Strong hydrographic controls on spatial and seasonal variability of dissolved organic carbon in the Chukchi Sea

A detailed analysis of dissolved organic carbon (DOC) distribution in the Western Arctic Ocean was performed during the spring and summer of 2002 and the summer of 2003. DOC concentrations were compared between the three cruises and with previously reported Arctic work. Concentrations of DOC were highest in the surface water where they also showed the highest degree of variability spatially, seasonally, and annually. Over the Canada Basin, DOC concentrations in the main water masses were: (1) surface layer (71±4 μM, ranging from 50 to 90 μM); (2) Bering Sea winter water (66±2 μM, ranging from 58 to 75 μM); (3) halocline layer (63±3 μM, ranging from 59 to 68 μM), (4) Atlantic layer (53±2 μM, ranging from 48 to 57 μM), and (5) deep Arctic layer (47±1 μM, ranging from 45 to 50 μM). In the upper 200 m, DOC concentrations were correlated with salinity, with higher DOC concentrations present in less-saline waters. This correlation indicates the strong influence that fluvial input from the Mackenzie and Yukon Rivers had on the DOC system in the upper layer of the Chukchi Sea and Bering Strait. Over the deep basin, there appeared to be a relationship between DOC in the upper 10 m and the degree of sea-ice melt water present. We found that sea-ice melt water dilutes the DOC signal in the surface waters, which is contrary to studies conducted in the central Arctic Ocean.     

The natural basis of the formation of the dual-nuclei structural model

The dual-nuclei spatial structure is composed of a regional central city, a port city and their spatial relations in certain regions. In general, this spatial structure could be found in most of the coastal regions or regions along big rivers. In terms of the mechanism, the dual-nuclei structure is the result of the spatial interaction and the complementary characteristics of the center city and the port city. The "marginal function" of the port city and its relationship with the central city has long been discussed in the literature. On the one hand, drainage area is the main natural geographical background of the formation of the dual-nuclei spatial structure; therefore, we can build a theoretical geographic structure that is based on the drainage area. On the other hand, vicissitude of the coastline also has important influence on the formation of the dual-nuclei spatial structure. It is especially meaningful if we can notice this when we examine deeply the research on the spatial structure of delta.     

Social Attitudes Predict Biases in Geographic Knowledge*

Three principal components were found to underlie Texas university students' experiences with and attitudes toward Canada, the United States, and Mexico: diversity orientation, Mexican experiences, and Canadian experiences. Diversity orientation included positive attitudes toward Hispanics, Canadians, minorities, interethnic friendships, and dating and was negatively correlated with natio‐centrism (e.g., believing U.S. citizens receive the world's best education). Diversity orientation and natio‐centrism were not related to experiences with Mexico or Canada. Students estimated the locations of Canadian cities too far north and Mexican cities too far south. Biased estimates for Mexican cities were negatively correlated with diversity orientation, not experience with Mexico.     

Evaluation of Hydrologically Relevant PCM Climate Variables and Large-Scale Variability over the Continental U.S.

The ability of the Parallel Climate Model (PCM) to reproduce the mean and variability of hydrologically relevant climate variables was evaluated by comparing PCM historical climate runs with observations over temporal scales from sub-daily to annual. The domain was the continental U.S, and the model spatial resolution was T42 (about 2.8 degrees latitude by longitude). The climate variables evaluated include precipitation, surface air temperature, net surface solar radiation, soil moisture, and snow water equivalent. The results show that PCM has a winter dry bias in the Pacific Northwest and a summer wet bias in the central plains. The diurnal precipitation variation in summer is much stronger than observed, with an afternoon maximum in summer precipitation over much of the U.S. interior, in contrast with an observed nocturnal maximum in parts of the interior. PCM has a cold bias in annual mean temperature over most of the U.S., with deviations as large as ?8 K. The PCM daily temperature range is lower than observed, especiallyin the central U.S. PCM generally overestimates the net solar radiation over most of the U.S, although the diurnal cycle is simulated well in spring, summer and winter. In autumn PCM has a pronounced noontime peak in solar radiation that differs by 5–10% from observations. PCM'ssimulated soil moisture is less variable than that of a sophisticated land-surface hydrology model, especially in the interior of the country. PCM simulates the wetter conditions over the southeastern U.S. and California during warm (El Niño) events, but shifts the drier conditions in the PacificNorthwest northward and underestimates their magnitude. The temperature response to the North Pacific Oscillation is generally captured by PCM, but the amplitude of this response is overestimated by a factor of about two.     

Effects of nitrate and phosphate on growth and C2 toxin productivity of Alexandrium tamarense CI01 in culture

Growth and C2 toxin productivity of a marine dinoflagellate, Alexandrium tamarense CI01 (ATCI01) which predominantly produces C2 toxin, were studied in unialgal batch cultures to optimize the concentrations of nitrate and phosphate for a maximal toxin yield. A range of start concentrations of the two major nutrients was determined in which algal growth was proportional to the nutrient concentrations used. The highest concentrations of nitrate and phosphate in this growth-enhancing range were 264 and 20 μM, respectively. In this concentration range, the C2 toxin yield (μg/l) and cellular toxin content (Qt, fmole per cell) reached a maximum at the lowest end of phosphate (5 μM) and the highest end of nitrate (264 μM). Further increase in the supply of nitrate continued to enhance the toxin yield. Our results indicated that the growth and toxin productivity of this algal strain in batch cultures had distinctly different optimal ranges of nitrate and phosphate concentrations. For a maximum toxin yield, a judicious use of phosphate under a nitrate-replete condition is called for.     

Influence of soil aggregation on slope stability in the Oregon Coast Ranges

Two major cohesionless soil series of the central Coast Ranges of Oregon were examined for soil and hydrologic properties. Although derived from different parent material, the Bohannon and Klickitat series exhibited nearly identical values of soil and hydrologic properties. Aggregation in both soils was found to be the most important property, for it influences shear strength and subsurface water movement, prime components of slope stability. The unusually high angle of internal friction of both cohesionless soils was 40° to 41°. The angle of internal friction was affected significantly by the mode of wetting. Subsurface water movement was predominantly by unsaturated flow. The influence of soil aggregation on pore-size distribution and arrangement created conditions where unsaturated flow was an effective means for water dispersal in both soils during most observed storm events. Considering the large area covered by these two soil series, aggregation appears to be an important slope-stability property with regional significance.     

Geology of Santa Fe island: The oldest galapagos volcano

Santa Fe Island was a volcanic center when it emerged 3.9 ± 0.6 m.y. ago. Later upfaulting of a horst along the central axis of the island dominates its present morphology. Santa Fe is made up of evolved transitional lavas that are not related by fractional crystallization alone. Source heterogeneties, differing degrees of melting, or open-system magma chambers may explain the observed trace element variations.Santa Fe, Baltra, and Española make up a geologic subprovince in the central Galapagos: they are older than the other islands, and their lavas are compositionally similar. At the time of their emergence, the three islands were in a tectonic setting similar to that of the young western and central Galapagos Island.