(Table 1) Temperature and foraminiferal Mg/Ca ratios of samples off Japan

We studied Mg/Ca in high-Mg, shallow-water benthic foraminifera in culture and in samples from natural environments, in order to evaluate the expression of latitudinal and seasonal temperature variability in Mg/Ca in their tests. We cultured Planoglabratella opercularis (d'Orbigny) and Quinqueloculina yabei Asano under controlled temperature (10°-25°C) and salinity (30-38) conditions. Both species show a linear correlation between Mg/Ca and temperature, but they differ in temperature sensitivity. Salinity does not significantly influence Mg/Ca. In the samples collected in nature, Mg/Ca and seawater temperatures are positively correlated, but there are more complexities than in the records for cultured specimens due to such factors as seasonal fluctuations in temperature. We conclude that Mg/Ca ratios in monospecific benthic foraminiferal samples may be used as a reliable temperature proxy, if the lifetime of the species is taken into account.

Stable carbon and oxygen isotopes and Mg/Ca ratios of foraminifers from ODP Site 202-1241 sediments

A combination of stable isotope records and Mg/Ca temperature estimates of four different planktonic foraminiferal species from Ocean Drilling Program Site 1241 allows differentiation between temperature and salinity changes in the tropical east Pacific (TEP) upper water column during the Pliocene (~5.7-2.1 Ma). The deviation of d18O records and Mg/Ca temperature estimates from thermocline-dwelling planktonic foraminifers suggests that local changes in salinity exerted a much stronger control on Pliocene TEP upper ocean water mass signatures than previously assumed. The most pronounced Pliocene change in TEP upper ocean stratification was the shoaling of the thermocline from ~4.8 to 4.0 Ma that was possibly triggered by changes in the configuration of low-latitude ocean gateways. During this time interval, mixed-layer temperatures and salinities remained relatively constant in contrast to a pronounced temperature (~6°C) and salinity decrease at the bottom of the photic zone. This change led to a new state in the thermal structure of the TEP, as the thermocline remained relatively shallow until ~2.1 Ma.

(Table 2) Mg/Ca and Sr/Ca composition of planktonic foraminifera from ODP Hole 143-865B

To understand the climate dynamics of hypothesized past greenhouse intervals, it is essential to constrain tropical sea-surface temperatures (SST), yet existing proxy records give conflicting results. Here we present the first Mg/Ca-based study of pre-Quaternary SST and investigate early Paleogene (late Paleocene through late middle Eocene; 58.6-39.8 Ma) tropical temperatures, using planktonic foraminifera belonging to the genus Morozovella from Ocean Drilling Program Site 865 on Allison Guyot (western central equatorial Pacific Ocean). Calcification temperatures similar to or warmer than modern tropical SST are calculated using a range of assumptions regarding diagenesis, temperature calibration, and seawater Mg/Ca. Long-term warming is observed into the early Eocene (54.8-49.0 Ma), with peak SST between 51 and 48 Ma and rapid cooling of 4°C beginning at 48 Ma. These findings are inconsistent with the d18O-based SST previously estimated for this site.

Mg/Ca ratio, Sr/Ca ratio and stable isotopes of the foraminifera Oridorsalis umbonatus in surface sediment samples

We investigate the influence of carbonate system parameters (carbonate ion concentration, [CO3**2-]; carbonate ion saturation, Delta [CO3**2-]) on the trace element and stable isotope ratios in the endobenthic foraminifera Oridorsalis umbonatus. Data from modern core top samples from the Namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore-water. For these organic-rich sediments, the impact of ocean bottom water properties on both pore-water and shell chemistry is surprisingly small. Sr/Ca correlates positively with [CO3**2-] and to a lesser extent with Delta [CO3**2-], which is opposed to previous results. A [CO3**2-] decrease of 10 µmol/kg leads to an increase of 0.05 mmol/mol in Sr/Ca. We observe a correlation between shell d18O (corrected for temperature and d18O seawater) and [CO3**2-], however, the variability of the corrected d18O is close to the analytical limit. No clear dependences were observed for d13C and Mg/Ca.

Foraminifera Mg/Ca, test weight and XDX for sediment core WIND28K

A record of deep-sea calcite saturation (D[CO3**-2]), derived from X-ray computed tomography-based foraminifer dissolution index, XDX, was constructed for the past 150 ka for a core from the deep (4157 m) tropical western Indian Ocean. G. sacculifer and N. dutertrei recorded a similar dissolution history, consistent with the process of calcite compensation. Peaks in calcite saturation (~15 µmol/kg higher than the present-day value) occurred during deglaciations and early in MIS 3. Dissolution maxima coincided with transitions to colder stages. The mass record of G. sacculifer better indicated preservation than did that of N. dutertrei or G. ruber. Dissolution-corrected Mg/Ca-derived SST records, like other SST records from marginal Indian Ocean sites, showed coolest temperatures of the last 150 ka in early MIS 3, when mixed layer temperatures were ~4°C lower than present SST. Temperatures recorded by N. dutertrei showed the thermocline to be ~4°C colder in MIS 3 compared to the Holocene (8 ka B.P.).

Benthic (C. wuellerstorfi) d18O, d13C and Cd/Ca in sediment core NEAP 4K across the last deglaciation

We present evidence that the characteristic chemical signature (based on coupled benthic foraminiferal Cd/Ca and d13C) of Antarctic Intermediate waters (AAIW) penetrated throughout the intermediate depths of the Atlantic basin to the high-latitude North Atlantic during the abrupt cooling events of the last deglaciation: Heinrich 1 and the Younger Dryas. AAIW may play the dynamic counterpart to the "bipolar seesaw" when near-freezing salty bottom waters from the Antarctic (AABW) sluggishly ventilate the deep ocean. Our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters (NADW) and fresh southern sourced waters (AABW and AAIW). Further, the glacial ocean may be susceptible to the more finely balanced relative densities of NADW and AAIW, due to either freshwater input or a reversal of the salinity gradient, such that the ocean is poised for NADW collapse via a negative salinity feedback. The unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters.

Sea Surface Temperature (SST) Mg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides

We generated a high-resolution SSTMg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SSTMAT). The two temperature records display similar patterns during the last 28,000 years but the SSTMg/Ca estimates are several degrees warmer (~+4 °C) than SSTMAT. The temperature shift between SSTMg/Ca and SSTMAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G. bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G. bulloides for which a specific Mg/Ca-temperature calibration is needed.

Nd/Ca ratios in plankton-towed and core top foraminifera

Planktic foraminifera have been used as recorders of the neodymium (Nd) isotopic composition of seawater, although there is still controversy over the precise provenance of the Nd signal. We present an extensive, multispecific plankton tow Nd/Ca data set from several geographic locations (SE Atlantic, NE Atlantic, Norwegian Sea, and western Mediterranean), together with core top samples from the Mediterranean region. The range of Nd/Ca ratios in plankton-towed foraminifera, cleaned only of organic material, from all regions (0.01-0.7 µmol/mol), is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps, with distribution coefficients (Kd) ranging between 4 and 302. For the Mediterranean, where core top and plankton tow data are both available, the range for plankton tows (0.05-0.7 µmol/mol) is essentially identical to that for the core tops (0.1-0.5 µmol/mol). Readsorption of Nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process. We find a relationship between manganese (Mn) and Nd in plankton tow samples that is mirrored by a similar correlation in core top samples. This relationship suggests that Fe-Mn coatings are of negligible importance to the Nd budgets of foraminifera as the Nd/Mn ratio it implies is over an order of magnitude greater than that seen in other Fe-Mn oxide phases. Rather, since both plankton tows and core tops present a similar behavior, the Nd/Mn relationship must originate in the upper water column. The data are consistent with the acquisition of Nd and Mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes. Collectively, the results help to explain two abiding puzzles about Nd in sedimentary planktic foraminifera: their high REE contents and the fact that they record a surface water Nd isotopic signal, regardless of the cleaning procedure used.

Radiocarbon age, Mg/Ca and d18O measurements on planktonic foraminifera of sediment core GeoB12605-3

The sea surface temperature (SST) of the tropical Indian Ocean is a major component of global climate teleconnections. While the Holocene SST history is documented for regions affected by the Indian and Arabian monsoons, data from the near-equatorial western Indian Ocean are sparse. Reconstructing past zonal and meridional SST gradients requires additional information on past temperatures from the western boundary current region. We present a unique record of Holocene SST and thermocline depth variations in the tropical western Indian Ocean as documented in foraminiferal Mg/Ca ratios and d18O from a sediment core off northern Tanzania. For Mg/Ca and thermocline d18O, most variance is concentrated in the centennial to bicentennial periodicity band. On the millennial time scale, an early to mid-Holocene (~7.8-5.6 ka) warm phase is followed by a temperature drop by up to 2°C, leading to a mid-Holocene cool interval (5.6-4.2 ka). The shift is accompanied by an initial reduction in the difference between surface and thermocline foraminiferal d18O, consistent with the thickening of the mixed layer and suggestions of a strengthened Walker circulation. However, we cannot confirm the expected enhanced zonal SST gradient, as the cooling of similar magnitude had previously been found in SSTs from the upwelling region off Sumatra and in Flores air temperatures. The SST pattern probably reflects the tropical Indian Ocean expression of a large-scale climate anomaly rather than a positive Indian Ocean Dipole-like mean state.

Delta 44/40 Ca, Mg/Ca and Sr/Ca record of Globigerinoides sacculifer and calculated temperatures and salinity changes of ODP Hole 165-999A

The delta18O values of planktonic foraminifera increased in the Caribbean by about 0.5? relative to the equatorial East Pacific values between 4.6 and 4.2 Ma as a consequence of the closure of the Central American Gateway (CAG). This increase in delta18O can be interpreted either as an increase in Caribbean sea surface (mixed layer) salinity (SSS) or as a decrease in sea surface temperatures (SST). This problem represents an ideal situation to apply the recently developed paleotemperature proxy delta44/40Ca together with Mg/Ca and d18O on the planktic foraminifer Globigerinoides sacculifer from ODP Site 999. Although differences in absolute temperature calibration of delta44/40Ca and Mg/Ca exist, the general pattern is similar indicating a SST decrease of about 2-3 8C between 4.4 and 4.3 Ma followed by an increase in the same order of magnitude between 4.3 and 4.0 Ma. Correcting the delta18O record for this temperature change and assuming that changes in global ice volume are negligible, the salinity-induced planktonic delta18O signal decreased by about 0.4? between 4.4 and 4.3 Ma and increased by about 0.9? between 4.3 and 4.0 Ma in the Caribbean. The observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the Caribbean and the Pacific in response to the shoaling of the Panamanian Seaway, possibly accompanied by a southward shift of the Intertropical Convergence Zone (ITCZ) between 4.4 and 4.3 Ma. Differences in Mg/Ca- and delta44/40Ca-derived temperatures can be reconciled by corrections for secular variations of the marine Mg/Ca[sw] and delta44/40Ca, a salinity effect on the Mg/Ca ratio and a constant temperature offset of ~2.5 °C between both SST proxy calibrations.