp.proc.sr.114.118.1991), Stanton (1997), and Murphy et al. (2002, doi:10.1016/S0031-0182(01)00495-3). The samples were first weighed, then separated by sieving into four size fractions: <150 microns, 150-250 microns, 250 microns to 2 mm, and >2 mm. The medium to coarse sand size fraction (250 microns to 2 mm) was utilized for our study. Within this, a split of about 1000 grains was obtained; the grains in this split were counted. Grains that were counted within categories that included: quartz, feldspar, mafic minerals, lithic fragments, volcanic lithics, volcanic ash, diatoms, planktic forams, benthic forams, radiolarians, and 'other'. The counts of quartz, feldspar, mafic minerals and lithic non-volcanic fragments were then summed as IRD. Following the suggestion of Murphy et al. (2002), the final step of this stage was a brief overview of the non-counted portion of the 250 micron to 2 mm size fraction, primarily to look for 'background rafting'. Background rafting refers to the presence of IRD in the non-counted portion (i.e., outside of the counted split) of the size fraction. For this study, a note was made of the presence or absence only of any IRD clasts in the non-counted portion.