ALBERT

Beschreibung: Prior to this work, the planktic foraminiferal genus Beella Banner and Blow (1960) has never been described from Pleistocene sediments from the Norwegian-Greenland Sea (NGS). The general characteristics of this species agree well with the most recent emendation of the genus Beella. Accordingly, the described species is considered to be Beella megastoma (Earöamd). Test sizes range from 200-700 μm, but specimens are mainly confined to the 250-500 μm mesh-size fraction. Interpretations of stable isotopes, sedimentological, and other micropaleontological data indicate that this species is not simply a "warm-water form" and, despite its low abundances, it is a species of major paleoceanographic significance. Stratigraphically, it is confined to meltwater events of Termination II, III, and VI (oxygen isotopic stage boundary 5/6, 7/8, and 15/16) and not to the ensuing interglacial maximum. Hence, these "Beella-events" represent a particular oceanographic phenomenon and are designated in accordance with the present numerical system of deglacial terminations as Event B2, B3, and B6 respectively.

Beschreibung: The biological response to extreme temperatures and salinities is investigated in the laboratory for seven species of planktonic foraminifera: Globigerinoides sacculi/er (Brady), Globigerinoides ruber (d'Orbigny), Globigerinoides conglobatus (Brady), Globigerine/la siphonifera (d'Orbigny), Orbulina universa d'Orbigny, Neogloboquadrina dutertrei (d'Orbigny) and Globorotalia menardii (d'Orbigny). When one of the vital processes, food acceptance, growth or reproduction is inhibited by a culture variable, the absolute survival limit is reached. The measured in vitro temperature ranges compare well with the global temperature distribution patterns of these species, suggesting that this parameter plays a major role in their biogeographical distribution. The salinity ranges that are tolerated in laboratory cultures exceed the range encountered in modern oceans. Thus salinity does not limit the distribution of the species investigated herein. In general, larger mean final shell sizes are attained and the total shell length increase is larger at optimum temperatures and salinities than at extreme culture conditions, but the differences were not always statistically significant. Marginal temperature and salinity conditions do not induce contained growth in expatriated specimens. Under extreme culture conditions, the relative frequency of the different shell morphologies is altered relative to normal conditions. "Abnormal" phenotypes are more frequent under normal conditions and the "normal" morphology is found more often under extreme conditions. As opposed to previous reports, the frequency of kummerform chambers generally decreases toward extreme temperature and salinity culture conditions, indicating that kummerform phenotypes are not indicative of environmental stress. The incidence of sac-like chambers in G. sacculi/er and the formation of spherical chambers in adult 0. universa decrease toward extreme temperature and salinity culture conditions, demonstrating that maturation is suppressed in stress situations. SEM investigations show that changes in shell porosity are correlated with treatment variables in culture. The highest porosities are attained at higher temperatures and lower salinities. Generally, an increase in total porosity is achieved by an increase of the pore area accompanied by a reduction of the pore density. The in vitro experiments explain the changes that occurred in the Pleistocene foraminiferal assemblages from the Red Sea around 18 thousand years ago and earlier. During glacial periods, salinity approximated or even exceeded the upper thresholds that were tolerated under laboratory conditions. Under these circumstances, species disappeared from the water column. The order of disappearance as recorded in the sediments may be explained with the upper salinity limits found in this study. Also, the recurrent shifts of dominance between G. sacculi/er and G. ruber are well documented for this fossil assemblage. The present experiments support the conclusion that salinity is the driving mechanism behind this phenomenon. Observations in modern oceans suggest that the fertility of the water mass is probably also an important factor behind the shifts of dominance between G. sacculi/er and G. ruber.

Beschreibung: The restudy of Buliminoides species leads to the redefinition of both the genus and the family Buliminoididae. Buliminoides differs from buliminid taxa in lacking a toothplate, possessing discoidal chambers not arranged in a trochospiral, and in having a unique apertural face. The genus bears no relation to Glabratella, since their respective apertural faces are not equivalent. A lectotype is designated for Buliminoides williamsonianus; Buliminoides bantamensis is refigured, the holotype having perished; and Buliminella choctawensis is tentatively reclassified in Buliminoides.