Is the outcrop topology of dolerite dikes of the Precambrian Singhbhum Craton fractal?     

Nibir Mandal  Atin Kumar Mitra  Santanu Misra  Chandan Chakraborty 《Journal of Earth System Science》2006,115(6):643-660

In the Precambrian Singhbhum Craton of eastern India, newer dolerite dikes occur profusely with varying outcrop lengths. We have analysed the nature of their length-size and orientation distributions in relation to the theory of fractals. Two orientational sets of dikes (NW-SE and NE-SW) are present. Both the sets show strongly non-power-law size distributions, as reflected in non-linear variations in logarithmic space. We analyzed thousands of data, revealing that polynomial functions with a degree of 3 to 4 are the best representatives of the non-linear variations. Orientation analysis shows that the degree of dispersions from the mean trend tends to decrease with increasing dike length. The length-size distributions were studied by simulating fractures in physical models. Experimental fractures also show a non-power-law distribution, which grossly conforms to those of the dolerite dikes. This type of complex size distributions results from the combined effects of nucleation, propagation and coalescence of fractures.  相似文献   

Mountains as vulnerable places: a global synthesis of changing mountain systems in the Anthropocene     

Chakraborty  Abhik 《GeoJournal》2021,86(2):585-604

GeoJournal - This article provides a comprehensive review of mountains as a highly heterogeneous, dynamic, yet increasingly vulnerable terrestrial environment undergoing rapid change in the...  相似文献   

Carbonate Alkalinity Enhances Triclosan Photolysis     

Albanese  Katie A.  Chakraborty  Mrinal  Hadad  Christopher M.  Chin  Yu-Ping 《Aquatic Geochemistry》2021,27(3):159-171

Triclosan (TCS) is an antimicrobial compound found in many household products used across the world. TCS is not completely removed in wastewater systems, resulting in trace-level concentrations present ubiquitously in surface waters. The direct photodegradation of TCS has been widely studied, with results indicating that TCS breaks down to chlorophenols and dioxins. To date, no studies have specifically investigated the effects of alkalinity on the photolysis of the acidic form of TCS. This study assessed the effect of carbonate/bicarbonate alkalinity, which is ubiquitous in natural waters, on the photolysis rate of TCS. Results indicate that bicarbonate enhances the photodegradation of TCS at pH values well below the pK_a of TCS (7.9), with direct photolysis reaction kinetics that are very slow in the absence of buffers, but significant in the presence of bicarbonate (0.711 h^?1 at pH 6.55). At pH values well above its pK_a, both unbuffered- and buffered-mediated photolysis increased dramatically (1.92 h^?1 for direct photolysis and 2.86 h^?1 in buffered water) and is attributable to the increased photoreactivity of TCS by its conjugate base. Photolysis of methyl triclosan (MeTCS), a non-acidic analog of TCS, demonstrated the importance of TCS’s acidic functionality as MeTCS did not degrade at any pH. The observed influence of alkalinity on the acidic form of TCS photolysis was attributed to both a decrease in its excited state pK_a, coupled with TCS deprotonation through an excited state proton transfer to a base (bicarbonate and to a lesser degree hydrogen phosphate) resulting in the more photo-labile conjugate base form of TCS.

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Bathymetry and sediments on the carbonate platform off western India: Significance of Halimeda bioherms in carbonate sedimentation     

V Purnachandra Rao  V P Mahale  B Chakraborty 《Journal of Earth System Science》2018,127(8):106

Bathymetry across the carbonate platform off western India indicated small-size pinnacles and their lateral coalescence into 2 -6-m high mounds landward, and linear elongated carbonate ridges and troughs, mounds and banks up to a height of 20-m seaward of the platform. Seismic data indicated that these mounds were transparent with no rigid internal structure and can be defined as bioherms. The sediments were abundantly aragonite faecal pellets, Halimeda grains and ooids and their radiocarbon ages ranged from 11 to 7.5 ka BP. It appears that the growth of Halimeda bioherms on the platform was facilitated by intense upwelling during the early Holocene. The terrigenous sediments brought by rivers were deposited in the inner shelf and have not affected the growth of bioherms. It is estimated that the platform comprises at least 1.85 Gt of mass CaCO\(_3\) accumulated during the early Holocene and comparable to those on the Great Barrier Reef. Halimeda bioherms produce abundant carbonate sediments and their growth period represents a geological carbonate sink and release of high CO\(_2\) to the atmosphere. Detailed shallow seismic studies and sediment cores are needed to quantify the exact mass content of CaCO\(_3\) and model climate change during the early Holocene.  相似文献   

The Mechanism of the 20°C Isotherm Depth Oscillations for the Bay of Bengal     

Sourav Sil  Arun Chakraborty 《Marine Geodesy》2013,36(3):233-245

The monthly variation of thermocline depth in terms of 20°C isotherm depth (Z20) in the Bay of Bengal has been studied using SODA and ARGO datasets. During a southwest monsoon, the Bay of Bengal is deepest in the western basin and shallowest in the eastern basin while it is the opposite during northeast monsoon. The Z20 oscillation is not only affected by semiannual reversing wind forcing but also influenced by coastal Kelvin waves from the eastern coast and remote effect from the Northern Indian Ocean and Malacca Strait. A linear relationship between SSHA and Z20 has been found from both SODA and observational studies.  相似文献