Mg/Ca and Sr/Ca ratios of planktonic foraminifera from North Atlantic surface sediments

Reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstruct past upper water column temperature gradients and past oceanic heat content. This work examines the relationships between trace element ratios in fossil shells and seawater temperature for surface-dwelling foraminifera species, Globigerinoides ruber (white) and Globigerina bulloides, and deep-dwelling species, Globorotalia inflata, Globorotalia truncatulinoides (dextral and sinistral) and Pulleniatina obliquiloculata. Mg/Ca and Sr/Ca ratios in shells picked in 29 modern core tops from the North Atlantic Ocean are calibrated using calculated isotopic temperatures. Mg/Ca ratios on G. ruber and G. bulloides agree with published data and relationships. For deep-dwelling species, Mg/Ca calibration follows the equation Mg/Ca = 0.78 (±0.04) * exp (0.051 (±0.003) * T) with a significant correlation coefficient of R**2 = 0.74. Moreover, there is no significant difference between the different deep-dwellers analyzed. For the Sr/Ca ratio, the surface dwellers and P. obliquiloculata do not record any temperature dependence. For the Globorotalia species, the thermo dependence of Sr/Ca ratio can be described by a single linear relationship: Sr/Ca = (0.0182 (±0.001) * T) + 1.097 (±0.018), R**2 = 0.85. Temperature estimates with a 1 sigma error of ±2.0°C and ±1.3°C can be derived from the Mg/Ca and Sr/Ca ratios, respectively, as long as the Sr geochemistry in the ocean has been constant through time.

Stable isotope ratios of planktonic foraminifera from North Atlantic surface sediments

We measured the oxygen isotopic composition of the deep-dwelling foraminiferal species G. inflata, G. truncatulinoides dextral and sinistral, and P. obliquiloculata in 29 modern core tops raised from the North Atlantic Ocean. We compared calculated isotopic temperatures with atlas temperatures and defined ecological models for each species. G. inflata and G. truncatulinoides live preferentially at the base of the seasonal thermocline. Under temperature stress, i.e., when the base of the seasonal thermocline is warmer than 16°C, G. inflata and G. truncatulinoides live deeper in the main thermocline. P. obliquiloculata inhabits the seasonal thermocline in warm regions. We tested our model using 10 cores along the Mauritanian upwelling and show that the comparison of d18O variations registered by the surficial species G. ruber and G. bulloides and the deep-dwelling species G. inflata evidences significant glacial-interglacial shifts of the Mauritanian upwelling cells.

Annotated record of the detailed examination of Mn and phosphate deposits from GOS74 Expedition stations

The purpose of the cruise was to map the manganese rich pavements of the Blake Plateau area which had been extensively investigated by ships of the Woods Hole Oceanographic Institution since 1956. From August until September 1965, 112 sites were sampled from R/V Gosnold on a joint USGS-WHOI expedition. At most of the stations on the Blake pavement, large slabs of manganese were recovered along with phosphate rich nodules.

Annotated record of the detailed examination of Mn and phosphate deposits from GYRE 82-11 Expedition stations

The purpose of the expedition was to test new techniques to determine thickness, distribution and quality of mineral deposits on the Blake Plateau with special reference to manganese nodules and manganese-phosphate pavements.