Grochrmw et ~~~wmrhrmrca .4rro Vd 47. pp IOX-103 I C Pergamon Press Ltd 19R3 Pnntcd I” U S.A. Experimental paleotemperature equation for planktonic foraminifera JONATHAN EREZ The Hebrew University of Jerusaiem. The l-i. Steinitz Marine Biology Laboraiory. Eilat. P.O. Box 469. israei and BOAZ LUZ Dept. of Geology. The Hebrew University of Jerusalem. Jerusalem. Israel (Received April 22. 1982: accepted in revised,fbrm Februar;, 24. 1983) Abstract-Small live individuals of Globigerrnoides sacculj/h’ which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14’ to 30°C) and water isotopic composition. and a correction was made lo account for the isotopic composition of the original skeleton using control groups. Comparison of.the actual growth temperatures with the calculated temperature based on paleotem- perature equations for inorganic CaCOz indicate that the foraminifera precipitate their CaC03 in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with CRAIG’S (I 965) equation yields: I = -0.07 + l.Oli (r = 0.95) where I is the actual growth temperature and iis the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate. is equally applicable for the planktonic foraminifer G. saccu/jj?r. Second order regression of the culture temperature and the delta difference (6”Oc - 6’*Oro) yield a correlation coefficient of r = 0.95: i = 17.0 - 4.52(6’“Oc - ~‘“OW) + O.O3(b’“Oc - ~“‘OW)’ i, d”Oc and b’RO~, are the estimated temperature. the isotopic composition of the shell carbonate and the sea water respectively. A possible cause for nonequilibrium isotopic compositions reported earlier for living planktonic for- aminifera is the improper combustion of the organic matter. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP INTRODUCT’ION IN 1974 H. UREY suggested that stable oxygen iso- tope ratios in carbonate materials can be used to de- duce paleotemtiratures. Following his suggestion EPSTEIN ef al. ( 195 1, 1953) developed a paleotem- perature scale (or equation) for biogenic CaC03. They analyzed molluscs carbonate that grew at known temperatures and known water isotopic com- position. The result was the following familiar equa- tion: i = 16.5 - 4.3(6’RO~ - 6”Ow) + O.l4(6’8Oc - b’8Ow)? where zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA iis the estimated temperature (or isotopic tem- perature) and d”Oc and 6”~ are the oxygen isotopic compositions of the carbonate and sea water. re- spectively. This equation was later modified by CRAIG ( 1965) to account for “0 and instrumemal inaccuracies: i = 16.9 - 4.2(6”Oc - 6”Ow) + O.l3(6’8Oc - 6’80M’)’ These equations match well the experimental data of MCCREA (1950) and O’NEILL et al. (1969) for inorganic calcite within experimental errors. EMILI- ANI (1954. 1955, 1966) applied these equations for the first time to planktonic foraminifera in deep sea cores, and concluded that planktonic foraminifera deposit their skeleton in isotopic equilibrium with sea water and hence they can be used for paleoenviron- mental studies provided that d”Ow can be estimated. (See also SAWN and DOUGLAS, 1973; SHACKLETON and VINCENT, 1978; and BERGER ef al., 1978.) Fol- lowing EMILIANI,a considerable body of information on stable isotope distributions in planktonic fora- minifera has been gathered, and as a result much insight has been gained into Pleistocene paleoenvi- ronmental conditions (e.g., SHACKLETON and OP- DYKE 1973, 1976: SHACKLETON 1977: EMILIANI, 1955, 1966, 197 i; EMILIANI and SHACKLETON, 1974; HECHT, 1973, 1974; DUPLESSY et al., 1975; VAN DONK, 1977; and many others). Despite the vast amount of data on stable isotopic compositions in planktonic foraminifera, until re- cently little attention was given to the fact that the paleotemperature equation was tested for mollusca and not for foraminifera. Questions about the validity of the basic equilibrium assumption were first asked when it was found that different benthonic forami- nifera have different specific isotopic fractionations (DUPLESSY et al., 1970; VINOT-BERTOUILLE and DUPLESSY, 1973). Attempts to test whether plank- 1025