Pleistocene fluctuations in the Agulhas Current Retroflection based on the calcareous plankton record

Piston core (PS2487-6), recovered south of Cape Town, and sediment surface samples, recovered in the area of the Agulhas Current retroflection, were used to construct paleoceanographic scenarios for the late Quaternary in a region with an important role in global water mass transfer. Coccolithophore (calcareous nannofossil) and planktonic foraminifera assemblages and oxygen isotope data were collected. Stratigraphic control is based on calibration of the δ¹⁸O stratigraphic signals with calcareous nannofossil events that are thought to be synchronous over a broad range of latitudes. Study of the surface sediments permits the characterisation of the Agulhas Current, Subtropical Convergence and Subantarctic coccolithophore assemblages. The Agulhas Current assemblage has relatively high proportions of Florisphaera profunda, Gephyrocapsa oceanica and Umbilicosphaera spp. These species are absent or present in low proportions in subantarctic waters. The abundance of coccolithophores during isotope stages 1, 5 and 7 is characteristic of relatively warm, stratified surface waters, with a deep nutricline and chlorophyll maximum, which strongly suggests that the area was under the influence of the Agulhas Current retroflection. The incursion of Globigerinoides ruber, abundant today in the Agulhas Current, also supports this interpretation. Conversely, during glacial stages 2–4 and 6, a strong reduction in warm and stratified water indicators can be observed, together with an increase in cold-eutrophic species.The interval from isotope stages 8 to 12 displays an assemblage dominated by Gephyrocapsa caribbeanica, the highest values being seen in the so-called Mid-Brunhes event, accompanied by a clear reduction in subtropical Holocene species. During the glacial interval from isotope stages 10–12, G. caribbeanica dominated the assemblage. The ecological interpretation of this species is controversial due to a clear evolutionary overprint. Isotope stage 12 is here interpreted as having been the coldest one in the period studied. It is characterised by a strong increase in Neogloboquadrina pachyderma (dextral and sinistral) and a remarkable decrease in tropical and subtropical planktonic foraminifera. From isotope stage 13 to 18, a hiatus is interpreted. Below this hiatus the stratigraphic resolution is poorer, although the glacial–interglacial cyclicity is well defined in the Agulhas Current Retroflection area (Core PS2487-6) for the last 25 isotope stages. The glacial–interglacial cyclicity is thought to be due to a fluctuation in the Subtropical Convergence Zone, probably linked to the eastward and westward displacement of the Agulhas Current retroflection. In any case, the core studied was always in a subtropical environment, under the influence of the Agulhas Current, which was enhanced during interglacial periods. For the whole of the interval studied, increases in Calcidiscus leptoporus, Umbilicosphaera spp., and Syracosphaera spp. among the calcareous nannofossils, and in G. ruber and Globigerinoides sacculifer within the planktonic foraminifera, clearly respond to interglacial pulses, reaching maximum values during short periods close to the major deglaciations.     

Temperature sensitivity of planktic foraminifera and its influence on the oxygen isotope record

We used oxygen isotope measurements from Holocene surface sediments to infer optimum temperature and temperature sensitivity of the planktic foraminiferal species Globigerinoides ruber (pink) and Globigerinoides sacculifer. The (isotopic) optimum temperature of G. ruber (pink) is close to 27°C. G. sacculifer seems to have optimum vital conditions around 22°C and is less temperature sensitive than G. ruber (pink). Our estimations of optimum temperature and temperature sensitivity are in good accordance with laboratory and field investigations. Two simple experiments show that the temperature sensitivity of planktic foraminifera, determined from oxygen isotopes, can influence phase and amplitude of oxygen isotope records, if the temperature distribution at the sea surface changes through time. To use this distortion for paleoceanography, we suggest to derive an ‘isotopic transfer function’ which allows the calculation of average temperature, temperature variability and the isotopic composition of seawater if the oxygen-isotope differences between at least three species are known.     

A structural transition in egg lecithin-cholesterol bilayers at 12 °C

The thermal coefficient of expansion of egg lecithin bilayer thickness, αd₁, was measured as a function of its cholesterol content up to mole ratio lecithin/cholesterol of 1:1, and over the temperature range 0–40 °C. At all cholesterol contents αd₁ changes abruptly at approximately 12 °C indicating a structural transition at this temperature. Above 12 °C, αd₁ decreases monotonically from −2·10⁻³ for pure egg lecithin to −1·10^–3 at mole ratio 1:1. Below 12 °C αd₁ is walways higher than above 12 °C and shows a sharp, anomalously high value of −6·10⁻³ at the mole ratio 2:1. The results have been interpreted as the movement of cholesterol into the bilayer or the formation of lecithin-cholesterol “complexes” at temperatures below 12 °C. Similar studies with phosphatidylinositol containing cholesterol showed no structural transition and lysolecithin containing cholesterol behaved differently giving two lamellar phases in equilibrium.     

Stable carbon and nitrogen isotope discrimination in soft tissues of the leatherback turtle (Dermochelys coriacea): Insights for trophic studies of marine turtles

The trophic ecology of marine vertebrates has been increasingly studied via stable isotope analysis of body tissues. However, the theoretical basis for using stable isotopes to elucidate consumer–prey relationships remains poorly validated for most taxa despite numerous studies using this technique in natural systems. In this study, we measured stable carbon and stable nitrogen diet-tissue discrimination (Δ_dt) in whole blood, red blood cells, blood plasma solutes, and skin of leatherback sea turtles (Dermochelys coriacea; N = 7) maintained in captivity for up to 424 days and fed an isotopically consistent control diet with a mean C:N ratio of 2.94:1.00 and an energetic content of 20.16 ± 0.39 kJ g^− 1 Dry Mass. We used a random-effect repeated measure model to evaluate isotopic consistency among tissue samples collected on days 276, 348, and 424. Both δ¹³C and δ¹⁵N remained consistent among sampling events in all tissues (all 95% posterior intervals for the slopes of a linear model included zero), indicating that all tissues had fully integrated diet-derived stable isotope compositions. Mean tissue-specific δ¹³C ranged from − 18.30 ± 0.16‰ (plasma solutes) to − 15.54 ± 0.14‰ (skin), whereas mean δ¹⁵N was from 10.06 ± 0.22‰ (whole blood) to 11.46 ± 0.10‰ (plasma solutes). The computed Δ_dt factors for carbon ranged from − 0.58‰ (plasma solutes) to + 2.25‰ (skin), whereas Δ_dt for nitrogen was from + 1.49 (red blood cells) to + 2.85 (plasma solutes). As the only discrimination factors available for leatherback turtles, our data will be useful for future interpretations of field-derived stable isotope data for this species. The inherent variability in Δ_dt values among individuals was low, which supports the value of these data for dietary reconstructions. However, it is important to note that tissue-specific discrimination factors for leatherbacks contrast with the widely accepted values for endothermic species (0–1‰ for C, 3–5‰ for N), and are also different from values established for hard-shelled turtles. This underscores the need for species- and tissue-specific discrimination factors before interpreting trophic studies of wild animals, including marine turtles.     

Export production of coccolithophores in an upwelling region: Results from San Pedro Basin, Southern California Borderlands

A seven month-long time series sediment trap project was carried out in San Pedro Basin (Southern California Borderlands) in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes. This region is periodically influenced by upwelling, particularly during the spring and early summer. The highest fluxes of both whole coccospheres and individual coccoliths occurred during winter (January-February), a period when the fluxes of diatoms and planktic foraminifera were low. The highest coccolithophore fluxes were recorded in the mid-February with 860 × 10⁶ coccoliths m⁻² day⁻¹, 8 × 10⁶ whole coccospheres m⁻² day⁻¹, and 80 mg of coccolith carbonate m⁻² day⁻¹. Coccolith carbonate fluxes in January and February account for most of the total carbonate fluxes measured during this period. The season of maximum coccolithophore production in this region (winter) is correlated with weak stratification of the upper water column, low total primary production, low nutrient contents, and low temperatures.Emiliania huxleyi and Florisphaera profunda are the two most abundant species in this region. While E. huxleyi displays no distinct seasonal changes in flux, F. profunda shows a clear preference for cold, low nutrient water conditions and low light levels. Helicosphaera spp. flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity.     

The acetylcholine receptor: Isolation of a brain nicotinic receptor and its preliminary characterization in lipid bilayer membranes

The technique of affinity chromatography with the curarizing neurotoxins of Naja naja venom has been employed to extract nicotinic acetylcholine receptors from the brain tissues of mouse and hog. Both carbochol and hexamethonium were used as linear or step gradients to elute the receptor and its properties were investigated in lipid bilayer membranes. Of particular interest is the observation that discrete quanta of conductance could be observed across an NaCl gradient of 1.0:0.1 M. By switching the voltage-clamp across the bilayer between a positive and negative 80 mV, the separate Na⁺ and Cl⁻ conductances of these quanta could be estimated and the following conductances of the smallest discrete quanta were observed: 3.7 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 5.9 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for mouse brain receptors; 3.8 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 4.7 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for hog brain receptors. Large aggregates of receptors appeared to activate and deactivate as multiples of a basic conductance size, although there is evidence that they may not represent the actual gating of ion channels. A “background noise” that is not within the temporal capability of the recording system is also present at an intensity that seems to parallel the number of activated receptors, and in view of recent electrophysiological evidence that the relaxation lifetime of the open channel state is of a millisecond duration, it may be that this “noise” actually represent the channel gating.     

Inhibition of sodium-plus-potassium-stimulated adenosine triphosphatase (Na-K-ATPase) by protein kinase C activators in the gills of Atlantic cod (Gadus morhua)

Exogenous (phorbol ester) and endogenous (diacylglycerol) activators of protein kinase C (PKC) inhibited sodium efflux across the gills of Atlantic cod Gadus morhua and inhibited sodium-plus-potassium-stimulated adenosine triphosphatase (Na⁺-K⁺-ATPase) in isolated chloride cells. The branchial sodium efflux measured in a perfused whole-body preparation was inhibited by 47% on administration of 10⁻⁶ mol.L⁻¹ phorbol 12, 13-dibutyrate (PDB). The branchial perfusion pressure was increased by 46% by 10⁻⁶ mol.L⁻¹ PDB. In contrast the synthetic diacylglycerol, 1-oleoyl-2-acetyl gycerol (OAG) did not alter significantly perfusion pressure but did reduce sodium efflux by 13% at a concentration of 4 × 10⁻⁶ mol.L⁻¹. The effects of these agents on Na⁺-K⁺-ATPase activity were determined in isolated chloride cells with a control activity of 30.9 ± 1.9 μmol Pi mg protein⁻¹ hour⁻¹. PDB and OAG both inhibited enzyme activity in a dose-dependent manner, with 10⁻⁵ mol.L⁻¹ causing 45% and 26% inhibition, respectively. These results suggest that PKC is involved in regulating sodium efflux in the gills of cod by modulating Na⁺-K⁺ATPase activity.     

Physiological acclimation to light in Chara intermedia nodes

In this study we investigated the ability of Chara intermedia to acclimate to different irradiances (i.e. “low-light” (LL): 20–30 μmol photons m⁻² s⁻¹ and “high-light” (HL): 180–200 μmol photons m⁻² s⁻¹) and light qualities (white, yellow and green), using morphological, photosynthesis, chlorophyll fluorescence and pigment analysis.Relative growth rates increased with increasing irradiance from 0.016 ± 0.003 (LL) to 0.024 ± 0.005 (HL) g g⁻¹ d⁻¹ fresh weight and were independent of light quality. A growth-based branch orientation towards high-light functioning as a mechanism to protect the plant from excessive light was confirmed. It was shown that the receptor responsible for the morphological reaction is sensitive to blue-light.C. intermedia showed higher oxygen evolution (up to 10.5 (HL) vs. 4.5 (LL) nmol O₂ mg Chl⁻¹ s⁻¹), photochemical and energy-dependent Chl fluorescence quenching and a lower Fv/Fm after acclimation to HL. With respect to qP, the acclimation of the photosynthetic apparatus depended on light quality and needed the blue part of the spectrum for full development. In addition, pigment composition was influenced by light and the Chl a/Car and Antheraxanthin (A) + Zeaxanthin (Z)/Violaxanthin (V) + A + Z (DES) ratios revealed the expected acclimation behaviour in favour of carotenoid protection under HL (i.e. decrease of Chl a/Car from 3.41 ± 0.48 to 2.30 ± 0.35 and increase of DES from 0.39 ± 0.05 to 0.87 ± 0.03), while the Chl a/Chl b ratios were not significantly affected. Furthermore it was shown that morphological light acclimation mechanisms influence the extent of the physiological modifications.     

Transition-state structure for a conformation change of ribonuclease

The rate constants k₁₂ⁿ for isomerization of the E₁H isomer (pK_a 8 in H₂O) of ribonuclease-A to the E₂H isomer (pK_a = 6.1 in H₂O), determined from proton-uptake measurements by the temperature-jump technique, in mixtures of protium and deuterium oxides (atom fraction of deuterium n), are described by the equation k₁₂ⁿ = (733 ± 16)(1 − n + [0.46 ± 0.04]n)(1 − n + 0.69n)²sec⁻¹ at 25°C. On the basis of the absolute magnitude of the rate constant, the magnitude of the solvent isotope effect and the proton inventory, it appears that the rate-determining step is proton transfer to a water molecule from the imidazolium form of a histidine residue, with a product-like activated complex resembling a hydronium ion. The subsequent motion of the protein structure to generate the new isomer (conformation change) must then occur in a time approaching a vibrational period. Alternative but less likely mechanisms include rate-limiting protein reorganization concerted with proton transfer to water, rate-limiting diffusion of hydronium ion away from the enzyme, or “solvation catalysis” of protein reorganization.     

Growth of dinoflagellates, Ceratium furca and Ceratium fusus in Sagami Bay, Japan: The role of temperature, light intensity and photoperiod

Seasonal changes of field populations and growth rates of two dinoflagellates, Ceratium furca and Ceratium fusus, were examined in the temperate coastal water of Sagami Bay, Japan. Weekly field sampling was conducted from August 2002 to August 2003, and laboratory experiments were also carried out to investigate effects of temperature, irradiance and photoperiod on the growth rates of these two Ceratium species. In the field, the abundances of both species increased significantly from April to August 2003, were gradually decreased from November 2002 and were not observed in January 2003. C. fusus was able to increase at lower temperatures in February 2003 compared to C. furca. In the laboratory, the two species did not grow at <10 °C or >32 °C. The highest specific growth rate of C. furca was 0.72 d⁻¹ at 24 °C and 600 μmol m⁻² s⁻¹. Optimum growth rates (>0.4 d⁻¹) of C. furca were observed at temperatures from 18 to 28 °C and at irradiances from 216 to 796 μmol m⁻² s⁻¹. The highest growth rate of C. fusus was 0.56 d⁻¹ at 26 °C and 216 μmol m⁻² s⁻¹. Optimum growth rates of C. fusus were observed at the same irradiance rage of C. furca, whereas optimum temperature range was narrower (26–28 °C). The growth curves of both species indicated saturation of the growth rates when light intensity was above 216 μmol m⁻² s⁻¹, and did not show photoinhibition at irradiances up to 796 μmol m⁻² s⁻¹. The specific growth rates of both Ceratium species were clearly decreased at L:D = 10:14 relative to those at L:D = 14:10 and L:D = 12:12. The present study indicates the two Ceratium species can adapt to a wide range of temperature and irradiance.     

Seasonal and spatial variability of coccolithophore export production at the South-Western margin of Crete (Eastern Mediterranean)

Six moorings were deployed at different locations in the deep submarine canyons along the south–west margin of Crete, providing a total of eight sediment-trap time series from June 2005 to May 2006. Within this dataset, we analyzed the record from intact coccospheres, which represent the signal of export production from the coccolithophore community. The most abundant species at all stations during the whole investigated period were E. huxleyi and A. robusta, followed by S. pulchra HET, G. flabellatus, H. carteri, F. profunda, S. pulchra HOL oblonga, while the rest of the species represented ≤ 1% of the assemblage. Overall the assemblage composition was comparable at all stations, with slight variations mostly related to the different preservation of coccosphere integrity at the different collection depths. The consistent pattern of seasonal variation in species distribution and total coccolithophore export allowed us to define the occurrence of three main periods: a) March to June, with high overall coccosphere flux (up to 4.3 × 10⁵–3.4 × 10⁶ coccospheres m^− 2 day^− 1), increased abundance of E. huxleyi and subordinate H. carteri s.s., Umbilicosphaera spp. and S. pulchra; b) June to November, with high but gradually decreasing total coccosphere flux (up to 7 × 10⁵–1.4 × 10⁶ coccospheres m^− 2 day^− 1) and high relative abundance of the deep photic zone species A. robusta, F. profunda, G. flabellatus as well as S. pulchra and Coronosphaera spp., R. clavigera, U. tenuis, D. tubifera and holococcolithophores; c) November to February, with low overall export fluxes (3.5–9 × 10⁴ coccospheres m^− 2 day^− 1) and high relative abundance of A. robusta, S. pulchra and Syracosphaera spp. These three periods correspond to the seasonal changes in sea surface temperature, surface mixed layer depth and rainfall and are associated with varying total surface primary production, as detected through remote sensing in the surface waters.     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Variation in δC values for the seagrass Thalassia testudinum and its relations to mangrove carbon

Carbon isotope ratios (¹³C/¹²C) were measured for the leaves of the seagrass Thalassia testudinum Banks ex König and carbonates of shells collected at the seagrass beds from seven sites along the coast of southern Florida, U.S.A. The δ¹³C values of seagrass leaves ranged from −7.3 to −16.3‰ among different study sites, with a significantly lower mean value for seagrass leaves from those sites near mangrove forests (−12.8 ± 1.1‰) than those far from mangrove forests (−8.3 ± 0.9‰; P < 0.05). Furthermore, seagrass leaves from a shallow water area had significantly lower δ¹³C values than those found in a deep water area (P < 0.01). There was no significant variation in δ¹³C values between young and mature leaves (P = 0.59) or between the tip and base of a leaf blade (P = 0.46). Carbonates of shells also showed a significantly lower mean δ¹³C value in the mangrove areas (−2.3 ± 0.6‰) than in the non-mangrove areas (0.6 ± 0.3‰; P <0.025). In addition, the δ¹³C values of seagrass leaves were significantly correlated with those of shell carbonates (δ¹³C seagrass leaf = −9.1 + 1.3δ¹³C shell carbonate (R² = 0.83, P < 0.01)). These results indicated that the input of carbon dioxide from the mineralization of mangrove detritus caused the variation in carbon isotope ratios of seagrass leaves among different sites in this study.     

Studies on fungal polysaccharide XVII. A new glucuronan “protuberic acid” produced by a fungus Kobayashi Nipponica

A water-soluble glucuronan “protuberic acid”, [α]_d²² −83.6° and purified from Kobayashia Nipponica, and its physicochemical properties were investigated.The purified protuberic acid was homogeneous as shown by zone electrophoresis, gel filtration over Sepharose 4B, and ultracentrifugation. The sedimentation coefficient was 1.8 S and its intrinsic viscosity was 1.1 dl/g. By gel filtration the molecular weight was estimated to be about 170 000. The results of periodate oxidation, methylation analysis, and partial acid hydrolysis indicated that this acidic polysaccharide has a linear structure of mainly 1,4-linkages and containing an acid-labile linkage. Reduced protuberic acid, [α]_d²² −44°, is also described.     

Determination of Cr(VI) and Cr(III) species in parenteral solutions using a nanostructured material packed-microcolumn and electrothermal atomic absorption spectrometry

A sequential on-line preconcentration and separation system for Cr(VI) and Cr(III) species determination was developed in this work. For this purpose, a microcolumn filled with nanostructured α-alumina was used for on-line retention of Cr species in a flow-injection system. The method involves the selective elution of Cr(VI) with concentrated ammonia and Cr(III) with 1 mol L⁻¹ nitric acid for sequential injection into an electrothermal atomic absorption spectrometer (ETAAS).Analytical parameters including pH, eluent type, flow rates of sample and eluent, interfering effects, etc., were optimized. The preconcentration factors for Cr(VI) and Cr(III) were 41 and 18, respectively. The limit of detection (LOD) was 1.9 ng L⁻¹ for Cr(VI) and 6.1 ng L⁻¹ for Cr(III). The calibration graph was linear with a correlation coefficient of 0.999. The relative standard deviation (RSD) was 8.6% for Cr(VI) and 6.1% for Cr(III) (c=10 μg L⁻¹, n=10, sample volume=25 mL). Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1643e “Trace elements in natural water”) with a reported Cr content of 20.40±0.24 μg L⁻¹. Using the proposed methodology the total Cr content, computed as sum of Cr(III) and Cr(VI), in this SRM was 20.26±0.96 μg L⁻¹. The method was successfully applied to the determination of Cr(VI) and Cr(III) species in parenteral solutions. Concentration of Cr(III) species was found to be in the range of 0.29–3.62 μg L⁻¹, while Cr(VI) species was not detected in the samples under study.     

Inter and intra-species-related differences in the regulation of the cardiac autonomic system

The heart rate response to isoproterenol (HR-Iso), density and affinity (k_d) of β-adrenergic (β-AR) and muscarinic (M₂) receptors were compared among three rodents with different generation-life histories of confinement and of high altitude exposure. The European guinea pig (Cavia porcellus) (EGp), a laboratory animal that arrived in Europe after the Spanish Conquest of South America and the Peruvian guinea pig (C. porcellus) (PGp), a semi-wild animal that came from the altiplano to sea level at least 25 generations ago, were used for intra-species comparison. Wistar rats (WR) were used for inter-species comparison as representative of a typical sea level laboratory animal. The HR-Iso was lower in EGp than in the PGp. The PGp showed the highest β-AR density (P<0.0005) and the highest β-AR k_d values (P<0.0005) when compared to both EGp and WR groups (β-AR B_max (fmol mg⁻¹ prot), WR, 19±4; Egp, 34±10; PGp, 74±15. β-AR k_d (pM), WR, 24±10; Egp, 17±7; PGp, 39±14). In contrast, PGp showed lower M₂ receptor density values than the EGp (P<0.0005). The WR had the highest M₂ receptor densities (M₂ B_max (fmol mg⁻¹ prot), WR, 188±15; Egp, 147±9; PGp, 118±6 and M₂ k_d (pM), WR, 65±12; Egp, 67±6; PGp, 92±2). The inter and intra-species differences found may be related to their respective history of confinement rather than to their history of exposure to high altitude.     

Recent Arctic marine diatom assemblages from bottom sediments in Baffin Bay and Davis Strait

This study investigates the present geographical boundaries and environmental limits of the diatom flora in the Baffin Bay and Davis Strait area. Seventy-four sea floor surface samples were examined. The raw data were analyzed with the CABFAC factor analysis program. Five factor assemblages, explaining 87% of the observed variance, emerged from this test. The statistically most important assemblage is the “Baffin Current assemblage”, composed ofThalassiosira gravida spores. The second assemblage is the “summer pack ice assemblage”, consisting ofActinocyclus curvatulus, with a lesser contribution ofThalassiosira trifulta. A third assemblage, dominated byThalassiosira hyalina, is located along the southwest coast of Greenland, indicating low ice concentration. The fourth assemblage consists ofPorosira sp. spores and indicates fast ice conditions. The fifth assemblage is dominated byThalassionema nitzschioides andPorosira glacialis (vegetative cells), and indicates the coastal environment. Diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses, such as salinity and ice conditions. These findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments.     

Fasting metabolism in Antarctic fur seal (Arctocephalus gazella) pups

The metabolism of 52–73-day old Antarctic fur seal pups from Bird Island, South Georgia, was investigated during fasting periods of normal duration while their mothers were at sea foraging. Body mass decreased exponentially with pups losing 3.5–3.8% of body mass per day. Resting metabolic rate also decreased exponentially from 172–197 ml (O₂)·min⁻¹ at the beginning of the fast and scaled to M_b^0.74 at 2.3 times the level predicted for adult terrestrial mammals of similar size. While there was no significant sex difference in RMR, female pups had significantly higher (F_1,18=6.614, P<0.019) mass-specific RMR than male pups throughout the fasting period. Fasting FMR was also significantly (t₁₅=2.37, P<0.035) greater in females (823 kJ·kg⁻¹·d⁻¹) than males (686 kJ·kg⁻¹·d⁻¹). Average protein turnover during the study period was 19.3 g·d⁻¹ and contributed to 5.4% of total energy expenditure, indicating the adoption of a protein-sparing strategy with a reliance on primarily lipid catabolism for metabolic energy. This is supported by observed decreases in plasma BUN, U/C, glucose and triglyceride concentrations, and an increase in β-HBA concentration, indicating that Antarctic fur seals pups adopt this strategy within 2–3 days of fasting. Mean RQ also decreased from 0.77 to 0.72 within 3 days of fasting, further supporting a rapid commencement of protein-sparing. However, RQ gradually increased thereafter to 0.77, suggesting a resumption of protein catabolism which was not substantiated by changes in plasma metabolites. Female pups had higher TBL (%) than males for any given mass, which is consistent with previous findings in this and other fur seal species, and suggests sex differences in metabolic fuel use. The observed changes in plasma metabolites and protein turnover, however, do not support this.     

“Too low” δO of paleo-meteoric, low latitude, water; do paleo-tropical cyclones explain it?

Isotopic analysis of rock samples showed anomalously ¹⁸O-depleted reconstructed isotopic composition of paleo-meteoric water over southern Israel between the Late Cretaceous and the Early Miocene, with δ¹⁸O_W as low as −14‰ [SMOW]. This range is significantly “lighter” than the expected values for rain at the relevant paleo-latitudes (~ 8^°N to 25^°N). It is similar or lighter than areas with meteoric water at the present climate, in which rainfall contribution from tropical cyclone (TC) is significant. Rainfall from TCs is ¹⁸O-depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles. A paleo-geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area. Thus, TCs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east. The reconstructed composition of the rainwater implies dominance of TCs at these times. Furthermore, the combination of warmer seas and lighter rainwater than at present suggests that the TCs were more dominant than in the most TC-prone coastal areas at the present climate. The results of the present study suggest that climate during the relevant time periods was very different from the present, with TC activity similar or exceeding the most TC prone locations in the world at the present climate. This might also hint that warmer sea waters in the geological past were conducive to greater TC activity than in the present climate. Answering this question requires additional research.