Cosmic ray produced silicon-32 in near-coastal waters

The specific activity of Silicon-32 is measured is near-coastal seawaters using anin situ method for the extraction of dissolved silica. The results are discussed in relation to the input of Si32 at the surfacevia rains, the expected variation in its concentrations due to continental run-off and influx of open ocean surface waters. The experimental results clearly demonstrate the usefulness of Si32 as a tracer for the study of the vertical structure of the ocean in the upper layers, and of seasonal variations in the types of waters entering in the coastal regions

Concerning mercury in meteorites

The mercury concentration of all analyzed meteorites (falls) shows an increasing trend with their terrestrial age. Such a trend, in view of the intense Hg pollution of the earth, warrants careful selection of well preserved and well documented specimens for analysis

Mixing in the surface waters of the western Bay of Bengal using 228Ra and 226Ra

228Ra and 226Ra have been measured in the surface waters of the western Bay of Bengal during five cruises conducted between 1988 and 1999. The ranges and mean (given in brackets) concentrations for 228Ra and 226Ra are 6.8-42.1 (17.8 ± 7.9) dpm/100 kg and 6.0-16.7 (9.2 ± 2.2) dpm/ 100 kg, respectively. (228Ra/226Ra) Activity Ratio (henceforth denoted as [228/226]) ranges from 0.8 to 3.4 with a mean of 1.9 ± 0.5. Both 228Ra and 226Ra show inverse correlation with salinity, the former much stronger. A surface 2-D diffusion-advection model is used with a new approach. A simple bivariate function, C(x,y) = C0e-Ax·e-By where C0, A and B are constants, is fitted to the whole 228Ra and 226Ra data C(x,y). Substituting C(x,y) in the two-dimensional steady-state diffusion equation of Ra, the estimated values of the constants A and B can be related to eddy diffusivities and advection velocities in the zonal (x) and meridional (y) directions. From this relationship, the horizontal eddy diffusivities in the zonal and meridional directions are inferred to be 1.3 × 107 and 2.1 × 108 cm2s-1, respectively in the absence of advection terms. Similarly, neglecting the influence of diffusion, one can estimate the advection velocities, wx and wy in the zonal and meridional directions, as 0.2 and 1.1 cm s-1, respectively. The model-fit values C(x,y) of 228Ra concentrations are in good agreement with the measured values except in regions showing exceptionally high and low values. Incorporating both the advection rates and eddy diffusivities into the equation, it is found that increasing advection velocities depending on the direction can decrease or increase the eddy diffusivities and that such changes are more effective in the meridional direction compared to zonal direction in the region of study. On the whole, 228Ra appears a good tracer to derive rates of mixing between low salinity waters in the north and their high salinity southern counterparts of the western Bay of Bengal. The eddy diffusivities, Kx and Ky (without advection) derived for the Bay of Bengal are higher by about an order of magnitude than the ones similarly obtained for the Arabian Sea. This is not unexpected due to the turbulent conditions prevailing in the Bay of Bengal for most of the year

<SUP>14</SUP>C in air over the Arabian Sea

Global monitoring of radiocarbon in atmospheric CO2 began during the mid fifties to determine the time scales of exchange of radiocarbon (and CO2) between the atmosphere and other terrestrial reservoirs. The distribution of natural radiocarbon in the environment was perturbed significantly during the 1960s through injection of 14C from nuclear weapon tests. This 'bomb 14C has proved to be an excellent tracer to characterize and quantify CO2 exchange between various reservoirs. We have measured radiocarbon activity of marine air over the central and eastern Arabian sea during 1993-95. The mean A 14C values are 121 ±6, 116 ±6 and 105±5%o respectively for these three years. These values, in conjunction with those reported in the literature for troposphere for the decades of 60s through 80s, show that the 14C activity in the tropospheric air has been decreasing exponentially with an e-folding time of -16 years

Susceptibility as a tool for studying magnetic stratigraphy of marine sediments

Eighty six gravity cores collected from the Pacific Ocean by the Scripps Institution of Oceanography have been logged for magnetic susceptibility using a simple and rapid technique. These logs fall into three types: Type 1 showing several highs and lows, Type 2 with a single-broad-hump, and Type 3 showing nearly constant susceptibility with depth. Type 1 cores are found to be mainly from sediment-trap (trenches) areas which are close to the active volcanoes and the high peaks probably correspond to a slump or deposition of volcanic material; these events occurred between 0.1 and 2.8 million years ago. Type 2 cores are by far the most common, (56 out of 86) and show a maximum deposition of magnetic material (i.e. crest region of the hump) in the range of 0.2 and 1.7 million years. The susceptibility during this period was about a factor of two higher for several cores compared to their respective values during the last 0.1 million years. Oceanwide deposition of volcanic material and/or the atmospherically transported dust rich in magnetic material (cosmic and/or terrestrial) by our planet can account for such an increase. A third possibility may be the change (decrease) in accumulation rates of the sediments during this period. In type 3 cores the susceptibility is almost constant with depth and these are randomly distributed (excluding the sediment trap areas) analogous to the case of type 2 cores. A high deposition rate in these areas can alter type 2 into type 3. It appears that the maximum of type 2 hump can act as a stratigraphic marker since type 2 cores are the most common ones and are widely distributed over the entire Pacific

Solar control of Southwest monsoon on centennial timescales

Solar forcing is proposed to be a major governing factor for the southwest monsoon (SWM) strength during the Holocene. The southeastern Arabian Sea is significantly affected by monsoon run-off and is an ideal testing ground. We analysed stable oxygen isotopic composition (δ18O) of three species of planktonic foraminifera (Globigerinoides ruber, Gs. sacculifer and Globarotalia menardii) with high time-resolution (~50 yrs) in a sediment core raised from the region, and documented past variations in SWM precipitation. High-resolution isotopic and spectral analyses show that solar forcing indeed played a major role in governing the past variations in SWM precipitation on centennial timescales

Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin

The miliolite deposits of Saurashtra have been dated by 234U, 230Th, 231Pa and 14C methods. Concordant ages of ~105 years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting a contemporaneous origin for both. The lower 14C ages (≤40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute only ≤ 10% by weight, as such the aeolian characteristics of quartz grains may not be relevant to the origin of the miliolites

AMS facility at institute of physics, Bhubaneswar: inter-laboratory comparison of results

Radiocarbon dating has found wide applications in many areas of science like archaeology, geology, oceanography, palaeoseismology and palaeoclimatology. As a tracer, radiocarbon has applications in biology and medicine. Radiocarbon dating using Accelerator Mass Spectrometry (AMS) provides several advantages over the conventional decay counting method. The first AMS facility in India for radiocarbon dating has become operational at the Institute of Physics, Bhubaneswar. This note describes the operational features of this facility and inter-laboratory comparison of data

Discovery of a tephra bed in the Quaternary alluvial sediments of Pune district (Maharashtra), Peninsular India

This article does not have an abstract