Mixed layer variability in Northern Arabian Sea as detected by an Argo float

Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April - May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.3 °C and ocean gained an average of 99.8 Wm⁻². Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained abnormally low ∼18 Wm⁻² and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm⁻². Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively. Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided well with short term variability of surface forcing.     

Spatial and Temporal Variations of Sound Speed at the PN Section

Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Methane-dominated thermochemical sulphate reduction in the Triassic Feixianguan Formation East Sichuan Basin, China: towards prediction of fatal H2S concentrations

New sour pools have recently found in the Lower Triassic Feixianguan Fm carbonate reservoirs in the East Sichuan Basin in China with H₂S up to 17.4% by volume. A recent blowout from a well drilled into this formation killed hundreds of people as a result of the percentage concentrations of H₂S. In order to assess the origin of fatal H₂S as well as the cause of petroleum alteration, H₂S concentrations and the isotopes, δ³⁴S and δ¹³C have been collected and measured in gas samples from reservoirs. Anhydrite, pyrite and elemental sulphur δ³⁴S values have been measured for comparison. The high concentrations of H₂S gas are found to occur at depths >3000 m (temperature now at 100 °C) in evaporated platform facies oolitic dolomite or limestone that contains anhydrite nodule occurrence within the reservoirs. Where H₂S concentrations are greater than 10% its δ³⁴S values lie between +12.0 and +13.2‰ CDT. This is within the range of anhydrite δ³⁴S values found within the Feixianguan Fm (+11.0 to +21.7‰; average 15.5±3.5‰ CDT). Thus H₂S must have been generated by thermochemical sulphate reduction (TSR) locally within the reservoirs. Burial history analysis and fluid inclusion data reveal that the temperature at which TSR occurred was greater than about 130–140 °C, suggesting that the present depth-temperature minimum is an artifact of post-TSR uplift. Both methane and ethane were actively involved in TSR since the petroleum became almost totally dry (no alkanes except methane) and methane δ¹³C values become significantly heavier as TSR proceeded. Methane δ¹³C difference thus reflects the extent of TSR. While it is tempting to use a present-day depth control (>3000 m) to predict the distribution of H₂S in the Feixianguan Fm, this is an invalid approach since TSR occurred when the formation was buried some 1000–2000 m deeper than it is at present. The likelihood of differential uplift across the basin means that it is important to develop a basinal understanding of the thermal history of the Feixianguan Fm so that it is possible to determine which parts of the basin have been hotter than 130–140 °C.     

Seasonal variations of water system distribution and flow patterns in the southern sea area of Hokkaido,Japan

Hydrographic data and composite current velocity data (ADCP and GEK) were used to examine the seasonal variations of upper-ocean flow in the southern sea area of Hokkaido, which includes the “off-Doto” and “Hidaka Bay” areas separated by Cape Erimo. During the heating season (April–September), the outflow of the Tsugaru Warm Current (TWC) from the Tsugaru Strait first extends north-eastward, and then one branch of TWC turns to the west along the shelf slope after it approaches the Hidaka Shelf. The main flow of TWC evolves continuously, extending eastward as far as the area off Cape Erimo. In the late cooling season (January–March), part of the Oyashio enters Hidaka Bay along the shallower part of the shelf slope through the area off Cape Erimo, replacing almost all of the TWC water, and hence the TWC devolves. It is suggested that the bottom-controlled barotropic flow of the Oyashio, which may be caused by the small density difference between the Oyashio and the TWC waters and the southward migration of main front of TWC, permits the Oyashio water to intrude along the Hidaka shelf slope.     

Atmospheric forcing of fine-sand transport on a low-energy inner shelf: south-central Louisiana,USA

Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s^-1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s^-1 at the landward site, and 11.4 and 2.7 cm s^-1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s^-1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25-75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf.     

Tectonic control over topography and channel sedimentation across the forearc slope of the southern Kurile Trench

A high-resolution seismic survey covering more than 2,000 km² has revealed the processes responsible for the slope morphology and channel sedimentation across the forearc slope-basin of the Kurile Arc–NE Japan Arc collision zone, offshore from Tokachi (Hokkaido, Japan). The dominant slope contours parallel the trench but, in the middle and lower reaches of the southern slope, contours are convex-shaped with an offshore trend. This sector of the slope is traversed diagonally by the Hiroo submarine channel. The offshore-trending convex contours and the channel course have developed through the interplay of tectonic and sedimentary processes, including the development of anticlines, anticline-induced lobe sedimentation and channel avulsion. In its upper reaches, the channel is restricted by a topographic low associated with NNW–SSE-trending anticlines which developed within the upper and middle slope sectors during late Miocene uplift. The uplift timing and trend of these anticlines indicate that they resulted from collision, the channel sedimentology and slope morphology of the middle and lower slopes having been influenced by Pliocene uplift of NE–SW-trending anticlines. The trends of these anticlines parallel those of the Kurile Trench. The Pliocene and early Pleistocene strata of the middle and lower slopes consist of ponded lobe sediments deposited along the palaeo-Hiroo submarine channel on the landward side of the anticlines. As a lobe pile accumulated, the channel thalweg shifted to the north of the stack, allowing the channel to bypass the topographic high formed by the growing stack. Thick levee deposits built up along the channel course during the late Pleistocene and Holocene. These levees, along with the Pliocene and early Pleistocene lobes, are reflected in the present-day sigmoid-shaped, convex offshore-trending contours. Thus, the interplay of subduction- and collision-related anticlines, tectonic-related channel ponding, and avulsion has contributed to the slope morphology of the southern Kurile Trench.     

潜水员水下用电安全技术规范的编制与认识

本文介绍了国家标准《潜水员水下用电安全技术规范》的研究、编制过程，以及编者对该标准性质、适用范围、总体结构、电气安全数值取舍等的基本认识，并就该标准制定实施后的经济、社会效益进行了初步预测。     

Anomalous change of the Antarctic sea ice and global sea level change

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Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data

The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking. An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor. In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships. The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for robust seafloor characterization.