Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8° ± 0.7°C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5°C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.

https://science.sciencemag.org/content/sci/289/5485/1719.full.pdf

Climate Impact of Late Quaternary Equatorial Pacific Sea Surface Temperature Variations

Cultured planktonic foraminifera, Orbulina universa (symbiotic) and Globigerina bulloides (nonsymbiotic), are used to reexamine temperature:δ18O relationships at 15°–25°C. Relationships for both species can be described by linear equations. Equations for O. universa grown under low light (LL) and high light (HL) share a slope of −4.80 (0.21‰ °C−1) with a HL-LL offset of −0.33‰ due to symbiont photosynthetic activity. The effect of [CO32−] on O. universa is −0.002‰ µmol−1 kg−1 and is insensitive to temperature. For G. bulloides, ontogenetic effects produce size-related trends in temperature:δ18O, whereby larger shells are enriched in 18O relative to smaller specimens. The O. universa temperature:δ18O relationships are more accurate than previously published equations for describing plankton tow data. Our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic Cibicidoides data below 10°C. Temperature:δ18O relationships for G. bulloides provide good agreement with field data for this species from the northeast Pacific.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98PA00070

Reevaluation of the oxygen isotopic composition of planktonic foraminifera: Experimental results and revised paleotemperature equations

Sea-land oxygen isotopic relationships from planktonic foraminifera and speleothems in the Eastern Mediterranean region and their implication for paleorainfall during interglacial intervals

Stable oxygen and carbon isotope measurements on biogenic calcite and aragonite have become standard tools for reconstructing past oceanographic and climatic change. In aquatic organisms, 18O/16O ratios in the shell carbonate are a function of the ratio in the sea water and the calcification temperature1. In contrast, 13C/12C ratios are controlled by the ratio of dissolved inorganic carbon in sea water and physiological processes such as respiration and symbiont photosynthesis2. These geochemical proxies have been used with analyses of foraminifera shells to reconstruct global ice volumes3, surface and deep ocean temperatures4,5, ocean circulation changes6 and glacial–interglacial exchange between the terrestrial and oceanic carbon pools7. Here, we report experimental measurements on living symbiotic and non-symbiotic plankton foraminifera (Orbulina universa and Globigerina bulloides respectively) showing that the 13C/12C and 18O/16O ratios of the calcite shells decrease with increasing seawater [CO32−]. Because glacial-period oceans had higher pH and [CO32−] than today8, these new relationships confound the standard interpretation of glacial foraminiferal stable-isotope data. In particular, the hypothesis that the glacial–interglacial shift in the 13C/12C ratio was due to a transfer of terrestrial carbon into the ocean7 can be explained alternatively by an increase in ocean alkalinity25. A carbonate-concentration effect could also help explain some of the extreme stable-isotope variations during the Proterozoic and Phanerozoic aeons9.

/pdf/effect-of-seawater-carbonate-concentration-on-foraminiferal-48xq21tel2.pdf

Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes

Stable oxygen and carbon isotope measurements on biogenic calcite and aragonite have become standard tools for reconstructing past oceanographic and climatic change. In aquatic organisms, 18O/16O ratios in the shell carbonate are a function of the ratio in the sea water and the calcification temperature. In contrast, 13C/12C ratios are controlled by the ratio of dissolved inorganic carbon in sea water and physiological processes such as respiration and symbiont photosynthesis. These geochemical proxies have been used with analyses of foraminifera shells to reconstruct global ice volumes, surface and deep ocean temperatures,, ocean circulation changes and glacial–interglacial exchange between the terrestrial and oceanic carbon pools. Here, we report experimental measurements on living symbiotic and non-symbiotic plankton foraminifera (Orbulina universa and Globigerina bulloides respectively) showing that the 13C/12C and 18O/16O ratios of the calcite shells decrease with increasing seawater [CO32−]. Because glacial-period oceans had higher pH and [CO32−] than today, these new relationships confound the standard interpretation of glacial foraminiferal stable-isotope data. In particular, the hypothesis that the glacial–interglacial shift in the 13C/12C ratio was due to a transfer of terrestrial carbon into the ocean can be explained alternatively by an increase in ocean alkalinity. A carbonate-concentration effect could also help explain some of the extreme stable-isotope variations during the Proterozoic and Phanerozoic aeons.

A model1,2, which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western North Atlantic and is comprised of three tenets: (1) The conditions in the photic zone (upper 80–100 m) exclusively dictate planktonic foraminifera species composition and abundance throughout the water column. (2) Species are vertically stratified within the photic zone according to their temperature preference. Depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments. Due to seasonal temperature variations, seasonal variations in the δ18O composition of seawater, and species-specific isotope fractionation, rigorous proof of this hypothesis cannot be provided from sediment analyses alone. (3) The chlorophyll maximum is a major food source zone, which is preferentially exploited by foraminifera. Our data from the Panama Basin, which are presented here, are confirmation of this model. The Panama Basin in the eastern equatorial Pacific, which has a shallow and steep thermocline, was sampled for living planktonic foraminifera. A multiple opening–closing net and environmental sensing system (MOCNESS)4 was used to collect 13 sets of eight vertically stratified oblique samples. We report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four MOCNESS tows taken over 5 days, during August 1979 (RV Knorr cruise 73) at 5°20′ N, 8°50′ W. Each tow consisted of eight samples which integrated ∼12.5-m intervals from 0 to 100 m for MOC 126, 25-m intervals from 0 to 200 m for MOC 127, 100–150-m intervals from 0 to 1,000 m on MOC 128 and 250-m intervals from 0 to 2,000 m on MOC 131.

Marc S. Sverdlove

Papers

Vertical distribution and isotopic fractionation of living planktonic foraminifera from the Panama Basin

Standing stock, vertical distribution and flux of planktonic foraminifera in the panama basin

Taxonomic and ecological significance of embryonic and juvenile planktonic foraminifera