TY - JOUR
T1 - Climate proxies from Sr/Ca of coccolith calcite
T2 - Calibrations from continuous culture of Emiliania huxleyi
AU - Stoll, Heather M.
AU - Rosenthal, Yair
AU - Falkowski, Paul
N1 - Funding Information:
This study was partially supported by National Science Foundation grant OCE9986716 to Yair Rosenthal, Binational Science Foundation grant 97-00335/1 to Paul Falkowski, North Atlantic Treaty Organization grant DGE-98-04555 to Heather M. Stoll, and a postdoctoral fellowship from the II Plan Regional de Investigación del Principado de Asturias (awarded in 1999 to Heather M. Stoll). We thank Kevin Wyman, Joshua Nelson, and Karen Weber for their help in the maintenance of the culture chambers at Rutgers. We thank Bruce Watson and Yan Liang for providing us with their source code for the surface enrichment model and Harry Stoll for translating source code into Visual Basic. We thank the participants of the September 2000 CODENET workshop, especially Jeremy Young, for their insights on mechanisms of crystal growth in coccolith calcite, which permitted application of the surface enrichment model to coccoliths. Thoughtful and constructive reviews were provided by Peggy Delaney and two anonymous reviewers.
PY - 2002/3/15
Y1 - 2002/3/15
N2 - Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of crystal growth indicate that kinetic effects on Sr partitioning in calcite due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with "b," the slope of the dependence of carbon isotope fractionation in biomarkers (εp on CO2(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone εp may improve paleo-CO2 determinations.
AB - Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of crystal growth indicate that kinetic effects on Sr partitioning in calcite due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with "b," the slope of the dependence of carbon isotope fractionation in biomarkers (εp on CO2(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone εp may improve paleo-CO2 determinations.
UR - http://www.scopus.com/inward/record.url?scp=0000329422&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0000329422&partnerID=8YFLogxK
U2 - 10.1016/S0016-7037(01)00836-5
DO - 10.1016/S0016-7037(01)00836-5
M3 - Article
AN - SCOPUS:0000329422
SN - 0016-7037
VL - 66
SP - 927
EP - 936
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 6
ER -