Satellite detection of red tide in Ariake Sound, 1998–2001

High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement to accurately estimate chlorophyll in highly turbid water and in red tide areas.     

Recovery of thermohaline circulation under CO2 stabilization and overshoot scenarios

In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO₂ stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO₂ levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries.     

Application of AVO Analysis to Seismic Data for Detection of Gas below Methane Hydrate Stability Zone in Nankai Trough Area

Abstract. For the purpose of development of methane hydrate, occurring in the deep marine subsurface, as a resource, the most important issue is to understand the methane hydrate system (generation, migration and accumulation) as well as to delineate the methane hydrate reservoir properties. We have applied the Amplitude Versus Offset (AVO) analysis to the seismic data acquired in the Nankai Trough, offshore Japan, in order to confirm the occurrence of gas just below the methane hydrate-bearing zone, assuming that gas will show a so-called Class-3 AVO response. Knowledge of the amount and occurrence of gas in the sediment below methane hydrate-bearing zone is one of the keys to understand the methane hydrate system.
We have utilized the qualitative analysis of AVO methodology to delineate how gas is located below the BSR, which is thought to be the reflection event from the interface between the methane hydrate-bearing zone and the underlying gas-bearing zone. In the region of MITI Nankai Trough Well PSW-3, we observe two BSRs separated by 25 ms. After AVO modeling using well data, we applied AVO attribute analysis and attribute crossplot analysis to the seismic data. Finally we applied an offset-amplitude analysis to CMP gather data at specific locations to confirm the results of AVO attribute analysis. The AVO analysis shows that there is very little gas located in the underlying sediment below methane hydrate-bearing zone. This result supports the fact that we could not obtain any clear evidence of gas occurrence just below the methane hydrate-bearing zone in the Nankai Trough well drilling.     

Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific and Baltic‐Skagerrak region: calibration as an annual density proxy and first evidence of pseudo‐cryptic speciation

Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparède et Lachmann) Bütschli in surface sediments from the North Pacific was investigated. The average process length showed a significant inverse relation to annual seawater density: σ_{t annual} = ?0.8674 × average process length + 1029.3 (R² = 0.84), with a standard error of 0.78 kg m^?3. A sediment trap study from Effingham Inlet in British Columbia revealed the same relationship between average process length and local seawater density variations. In the Baltic–Skagerrak region, the average process length variation was related significantly to annual seawater density: σ_{t annual} = 3.5457 × average process length ? 993.28 (R² = 0.86), with a standard error of 3.09 kg m^?3. These calibrations cannot be reconciled, which accentuates the regional character of the calibrations. This can be related to variations in molecular data (small subunit, long subunit and internal transcribed spacer sequences), which show the presence of several genotypes and the occurrence of pseudo‐cryptic speciation within this species. Copyright © 2012 John Wiley & Sons, Ltd.     

Rock weathering processes and landform development in the Sør Rondane Mountains, Antarctica

Field observations of weathering processes and the related landforms, combined with laboratory analyses of weathering products, permit a synthetic evaluation of Late Cenozoic weathering environments in the Sør Rondane Mountains, Antarctica, an arid upland characterized by low temperatures and strong winds. Rates and character of weathering depend mainly on moisture availability and the bedrock geology. Under the humid weathering regime that occurs only locally around the margin of the present sheet, frequent diurnal freeze-thaw cycles in summer cause relatively rapid rock fragmentation. Most of the mountains are situated in the arid weathering regime, under which rock breakdown is very slow unless the rock contains plenty of salts. Salt weathering becomes more intensive and extensive with exposure age, as a result of salt accumulation in rock, eventually producing soils as small as fine-silt size. Lack of clay mineralization even in weathered rocks having been exposed above the ice sheet prior to 4 Ma ago indicates that hydrolysis or carbonation of rock minerals has been insignificant during the past 4 Ma. The final products of weathering are due mainly to salt action and reflect the parent lithology. Resistant fine-grained granite forms strongly oxidized tors carved with tafoni, or fields of mushroom-like boulders overlying the fractured bedrock. Less resistant rocks, like biotite gneiss and amphibolite, produce stone pavements underlain by saline, silty soils up to 30–40 cm thick, the thickness of which corresponds to the maximum thaw depth.     

The rate of bedrock weathering by frost action: Field measurements and a predictive model

Shattering rate, surface temperature, moisture content, and the physical and strength properties of bedrock were measured in four rockwall sites of the Japanese Alps. Five-year observations revealed that the bedrock shattering rate was usually much higher in the freeze-thaw period from October to next May than in the frost-free period from June to September. This indicates that frost action is the most important shattering process, although unusual heavy rainstorms in summer are also responsible for the shattering. A combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate. This model shows that the annual shattering rate is dependent on the annual freeze-thaw frequency on the rock surface, and the degree of saturation and tensile strength of the rock masses. The coefficients involved in the model were determined using the field data.     

Rates of tafoni weathering on uplifted shore platforms in Nojima-Zaki,Boso Peninsula,Japan

Many tafoni occur on the faces of marine cliffs on three uplifted shore platforms with different altitudes and with known ages of emergence. The mean value of the ten largest depths of tafoni, D (cm), was obtained and the period of their formation, t (years), was estimated. The relationship between the two variables was found to be D = 20·3 × (1?e^?0.005t).     

Mesozoic radiolarians and radiolarian-bearing sequences in the circum-Pacific regions: A report of the symposium-'Radiolarians and Orogenic Belts'

Abstract This paper contains extended abstracts of the seven papers presented at the symposium 'Radiolarians and Orogenic Belts' held at the seventh meeting of the International Association of Radiolarian Paleontologists (INTERRAD). Important results of the symposium include the following: (1) Upper Paleozoic and Mesozoic cherts are widely distributed within accretionary complexes in the circum-Pacific orogenic belt. Radiolarian dating reveals that long durations of chert sedimentation in a pelagic environment are recorded on both sides of Pacific-rim accretionary complexes (e.g. New Zealand, Japan, Russian Far East, Canadian Cordillera). (2) Triassic radiolarian faunas from New Zealand and the Omolon Massif, northeast Siberia are similar in composition and are characterized by the absence of typical Tethyan elements. This suggests that radiolarian faunal provincialism may have been established as early as the Triassic. High-latitude radiolarian taxa exhibit a bi-polar distribution pattern. (3) The Lower Triassic interval in chert dominant pelagic sequences is mechanically weaker than other levels and acted as a décollement in accretionary events. This lithologic. contrast in physical property is considered to reflect radiolarian evolution, such as the end-Permian mass extinction.     

Seasonal dynamics influencing coastal primary production and phytoplankton communities along the southern Myanmar coast

Myanmar is tenth among the world’s fish-producing countries and third in ASEAN (Association of Southeast Asian Nations). To understand the mechanisms underlying the high production, oceanographic and phytoplankton surveys, including primary productivity measurements based on pulse amplitude modulation fluorometry, were conducted near an active fishing ground near Myeik City. Three surveys, one in each of the representative seasons and covering the characteristic coastal environments, showed well-defined seasonality in primary production and phytoplankton occurrence. End of the dry season was the most productive, with productivity of 2.59 ± 1.56 g C m^?2 day^?1 and high concentration of chlorophyll a (3.14 ± 2.64 µg L^?1). In this season, the phytoplankton population was dominated by high densities of the diatoms Bellerochea horologicalis and Chaetoceros curvisetus, whereas primary productivity was low at the onset of the dry season, 1.36 ± 0.77 g C m^?2 day^?1. However, this low primary production might be compensated by activation of microbial food chains originating from high dissolved organic carbon. The rainy season exhibited the lowest production, 6.6% of the end of the dry season, due to the extensive discharge of turbid water from the rivers which lowered euphotic layer depth and resulted in an unusually high diffuse attenuation coefficient of 2.30 ± 1.03 m^?1. This incident of turbid water may be related to soil erosion from deforestation and mangrove deterioration. This research reveals the seasonal trend in Myanmar’s coastal productivity and its relationship to the tropical monsoon climate as well as emphasizing the importance of tropical coastal environments to the sustainability of the fisheries.     

Diurnal freeze–thaw depth in rockwalls: Field measurements and theoretical considerations

Rock temperatures were monitored for a year at two alpine rockwalls in the Akaishi Range, Japan, where permafrost is absent. Diurnal frost and thaw penetration depths were evaluated from subsurface isotherms drawn on the basis of the temperature records at 0, 10 and 40 cm depths. The surface of the rockwalls experienced more than 100 diurnal freeze-thaw cycles, most of which accompanied a frost or thaw penetration shallower than 50 cm, and several long duration cycles with deeper frost or thaw penetration. Theoretical frost and thaw depths were also calculated by incorporating the surface freezing indices into the modified Berggren equation, the results from which were then compared with the actual values. The modified Berggren equation provided values that showed a strong correlation with observed depths, despite somewhat underestimating the actual values. Using the modified Berggren equation, the seasonal frost depth in the observed winter was estimated to be about 4·5 m. The frost and thaw depths are considered to give the maximum estimation of the depth to which frost-induced cracking can propagate in the bedrock.