Maestrichtian planktonic foraminifera of the Maud Rise

The southernmost record of Maestrichtian pelagic carbonate sedimentation was recovered from ODP Leg 113 Holes 689B and 690C, drilled on the Maud Rise in the eastern Weddell Sea sector of the Southern Ocean (65°S). Well preserved and abundant planktonic foraminifers occur throughout Maestrichtian cores from both holes, providing a nearly complete biogeographic and biostratigraphic history of this region. Diversity is low compared to tropical and subtropical assemblages, with a maximum within sample diversity of 16 planktonic foraminifer species and a diversity total for the Maestrichtian of 24 species. The assemblages are dominated throughout by Heterohelix, Globigerinelloides, and a new species of Archaeoglobigerina, whereas keeled taxa are completely absent from the lower Maestrichtian and rare in the middle through upper Maestrichtian sediments. Three planktonic foraminifer species are described as new and are recognized as being endemic to the Austral Province. These include Archaeoglobigerina australis n. sp., Hedbergella sliteri n. sp., and Archaeoglobigerina mateola n. sp. The former two species were previously illustrated in reports on Late Cretaceous foraminifers from the Falkland Plateau and the northern Antarctic Peninsula. Two keeled and five non-keeled planktonic foraminifers, previously not found in high latitude Maestrichtian sediments, first appeared at the Maud Rise during the late early and late Maestrichtian. Correlation with their stratigraphic ranges in low latitude sequences shows that their first appearance datums are considerably younger at the Maud Rise than in the lower latitudes. The most likely explanation for this observation is that there was a warming in the south polar region during the late early and late Maestrichtian and a concomitant poleward migration of stenothermal taxa. However, oxygen isotopic paleotemperature results from Sites 689 and 690 (Barrera and Huber, 1990, doi:10.2973/odp.proc.sr.113.137.1990) show a long-term cooling trend throughout the Maestrichtian, indicating that other factors may have played a more important role than temperature in the distribution of Maestrichtian planktonic foraminifers. A new biostratigraphic scheme is proposed for the Antarctic because of the absence of thermophilic planktonic foraminifers used to identify existing low to middle latitude zones. The Globigerinelloides impensus Partial Range Zone is defined for the late Campanian-Maestrichtian, the Globotruncanita havanensis Partial Range Zone is redefined for the early to late early Maestrichtian, and the Abathomphalus mayaroensis Total Range Zone is recognized. Good quality magnetic polarity data obtained from both Maud Rise sites (Hamilton, 1990, doi:10.2973/odp.proc.sr.113.179.1990) enables magnetobiostratigraphic correlation of twelve foraminifer datums with the geomagnetic polarity time scale of Haq et al. (1987). The geochronology thus obtained is crucial for accurate cross-latitudinal correlation and interpretation of the paleoceanographic history of the Antarctic region during the Maestrichtian time period.

Mg/Ca values for planktonic foraminifera N. pachyderma and G. bulloides from ocean sediment core MD02-2496 on the Vancouver margin, Northeastern Pacific Ocean

A new, high-resolution planktonic foraminiferal Mg/Ca-based ocean temperature record has been generated for deep sea core MD02-2496, sited offshore of Vancouver Island, Western Canada during the last deglaciation (21-12 ka). The relationship between Cordilleran Ice Sheet (CIS) retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in MD02-2496 that capture tidewater glacier response to surface ocean thermal forcing. At CIS maximum extent, the marine margin of the ice sheet advanced onto the continental shelf. During this interval, ocean temperatures recorded by surface ocean dwelling Globigerina bulloides remained a relatively constant ~7.5°C while subsurface dwelling Neogloboquadrina pachyderma (s.) recorded temperatures of ~5°C. These ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern Alaskan tidewater glacial systems. During the deglacial retreat of the CIS, the N. pachyderma temperature record shows two distinct warming steps of ~2 and 2.5°C between 17.2-16 and 15.5-14 ka respectively, coincident with ice rafting events from the CIS, while G. bulloides records an ~3°C warming from 15 to14 ka. We hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from CIS tidewater glaciers during the initial stages of deglaciation.

Stable carbon and oxygen isotope record of planktonic foraminifera across the Paleocene-Eocene boundary

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic 'events' near the Paleocene-Eocene boundary provide strati-graphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera bio-stratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean's carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO2. As a consequence of this exchange of 12C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.

Respiration rates and abundances of dominant copepods of the northern Benguela Current System

Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Individual respiration rates were standardised to a mean copepod body mass and a temperature regime typical of the northern Benguela Current. These adjusted respiration rates revealed two different activity levels (active and resting) in copepodids C5 of Calanoides carinatus and females of Rhincalanus nasutus, which reduced their metabolism during dormancy by 82% and 62%, respectively. An allometric function (Imax) and an energy budget approach were performed to calculate ingestion rates. Imax generally overestimated the ingestion rates derived from the energy budget approach by >75%. We suggest that the energy budget approach is the more reliable approximation with a total calanoid copepod (mainly females) consumption of 78 mg C m-2 d-1 in neritic regions and 21 mg C m-2 d-1 in oceanic regions. The two primarily herbivorous copepods C. carinatus (neritic) and Nannocalanus minor (oceanic) contributed 83% and 5%, respectively, to total consumption by calanoid copepods. Locally, C. carinatus can remove up to 90% of the diatom biomass daily. In contrast, the maximum daily removal of dinoflagellate biomass by N. minor was 9%. These estimates imply that C. carinatus is an important primary consumers in the neritic province of the northern Benguela system, while N. minor has little grazing impact on phytoplankton populations further offshore. Data on energy requirements and total consumption rates of dominant calanoid copepods of this study are essential for the development of realistic carbon budgets and food-web models for the northern Benguela upwelling system.

Adaptive variability to low-pH river discharges in Acartia tonsa and stress responses to high PCO2 conditions

Environmental transitions leading to spatial physical-chemical gradients are of ecological and evolutionary interest because they are able to induce variations in phenotypic plasticity. Thus, the adaptive variability to low-pH river discharges may drive divergent stress responses [ingestion rates (IR) and expression of stress-related genes such as Heat shock protein 70 (Hsp70) and Ferritin] in the neritic copepod Acartia tonsa facing changes in the marine chemistry associated to ocean acidification (OA). These responses were tested in copepod populations inhabiting two environments with contrasting carbonate system parameters (an estuarine versus coastal area) in the Southern Pacific Ocean, and assessing an in situ and 96-h experimental incubation under conditions of high pressure of CO2 (PCO2 1200 ppm). Adaptive variability was a determining factor in driving variability of copepods' responses. Thus, the food-rich but colder and corrosive estuary induced a traits trade-off expressed as depressed IR under in situ conditions. However, this experience allowed these copepods to tolerate further exposure to high PCO2 levels better, as their IRs were on average 43% higher than those of the coastal individuals. Indeed, expression of both the Hsp70 and Ferritin genes in coastal copepods was significantly higher after acclimation to high PCO2 conditions. Along with other recent evidence, our findings confirm that adaptation to local fluctuations in seawater pH seems to play a significant role in the response of planktonic populations to OA-associated conditions. Facing the environmental threat represented by the inter-play between multiple drivers of climate change, this biological feature should be examined in detail as a potential tool for risk mitigation policies in coastal management arrangements.

Ingestion rate and egg production of copepods collected in the upper 20m in the eastern Mediterranean Sea in March and April 2008 during SES_GR1

The ingestion on ciliates and phytoplankton dataset is based on samples taken during April 2008 in Northern Aegean Sea, the area influenced by the Black Sea water outflow. A Lagrangian experiment was established and copepod ingestion was estimated from experiments performed at stations according to the different positions of drifters during the cruise. Copepods for the experiments were obtained with slow non-quantitative tows from the upper 20 m layer of the water column using 200 µm mesh size nets fitted with a large non-filtering cod end. For the grazing experiments we used the following copepod species: Centropages typicus and Calanus helgolandicus according to the relevant reference (Bamstedt et al. 2000). Copepod clearance rates on ciliates were calculated according to Frost equations (Frost 1972). Ingestion rates were calculated by multiplying clearance rates by the initial standing stocks (Bamstedt et al. 2000). The egg production dataset is based on samples taken during April 2008 in Northern Aegean Sea, the area influenced by the Black Sea water outflow. A Lagrangian experiment was established and copepod egg production was estimated from experiments performed at stations according to the different positions of drifters during the cruise. Egg production rates of the dominant calanoid copepods were determined by incubation of fertilised females (eggs female/day) collected in the 0-20m layer. Copepod egg production was measured for the copepods Centropages typicus, Calanus helgolandicus. On board experiments for the estimation of copepod egg production were taken place. For the estimation of copepod production (mgC/ m**2 /day), lengths (copepods and eggs) were converted to body carbon (Hopcroft et al., 1998) and production was estimated from biomass and weight-specific egg production rates, by assuming that those rates are representative for juvenile specific growth rates (Berggreen et al., 1988).

Ingestion rate and egg production of copepods collected in the upper 20m in the eastern Mediterranean Sea in Oktober 2008

This dataset based on samples taken during October 2008 in Dardanelles Straits, Marmara Sea and Bosporus Straits at the third priority stations. Copepods for the experiments were obtained with slow non-quantitative tows from the upper 50 m layer of the water column using 200 µm mesh size nets fitted with a large non-filtering cod end. For the grazing experiments we used the following copepod species: Oithona spp., Clausocalanus furcatus, Acartia clausi and Oncaea spp. and in one cladoceran species Penilia avirostris according to the relevant reference (Bamstedt et al. 2000). Copepod clearance rates on ciliates were calculated according to Frost equations (Frost 1972). Ingestion rates were calculated by multiplying clearance rates by the initial standing stocks (Bamstedt et al. 2000). Egg production rates of the dominant calanoid copepods were determined by incubation of fertilised females (eggs/female/day) collected in the 0-20m layer. Copepod egg production was measured for the copepods Clausocalanus furcatus, Paracalanus parvus,Acaria clausi. On board experiments for the estimation of copepod egg production were taken place. For the estimation of copepod production (mg/m**2/day), lengths (copepods and eggs) were converted to body carbon (Hopcroft et al., 1998) and production was estimated from biomass and weight-specific egg production rates, by assuming that those rates are representative for juvenile specific growth rates (Berggreen et al., 1988).

Planktonic foraminifera of sediment core T89-40 on the Walvis Ridge, South Atlantic

Core T89-40, eastern Walvis Ridge between the subtropical gyre and Benguela coastal upwelling system, contains three types of levels of abundant left-coiled Neogloboquadrina pachyderma, a cold, eutrophic species, next to subtropical species. Type A peaks (362, 110 and 53-43 ky BP) are accompanied with high percentages of other eutrophic species. They are attributed to intensified upwelling in the Northern Benguela region. Type B peaks (129 and 92 ky BP) are accompanied by moderate (<48%) contributions of other eutrophic species and increased numbers of subtropical species. These suggest intensified upwelling in the Northern Benguela cells and may reflect increased seasonal contrasts between the winter upwelling and the subtropical summer conditions. The highest C-peaks, up to 38%, are associated with strongly reduced percentages of other eutrophic species and with abundant subtropical species (Marine Isotopic Stage 11.3 (401 ky) and 9.3 (326 ky)). The subtropical species preceeded the C-peaks by ca 8 ky. We argue that the C-peaks were not produced by local reproduction but expatriated from the Northern Benguela upwelling cells. Here more nutrient-rich waters may have produced a mono-specific Neogloboquadrina pachyderma (left) fauna during strong polewards shifts of the frontal systems in the South Atlantic, which could have been transported 700 km offshore to the core location, unadmixed with eutrophic species from the surrounding waters. We propose meandering shelf-edge jets, strong contour jets, as a mechanism for the transport. The timing of the C-peaks and associated subtropical peaks agrees with the known precessional cyclicity of the SE Atlantic front movements and zonality of the trade winds, which supports the shelf-edge jet hypothesis.

Late Cretaceous planktonic foraminiferal assemblages from the Exmouth Plateau, ODP Sites 122-762 and 122-763, eastern Indian Ocean

The evolution of planktonic foraminifera during the Late Cretaceous is marked in the Santonian by the disappearance of complex morphotypes (the marginotruncanids), and the contemporary increasing importance and diversification of another group of complex taxa, the globotruncanids. Upper Turonian to lower Campanian planktonic foraminiferal assemblages from Holes 762C and 763B (Ocean Drilling Program, Leg 122, Exmouth Plateau, 47°S palaeolatitude) were studied in detail to evaluate the compositional variations at the genus and species level based on the assumption that, in the Cretaceous oceans as in the modern, any faunal change was associated with changes in the characteristics and the degree of stability of the oceanic surface waters. Three major groups were recognised based on gross morphology, and following the assumption that Cretaceous planktonic foraminifera, although extinct, had life-history strategies comparable to those of modern planktonics: 1 - r-selected opportunists; 2 - k-selected specialists; 3 - r/k intermediate morphotypes which include all genera that display a range of trophic strategies in-between opportunist and specialist taxa. Although planktonic foraminiferal assemblages are characterised by a progressive appearance of complex taxa, this trend is discontinuous. Variation in number of species and specimens within genera has allowed recognition of five discrete intervals each of them reflecting different oceanic conditions based on fluctuations in diversity and abundance of the major morphotypes. Planktonic forms show cyclical fluctuations in diversity and abundance of cold (r-strategists) and warm taxa (k-strategists), perhaps representing alternating phases of unstable conditions (suggesting a weakly stratified upper water column in a mesotrophic environment), and well-stratified surface and near-surface waters (indicating a more oligotrophic environment). Interval 1, middle Turonian to early Coniacian in age, is dominated by the r/k intermediate morphotypes which alternate with r-strategists. These cyclical alternations are used to identify three additional subintervals. Interval 2, aged middle to late Coniacian, is characterised by the increasing number of species and relative abundance of k-strategists. After this maximum diversification the k-strategists show a progressive decrease reaching a minimum value in Interval 3 (early to late Santonian), which corresponds to the extinction of the genus Marginotruncana. In the Interval 4, latest Santonian in age, the k-strategists, represented mainly by the genera Globotruncana, increase again in diversity and abundance. The last Interval 5 (early Campanian) is dominated by juvenile globotruncanids and r-strategists which fluctuate in opposite phase. The positive peak (Interval 2) related to the maximum diversification of warm taxa (k-strategists) in the Coniacian seems to correspond to a warmer episode. It is followed by a marked decrease in the relative abundance of warm taxa (k-strategists crisis) with a minimum in the late Santonian (Interval 3), reflecting a decrease in temperature. Detailed analysis of faunal variations allows the Santonian faunal turnover to be ascribed to a cooling event strong enough to cause the extinction of the marginotruncanids.

Planktonic foraminifera in Core ML2_66, North Atlantic

Evolution of approaches and methods for reconstruction of paleoenvironmental conditions from microfossils contained in bottom sediments is assessed. Authors elaborated a new actualistic basis for such reconstructions, consisting of a database on contents of tests of planktonic foraminifers in the surface layer of Atlantic sediments and a package of mathematical tools for computer data processing. Structure of the database is described. It contains data on test contents for 29 species and varieties of planktonic foraminifers in 381 samples. A mathematical model designed for reconstructions is based on factor analysis and multidimensional spline interpolation. The model allows one to deduce Quaternary hydrological parameters (paleotemperature, paleosalinity) for standard hydrological levels down to depth of 250 m for the four seasons of the year. Reconstructions are illustrated by an example of a sedimentary core from the North Atlantic representing a period of 300 ky. During the next to last and the last maxima of continental glaciation (oxygen isotope stages 8, 6, 4, and 2), the subarctic water mass was spread here. Winter and summer surface water temperatures comprised 1-5° and 5-7°C, respectively. During interglacials and in Holocene the conditions were close to present ones: winter and summer surface water temperatures comprised 10-12 and 15-17°C, respectively. Vertical paleohydrological profiles compiled for peaks of climatostratigraphic intervals suggest that during cold intervals water stratification was stronger than during the warm ones. At depth 50 m seasonal salinity oscillations did not exceed 0.4 per mil and commonly salinity was minimum in winter and maximum in summer.