Groeneveld, Jeroen et al. (2003): Influence of salinity on planktic foraminiferal Mg/Ca as deduced from a reconstruction of the shoaling of the Isthmus of Panama

ODP 138
ODP 165
ODP 165 1000
ODP 138 846

Groeneveld, Jeroen
GEOMAR, Paleoceanology, Kiel, Federal Republic of Germany

Nuernberg, Dirk

Steph, Silke

Tiedemann, Ralf

Influence of salinity on planktic foraminiferal Mg/Ca as deduced from a reconstruction of the shoaling of the Isthmus of Panama
In: Anonymous, Geological Society of America, 2003 annual meeting
Geological Society of America (GSA), Boulder, CO, United States
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.
Coverage:Geographic coordinates:
West:-83.0200East: -77.1000

Stratigraphy; Isotope geochemistry; alkaline earth metals; Atlantic Ocean; benthic taxa; biochemistry; calcium; Caribbean Sea; Cenozoic; Central America; chemical ratios; chemostratigraphy; cycles; Foraminifera; geochemistry; Globigerinacea; Globigerinidae; Globigerinoides; Globigerinoides sacculifer; Invertebrata; isotope ratios; isotopes; Isthmus of Panama; Leg 138; Leg 165; lower Pliocene; magnesium; marine environment; metals; Mg/Ca; microfossils; Neogene; North Atlantic; O-18/O-16; Ocean Drilling Program; ODP Site 1000; ODP Site 846; oxygen; paleo-oceanography; paleoclimatology; paleoecology; paleosalinity; paleotemperature; Panama; planktonic taxa; Pliocene; Protista; Rotaliina; sea-surface temperature; shoaling; stable isotopes; Tertiary;