Traces of dissolved particles, including coccoliths, in the tests of agglutinated foraminifera from the Challenger Deep (10,897m water depth, western equatorial Pacific)

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.11.003 Byline: A.J. Gooday (a), K. Uematsu (b), H. Kitazato (c), T. Toyofuku (c), J.R. Young (d) Keywords: Hadal; Deep-sea trench; Coccolithophorids; Phytodetritus; Dissolution; Organic test lining Abstract: We examined four multilocular agglutinated foraminiferan tests from the Challenger Deep, the deepest point in the world's oceans and well below the depth at which biogenic and most detrital minerals disappear from the sediment. The specimens represent undescribed species. Three are trochamminaceans in which imprints and other traces of dissolved agglutinated particles are visible in the orange or yellowish organic test lining. In Trochamminacean sp. A, a delicate meshwork of organic cement forms ridges between the grain impressions. The remnants of test particles include organic structures identifiable as moulds of coccoliths produced by the genus Helicosphaera. Their random alignment suggests that they were agglutinated individually rather than as fragments of a coccosphere. Trochamminacean sp. C incorporates discoidal structures with a central hole; these probably represent the proximal sides of isolated distal shields of another coccolith species, possibly Hayaster perplexus. Imprints of planktonic foraminiferan test fragments are also present in both these trochamminaceans. In Trochamminacean sp. B, the test surface is densely pitted with deep, often angular imprints ranging from roughly equidimensional to rod-shaped. The surfaces are either smooth, or have prominent longitudinal striations, probably made by cleavage traces. We presume these imprints represent mineral grains of various types that subsequently dissolved. X-ray microanalyses reveal strong peaks for Ca associated with grain impressions and coccolith remains in Trochamminacean sp. C. Minor peaks for this element are associated with coccolith remains and planktonic foraminiferan imprints in Trochamminacean sp. A. These Ca peaks possibly originate from traces of calcite remaining on the test surfaces. Agglutinated particles, presumably clay minerals, survive only in the fourth specimen ('Textularia' sp.). Here, the final 4-5 chambers comprise a pavement of small, irregularly shaped grains with flat surfaces and no obvious intervening cement. Our observations suggest that (1) small biogenic particles can reach the deepest parts of the ocean intact in rapidly sinking phytodetrital aggregates or faecal pellets and (2) some agglutinated foraminifera living at extreme hadal depths construct a test from biogenic or detrital particles, which subsequently dissolve, leaving imprints and other remnants in the organic matrix of the test. Author Affiliation: (a) National Oceanography Centre, Southampton, European Way, Southampton, Hampshire, SO14 3ZH, UK (b) Marine Works Japan LTD., 2-15 Natsushima-cho,Yokosuka 237-0061, Japan (c) Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan (d) Palaeontology Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK Article History: Received 30 June 2009; Revised 4 November 2009; Accepted 6 November 2009