BLEACH REMOVES LABILE AMINO-ACIDS FROM DEEP-SEA PLANKTONIC FORAMINIFERAL SHELLS

Chemotaxonomic and aminostratigraphic use of planktonic foraminiferal shell amino acid compositions assume that recovered amino acids are fr om organic material originally produced by the living foraminifer. Dee p sea planktonic foraminiferal shells that were bleached prior to amin o acid analysis show evidence of a labile, amino acid-containing organ ic fraction which may include contaminating adsorbed material. The lab ile organic matter composition and amount have been inferred by compar ing amino acid recoveries from samples cleaned only by ultrasonication in buffered sodium hexametaphosphate or methanol, to those additional ly bleached with sodium hypochlorite. The labile fraction is chemicall y accessible to bleach, contains an unknown proportion of adsorbed con tamination, and has a different amino acid composition than the chemic ally inaccessible fraction. The amino acid composition of the labile m aterial differs between Globigerinoides sacculifer, Globorotalia tumid a, and Globorotalia inflata samples from different core samples. Labil e material is not always present: amino acids were removed by bleachin g late Pliocene Globorotalia inflata samples from DSDP 588-4-1, but no t by bleaching late Pliocene samples of the same species from DSDP 588 -5-1. Bleached late Pliocene Globorotalia inflata samples from DSDP 58 8-4-1 also had a higher D-allo-isoleucine to L-isoleucine ratio (aIle/ Ile) than unbleached samples. The amount of labile material removed va ried from 0.6 to 1.3 mumole/g calcite. Amino acid recovery from bleach ed samples with the labile fraction removed ranged from 1-2 mumole/g c alcite. Labile fraction amino acids losses thus represented 23%-42% of unbleached total recoveries. The amino acid composition of the chemic ally inaccessible fraction retained a species specificity among the th ree planktonic foraminiferal species examined. Removal of labile, poss ibly exogenous, material by oxidative treatment is recommended prior t o amino acid analysis of all foraminiferal shell samples for aminostra tigraphy and chemotaxonomy, so that only amino acids from the chemical ly inaccessible organic material are compared.