ALBERT

Description: A new 30-arc second resolution global topography/bathymetry grid (SRTM30_PLUS) has been developed from a wide variety of data sources. Land and ice topography comes from the SRTM30 and ICESat topography, respectively. Ocean bathymetry is based on a new satellite-gravity model where the gravity-to-topography ratio is calibrated using 298 million edited soundings. The main contribution of this study is the compilation and editing of the raw soundings, which come from NOAA, individual scientists, SIO, NGA, JAMSTEC, IFREMER, GEBCO, and NAVOCEANO. The gridded bathymetry is available for ftp download in the same format as the 33 tiles of SRTM30 topography. There are 33 matching tiles of source identification number to convey the provenance of every grid cell. The raw sounding data, converted to a simple common format, are also available for ftp download.

Description: Data from New Zealand and northern Victoria Land, Antarctica, indicate that the Cambrian Takaka Terrane intra-oceanic arc/backarc assemblage and the Bowers Terrane intra-oceanic arc/back-arc assemblage were accreted to the Gondwana margin by the Late Cambrian. Compelling similarities between the arc rocks and the immediate post-arc sediments firmly place the two regions in the same tectonic framework and imply close paleogeographic proximity. Currently, the Ross Orogen is thought to be the result of sinistral oblique convergence with west-directed subduction, and accretion of the arc assemblages is attributed to closure of backarc basins. Syntectonic fluvial conglomerates in both regions attest to the development of fluvial systems draining both the accreted arc and the contemporaneous continental margin arc. Trilobite faunas indicate that fluvial sedimentation commenced earlier in New Zealand than in northern Victoria Land. In the context of the widely accepted sinistral oblique convergence model, these data suggest an original position for New Zealand to the south of northern Victoria Land, probably in the region of the southern Ross Sea.

Description: The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006SAMUMfield campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers.

Description: The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.

Description: The NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), is used to study the atmospheric response from the surface to the lower thermosphere to changes in solar and geomagnetic forcing over the 11-year solar cycle. WACCM3 is a general circulation model that incorporates interactive chemistry that solves for both neutral and ion species. Energy inputs include solar radiation and energetic particles, which vary significantly over the solar cycle. This paper presents a comparison of simulations for solar cycle maximum and solar cycle minimum conditions. Changes in composition and dynamical variables are clearly seen in the middle and upper atmosphere, and these in turn affect terms in the energy budget. Generally good agreement is found between the model response and that derived from satellite observations, although significant differences remain. A small but statistically significant response is predicted in tropospheric winds and temperatures which is consistent with signals observed in reanalysis data sets.

Description: The behaviour of Chelophyes has been analysed from the point of view of coordination between stem and nectophores, and an electron microscope study of the effectors and conducting elements has been carried out. Coordination between the stem and anterior nectophore involves two pathways, one epithelial and the other nervous. The nervous link consists of a bundle of small neurites and a single giant axon. There is some evidence that this mediates rapid escape behaviour. After the nerves have been cut, coordination is maintained via the epithelial route. Impulses can jump from epithelial cells into nerves but the transmission process is unclear. Neuro‐epithelial transmission involves conventional synapses. As in physonectid siphonophores, the stem has two nervous systems each with its own giant fibre, and a slow system, the endodermal epithelium. In the nectophore, marginal nerve centres generate a swimming rhythm. Conduction in the subumbrellar muscle is myoid. The exumbrellar epithelium and the subumbrellar endoderm are conducting tissues. Histological study reveals synapses in the predicted locations and gives details of myo‐epithelial organization and nervous layout. Novel histological features include elements resembling steroid‐secreting cells, which ensheath nerves and are innervated by them, and innervated giant non‐nervous cells lying between the nerve ring and the hydroecium. The subumbrellar muscle cells are shown to have sarcolemmal invaginations reminiscent of the f‐tubule system of vertebrate muscle.

Description: Application of biogeochemical models to the study of marine ecosystems is pervasive, yet objective quantification of these models' performance is rare. Here, 12 lower trophic level models of varying complexity are objectively assessed in two distinct regions (equatorial Pacific and Arabian Sea). Each model was run within an identical one-dimensional physical framework. A consistent variational adjoint implementation assimilating chlorophyll-a, nitrate, export, and primary productivity was applied and the same metrics were used to assess model skill. Experiments were performed in which data were assimilated from each site individually and from both sites simultaneously. A cross-validation experiment was also conducted whereby data were assimilated from one site and the resulting optimal parameters were used to generate a simulation for the second site. When a single pelagic regime is considered, the simplest models fit the data as well as those with multiple phytoplankton functional groups. However, those with multiple phytoplankton functional groups produced lower misfits when the models are required to simulate both regimes using identical parameter values. The cross-validation experiments revealed that as long as only a few key biogeochemical parameters were optimized, the models with greater phytoplankton complexity were generally more portable. Furthermore, models with multiple zooplankton compartments did not necessarily outperform models with single zooplankton compartments, even when zooplankton biomass data are assimilated. Finally, even when different models produced similar least squares model-data misfits, they often did so via very different element flow pathways, highlighting the need for more comprehensive data sets that uniquely constrain these pathways.