Rapid palaeoceanographic changes in the Benguela Upwelling System for the last 160,000 years as indicated by abundances of planktonic foraminifera

Two sediment cores retrieved from the continental slope in the Benguela Upwelling System, GeoB 1706 (19°33.7′S 11°10.5′E) and GeoB 1711 (23°18.9′S, 12°22.6′E), reveal striking variations in planktonic foraminiferal abundances during the last 160,000 years. These fluctuations are investigated to assess changes in the intensity and position of the upwelling centres off Namibia. Four species make up over 95% of the variation within the core, and enable the record to be divided into episodes characterized by particular planktonic foraminiferal assemblages. The fossil assemblages have meaningful ecological significance when compared to those of the modern day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s)], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterize the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the subtropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity, and the associated increase in nutrients. The N. pachyderma (s) record suggests temporal shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial-interglacial pattern. Periods of high N. pachyderma (s) abundance describe rapid, discrete events dominating isotope stages 3 and 2. The timing of these events correlates to the temporal shifts of the Angola-Benguela Front (Jansen et al., 1997) situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicates that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current System. The coincidence of increased upwelling intensity with the movement of the Angola-Benguela Front can be interpreted mainly by changes in strength and zonality of the trade wind system.     

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

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

Neogene paleoceanographic events recorded in an active-margin setting: Humboldt basin, California

Recognition of North Pacific paleoceanographic events in the marginal Humboldt (Eel River) basin of northern California enables correlation of stratigraphic sections and development of a chronostratigraphy. Paleoclimatically related coiling shifts in Neogloboquadrina pachyderma (Ehrenberg) and benthic foraminiferal datums form the basis of the chronostratigraphy. Benthic foraminiferal datums are defined by the occurrence of selected benthic species and abundance maxima of benthic biofacies. The compiled chronostratigraphy is used to refine reconstructions of the depositional history of Humboldt basin. Paleoceanographic events, recognized by the distribution of benthic foraminiferal biofacies, are used to infer paleoceanographic history along the northeastern Pacific margin.

The similarity in coiling curves of N. pachyderma from the marine sequence at DSDP Site 173 and the coastal Centerville Beach section of Humboldt basin and at other independently dated sites along the northeastern Pacific margin demonstrates that matching records of climatic oscillations is a reliable method of correlating marine sequences. Benthic fauna from the Centerville Beach section vary in phase with climatically related coiling shifts in N. pachyderma. In particular these data show an increase in displaced neritic fauna during inferred warm intervals and resurgence of deeper bathyal fauna during inferred cool events. Similar data are observed from the inland Eel River section, demonstrating that benthic foraminiferal trends recognized at Centerville Beach can be identified elsewhere in Humboldt basin. This in-phase benthic response to climatic fluctuations probably results from changes in vertical depth range of many benthic species in response to paleoclimatically related vertical changes in water-mass position.

Depositional histories reconstructed for two key sites in southern Humboldt basin indicate low rates of sediment accumulation during early basin filling with hemipelagic sediments. Initiation of turbidite sedimentation in the early Pliocene resulted in a sharp increase in rate of sediment accumulation. This increase in rate of sediment accumulation is partially a response to tectonic uplift in the northern Coast Ranges and may be an effect of realignment of motion between the Pacific and North American plates at about this time. The inland site shoaled more rapidly during turbidite sedimentation as a result of a higher rate of sediment accumulation. The rate of sediment accumulation increased again at this site in the late Pliocene during deposition of shelf and nearshore facies. The Eel River region subsided concurrent with deposition of these shallow-water deposits.     

Oocysts of Neospora caninum, Hammondia heydorni, Toxoplasma gondii and Hammondia hammondi in faeces collected from dogs in Germany

Faecal samples of 24,089 dogs were examined coproscopically in two veterinary laboratories in Germany between March 2001 and October 2004. In 47 dogs, oocysts of 9–14 μm size were found. Their morphology was similar to those of Hammondia heydorni and Neospora caninum. Samples of 28 of these dogs were further examined by inoculation into gerbils: seven isolates induced a specific antibody response against antigens of N. caninum NC-1 tachyzoites. This response suggests that the isolates contained N. caninum. In addition to H. heydorni (12 times isolated), Toxoplasma gondii occysts (twice) and Hammondia hammondi oocysts (twice) were observed in dog faeces. The latter findings suggest that coprophagia with a subsequent intestinal passage by dogs plays a role in the dissemination of coccidian parasites for which cats are definitive hosts. Five of the seven N. caninum (NC-GER2, NC-GER3, NC-GER4, NC-GER5, NC-GER6) and the two T. gondii isolates (TG-dgGER1, TG-dgGER2) were successfully passaged into cell culture and are now available for detailed characterization. In contrast to oocysts of other parasites, N. caninum oocysts were predominantly found between January and April (Fisher exact; P=0.038). In the sera of dogs shedding N. caninum, no reactions against the immunodominant antigens with apparent molecular weights of 19, 29, 30, 33 and 37 kDa of N. caninum tachyzoites were observed 3–5 weeks after shedding. However, the animals recognized a 152-kDa N. caninum antigen. Compared with those identified as H. heydorni, T. gondii or H. hammondi, N. caninum oocyst isolates were significantly smaller in length with the 75th percentiles ≤10.7 μm when measured in concentrated sucrose solution and smaller length–width ratios with the 75th percentiles ≤1.06. It may thus be possible to develop criteria for a preliminary identification of N. caninum in dog faeces based on the oocyst morphology.     

Miocene phosphorites from the Murray Ridge, northwestern Arabian Sea

Phosphorites from the Murray Ridge, NW Arabian Sea comprise nodules, bioclasts, and bone fragments. The nodules are made up of a homogeneous, light-colored phosphate nucleus consisting of Rivulariacean filamentous cyanobacteria and a thin dark-grey colored phosphate cortex showing abundant microbial filaments and microborings. The bioclasts comprise of  14–14.5 Ma old planktonic foraminifers, accepted as the time of deposition. Spherical to ovoid-shaped apatite microparticles resembling fossil bacteria are distinct components in the bioclasts. Bone fragments exhibit apatite fillings. The nodules and bone fragments consist entirely of carbonate fluorapatite (CFA) with low Al, K, and Th concentrations suggesting absence of continental detritus. Shale-normalized REE patterns of the samples support a seawater-derived composition. The highly uniform initial _Nd values of − 4.8 to − 5.1 are interpreted as the seawater value at the onset of phosphatization  14 Ma ago. In contrast, ⁸⁷Sr/⁸⁶Sr ratios show a large range of 0.709055 to 0.709124 corresponding to unusually young stratigraphic ages of  1 to 3 Ma. The data are interpreted as evidence for post-depositional Sr exchange of the recrystallizing phosphorites with fluids isotopically not much different from modern seawater. It is concluded that the phosphorites formed under oxic, shallow-water conditions where microbial populations assimilated phosphorus primarily from seawater and mediated precipitation of CFA during early diagenesis at the sediment–water interface on different substrates.     

Lattice deformation and thermal stability of crystals in spider silk

The X-ray diffraction of dragline silks, produced by Nephila and Cyrtophora spiders, were measured by synchrotron radiation in their original states or in situ during stretching and heating. Nephila pilipes spiders construct a two-dimensional orb web that must be rebuilt in one or 2 days, but Cyrtophora spiders form a three-dimensional tent web that can exist for several weeks in a tropical forest. Diffraction patterns of N. pilipes and Cyrtophora draglines resemble each other. Crystals of two kinds are identified in these draglines; one is aligned parallel to the silk direction and another is less oriented. The less oriented crystal in Cyrtophora dragline is aligned better than that in N. pilipes dragline, which generates about three times stronger diffract intensity. Crystals in N. pilipes and C. moluccensis dragline silks have remarkable thermal stability. Equatorial reflections remain undiminished until 350 and 450 °C for N. pilipes and C. moluccensis, respectively. In contrast, the meridional reflections S and (0 0 2), which are parallel to the silk thread, disappear at a temperature less than 100 °C for C. moluccensis but remain for Nephila up to 100 °C. Meridional reflections S and (0 0 2) shift to a smaller angle during stretching, whereas equatorial reflections remain constant in a range 1.0–1.3 times the original length. The position of the S reflection shifts rapidly in the first 10% of elongation from the original length but remains constant during subsequent stretching, whereas the (0 0 2) reflection shifts rapidly during the first 5% elongation from the original length and continues to shift subsequently. In contrast, the features of N. pilipes dragline alter insignificantly during stretching. Examination of the composition of amino acids of the draglines of N. pilipes and C. moluccensis indicates that a dragline of N. pilipes contains more glycine, but much less alanine, than that of C. moluccensis.     

Experimentally induced effects of water temperature and immersion time on reproductive output of bivalves in the Wadden Sea

Results of experiments are reported on the effects of water temperature and immersion time in winter on egg size and egg numbers in three intertidally living bivalves in the Dutch Wadden Sea, the Baltic tellin Macoma balthica, the common cockle Cerastoderma edule and the common mussel Mytilus edulis. Macoma (14–17 mm shell length) produced large eggs (diameter of 107 μm) in relatively small numbers (20 000–70 000) in early spring. Later in spring, Cerastoderma (28–33 mm shell length) produced smaller eggs (77 μm, excluding the surrounding jelly layer) in tenfold larger numbers (200 000–700 000). Mytilus (45–55 mm shell length) spawned even smaller eggs (72 μm) in high (but not easily assessed) numbers over a more extended period. In Macoma egg size was not affected by winter temperatures or immersion time. Effects of winter–spring temperatures and immersion time on egg size could be demonstrated in Cerastoderma. Smaller eggs were produced at the higher temperatures. Effects of immersion time were non-consistent: at lower water temperatures larger, but at higher temperatures smaller eggs were produced by animals kept at longer immersion times. In Mytilus, no temperature effects were observed. However, a longer immersion time resulted in larger eggs. In Macoma as well as in Cerastoderma significantly more eggs were produced at the lower temperature. Immersion time effects were most pronounced at the lower temperature, where more eggs were produced at the subtidal level than at the tidal level. At the higher water temperature differences between egg numbers produced at the two tidal levels were small. Just prior to spawning, egg numbers were strongly positively related to body mass at a certain shell length.     

Analysis of the fixed oils of the genus Nigella L. (Ranunculaceae) in Turkey

The fatty acid composition of fixed oils obtained from the seeds of 10 species of Nigella (Nigella orientalis L., Nigella oxypetala L., Nigella latisecta P.H. Davis, Nigella segetalis Bieb., Nigella arvensis L., Nigella damascena L., Nigella elata Boiss., Nigella nigellastrum (L.) Willk., Nigella unguicularis (Lam.) Spenner, and Nigella lancifolia Hub.-Mor.) from Turkey have been investigated. The seeds contained 17.6–41.3% fixed oils. Linoleic (31.21–69.5%) and oleic acids (15.79–36.03%) were the major fatty acids in the oils. Eicosenoic acid was found in high amounts in the oils of N. nigellastrum and N. unguicularis seeds (23.12 and 17.47%, respectively). N. nigellastrum, N. elata and N. unguicularis seed oils showed the highest concentration of eicosadienoic acid (9.40, 8.39 and 7.17%, respectively). In all fixed oils, the quantities of unsaturated fatty acids were higher than those of the saturated analogues.     

New observations on the tontoniid ciliate Spirotontonia grandis (Suzuki and Han, 2000) Agatha, 2004 (Ciliophora, Oligotrichida, Tontoniidae); comparison with the similar Laboea strobila

Spirotontonia grandis (Suzuki and Han, 2000) Agatha, 2004 belongs to the family Tontoniidae Agatha, 2004 because it has a contractile tail. It is the type of the genus Spirotontonia Agatha, 2004, which is characterized by a sinistrally spiralled girdle kinety. Supplementary observations on protargol-impregnated and, especially, live specimens of S. grandis from the Irish Sea are provided. These new findings are included in an improved species diagnosis. Furthermore, they contribute to a better separation of the tontoniid S. grandis from the strombidiid Laboea strobila, which also has a screw-like appearance, a sinistrally spiralled girdle kinety, and multiple macronuclear nodules, but lacks the tontoniid tail. Since the tail of S. grandis, the main distinguishing feature between the two species, is highly contractile and easily lost, further differences are emphasized, e.g., the lower number of girdle kinety whorls (3.0–3.5 vs. 4.5–5.0), the larger cell size (110–170×55–80 μm vs. 80–110×40–60 μm after protargol impregnation), the relatively larger size of the ventral portion of the membranellar zone (51% vs. 40% of body length), and the overlapping cortical platelets (present vs. absent). The record of S. grandis from the Irish Sea is the first record outside the East China Sea and the second worldwide.     

The chemical microenvironment of the symbiotic planktonic foraminifer Orbulina universa

Microsensor measurements of CO₂, O₂, pH and Ca²⁺ in the vicinity of the symbiont-bearing planktonic foraminifer Orbulina universa showed major light-modulated changes in the chemical microenvironment due to symbiont photosynthesis, respiration of the holobiont, and precipitation of the calcite shell. Under saturating light conditions, microprofiles measured towards the shell surface showed an O₂ increase of up to 220% air saturation, a decrease in CO₂ concentration to 4.9 μM, and a pH increase to 8.8 due to symbiont photosynthesis. The Ca²⁺ concentration decreased to ∼9.6 mM in two specimens, while it increased to 10.2-10.8 mM in three other specimens kept in light. In darkness, the respiration of the community decreased the O₂ concentration to 82% of air saturation, CO₂ increased up to 15 μM, the pH decreased to 8.0, and the Ca²⁺ concentration increased up to 10.4 mM. These data, and derived calculations of the distribution of HCO₃^- and CO₃^2- near the shell, showed that the carbonate system in the vicinity of O. universa was significantly different from conditions in the surrounding seawater, both in light and darkness, due to the metabolism of the foraminifer and its associated algae. Experimental light-dark cycles indicated a sufficient CO₂ supply sustaining high carbon fixation rates of the symbiotic algae via conversion of HCO₃^- or via CO₂ release from calcification and host respiration. Our findings on irradiance-dependent CO₂ and pH changes in the vicinity of symbiont-bearing planktonic foraminifera give direct experimental evidence for the predictions of isotope fractionation models used in palaeoclimatology stating that metabolic processes affect the isotopic carbon signal (δ¹³C) in foraminifera.     

Distribution of living planktonic foraminifera in the Ross Sea and the Pacific sector of the Southern Ocean (Antarctica)

In order to determine the factors controlling the distribution of planktonic foraminifera as a proxy for reconstruction of paleoenvironments, we present data on live assemblages collected in the Southern Ocean. Plankton tows and hydrographic measurements were taken in the upper 400 m of the water column at different sites in the Ross Sea (site B) and at the Polar Front of the Pacific Ocean (site O) during austral summers from 1998 to 2003.Based on qualitative micropaleontological observations we discriminated between Neogloboquadrina pachyderma dextral (dex) and N. pachyderma sinistral (sin). In addition for N. pachyderma (sin) we distinguished four morphs: the first one (1) has a thickened test and depressed sutures; the second morph (2) is represented by specimens characterized by a subspheric and heavily encrusted test; the third morph (3) has a thin and lobate walled test; the fourth one (4) represent the juvenile stage of N. pachyderma (sin) and is characterized by a smaller average size.The microfauna collected in the Ross Sea (site B) is characterized by the dominance of N. pachyderma (sin) (morphs 1 and 2), whereas low occurrences of Turborotalia quinqueloba, N. pachyderma (dex) and Neogloboquadrina dutertrei were noted in the first 50 m of the water column. The water column at this station is characterized by a marked and shallow stratification and a marked thermocline during the sampling season.At the ocean station (site O), the assemblage shows increasing diversification: T. quinqueloba, G. bulloides, N. pachyderma (dex) and few specimens of Globigerinita uvula characterize the planktonic microfauna. There is a predominance of non-encrusted morphs and juvenile specimens (3 and 4). At this station the mixed surface layer is deeper than in the Ross Sea (60–70 m), the pycnocline and the thermocline less marked.The depth and the intensity of the Deep Chlorophyll Maximum (DCM) influence foraminiferal distribution: N. pachyderma (sin) shows abundance peaks at or just below the DCM while G. bulloides peaks above the DCM. Coiling direction of N. pachyderma seems to be not controlled exclusively by Sea Surface Temperature (SST): probably the two coiling types are genetically different.Results document that diversity of planktonic foraminifera, number of specimens and variations in test morphology are related to regional differences in water properties (temperature, salinity, and DCM depth).     

Phased evolution of the south–north hydrographic gradient in the South China Sea since the middle Miocene

The hydrography of the South China Sea (SCS) is characterized by a south–north (S–N) thermocline gradient in the upper water column from the northern margin of the western Pacific warm Pool (WPWP) to the sea area largely controlled by the East Asian monsoon. Here we examine the records of planktonic foraminifers from Ocean Drilling Program (ODP) Sites 1143 and 1146 in the southern and northern parts of the SCS, respectively, that identify three stages of evolution of the S–N hydrographic gradient in the SCS since the middle Miocene: first, the S–N thermocline gradient possibly occurred in the SCS for the first time during the period 11.510.6 Ma, reflected by an opposite change in the relative abundance of deep-dwelling planktonic foraminiferal species in the south and north; next, the S–N thermocline gradient weakened or even disappeared during the period 10.64.0 Ma, indicated by similar changes in the relative abundance of deep-dwelling species in the south and north; last, the S–N thermocline gradient substantially increased from about 4.03.2 Ma, marked by a major increase in abundance of deep-dwelling species in the northern SCS and a decrease in the southern SCS. Based on the results of oceanic and coupled ocean–atmosphere model experiments and previous studies on planktonic foraminifers in the Pacific Ocean, it is inferred that the initial WPWP was probably formed during the period of 11.510.6 Ma in response to the closure of the Indonesian seaway; The WPWP then weakened or became extremely unstable, before developing its present expression about 4.0–3.2 Ma, induced by the emergence of the Isthmus of Panama. Our observations and model experiments support the argument that the stages in evolution of the WPWP are linked to tectonic changes in ocean gateways.     

Population dynamics of the harmful diatom Eucampia zodiacus Ehrenberg causing bleachings of Porphyra thalli in aquaculture in Harima-Nada, the Seto Inland Sea, Japan

The diatom Eucampia zodiacus Ehrenberg is one of the harmful diatom species which indirectly cause bleachings of Nori (Porphyra thalli) in aquaculture through competitive utilizing of nutrients (especially nitrogen) and resultant nutrient depletion in water columns during the bloom events. The seasonal changes in environmental factors, cell density and cell size of E. zodiacus were investigated for 4 years (April 2002–December 2005) to understand the population ecology of this diatom in Harima-Nada, the eastern part of the Seto Inland Sea, Japan. Vegetative cells of E. zodiacus were usually detected year-round. Total cell densities of E. zodiacus annually peaked from mid-February to early April, and high cell densities were observed in the whole water columns during the bloom-period. Nutrient concentrations decreased with the increase of cell density of E. zodiacus, and low nutrients concentrations continued throughout the E. zodiacus bloom-period. The average cell size (length of apical axis) of E. zodiacus populations ranged from 10.8 μm to 81.2 μm, and the restoration of cell size occurred once in autumn every year just after reaching the minimum cell size. In addition, its great seasonal regularity was confirmed by the decrease and restoration of its cell size through 4-year study period. Temperature and nutrients were suitable in autumn for the growth of E. zodiacus, its blooms never occur in that season. These results strongly suggest that E. zodiacus did not have a resting stage, and it spends autumn for size restoration and starts to bloom thereafter in Harima-Nada in winter and spring, causing fishery damage to Nori aquaculture by resulting nutrient deprivation.     

Chemoenzymatic synthesis of CMP-sialic acid derivatives by a one-pot two-enzyme system: comparison of substrate flexibility of three microbial CMP-sialic acid synthetases

Three C terminal His₆-tagged recombinant microbial CMP–sialic acid synthetases [EC 2.7.7.43] cloned from Neisseria meningitidis group B, Streptococcus agalactiae serotype V, and Escherichia coli K1, respectively, were evaluated for their ability in the synthesis of CMP–sialic acid derivatives in a one-pot two-enzyme system. In this system, N-acetylmannosamine or mannose analogs were condensed with pyruvate, catalyzed by a recombinant sialic acid aldolase [EC 4.1.3.3] cloned from E. coli K12 to provide sialic acid analogs as substrates for the CMP–sialic acid synthetases. The substrate flexibility and the reaction efficiency of the three recombinant CMP–sialic acid synthetases were compared, first by qualitative screening using thin layer chromatography, and then by quantitative analysis using high performance liquid chromatography. The N. meningitidis synthetase was shown to have the highest expression level, the most flexible substrate specificity, and the highest catalytic efficiency among the three synthetases. Finally, eight sugar nucleotides, including cytidine 5′-monophosphate N-acetylneuraminic acid (CMP–Neu5Ac) and its derivatives with substitutions at carbon-5, carbon-8, or carbon-9 of Neu5Ac, were synthesized in a preparative (100–200 mg) scale from their 5- or 6-carbon sugar precursors using the N. meningitidis synthetase and the aldolase.     

Humoral and cellular responses to homologous extracts of Nematospiroides dubius and Nippostrongylus brasiliensis

and 1986. Humoral and cellular responses to homologous extracts of Nematospiroides dubius and Nippostrongylus brosiliensis. International Journal for Parasitology 16: 601–606. Humoral and cellular responses to homologous parasite extracts were studied in C57BL mice infected with Nematospiroides dubius or Nippostrongylus brasiliensis, to determine whether these parasites induced specific immunosuppression which might facilitate their survival. IgG and IgM titres to adult, excretory-secretory, larval and egg antigens from N. dubius and adult antigen from N. brasiliensis increased progressively for several weeks, irrespective of parasite rejection. Delayed-type hypersensitivity responses to the same antigens peaked after about 2 weeks and then remained constant in N. dubius -infected mice, but declined after the rejection of N. brasiliensis. The specific lymphoproliferative responses of spleen cells to these extracts reached peak values 1–3 weeks after infection and were anti-Thy 1.2-sensitive. They then declined sharply, but remained above the levels seen in uninfected mice. These results should be considered in the interpretation of any investigations into the stable host-parasite relationship which exists during a primary N. dubius infection.     

Early Cretaceous calcareous nannofossils from high latitudes: implications for palaeobiogeography and palaeoclimate

In order to better understand the palaeoceanography and palaeoclimate of the Early Cretaceous, nannofossil data have been obtained from high-latitudinal sites from offshore mid-Norway and from the Barents Sea. No consistent nannofossil data are yet available for Early Cretaceous high latitudes, which should more clearly reflect possible palaeoclimatic changes, as recorded in fluctuations of diversity and abundance. Existing data from France, Italy, Romania, Poland and NW Europe (Germany, North Sea, England) have been complemented by material from higher latitudes. In order to record the Arctic–Boreal nannofossil assemblages, 400 samples from the Norwegian Shelf and the Barents Sea have been analysed. Sixty samples, covering the Berriasian–Barremian interval, yielded calcareous nannofossils. These are derived from cores between 63 and 73°N of present-day latitudes. The nannofossil assemblages recorded are generally of a low diversity and characterized by abundant Watznaueria barnesae and Crucibiscutum salebrosum, whereas Biscutum constans is less common. C. salebrosum, rare or absent at low latitudes, is extremely common in the Norwegian samples. It shows a bipolar distribution especially during Valanginian–Hauterivian times. In the early Valanginian, a distinctive latitudinal gradient in the abundance of C. salebrosum, impoverished in low latitudes and abundant in high latitudes, possibly reflects latitudinal differences in temperature. Restricted palaeoceanographic settings, caused by a sea-level lowstand, may have amplified these thermal gradients. Palaeoclimatically this implies the existence of climatic belts throughout parts of the Early Cretaceous (early Valanginian, Hauterivian), resulting from considerable temperature gradients from north to south. The palaeobiogeographic patterns discussed resulted in the formation of distinctive latitudinally bound nannofossil zones, which, to a certain extent, are similar to those of modern oceans. The palaeobiogeographic patterns described support the idea of an ice-house phase for the early Valanginian and disagree with the suggestion of a globally warm equable climate during that time.     

High-resolution sea surface temperature records derived from foraminiferal Mg/Ca ratios during the last 260 ka in the northern South China Sea

High-resolution sea surface temperatures (SST) derived from Mg/Ca ratios of Globeriginoides sacculifer at ODP Site 1144 were reported to reveal the SST changes during the last 260 ka in the northern South China Sea (SCS). The results indicate an average Holocene SST of about 26.7 °C, about 3.6 °C increase from LGM to the Holocene, and higher temperature during MIS 5.5 than the Holocene. These agree well with other foraminifer Mg/Ca and U^k₃₇ SST records in this region. The Mg/Ca records suggest warmer SSTs during MIS 3 in the northern SCS, compared with those in the eastern Pacific. Strong East Asian summer monsoon during MIS 3 indicated by paleoclimate records from nearby continents may account for it. Step-wise increases during terminations are shown in our SST record, and the beginning of deglacial warming occurs at about 19 ka, which precedes the change of oxygen isotopes, suggesting a tropical driven forcing for the SST change in the northern SCS. This is further supported by a robust semi-precessional cycle centering at  9.1 ka in the spectra of the SST record, which is absent in that of the oxygen isotopes. However, tropical driven forcing seems not to be indicated in another Mg/Ca SST record in the northern SCS [Oppo, D.W. and Sun, Y.B., 2005. Amplitude and timing of sea-surface temperature change in the northern South China Sea: Dynamic link to the East Asian monsoon. Geology, 33 (10): 785–788.]. The discrepancy may be caused by different post-deposition dissolutions of foraminifer tests at these two sites. Details about the modification of foraminifer Mg/Ca ratios after burial, however, are not well known in this region, and further studies are needed.     

The role of host generated free radicals in helminth infections: Nippostrongylus brasiliensis and Nematospiroides dubius compared

and 1986. The role of host generated free radicals in helminth infections: Nippostrongylus brasiliensis and Nematospiroides dubius compared. International Journal for Parasitology 16: 617–622. The possibility that free radicals are involved in the expulsion of Nippostrongylus brasiliensis from the small intestine of its mice host was explored by comparing the susceptibilities to free radicals, and levels of protective enzymes, of adult N. brasiliensis and Nematospiroides dubius, a closely related intestinal parasite of mice. Nippostrongylus brasiliensis was markedly more susceptible to in vitro free radical damage than N. dubius. The difference in susceptibility is probably related to differences in enzymatic protection against free oxygen radicals as N. dubius had roughly twice as much Superoxide dismutase, about 3 times as much catalase and about 4 times as much glutathione reductase as N. brasiliensis. This result may indicate that N. dubius persists in the rodent small intestine, whilst N. brasiliensis is spontaneously expelled, because of a more efficient enzymatic defence system against host-generated free oxygen radicals.     

Sea surface environment inferred from planktonic foraminifera in the southern South China Sea since the last glacial period

Detailed analyses of planktonic foraminifera at Site 17964 from the southern South China Sea (SCS) disclose that warm-water species have a higher percentage during the Holocene, while temperate-water species have a higher content for the last glacial period. Therefore, the sea surface temperature (SST) is a main factor that affects the foraminiferal assemblage at this site. A remarkable faunal variation at Site 17964 is recognized for Pulleniatina obliquiloculata over the last glacial–interglacial periods: higher P. obliquiloculata content during the glacial period and abrupt drop at the beginning of Termination I (16.5–15 kyr B.P.). The characteristic P. obliquiloculata variation can be correlated with other sites in the southern SCS and thus can be adopted as a stratigraphic tool in the region. A detailed analysis of Orbulina universa shell morphometrics at Site 17964 shows the test size from 0.83 to 1.45 mm and the shell porosity up to 36.7%, much larger than those in the Indian and Atlantic Oceans, which indicates a warmer and less saline surface water in the equatorial–tropical western Pacific. The diameter and shell porosity of O. universa increased from the last glacial to the Holocene, corresponding to the increase of SST recorded by the U^k₃₇ alkenone index. A higher correlation coefficient (89%) between the O. universa test size and SST implies that intraspecific O. universa test size be used as an index of the sea surface temperature in the South China Sea.     

Oxygen minimum expansion in the Sulu Sea,western equatorial Pacific,during the last glacial low stand of sea level

The Sulu Sea in the western equatorial Pacific is presently a shallowly-silled, dysaerobic, deep-marine basin. Deep waters in the Sulu Sea are ventilated through a single sill at 420 m depth which connects it to the China Sea. Benthic and planktonic foraminiferal oxygen and carbon isotope records, benthic and planktonic foraminiferal census data and total organic carbon measurements have been used to evaluate changes in water mass conditions in the Sulu Sea between the last glacial maximum (18,000 yrs. B.P.) and the present day.An increase in the abundance of the planktonic foraminiferaNeogloboquadrina dutertrei and relatively light planktonic foraminiferal δ¹⁸O values suggest that during the last glacial maximum surface water salinities were reduced in the Sulu Sea. Enhanced isolation of the basin due to glacio-eustatic lowering of sea level and reduced surface salinities resulted in stagnation of deep water and an expansion of the mid-water oxygen minimum layer. Increased organic carbon preservation at mid-water depths occurs at this time. Benthic carbon isotope data and an increase in the abundance of benthic foraminiferal species considered to prefer low oxygen environments support the conclusion of an oxygen-minimum expansion at mid-water depths during the last glacial maximum. At water depths greater than 4000 m, bottom waters appear to have maintained some degree of oxygenation during the last glacial maximum. Stronger Pacific Ocean trade winds at this time may have caused the influx of denser Celebes Sea surface water into the southern part of the Sulu Sea. The slow sinking of this water would have then ventilated bottom waters in this part of the basin.At the transition from glacial to interglacial conditions, rising sea level caused denser water to flow over the deepest sill into the Sulu Sea. Vertical circulation increased, resulting in a greater downward flux of oxygen and a dissipation of the oxygen minimum. Continued post-glacial sea level rise caused periodic ventilation of deep water until the present dysaerobic conditions were established.