Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ

In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox conditions. Foraminiferal tests are often contaminated by diagenetic coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings. Thus, it is substantial to assure that the cleaning protocols are efficient or that spots chosen for microanalyses are free of contaminants. Prior to the determination of the element/Ca ratios, the distributions of several elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow infaunal species Uvigerina peregrina and Bolivina spissa were mapped with an electron microprobe (EMP). To visualize the effects of cleaning protocols uncleaned and cleaned specimens were compared. The cleaning protocol included an oxidative cleaning step. An Fe rich phase was found on the inner test surface of uncleaned U. peregrina specimens. This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was found at the inner test surface of B. spissa. Specimens of both species treated with oxidative cleaning show the absence of this phase. Neither in B. spissa nor in U. peregrina were any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca and Fe/Ca ratios of single specimens of B. spissa from different locations have been determined by secondary ion mass spectrometry (SIMS). Bulk analyses using solution ICP-MS of several samples were compared to the SIMS data. The difference between SIMS analyses and ICP-MS bulk analyses from the same sampling sites was 14.0-134.8 µmol mol-1 for the Fe/Ca and 1.68(±0.41) µmol mol-1 for the Mn/Ca ratios. This is in the same order of magnitude as the variability inside single specimens determined with SIMS at these sampling sites (1sigma[Mn/Ca] = 0.35-2.07 µmol mol-1; 1sigma[Fe/Ca] = 93.9-188.4 µmol mol-1). The Mn/Ca ratios in the calcite were generally relatively low (2.21-9.93 µmol mol-1) but in the same magnitude and proportional to the surrounding pore waters (1.37-6.67 µmol mol-1). However, the Fe/Ca ratios in B. spissa show a negative correlation to the concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca ratios (87.0-101.0 µmol mol-1) were found at 465 m water depth, a location with a strong sharp Fe peak in the pore water next to the sediment surface and respectively, high Fe concentrations in the surrounding pore waters. Previous studies found no living specimens of B. spissa at this location. All these facts hint that the analysed specimens already were dead before the Fe flux started and the sampling site just recently turned anoxic due to fluctuations of the lower boundary of the OMZ near the sampling site (465 m water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for redox conditions, if cleaning protocols are carefully applied. The data presented here may be rated as base for the still pending detailed calibration.

Westerschelde, Netherlands and Belgium, ca. 1799 (Image 2 of 3) (Raster Image)

This layer is a georeferenced raster image of the historic paper map entitled: Reconnoissance du cours du Hont ou Wester Schelde (Escaut occidental) depuis Anwerpen (Anvers) jusqu'à l'embouchure, faite par ordre du Ministre de la marine et des colonies, en thermidor et fructidor, an VII, vendémiaire et brumaire, an VIII, par Beautemps-Beaupré; assisté des Cens. Daussy et Portier, et de Jh. Raoul. It was published ca. 1799. Scale [ca. 1:41,300]. Covers Westerschelde, Netherlands and Belgium, from Middelburg to Antwerp. This layer is image 2 of 3 total images of the three sheet source map, representing the center portion of the map. Map in French.The image inside the map neatline is georeferenced to the surface of the earth and fit to the RD_New (Rijksdriehoekstelsel), GCS Amersfoort coordinate system. All map collar and inset information is also available as part of the raster image, including any inset maps, profiles, statistical tables, directories, text, illustrations, index maps, legends, or other information associated with the principal map. This map shows coastal features such as rocks, channels, points, ports, coves, islands, flats, canals, and more. Includes also selected land features such as roads, towns, fortification, drainage, land cover, selected buildings, and more. Relief shown pictorially and with hachures. Depths shown by contours and soundings. Includes "Nota" and text with insigne of the Dépôt général de la marine.This layer is part of a selection of digitally scanned and georeferenced historic maps from the Harvard Map Collection. These maps typically portray both natural and manmade features. The selection represents a range of originators, ground condition dates, scales, and map purposes.