Esteban Boltovskoy

Morphological variations of benthic foraminiferal tests in response to changes in ecological parameters; a review

Some of the relatively recent literature correlating morphological variation in benthic foraminifera with environmental parameters such as temperature, salinity, carbonate solubility, depth, nutrition, substrate, dissolved oxygen, illumination, pollution, water motion, trace elements, and rapid environmental fluctuation is reviewed. It appears some variables (most notably depth) are recorded more frequently, which may affect some conclusions. Although each variable is treated separately, it appears that almost no variables act independently on test morphologies. In reviewing the literature, it becomes clear that there are many individual trends, especially with shell ornamentation, but few broad ones, and that it is almost impossible, with exception of some of the larger reef-dwelling, symbiont-bearing foraminifera, to predict how any species will react to various parameters. The broad trends concern thinning or thickening of carbonate tests with changing carbonate availability, temperature, and salinity. It appears that many observations of morphological changes within species may not be recorded in the literature, perhaps because authors did not recognize the importance of small details that would be of importance at a later time.

Atlas of Benthic Shelf Foraminifera of the Southwest Atlantic

Area of Study.- Water masses.- Cape Horn current.- Malvin current.- Coastal Argentine waters.- Area influenced by the Rio de la Plata.- Coastal waters of Uruguay and Southern Brazil.- Benthic foraminifera provinces.- North Patagonian subprovince.- South Patagonian subprovince.- Malvin subprovince.- Summary of Benthic Foraminiferal Investigations in the Area.- Principal Factors Influencing the Benthic Foraminiferal Distribution.- Salinity.- Euhaline foraminifera.- Hypohaline foraminifera.- Fresh water foraminifera.- Salt marsh foraminifera.- Temperature.- Depth.- Water mass.- Systematics and Distribution.- Euhaline species.- Hypohaline and fresh water species.- References.- Plates.- Maps.

Planktic foraminifera from the southwestern Atlantic (30 °–60 °S): species-specific patterns in the upper 50 m

Abstract Planktic foraminifers were studied in 96 samples collected in the southwestern Atlantic (30 °–60 °S, along 53 °W) in November 1993, mainly from depths between 0 and 50 m. Very high proportions of juveniles (unidentified) were present throughout the area, especially north of 37 °S, where they accounted for up to 70–80% of all shells recorded. For most species no clear vertical specific stratification was detected in the 0–50 m layer. Zoogeographic grouping of the 18 species identified allowed the defining of 5 distinct zones along the transect: Subtropical (north of 31 °S, 80% warm water individuals); Warm-Transitional (34 °–37 °S, 35% warm water); Transitional (37 °–49 °S, 99% cold water); Subantarctic (49–55 °S, 100% cold water); and Antarctic (south of 56 °S, 100% cold water). Boundaries between foraminiferal assemblage zones are in good agreement with hydrological fronts described for the area. Comparison of the present data with planktic collections from the North Atlantic show large differences in the proportions of various taxa. In the 14–24 °C range, G. bulloides is much more abundant in the northern hemisphere than in the southern one, whereas G. quinqueloba G. inflata and G. rubescens show the opposite trend. On the other hand, temperature-related percentage contributions within the 14 °–24 °C range indicate that the preferred thermic regimes of the 9 species considered are remarkably similar in the North and South Atlantic collections compared. The southernmost planktic distributional ranges of selected warm water taxa are roughly coincident with those established previously on the basis of surface sediments, disagreements being chiefly attributable to selective dissolution on the bottom. In contrast, at the bottom percentages of cold water foraminifers ( G. bulloides G. pachyderma ) are significantly enhanced with respect to their planktic populations, and their sedimentary northward limits extend well beyond their maximum ranges in the upper-layer plankton. It is suggested that submergence of these cold water species and northward displacement at subsurface depths is chiefly responsible for the mismatching patterns observed. Dissimilar species proportions in both hemispheres and plankton-sediment uncoupling can conceivably engender erroneous conclusions when distributional data are used for paleoecologic reconstructions with the aid of numerical analyses such as the Imbrie-Kipp transfer-function technique.

Late Cenozoic benthonic foraminifera of the Ninetyeast Ridge (Indian Ocean)

Abstract A study was made of the benthonic foraminifera recovered from 242 sediment samples (ranging from Upper Oligocene through Quaternary) at five DSDP sites (214, 216, 217, 253 and 254) located on the Ninetyeast Ridge (Indian Ocean). The sites lie at depths varying between 1,253 and 3,010 m. The sediments cored are believed to be undisturbed and do not contain reworked specimens. The stratigraphic subdivision was made on the basis of previous planktonic foraminiferal and other microplankton studies. In total 170 species were identified. About twenty species turned out to be unidentifiable. Two species were put in nomenclatura aperta . No new taxon has been described. The fauna studied exhibits strong dominance. The following species were found consistently and often frequently in the whole sequence: Anomalina globulosa, Cibicides kullenbergi, Epistominella exigua, Eponides bradyi, Gyroidina lamarckiana , s.l., G. soldanii, Oridorsalis umbonatus, Pullenia osloensis, Stilostomella ex gr. S. lepidula and Uvigerina proboscidea , s.l. Very few species were found to be stratigraphically diagnostic. It was impossible to detect the Oligocene/Lower Miocene boundary by means of benthonic foraminifera. The Lower Miocene/Middle Miocene boundary is characterized by: (1) the dramatic decrease of the Planulina marialana gigas population and increase of the Cibicides wuellerstorfi population; and (2) the first appearance of a very typical foraminifer of uncertain origin named conditionally “ Bulava indica ”. The Middle Miocene/Upper Miocene boundary is characterized by the first appearance of Bolivina globulosa and the extinction of Bolivinopsis cubensis, Bulimina jarvisi and Cassidulina caudriae . At the Upper Miocene/Pliocene boundary “ Bulava indica ”, Cassidulina cuneata, C. subglobosa horizontalis , and Rectuvigerina royoi disappear. Two evolutionary trends: Planulina marialana gigas → Cibicides wuellerstorfi and Cassidulina cuneata → Cassidulina subglobosa were observed.

Paleocene-Pleistocene Benthic Foraminiferal Evidence of Major Paleoceanographic Events in the eastern South Atlantic (DSDP Site 525, Walvis Ridge)

Abstract Benthic foraminifers in the size-fraction greater than 0.073 mm were studied in 88 Paleocene to Pleistocene samples from Deep Sea Drilling Project Site 525 (Hole 525A, Walvis Ridge, eastern south Atlantic). Clustering of the samples on the basis of the 86 most abundant foraminifers (in total, 331 taxa were identified) allowed separating two major assemblage zones: the Paleocene to Eocene interval, and the Oligocene to Pleistocene interval. Each of these, in turn, were subdivided into three minor subzones as follows: lower upper Paleocene (approx. 62.4 to 57.8 Ma); upper upper Paleocene (56.6 to 56.2 Ma); lower and middle Eocene (55.3 to 46.8 Ma); upper Oligocene to middle Miocene (25.3 to 16 Ma); middle Miocene to Pliocene (15.7 to 4.2 Ma); and lower Pleistocene (0.4 to 0.02 Ma), with only minor differences with the previous zone. Some very abundant taxa span most of the column studies (Bolivina huneri, Cassidulina subglobosa, Eponides bradyi, E. weddellensis, Gavelinella micra, Oridorsalis umbonatus, etc.). Several of the faunal breaks recorded coincide with conspicuous minima in the specific diversity curve, thus suggesting that the corresponding turnovers signal the final stages of periods of faunal impoverishment. At least one major bottom-water temperature drop (as derived from δ18O data) is synchronous with a decrease in the foraminiferal specific diversity. On the other hand, a specific diversity maximum in the middle Miocene might be associated with a δ13C increase at approx. 16 to 12 Ma. Highest foraminiferal abundances (up to 600–800 individuals per gram of dry sediment) occurred in the late Paleocene and in the early Pleistocene, in coincidence with the lowest diversity figures calculated. The magnitude of the most important faunal turnover recorded, between the middle Eocene and the late Oligocene, is magnified in our data set by the large hiatus which separates the middle Eocene from the upper Oligocene sediments. Considerably smaller overturns occurred within the late Paleocene (in coincidence with changes in the specific diversity, absolute abundance of foraminiferal tests, and δ13C), and in the middle Miocene (in coincidence with a specific diversity maximum and a δ13C excursion). New information on the morphology and the stratigraphic ranges of several species is furnished. For all the taxa recorded the number of occurrences, total number of individuals identified and first and last appearances are listed.

Planktonic Foraminifera from southwestern Atlantic epipelagic waters: abundance, distribution and year-to-year variations

The abundance and latitudinal and vertical (0-100 m) distribution of planktonic Foraminifera was investigated on the basis of 38 samples collected in November 1994 in the southwestern Atlantic Ocean (34-60°S, along 51-56°W). Mean foraminiferal densities were 1.5 ind. l −1 (range: 0.15.9 ind. l −1 ), with highest concentrations in subsurface waters (20-50 m). Couplings between the distribution of chlorophyll a and foraminiferal abundances were very loose. Distribution patterns of the 15 species recorded allowed 6 distinct areas to be defined along the transect surveyed. From north to south these are: Subtropical (dominated by Globigerinoides ruber and G. trilobus ), Cold intrusion ( Globigerinita uvula ), Transitional-Subtropical and Transitional ( Globigerina bulloides , Globigerina quinqueloba ), Subantarctic ( G. quinqueloba ), and Antarctic ( Neogloboquadrina pachyderma , left coiling). Close comparisons with the yields of a similar data set collected in November 1993 show very good agreement. Foraminiferal thermic regimes were also similar in 1993 and in 1994, but for some species significant differences with previous data were detected. While the southwards extensions of the ranges of warm water species are fairly well circumscribed by the Brazil current-influenced waters, several foraminifers widely used as indicators and palaeoindicators of cool waters (in particular Globigerina bulloides , Globigerina quinqueloba and Globigerinita uvula ) were recorded in very significant numbers at temperatures as high as 20-24°C. The implication of these findings for hydrological, ecological, and palaeoecological interpretations is discussed.

Planktonic Foraminifera as Indicators of Different Water Masses in the South Atlantic

The geographic position of the convergence of subtropical and subantarctic waters in the South Atlantic has been determined by means of the planktonic foraminifera encountered in 98 surface samples. The species that can be considered indicators of the different water masses and of their mixtures were established, and the results are summarized in a chart showing the distribution of the water masses. Planktonic foraminifera as indicators of different water masses in the South Atlantic

Ecology of the planktonic Foraminifera living in the surface layer of Drake Passage

The planktonic foraminiferal fauna was studied in 104 surface plankton samples collected by the author during the crossing in both directions of Drake Passage between Tierra del Fuego and Elephant Island off the Palmer Peninsula, Antarctica, during the months of January and February, 1969. Samples were gathered by means of a fire pump. This method is discussed and recommended for planktonic foraminiferal collection. Eight species were determined, and their horizontal distribution was established. The percentage abundance of each species, as well as the number of specimens per cubic meter of filtered water, were calculated for every station. Distribution patterns of foraminifers were compared with those obtained by previous authors and were related to the surface hydrology. Some discrepancies were found and discussed. The most simple means of separating Globigerina pachyderma from G. quinqueloba is proposed and the most simple means of locating the Antarctic Convergence by the use of foraminifers is discussed. Abnormal spinosity of foraminiferal tests is considered. Ecology of the planktonic foraminifera living in the surface layer of Drake Passage

Distribution of the marine littoral Foraminifera in Argentina, Uruguay and Southern Brazil

Benthic foraminifers collected in the marine littoral zone (sensu lato) of Argentina, Uruguay and Southern Brazil have been studied and compared with the Foraminifera collections from the same area studied previously. Two figures have been prepared, which show the geographical range and relative abundance of the most important species (cosmopolitan and non-cosmopolitan). The following biogeographical conclusions were drawn on the basis of an analysis of these figures. The whole area, from a latitude of about 32° S up to the southern coast of Tierra del Fuego, should be considered as one biogeographical unit (a “kingdom” of Buccella peruviana, sensu lato). This unit has 2 internal boundaries, which are located approximately at latitudes 41° and 52° S. They divide the whole area into 3 sub-areas which can be called (from North to South): North Patagonian (32° to 41° S), South Patagonian (41° to 52° S) and Malvinian (52° S—southern coast of Tierra del Fuego). With the exception of Buccella peruviana, sensu lato, which is typical of all 3 sub-areas, these sub-areas are characterized by the following faunal features. The North Patagonian sub-area contains abundant numbers of Elphidium discoidale. The South Patagonian sub-area is characterized by abundant numbers of Elphidium macellum. The Malvinian sub-area contains abundant numbers of Elphidium macellum, and also several very typical representatives of the Malvin current water, for instance, Cassidulina crassa, sensu stricto, Angulogerina angulosa, Uvigerina bifurcata, Cassidulinoides parkerianus, Ehrenbergina pupa and others. It is a matter of opinion whether the sub-areas cited be considered biogeographical sub-provinces, or even smaller units. They cannot be interpreted as biogeographical provinces.

Biostratigraphy of Tertiary and Quaternary benthic bathyal foraminifers of DSDP Site 317 (Tropical Pacific)

Abstract A study is made of the benthic foraminifers (size fraction > 63 μm) recovered from 59 upper Eocene through Quaternary sediment samples at DSDP Site 317 (Leg 33), located at a depth of 2598 m in the central part of the Manihiki Plateau (South Pacific). The sediments cored are disturbed in only two samples. The stratigraphic assignements used are based on previous studies of planktic foraminifers and other microfossils. In total, 216 taxa are identified. A cluster analysis based on the 77 species which comprised 5% or more of the entire foraminiferal assemblage in at least one sample suggests the presence of 3 major biostratigraphic zones corresponding approximately to the following ages, zone A: middle Miocene-Quaternary; zones B-C: early Miocene-Oligocene; and zone D: Eocene. The most important faunal turnover occurred between the Eocene and the Oligocene; a less pronounced break took place between the early and the middle Miocene, and an additional minor turnover between the Oligocene and the early Miocene. Eighteen taxa are long-ranging, being recorded from the middle Eocene through the Pliocene-Quaternary. It is concluded that, in general, benthic foraminifers of the bathyal zone are poor worldwide stratigraphic guide fossils; the following taxa are conditionally considered as the most suitable in the Eocene-Quaternary sequence:Aragonia aragonensis, Quadrimorphina profunda, Nuttallides truempyi, Abyssamina poagi, Buliminella grata, Bulimina jarvisi, B. macilenta, Turrilina alsatica, Cibicides notocenicus, C. wuellerstorfi, Pyrgo murrhina. However, most of these species are relatively rare.