Studies on a very flare-active δ group: Peculiar δ spot evolution and inferred subsurface magnetic rope structure

The complex subsurface magnetic rope structure of a very flare-active isolated group (McMath 13043, July 1974) is studied by means of high-resolution evolutionary data from BBSO magnetic and velocity data. This group showed unusually fast evolution accompanied by a number of intense flares occurring on the neutral line of a spot, and provided an excellent opportunity to study the inherent relation of flare occurrence to changes of the magnetic configuration. We first examine the abnormal evolution of this group started by formation of a large, compact, reversed spot by squeezing of multipoles. The configuration was deformed by penetration into the opposite polarity umbra and its subsequent disappearance, decaying by rapid shear motions. Strong transverse fields over 4000 G were detected in the penumbrae and some umbral components.Combining these data with the August 1972 region, the evolution of these isolated groups is shown to decompose into two flare-associated elementary modes: (A) shearing produced by spot growth and (B) reduction of shear as spots disappear. We propose a model of an emerging twisted magnetic knot to explain the two modes and apply realistically to the present evolution. The inferred magnetic topological structure of this region consists of tightly twisted (sheet-like) knots and a long-winding twisted rope with an internally reversed loop and a hooked bottom struture. Their consecutive emergences are suggested to explain the abnormal evolution of this 5 group. This result indicates that the origin of the concentrated flare activity in these isolated groups may be traced to internal magnetic activity responsible for forming anomalous magnetic ropes.The author died on January 2, 1990. This paper, prepared for publication at the time of his death, was edited by Professor H. Zirin.     

A high accuracy method for determining nitrogen, argon and oxygen in seawater

An improved gas chromatographic system was constructed to analyze oceanic dissolved N₂, Ar and O₂ with a higher accuracy and shorter analytical time. To obtain a higher accuracy of N₂, Ar and O₂ measurements, the following was added to the system: (I) an air trapping system; (II) a N₂–CO₂ trapping system after the operation of the air trapping system; (III) an active carbon column system for separating N₂ and CO₂ completely and (IV) the introduction of automatic valves controlling most of the system. Compared to previous studies, the precision of the measurements of N₂, Ar and O₂ concentrations was higher at 0.04%, 0.05% and 0.02%, respectively, and our analytical time was shorter at 600 s. Using the improved analytical technique, concentrations of N₂ (C_N2, 561.69–611.81 μmol/kg) and Ar (C_Ar, 15.126–16.238 μmol/kg), saturation states of N₂ (ΔN₂, − 5.1–0.9%) and Ar (ΔAr, − 7.0 to − 1.1%) from 0 m to 3000 m depth in the western North Pacific were observed during March 2005. Based on these data, we propose a new concept for estimating the amount of bubble injection (B). The total error in calculating B was estimated to be about 20%. We estimated B from 12 to 43 μmol/kg in this region using the observational values of N₂ and Ar. As each water mass had a significantly different value of B even with an error of 20%, it is possible to use it as an index of sea surface state for when each water mass is produced in the sea surface mixed layer. Moreover, based on our values of B, we estimated preformed dissolved oxygen (DO) (C_preDO, 309–332 μmol/kg) and the saturation state of C_preDO (ΔpreDO, − 7.0 to − 1.2%) in this region. Thus, the difference between C_preDO and DO content in the ocean interior may be a more useful index for biogenic organic decomposition in the ocean field compared to Apparent Oxygen Utilization (AOU). Until now, the estimation of oceanic uptake of anthropogenic CO₂ has used AOU as a major parameter. Therefore, it may be necessary to re-evaluate the oceanic uptake of anthropogenic CO₂ based on our new concept of B.     

Japanese anchovy egg accumulation at the sea surface or pycnocline—Observations and model

Near surface vertical distributions of Japanese anchovy eggs (isolated and pelagic) were studied at western Wakasa Bay, Japan. Samples were collected in horizontal tows with four plankton nets simultaneously operated at different four depths of 0, 0.5, 1.0, and 2.0 m. The egg concentration was found to decrease exponentially with depth. The egg concentration profile can be explained by considering the balance of the eggs' ascent and vertical diffusion. Taking further into account vertical difference in rising/sinking rates of the eggs, a clear accumulation of the eggs on a pycnocline, observed elsewhere, also can be explained. Vertical eddy diffusivity in the surface layer in a calm sea was 1–10 cm² s^–1, as estimated from the egg concentration profile and the velocities of the eggs in the vertical direction.     

Growth and mortality of larval and juvenile Japanese seaperch Lateolabrax japonicus in relation to seasonal changes in temperature and prey abundance in the Chikugo estuary

Japanese seaperch Lateolabrax japonicus migrate from Ariake Bay to the estuarine turbidity maximum (ETM) zone of the Chikugo River and inhabit there through the post-migration period (15–20 mm in standard length). The feeding, growth and mortality during the post-migration period of Japanese seaperch were analyzed in relation to seasonal changes in temperature and prey concentration. Larvae and juveniles were collected from ten sampling stations at 4–7 day intervals from 24 February to 24 April 2005 in the Chikugo estuary. Based on the otolith microstructure analysis the sampled fish were divided into nine cohorts, each cohort covering a 5 day hatch date period (22 December 2004 to 4 February 2005). The growth coefficient (G, day⁻¹) was higher and the mortality coefficient (M, day⁻¹) was lower in the later cohorts. The ratio of G to M as an index of stage-specific survival during the post-migration period significantly increased as the season progressed and exceeded 1.0 in the last cohort examined. Variability in abundance of the major prey organism, Sinocalanus sinensis, had a significant effect on the Japanese seaperch ingestion rate. Increase in temperature and spring bloom of S. sinensis is concluded to provide the later cohorts with a higher survival probability through increasing ingestion and growth rates during their post-migration period in spring 2005.     

Modified Method for the Analysis of Nitrogen Isotopic Composition of Oceanic Nitrate at Low Concentration

A method for the determination of the δ¹⁵N of nitrate in seawater described by Cline and Kaplan (1975) has been modified for application to low-level nitrate samples. We have minimized the reagent blank problem by replacing the Devarda's alloy with an aluminum reagent, and have also established a procedure that yields quantitative (93 ± 2%) extraction of nitrogen even at low nitrate levels. Though the amounts and the δ¹⁵N of the blank N varied from one reagent set to another, with these modifications, an overall N blank was reduced to approximately 0.80 ± 0.33 μmole N having an estimated δ¹⁵N value of −1.8‰. After blank and yield corrections, the measured isotopic composition of nitrate differed by approximately 0.1‰ from the actual value while the precision was within ±0.2‰ at the 1.25 μM level. The modified procedure was applied to seawater samples collected from the equatorial Pacific in order to compare the N blanks in field samples with those derived from laboratory experiments. The results support the suitability of the modified approach for isotopic analysis of oceanic nitrate in shallow water. This revised version was published online in July 2006 with corrections to the Cover Date.     

A sediment trap experiment in Funka Bay, Japan: “upward flux” of particulate matter in seawater

Sediment trap experiments were carried out ten times in one year (1977) at three depths in Funka Bay. The material obtained in the traps was analyzed for metals, organic elements and radionuclides, together with the suspended matter in the overlying water column. Two groups with extremely different downward fluxes were found, a group with a small flux increasing with depth, and another with a large flux that is rather constant with depth and is observed only in winter. The flux in winter, and sometimes in the bottom layer below the summer thermocline was larger than the net sedimentation rate for total dry matter or for each chemical constituent. The flux was also larger than the net removal flux for ²³⁴Th. A most striking fact is that the specific activity of short-lived ²³⁴Th did not decrease in winter, indicating that the large flux in winter was not caused by the re-suspension of old bottom sediments. The concentration of suspended matter in winter was not much greater than that in other seasons. These results suggest that the downward flux observed in sediment trap experiments is not a net removal rate and that there must be an upward particulate flux in the bay.     

Gram Stain Index (GSI) of Bacterial and Archaeal Cells in the Natural Microbial Communities of Slightly and Extremely Saline Environments

The use of GSI (Gram Stain Index) was studied for natural microbial cells in slightly and extremely saline environments. The GSI spectra of archaeal cells in an extremely saline environment showed unique profiles, different from those of Bacteria. These profiles can be applied for structural analysis of the microbial communities in aquatic environments.     

Citrate-dithionite-bicarbonate extractable phosphorus (CDB-P) pool in the suspended and surface sediments of the tidal flat area in inner Ariake Bay,Japan

CDB-P (phosphorus extractable by the citrate-dithionite-bicarbonate extraction procedure) was used as the indicator of bio-available inorganic P in the suspended and surface sediments in the inner part of Ariake Bay. The CDB-P pool of suspended and surface sediments in the tidal flat area was estimated to be 10 ton and 90 ton, respectively (total of 100 ton), which corresponds to 1.5 times the average dissolved inorganic phosphorus standing stock. During the summer periods of hypoxia, the CDB-P concentration in the surface sediments decreased with the decline of Eh, losing 43–47% of the CDB-P observed in April. These results suggest that the phosphorus dynamics have been affected by the decrease of resuspended sediment concentrations brought about by the reduction of the tidal currents and phosphate release from the surface sediments during frequently occurring summer hypoxia events.     

Validation of ADEOS-II GLI ocean color products using in-situ observations

The Global Imager (GLI) aboard the Advanced Earth Observing Satellite-II (ADEOS-II) made global observations from 2 April 2003 to 24 October 2003. In cooperation with several institutes and scientists, we obtained quality controlled match-ups between GLI products and in-situ data, 116 for chlorophyll-a concentration (CHLA), 249 for normalized water-leaving radiance (nLw) at 443 nm, and 201 for aerosol optical thickness at 865 nm (Tau_865) and Angstrom exponent between 520 and 865 nm (Angstrom). We evaluated the GLI ocean color products and investigated the causes of errors using the match-ups. The median absolute percentage differences (MedPD) between GLI and in-situ data were 14.1–35.7% for nLws at 380–565 nm, 52.5–74.8% nLws at 625–680 nm, 47.6% for Tau_865, 46.2% for Angstrom, and 46.6% for CHLA, values that are comparable to the ocean-color products of other sensors. We found that some errors in GLI products are correlated with observational conditions; nLw values were underestimated when nLw at 680 nm was high, CHLA was underestimated in absorptive aerosol conditions, and Tau_865 was overestimated in sunglint regions. The error correlations indicate that we need to improve the retrievals of the optical properties of absorptive aerosols and seawater and sea surface reflection for further applications, including coastal monitoring and the combined use of products from multiple sensors.