[1] The conventional method to distinguish live from dead benthic foraminifers uses Rose Bengal, a stain that reacts with both live and dead cytoplasm. CellTracker Green CMFDA is a fluorogenic probe causing live cells to fluoresce after proper incubation. To determine the more accurate viability method, we conducted a direct comparison of Rose Bengal staining with CellTracker Green labeling. Eight multicore tops were analyzed from Florida Margin (SE United States; 248-751 m water depths), near Great Bahama Bank (259-766 m), and off the Carolinas (SE United States; 220 and 920 m). On average, less than half the Rose Bengal-stained foraminifera were actually living when collected. Thus, while Rose Bengal can significantly overestimate abundance, combined analyses of CellTracker Green and Rose Bengal can provide insights on population dynamics and effects of episodic events. Initial stable isotope analyses indicate that the CellTracker Green method does not significantly affect these important paleoceanographic proxies.

Abstract. We present empirically based calibrations of our measurements made on a Finnigan MAT252 equipped with a Kiel Device to Vienna Pee Dee belemnite, using an enriched •1sO standard. Calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the Kiel Device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source. After correcting for these biases, the precision of 2200 NBS19 analyses (10-300/•g ) is +0.07 for •1sO and +0.03 for •1•C. We have shared our standard enriched in •1sO with 18 laboratories engaged in paleoceanographic research, producing the first large-scale interlaboratory calibrations for this community. Using correction procedures reported here, water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature-salinity and density variability in the deep ocean.

Planktonic foraminifera collected in sediment traps in the Arabian Sea during 1986 and 1987 responded to the southern Asian monsoon with changes in productivity, relative abundance of species and isotopic shell chemistry. Most species of foraminifera increased in flux shortly after the advent of the southwest monsoon. G. bulloides increased its production rate by three orders of magnitude. The isotopic chemistry of G. ruber recorded the increase in monsoon upwelling by increasing its δ 18 O values by about 1‰, accurately reflecting the average 4°C sea surface temperature decrease associated with the upwelling. The mean value of δ 18 O for G. ruber was greater in the western Arabian Sea than in the central or eastern basins because upwelling in that region cools surface water. The carbon isotopic composition of G. ruber does not have a clear temporal or geographical relationship to upwelling. While its δ 13 C values decreased in the western Arabian Sea during the upwelling event, the mean δ 13 C values remained higher in the western than in the eastern and central Arabian Sea. This longitudinal gradient is opposite to that expected from the geographical gradient of upwelling: the region with the most intense upwelling should have lower δ 13 C values in surface waters because of the upwelling of low-δ 13 C water to the surface.

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Major benthic foraminiferal changes occurred in the late Eocene at Site 549. A Nuttallides truempyi-dominated assemblage was replaced by a buliminid assemblage (-40-38.5 m.y. ago); this change in faunal abundance was apparently a circum-Atlantic event. The buliminid assemblage was replaced, in turn, by an assemblage dominated by stratigraphically long-ranging and bathymetrically wide-ranging taxa just below the Eocene/Oligocene boundary (~37.5 m.y. ago). A series of late Eocene to earliest Oligocene first and last appearances of taxa accompanied these abundance changes. Similar changes in faunal abundance occurred at Site 548, but the incomplete record recovered at Site 548 prevents a firm dating of the changes. No major benthic foraminiferal changes (denoted by the extinction of Hαntkeninα, Cribrohαntkeninα, and Globorotαliα cerroαzulensis) were associated with the Eocene/Oligocene boundary at these sites; instead, benthic foraminiferal abundance changes, last appearances (both extinctions and local disappearances), and first appearances occurred throughout the late Eocene to earliest Oligocene interval (-40-36 m.y. ago).Benthic foraminiferal δ 18 θ increased ~ l.O‰ in the late Eocene to earliest Oligocene (~ 38-36.5 m.y. ago) at Site 549. Most (~ 0.7‰) of this increase occurred simultaneously with a 0.6‰ increase in benthic foraminiferal δ 13 C as a geologically rapid event in the earliest Oligocene (-36.5 m.y. ago). The major benthic foraminiferal abundance change (-40-38 m.y. ago) predates the major isotopic enrichments. A prominent seismic horizon, Reflector R4, has been noted in the Labrador Sea, Rockall, and Biscay regions, and has been dated as latest Eocene to early Oligocene. This horizon marks the onset of increased intensity of abyssal circulation associated with the initial entry of bottom water from the Norwegian-Greenland Sea and/or Arctic Ocean into the North Atlantic. The interval during which Reflector R4 was formed may encompass both the faunal and isotopic changes; the best estimate for the age of this horizon and the associated circulation change suggests that it correlates with the δ 18 θ increase. Our interpretation of these data suggests that a temperature drop, decrease in age (increased O 2 , lowered CO 2 , increased pH, hence decreased corrosiveness) of bottom water, and an increase in intensity of abyssal circulation occurred in the late Eocene to earliest Oligocene of the North Atlantic. Graciansky, P. C. de, Poag, C. W., et al., Init. Repts. DSDP, 80: Washington (U.S. Govt. Printing Office).