Sea-surface temperature from coral skeletal strontium/calcium ratios

Seasonal records of tropical sea-surface temperature (SST) over the past 10(5) years can be recovered from high-precision measurements of coral strontium/calcium ratios with the use of thermal ionization mass spectrometry. The temperature dependence of these ratios was calibrated with corals collected at SST recording stations and by (18)O/(16)O thermometry. The results suggest that mean monthly SST may be determined with an apparent accuracy of better than 0.5 degrees C. Measurements on a fossil coral indicate that 10,200 years ago mean annual SSTs near Vanuatu in the southwestern Pacific Ocean were about 5 degrees C colder than today and that seasonal variations in SST were larger. These data suggest that tropical climate zones were compressed toward the equator during deglaciation.     

Strontium Uptake in Shell Aragonite from the Freshwater Gastropod Limnaea stagnalis

Shell aragonite from 96 specimens of the freshwater gastropod Limnaea stagnalis grown in laboratory tanks at different temperatures in water with variable strontium/calcium ratios have been analyzed for its strontium content in order to evaluate the mechanisms of strontium uptake in molluskan aragonite. Within the limits defined by natural freshwater environments, the strontium/calcium ratio in the aragonite was found to be linearly related to the strontium/calcium ratio in the water. A distribution coefficient k(A)(Sr) = 0.237 +/- 0.029, unaffected by variations in temperature and growth rate, has been found. This finding substantiates the existence of a strontium-discriminating effect in aragonite precipitated by mollusks as compared to the case for nonbiogenic aragonite which contains about five times as much strontium when precipitated under the same conditions.     

Gas-phase inorganic chemistry: monovalent derivatives of calcium and strontium

The chemistry and spectroscopy of monovalent derivatives of calcium and strontium are described. Laser-driven chemical reactions of calcium and strontium vapors with a variety of small molecules have provided many new free radicals. In general, these species are analogous to the stable molecules obtained in traditional inorganic or organometallic chemistry, but some new families of molecules have been discovered.     

A transient rise in tropical sea surface temperature during the Paleocene-Eocene thermal maximum

The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8 degrees to 10 degrees C) and in bottom water temperatures (4 degrees to 5 degrees C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4 degrees to 5 degrees C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.     

Climate impact of late quaternary equatorial pacific sea surface temperature variations

Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8 degrees +/- 0.7 degrees C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5 degrees C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.     

The mid-Pleistocene transition in the tropical Pacific

A sea surface temperature (SST) record based on planktonic foraminiferal magnesium/calcium ratios from a site in the western equatorial Pacific warm pool reveals that glacial-interglacial oscillations in SST shifted from a period of 41,000 to 100,000 years at the mid-Pleistocene transition, 950,000 years before the present. SST changes at both periodicities were synchronous with eastern Pacific cold-tongue SSTs but preceded changes in continental ice volume. The timing and nature of tropical Pacific SST changes over the mid-Pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time.     

Abrupt decrease in tropical Pacific sea surface salinity at end of Little Ice Age

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific.     

Strontium-calcium thermometry in coral skeletons

The strontium to calcium ratio of skeletal aragonite in three genera of reef-building corals varies as a simple function of temperature and the strontium to calcium ratio of the incubation water. The strontiumlcalcium distribution coefficients of coral aragonite apparently differ from the corresponding coefficient of inorganically precipitated aragonite. With some care, coral skeletons can be used as recording thermometers.     

Strontium induced rickets: metabolic basis

Dietary strontium inhibits both the synthesis of 1,25-dihydroxycholecalciferol and intestinal calcium absorption in vitamin D(3)-repleted chicks. 1,25-Dihydroxycholecalciferol restores calcium absorption to normal, while 25-hydroxycholecalciferol is without effect in the strontium-fed chick. It is suggested that strontium induces rickets by blocking the biosynthesis of 1,25-dihydroxycholecalciferol, the metabolically active form of vitamin D in the intestine.     

Clams As recorders of ocean ridge volcanism and hydrothermal vent field activity

The clam Calyptogena magnifica lives at abyssal depths in association with hydrothermal venting on midocean ridges. Analysis of strontium/calcium ratios in C. magnifica shells provides a temperature proxy with submonthly time resolution. A 21-year strontium/calcium record of two clams from 9 degrees50'N on the East Pacific Rise captures the known 1991 and 1992 eruptive events, documents several additional events between 1992 and 1996, and demonstrates the absence of major hydrothermal episodes during the period 1974 to 1991. These clam archives can increase our understanding of the thermal and chemical history of midocean ridge hydrothermal and volcanic activity on decadal time scales.     

Strontium accumulation by sarcoplasmic reticulum and mitochondria in vascular smooth muscle

Electron-opaque deposits of strontium were observed in the sarcoplasmic reticulum and in mitochondria of spontaneously contracting vascular smooth muscles that had been incubated in a strontium-containing solution prior to fixation. The deposits were present in those elements of the sarcoplasmic reticulum that are in close contact with the surface membrane and also in more centrally located portions. In vascular smooth muscle that does not contract spontaneously, similar deposits of strontium were only seen if the muscle was depolarized during or glycerinated before exposure to the strontium-containing solution. Strontium was also deposited in the sarcoplasmic reticulum of the endothelium. It is suggested that translocation of calcium from the sarcoplasmic reticulum that is in close contact with the surface membrane, and now shown to accumulate divalent cations, is responsible for the action potential-triggered contractions of rabbit and guinea pig mesenteric veins. Strontium may also be a suitable marker for identifying sites that accumulate calcium in other types of cells in which translocation of calcium plays a major regulatory function.     

Strontium incorporation into dental enamel

Rats were raised on diets either rich or poor in strontium. Powder x-ray diffraction patterns suggest that isomorphous substitution of strontium for calcium occurs in the apatite of tooth enamel, and that strontium may form Sr(6)H(3)(PO(4)) * 2H(2)O, a compound hitherto unreported in biologic systems.     

Calcium absorption and calcium-binding protein synthesis: solanum malacoxylon reverses strontium inhibition

The ingestion of diets containing high concentrations of stable strontium inhibits calcium absorption and intestinal calcium-binding protein synthesis and, as shown by others, does so by inhibiting the conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol, the active form of vitamin D. The addition of the South American plant Solanum malacoxylon to strontium-containing diets counteracts the inhibitory action of dietary strontium, thereby indicating that the plant contains a factor which can mimic the action of 1,25-dihydroxycholecalciferol and representing the first such factor identified in a botanical source.     

Anomalous scattering study of the bi distribution in the 2212 superconductor: implications for cu valency

The distribution of the bismuth atoms over the cation sites in the 2212 Bi-Sr-Ca-Cu-O superconductor has been determined by anomalous scattering synchrotron crystallography. The analysis of reflection pairs measured at wavelengths of 0.9243 and 0.9600 angstrom shows a delocalization of the bismuth atoms over the calcium and strontium sites. The "mixed" plane between the CuO(2) layers contains 6.0(1.4) percent bismuth (where the number in brackets represents the statistical standard deviation derived from the least-squares refinement of the data), and a much smaller amount of strontium than often assumed. The strontium deficiency is charge-compensated by the creation of electron holes in the CuO(2) layer. The result supports the view that neither extra oxygen nor overlap of the bismuth 6p and copper 3d bands is needed to account for the holes, which are an essential feature of the superconductivity mechanism.     

Imaging powders with the atomic force microscope: from biominerals to commercial materials

Atomically resolved images of pressed powder samples have been obtained with the atomic force microscope (AFM). The technique was successful in resolving the particle, domain, and atomic structure of pismo clam (Tivela stultorum) and sea urchin (Strongylocentrotus purpuratus) shells and of commercially available calcium carbonate (CaCO(3)) and strontium carbonate (SrCO(3)) powders. Grinding and subsequent pressing of the shells did not destroy the microstructure of these materials. The atomic-resolution imaging capabilities of AFM can be applied to polycrystalline samples by means of pressing powders with a grain size as small as 50 micrometers. These results illustrate that the AFM is a promising tool for material science and the study of biomineralization.     

El Niño-like pattern in ice age tropical Pacific sea surface temperature

Sea surface temperatures (SSTs) in the cold tongue of the eastern equatorial Pacific exert powerful controls on global atmospheric circulation patterns. We examined climate variability in this region from the Last Glacial Maximum (LGM) to the present, using a SST record reconstructed from magnesium/calcium ratios in foraminifera from sea-floor sediments near the Galápagos Islands. Cold-tongue SST varied coherently with precession-induced changes in seasonality during the past 30,000 years. Observed LGM cooling of just 1.2 degrees C implies a relaxation of tropical temperature gradients, weakened Hadley and Walker circulation, southward shift of the Intertropical Convergence Zone, and a persistent El Ni?o-like pattern in the tropical Pacific. This is contrasted with mid-Holocene cooling suggestive of a La Ni?a-like pattern with enhanced SST gradients and strengthened trade winds. Our results support a potent role for altered tropical Pacific SST gradients in global climate variations.     

Strontium-calcium movement from soil to man

The calcium reservoirs of the biosphere are becoming labeled to varying degrees with strontium-90 from nuclear weapons. These reservoirs include the human and animal skeleton, the milk, the vegetation, the upper layers of soil, and the waters. The degree of labeling is governed by the dilution that occurs, or the differential behavior of calcium and strontium in various steps of the food chain. This differential behavior normally provides a factor of protection against strontium-90 in the soil and vegetation that may be as high as 25 for the newborn and is most likely not less than 6 for adults, depending on food habits. The physiological steps that are important in the movement of the two elements in the biosphere are described to provide a basis for an approach toward increase of the discrimination against strontium in favor of calcium. Some aspects of agricultural practices are discussed from this standpoint. The matter of hazard from levels now existing and the present need to undertake remedial measures are not discussed, in major part because of lack of experimental data on which to base such considerations.     

Strontium uptake in rats on alginate-supplemented diet

Rats were fed a basic diet supplemented with sodium alginate and with tracer amounts of strontium-85 and calcium-45. Absorption of strontium was always inhibited by the alginate to a greater extent than absorption of calcium. Discrimination against strontium was greatest in alginate containing a high proportion of guluronic acid.     

Coral record of equatorial sea-surface temperatures during the penultimate deglaciation at huon peninsula

Uplifted coral terraces at Huon Peninsula, Papua New Guinea, preserve a record of sea level, sea-surface temperature, and salinity from the penultimate deglaciation. Remnants have been found of a shallow-water reef that formed during a pause, similar to the Younger Dryas, in the penultimate deglaciation at 130,000 +/- 2000 years ago, when sea level was 60 to 80 meters lower than it is today. Porites coral, which grew during this period, has oxygen isotopic values and strontium/calcium ratios that indicate that sea-surface temperatures were much cooler (22 degrees +/- 2 degreesC) than either Last Interglacial or present-day tropical temperatures (29 degrees +/- 1 degreesC). These observations provide further evidence for a major cooling of the equatorial western Pacific followed by an extremely rapid rise in sea level during the latter stages of Termination II.     

Dynamical response of the tropical Pacific Ocean to solar forcing during the early Holocene

We present a high-resolution magnesium/calcium proxy record of Holocene sea surface temperature (SST) from off the west coast of Baja California Sur, Mexico, a region where interannual SST variability is dominated today by the influence of the El Ni?o-Southern Oscillation (ENSO). Temperatures were lowest during the early to middle Holocene, consistent with documented eastern equatorial Pacific cooling and numerical model simulations of orbital forcing into a La Ni?a-like state at that time. The early Holocene SSTs were also characterized by millennial-scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability, with inferred solar minima corresponding to El Ni?o-like (warm) conditions, in apparent agreement with the theoretical "ocean dynamical thermostat" response of ENSO to exogenous radiative forcing.