Deep-sea Benthic Foraminifera Research Articles

Blake Outer Ridge: Late Neogene variability in paleoceanography and deep-sea biota

Carbon isotope and benthic foraminiferal data from Blake Outer Ridge, a sediment drift in the western North Atlantic (Ocean Drilling Program Sites 994 and 997, water depth ~ 2800 m), document variability in the relative volume of Southern Component (SCW) and Northern Component Waters (NCW) over the last 7 Ma. SCW was dominant before ~ 5.0 Ma, at ~ 3.6–2.4 Ma, and 1.2–0.8 Ma, whereas NCW dominated in the warm early Pliocene (5.0–3.6 Ma), and at 2.4–1.2 Ma. The relative volume of NCW and SCW fluctuated strongly over the last 0.8 Ma, with strong glacial–interglacial variability. The intensity of the Western Boundary Undercurrent was positively correlated to the relative volume of NCW. Values of Total Organic Carbon (TOC) were > 1.5% in sediments older than ~ 3.8 Ma, and not correlated to high primary productivity indicators, thus may reflect lateral transport of organic matter. TOC values decreased during the intensification of the Northern Hemisphere Glaciation (NHG, 3.8–1.8 Ma). Benthic foraminiferal assemblages underwent major changes when the sites were dominantly under SCW (3.6–2.4 and 1.2–0.8 Ma), coeval with the ‘Last Global Extinction’ of elongate, cylindrical deep-sea benthic foraminifera, which has been linked to cooling, increased ventilation and changes in the efficiency of the biological pump. These benthic foraminiferal turnovers were neither directly associated with changes in dominant bottom water mass nor with changes in productivity, but occurred during global cooling and increased ventilation of deep waters associated with the intensification of the NHG.

Deep-sea benthic foraminifera, carbonate dissolution and species diversity in Hardangerfjord, Norway: An initial assessment

This is the first record of live (stained) deep-sea benthic foraminifera in the 850 m deep silled Hardangerfjord, the second deepest fjord in Western Norway. Estimates of organic carbon flux (∼2.5 g Cm −2 y −1) show that the fjord-values are comparable to similar depths on the continental slope. Accordingly, although these first samples only provide relative abundance data, the low proportion of live to dead individuals in the top cm of the sediment suggests a low foraminifera biomass. Another similarity with the deep sea is that the abiotic environment of the deep basins is stable even though the deepest basins are isolated from the open deep sea by the continental shelf and sills in the outer parts of the fjord suggesting that the deep-sea species are introduced as propagules during deep-water renewals. There is evidence of an increase in dissolution of fragile calcareous tests (e.g., Nonionella iridea) especially in the innermost part of Hardangerfjord since the 1960s and this has led to a relative increase in dead agglutinated assemblages. The presence of larger forms with tests >1 mm provides substrata for the attachment of smaller forms and therefore an increase in species diversity. Indeed, the diversity is comparable both to that of the open deep sea and that of reported macrofauna from the same sites, reflecting similar ecological status. Holtedahl (1965) suggested that there may be some down-slope transport of sediment into the deep basins with the deposition of turbidites. Despite some evidence of transport, no major recent disturbance due to turbidite deposition seems to have occurred and hence Hardangerfjord presents a unique environment with elements of deep-sea faunas in a land-locked setting.

Deep-sea benthic foraminiferal changes in the eastern Indian Ocean (ODP Hole 757B): Their links to deep Indonesian (Pacific) flow and high latitude glaciation during the Neogene

This study analyses 26.5 Ma record of deep-sea benthic foraminifera from 194 samples from Ocean Drilling Program Hole 757B (latitude 17°01.458' S, longitude 88°10.899' E, water depth of 1652.1 m) located on the Ninetyeast Ridge, southeastern Indian Ocean below equatorial divergence zone. The data document important changes in benthic foraminiferal population at Hole 757B since the late Oligocene. The welloxygenated, oligotrophic species including Cibicides cicatricosus, C. pseudoungerianus and Oridorsalis umbonatus were dominant during the late Oligocene to the early Miocene. These species began to decline as site 757 moved northward into the influence of the Indonesian Throughflow (ITF) beneath surface and subsurface water masses from the Pacific Ocean. Cibicides cicatricosus and C. pseudoungerianus disappeared in the late Miocene (10-8 Ma) at Hole 757B. The lower bathyal to abyssal species Nuttallides umbonifera shows a major increase at ~11.5 Ma coinciding with a significant increase in Neodymium (Nd) isotope values, indicating substantial transport of deep Pacific water to the Indian Ocean through the Indonesian seaway. Nuttallides umbonifera decreases drastically during 3-2.8 Ma, though the Nd isotope values do not show a decrease. We relate this change to a low sample resolution in the latter study. This event coincides with the final closure of the Indonesian seaway and a switch in shallow ITF source from warm, saline South Pacific to cool, fresh North Pacific thermocline water, which triggered global cooling and major expansion of Northern Hemisphere glaciation.

What happens when the ocean is overheated? The foraminiferal response across the Paleocene-Eocene Thermal Maximum at the Alamedilla section (Spain)

The global warming and major perturbation of the global carbon cycle that occurred during the Paleocene–Eocene Thermal Maximum (PETM) have been investigated in the lower bathyal–upper abyssal Alamedilla section (Spain). Geochemical anomalies and dramatic faunal changes (including the globally recognized extinction event of deep-sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils) are associated with the PETM at Alamedilla. Biotic changes in the plankton and benthos indicate environmental instability ∼11–14 k.y. before the onset of carbon isotope excursion that marks the Paleocene/Eocene boundary. The reorganization of the planktic ecosystem points to warm and oligotrophic conditions in surface waters during the earliest Eocene, whereas faunal and geochemical data indicate that the extinctions of benthic foraminifera occurred over an interval with a high CaCO3 content and oxic conditions at the seafloor. The proliferation of disaster taxa ( Glomospira spp.) after the extinctions has been related to a potential source of isotopically light carbon in the western Tethys and North Atlantic. Significant changes in foraminiferal test size are documented across the PETM. We suggest that increased temperatures played an important role in benthic foraminiferal test size, increasing their metabolic rates and, consequently, their food requirements. Decreased planktic foraminiferal test size may be related to decreased nutrient availability or surface-water density. However, the differences in test size evolution among different species of both benthic and planktic foraminifera may be related to interspecific competition and ecological adaptations to direct or indirect consequences of the carbon addition during the PETM.

Calibration of δ<sup>18</sup>O of cultured benthic foraminiferal calcite as a function of temperature

Abstract. The geochemical composition of deep-sea benthic foraminiferal calcite is widely used to reconstruct sea floor paleoenvironments. The calibration of the applied proxy methods has until now been based on field observations in complex natural ecosystems where multiple factors are interfering. However, laboratory experiments with stable physico-chemical conditions appear to be the ideal way to evaluate the influence of a single parameter. In this paper, we present the oxygen isotopic composition of deep-sea benthic foraminiferal shells entirely calcified under controlled experimental conditions over a large temperature range (4 to 19 °C). The new laboratory protocols developed for this study allowed us to produce large quantities of shells in stable conditions, so that also the shell size effect could be investigated. It appears that when considering a narrow test size range, the curve describing the temperature dependency of δ18O in Bulimina marginata is parallel to the thermodynamically determined curve observed in inorganically precipitated calcite (−0.22‰ °C−1). This observation validates the use of δ18O of this benthic species in paleoceanographical studies. Over the studied size range (50 to 300 μm), the effect of test size was 0.0014‰ μm−1, confirming previous suggestions of a substantial test size effect on δ18O of benthic foraminifera. This study opens new perspectives for future proxy calibrations in laboratory set-ups with deep-sea benthic foraminifera (e.g. quantification of the influence of the carbonate chemistry).

CENOZOIC RECORD OF ELONGATE, CYLINDRICAL, DEEP-SEA BENTHIC FORAMINIFERA IN THE INDIAN OCEAN (ODP SITES 722, 738, 744, 758, AND 763)

A group of ,100 species of elongate, cylindrical deep-sea benthic foraminifera (families Stilostomellidae, Pleurostomellidae, Nodosariidae) with complex, often constricted apertural structures, became extinct during increasingly cold glacial periods in the late Pliocene to mid-Pleistocene Climate Transition (MPT, ,2.6–0.6 Ma). We document the evolutionary history and architecture of this Extinction Group (Ext. Gp) through the Cenozoic at four lower bathyalupper abyssal Indian Ocean sites (ODP 722, 744/738, 758, 763), seeking clues to the cause of this morphologicallytargeted extinction episode late in the Cenozoic. Eighty percent of the 116 Ext Gp. species present in the Cenozoic of the Indian Ocean originated globally in the Eocene or earlier, compared with 23–37% of other Quaternary deep-sea foraminifera. The Ext. Gp had its peak species richness and relative and absolute abundances in the late Eocene. The rapid warming of the Paleocene-Eocene Thermal Maximum, that resulted in a loss of 30–50% of deep-sea foraminiferal species, had no impact on the Ext. Gp in the one Indian Ocean section (ODP 744/738) studied. Major Cenozoic changes in the Ext. Gp, including increased species turnover, changes in dominant species, a decline in abundance, loss in diversity, and finally extinction, mostly occurred during the middle Eocene to early Oligocene, middle to late Miocene, and late Pliocene to middle Pleistocene. These were times of stepped increase in the volume of polar ice, global oceanic cooling, surface-water eutrophication, seasonality of phytoplankton production, deep-water ventilation, and southern deep-water carbonate corrosiveness. The final decline and disappearance of the Ext. Gp began in the late Miocene at high latitudes (744/738), but not until the late Pliocene (758, 763) or MPT (722) at lower latitudes. We hypothesize that the loss of the Ext. Gp of deep-sea foraminifera may have been caused by the decline or demise of their specific food source (detrital phytoplankton or bottom-dwelling microbes) that was abundant in the Greenhouse World and was decimated by the stepwise cooling, ventilation, or eutrophication of the oceans that began in the middle and late Eocene.

Deep-sea faunal provinces and their inferred environments in the Indian Ocean based on distribution of Recent benthic foraminifera

Multivariate analysis was performed on percentages of 46 species of unstained deep-sea benthic foraminifera from 131 core-top to near-core-top samples (322–5013 m) from across the Indian Ocean. Faunal data are combined with GEOSECS geochemical data to investigate any relationship between benthic foraminifera (assemblages and species) and deep-sea properties. In general, benthic foraminifera show a good correlation to surface productivity, organic carbon flux to the sea floor, deep-sea oxygenation and, to a lesser extent, to bottom temperature, without correlation with the water depths. The foraminiferal census data combined with geochemical data has enabled the division of the Indian Ocean into two faunal provinces. Province A occupies the northwestern Indian Ocean (Arabian Sea region) where surface primary production has a major maximum during the summer monsoon season and a secondary maximum during winter monsoon season that leads to high organic flux to the seafloor, making the deep-sea one of the most oxygen-deficient regions in the world ocean, with a pronounced oxygen minimum zone (OMZ). This province is dominated by benthic foraminifera characteristic of low oxygen and high organic food flux including Uvigerina peregrina, Robulus nicobarensis, Bolivinita pseudopunctata, Bolivinita sp., Bulimina aculeata, Bulimina alazanensis, Ehrenbergina carinata and Cassidulina carinata. Province B covers southern, southeastern and eastern parts of the Indian Ocean and is dominated by Nuttallides umbonifera, Epistominella exigua, Globocassidulina subglobosa, Uvigerina proboscidea, Cibicides wuellerstorfi, Cassidulina laevigata, Pullenia bulloides, Pullenia osloensis, Pyrgo murrhina, Oridorsalis umbonatus, Gyroidinoides (= Gyroidina) soldanii and Gyroidinoides cf. gemma suggesting well-oxygenated, cold deep water with low (oligotrophic) and pulsed food supply.

Incorporation of Mg and Sr in calcite of cultured benthic foraminifera: impact of calcium concentration and associated calcite saturation state

Abstract. We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (Ω) on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing) and Ammonia tepida (low-Mg calcite, symbiont-barren) were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite)/(TE/Caseawater). The culturing study shows that DMg of A. tepida significantly decreases with increasing Ω at a gradient of −4.3×10−5 per Ω unit. The DSr value of A. tepida does not change with Ω, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing Ω, while DSr increases considerably with Ω at a gradient of 0.009 per Ω unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50–100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep-sea benthic foraminifera typically used for paleostudies, the higher Ca concentrations in the past may potentially bias temperature reconstructions to a considerable degree. For instance, 25 Myr ago Mg/Ca ratios in A. tepida would have been 0.2 mmol/mol lower than today, due to the 1.5 times higher [Ca2+] of seawater, which in turn would lead to a temperature underestimation of more than 2 °C.

Cenozoic record of elongate, cylindrical, deep-sea benthic foraminifera in the North Atlantic and equatorial Pacific Oceans

In the late Pliocene–middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal–abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20–70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction? In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene–early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene–Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle–late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene–early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene–middle Pleistocene. Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.

Deep-sea palaeoceanography of the Maldives Islands (ODP Hole 716A), equatorial Indian Ocean during MIS 12-6

Deep-sea benthic foraminifera, planktic foraminifer Globigerina bulloides and pteropods have been quantitatively analysed in 451 samples from Ocean Drilling Program (ODP) Hole 716A, to understand both surface and deep-sea palaeoceanographic changes in the equatorial Indian Ocean basin during the late Quaternary (approximately 444-151 Kyrs). Benthic foraminifera were analysed from >125 microm size fraction whereas Globigerina bulloides and pteropods were analysed from > 150 microm size fraction. Factor analysis of most dominant benthic foraminiferal species over the studied time span made it possible to identify three biofacies characterizing distinct deep-sea environmental settings at Hole 716A. The environmental interpretation of each species is based on the ecology of recent deep-sea benthic foraminifera. The faunal record indicates fluctuating deep-sea conditions including changes in surface productivity, organic food supply and deep-sea oxygenation linked to changing wind intensities. These changes are pronounced on glacial-interglacial time scales driven by summer monsoon winds.

Food supply to the seafloor in the Pacific Ocean after the Cretaceous/Paleogene boundary event

Deep-sea benthic foraminifera show important but transient assemblage changes at the Cretaceous/Paleogene (K/Pg) boundary, when many biota suffered severe extinction. We quantitatively analyzed benthic foraminiferal assemblages from lower bathyal–upper abyssal (1500–2000 m) northwest Pacific ODP Site 1210 (Shatsky Rise) and compared the results with published data on assemblages at lower bathyal (~ 1500 m) Pacific DSDP Site 465 (Hess Rise) to gain insight in paleoecological and paleoenvironmental changes at that time. At both sites, diversity and heterogeneity rapidly decreased across the K/Pg boundary, then recovered. Species assemblages at both sites show a similar pattern of turnover from the uppermost Maastrichtian into the lowermost Danian: 1) The relative abundance of buliminids (indicative of a generally high food supply) increases towards the uppermost Cretaceous, and peaks rapidly just above the K/Pg boundary, coeval with a peak in benthic foraminiferal accumulation rate (BFAR), a proxy for food supply. 2) A peak in relative abundance of Stensioeina beccariiformis, a cosmopolitan form generally more common at the middle than at the lower bathyal sites, occurs just above the buliminid peak. 3) The relative abundance of Nuttallides truempyi, a more oligotrophic form, decreases at the boundary, then increases above the peak in Stensioeina beccariiformis. The food supply to the deep sea in the Pacific Ocean thus apparently increased rather than decreased in the earliest Danian. The low benthic diversity during a time of high food supply indicates a stressed environment. This stress might have been caused by reorganization of the planktic ecosystem: primary producer niches vacated by the mass extinction of calcifying nannoplankton may have been rapidly (<10 kyr) filled by other, possibly opportunistic, primary producers, leading to delivery of another type of food, and/or irregular food delivery through a succession of opportunistic blooms. The deep-sea benthic foraminiferal data thus are in strong disagreement with the widely accepted hypothesis that the global deep-sea floor became severely food-depleted following the K/Pg extinction due to the mass extinction of primary producers (“Strangelove Ocean Model”) or to the collapse of the biotic pump (“Living Ocean Model”).

Degradation of algal lipids by deep-sea benthic foraminifera: An in situ tracer experiment

We conducted an in situ feeding experiment using 13C-labeled unicellular algae in Sagami Bay, Japan (water depth, 1450 m), in order to understand the fate of lipid compounds in phytodetritus at the deep-sea floor. We examined the incorporation of excess 13C into lipid compounds extracted from bulk sediments and benthic foraminiferal cells. 13C-enriched fatty acids derived from 13C-labeled algae were exponentially degraded during 6 days of incubation in the sediment. Subsequent enrichments in 13C in sedimentary n-C 15, anteiso-C 17, and C 17 fatty acids indicated the microbial degradation of algal material and production of bacterial biomass in the sediment. We observed the incorporation of 13C-labeled algal phytol and fatty acids into foraminiferal cells. The compositions of 13C-labeled algal lipids in foraminiferal cells were different from those in the bulk sediments, indicating that foraminiferal feeding and digestion influenced the lipid distribution in the sediments. Furthermore, some sterols in Globobulimina affinis (e.g., 24-ethylcholesta-5,22-dien-3β-ol, 24-ethylcholest-5-en-3β-ol, and 23,24-dimethylcholesta-5,22E-dien-3β-ol) were newly produced via the modification of dietary algal sterols within 4–6 days. In addition to the effects of bacteria, feeding by benthic foraminifera can result in a significant reorganization of the composition of organic matter and influence benthic food webs and carbon cycling at the deep-sea floor.

Book Reviews/Buchbesprechungen

Journal of Zoological Systematics and Evolutionary ResearchVolume 36, Issue 3 p. 158-158 Book Reviews/Buchbesprechungen First published: 27 April 2009 https://doi.org/10.1111/j.1439-0469.1998.tb00836.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Book Reviewed in this article: Fossils & Strata, 44 (1997). Containing: Christensen, W. K. & Schulz, M.-G. Capy, P.; Bazin, C.; Higuet, D.; Langin, T.: Dynamics and Evolution of Transposable Elements. Widmark, J. G. V.: Deep-sea benthic foraminifera from Cretaceous/Paleogene boundary strata in the South Atlantic – taxonomy and paleoecology. Volume36, Issue3September 1998Pages 158-158 RelatedInformation

The Early Pliocene re-colonisation of the deep Mediterranean Sea by benthic foraminifera and their pulsed Late Pliocene–Middle Pleistocene decline

Ninety-five species and 19 genera of cosmopolitan, deep-sea benthic foraminifera belonging to the families Pleurostomellidae, Stilostomellidae and Nodosariidae, became extinct during the Late Pliocene–Middle Pleistocene. Only 50% of these (44 species) were present in the Pliocene or Pleistocene of the deep Mediterranean Sea (ODP Sites 654, 966, 967, 975, 976), being those which had successfully migrated in via the Strait of Gibraltar from the deep Atlantic following the annihilation of the Mediterranean deep-sea fauna during the Late Miocene Messinian Crisis. Most colonisation occurred within the first 0.8 myrs (5.3–4.5 Ma) after re-establishment of the Mediterranean–Atlantic link, with possibly a second lesser period of immigration in the Late Pliocene (3.4–3.0 Ma). We infer that colonisations may have been fortuitous and few in number, as some common members of the group in the Atlantic never succeeded in establishing in the Mediterranean Sea. There is no evidence of any new immigration events during the Pleistocene, implying that the present anti-estuarine circulation may have been in place throughout this period. Our studies suggest that these deep-water, low-oxygen-tolerant foraminifera survived the many periods of deep-water sapropel formation in the Pliocene–Early Pleistocene, possibly in somewhat shallower (~ 500 m) refuges with dysoxic, rather than anoxic conditions. The Pliocene–Pleistocene stratigraphic record of this group of elongate, cylindrical benthic foraminifera with constricted and specialised apertures is similar in the west and east Mediterranean basins. The group declined in abundance (flux) and diversity in two pulses, during the Late Pliocene (3.1–2.7 Ma) and the late Early Pleistocene (1.3–1.0 Ma) in concert with global, southern-sourced, deep-water sites (AABW, CPDW) and earlier than the single decline (1.0–0.6 Ma) in global, intermediate water sites (uNADW, AAIW). All species, with one possible exception, disappeared earlier in the Mediterranean than globally. The highest occurrence of any species of this group in Mediterranean sites was 0.8–0.43 Ma, comparable with 0.7–0.2 Ma outside with the youngest survivors being in abyssal, deep-water. Thus, despite the unusual oceanographic conditions and isolation, the deep Mediterranean Sea was in this case neither the centre for the evolution of new species nor a refuge where species survived after they had disappeared elsewhere.

Environmental and intraspecific dimorphism effects on the stable isotope composition of deep-sea benthic foraminifera from the Southern Gulf of California, Mexico

We studied the influence of microhabitat, organic matter flux, and metabolism on the stable oxygen and carbon isotope composition of live (Rose Bengal stained) and dead (empty tests) dimorphic generations (microspheric/sexual and megalospheric/asexual) of deep-sea benthic foraminifera from the southern Gulf of California. Despite the range of environmental conditions that exists between the investigated sites, the distribution and live abundance of dimorphic generations of Bolivina subadvena Cushman and B. argentea Cushman were similar: in every site, each dimorphic generation displayed the same relative depth distribution. Maximum abundance of megalospheric B. argentea was observed between 0 and 2 mm, whereas the microspheric generation of this species is most abundant at depths between 1 and 3 mm. For B. subadvena, megalospheric individuals concentrated at the organic-rich boundary layer (0–1 mm), while individuals of the microspheric generation were most abundant deeper in the sediment (4 and 6 mm). Different specific responses to carbon rain variability were indicate by the variation in the proportions of dimorphic generation and by the consistently lighter δ 13C and δ 18O values observed in B. subadvena compared to B. argentea. Indicating that B. subadvena populations are being maintain, largely, through asexual reproduction (megalospheric generation), which requires high metabolic rates that account for a larger incorporation of metabolic CO 2 into their tests. The comparison of isotopic measurements from three size classes (125, 150 and 250 µm) in dimorphic generations of B. subadvena showed that isotopic fractionation related to ontogeny is small compared to the variation due to dimorphism, illustrating the potential use of the isotopic signals of these two species in the reconstruction of past organic matter fluxes, if the species life strategies are considered.

Late Quaternary benthic foraminifera from Ocean Drilling Program Hole 716A, Maldives Ridge, southeastern Arabian Sea - PART 1

A study on deep-sea benthic foraminifera from the interval ~445 ka BP to the Present of the Ocean Drilling Program (ODP) Hole 716A (4°56.0′N, 73°17.0′E; present water depth 533.3m), Maldives Ridge, southeastern Arabian Sea, documented 201 species belonging to 105 genera. These taxa were examined under scanning electron microscope (SEM) to illustrate their interspecificmorphological variations. Several of these species are dominant showing significant down core fluctuations in their abundances whereas some are rare and sporadic.

Late Quaternary benthic foraminifera from Ocean Drilling Program Hole 716A, Maldives Ridge, southeastern Arabian Sea - PART 2

A study on deep-sea benthic foraminifera from the interval ~445 ka BP to the Present of the Ocean Drilling Program (ODP) Hole 716A (4°56.0′N, 73°17.0′E; present water depth 533.3m), Maldives Ridge, southeastern Arabian Sea, documented 201 species belonging to 105 genera. These taxa were examined under scanning electron microscope (SEM) to illustrate their interspecific morphological variations. Several of these species are dominant showing significant down core fluctuations in their abundances whereas some are rare and sporadic.

Cretaceous evolution of the genus Adercotryma (Foraminifera) in the deep Pacific

Adercotryma glomeratum is one of the most geographically and bathymetrically widespread species of Recent deep-sea benthic foraminifera, but the evolutionary history of this distinct agglutinated species is poorly known. In addition to one or two Recent species probably closely related to A. glomeratum, the Eocene-Oligocene species Adercotryma agterbergi has been described, but we suggest that this species be assigned to the genus Ammogloborotalia. A very rare, unnamed species has been described from the Campanian in the western Pacific Ocean, and it has been speculated that the genus originated at about that time in the western Pacific, possibly from the ancestor Ammogloborotalia gyroidinaeformis. We describe the Maastrichtian occurrence of a previously unknown species, which we named Adercotryma kuhnti. This species occurs in the Maastrichtian Abathomphalus mayaroensis planktonic foraminiferal Zone, Micula prinsii nannofossil zone CC26, in the lower bathyal to abyssal ODP Site 1210 (ODP Leg 198, Shatsky Rise, northwest Pacific Ocean), where it constitutes up to 14.7% of the benthic foraminiferal assemblages. We looked for the species in coeval material from many locations in and around the Atlantic Ocean, and DSDP Site 465 in the Pacific (Hess Rise), but did not find it. The occurrence as a geographically restricted species agrees with speculation of a Cretaceous origin of the genus in the western Pacific, and evolution as a deep-sea species rather than migration from shallow waters.

The influence of a simulated diatom bloom on deep-sea benthic foraminifera and the activity of bacteria: A mesocosm study

Live benthic foraminifera were collected from the Portuguese continental margin from 900 m water depth. Under controlled laboratory conditions, Thalassiosira pseudonana, was used to create an artificial diatom bloom. Two different diatom loads, high (240 μg C/cm 2) and low (80 μg C/cm 2) load, were fed to benthos. The response of the benthic foraminifera, total standing stocks (63–150 μm, >150 μm size fractions) and vertical distribution in the sediment, was analysed at 28 and 56 days following the simulated food pulse. The treated cores, or mesocosms, were compared to controls that were harvested at the experimental setup, prior to the feeding, and at the end of the experiment. Bacterial activity was assessed in terms of benthic nitrate and ammonium fluxes across the sediment–water interface. Prior to the simulated diatom bloom the total standing stocks of foraminifera declined significantly. The population recovered following the feeding and, especially under the higher diatom load, increased in comparison to the control cores. In general, a ‘two-phased’ response was measured in different size classes of foraminifera. An increase in the smaller-sized (63–150 μm) subpopulation was followed by an increase in the larger-sized (>150 μm) subpopulation. Elevated effluxes of ammonium were measured following the simulated diatom bloom. The highest effluxes were seen in the high-load treatment, reflecting the highest remineralised carbon load. The ammonium effluxes normalised to control levels around 25 days after the bloom. In addition, high effluxes of nitrate were measured, indicating enhanced nitrification following the diatom deposition. The nitrate effluxes normalised to control levels around 40 days after the feeding event. Several foraminiferal taxa, e.g. Melonis barleeanum, Bigenerina cylindrica, Chilostomella oolina, responded to the diatom bloom (or increased bacterial activity) and increased in numbers. However, the vertical distribution of these infaunal species was not influenced by the added food. Only two infaunal species, Pullenia sp. and Trochammina sp., were observed to increase in numbers in the surficial sediments. These two taxa most likely migrated to the surface to consume the labile organic matter. In contrast, the other infaunal species perhaps benefited from the diatom bloom indirectly, e.g. from increased bacterial activity in the sediment.

A major change in monsoon-driven productivity in the tropical Indian Ocean during ca 1.2–0.9 Myr: Foraminiferal faunal and stable isotope data

Tropical climate is variable on astronomical time scale, driving changes in surface and deep-sea fauna during the Pliocene–Pleistocene. To understand these changes in the tropical Indian Ocean over the past 2.36 Myr, we quantitatively analyzed deep-sea benthic foraminifera and selected planktic foraminifera from > 125 μm size fraction from Deep Sea Drilling Project Site 219. The data from Site 219 was combined with published foraminiferal and isotope data from Site 214, eastern Indian Ocean to determine the nature of changes. Factor and cluster analyses of the 28 highest-ranked species distinguished four biofacies, characterizing distinct deep-sea environmental settings. These biofacies have been named after their most dominant species such as Stilostomella lepidula– Pleurostomella alternans (Sl–Pa), Nuttallides umbonifer– Globocassidulina subglobosa (Nu–Gs), Oridorsalis umbonatus– Gavelinopsis lobatulus (Ou–Gl) and Epistominella exigua– Uvigerina hispido-costata (Ee–Uh) biofacies. Biofacies Sl–Pa ranges from ~ 2.36 to 0.55 Myr, biofacies Nu–Gs ranges from ~ 1.9 to 0.65 Myr, biofacies Ou–Gl ranges from ~ 1 to 0.35 Myr and biofacies Ee–Uh ranges from 1.1 to 0.25 Myr. The proxy record indicates fluctuating tropical environmental conditions such as oxygenation, surface productivity and organic food supply. These changes appear to have been driven by changes in monsoonal wind intensity related to glacial–interglacial cycles. A shift at ~ 1.2–0.9 Myr is observed in both the faunal and isotope records at Site 219, indicating a major increase in monsoon-induced productivity. This coincides with increased amplitude of glacial cycles, which appear to have influenced low latitude monsoonal climate as well as deep-sea conditions in the tropical Indian Ocean.