Calcareous Plankton Assemblages Research Articles

Climate-induced surface water variability at Monte San Nicola type-section (Sicily, southern Italy): New data across the Gelasian GSSP

We present the first high-resolution results on planktonic foraminiferal stable oxygen isotopes and calcareous plankton assemblages at the Monte San Nicola GSSP section (near Gela, Sicily), the type-section for the Lower Pleistocene Gelasian Stage. The oxygen isotope profile is remarkably similar to the Eastern Mediterranean oxygen isotope record and indicates that the studied section, extending from marine isotope stage (MIS) G4 to MIS 103, clearly records glacial-interglacial variability. Cyclic changes of calcareous plankton assemblages (calcareous nannofossils and foraminifera) indicate that warmer and stratified surface waters occurred during interglacials, while cooler and unstable conditions developed during glacial phases. Signatures of further increase in surface water stratification are also captured by our surface water proxies and are coeval with enhanced monsoon run-off, developed during precession minima/insolation maxima. The surface water changes recorded at the Monte San Nicola section are in phase with North Atlantic climate variability, even at suborbital scale, and reveal evidence of the first significant southward migration of the Subarctic Front in the mid-latitudes during MIS 104, slightly below the GSSP. The overall dataset provides precise alignment of the Gelasian GSSP within MIS 103 as well as new climatostratigraphic constraints, close to the GSSP, thus improving its correlation potential outside the type-area.

Climate evolution in the Adriatic Sea across the last deglaciation: A multiproxy approach combining biomarkers and calcareous plankton

A multiproxy study combining calcareous plankton assemblages (coccolithophore and planktonic foraminifera), terrestrial (n-alkanes) and marine (alkenones) biomarkers was carried out in a sediment core (ND14Q-AR2) from the South Adriatic Sea. The focus of the study is to investigate millennial-to-centennial scale climate variability in the Eastern Mediterranean during the last deglaciation, between 20 and 11 ka BP. The high-resolution reconstruction allows for the characterization of the impact of the Heinrich Stadial 1 (HS1, here identified between 17.1 and 14.9 ka BP) at a centennial/multi-decadal time scale resolution. Based on terrestrial proxies, the HS1 interval has a two-fold partition: HS1a (17.1–15.9 ka BP), characterized by decreasing temperatures and relative high humidity, and HS1b (15.9–14.9 ka BP), characterized by the coldest temperatures and drier conditions on land. Terrestrial proxies suggest changes in moisture availability on land and ice melting delivery from the Alps during HS1. This period is followed by the Bølling-Allerød record (B-A, 14.9–12.3 ka BP) indicating ameliorated climate conditions and distinct local hydrological signals, related to global melt events similar to the Melt Water Pulse-1A. Finally, the comparison of our results with other Northern Hemisphere climatic records shows a good correspondence between the temperature variations in the South Adriatic Sea and the Greenland ice core oxygen isotope record, highlighting the climatic response of the South Adriatic to global climate variations. Comparison with other Mediterranean paleoclimatic records suggests a two-steps reorganization of the ocean/atmospheric circulation during the HS1 in the mid- and low-latitudes during the HS1 interval, but also a connection with the tropical Northern Hemisphere climate.

Holocene climate variability of the Western Mediterranean: Surface water dynamics inferred from calcareous plankton assemblages

A high-resolution study (centennial scale) has been performed on the calcareous plankton assemblage of the Holocene portion of the Ocean Drilling Program Site 976 (Alboran Sea) with the aim to identify the main changes in the surface water dynamic. The dataset also provided a seasonal foraminiferal sea surface water temperatures (SSTs), estimated using the modern analog technique SIMMAX 28, and it was compared with available geochemical and pollen data at the site. Three main climate shifts were identified as (1) the increase in abundance of Syracosphaera spp. and Turborotalita quinqueloba marks the early Holocene humid phase, during maximum summer insolation and enhanced river runoff. It is concomitant with the expansion of Quercus, supporting high humidity on land. It ends at 8.2 ka, registering a sudden temperature and humidity reduction; (2) the rise in the abundances of Florisphaera profunda and Globorotalia inflata, at ca. 8 ka, indicates the development of the modern geostrophic front, gyre circulation, and of a deep nutricline following the sea-level rise; and (3) the increase of small Gephyrocapsa and Globigerina bulloides at 5.3 ka suggests enhanced nutrient availability in surface waters, related to more persistent wind-induced upwelling conditions. Relatively higher winter SST in the last 3.5 ka favored the increase of Trilobatus sacculifer, likely connected to more stable surface water conditions. Over the main trends, a short-term cyclicity is registered in coccolithophore productivity during the last 8 ka. Short periods of increased productivity are in phase with Atlantic waters inflow, and more arid intervals on land. This cyclicity has been related with periods of positive North Atlantic Oscillation (NAO) circulations. Spectral analysis on coccolithophore productivity confirms the occurrence of millennial-scale cyclicity, suggesting an external (i.e. solar) and an internal (i.e. atmospheric/oceanic) forcing.

Surface and deep water variability in the Western Mediterranean (ODP Site 975) during insolation cycle 74: High-resolution calcareous plankton and molecular biomarker signals

We reconstructed changes in productivity and surface/subsurface and deep-water dynamics in the Western Mediterranean through a multi-proxy study of Ocean Drilling Program Site 975 between late Marine Isotope Stage (MIS) 20 and early interglacial MIS 19. Our high-resolution study (down to ~200-year resolution) combines calcareous plankton assemblages (coccolithophores and foraminifera), biomarkers (C37-alkenones, n-alkanes, n-alcohols) and elemental proxies (total organic carbon, total nitrogen, calcium carbonate). Surface water conditions are derived (i) from high-resolution δ18O and δ13C records obtained from the planktonic foraminifer Globigerina bulloides, and (ii) from summer and winter, foraminifera-based sea surface temperature reconstructions (SSTJAS-foram, SSTJFM-foram) achieved through transfer function. The integration of the whole dataset makes it possible to identify in the Balearic Sea, and to accurately characterize for the first time, an Organic Rich Layer (ORL) during latest MIS 20-early MIS 19, close to i-cycle 74. Its presence is marked firstly by higher values of total nitrogen (TN) and an increase of total C37-alkenone and total organic carbon (TOC) preserved in the sediments. The multi-proxy approach reveals that the deglacial phase played a prominent role for ORL formation that was characterized by centennial scale phases. The alcohol preservation index (API) suggests that the shoaling of the circulation, which boosted marine productivity, started in the deglaciation and, in combination with freshening by Atlantic water inflow/riverine input and surface water buoyancy during sea level rising, culminated during the ORL event. At this time calcareous plankton proliferated on subsurface-surface waters, benefiting from ameliorating conditions, which promoted maximum marine productivity and higher organic matter preservation on the seafloor.

Reconstruction of surface water dynamics in the North Atlantic during the Mid-Pleistocene (~540–400 ka), as inferred from coccolithophores and planktonic foraminifera

Abstract Changes in paleoclimate and paleoproductivity patterns have been identified by analyzing the coccolithophore assemblages from the IODP Site U1314, located in the subpolar North Atlantic, together with other proxy data available during the time interval from the Marine Isotope Stages (MIS) 14 to MIS 11 (ca. 540 to 400 ka). The comparison of this data with that of MD03–2699, located off the Iberian Margin, allowed us to study their common response to environmental changes in terms of paleoproductivity and temperature variability. Statistical analyses of the composition of coccolithophore assemblages revealed that the calcareous plankton dynamics were mainly driven by eccentricity, which controlled the alternating migration of the Polar Front (PF) and the North Atlantic Current (NAC) at glacial-interglacial timescales. The high frequency variability of paleoproductivity, over imposed onto glacial/interglacial variability at both sites, were related to NAC intensifications on a precessional timescale. The northward (southward) migration of the PF caused a strengthening (weakening) of the NAC, which created an intensification (weakening) of the Irminger Current (IC) at Site U1314 and the Portugal Current (PC) at MD03–2699. Furthermore, low-latitude processes have been shown to influence climate in the high-latitude during the late Pleistocene. During MIS 14 and 12, enhanced glacial strength affected both coccolithophores and planktonic foraminifera, indicating a southward movement of the NAC. Using the same proxies, a northward movement of the NAC is recorded during MIS 13 and 11. Alternatively, the spectral analyses performed on calcareous plankton assemblages allowed the identification of a pattern of periodic response of the plankton at the orbital and, in some cases, millennial level, as well as abrupt Heinrich-type time-scale variability during Termination V (TV). This was the most extreme event and was related to a massive iceberg discharge from high to mid-latitudes.

High-frequency climate fluctuations over the last deglaciation in the Alboran Sea, Western Mediterranean: Evidence from calcareous plankton assemblages

A high resolution study, with a centennial scale resolution, has been performed on the calcareous plankton assemblage (coccolithophores and planktonic foraminifera) at Ocean Drilling Program Site 976, Alboran Sea (Western Mediterranean), focusing on the interval between 20 and 9 ka, in order to reconstruct changes in surface and subsurface water dynamics and productivity. The biotic surface water proxies integrate the extremely detailed (multi-decadal scale) geochemical data set and the pollen record already available at the core, thus providing a complete paleoenvironmental/paleoceanographic reconstruction. The results highlight the sensitivity of the calcareous plankton in recording stadial/interstadial phases and higher-frequency climatic events, that produced changes in sea water features. Wind-induced upwelling and river discharge during the Last Glacial Period favored nutrient availability and moderate productivity. During Heinrich Stadial 1 (HS1), the arrival of cold and fresher waters from iceberg melting in the North Atlantic, significantly hampered productivity, at its lowest values of the whole investigated interval. Calcareous plankton behavior supports the hypothesis that HS1 is a composite event, marked by three phases: HS1a characterized by the coldest SST, polar Atlantic water inflow into the basin and a first step toward a dry climate on the continent; HS1b recording enhanced freshwater inflow and drought on land, and HS1c indicating reduced polar water influx. The Bølling-Allerød (BA) interstadial sees the highest rate of productivity in the entire interval and accompanies the deposition of Organic Rich Layer 1; during the BA coccolithophore assemblage also marks higher frequency changes in hydrographic conditions, apparently in relation with Greenland Interstadial I (GI-I) high variability. The Younger Dryas Stadial (YD) is characterized by refunding cold and dry conditions, although not as severe as during HS1, and by enhanced detrital input in surface water during drier conditions on land. The Holocene onset records climate amelioration both in the marine and continental environment, although coccolithophore productivity is not as high as during the BA. The rapid shifts in climate sensitive taxa support the hypothesis that each of the climate phases-subphases is characterized by a complex pattern forced by strong interaction between ice-sheet instability, meltwater discharge entering the Gibraltar Strait, North Atlantic westerlies and moisture availability, clearly impacting over surface water temperature, productivity and land masses.

Environmental perturbations at the early Eocene ETM2, H2, and I1 events as inferred by Tethyan calcareous plankton (Terche section, northeastern Italy)

AbstractSeveral early Eocene hyperthermals have been recently investigated and characterized in terms of temperature anomalies and oceanographic changes. The effects of these climatic perturbations on biotic communities are much less constrained. Here we present new records from the Terche section (northeastern Italy) that, for the first time, integrates data on planktic foraminifera and calcareous nannofossils across three post‐Paleocene‐Eocene Thermal Maximum negative carbon isotope excursions (CIEs). The biomagnetostratigraphic framework generated at Terche allows us to confidently relate such CIEs to the Eocene Thermal Maximum 2 (ETM2), H2, and I1 events. Each of these events coincides with lithological anomalies characterized by significantly lower calcium carbonate content (marly units, MUs). We interpret these MUs as mainly linked to an effect of increased terrigenous dilution, as dissolution proxies do not display significant variations. Calcareous plankton assemblages change significantly across these events and radiolarians increase. Observed changes suggest that transient warming and environmental perturbations, though more intense during ETM2, occurred during each of the three investigated perturbations. Variations among calcareous plankton suggest increase in surface‐water eutrophication with respect to the pre‐event conditions, coupled with a weakening of the upper water‐column thermal stratification. Higher nutrient discharge was related to intensification of the hydrological cycle as a consequence of the warmer climate. These conditions persisted during the early CIE recovery, implying slower recovery rates for the environment and biota than for the carbon cycle.

Sea surface water variability during the Mid-Brunhes inferred from calcareous plankton in the western Mediterranean (ODP Site 975)

Planktonic foraminifera and calcareous nannoplankton were analyzed in core Ocean Drilling Program Site 975, located in the western Mediterranean, in order to study their response to environmental changes across the Mid-Brunhes interval and specifically through Marine Isotope Stage (MIS) 15 and 8 (ca. 650–230ka). Multivariate analysis of assemblage composition revealed that the calcareous plankton dynamics were mainly driven by surface water temperatures both on glacial-interglacial and stadial-interstadial time scales. Throughout the studied interval, foraminiferal and nannoplankton assemblages responded to environmental forcing in concert, except during MIS 15, when multiple environmental factors appear to have been superimposed on the otherwise dominating effect of temperature variability. Sea surface temperature (SST) has been estimated from planktonic foraminiferal assemblages using the artificial neural networks method pointing out relevant seasonal variations through the record. Our reconstructions reveal that calcareous plankton assemblages also responded to other environmental factors than temperature, including modification in surface water stratification, nutrient availability and detrital input. Specifically, a more stable, stratified water column seems to have accompanied the interval through MIS 15–13. On the other hand, across the Mid-Brunhes interval, from MIS 12 onwards, the enhanced glacial strength affected both planktonic foraminifera and calcareous nannofossils: planktonic foraminifera indicate that mixed and productive surface waters developed during glacials and stadials, accompanied by episodes of increased detrital input as suggested by calcareous nannoplankton assemblages. Enhanced food availability was likely driven by wind-induced upwelling and/or by continental coastal input during dry conditions persisting in the Mediterranean region and over North Africa. Finally, spectral and wavelet analyses of calcareous plankton time series allowed to identify the pattern of periodic response of the plankton at Milankovitch cycles and, in some cases, at millennial variability. The dominant 100kyr periodicity recorded in surface water temperature proxies clearly reflects a major response of the planktonic community to the global glacial-interglacial climate pattern. High-frequency variation (~5–8, ~11–13ky) of surface water temperature proxies and of selected taxa abundance highlights the occurrence of millennial-scale instability superimposed on the paleoenvironmental modifications occurring through the Mid-Brunhes interval climate transition. This framework accounts for the occurrence of different surface water dynamics across the Mid-Brunhes interval and is in favor of the hypothesis that the millennial scale surface water temperature variations are modulated by the harmonics of the precession forcing.

The Uniqueness of Planktonic Ecosystems in the Mediterranean Sea: The Response to Orbital- and Suborbital-Climatic Forcing over the Last 130,000 Years

AbstractThe Mediterranean Sea is an ideal location to test the response of organisms to hydrological transformations driven by climate change. Here we review studies carried out on planktonic foraminifera and coccolithophores during the late Quaternary and attempt the comparison of data scattered in time and space. We highlight the prompt response of surface water ecosystems to both orbital- and suborbital-climatic variations.A markedly different spatial response was observed in calcareous plankton assemblages, possibly due to the influence of the North Atlantic climatic system in the western, central and northern areas and of the monsoon system in the easternmost and southern sites. Orbital-induced climatic dynamics led to productive surface waters in the northern, western and central Mediterranean Sea during the last glacial and to distinct deep chlorophyll maximum layers in the eastern Mediterranean Sea coinciding with bottom anoxia episodes. High-frequency planktonic modifications are well documented in the Sicily Channel and Alboran Sea and highlight the occurrence of different steps within a single stadial (cold phase)/interstadial (warm phase) oscillation.The review of planktonic organisms in the marine sedimentary archive casts light on the uniqueness of the Mediterranean Sea, especially in terms of climatic/oceanographic/biological interaction and influence of different climatic systems on distinct areas. Further research is needed in the eastern Mediterranean Sea where results are obscured by low-resolution sedimentary records and by a strong focus on sapropel deposition dynamics.

New microplanktonic biostratigraphy and depositional sequences across the Middle–Late Eocene and Oligocene boundaries in eastern Jordan

ABSTRACTThe first detailed calcareous nannofossil and planktonic foraminiferal biostratigraphic and integrated lithofacies analyses of the Eocene–Oligocene transition at the Qa’ Faydat ad Dahikiya area in the Eastern Desert of Jordan, on the border with Saudi Arabia, is presented. Three calcareous nannofossil zones namely: Discoaster saipanensis (NP17), Chiasmolithus oamaruensis (NP18) and Ericsonia subdisticha (NP21), and three planktonic foraminiferal zones: upper part of Truncorotaloides rohri (E13), Globigerinatheka semiinvoluta (E14) and Cassigerinella chipolensis/Pseudohastigerina micra (O1) are identified.Calcareous nannofossil bioevents recorded in the present study show numerous discrepancies with the Standard biostratigraphic zonal schemes to detect the Middle/Upper Eocene boundary (e.g. the highest occurrences (HOs) of Chiasmolithus solitus, C. grandis, and lowest occurrences (LOs) of C. oamaruensis, Isthmolithus recurvus are not considered reliable markers for global correlation). The Middle/Upper Eocene boundary occurs in the current study above the extinctions of large muricate planktonic foraminifera (large Acarinina and Truncorotaloides spp.) which coincide within the equivalent calcareous nannofossil NP18 Zone. These microplanktonic bioevents seem to constitute more reliable markers for the base of the Upper Eocene in different provinces. The uppermost portion of the Middle Eocene is characterized by an observed drop in faunal content and, most likely, primarily denotes the effect of the major fall in eustatic sea level.A major unconformity (disconformity) marked by a mineralized hardground representing a lowstand is recorded in the present study at the Eocene–Oligocene transition that reveals an unexpected ca. 2.1 Myr duration, separating Eocene (NP18/E14 zones) from Oligocene (NP21/O1 zones). Furthermore, the microfossil turnover associated with a rapid decline of the microfossil assemblages shows a distinct drop in diversity and abundance towards the Eocene/Oligocene unconformity and is associated with a sharp lithological break marked, at the base, by a mineralized hardground representing a major sequence boundary. These bioevents, depositional sequences and the depositional hiatus correlate well with different parts of the Arabian and African plates, but the magnitude of the faunal break differs from place to place as a result of intraplate deformation during the regional Oligocene regression of Neo-Tethys on the northern Arabian Plate. The presence of the Lower Oligocene shallow-marine calcareous planktonic assemblages in the study area indicate that communication between the eastern and western provinces of the western Neo-Tethys region still existed at this time.

Evaluation of foraminifera and calcareous nannofossils changes across the Late Paleocene/Early Eocene transition at Nag El-Quda section, Upper Nile Valley, Egypt

A quantitative study of calcareous nannofossils, planktonic, and benthic foraminiferal assemblages have been performed on fifty six samples collected from ∼40 m interval across the Paleocene/Eocene transition at Nag El-Quda section in Upper Nile Valley, Egypt. I study this interval to evaluate the faunal and floral changes across the P/E transition. Four biozones of calcareous nannofossils and seven planktonic biozones have been recorded. The benthic foraminifera extinction event (BFEE) and the characteristic datum of both calcareous nannofossils, planktonic foraminifera, have been recognized. The absence of deep-sea benthic foraminifera (Stensioeina beccariiformis), the low abundance of (Angulogavelinella avnimelechi and Gavelinella rubiginosus) and increasing dominance of shallow-marine taxa (buliminids, Loxostomoides applinae) indicate deposition of the interval in shallow water environments (100–150 m depth). The benthic foraminiferal assemblages are dominated by Loxostomoides applinae, buliminids, and Lenticulina spp and indicate dysoxic conditions. Quantitative analyses have revealed a change in the species richness and fluctuations in abundance of foraminifera and calcareous nannofossils.

Calcareous plankton response to orbital and millennial-scale climate changes across the Middle Pleistocene in the western Mediterranean

The paleoenvironmental conditions through MIS 15-9 at the Mediterranean Ocean Drilling Program (ODP) Site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available δ18O and δ13C records and high resolution paleoclimate proxies from the Atlantic Ocean. Sea Surface Temperatures (SSTs) have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method. Calcareous plankton varied dominantly on a glacial–interglacial scale as testified by the SST record, foraminiferal diversity, total coccolith abundance and changes in warm-water calcareous nannofossil taxa. A general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials. Warmest SSTs are reached during MIS 11, while MIS 12 and MIS 10 represent the coldest intervals of the studied record. During MIS 12, one of the most extreme glacials of the last million years, occurrence of Globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between Atlantic inflowing and Mediterranean outflowing waters. Among calcareous nannofossils the distribution of Gephyrocapsa margereli–Gephyrocapsa muellerae>4μm also supports a reduced Atlantic–Mediterranean exchange during MIS 12. Superimposed on glacial–interglacial variability, six short-term coolings are recognized during MIS 12 and 10, which appear comparable in their distribution and amplitude to the Heinrich-type events documented in the Atlantic Ocean in the same interval. During these H-type events, Neogloboquadrina pachyderma (s) and G. margereli–G. muellerae>4μm increase as a response to the enhanced inflow of cold Atlantic water into the Mediterranean via the Strait of Gibraltar. Mediterranean surface water hydrography appears to have been most severely affected at Termination V during the H-type event Ht4, possibly as a response to a large volume of Atlantic meltwater inflow via the Strait of Gibraltar and/or to freshwater/terrigenous input deriving from local mountain glaciers. Three additional SST coolings are recorded through MIS 14–16, but these are not well correlated with Heinrich-type events documented in the Atlantic Ocean in the same interval; during these cooling episodes only the subpolar Turborotalita quinqueloba increases. These results highlight the sensitive response of the Mediterranean basin to millennial-scale climate variations related to Northern Hemisphere ice-sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and Mediterranean sea surface water features can be traced through the Middle Pleistocene.

Stratigraphy of the Middle Eocene – Lower Oligocene successions in northwestern and eastern Jordan

Rocks of Eocene and Oligocene age, consisting mainly of carbonate ramp facies, are widely distributed in Jordan, but no previous stratigraphic works have dealt with the Eocene – Oligocene contact. Stratigraphic analysis, based on field exploration, and detailed lithostratigrapic and biostratigraphic preliminary data detected a major hiatus that separates the Middle Eocene (Lutetian) from the Early Oligocene (Rupelian) in the studied exposures in the Wadi El Ghadaf and Ash Shunah areas of Jordan. Our results reveal that the planktonic foraminifera Turborotalia cerroazulensis/Pseudohastigerina spp. (P18) Zone and the calcareous nannoplankton Ericsnia subdisticha (NP21) Zone of early Oligocene age were recorded immediately above the Morozovelloides lehneri (E11) Zone and the Discoaster tanii nodifer (NP16) Zone indicating, a period of non-deposition as a result of tectonic activity and/or sea level changes. A correlative hiatus and time gap were also reported in different parts of the Arabian and African plates, which representing the contemporaneous paleo-high areas. The presence of the early Oligocene shallow marine calcareous planktonic assemblages indicates that shallow shelves of the Tethys Ocean occupied the paleotopographic lows of Jordan, with deepening of the depositional basin toward the north.

Paleoenvironmental changes at the lower Pleistocene Montalbano Jonico section (southern Italy): Global versus regional signals

Integrated high resolution data from calcareous plankton assemblages (foraminifera and nannofossils) together with geochemical and mineralogical investigations have been collected at the on-land Montalbano Jonico section (southern Italy) in order to reconstruct the paleoenvironmental changes through Marine Isotope Stages (MIS) 23–37. Time-series analysis on Globigerina bulloides and Cassidulina carinata δ18O records and on selected calcareous plankton proxies mainly revealed the occurrence of precession and obliquity forcing. The deposition of sapropel layers, which are interbedded in the Montalbano Jonico section, was driven by water column stratification (insolation cycle i-104) and enhanced sea surface water productivity (insolation cycle i-112, i-102 and i-86). Different paleoenvironmental conditions mark the sedimentary evolution of the section. From 1240 to 1082ka (MIS 37–MIS 32), high percentage abundances of warm and oligotrophic planktonic foraminifera and calcareous nannofossil taxa indicate the establishment of oligotrophic and stratified surface water conditions. A key paleoenvironmental change occurred during MIS 31 (from about 1080 to 1065ka), which was a very warm interglacial characterized by an increase of tropical–subtropical (Globigerinoides ruber group and Globigerinoides trilobus) and low salinity (Braarudosphaera bigelowii) sea surface water taxa. During this interval, more humid climate conditions coupled with changes in local paleomorphology may have triggered a higher and unusual freshwater input and the creation of a new entry point for sediment supply into the basin from a different drainage area. From about 1065 to 1010ka (MIS 30–MIS 29), a cool and dry climate prevailed in the circum-Mediterranean area during a time of precession maxima. This favored lowered sea surface temperatures and an increase of polar-water Neogloboquadrina pachyderma left coiling. There are also indications of a reduction of the terrigenous input from the new source area. From 1010ka upward (MIS 28–MIS 23), the higher abundances of Globigerina bulloides, Turborotalita quinqueloba and Calciosolenia spp. indicate enhanced productivity conditions probably related to high turbidity of sea surface waters triggered by a more conspicuous sediment input from land. Analysis of the long-term trends in the multiproxy patterns suggests that the major paleoenvironmental changes occurred as a consequence of the combined effect of orbitally-controlled global climate and regional processes.

The middle Eocene climatic optimum event in the Contessa Highway section, Umbrian Apennines, Italy

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semiquantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal zone P11 to the lower part of zone P15 and from calcareous nannofossil zone NP15 to the upper part of zone NP17, which results in refi nement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity time scale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from chrons C21n (47 Ma) through to subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the fi rst evidence in the Northern Hemisphere of the middle Eocene climatic optimum, which has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO 2 levels during the late middle Eocene and consequent global CO 2 -driven climate change.

Astronomic forcing on the planktonic foraminifera assemblage in the Piacenzian Punta Piccola section (southern Italy)

A high‐resolution quantitative analysis of the calcareous planktonic assemblages (planktonic foraminifers and calcareous nannofossils) at the Punta Piccola section (at the base of which, the global standard stratotype‐section and point of the Piacenzian stage is defined) provided a more accurate biostratigraphy for the Mediterranean middle Pliocene (2.6–3.6 Ma). In particular, an astronomically calibrated age of 2.87 Ma was estimated for the Pliocene first occurrence ofNeogloboquadrina atlanticainstead of the younger previously proposed age of 2.72 Ma. Spectral analysis performed on theGlobigerinoidesspecies (spp.) planktonic foraminifera assemblage along with cross‐spectral analysis between the same record and the astronomic target curve La(041,1) calculated for the summer season (June–July) at 65°N provided solid evidence that theGlobigerinoidesspp. group of planktonic species is a reliable recorder of orbital forcing and can be appropriately used for astronomical tuning of marine sedimentary records. The same procedures of spectral analysis were applied to the individual species that constitute theGlobigerinoidesspp. group (G. ruber,G. obliquus, andG. quadrilobatus), thus resolving their different frequency structures and species‐specific response to the different astronomic periodicities. WhereasG. obliquusandG. quadrilobatusappear primarily controlled by precession,G. ruberis largely forced by obliquity. Small ecological differences, mainly related to dissimilar food quality requirements, were assumed to distinctively control the time distribution of the two groups of species. Precessionally forced oligotrophic conditions in the surface Mediterranean waters, induced by summer continental runoff, led to a dominance of copepods‐based dietary, typical ofG. quadrilobatus. Conversely, obliquity cycles drove the abundance distribution ofG. ruberin the sea surface waters of the Mediterranean, influencing the sea surface temperature, light intensity, and/or phytoplankton distribution. Sub‐Milankovitch periodicities (cycles ∼1500, 2500, 3000, and 4500 years long) are reliably detected in the faunal records, suggesting that millennial‐scale variability punctuated the Mediterranean climate regime during the interval of the middle Pliocene Northern Hemisphere glaciation.

Regional and interannual productivity of biogenic components and planktonic foraminiferal fluxes in the northwestern Pacific Basin

Time-series sediment trap experiments at subtropical (WCT-1) and subarctic (WCT-2) stations in the northwestern Pacific indicate seasonal, latitudinal and depth variations in total particulate, biogenic and foraminiferal fluxes. At the subtropical station, the average total mass flux was 19.4 mg m −2 day −1 in the shallow trap (1060 m) and 21.5–26.1 mg m −2 day −1 in the deep trap (3930 m) during the sampling period. At subarctic station, these values were 91.5–176.9 mg m −2 day −1 in the shallow and 68.6–112.3 mg m −2 day −1 in the deep trap. We recognized 12 and 15 planktonic foraminiferal species at Station WCT-1 and Station WCT-2, respectively. The planktonic foraminiferal flux and species turnover are related to seasonal and interannual changes in source water and water column conditions at both stations. At Station WCT-1, the highest flux was recorded during the summer, with a peak in mid to late June associated with similar flux patterns of the dominant species, Globigerinoides ruber and Globigerinita glutinata. The total flux of foraminiferal tests at the shallow and deep traps is similar in numbers and magnitude. At Station WCT-2, the peaks of total flux of foraminiferal tests at the two trap depths differ in number, and their magnitude in the deep trap is almost half of that in the shallow trap. A distinctive seasonal pattern occurred in the shallow and the deep trap, with a peak in total foraminiferal flux in mid June to mid July. Globigerina quinqueloba, Neogloboquadrina pachyderma and Neogloboquadrina dutertrei dominate the planktonic population throughout the year. Subtropical Station WCT-1 was characterized by low total foraminiferal fluxes and low total mass flux, which is dominated by calcium carbonate and depleted in opal, whereas high foraminiferal fluxes and a high total mass flux dominated by high biogenic opal, and less calcium carbonate and organic matter characterize subarctic Station WCT-2. The foraminiferal carbonate that reaches the seafloor accounts for an average 20–27% and 22–23% of the total calcium carbonate at Station WCT-1 and Station WCT-2, respectively. The primary reason for the difference in flux at both stations thus lies in the different contributions of siliceous and calcareous planktonic assemblages. The seasonal variation in biogenic particulate flux at both stations implies that temporal changes in biological productivity are governed by large-scale seasonal climatic variability and local hydrography.

Long-term biogenic particle fluxes in the Bering Sea and the central subarctic Pacific Ocean, 1990–1995

Time-series sediment traps were deployed for five consecutive years in two distinctively different subarctic marine environments. The centrally located subarctic pelagic Station SA (49°N, 174°W; water depth 5406 m) was simultaneously studied along with the marginal sea Station AB (53.5°N, 177°W; water depth 3788 m) in the Aleutian Basin of the Bering Sea. A mooring system was tethered to the sea-floor with a PARFLUX type trap with 13 sample bottles, which was placed at 600 m above the sea-floor at each of the two stations. Sampling intervals were synchronized at the stations, and they were generally set for 20 days during highly productive seasons, spring through fall, and 56 days during winter months of low productivity. Total mass fluxes, which consisted of mainly biogenic phases, were significantly greater at the marginal sea Station AB than at the pelagic Station SA for the first four years and moderately greater for the last year of the observations. This reflects the generally recognized higher productivity in the Bering Sea. Temporal excursion patterns of the mass fluxes at the two stations generally were in parallel, implying that temporal changes in their biological productivity are strongly governed by a large-scale seasonal climatic variability over the region rather than local phenomena. The primary reason for the difference in total mass flux at the two stations stems mainly from varying contributions of siliceous and calcareous planktonic assemblages. A significantly higher opal contribution at Station AB than at Station SA was mainly due to diatoms. Diatom fluxes at the marginal sea station were about twice those observed at the pelagic station, resulting in a very high opal contribution at Station AB. In contrast to the opal fluxes, CaCO 3 fluxes at Station AB were slightly lower than at Station SA. The ratios of C org/C inorg were usually significantly greater than one in both regions, suggesting that preferentially greater organic carbon from cytoplasm than skeletal inorganic carbon was exported from the surface layers. Such a process, known as the biological pump, leads to a carbon sink which effectively lowers p CO 2 in the surface layers and then allows a net flux of atmospheric CO 2 into the surface layer. The efficiency of the biological pump is greater in the Bering Sea than at the open-ocean station.

Late glacial to recent paleoenvironmental changes in the Gulf of Cadiz and formation of sandy contourite layers

Planktonic foraminifera and coccoliths were analyzed from six gravity cores obtained on a deep terrace located on the upper continental slope of the Gulf of Cadiz, between 400 and 700 m water depth. The lithology of these cores consists mainly of muds with some interbedded sandy or silty foraminifer-rich layers that have been reported as contourites originated by the action of the Mediterranean Outflowing Waters (MOW) sweeping the sea-bottom today. After the Last Glacial, characterized by muddy sedimentation, sandy contourites start to deposit in the Gulf of Cadiz during the Bølling–Allerød (14–11 14C kyr BP) climatic optimum. This trend was broken during the Younger Dryas (11–10 14C kyr BP) and started again after the end of the Younger Dryas. This pattern is recorded in most of the cores by a single sandy contourite layer formed during the first deglaciation stage (Bølling–Allerød time) and a sandy contourite interval that initiates immediately after the end of the Younger Dryas, during the second stage of the deglaciation and continues during the Holocene. The stratigraphy and climatic reconstruction was based on the evolution of the calcareous plankton assemblages during the last climatic transition, from the Last Glacial to the recent Holocene. The sharp reduction of sinistral N. pachyderma along with the reduction of G. quinqueloba mark the base of Bølling–Allerød time. This is also related to a prominent peak of the subtropical species ( G. sacculifer and G. ruber). The Younger Dryas is identified by a reduction in abundance of the subtropical species, that again increase just after this period. The second step of deglaciation is marked by a sharp decrease in the relative abundance of dextrally coiled N. pachyderma. In previous papers the sequence of sandy contourites has been related to sea level rise, greater Gibraltar sill depth and enhanced energy of the MOW. In this work, we suggest that the individual sand layer episodes are condensed layers originating during times of rapid warming and relative sea-level rise within the last deglaciation. During these times the coastline migrated more rapidly landward and the terrigenous input decreased as it began to be trapped on land and on the shelf, resulting in a major drop in sedimentation rate on the upper continental slope. In times of low sedimentation rate the particles would have a longer residence time within the upper mixed layer of the near surface sediment and therefore the energy of currents would act longer, producing a more efficient winnowing of the sediment. At the same time more generations of benthic organisms would rework the mixed layer, favoring this winnowing.

Biostratigraphic Relation of Neogene Benthic Foraminifera from Southern California Outer Continental Borderland to Monterey Formation: ABSTRACT

In recent years there has been considerable discussion concerning the biostratigraphic correlations between planktonic zonations and the classical Neogene California benthic foraminiferal stages. One of the primary objectives of IPOD Leg 63 was to explore these correlations and to determine the possibility of temporal variation of the benthic stages between the outer continental borderland and land sections. Site 468 was drilled on the Patton Escarpment, which lies under the present southeastern margin of the California current system. The sediments yielded well-preserved calcareous and siliceous planktonic assemblages that ranged in age from Holocene to middle Miocene. Samples also contain abundant benthic foraminiferal assemblages that consist of species characteristic of both oceanic and continental margin environments. The benthic foraminiferal assemblages range from the Venturian stage of the Pleistocene to the Luisian-Relizian stages of the middle Miocene. Because of the dependence of benthic species on bottom environmental parameters, the dominant occurrence of lower bathyal to abyssal faunas present problems for direct correlations to local California stages. The majority of key species needed for recognition of the late and middle Miocene benthic stages, as defined in land sections, are indicative of upper to middle bathyal environments and are excluded from the deeper habitats because of environmental restrictions. The occurrence of the lower bathyal pseudo-Saucesian assemblage as a major faunal constituent in the late and middle Miocene samples furthers adds to the complexity of correlations etween the planktonic zonations and benthic foraminiferal stages. End_of_Article - Last_Page 902------------