This Week in Science

Science  29 Nov 1996:
Vol. 274, Issue 5292, pp. 1441
  1. Pool moves

    The western equatorial Pacific Ocean is characterized by the warm pool, a region of higher sea surface temperatures. The warm pool drives the world's most intense atmospheric convection, and the migration of its eastern edge is an essential feature of the El Niño-Southern Oscillation. Picaut et al. (p. 1486) investigated the migration mechanism by deriving near-surface and surface current fields from buoy and satellite data, in combination with ocean model studies. Evidence for zonal convergence of water masses and a well-defined salinity front at the eastern edge of the warm pool was obtained, showing that zonal advection dominates the migration. The warm pool, composed of low-density fresher and warm water, is relatively isolated from the surrounding Pacific, explaining why it can easily be displaced by wind-driven currents

  2. Ice on the moon?

    The Clementine spacecraft performed a bistatic radar experiment to identify the structure and composition of the lunar poles. Nozette et al. (p. 1495) believe that the same-sense polarization enhancement of the radar echo they observed in the permanently shadowed regions of the south pole are caused by the presence of ice, possibly mixed or covered with the rocky regolith. Although icy patches may not provide a unique solution for the radar signal, the authors suggest a mechanism for their presence: Volatiles, which degassed from the proto-moon or were brought in by comets, condensed and concentrated in the permanently shadowed patches of the lunar poles.

  3. Fast, tiny dust

    The cosmic dust detector on board the Ulysses spacecraft detected 11 streams of dust before, during, and after its closest approach to Jupiter in 1991 and 1992, most of which appear to emanate from the direction of Jupiter. Zook et al. (p. 1501) simulated the trajectory of the particles that impacted the detector backward in time to a specified point of origin near Jupiter and found that those dust grains that fit their model had to be faster and much smaller than had been previously thought. These simulations provide a more accurate estimate of the particle characteristics and indicate the strong influence the solar magnetic field can have on accelerating jovian dust grains away from their source.

  4. Open-ocean climate record

    Detailed climate records covering the last several hundred to thousand years are needed to provide a base line with which to evaluate the effects of anthropogenic emissions on climate. Although there are several detailed records available on land (ice cores, for example), records for the open oceans have been difficult to obtain because a core with a high sedimentation rate is required. Keigwin (p. 1504) now describes a record from the Sargasso Sea that has sufficient resolution. The record shows that sea surface temperatures were about 1oC cooler than today during the Little Ice Age (about 400 years ago) and about 1oC warmer than today during the Medieval Warm Period (about 1000 years ago).

  5. Carbohydrate library

    Cell surface carbohydrates play an important role in biological recognition processes. Screening strategies to identify carbohydrate derivatives that bind to particular protein targets are hampered, however, by the synthetic difficulties because, unlike peptides and nucleic acids, stereochemistry must be controlled as monomers are added to a carbohydrate chain. Liang et al. (p. 1520) describe the use of anomeric sulfoxides to produce a solid-phase library of about 1300 di- and trisaccharides. They identified two ligands that bind more strongly to the Bauhinia purpurea lectin than does the natural ligand.

  6. Special delivery

    Fertilization in higher plants depends on growth of the pollen tube, through which sperm cells are delivered to the ovule. Wilhelmi and Preuss (p. 1535) have identified two genes in Arabidopsis that, when mutated, disrupt the guidance mechanisms that direct each pollen tube to an available ovule. That both pollen and pistil tissue must carry the mutant genes in order for guidance to be disrupted suggests the genes may encode molecules that mediate cell-cell adhesion.

  7. Snail neurotrophic factor

    The existence of substances in mollusks that promote neuronal growth has been controversial. Fainzilber et al. (p. 1540) describe the isolation of a peptide from snails that can cause neuronal sprouting and growth. The new factor binds to one of the mammalian neurotrophic factor receptors—known as p75—but the factor itself shows no homology to any previously identified neurotrophins.

  8. T cell turnover in HIV-1 infection

    One theory for why CD4+ cell counts decline during the course of HIV-1 (human immunodeficiency virus-type 1) infection is that rapid turnover in the effort to replace these T cells exhausts their regeneration capacity. If so, then one would expect that the length of telomeres, the structures at the ends of chromosomes, would decrease in CD4+ cells over time. Wolthers et al. (p. 1543) examined telomere length in CD8+ and CD4+ cells from samples obtained over a several year period in HIV+ individuals and found that while telomere lengths decreased in CD8+ cells, there was no significant change in CD4+ cells. This difference was not caused by some change in telomere processing, as CD4+ cells from these individuals did show decreases in telomere length after division in cell culture. These results suggest that HIV-1 infection may interfere with cell renewal in CD4+ cells.

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