Southwest Monsoon Period Research Articles

Fine-scale spatial and temporal acoustic occurrence of island-associated odontocetes near a mid-oceanic atoll in the northern Indian Ocean

Temporal patterns of oceanic predators can provide valuable information on both lunar and diel influences not just on the distributions of these predators, but also on prey patches that are often difficult to study. Mid-oceanic island chains in the northern Indian Ocean have high odontocete occurrence, but the ecology of these animals is not well characterized. We investigated fine-scale spatial and temporal patterns of island-associated odontocetes using passive acoustic monitoring from January 2019 to January 2020 around Kavaratti Island, Lakshadweep, India. Based on opportunistic recordings in the presence of odontocetes, the majority of the detected whistles were likely made by spinner dolphinsStenella longirostris. We identified a resident population whose whistle occurrence was significantly influenced by month, site, and diel and lunar cycles. More acoustic detections were made in the northeast monsoon month of November and fewer during pre-monsoon and southwest monsoon periods. Distinct day-night differences along with fine-scale temporal variability were also observed, suggesting that delphinids use nearshore waters as a daytime resting habitat. Odontocete detections were highest during the new moon period and lowest during the first quarter phase. Detection rates were higher on the south side of the island. Our study shows that solar and lunar cycles modulate odontocete vocal occurrence, presumably through influences on their prey. Similarities of odontocete occurrence around Lakshadweep to other mid-oceanic island chains suggests that an island-associated micronekton community may exist around Lakshadweep that may also be important to other pelagic species targeted by local fisheries.

Large Scale Processes for Understanding Extreme Rain Storm Over Rangamati on 12 June 2017- A Case Study

Attempts have been made to study the large-scale surface and upper air synoptic processes associated with a monsoon depression during 11-12 June 2017. In this study, Grid Analysis and Display System (GrADS) software has been used to prepare the large-scale sea level pressure and upper flow patterns by analyzing the FNL re-analysis data. In this analysis, FNL dataset is used to characterize the rainstorms, with key hydrometeorological variables describing the prior conditions of the very heavy rainfall event presented the study. National Center for Environmental Prediction (NCEP) Final (FNL) analysis data of 1o by 1o grids for every 6 hours are used for large scale synoptic analysis. The disastrous event was a strong monsoon depression in the early period of southwest monsoon 2017. Due to this depression, very heavy rainfall occurred in the southeastern Bangladesh. Rangamati recorded 343 mm of rainfall in the 24 hours on 12 June 2017. Massive landslides occurred in three districts such as Rangamati, Bandarban and Chittagong. The analysis of surface and upper air synoptic conditions has revealed that a well-marked low was formed over the northwest Bay of Bengal within the low-pressure belt passing from Somalia coast extending through southern Pakistan, and India up to east central Bay of Bengal and adjoining Bangladesh. The wind speed is calculated from the pressure distribution and is found to be 24.23ms-1, which is at par with the observed one. The well-marked low was subsequently intensified into a depression and moved northeastwards over Bangladesh. Strong southsouthwesterly winds were associated in the eastern side of the depression, especially over Chittagong Hill Tracts. The depression was found to extend up to 500 hPa level as seen from the distribution of geopotential and strong circulation around the centre. Winds were advecting from large continental and Ocean areas over the South Asia. Strong winds and moisture influx, strong narrow coma-like trough from a micro low at the surface to 500 hPa level as well as strong wind shear were responsible for the heavy rainfall, disastrous effects and massive landslides over Rangamati and adjoining areas.
 Journal of Engineering Science 11(2), 2020, 87-97

Spatial and temporal distributions of stable isotopes in precipitation over Thailand

AbstractSpatial and temporal variations of the isotopic composition of precipitation over Thailand were investigated. The local meteoric water line for Thailand deviates slightly from the global meteoric water line, with lower slopes (7.62 ± 0.07, 7.59 ± 0.08) and intercepts (6.42 ± 0.39, 6.22 ± 0.42) using ordinary and precipitation weighted methods. Differences in spatial and temporal δ18O distributions between the tropical monsoon and tropical savanna climate zones were found due to differing moisture source contributions and seasonal precipitation patterns. The temporal data reveals that the northeast monsoon rains originate from isotopically‐enriched local moisture with isotope values of −9.36 to −0.09‰ (mean − 3.73 ± 0.42‰), whereas the southwest monsoon clouds had a more significant rainout effect from Rayleigh distillation, with isotope values of −9.56 to −1.78‰ (mean − 5.40 ± 0.38‰). The precipitation amount at each site was negatively correlated with δ18O (−0.24 to −3.20‰ per 100 mm, R2 = 0.1–0.9). Furthermore, δ18O was negatively correlated with geography (latitude, altitude) for the southwest monsoon periods, as expected based on other observed correlations. However, an inverse correlation was seen in the northeast monsoon due to differing moisture transportation as part of the continental effect. The correlation coefficient (R) was higher in the southwest monsoon (−0.84 for latitude effect, −0.64 for altitude effect) than the northeast monsoon (0.67 for latitude effect, 0.35 for altitude effect). The spatial pattern of isotopic composition reflects the southwest monsoon more clearly than the northeast monsoon, but the two monsoons also have a cancelling impact on orographic patterns. An agreement of the δ18O and deuterium excess (d‐excess) was a negative correlation and found to reflect precipitation sources and re‐evaporation processes. The d‐excess was slightly higher for the northeast monsoon, bringing moisture from the Pacific Ocean and travelling across the continent before reaching the observed stations. By contrast, the d‐excess was relatively lower for the Indian Ocean's moisture in the southwest monsoon.

Provenance tracing of long-range transported dust over the Northeastern Arabian Sea during the southwest monsoon

One of the major pathways for dust supply to surface water of the Arabian Sea is via wet deposition, which is significant during southwest Monsoon (June-September). Aeolian dust supplies macro and micronutrients, which can impact on several marine biogeochemical processes. Here we report, major elements and rare earth elements (REEs) content as well as mineralogical and Sr-Nd isotopic composition of particulate collected from wet deposition (WDP) during the southwest monsoon period over the Northeastern Arabian Sea (NEAS) (Goa; 15.4° N, 73.8° E) in 2013. The collected WDP samples are classified into three categories based on changing wind regime, namely: (1) beginning of monsoon (BM; June); (2) mid of monsoon (MM; July-August) and (3) end of monsoon (EM; September). Our result highlights a significant temporal variability in REEs pattern showing a decreasing trend of Lan/Ybn and relatively higher Eu*/Eu anomaly during mid of monsoon compared to beginning and end of monsoon period. High palygorskite (P) with moderate smectite (S) is observed for beginning of monsoon and majority of mid monsoon samples, however, high smectite with moderate palygorskite and negligible palygorskite and smectite abundance is observed for few of mid monsoon and end of monsoon samples, respectively, indicating change in dust sources during the southwest monsoon period. We also observed temporal variability in 87Sr/86Sr (0.7090–0.7193) and εNd (−2.3 to −9.1) isotopic compositions wherein less radiogenic 87Sr/86Sr and relatively more positive εNd is exhibited by mid of monsoon samples compared to those observed in beginning and end of monsoon collections. The seasonal variability in geochemical tracers are related to changes in the dust source areas which are identified as (1) the Arabian Peninsula contributing significantly in beginning of monsoon and majority of mid monsoon samples; (2) Northeastern Africa contributing to some of the mid monsoon samples and (3) Southwest Asia and Thar Desert in end of monsoon samples. These source identification using geochemical tracers are corroborated by the satellite images (CALIPSO and aerosol index maps) and back-trajectory analyses.

C-band dual-polarization Doppler weather radar at Thumba (8.537°N, 76.865°E): initial results and validation

Recently, a C-band dual-polarization Doppler weather radar (C-DWR) was installed at Thumba (8.537°N, 76.865°E), a coastal station in the southern peninsula of India known as “Gateway of Indian Summer Monsoon.” The C-DWR operates in the frequency range of 5.6 to 5.65 GHz with a peak transmitting power of 250 kW at 0.004 duty ratio and employs the state-of-the-art technology for both transmitting and receiving subsystems. Apart from providing regular base products such as reflectivity (Z), radial velocity (V), and spectral width (σ), the DWR being equipped with dual-polarization capability provides differential reflectivity (Zdr), differential phase shift (ϕdp), and correlation coefficient (ρhv). This is the first DWR with polarimetric capability developed indigenously in India. The C-DWR was operated during North-East as well as South-West monsoon period to evaluate its performance with special emphasis on the reflectivity and rainfall intensity measurements. Before the commencement of the campaign, the C-DWR was calibrated using a metallic sphere and the appropriate corrections were made to the radar constant. The preliminary results show that the radar products are consistent with present understanding of precipitating cloud systems. The simultaneous observations of precipitating clouds by C-DWR and Global Precipitation Measurement mission are used to evaluate the former. The comparison of spatial pattern of reflectivity from space-based radars and C-DWR shows very good agreement, qualitatively. The C-DWR-derived rainfall observations also show very good agreement with ground-based laser precipitating monitor measurements. The regression analysis between the C-DWR and laser precipitation monitor-derived rainfall shows a correlation coefficient of 0.89. The C-DWR observations during the passage of tropical cyclone Ockhi are also discussed. The significance of this study lies in describing the first indigenously developed C-band dual-polarization radar and its validation using the space- and ground-based observations.

Chemical characteristics of rainwater in the tropical rainforest region in northwestern Borneo

A comprehensive study of the chemical composition of rainwater was carried out from October 2016 to September 2017 in the equatorial tropical rainforest region of northwestern Borneo. Monthly cumulative rainwater samples were collected from different locations in the Limbang River Basin (LRB) and were later categorized into seasonal samples representing northeast monsoon (NEM), southwest monsoon (SWM), and inter-monsoon (IM) periods. Physical parameters (pH, EC, TDS, DO, and turbidity), major ions (HCO3-, Cl-, Ca2+, Mg2+, Na+, and K+) and trace metals (Co, Ni, Cd, Fe, Mn, Pb, Zn, and Cu) were analyzed from collected rainwater samples. Rainwater is slightly alkaline with mean pH higher than 5.8. Chloride and bicarbonate are the most abundant ions, and the concentration of major ions in seasonal rainwater has shown slight variation which follows a descending order of HCO3-> Cl-> Na+ > Ca2+ > Mg2+ > K+ in NEM and Cl- > HCO3- > Na+ > Ca2+ > K+ > Mg2+ in SWM and Cl- > HCO3- > Na+ > Ca2+ > Mg2+ > K+ in IM period. Trace metals such as Fe and Ni have shown dominance in seasonal rainwater samples, and all the metals have shown variation in concentration in different seasons. Variation in chemical characteristic of seasonal rainwater samples identified through piper diagram indicates dominance of Ca2+-Mg2+-HCO3- and mixed Ca2+-Mg2+-Cl- facies during NEM, SWM, and IM periods. Statistical analysis of the results through two-way ANOVA and Pearson's correlation also indicates significant variation in physico-chemical characteristics. This suggests a variation in contributing sources during the monsoon seasons. Factor analysis confirmed the source variation by explaining the total variance of 79.80%, 90.72%, and 90.52% with three factor components in NEM, SWM, and IM rainwater samples with different loading of parameters. Enrichment factor analysis revealed a combined contribution of marine and crustal sources except K+ which was solely from crustal sources. Sample analysis of backward air mass trajectory supports all these findings by explaining seasonal variation in the source of pollutants reaching the study area. Overall, the results show that the chemical composition of seasonal rainwater samples in LRB was significantly influenced by natural as well as anthropogenic processes. These include (long-range and local) industrial activities, fossil fuel combustion, forest burning, transportation activities including road transport and shipping activities, and land-derived soil dust along with chemical constituents carried by seasonal wind.

An Assessment of Onshore and Offshore Wind Energy Potential in India Using Moth Flame Optimization

Wind energy is one of the supremely renewable energy sources and has been widely established worldwide. Due to strong seasonal variations in the wind resource, accurate predictions of wind resource assessment and appropriate wind speed distribution models (for any location) are the significant facets for planning and commissioning wind farms. In this work, the wind characteristics and wind potential assessment of onshore, offshore, and nearshore locations of India—particularly Kayathar in Tamilnadu, the Gulf of Khambhat, and Jafrabad in Gujarat—are statistically analyzed with wind distribution methods. Further, the resource assessments are carried out using Weibull, Rayleigh, gamma, Nakagami, generalized extreme value (GEV), lognormal, inverse Gaussian, Rician, Birnbaum–Sandras, and Bimodal–Weibull distribution methods. Additionally, the advent of artificial intelligence and soft computing techniques with the moth flame optimization (MFO) method leads to superior results in solving complex problems and parameter estimations. The data analytics are carried out in the MATLAB platform, with in-house coding developed for MFO parameters estimated through optimization and other wind distribution parameters using the maximum likelihood method. The observed outcomes show that the MFO method performed well on parameter estimation. Correspondingly, wind power generation was shown to peak at the South West Monsoon periods from June to September, with mean wind speeds ranging from 9 to 12 m/s. Furthermore, the wind speed distribution method of mixed Weibull, Nakagami, and Rician methods performed well in calculating potential assessments for the targeted locations. Likewise, the Gulf of Khambhat (offshore) area has steady wind speeds ranging from 7 to 10 m/s with less turbulence intensity and the highest wind power density of 431 watts/m2. The proposed optimization method proves its potential for accurate assessment of Indian wind conditions in selected locations.

Rainfall Variation in Major River Basins in India and the Association with the Indo-Pacific Oceans

Varikoden, H.; Roja, C.; Revadekar, J.V., and Milind, M., 2020. Rainfall variation in major river basins in India and the association with the Indo-Pacific Oceans. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 1-6. Coconut Creek (Florida), ISSN 0749-0208.The summer monsoon rainfall is the major water source for most parts of India and people depend on this water source for their livelihood. The rainfall during this season is highly variable over space and time. The rainfall during the southwest monsoon period is the main source of flow discharge in most of the rivers in India. In the present study, we made an attempt to explore the variability and trends in rainfall over the Ganges, Brahmaputra, Godavari and Krishna river basins. Northern river basins show a negative trend indicating the decrease of rainfall and increasing trends are observed in peninsular river basins. The Brahmaputra river basin shows a significant decreasing trend (-0.16 mm day-1 decade-1). Moreover, the variability in multi-time scale is also different for different basins. Among all the river basins considered in the study, the Brahmaputra river basin registered high average rainfall (15.11 mm day-1 with a standard deviation of 2.23 mm day-1) and the Krishna river basin the least (3.57 mm day-1 with a standard deviation of 0.87 mm day-1). Further, the large scale teleconnection of the rainfall with individual river basins has also been assessed. The Ganga river basin is one of the largest river basins and this region is highly influenced by the Arabian Sea and the west Pacific Ocean (Nino 3.4 region). However, the Brahmaputra basin does not show much connection with Sea Surface Temperatures (SST) over the west Pacific Ocean, the Arabian Sea or the Bay of Bengal. The rainfall in the Godavari and Krishna river basins have more influence on SSTs over the central Pacific Ocean.

Wave Height Trends off Central West Coast of India

Kerkar, J.P.; Seelam, J.K., and Jena, B.K., 2020. Wave height trends off central west coast of India. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 97-104. Coconut Creek (Florida), ISSN 0749-0208.Wave height trends off three sites along 100 m and 20 m depth contours off the central west coast of India have been estimated using 46 years hindcast-wind-wave data simulated for the Indian Ocean region. The wind waves were simulated with NCEP/NCAR winds as input to a third generation spectral wind wave model. This study showed an increasing trend for the annual mean significant wave heights from south to north ranging between 0.25 and 0.36 cm/year. The wave heights during the southwest monsoon and fair weather periods were observed to have similar trends. The study also showed increasing trends in water depths of 20 m compared to that of 100 m water depth, wherein a maximum increase of 0.22 cm/year is observed.

Analytical study of the performance of the IMERG over the Indian landmass

AbstractThe paper compares the final run of Integrated Multi‐Satellite Retrieval of Global Precipitation Mission (IMERG) products with India Meteorological Department (IMD) gridded data over the Indian land mass during the southwest monsoon period (June–September) in the period 2014–2017. Spatiotemporal variations of the IMERG are evaluated with IMD rainfall by employing different statistical techniques, and the capability of the IMERG is examined using the categorical skill metrics. A region in central India is the focus in order to study the southwest monsoon's static and dynamic characteristics, such as rainfall distribution and monsoon activity, using the IMERG in conjunction with IMD rainfall data sets. The integrated condensation rate (ICR) was estimated using the specific humidity profiles, and it correlated with the IMERG and IMD rainfall. The IMERG is found to be a potential source for adequately reflecting the ground gauge‐gridded data of categorical rainfall amounts, from very light rain (trace–2.4 mm) to very heavy rain (about 115.6–204.4 mm). However, the IMERG does not reflect satisfactorily the extreme heavy rain events (≥ 204.5 mm·day–1) during the study period. The significant correlation between IMERG/IMD rainfall and the ICR suggests that improved adjustments methods are required for better results when depicting accurate extreme heavy rainfall events by the IMERG.

Monsoonal variation of the marine phytoplankton community in Kota Kinabalu, Sabah

Monsoon-driven changes of environmental factors have been reported to be significantly variable and affects the phytoplankton community in tropical waters. This study examined the monsoonal changes of environmental parameters and the coastal phytoplankton community, including potential harmful algal bloom species, in the waters of Kota Kinabalu, Sabah, Malaysia. Bi-weekly observations were conducted from August 2017 to January 2019, covering the Southwest Monsoon (SWM), Northeast Monsoon (NEM), and inter-monsoon periods (IMPs). Sea surface temperature, salinity, and daily average photosynthetic active radiation (PAR) were significantly different between the SWM and the NEM. Total phytoplankton densities were significantly higher in the SWM with median cell densities of 1.12 × 104 cells L−1 compared to the NEM with 3.98 × 103 cells L−1. Nutrient measurements indicated that the waters were mesotrophic, with low phosphate (P) levels (<0.3 μM-P on average). N:P ratios were often above the Redfield ratio (16N:1P), while high Si:N (>1) and Si:P ratios (>16Si:1P) indicated that silicate was not limiting, a condition favourable for diatom growth. Phytoplankton dynamics shifted from a dinoflagellate-dominant community (Protoperidinium spp. and Prorocentrum spp.) to a diatom-dominant community (Leptocylindrus spp. and Dactyliosolen spp.) during the NEM, which was preceded by a peak in silicate and nitrate. Later, Chaetoceros spp. became dominant during the second SWM. The presence of intermittent increases in Margalefidinium polykrikoides and Pyrodinium bahamense var. compressum cell densities may trigger future blooms in these waters. Canonical Correspondence Analysis suggests that the dinoflagellate-dominant community was driven by changes in PAR and Si:N while changes in N:P and salinity shaped the diatom-dominant community. The shifts of the phytoplankton community composition in relation to the different monsoonal periods suggests that the monsoons function as environmental drivers which structure the phytoplankton community of this coastal ecosystem.

Influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the Upper Gulf of Thailand

Organic carbon cycling in SE Asia is data-sparse and poorly studied, although high sediment yield and organic carbon intensity occur in the tropical region. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT). This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during November 2013 when tropical cyclones impacted. POC in the estuarine sections is more significantly influenced by the seasonal shift compared with the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the estuarine sections impacted by CHAO and MK. Anthropogenic inputs and dam regulation also influences the river export of organic matter during the high precipitation periods. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is more obviously influenced by marine-derived factors. TOC in sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr−1) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate-controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.

Freshening of seawater in the Mahim Bay, Mumbai, India: Insight from an environmental isotope study

ABSTRACT An environmental isotope study was conducted to assess the cause for the freshening of seawater observed in the Mahim Bay, Mumbai, India after a storm event during the southwest monsoon period. Water samples were collected from the various locations of the coastal water and the suspected inland water sources such as rain, river and groundwater and analysed for major ion species and stable isotopes (δ18O and δ2H). Dissolved radon (222Rn) in the coastal water was monitored in-situ. Field monitoring survey in the coastal water indicated lower electrical conductivity (1,730 μS/cm) near Mahim Mosque compared to the surrounding shelf waters. Relatively high excess 222Rn activities (up to 55 Bq/m3) were observed in the Mahim Bay, even after 13 days of seawater freshening event. Based on the hydrochemical and isotope results, various prevailing hypotheses on the occurrence of low salinity water in the Mahim Bay were tested. It is inferred that the low salinity coastal water was associated with groundwater discharge occurring in the Mahim Bay and in the Mithi River and were unlikely due to the overflow of Vihar and Powai Lakes in the catchment of Mithi River and surface runoff because of the rain/storm events. Temporal variations of electrical conductivity and stable isotopic composition of coastal water in the Mahim Bay showed that the groundwater inputs were decreasing after the storm event. 222Rn was found to be a useful tracer for distinguishing the subsurface flow of water to the coastal system.

Impact of seasonal rainfall trend and its variability on crop production in rainshadow districts of Chhattisgarh: A case study in Kawardha district

In this research work we studied the impact of seasonal rainfall trend and its variability on production of major crops at Kawardha district of Chhattisgarh state. For this study, long term rainfall data (1962-2015) and crop data (2000-2014) were used. The mean annual rainfall of 983.8 mm was recorded in Kawardha with coefficient of variation of 17 %. The coefficient of variation was lowest during monsoon season like the CV during July and August is less than 40 % where as it is more than 50 % but less than 60 % in June and September months. In Kawardha district, mean annual rainfall of 983.8 mm was observed out of which south- west monsoon received 854.7 mm with coefficient of variation 18 percent. During south-west monsoon period mean of 46 days was observed with coefficient of variation of 19 percent. Rest of seasons received mean rainy days of less than 6 with coefficient of variation more than 70 percent. Rest of seasons received the mean rainfall of less than 70 mm with coefficient of variation of more than 90 percent. The CV of less than 100 percent was found during the season of north-east monsoon period. The seasonal rainfall pattern in this area is similar to annual rainfall as more than 90 per cent of annual rainfall is received during kharif season. There is a statistically non significant trend of seasonal rainfall has been found in this district but a significant rainfall trend was found in the month of August at 5 % level of significance. The area, production and productivity of all the selected crops are showing a significant increasing trend with some exception in Maize (decreasing trend of area), Soyabean(productivity trend is not significant) and arhar (non significant value).The main crop production of the district was concentrated on this seasonal rainfall pattern. So, water harvesting and storage is more convenient steps towards this.

Changes in Wave Energy in the Shelf Seas of India during the Last 40 Years Based on ERA5 Reanalysis Data

Ocean wave energy is one of the cleanest renewable energy sources around the globe, but wave energy varies widely from place to place and from time to time. The long-term variability of wave power at 20 locations in the Indian shelf seas from 1979 to 2018 is described here using the European Centre for Medium-Range Weather Forecasts recently released ERA5 reanalysis hourly data. The variability is calculated on a yearly and monthly basis for the locations based on the coefficient of variation. The annual average wave power varied from 2.3 (at location 16 in the western Bay of Bengal) to 11 kW/m (at location 2 in the northeastern Arabian Sea). Along the western shelf seas, the maximum value of wave power is during the southwest monsoon period and along the east coast, it is during the tropical cyclone period. The standard deviation in wave power is more than the mean value at locations along the northern shelf seas of India, indicating a large variability in wave power in an annual cycle. The west coast locations are shown to have a slightly higher increasing trend with an average of 0.024 kW/m per year, while the increasing trend in wave power of east coast locations is with an average of 0.015 kW/m per year. The study also examines the variation in wave power from deep to shallow water at 2 locations using the wave characteristics obtained from the numerical model SWAN. The electric power output from a few wave energy converters are calculated for all the locations and found that the southernmost locations have a steady and higher percentage of power production.

The large-bodied copepods off Masirah Island, Oman: An investigation of Southwest Monsoon onset and die-off

Abstract Masirah Island, situated off the southern coast of Oman in the Arabian Sea, is surrounded by upwelled water during the Southwest Monsoon (SWM) and was used as a base for time-series studies of the copepod community for a decade beginning in 2006, covering the Spring Intermonsoon (SIM), April–May, and including June, and the SWM period, August–October. Subeucalanus pileatus and Calanoides natalis were the two most abundant copepod species (33.9% and 32.7% respectively of the total abundances). These two species shifted their dominance during the two main seasonal periods. During the SWM, C. natalis was the dominant species occurring mainly at sea surface temperatures (SST) between 18 and 27 °C while S. pileatus dominated during the SIM occurring at warmer SSTs, frequently between 25 and 28 °C. Results from generalized linear models indicated that the season and the SST were the best predicted variables affecting the abundances of C. natalis and S. pileatus. Calanoides carinatus was also affected by wind speed and wind direction, meaning that strong SWM winds and low temperatures (seasonal upwelling) favor the occurrence of this species. Upwelling favorable winds lasted longer in 2015/2016 than in 2009/2010; peak winds shifted from June in 2009–2011 to July in 2012–2016. The SST was higher in 2016 than in the previous five years. Time-series of C. natalis life stages showed three large peaks of early copepodites from June through September 2016 during the SWM season, in contrast to only one peak observed at the beginning of the SWM season from previous years. This result suggests that C. natalis was able to capitalize on the longer SWM in 2016 by continuing to reproduce throughout September. Diapausing C. natalis reached the surface in mid-to-late June as stage CV, ruling out any reproduction by this species at its overwintering depth. Unfavorable SST at the end of the SWM corresponded to a downward migration by C. natalis in 2015. Overall, the physical forcing of this upwelling region appears to be changing and C. natalis seems to be adapting to these changing conditions by continuing to reproduce at the surface as long as SST is favorable.

Spatial and statistical trend characteristics of rainfall erosivity (R) in upper catchment of Baram River, Borneo.

The upper catchment region of the Baram River in Sarawak (Malaysian Borneo) is undergoing severe land degradation due to soil erosion. Heavy rainfall with high erosive power has led to a number of soil erosion hotspots. The goal of the present study is to generate an understanding about the spatial characteristics of seasonal and annual rainfall erosivity (R), which not only control sediment delivery from the region but also determine the quantity of material potentially eroded. Mean annual rainfall and rainfall erosivity range from 2170 to 5167mm and 1632 to 5319MJmmha-1h-1year-1, respectively. Seasonal rainfall and rainfall erosivity range from 848 to 1872mm and 558 to 1883MJmmha-1h-1year-1 for the southwest (SW) monsoon, 902 to 2200mm and 664 to 2793MJmmha-1h-1year-1 for the northeast (NE) monsoon and 400 to 933mm and 331 to 1075MJmmha-1h-1year-1 during the inter-monsoon (IM) period. Linear regression, Spearman's Rho and Mann Kendall tests were applied.Considering the regional mean rainfall erosivity in the study area, all the methods show an overall non-significant decreasing trend (- 9.34, - 0.25 and - 0.30MJmmha-1h-1year-1, respectively for linear regression, Spearman's Rho and Mann Kendall tests). However, during SW monsoon and IM periods, rainfall erosivity showed a non-significant decreasing trend (- 25.45, - 0.52, - 0.40, and - 8.86, - 1.07, - 0.77MJmmha-1h-1year-1, respectively) whereas in NE, monsoon season erosivity showed a non-significant increasing trend (14.90, 1.59 and 1.60MJmmha-1h-1year-1, respectively). The mean erosivity density ranges from 0.77 to 1.38MJha-1h-1year-1 and shows decreasing trend. Spatial distribution pattern of erosivity density indicates significantly higher occurrence of erosive rainfall in the lower elevation portion of the study area. The spatial pattern of mean rainfall erosivity trends (linear, Spearman's Rho and Mann Kendall) suggests that the study area can be divided into two zones with increasing rainfall erosivity trends in the northern zone and decreasing trends in the southern zone. These results can be used to plan conservation measures to reduce sediment delivery from localized soil erosion hotspots.

Reproductive Biology of Malabar Pufferfish Carinotetraodon travancoricus (Tetraodontidae)

Carinotetraodon travancoricus, is endemic to rivers of Western Ghats of India and supports a lucrative export trade of live aquarium fishes from India. Aspects of its reproduction are studied from fishes collected from the Pampa River, South India. Among 966 fishes analyzed females predominated in March and males in May. However, the overall sex ratio was close to 1 : 1. Ripe gonads could be encountered in almost all months, but registered significantly higher preponderances during May to August. A total length of 18.33 mm is observed as the size at first maturity in males and 18.0 mm in females. Highest mean gonadosomatic index was recorded in August (1.4%) in males and in June in females (6.1%). Significant variation in oocyte diameter among different ovary maturity stages has been observed. Primary oocytes at the previtellogenic stages, oocytes with perinulceolar stage as well as with advanced vitellogenic stage were present in ripe ovaries, indicating asynchronous maturation. The absolute fecundity ranges from 139 (21 mm TL) to 480 (29 mm TL). The present results indicate that though fishes with ripe gonads occur throughout the year, the peak spawning period for C. travancoricus inhabiting the Pampa River extends from May to August concurring with South-West monsoon period.

Seasonal dynamics of microzooplankton communities in the Sea of Oman (Arabian Sea)

Seasonal dynamics of microzooplankton and changes in environmental condition were analysed during a one-year field sampling campaign in the Sea of Oman at two different stations. Monsoon winds in this region cause distinct seasonality patterns with high primary productivity during the south-west monsoon in summer (June to October) and north-east monsoon periods in winter (November to March). Microzooplankton in the Sea of Oman showed several biomass peaks throughout the year. In general, higher biomass occurred during the south-west monsoon when compared to the north-east monsoon period with maxima of 190 µg C l−1at the inshore station Bandar Al-Khyran at 1m and 308 µg C l−1 at 10m water depth. At the offshore-station, peaks of 372 µg C l−1 (1m) and 256 µg C l−1 (20m) occurred during the south-west monsoon. A strong coupling between phytoplankton and microzooplankton was observed during monsoon periods but some microzooplankton peaked during inter-monsoon periods when chlorophyll concentration was low (Bandar Al-Khyran: 372 µg C l−1 at 1m and 196 µg C l−1, 10m; Offshore-station: 419 µg C l−1, 20 m). The initiation of phytoplankton blooms in the Sea of Oman was bottom-up controlled due to strong seasonal nutrient influx during south-west and north-east monsoon periods. Highest microzooplankton biomass occurred during monsoon periods with a dominance of Noctiluciphyceae and peaks of 7596 µg C l−1 at Bandar Al-Khyran (1m) and 5942 µg C l−1 (10m). Copepod nauplii, Amoebozoa and Larvacea contributed substantially to microzooplankton biomass throughout the year. Ciliophora contributed low proportion to the total microzooplankton biomass peaking both during monsoon and inter-monsoon periods. During the spring inter-monsoon, choreotrich ciliates (tintinnids) showed distinct peaks of 15.9 µg C l−1 at Bandar Al-Khyran (1m) and 17.7 µg C l−1 (10m) as well as 18.2 µg C l−1 at Offshore-station (20m). The interplay between bottom-up controlled primary production and top-down control mechanisms regulates the phenology patterns of specific microzooplankton groups in the Sea of Oman thus pointing at complex trophodynamic interactions at the lowermost foodweb level in this low-latitude ecosystem.

Influence of Oceanographic Parameters on the Seasonal Potential Fishing Grounds of Rastrelliger kanagurta using Maximum Entropy Models and Remotely Sensed Data

Understanding of the spatial distribution of fish habitats is crucial in order to achieve optimum fishing and to increase efficiency of marine resource management. In this study, seasonal potential suitability habitat model for Rastrelliger kanagurta off the east coast of Peninsular Malaysia was derived using maximum entropy (MaxEnt) by utilizing fishing locations and environmental parameters from remotely sensed sea surface temperature (SST) and chl-a concentration (chl-a) data. The influence of environmental parameters on the formation of the potential fishing zones was also determined. The results showed that all the seasonal models performed significantly better than random with AUC > 0.80, which indicated that the constructed models were applicable with ‘good’ to ‘excellent’ predictive accuracy. The model also showed that chl-a influenced R. kanagurta’s potential fishing ground during northeast and intermediate monsoon of October. Meanwhile, SST contributed more in defining the potential fishing grounds during southwest and intermediate monsoon period of April. The seasonal and spatial extents of potential fishing grounds were largely explained by chl-a (0.32-0.42 mg/m3 during northeast, 0.27-0.66 mg/m3 in April, 0.21-0.30 mg/m3 during southwest monsoon and 0.22-0.39 mg/m3 in October) and SST (29.05-29.94oC during northeast monsoon, 31.18-31.47oC in April, 31.17-31.48oC during southwest monsoon and 30.34-31.11oC in October). This indicated that seasonal changes in oceanographic parameters influenced spatial distribution of fish. The results also demonstrated the applicability and potential of MaxEnt in determination of potential fishing grounds and describing the influence of oceanographic factors on the formation of the area.