The post flare loops observed at the total eclipse of February 16, 1980

A post flare loop system was observed on the west limb at the total solar eclipse of February 16, 1980 in Kenya. Analyzing the monochromatic images and the flash spectra, we obtained the following results: (1) the lower part of the post flare loop system is characterized mainly by distinct cool loops of H and Fe x 6374. Fe x 6374 emitting plasma (T _e = 1.0 × 10⁶ K) is highly concentrated in the loops. The 6374 loops are broader in diameter and located very close to but a little higher than the corresponding H loops. The electron densities of the dense part in H and Fe x 6374 loops are 10¹¹ cm^-3 and 6 × 10⁹cm^-3, respectively; (2) the Ca xv emitting region (3.5 × 10⁶ K) is confined to the upper part of the post flare loops. The electron density of this hot region is estimated as 8 × 10⁹ cm^-3 from the Ca xv line intensity ratio, I(5694)I(5445). These observational results led us to construct an empirical model of the post flare loop system which is consistent with the reconnection model of Kopp and Pneuman (1976).Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 267.     

Characterization of humic and fulvic acids isolated from marine sediments of Sagami and Suruga Bays with C-13 and proton nuclear magnetic resonance

The C-13 and proton NMR spectra of marine humic and fulvic acids isolated from sediments of Sagami and Suruga Bays and Aldrich humic acid were obtained using pulse Fourier transform mode. The C-13 and proton NMR spectra, which clarified the differences in chemical characteristics among the various humic substances, showed that the marine humic acids had more aliphatic and less aromatic character than the Aldrich humic acid, and the marine fulvic acids had polysaccharide-like character. The C-13 NMR spectra of the marine humic substances, in particular, had many relatively well-resolved peaks with significant intensities, indicating the presence of variously bonded carbon atoms in them.     

Distribution of oxygen-containing functional groups and elements in humic acids from marine sediments

The elemental composition and oxygen-containing functional groups contents in the marine humic acids from the five sediment samples from Sagami Bay and Suruga Bay were determined. Kumada's method of classification of soil humic acids was applied to the marine humic acids. The carbon, nitrogen, hydrogen, oxygen and sulfur contents of the marine humic acids were, on average, 52.96, 5.12, 5.79, 34.99 and 1.13%, respectively, without wide variation. In comparison with terrestrial humic acids, the marine ones had relatively lower carbon content and higher hydrogen and nitrogen contents. It is suggested that the marine humic acids have more aliphatic and less aromatic character, as expected from their possible origins, e.g., phytoplankton. The total acidity, carboxyl, phenolic and alcoholic hydroxyl, carbonyl and methoxyl group contents in the marine humic acids were, on average, 5.80, 3.27, 2.53, 2.53, 3.09 and 0.41 milliequivalents per gram of dry ash-free humic acid (me g^–1), respectively. From quantitative data on the elemental composition and functional groups of the average marine humic acid, its empirical formula was calculated to be C₁₀₇H₁₃₈O₂₀(COOH)₉(OH)₇ ^phenolic (OH)₇ ^alcoholic (CO)₉(OCH)₃N₁₀S. The marine humic acids were similar to the so-called B type of soil humic acids with regard to the distribution of functional groups and spectroscopic properties.     

Spatial Variability of Living Coccolithophore Distribution in the Western Subarctic Pacific and Western Bering Sea

Vertical distributions of coccolithophores were observed in the depth range 0–50 m in the western subarctic Pacific and western Bering Sea in summer, 1997. Thirty-five species of coccolithophores were collected. Overall, Emiliania huxleyi var. huxleyi was the most abundant taxon, accounting for 82.8% of all coccolithophores, although it was less abundant in the western Bering Sea. Maximum abundance of this species was found in an area south of 41°N and east of 175°E (Transition Zone) reaching >10,000 cells L⁻¹ in the water column. In addition to this species, Coccolithus pelagicus f. pelagicus, which accounted for 4.2% of the assemblage, was representative of the coccolithophore standing crop in the western part of the subarctic Pacific. Coccolithus pelagicus f. hyalinus was relatively abundant in the Bering Sea, accounting for 2.6% of the assemblage. Coccolithophore standing crops in the top 50 m were high south of 41°N (>241 × 10⁶ cells m⁻²) and east of 170°E (542 × 10⁶ cells m⁻²) where temperatures were higher than 12°C and salinities were greater than 34.2. The lowest standing crop was observed in the Bering Sea and Oyashio areas where temperatures were lower than 6–10°C and salinities were less than 33.0. From the coccolithophore volumes, the calcite stocks in the Transition, Subarctic, and the Bering Sea regions were estimated to be 73.0, 9.7, and 6.9 mg m⁻², respectively, corresponding to calcite fluxes of 3.6, 0.5, and 0.3 mg m⁻²d⁻¹ using Stoke's Law. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mesozooplankton responses to iron-fertilization in the western subarctic Pacific (SEEDS2001)

A mesoscale iron-fertilization experiment was carried out in the western subarctic Pacific during summer 2001. The iron-patch was traced for 14 days after the fertilization, and the abundance and behavior of mesozooplankton were compared with those outside of the patch. The phytoplankton biomass in the patch rapidly increased to over 15 times the initial level by the later half of the observation period, and was composed of large-sized (>10 mm), centric diatoms. Dominant zooplankton species in the upper 200-m depth were large copepods: Neocalanus plumchrus, Neocalanus cristatus, Eucalanus bungii and Metridia pacifica. Mesozoplankton biomass as well as species composition did not change significantly in the patch over the observation period. Furthermore, no changes of vertical distribution or diel vertical migration were observed for any species or stages of mesozooplankton throughout the observation period. However, the abundance of the first copepodite stages of N. plumchrus and E. bungii increased several fold in the patch after the diatom bloom formation compared to the densities outside the patch. The increases of both species are considered to be due to lowered mortality during the egg and nauplius stages. Spawning of N. plumchrus takes place at depth using lipid storage, while spawning of E. bungii takes place in the surface layer supported by grazing. These facts suggest that the relative importance of nauplii in the diets of the large copepods was decreased in the patch by the diatom bloom. Gut-pigment contents of dominant copepods in the patch increased 4–18 times, and the maximum values were observed during the bloom peak. However, the grazing impact on phytoplankton was low throughout the experiment, especially during the bloom period (<6% of the primary production).     

Distribution of Diatoms and Development of Diatom-Based Models for Inferring Salinity and Nutrient Concentrations in Florida Bay and Adjacent Coastal Wetlands of South Florida (USA)

The composition and distribution of diatom algae inhabiting estuaries and coasts of the subtropical Americas are poorly documented, especially relative to the central role diatoms play in coastal food webs and to their potential utility as sentinels of environmental change in these threatened ecosystems. Here, we document the distribution of diatoms among the diverse habitat types and long environmental gradients represented by the shallow topographic relief of the South Florida, USA, coastline. A total of 592 species were encountered from 38 freshwater, mangrove, and marine locations in the Everglades wetland and Florida Bay during two seasonal collections, with the highest diversity occurring at sites of high salinity and low water column organic carbon concentration (WTOC). Freshwater, mangrove, and estuarine assemblages were compositionally distinct, but seasonal differences were only detected in mangrove and estuarine sites where solute concentration differed greatly between wet and dry seasons. Epiphytic, planktonic, and sediment assemblages were compositionally similar, implying a high degree of mixing along the shallow, tidal, and storm-prone coast. The relationships between diatom taxa and salinity, water total phosphorus (WTP), water total nitrogen (WTN), and WTOC concentrations were determined and incorporated into weighted averaging partial least squares regression models. Salinity was the most influential variable, resulting in a highly predictive model (r _apparent² = 0.97, r _jackknife² = 0.95) that can be used in the future to infer changes in coastal freshwater delivery or sea-level rise in South Florida and compositionally similar environments. Models predicting WTN (r _apparent² = 0.75, r _jackknife² = 0.46), WTP (r _apparent² = 0.75, r _jackknife² = 0.49), and WTOC (r _apparent² = 0.79, r _jackknife² = 0.57) were also strong, suggesting that diatoms can provide reliable inferences of changes in solute delivery to the coastal ecosystem.     

Geostatistical downscaling of fracture surface topography accounting for local roughness

This study proposes a new geostatistical methodology that accounts for roughness characteristics when downscaling fracture surface topography. In the proposed approach, the small-scale fracture surface roughness is described using a “local roughness pattern” that indicates the relative height of a location compared to its surrounding locations, while the large-scale roughness is considered using the surface semivariogram. By accounting for both components–the minimization of the local error variance and the reproduction of the local roughness characteristics–into the objective function of simulated annealing, the fracture surface topography downscaling process was improved compared to standard geostatistical methodologies such as ordinary kriging and sequential Gaussian simulation. Downscaled topography data were then assessed in terms of prediction errors and roughness distribution.     

Initiation of the Mekong River delta at 8 ka: evidence from the sedimentary succession in the Cambodian lowland

Modern deltas are understood to have initiated around 7.5–9 ka in response to the deceleration of sea-level rise. This episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea-level rises. The initial stage of the Mekong River delta, one of the world's largest deltas, is well recorded in Cambodian lowland sediments. This paper integrates analyses of sedimentary facies, diatom assemblages, and radiocarbon dates for three drill cores from the lowland to demonstrate Holocene sedimentary evolution in relation to sea-level changes. The cores are characterized by a tripartite succession: (1) aggrading flood plain to natural levee and tidal–fluvial channel during the postglacial sea-level rise (10–8.4 ka); (2) aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea (8.4–6.3 ka); and (3) a prograding fluvial system on the delta plain (6.3 ka to the present). The maximum flooding of the sea occurred at 8.0 ± 0.1 ka, 2000 years before the mid-Holocene sea-level highstand, and tidal flats penetrated up to 20–50 km southeast of Phnom Penh after a period of abrupt ～5 m sea-level rise at 8.5–8.4 ka. The delta progradation then initiated as a result of the sea-level stillstand at around 8–7.5 ka. Another rapid sea-level rise at 7.5–7 ka allowed thick mangrove peat to be widely deposited in the Cambodian lowland, and the peat accumulation endured until 6.3 ka. Since 6.3 ka, a fluvial system has characterized the delta plain, and the fluvial sediment discharge has contributed to rapid delta progradation. The uppermost part of the sedimentary succession, composed of flood plain to natural-levee sediments, reveals a sudden increase in sediment accumulation over the past 600–1000 years. This increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the Mekong, as with other Asian rivers.     

Stepwise decreases of the Huanghe (Yellow River) sediment load (1950–2005): Impacts of climate change and human activities

The sediment load delivered from the Huanghe (Yellow River) to the sea has decreased sharply to 0.15 × 10⁹ metric tons per year (0.15 Gt/yr) between 2000 and 2005, and now represents only 14% of the widely cited estimate of 1.08 Gt/yr. The river seems to be reverting to the pristine levels characteristic of the middle Holocene, prior to human intervention. Datasets from 1950 to 2005 from four key gauging stations in the main stream reveal distinct stepwise decreases in sediment load, which are attributed to both natural and anthropogenic impacts over the past 56 yr. Completions of two reservoirs, Liujiaxia (1968) and Longyangxia (1985), in the upper reaches of the river and their joint operations have resulted in stepwise decreases in sediment load coming from the upper reaches. Effective soil conservation practices in the middle reaches since the late 1970s, combined with the operation of the Sanmenxia and Xiaolangdi reservoirs, have also caused stepwise decreases in sediment load at Huayuankou in the middle reaches, but the decrease differs from that observed in the upper reaches. Decrease in precipitation is responsible for 30% of the decrease in sediment load at Huayuankou, while the remaining 70% is ascribed to human activities in the river basin, of which soil conservation practices contribute 40% to the total decrease. Sediment retention within reservoirs accounts for 20% of the total sediment load decrease, although there was notable sediment retention within the Xiaolangdi reservoir from 2000 to 2005. The remaining 10% of the decrease in sediment load is a result of the operation of reservoirs in the upper reaches. In the lower reaches, 20% of the sediment passing Huayuankou has been lost as a result of channel deposition and water abstraction. Soil conservation practices and the operation of reservoirs have lowered the content of coarser sediment (D > 0.05 mm) at Huayuankou, and reduced channel deposition in the lower reaches. In contrast, sediment loss owing to water abstraction in the lower reaches has increased considerably as water consumption for agricultural needs has increased. Therefore, the combined effects of climate change and human activities in the upper, middle, and lower reaches have resulted in stepwise decreases in the sediment load delivered from the Huanghe to the sea. The Huanghe provides an excellent example of the altered river systems impacted by climate change and extensive human activities over the past 56 yr. Further dramatic decreases in sediment load and water discharge in the Huanghe will trigger profound geological, morphological, ecological, and biogeochemical responses in the estuary, delta, and coastal sea.