Sample locations, CTD data, mean spring and annual temperatures and salinities from World Ocean Atlas (WOA, 2001), and ICP-OES Mg/Ca data

Due to its strong gradient in salinity and small temperature gradient the Mediterranean provides an ideal setting to study the impact of salinity on the incorporation of Mg into foraminiferal tests. We have investigated tests of Globorotalia inflata and Globigerina bulloides in plankton tow and core top samples from the Western Mediterranean using ICP-OES for bulk analyses and LA-ICP-MS for analyses of individual chambers in single specimens. Mg/Ca observed in G. inflata are consistent with existing calibrations, whereas G. bulloides had significantly higher Mg/Ca than predicted, particularly in core top samples from the easterly stations. Scanning Electron Microscopy and Laser Ablation ICP-MS revealed secondary overgrowths on some tests, which could explain the observed high core top Mg/Ca. We suggest that the Mediterranean intermediate and deep water supersaturated with respect to calcite cause these overgrowths and therefore increased bulk Mg/Ca. However, the different species are influenced by diagenesis to different degrees probably due to different test morphologies. Our results provide new perspectives on reported anomalously high Mg/Ca in sedimentary foraminifera and the applicability of the Mg/Ca paleothermometry in high salinity settings, by showing that (1) part of the signal is generated by precipitation of inorganic calcite on the foraminifer test due to increased calcite saturation state of the water and (2) species with high surface-to-volume shell surfaces are potentially more affected by secondary Mg-rich calcite encrustation.

Diagenesis of siliceous particles in ODP Hole 114-699A

A number of neogenic opaline structures, not previously reported in the literature, as well as other neogenic phases are described from four Oligocene to Pliocene biosiliceous sediment samples from Hole 699A. The possible influence of microbes on the formation or the morphology of some of them is discussed. The samples, which are early Pliocene, early to middle Miocene, and late Oligocene (two) in age, were histologically fixed aboard ship upon retrieval. Investigations of the samples used SEM (with Edax/Tracor) and XRD methods. Diagenesis has affected all four samples, but the most extensive development of neoformed structures occurs in the Miocene and uppermost Oligocene samples, where microbial filaments (0.05 to 10 ?m long), microbial colonies, and siliceous microhemispheroids (0.2 to 0.7 µm diameter) were observed. The latter encrust filaments, diatoms, and detrital grains to varying degrees. Other neoformed structures include (1) flakes formed by coalesced microhemispheroids, some of which are guided by short, stubby filaments, which occur only in the Miocene and uppermost Oligocene samples, and (2) flakes characterized by smooth or microfissured surfaces, which grow on diatom frustules and in pore spaces and have a more widespread distribution. The XRD data indicate possible cristobalite formation in the Miocene and uppermost Oligocene samples; we believe that the neoformed opaline structures (encrusted filaments and microhemispheroids) may represent an early phase of opal-CT. The timing of neoformation of most of these features appears to have been fairly recent, continuing even at the time of sampling. There appears to be no direct correlation of this incipient, lower Miocene-uppermost Oligocene diagenetic layer and the pore-water chemistry profiles; a massive increase in shear strength in these sediments, however, may indicate some cementation. Smectite was identified by XRD as the most prominent clay mineral in these generally clay-poor sediments. Honeycombed minerals with filamentous edges, which could correspond to smectite, were observed with SEM in the pore spaces.