Below- and Aboveground Spartina alterniflora Production in a Louisiana Salt Marsh

The monthly variations of below- and aboveground biomass of Spartina alterniflora were documented for a south Louisiana salt marsh from March 2004 to March 2005, and in March 2006 and 2007. The annual production rate above- and belowground was 1821 and 11,676 g m^?2, respectively (Smalley method), and the annual production rate per biomass belowground was 10.7 g dry weight^?1, which are highs along the latitudinal distributions of the plant’s range. The average root + rhizome/shoot ratio (R&R/S) was 2.6:1, which is lower than the R&R/S ratios of 4 to 5.1 reported for Spartina sp. marshes in the northeastern US. The belowground biomass increased from July to September and fluctuated between October and November, after which it declined until February when the growing season began. The belowground biomass was dominated by rhizomes, which declined precipitously in spring and then rose to a seasonal high in the month before declining again as the late summer rise in inflorescence began. Over half of the root biomass in a 30-cm soil profile was in the upper 10 cm, and in the 10- to 20-cm profile for rhizomes. The maximum March biomass above- and belowground was four to five times that of the minimum biomass over the four sampling years. The net standing stock (NSS) of N and P in live biomass aboveground compared to that in the belowground biomass was about 1.7 times higher and equal, respectively, but the NSS of N and P for the live + dead biomass was about six times higher belowground. The average nitrogen/phosphorous molar ratios of 16:1 aboveground is in agreement with the often tested N limitation of biomass accumulation aboveground, whereas the 37:1 belowground ratio suggests that there is an influence of P on R&R foraging for P belowground. Some implications for management and restoration are, in part, that salt marshes should be evaluated and examined using information on the plant’s physiology and production both below- and aboveground.     

A high resolution relative paleointensity record from the Gerlache-Boyd paleo-ice stream region, northern Antarctic Peninsula

Herein we document and interpret an absolute chronological dating attempt using geomagnetic paleointensity data from a post-glacial sediment drape on the western Antarctic Peninsula continental shelf. Our results demonstrate that absolute dating can be established in Holocene Antarctic shelf sediments that lack suitable material for radiocarbon dating. Two jumbo piston cores of 10-m length were collected in the Western Bransfield Basin. The cores preserve a strong, stable remanent magnetization and meet the magnetic mineral assemblage criteria recommended for reliable paleointensity analyses. The relative paleomagnetic intensity records were tuned to published absolute and relative paleomagnetic stacks, which yielded a record of the last ∼8500 years for the post-glacial drape. Four tephra layers associated with documented eruptions of nearby Deception Island have been dated at 3.31, 3.73, 4.44, and 6.86 ± 0.07 ka using the geomagnetic paleointensity method. This study establishes the dual role of geomagnetic paleointensity and tephrochronology in marine sediments across both sides of the northern Antarctic Peninsula.     

Contributions of Fuqing ZHANG to Predictability,Data Assimilation,and Dynamics of High Impact Weather: A Tribute

This article reviews Fuqing ZHANG’s contributions to mesoscale atmospheric science,from research to mentoring to academic service,over his 20-year career.His fundamental scientific contributions on predictability,data assimilation,and dynamics of high impact weather,especially gravity waves and tropical cyclones,are highlighted.His extremely generous efforts to efficiently transmit to the community new scientific knowledge and ideas through mentoring,interacting,workshop organizing,and reviewing are summarized.Special appreciation is given to his tremendous contributions to the development of mesoscale meteorology in China and the education of Chinese graduate students and young scientists.     

Ecosystem history of Mississippi River-influenced continental shelf revealed through preserved phytoplankton pigments

Pigments determined by high performance liquid chromatography (HPLC) provide useful information concerning water column and epibenthic plant and microbial communities in both extant communities and accumulated sediments in lakes, estuaries and the ocean. Chlorophyll and its degradation products provide an estimate of overall biomass, and carotenoid pigments provide taxonomic biomarkers of phytoplankton. We examined the pigments preserved in sediment cores from the Louisiana continental shelf adjacent to the outflow of the Mississippi River system to document changes in phytoplankton community composition, phytoplankton abundance, and conditions of hypoxia over time. Carbon accumulated in sediments from water depths of 20-60 m is primarily derived from marine phytoplankton and represents the history of phytoplankton communities in the overlying water. There is a general increase in chlorophyll a, pheopigments, zeaxanthin, fucoxanthin and most carotenoids over time, with the change gradual from 1955 to 1970, followed by a fairly steady increase to 1997. The highest chloropigment concentrations are in cores from areas more likely to be exposed to seasonal hypoxia. These indicate an increase in eutrophication in the form of greater diatom and cyanobacterial production, or a worsening of hypoxia, or both. This trend expanded westward along the Louisiana shelf in the 1990s.     

Seasonal distribution of rainfall in Australia analysed by Fourier methods

Summary A harmonic or Fourier analysis of mean monthly rainfall data is found useful in objectively describing and mapping the seasonality of rainfall within Australia. Over large areas the seasonal component is well described by the first and second harmonic terms, leaving as a residual variance only a small proportion of the observed total variance. Care must be taken in the interpretation of second harmonic contributions within those areas of tropical Australia under strong monsoonal influences. This is because pecularities in the form of the annual rainfall regime make the first harmonic term inadequate in itself to fully describe the annual trend. The technique is found particularly useful in defining the boundaries of areas of similar seasonality, and maps based upon the first and second harmonic amplitudes are shown to bear a close relationship with known physical controls.

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Zusammenfassung Zur objektiven Beschreibung der jahreszeitlichen Schwankung der Regenfälle in Australien und ihrer kartenmäßigen Darstellung wird mit Erfolg die harmonische Analyse der mittleren Monatsmengen des Niederschlags angewendet. Über weiten Gebieten wird die jahreszeitliche Schwankung durch die ersten beiden harmonischen Schwingungen gut dargestellt; die Reststreuung macht nur einen kleinen Bruchteil der beobachteten Gesamtstreuung aus. Vorsicht erscheint jedoch geboten bei der Interpretation des Anteils der zweiten Harmonischen in den Gebieten des tropischen Australien, die unter starkem Monsuneinfluß stehen. Hier machen Besonderheiten im Niederschlagsregime selbst die erste Harmonische ungenügend zur Beschreibung des Jahresganges. Die angewandte Methode ist besonders geeignet, die Grenzen zwischen Gebieten mit gleichartigem Jahreszeiteneinfluß festzulegen. Karten, die auf der ersten und zweiten harmonischen Schwingung beruhen, zeigen einen engen Zusammenhang mit bekannten physikalischen Faktoren.

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Résumé Afin de décrire objectivement les variations saisonnières des précipitations en Australie, on se sert avantageusement de l'analyse harmonique des sommes mensuelles moyennes. Cette méthode est également utilisée pour la représentation cartographique des dites variations. Les amplitudes saisonnières sont bien rendues par les deux premières harmoniques et cela pour de grandes étendues. L'amplitude qui reste ne représente qu'une faible fraction de l'amplitude totale observée. Il faut cependant procéder avec prudence lors de l'interprétation de la part revenant à la seconde harmonique dans les contrées tropicales de l'Australie, contrées qui subissent fortement l'influence de la mousson. Dans ce cas précis, les particularités du régime des précipitations ne permettent même pas d'utiliser la première harmonique pour décrire l'évolution des pluies au cours de l'année. La méthode proposée est surtout intéressante pour délimiter les régions soumises aux mêmes régimes. Des cartes basées sur la première et la seconde harmonique montrent un rapport étroit entre les précipitations et certains facteurs physiques connus.

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With 9 Figures     

Intraseasonal and interannual climate variability

Major advances in our understanding of intraseasonal-interannual climate variability during the past three decades are reviewed. Prospects for prediction on these time-scales are briefly discussed.Paper based on talk presented at the session honoring J. Murray Mitchell at the December 1986 AGU meeting in San Francisco, CA.     

Rare-Earth Element Reference Samples for Electron Microprobe Analysis

Fourteen rare-earth (plus scandium and yttrium) orthophosphates have been synthesized and characterized for use as electron microprobe reference samples. These reference samples are single-element phosphates that are homogeneous, stable under the electron beam, and free of interfering elements. They have a stoichiometric composition (RPO4) with the element of interest (R) ranging from 32 to 64 weight percent.     

Tide gauge records,water level rise,and subsidence in the Northern Gulf of Mexico

Long-term water level changes in the northern Gulf of Mexico were examined using tide gauge records for this century. Strong coherence exists between the annual mean water changes at Galveston, Texas, and (1) the relatively geologically-stable west coast of Florida, (2) global mean sea level, and 93) the subsiding Louisiana coast. Water levels at the Galveston gauge, one of the longest records (81 yr), have risen steadily, but not accelerated over the long-term. The apparent acceleration of water rise in the recent two decades is within the historical pattern, and is probably driven by regional or global, but not local climatic factors. Because eustatic sea level has risen steadily this century, the analysis supports the conclusion that regional geologic subsidence has not varied significantly over the tide gauge record (1909–1988). Variations in the estimates of subsidence in the surface layers are generally consistent with the generally accepted understanding of the geology of deltaic processes on this coast.