Groeneveld, Jeroen; Nuernberg, Dirk; Steph, Silke; Tiedemann, Ralf (2003): Influence of salinity on planktic foraminiferal Mg/Ca as deduced from a reconstruction of the shoaling of the Isthmus of Panama. Geological Society of America (GSA), Boulder, CO, United States, In: Anonymous, Geological Society of America, 2003 annual meeting, 35 (6), 585, georefid:2004-081702

Samples from ODP Site 1000 from a waterdepth of 916 m were used to reconstruct a Mg/Ca-record for the early Pliocene Caribbean Sea. Analyses were done on the planktonic foraminifer Globigerinoides sacculifer. By comparing Mg/Ca values and delta (super 18) O stable isotopes of G.sacculifer from the same samples we conclude that Mg/Ca is not only recording the temperature history in the Caribbean but also displays a considerable salinity-effect due to the shoaling of the Isthmus of Panama. The interval prior to 4.6 Ma, when there still existed a free exchange of upper ocean watermasses between the Pacific and the Atlantic, shows Mg/Ca and delta (super 18) O-records which are negatively correlated to each other, with SSTs varying between 26.5 degrees C and 29 degrees C. After 4.6 Ma, when the Panamanian sill shoaled to a waterdepth of less than 100 m, the Mg/Ca and delta (super 18) O records show a positive correlation. Unrealistic cyclicities with Mg/Ca-temperature variations of up to 5 degrees C and maximum temperatures over 34 degrees C suggest an additional factor influencing the Mg/Ca-record. The positive correlation between Mg/Ca and delta (super 18) O implies that maximum temperatures are accompanied by maximum salinities. Since increasing salinity is known to increase the Mg/Ca-ratio in foraminifers by 4-10%/1 psu (Nuernberg et al. '96, Lea et al. '99), we conclude that salinity changes of up to 4 psu have increased Mg/Ca-ratios by as much as 20-30% after 4.6 Ma. To determine the absolute salinity change during this interval, we extracted the temperature and ice-effect signals from the delta (super 18) O-record. We used the 2-2.5 degrees C cyclicity from prior to 5.6 Ma in the Mg/Ca-record to extract the temperature signal from the delta (super 18) O-record. The benthic delta (super 18) O-record from Site 846 was used as an initial approach to assess the ice-effect. The resulting Mg/Ca temperature reconstruction shows an increase in average SST after 4.6 Ma from 26.5 degrees C to 28.5 degrees C.
West: -83.0200 East: -77.1000 North: 9.4000 South: 7.1000
West: NaN East: NaN North: NaN South: NaN
Expedition: 138
Site: 138-846
Expedition: 165
Site: 165-1000
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