Changes In Foraminiferal Assemblages Research Articles

Integrated record of the Late Lutetian Thermal Maximum at IODP site U1508, Tasman Sea: The deep-sea response

The Late Lutetian Thermal Maximum (LLTM) was a transient and brief global warming event recorded in the middle Eocene, at 41.52 Ma. The biotic response to the LLTM has been documented at only a few marine sites so far. Here, we present the first record of deep-sea benthic foraminiferal assemblage changes during the LLTM in the southwest Pacific at International Ocean Discovery Program Hole U1508C (1609 m water depth) in the Tasman Sea. The LLTM coincides with a negative excursion in bulk sediment δ13C (0.47‰) and benthic foraminifera δ13C (0.36‰), with changes in the relative abundance of benthic foraminiferal species and in the deep-water organic geochemistry. The decrease in diversity of the assemblages indicates environmental stress during the event, potentially linked to oxygen deficiency, as evidenced by the occurrence of dysoxic taxa (e.g. Lenticulina spp., Turrillina brevispira). Although calcareous taxa dominate, the presence of corrosion-resistant species and poorly preserved foraminiferal tests suggest slightly CaCO3-corrosive bottom waters, but no dissolution was evident. We suggest the shallowing of the thermocline and enhanced water column stratification at this site during the LLTM.

Late Cretaceous Paleoceanographic Evolution and the Onset of Cooling in the Santonian at Southern High Latitudes (IODP Site U1513, SE Indian Ocean).

The latest Cenomanian to Santonian sedimentary record recovered at IODP Expedition 369 Site U1513 in the Mentelle Basin (SE Indian Ocean, paleolatitude 60°S at 85 Ma) is studied to interpret the paleoceanographic evolution in the Southern Hemisphere. The planktonic foraminiferal assemblage changes, the depth ecology preferences of different species, and the surface and seafloor temperature inferred from the stable isotopic values measured on foraminiferal tests provide meaningful information to the understanding of the Late Cretaceous climate. The hothouse climate during the Turonian‐Santonian, characterized by weak latitudinal temperature gradients and high atmospheric CO2 concentrations, is followed by a progressive cooling during the Campanian. At Site U1513 the beginning of this climatic transition is nicely recorded within the Santonian, as indicated by an ∼1‰ increase in δ18O values of planktonic foraminifera suggesting a decline in surface water paleotemperatures of 4°C. The onset of cooling is mirrored by changes in the planktonic foraminiferal assemblages including extinctions among surface and deep dwellers, appearances and diversification of newly evolving taxa, and changes from predominantly epifaunal oxic to infaunal dysoxic/suboxic taxa among co‐occurring benthic foraminifera. Overall, the data presented here document an interval in the Santonian during which the rate of southern high latitude cooling increased. Both surface and bottom waters were affected, although the cooling signal is more evident in the data for surface waters. This pattern of cooling ascribes the deterioration of the Late Cretaceous climate to decreased CO2 in the atmosphere and changes in the oceanic circulation correlated with enhanced meridional circulation.

Disentangling natural vs. anthropogenic induced environmental variability during the Holocene: Marambaia Cove, SW sector of the Sepetiba Bay (SE Brazil).

Multiproxy approach based on textural, mineralogical, geochemical, and microfaunal analyses on a 176-cm-long core (SP8) has been applied to reconstruct the Holocene paleoenvironmental changes and disentangling natural vs. anthropogenic variability in Marambaia Cove of the Sepetiba Bay (SE Brazil). Sepetiba Bay became a lagoonal system due to the evolution and development of the Marambaia barrier island during the Holocene and the presence of an extensive river basin. Elemental concentrations from pre-anthropogenic layers from the nearby SP7 core have been used to estimate the baseline elemental concentrations for this region and to determine metals enrichment factors (EF), pollution load index (PLI), and sediment pollution index (SPI). Record of the core SP8 provides compelling evidence of the lagoon evolution differentiating the effects of potentially toxic elements (PTEs) under natural vs. anthropic forcing in the last ~ 9.5 ka BP. The study area was probably part of coastal sand ridges between ≈ 9.5 and 7.8 ka BP (radiocarbon date). Events of wash over deposited allochthonous material and organic matter between ≈ 8.6 and 7.8 ka. Climatic event 8.2 ka BP, in which the South American Summer Monsoon was intensified in Brazil causing higher rainfall and moisture was scored by an anoxic event. Accumulation of organic matter resulted in oxygen depletion and even anoxia in the sediment activating biogeochemical processes that resulted in the retention of potentially toxic elements (PTEs). After ≈ 7.8 ka BP at the onset of the Holocene sea-level rise, a marine incursion flooded the Marambaia Cove area (previously exposed to subaerial conditions). Environmental conditions became favorable for the colonization of benthic foraminifera. The Foram Stress Index (FSI) and Exp(H'bc) indicate that the environmental conditions turned from bad to more favorable since ≈ 7.8 ka BP, with maximum health reached at ≈ 5 ka BP, during the mid-Holocene relative sea-level highstand. Since then, the sedimentological and ecological proxies suggest that the system evolved to an increasing degree of confinement. Since ≈ 1975 AD, a sharp increase of silting, Cd, Zn, and organic matter also induced by anthropic activities caused major changes in foraminiferal assemblages with a significant increase of Ammonia/Elphidium Index (AEI), EF, and SPI values and decreasing of FSI and Exp(H'bc) (ecological indicators) demonstrating an evolution from "moderately polluted" to "heavily polluted" environment (bad ecological conditions), under variable suboxic conditions. Thus, core SP8 illustrates the most remarkable event of anthropogenic forcing on the geochemistry of the sediments and associated pollution loads and its negative effect on benthic organisms.

Precessional Cyclicity of Seawater Pb Isotopes in the Late Miocene Mediterranean

AbstractAstronomical tuning in the Mediterranean region is primarily based on organically‐mediated proxies, such as cyclicity of organic rich layers or changes in foraminiferal assemblages. Both during and post deposition, organic proxies can be affected by complex processes not immediately related to the changes in precession (insolation) they are assumed to reflect. Here we present an isotopic proxy which exhibits precessional cyclicity yet is inorganic. Seawater lead (Pb) isotope records over four precessional cycles between 6.6 and 6.5 Ma, from bulk sediment leachates of three Messinian, circum‐Mediterranean marginal locations, show variations consistent with precessional cyclicity. During insolation minima, the Pb isotope signatures from all three sites converge to similar values, suggesting a regional process is affecting all three locations at that time. Data from the marginal sites are compared with new data from ODP Site 978 and published data from a variety of geological archives from the Mediterranean region to determine the mechanism(s) causing the observed variability. While the comparisons are not fully conclusive, the timing of events suggest that increased dust production from North Africa during insolation minima is the most likely control. This hypothesis implies that authigenic marine Pb isotope records have the potential to provide a reliable inorganic tie point for Mediterranean cyclostratigraphy where sub‐precessional resolution is required. An inorganic tie point could also provide the means to resolve long‐standing problems in Mediterranean stratigraphy on precessional and sub‐precessional timescales which have been obscured due to post‐depositional changes (e.g., sapropel burn‐down) or suboptimal ecological conditions (e.g., the Messinian Salinity Crisis).

Correction to: Seasonal changes in foraminiferal assemblages along environmental gradients in Adventfjorden (West Spitsbergen)

This correction stands to correct the original article as it was published with omitted funding information. To correct this, the authors have raised this correction and would like readers to know the following: “J.P. was supported by the National Science Centre Grant No. 2015/19/D/ST10/00244.” The original article has been corrected.

Changes in foraminiferal assemblages and environmental conditions during the T-OAE (Early Jurassic) in the northern Lusitanian Basin, Portugal

The foraminiferal assemblages and other microfossils from the Rabaçal area (Maria Pares section) in the Lusitanian Basin (Portugal) provide new insights regarding the Toarcian Oceanic Anoxic Event (T-OAE). Complementary analysis of the δ13C, total organic carbon (TOC) and geochemical redox and palaeoproductivity proxies reflect environmental changes that affected the microfossil assemblages. Detailed analyses of foraminiferal assemblages (their diversity, abundance, morphogroups and lifestyle) and geochemistry led us to discern phases of the biotic crisis and subsequent stages of recovery. Environmental instability, which began in the lattermost part of the Polymorphum Zone, is marked by a lesser abundance of foraminifera and ostracods, increased opportunist foraminifera, fluctuations in TOC values and the enrichment factor of phosphorous (PEF), as well as the onset of a negative carbon isotopic excursion (CIE). The peak phase of the biotic crisis corresponds with the lowest values for foraminiferal diversity and abundance (including a barren sample for benthic microfossils). The abundance and diversity of echinoderms, brachiopods, dinoflagellate cysts and calcareous nannofossils dropped sharply during the peak phase. This biotic crisis also entails extinction of the Order Metacopina and a local disappearance of echinoderms and brachiopods. Anoxic conditions at sea bottom did not develop, given the almost continuous record of foraminifera and trace fossils, yet oxygen-depleted conditions occurred. The lower part of the Levisoni Zone contains thin nodular limestones corresponding to a tempestitic–turbiditic facies. In this context, the re-oxygenation of bottom waters was favoured, as indicated by the presence of Thalassinoides and the low values of TOC and redox-sensitive elements (Mo, Ni and U). The survival phase in the wake of the biotic crisis is characterized by greater diversity and abundance of foraminifera and echinoderms (holothuroids and ophiuroids). The lowest δ13C values are recorded during this phase, with a dominance of opportunist (Eoguttulina) and facultative opportunist (Paralingulina tenera) foraminifera. Finally, recovery after the biotic crisis is evidenced by high values for specialists and potentially deep infaunal foraminifera, indicating oxic conditions in the sediment.

Depositional environments beneath the shelf-edge slopes of the Great Barrier Reef, inferred from foraminiferal assemblages: IODP Expedition 325

To understand sea-level changes since the Last Glacial Maximum (LGM) and their effects on coral reef systems, the shelf-edge slopes of the Great Barrier Reef (GBR) were cored during the Integrated Ocean Drilling Program (IODP) Expedition 325. Recovered unconsolidated sediments beneath the submerged shelf edge reefs contain abundant foraminiferal tests, which record changes in depositional environments and paleo-water depths. A total of 177 sediment samples were collected from 17 holes along three transects located within two geographical areas (Noggins Pass and Hydrographers Passage), and were analyzed to determine stratigraphic changes in foraminiferal assemblages (2–0.5 mm size fraction). Results show that four foraminiferal assemblages (A, B, C and D) are delineated by multivariate analyses (Q-mode cluster analysis and non-metric multidimensional scaling: NMDS), and these assemblages correspond to a back-reef to reef margin zone (0–10 m deep; Assemblage A), an upper photic zone (10–30 m deep) associated with hard substrates (Assemblage B), an intermediate to lower photic zone (30–90 m deep) characterized by soft substrates (Assemblage C), and a lower photic zone (90–130 m deep) only found in modern shelf slopes (Assemblage D). Gradual shifts in these four foraminiferal assemblages superimposed on a two-dimensional NMDS ordination mainly reflect water-depth gradients and the relative dominance of two substrate types (hard and soft substrates). Pre-LGM (older than Marine Isotope Stage 3: ≥MIS3) sediments along transects at Hydrographers Passage were deposited at intermediate to lower photic zones. In contrast, relatively shallow-water sequences found in ≥MIS3 deposits at Noggins Pass likely owe their origin to either turbidite and/or land slide processes. The lack of Assemblage D in ≥MIS3 deposits from all transects could be related to lowering temperature and/or increasing terrestrial influences (i.e. more light attenuation). Shallowing upward sequences found in LGM (MIS 2) deposits at Hydrographers Passage are likely related to stepwise sea-level falls to the full extent of the LGM. These foraminifer-based paleoenvironmental interpretations suggest that the GBR shelf edge slopes have changed their depositional environments continuously in response to sea-level fluctuations during the last glacial cycle.

Landward-directed Dispersal of Benthic Foraminiferal Propagules At Two Shallow-water Sites in the Doboy Sound Area (Georgia, U.S.A.)

Abstract Transport of foraminiferal propagules is an important mode of dispersal in benthic foraminifera. Known to occur from tidal marshes and estuaries to deep-water environments, the former are particularly vulnerable to ongoing climate change. Because rising sea levels can have profound implications on local salinity and associated faunal compositions, transport of foraminiferal propagules within these environments can be crucial for local assemblages to respond to changing conditions. Here we focus on a shallow-water environment in southeastern Georgia to evaluate whether propagule transport occurs evenly or whether it shows a predominant direction, such as land- or seaward. Two sites were sampled in the Doboy Sound area: the southern tip of Sapelo Island and a site on the North River located approximately 10 km inland. We applied the propagule method using the fine fraction of the sediments that contains the propagule bank. Experimental conditions in the laboratory included three temperatures (18, 24 and 30°C) and three salinities (15, 25 and 35) to simulate a range of environments that might trigger the growth of various foraminiferal species. While adult in situ assemblages of both sites were at least partly influenced by the adjacent salt marshes, experimentally grown assemblages were dominated by mudflat, estuarine or more open marine species. Thus, propagule transport from the more terrestrial side of the assemblage gradient is limited, while propagules of more marine species can be transported far into the extensive estuarine system of the study area, where they can remain viable within the local propagule banks. Results provide important insights into possible changes in foraminiferal assemblages with rising sea-level on the Georgia coast.

Planktic foraminiferal response to early Eocene carbon cycle perturbations in the southeast Atlantic Ocean (ODP Site 1263)

At low latitude locations in the northern hemisphere, striking changes in the relative abundances and diversity of the two dominant planktic foraminifera genera, Morozovella and Acarinina, are known to have occurred close to the Early Eocene Climatic Optimum (EECO; ~49–53Ma). Lower Eocene carbonate-rich sediments at Ocean Drilling Program (ODP) Site 1263 were deposited on a bathymetric high (Walvis Ridge) at ~40° S, and afford an opportunity to examine such planktic foraminiferal assemblage changes in a temperate southern hemisphere setting. We present here quantified counts of early Eocene planktic foraminiferal assemblages from Hole 1263B, along with bulk sediment stable isotope analyses and proxy measurements for carbonate dissolution. The bulk sediment δ13C record at Site 1263 resembles similar records generated elsewhere, such that known and inferred hyperthermal events can be readily identified. Although some carbonate dissolution has occurred, the well-preserved planktic foraminiferal assemblages mostly represent primary changes in environmental conditions. Our results document the permanent decrease in Morozovella abundance and increase in Acarinina abundance at the beginning of the EECO, although this switch occurred ~165kyr after that at low-latitude northern hemisphere locations. This suggests that unfavourable environmental conditions for morozovellids at the start of the EECO, such as sustained passage of a temperature threshold or other changes in surface waters, occurred at lower latitudes first. The remarkable turnover from Morozovella to Acarinina was widely geographically widespread, although the causal mechanism remains elusive. In addition, at Site 1263, we document the virtual disappearance within the EECO of the biserial chiloguembelinids, commonly considered as inhabiting intermediate water depths, and a reduction in abundance of the thermocline-dwelling subbotinids. We interpret these changes as signals of subsurface water properties, perhaps warming, and the associated contraction of ecological niches.

Changes in tropical Atlantic surface-water environments inferred from late Albian planktic foraminiferal assemblages (ODP Site 1258, Demerara Rise)

Abundance patterns of planktic and benthic foraminifera from the middle to upper Albian of tropical Atlantic Ocean Drilling Program Site 1258 (Demerara Rise) display a pronounced shift between two clearly distinguishable assemblages: (1) a foraminiferal fauna dominated by coiled taxa, which is inferred to represent a deep and/or weak oxygen minimum zone, and (2) abundant clavate and biserial taxa, inferred to record a shallow and/or strong oxygen minimum zone at Demerara Rise. The entire sequence is rich in organic matter (3–6 wt% TOC) of a marine phytoplankton origin (δ13C ∼ −28‰), consistent with a highly productive region. Both the high productivity and changes in foraminiferal assemblages are consistent with changes in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ) over the South American continent. Movements of the ITCZ are proposed to reduce the amount of runoff during the 'clavate-dominated' cycles, leading to the intensification of upwelling and therefore a stronger oxygen minimum zone compared to the intervals dominated by coiled foraminifera. We have previously found a similar hydrographic cycle in Turonian to Coniacian sections from the same area suggesting that this climate cyclicity and palaeogeography was long-lived off NE South America (∼15 million years). Due to the stratigraphic position of the interval with high abundances of clavate planktic foraminifera and the inferred strong oxygen minimum zone, it is tentatively proposed that this interval represents a local expression of the OAE 1c event within the long-living Demerara Rise upwelling system.

Penultimate and last glacial oceanographic variations in the Bering Sea on millennial timescales: Links to North Atlantic climate

We present high-resolution multi-proxy records from a marine sediment core (SO201-2-85KL) from the western Bering Sea to assess orbital- and millennial-scale paleoceanographic conditions during two last glacial intervals, including both terminations. Based on changes in foraminiferal assemblages, grain-size content and previously published TOC and δ13C records, we reconstruct variations in sea-surface biological productivity, intermediate-water oxygenation and sea-ice conditions during the last 180 kyr. Our data demonstrate remarkable differences between the penultimate (MIS 6) and last (MIS 4-2) glacial. Relatively high sea surface bioproductivity and reduced sea-ice cover are reconstructed for the penultimate glacial interval, whereas low bioproductivity and expanded sea-ice cover appear to be typical for the last glacial. Millennial-scale changes in intermediate water ventilation are inferred from faunal records for the middle part of the penultimate glacial. High-amplitude environmental variability during the penultimate glacial time in the Bering Sea resembles the well-known Dansgaard-Oeschger oscillations, and roughly corresponds to similar rapid climatic fluctuations found in North Atlantic records. The Termination II and I intervals display a similar succession of high-bioproductivity events, being more pronounced during the penultimate glacial-interglacial transition, probably due to the different orbital configuration. During the late phase of Termination II, two short intervals, characterized by high sea surface bioproductivity and low oxygen content of bottom waters, resemble the Bølling and Allerød warmings, whereas an episode with low bioproductivity occurs in between, similar to the Older Dryas. Our results provide support for a close circumpolar coupling between high-latitude environments on millennial timescales at least since the penultimate glacial.

The Coniacian–Santonian sedimentary record in southern Tanzania (Ruvuma Basin, East Africa): Planktonic foraminiferal evolutionary, geochemical and palaeoceanographic patterns

AbstractA 101 m thick stratigraphically complete late Coniacian–early Santonian (ca89 to 83 Ma) sedimentary sequence drilled in Tanzania (Tanzania Drilling Project Site 39) allows, for the first time, examination of the planktonic foraminiferal biostratigraphy and evolution, the depositional history, and geochemical patterns of the subtropical–tropical Indian Ocean region. The sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones. The occurrences of Tethyan marker species enable application of the tropical biozonation including identification of theDicarinella concavataandDicarinella asymetricaZones. In addition, Tanzania Drilling Project Site 39 is proposed as reference section for the Coniacian/Santonian boundary in the Indian Ocean with the boundary placed at the lowest occurrence ofGlobotruncana linneianain agreement with the Global Stratotype Section and Point (Spain). The record at Tanzania Drilling Project Site 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep‐dwelling taxa. Combined documentation of lithological and geochemical changes (%CaCO3, %Corg,δ13Ccarbandδ18Ocarb) reveals a setting influenced by continental‐derived nutrients in theDicarinella concavataZone (Lindi Formation) with a change to higher carbonate production and reduced surface water primary productivity in the overlyingDicarinella asymetricaZone (Nangurukuru Formation). Planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time. At the local scale, this palaeoceanographic scenario is consistent with the deepening of coastal Tanzania in response to the Late Cretaceous marine transgression registered in south‐east Tanzania. Because the tectonic evolution and sea‐level rise along the East Africa continental margin is superimposed on the Coniacian–Campanian global long‐term sea‐level high, this study hypothesizes that the epicontinental invasion of blue waters may have favoured radiation among deep‐dwelling taxa.

Planktonic foraminiferal turnover across the Cenomanian – Turonian boundary (OAE2) in the northeast of the Tethys realm, Kopet-Dagh Basin

Abstract Two Late Cenomanian – Early Turonian (C–T) intervals of the eastern part of the Kopet-Dagh basin, NE Iran have been investigated to evaluate the response of planktonic foraminifera to the geological event OAE2. The Gharesu and Taherabad sections with the thicknesses of 30 m and 22.5 m are composed of shale and marl interbedded with glauconitic sandstone. Three biozones Rotalipora cushmani, Whiteinella archaeocretacea and Helvetoglobotruncana helvetica were recognized based on study of planktonic foraminifera, in these sections. We observed the patterns of planktonic foraminiferal assemblage changes around the C–T boundary and divided this succession into several successive intervals. This study confirms that OAE2 was a long term event. A gradual perturbation in the study successions starts in the interval 1 with low abundance and diversity of planktonic foraminifera. An enhanced oxygen minimum zone (OMZ) occurs in the interval 3 which coincides with a temporary absence of planktonic foraminifera and sedimentation of framboidal pyrite. High diversity of planktonic foraminifera and appearance of new genera in the interval 5 indicate return of normal conditions to the basin. A significant short-term sea surface temperature cooling is also indicated by planktonic foraminiferal turnover and carbonate contents in the interval 2 which is comparable with other parts of the Tethys Ocean, Boreal sea and Atlantic region.

Pleistocene benthic foraminifers in the Arctic Ocean: Implications for sea-ice and circulation history

Abstract Three sediment cores from the Northwind, Mendeleev, and Lomonosov Ridges distributed across the western Arctic Ocean were investigated for foraminiferal composition with a focus on benthic assemblages. This investigation provides insights into middle to late Pleistocene history of paleoceanographic and sea-ice conditions on multi-millennial time scales. Calcareous foraminiferal abundances and assemblage composition show stratigraphically consistent development, including glacial–interglacial variability and long-term evolution of foraminiferal assemblages. Major long-term changes occurred at the end of the Mid-Pleistocene Transition (estimated ca. 0.7–0.8 Ma) and later near the bottom of Marine Isotope Stage 7 (ca. 0.25 Ma) and near the top of MIS 5 (ca. 0.1 Ma). These changes include notably a diminishing role of phytodetritus-related species, such as Epistominella exigua , at the expense of oligotrophic species adapted to live under persistent sea ice, presumably indicating an overall expansion of year-round ice cover in the Arctic during the Pleistocene. The pronounced MPT shift from mostly seasonal to perennial sea ice was coeval, and possibly related to a growth of North American ice sheets and the beginning of glacially-controlled sedimentation in the western Arctic Ocean. The ca. 0.25 Ma transition, interpreted as another step in sea-ice expansion, also co-occurs with signs of ice-sheet expansion in both North America and, especially, Eurasia. The apparent synchronicity of major steps in sea-ice and glaciation histories necessitates a more in-depth investigation of feedbacks involved and broader linkages beyond the Arctic region. The ca. 0.1 Ma change in foraminiferal assemblages marks a consistent stratigraphic event, expressed notably in a proliferation of the cosmopolitan species Oridorsalis tener , although its paleoenvironmental significance is not yet fully understood.

Foraminiferal record in a condensed marine succession: a case study from the Albian and Cenomanian (mid-Cretaceous) of Annopol, Poland

AbstractA condensed succession at Annopol is of key importance for the mid-Cretaceous palaeontology and palaeobiogeography in Poland. Here, the planktonic and benthic foraminifera from the Albian and Cenomanian intervals are studied. The local foraminiferal record is strongly influenced by burrowers. On the one hand, piping down of the foraminiferal tests through burrows disturbed the original succession, for example by introduction of the Cenomanian foraminifera into the Albian phosphorite horizon. On the other hand, the foraminifera in the burrow fills near the base of the Cenomanian provide the sole piece of evidence of a lower upper Cenomanian unit lost from the record by erosion. Changes in foraminiferal assemblages allow for the interpretation of the succession in terms of bathymetry and biological productivity. The highest rate of primary production is deduced for the Albian phosphorite horizon. Integration of foraminiferal and ammonite biostratigraphy with sedimentology allows for the comparison of a pattern of sea-level oscillations recorded at Annopol with the relevant portion of the classic graph of sea-level changes for the British Isles. It turns out that all important elements of the British curve, that is, transgressive peaks and regressive troughs or lows, left their distinctive, albeit highly residual, record in the Annopol succession. This study demonstrates that even extremely condensed marine deposits, such as those at Annopol, may provide a foraminiferal record of better quality, order and resolution than conventionally anticipated.

Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1–4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34 Ma) and the consequent development of a circumpolar proto-ACC.

Estuarine foraminifera record Holocene stratigraphic changes and Holocene climate changes in ENSO and the North American monsoon: Baffin Bay, Texas

During the last Quaternary sea level fall (120–ka), Baffin Bay was formed by the down-cutting of the Los Olmos, San Fernando, and Petronila Creeks of south Texas. When sea level rose, this incised valley was then filled with mixed siliciclastic/carbonate sediments that record coastal environmental change over the past 10ky. Previous sedimentological and seismic analysis shows that Baffin Bay contains atypical depositional environments as a result of its semi-arid climate setting and isolation from the Gulf of Mexico. Three prominent stratigraphic surfaces can be recognized within the bay deposits, and are chronostratigraphically constrained using radiocarbon dates. The purpose of the present study is to use foraminifera to create a separate account of change and to determine if foraminiferal data corroborate sedimentological evidence for sea level and climate fluctuations. Foraminifera were sampled at 20cm intervals from a 14.4m dated core and from surface and subsurface sediments of five cores along a dip transect. Multiple discriminate analysis was used to compare sections of the core by species proportions, and clearly delineates three different foraminiferal communities: deltaic, open-bay, and hypersaline. Breaks between these communities coincide with two of the surfaces observed in the core, one at about 8.0ky and the other around 5.5ky. Rapid sea level rise at the 8.0ky flooding surface corresponds with a shift from a deltaic to an open-bay foraminiferal assemblage, while faunal change across the 5.5ky surface is due to the formation of a large barrier island (Padre Island) and the onset of more arid climate conditions. Prior to the isolation of Baffin Bay at 5.5ky, foraminiferal assemblages do not correspond to climate change records, perhaps because open circulation with the Gulf of Mexico tempered regional climate effects on bay salinity. After 5.5ky, changes in foraminiferal assemblages correspond to independently derived records of the El Niño-Southern Oscillation and North American monsoon. Foraminiferal analysis supports sedimentological interpretations in that assemblages and sediments track climate change.

Foraminiferal evidence for paleogeographic and paleoenvironmental changes across the Coniacian–Santonian boundary in western Ukraine

Planktonic and benthic foraminiferal assemblages, oxygen stable isotopes, calcium carbonate content and total sulfur and magnetic susceptibility have been studied from the middle Coniacian to middle Santonian interval of the Dubivtsi succession (western Ukraine). At the Coniacian–Santonian boundary significant changes took place in foraminiferal assemblages. Keeled, deep-water forms, which are a common to dominant group in planktonic foraminiferal assemblages in the late Coniacian decline in abundance in the Santonian, where the assemblages are dominated by heterohelicids and Hedbergella. Late Coniacian benthic foraminiferal assemblages dominated by large, calcareous epifaunal (oxic) forms in the early Santonian became dominated by small, thin-walled, infaunal (dysoxic) species with significant increase of agglutinated foraminifers within assemblages. Changes in foraminiferal assemblages correspond with lithological changes from upper Coniacian limestones to lower Santonian marls. An increase in total sulfur in the lower Santonian and increase in magnetic successibility values up the succession are recorded. Changes in foraminiferal assemblages along with decreasing calcium carbonate content and increasing magnetic susceptibility indicate that during the early and middle Santonian the Tethyan connection with the studied part of the south-central European epicontinental sea was partially limited by an area uplifted as a consequence of Subhercynian tectonic movements; thus it constituted a partially restricted basin with sedimentation in an oxygen depleted environment.

Quantified intermediate water oxygenation history of the NE Pacific: A new benthic foraminiferal record from Santa Barbara basin

The oxygen minimum zone (OMZ) of the late Quaternary California margin experienced abrupt and dramatic changes in strength and depth in response to changes in intermediate water ventilation, ocean productivity, and climate at orbital through millennial time scales. Expansion and contraction of the OMZ is exhibited at high temporal resolution (107–126 year) by quantitative benthic foraminiferal assemblage changes in two piston cores forming a vertical profile in Santa Barbara Basin (569 m, basin floor; 481 m, near sill depth) to 34 and 24 ka, respectively. Variation in the OMZ is quantified by new benthic foraminiferal groupings and new dissolved oxygen index based on documented relations between species and water‐mass oxygen concentrations. Foraminiferal‐based paleoenvironmental assessments are integrated with principal component analysis, bioturbation, grain size, CaCO3, total organic carbon, and δ13C to reconstruct basin oxygenation history. Fauna responded similarly between the two sites, although with somewhat different magnitude and taxonomic expression. During cool episodes (Younger Dryas and stadials), the water column was well oxygenated, most strongly near the end of the glacial episode (17–16 ka; Heinrich 1). In contrast, the OMZ was strong during warm episodes (Bølling/Allerød, interstadials, and Pre‐Boreal). During the Bølling/Allerød, the OMZ shoaled to <360 m of contemporaneous sea level, its greatest vertical expansion of the last glacial cycle. Assemblages were then dominated by Bolivina tumida, reflecting high concentrations of dissolved methane in bottom waters. Short decadal intervals were so severely oxygen‐depleted that no benthic foraminifera were present. The middle to late Holocene (6–0 ka) was less dysoxic than the early Holocene.

Foraminiferal faunal evidence for Glacial–Interglacial variations in the ocean circulation and the upwelling of the Gulf of Tehuantepec (Mexico)

Abstract Three marine sediment cores from the Gulf of Tehuantepec (Eastern Tropical North Pacific) were used to determine variations in upwelling intensity and surface circulation patterns over the last 26 kyr BP. Changes in foraminiferal assemblages at glacial-interglacial timescale indicate a sequence of three major palaeoceanographic events in the study area: (1) The Late Pleistocene (including the Last Glacial Maximum, LGM), dominated by a Neogloboquadrina dutertrei–Globorotalia menardii assemblage, indicative of a stable thermocline, stratified water column and greater persistence of warm equatorial waters in the region. (2) The Termination 1, dominated by a Globigerinita glutinata assemblage, which indicates mixed surface water and transitional conditions between upwelling and stratified water column episodes. Changes in sedimentation rates and a clear reduction of the faunal abundances at this time, could be the result of eustatic sea level change. (3) The Holocene, dominated by a Globigerina bulloides–Globigerinoides ruber assemblage, indicates periods of elevated productivity, intense upwelling and the establishment of the modern ocean conditions. These findings are consistent with climate model results that suggest that regional surface ocean and upwelling conditions are mostly linked to changes in atmospheric circulation over the Laurentide Ice Sheet and shifts in the latitudinal position of the Intertropical Convergence Zone.