The Book "MONSOON BIOGEOCHEMISTRY (1993), contains 15 Articles dealing with various topics is edited by V. Ittekkot & R.R. Nair and published by the Im Selbstverlag des Geologisch-Pal„ontologischen Institutes der, Universit„t Hamburg, Germany. Each of the article is reviewed here seperately.
1. "The effect of Eurasian snow cover on regional and global climate variations" by T.P. Barnett, L. Diimenil, U. Schlese, E. Roeckner and M. Latif with the help of numerical simulations with a global atmospheric circulation model suggest large scale variations in the amount of snowfall over Eurasia in springtime are linked to the subsequent strength of the Asian Summer monsoon. The model results show snow cover effects to subsequently after the climatic fields known to be intimately associated with the El Nino-Southern Oscillation (ENSO) phenomenon.
The model used in this study is a low resolution version of the European Centre for Medium Range forecasting (ECMWF) weather prediction model. Interestingly, the model results suggest that the failure of the Asian monsoon is a part of a far larger modulation of the global climate system. Specifically, there appear to be important tele-connections between the large convection region of Southeast Asia and the atmospheric fields over the tropical pacific and North America.
This paper has 5 figures and shows the hypothesis that the amount and extent of Asian snow cover has a subsequent effect on the strength of the Asian monsoon with a sophisticated atmospheric circulation model. Increased snow cover leads to a poor monsoon, while halving the snow leads to a good monsoon.
2. "Inorganic grain size analysis of some major Bangladesh rivers" by K. Kranck, T. Milligan, S. Khatun, J.U. Ahmad, M. Hussain, S. Saifullah. According to the authors, an enormous amount of sediments are transported (2.5 billion tons annually) by the major rivers of Bangladesh, which is second only to the Yangtze with 3 billion tons. This large amount of sediment transport has a profound effect on the geomorphology and geochemistry of the Bangladesh Flood plains, downstream coastal region and the continental shelf of the Bay of Bengal.
A total of 500 samples were collected from the major rivers of Bangladesh, The Ganges, Brahmaputra, Meghna, Tista and their tributaries and distributaries. Grain size spectral analyses were carried out at the particle dynamics laboratory of the Bedford Institute of Oceanography as described by Milligan and Kranck (1991) (given in the references). The results of grain size analysis are listed as Volume Sediment in each size classes (ppm) and plotted as log-log frequency spectra of volume Vs. diameter (illustrated in the text with several figures).
The grain size distribution shows marked variation from one river to another. The Brahmaputra and Tista have greater population of larger particles while the Ganges and Meghna tend towards finer grains. This is ascribed to their individual transport histories. Each river presents its own history and origin of sediments which is evident from the grain size spectra. This brief paper does not discuss the anthropogenic effects on the grain size distribution.
3. "Cycling of inorganic nitrogen compounds between atmospheric and ocean in tropical areas off Southeast Asia" - P. Schafer, H. Kreilein, M. Miiller and G. Grarenhorst. The concentrations of inorganic nitrogen species were determined in the atmospheric gaseous and particulate phases and in rain sampled during two research cruises in spring and autumn 1988 in the Bay of Bengal, the South China Sea and in the Western Pacific. Inorganic nitrogen ions such as ammonium and nitrate contribute less than a few percent to the total mass of marine aerosol. Estimates of ammonia emission from the Western tropical pacific ocean to the atmosphere are similar to the deposition rates of ammonium in aerosol and rain, in contrast nitrate nitrogen is land derived. In comparison with primary productivity and sediment trap data from the three areas the contribution of atmospheric nitrate deposition to new production can be upto 82%.
With 10 tables and 2 figures, this paper gives an excellent account of the cycling of inorganic nitrogen compounds in the region. However, the authors feel the need for more measurements with better seasonal and regional coverage for a complete evaluation of nitrogen cycling between the atmosphere and the ocean.
4. "Salinity extreme in the Arabian Sea" - S.S.C. Shenoi, S.R. Shetye, A.D. Gouveia and G.S. Michael. The Arabian Sea exhibits distinct horizontal salinity gradients in the upper 1000m due to differences in precipitation and evaporation over the sea. Levitus (1982) climatology has been used to identify four extreme, three maxima and one minimum in the vertical salinity profiles in the Arabian Sea. Their geographical distribution, depth, Q-S characteristics and seasonal variablity are described. Two of the maxima arise from the influence of Red Sea and The Persian Gulf Water. The third, which lies at the bottom of the equatorial surface water, forms due to freshening at the surface of high salinity Arabian Sea near-surface waters.
5. "Biological Processes of the Northern Indian Ocean" - M. Madhupratap and A.M. Parulekar. The International Indian Ocean expedition (1960-65) gathered the first synoptic data on the biological mapping, studies on distribution and zoogeographical patterns in the region. Since then, more data bases have been available by scientists from National Institute of Oceanography, India. In this paper, the authors have recapitulated the known features in biological productivity and distribution and the processes leading to them. Along Coastal areas, upwelling during Southwest monsoon is one major process influencing the productivity. Unlike other oceans, in the Arabian Sea, Wind-driven upwelling is stronger along the western boundary than the eastern boundary system.
Coastal waters off Somali and Arabia are recognized to be some of the most productive areas in the world. The Bay of Bengal is considered to be less productive although many major world rivers bring in large quantities of nutrients. The less productivity is due to the narrow shelf, heavy cloud cover and less light penetration. The bio-productivity in different climatic conditions is described on the whole, the overall production in the northern Indian ocean, is quite high. Coastal upwelling during summer monsoon is a major physical process forcing the nutrients into the euphotic water column. Lateral advection may enhance production in offshore areas of the Northwestern Arabian Sea. Winter cooling and consequent convective overturning of surface waters in the northern Arabian Sea, wind induced entrainment of subsurface waters and equatorial divergence are other mechanisms cited for enrichment. The effect of the enormous production, modify in turn the physics and biogeochemical dynamics of the ocean. The low oxygen content leading to near anoxic conditions trigger nitrate reducing and denitrifying bacteria to switch over to the use of nitrate as an electron acceptor in energy generation. This paper with 6 figures gives lot of information on biological productivity and its variation in the Indian Ocean.
6. "Variable Relationships of DOC with oxygen in the Northwestern Indian Ocean and their ecological implications" - A. Rajendran, M. Dileep Kumar, N. Ramaiah, V. Ittekkot and B.N. Desai. Oceanic dissolved organic matter contains more carbon than the combined aquatic and terrestrial biospheres and forms an important pool in the global carbon cycle. Still, considerable uncertainty exists in the amount and nature of this important carbon pool. This paper discuses the factors controlling regional differences in DOC and its ecological implications.
The nature of DOC depends on the types of organisms present in an aquatic body wherein some might produce predominantly microbially degradable organic compounds. Vertical distribution of DOC shows that there is a marked mid-depth increase in DOC whereas this is absent in the northern Arabian Sea. This increase is attributed to horizontal advection or in similar production. There exists two different processes regulating the DOC dynamics in the Arabian Sea. The Southern Arabian Sea shows high values of DOC implying the dominance of nitrification whereas low DOC values in the Northern and Central regions prove the prevalence of denitrification. This paper is illustrated with 4 figures and 4 tables.
7. "Variability of Monsoonal upwelling signals in the deep western Arabian Sea" - B. Haake, T. Rixen and V. Ittekkot. This study is a report of four years of observations between 1986 and 1990 including four South-West monsoons of different intensities based on fluxes measured at a depth of 3000m. The primary maximum of particle fluxes occurs during the South-West monsoon with a secondary maximum during the North-East monsoon.
Particle fluxes reveal a bimodal pattern with the annual maximum between June and September and a secondary maximum between December and February. Carbonate is the major constituent of particulate matter contributing between 35% and 70% to bulk fluxes. The higher values are typical of the early South-West monsoon, inter monsoon periods and the Noth-East monsoon, whereas the lower values occur mostly during the flux peaks in the late South-West monsoon. Biogenic opal generally contributes less than 15% to total fluxes except during the South-West monsoon flux peaks when opal contents reach values upto 50%.
8. "Lithogenic fluxes to the Nothern Indian Ocean - an overview" - V. Ramaswamy. Total particulate and Lithogenic fluxes to the deep traps in the eastern, central and western Arabian Sea for the period May 1986 to November 1988 are presented. Lithogenic fluxes to the northern Indian ocean, measured by time-series sediment traps, exhibit a strong seasonality with the bulk of the material (40 to 80%) being deposited during the Southwest monsoon period. This seasonality is more pronounced in the Arabian Sea than in the Bay of Bengal. The Western and Central Arabian Sea receive predominantly colian dust from the Somali-Arabian deserts while the eastern Arabian Sea and the Bay of bengal receive mostly fluvial material from the rivers draining the Himalayas and the Indian peninsula.
Annual lithogenic fluxes in the Bay of Bengal (8.6 to 28.0 gm-2) are about five times that of the Arabian Sea (2.6 to 5.4 gm-2). Increase of lithogenic flux with depth is seen in areas where flurial input is more due to scavenging of the standing stock suspended matter by sinking biogenic aggregates. In areas where colian sediments predominate there is no significant increase of lithogenic flux with depth. This paper has 4 figures and 5 tables.
9. "Fluxes and decomposition of organic matter in the Western Arabian Sea: Amino acids and Hexosamines" - T. Rixen and B. Haake. Organic matter transfer from surface waters to the deep sea is one of the important sinks for atmospheric CO 2. Understanding the processes affecting the efficiency of this transfer is an important aspect for reconstruction of climate.
Fluxes of organic carbon, amino acids and dexosamines have been measured from 1986 to 1990 by time series sediment traps in the western Arabian Sea. The fluxes of organic carbon, amino acids and hexosamines reveal a binodal pattern with a pronounced maximum during the South-West monsoon and a less pronounced maximum during the North-East monsoon. The amount of organic carbon, amino acids and hexosamines transferred to the deep sea is more when the relative contribution of diatoms is higher. The main decomposition of particulate organic matter after its export from the surface water takes place between 100 and 1000m water depth. Bacterial hydrolysis of particulate organic matter can be mainly responsible for the observed particulate organic matter decomposition from the surface waters to the sediments. This paper has 8 figures and 5 tables.
10. "Fatty acids in settling particles in the Northern Indian Ocean" - T.Reemtsmaand V.Ittekkot. Fatty acids have been analyzed on settling particles collected during the summer- monsoon by time series sediment trap deployed at two depths in the Central Arabian Sea (732m, 2914m) and in the Nothern Bay of Bengal (809m, 1750m). In the Nothern Bay of Bengal, the fatty acids are the highest (797mg m-2d-1) and result from enhanced marine primary production from nutrients derived from the Ganges and Brahmaputra river system. Flux patterns in these two regions during summer monsoon differ depending on the dominant monsoonal effects, wind related effects in the Central Arabian Sea and the influence of river discharge in the northern Bay of Bengal.
The fatty acid composition revealed a higher relative contribution of terrigenous fatty acids in the Central Arabian Sea compared to the northern Bay of Bengal. It is an indication for the overwhelming stimulation of primary production by river effluent. This paper is presented with 3 figures and 3 tables.
11. "Sterol fluxes to the deep Arabian Sea as indicators for organic matter composition" - A. Jenisch, B. Haake and W. Michaelis.
Sterol data indicate differences in composition of organic matter which might be due to varying sedimentation processes related to monsoonal wind regimes. Sterols are widespread among organisms in which they serve as membrane constituents and are involved in the regulation of metabolic and transport processes, in energy storage, reproduction etc. They also provide information on digenetic transformations of organic matter.
The particulate matter of the western Arabina Sea revealed lower total sterol concentrations with a higher rate of preservation of the organic material than compared to those settling in the Central and Eastern Arabian Sea. The annual fluxes of sterols are substantially higher for the Arabian Sea.
12. "Some aspects of microfouling and corrosion of materials in the tropical marine environment" - N.B. Bhosle. Materials immersed in seawater experience a series of discrete chemical and biological events which result in the formation of a complex layer of attached organisms known as biofouling. This paper discusses on the microfouling material developed on aluminum panels after immersion in estuarine, coastal, shelf and oceanic waters. A single step scraping with nylon brush removed the highest amount of the microfouling material. The microfouling biomass is higher in coastal and shelf waters as compared to oceanic waters.
Corrosion of metals immersed in sea water is controlled by several factors such as temperature, dissolved oxygen, salinity, PH and hydrostatic pressure. Furthermore, nitrogen and sulfur containing organic compounds and several water soluble vitamins have been known to inhibit corrosion of metals in fresh and brackish waters as well as in acidic media. This paper discusses on the methods to remove microfouling material, distribution of microfouling biomass, biological and chemical composition ofmicrofouling biomass, as well as the corrosion of mild steel immersed in tropical marine environment.
13. "Aerosol dust in late quaternary sediments of the northern Indian Ocean" - F. Sirocko. Global maps of dust dispersal over the Nothern Indian Ocean show that there was frequent occurrence of dust plums in the region. The aerosol dust studies in the present paper indicate that the hemipelagic, not-turbiditic sediments of the Northwestern Indian ocean, the Arabian sea are composed mainly of wind-borne lithogenics derived from Arabia, Mesopotamia and Pakistan. Alluvial contributions are prominent in the Gulf of Oman, at the Indian Continental margin and in turbidities of the Indus deep fan.
The book gives a wealth of information on the physical, biological, geological and chemical aspects of the Indian Ocean. This should be made an important addition to all libraries dealing with the subjects.
DR. G.J. CHAKRAPANI
DEPARTMENT OF EARTH SCIENCES
UNIVERSITY OF ROORKEE
ROORKEE - 247 667 INDIA
SEA LEVEL RISE : A GLOBAL VOLUNTARY ASSESSMENT
SEA LEVEL RISE : A GLOBAL VOLUNTARY ASSESSMENT (1993). The Global Vulnerability Assessment : Vulnerability Assessment for Population, Coastal Wetlands and Rice Production on a Global Scale has been published to generate some first vulnerability results on a global scale related to people living along the world coasts, the vulnerable coastal ecosystems and significant rice production in the low lying regions.
The volume tried to address the following three important elements of the coastal zone and accompanying impacts.
i) Population at risk (i.e., the number of people subject to regular flooding) on a global scale;
ii) Coastal Wetlands of international importance at loss (i.e., the ecologically valuable coastal wetland area under a serious threat of loss) on a global scale;
iii) Rice Production of international importance at loss (i.e., the the changes in coastal rice yields due to less favourable conditions) in South, Southeast and East Asia.
In addition, a set of measures has been developed in this book which will help us to compare the "with - and without measures" situation in the case of Acceleration of Global Sea Level Rise (ASLR). Unit costs such measures have been highlighted in this study and combined with the results of the "World- wide Coast Estimate" prepared by the Coastal Zone Management Subgroup (CZMS) for the Intergovernmental Panel on Climate Change (IPCC) in 1990.
In this context, it is very satisfying to note that this study provides a worldwide estimate of socio- economic and ecological implications of ASLR even though the results have only limited accuracy and validity. In order to define and assess the vulnerability of a coastal zone to ASLR, uniform procedures are needed, so that regional and national studies on impacts of ASLR can be compared and integrated. The common methodology adopted in this report suggests a number of these procedures.
Crucial to these procedures are the concepts of values at risk, values at loss and values at changes which help to determine impacts in measurable and objective terms and it is very important to note that these concepts are used in this report.
To sum up, the report will serve as an excellent document for scientists and policy makers working in the area of Coastal Zone Management. It will enable the reader to build up enough confidence to take up more regional/Country case studies which will ultimately help us to reduce the uncertainities in Global Climate Change and the impact of the coastal zone due to global Sea Level Change.
Dr. R. RAMESH
CENTRE FOR WATER RESOURCES
ANNA UNIVERSITY, GUINDY
MADRAS - 600 025