Ž . Marine Geology 161 1999 247–255 www.elsevier.nlrlocatermargeo Excess aluminum in deep sea sediments of the Central Indian Basin J.N. Pattan ) , P. Shane National Institute of Oceanography, Geological Oceanography DiÕision, Dona Paula, Goa, 403 004, India Department of Geology, UniÕersity of Auckland, PriÕate Bag 92019, Auckland, New Zealand Received 9 September 1998; accepted 30 April 1999 Abstract The aluminum concentration in the marine sediments has long been considered an indicator of terrigenous abundance. Ž . The AlrTi values 48.5 of the Central Indian Basin subsurface siliceous sediment are up to three times that of Post-Archean Ž . Ž . Australian Shale PAAS . The estimation of structurally unsupported Al Al from six sediment cores suggests that an ex average of 40% of total Al is from noncrustal sources. Higher AlrTi or Al values are often, but not exclusively, associated ex with abundant volcanic unaltered glass shards. Electron microprobe analysis of 60 of these glass shards reveals that they are Ž . rhyolitic in composition and of Youngest Toba 74 ka origin from Northern Sumatra. These glass shards have very high Ž . AlrTi ratio of 175 mean . AlrTi values are also above the PAAS in sediment where glass shards are absent, which could be due to scavenging of dissolved Al by biogenic components. q 1999 Elsevier Science B.V. All rights reserved. Keywords: AlrTi; excess aluminum; volcanic glass; scavenging; Central Indian Basin 1. Introduction Ž . Aluminum Al is the third most abundant ele- Ž . ment in the earth’s crust 8.23% by wt. and has mean oceanic dissolved concentration of ; 2 nmolrkg with a residence time of - 200 years Ž . Orians and Bruland, 1985 . Al in the seawater oc- Ž . 0 Ž . y curs as Al OH and Al OH species and is very 3 4 Ž particle-reactive Orians and Bruland, 1985; Mea- . sures et al., 1986; Moran and Moore, 1988 . The sources of dissolved Al in the ocean include fluvial ) Corresponding author. Fax: q91-832-223340; E-mail: pattan@csnio.ren.nic.in and aeolian sources, as well as the diffusion of Ž dissolved Al from the sediment pore waters Hydes, . 1983 . Al and Ti concentrations in marine sediments have long been considered to be dominated by Ž . lithogenous phase. Murray et al. 1993 and Murray Ž . and Leinen 1996 suggested that AlrTi values in the biogenic sediment dominated by calcium carbon- Ž . ate CaCO ) 90% in the Equatorial Pacific reflect 3 particle flux, and by extension, therefore, the ocean Ž . productivity. Dymond et al. 1997 confirmed these Ž . observations of excess Al nondetrital source, but instead considered the AlrTi ratio to reflect opal rain to seafloor, based on the studies of settling particles collected by sediment traps. Recently, Tim- Ž . othy and Calvert 1998 speculated that high AlrTi 0025-3227r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0025-3227 99 00042-0