Southeast Monsoon Season Research Articles

Assemblage structure and distribution of fish larvae on the North Kenya Banks during the Southeast Monsoon season

The North Kenya Banks (NKB) is the broadest area of continental shelf along the Kenyan coast, and experiences higher productivity relative to neighbouring shelf regions. It is an area of great importance to Kenya with new emerging fisheries that have the potential to improve the livelihoods of local impoverished fishing communities. Managing these emerging fisheries successfully however is challenged by insufficient data on the fisheries and the local marine environment, and the lack of a management plan specifically for the NKB region. Here, baseline information on the ichthyoplankton assemblage across the NKB region during the Southeast Monsoon season is described and analysed to understand the effect biophysical parameters have on larval composition, abundance and distribution. The dominant fish larvae families were Engraulidae (29.5% of total) followed by Sphyraenidae (8.6%), Carangidae (8.2%), Scombridae (6.2%) and Lutjanidae (5.5%), whilst the dominant species within these families were Encrasicholina sp., Sphyraena sp., Thunnus albacares, T. alalunga and Lutjanus sp., respectively. A high prevalence of larvae from migratory species such as T. albacares, T. alalunga and Gempylus serpens was found across the northern part of the NKB, suggesting that the area may be an important nursery area for migratory fish with implications for fisheries across the wider Western Indian Ocean. Zooplankton abundance, temperature and conductivity played a positive role in determining the structure and composition of fish larvae assemblages across the NKB region. The high larval densities encountered out to the shelf break (200 m contour) imply that the NKB is a productive fishery and as such requires appropriate management oversight. Furthermore, the identification of a clear influence by temperature on larval distributions suggests that the NKB fishery may be susceptible to predicted future warming in this region with implications for both management of the resource and those fishing communities who benefit from the fisheries.

Natuna Off-Shelf Current (NOC) Vertical Variability and Its Relation to ENSO in the North Natuna Sea

During the northwest monsoon (NWM), southerly flow off the Natuna Islands appeared as the extension of the turning Vietnam coastal jet, known as Natuna off-shelf current (NOC). NOC is generated by the interaction of wind stress and the North Natuna Sea’s bottom topography. The purposes of the present study is to investigate the vertical variability of NOC and its relation to El Niňo Southern Oscillation (ENSO) using Marine Copernicus reanalysis data. The vertical variability refers to the spatial distribution of NOC pattern at the surface layer, thermocline layer, and deep/bottom layer. in 2014 as representative of normal ENSO condition. To investigate the effect of ENSO, the spatial distribution of NOC in 2011 and 2016 were compared which represent the La Niňa and El Niňo conditions, respectively. The results show that NOC starts to generate at the southeast monsoon season to the transition I season and peaks in the northwest monsoon season. The occurrence of NOC is identified at all depth layers with the weakened NOC at the deep layer. Related to the ENSO effect, La Niňa tends to strengthen NOC while El Niňo tends to weaken NOC. These are releted with the strengthening and weakening northerly wind speed during La Niňa and El Niňo, Respectively. During La Niňa events, the NOC occurs more frequently than during El Niňo. Thus, beside affecting the magnitude of NOC, ENSO also influence the frequency occurrence of NOC.

Northwest monsoon upwelling within the Indonesian seas

ABSTRACT The previous studies of upwelling within the Indonesian seas only focused on the Southeast Monsoon (SEM) season. The western coast of Sumatra Island; the southern coast of Java Island, Sunda Islands, and Sulawesi Island; the Banda Sea, the Maluku Sea, and the Arafura Sea are well-known SEM upwelling areas. However, the upwelling events during Northwest monsoon (NWM) have never been investigated. The investigation of NWM upwelling is challenging due to the broad cloud coverage, limiting the observation of infrared and visible sensors of the satellites. This study used the blended products of the satellite-based sea surface temperature (SST), chlorophyll-a (chl-a), sea level anomaly (SLA), surface wind, and rainfall to identify the NWM upwelling occurrences. Remote sensing reflectances 443 nm and 555 nm were also used to examine the influence of suspended sediment and organic matter which may bias the chl-a concentration. Along the northern coast of the Lesser Sunda Islands, the north coast of Papua Island and the Malacca Strait are the areas of NWM upwelling as denoted by the positive anomaly of chl-a, the negative anomaly of SST, and the negative anomaly of SLA. Focusing on the area along the northern coast of the Lesser Sunda Islands, the NWM upwelling is generated by offshore Ekman Mass Transport that reduces SST and increases chl-a. From 2010 onwards, El Niňo Southern Oscillation has a more consistent effect on the NWM upwelling than Indian Ocean Dipole. El Niňo (La Niňa) tends to weaken (strengthen) upwelling. The magnitude of NWM upwelling is weaker than SEM upwelling.

Chemical Characteristics of Atmospheric PM10 and PM2.5 at a Rural Site of Lijiang City, China.

Emissions from biomass burning are very serious in Southeast Asia and South Asia in April. In order to explore the effect of long-range transport of biomass emissions from the Indochina Peninsula in Southwest China during the period of the southeast monsoon season and to find out the main pollution sources in local atmospheric PM2.5, a field campaign was conducted from 6–26 April 2011 in Lijiang, China. Twenty-four-hour PM10 and PM2.5 filter samples were collected, and inorganic ions, elements, and carbonaceous components (including organic carbon (OC) and elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs (NPAHs)) were measured. The monthly mean mass concentrations of particulate matter (PM) were 40.4 and 14.4 μg/m3 for PM10 and PM2.5, respectively. The monthly mean concentrations of OC and EC in PM10 were 6.2 and 1.6 μg/m3, respectively. The weekly mean concentrations of ∑PAHs and ∑NPAHs were 11.9 ng/m3 and 289 pg/m3, respectively, in atmospheric PM10 of Lijiang. The diagnostic ratios of PAH and NPAH isomers were used to analyze the sources of PAHs and NPAHs in PM10. The ratios of Benz(a)anthracene/(Chrysene+Benz(a)anthracen), Fluoranthene/(Fluoranthene+Pyrene) and Indeno(1,2,3-cd)pyrene/(Benzo(g,h,i)perylene+Indeno(1,2,3-cd)pyrene) were 0.45 ± 0.04, 0.61 ± 0.01, and 0.53 ± 0.03, respectively, indicating the contribution from coal combustion and biomass burning. The 1-nitropyrene/Pyrene (1-NP/Pyr) ratio was 0.004 ± 0.001, suggesting that the contribution to NPAHs mainly came from coal combustion. Sulfate was the most prominent inorganic ionic species, with monthly mean levels of 2.28 and 1.39 μg/m3 in PM10 and PM2.5, respectively. The monthly mean mass ratios of NO3−/SO42− were 0.40 and 0.23 in PM10 and PM2.5, respectively, indicating that the contribution of atmospheric anions from coal combustion sources was much more important than that from other sources. Based on the relatively high SO42− concentrations and low NO3−/SO42− ratios, combined with the data analysis of isomer ratios of PAHs and NPAHs, we can conclude that coal combustion, traffic, and dust were the major contributors to local atmospheric PM in Lijiang city, while biomass burning may also have contributed to local atmospheric PM in Lijiang city to some degree.

Observations of Cross-Shore Chenier Dynamics in Demak, Indonesia

Cheniers are important for stabilising mud-dominated coastlines. A chenier is a body of wave-reworked, coarse-grained sediment consisting of sand and shells overlying a muddy substrate. In this paper we present and analyse a week of field observations of the dynamics of a single chenier along the coast of Demak, Indonesia. Despite relatively calm hydrodynamics during the one-week observational period, the chenier migrated surprisingly fast in the landward direction. The role of the tide and waves on the cross-shore chenier dynamics is explored using velocity moments as a proxy for the sediment transport. This approach shows that both tide and waves are capable of transporting the sediment of the chenier system. During calm conditions (representative for the south-east monsoon season), the tides generate a landward-directed sediment transport when the chenier crest is high relative to mean sea level. Waves only generate substantial sediment transport (direct, via skewness, and indirect, via stirring) when the chenier is submerged during periods with higher waves. The cross-shore chenier dynamics are very sensitive to the timing of tide and waves: most transport takes place when high water levels coincide with (relatively) high waves.

Characterisation of artisanal catches in selected fishing areas of the Lower Tana Delta and Malindi-Ungwana Bay, Kenya

Shore-based assessment of fisheries resources in Ngomeni, Kipini and Ozi fishing areas of Malindi-Ungwana Bay and the Lower Tana Delta on the north coast of Kenya was conducted from January to December 2017 to establish catch composition, species richness, and fishing effort (catch-rate, number and types of fishing gears and crafts) in the marine, estuarine and riverine habitats. Distinct catch composition (R = 0.27, P < 0.05) was observed across the three habitats. Catch composition differed significantly spatially and seasonally across the three fishing areas, and between the north east (NE) and south east (SE) monsoon seasons (R = 0.332, P < 0.05). The wolf herring, Chirocentrus dorab, was the most abundant fish species in Ngomeni, centrally located in Malindi-Ungwana Bay, while the catfishes, Arius africanus and Clarias gariepinus, were the most abundant species in Kipini and Ozi, respectively. Gillnets operated from dhows (mashua) and fibre-reinforced plastic (FRP) boats in Ngomeni (marine), and canoes using-basket traps in Ozi (riverine), landed significantly larger Spanish mackerel, Scomberomorus commerson, and sea catfish, Arius africanus (Kruskal Wallis test: Df = 2; F = 197.141; p < 0.001; Df = 2, F = 490, p < 0.001), respectively. Species diversity by area in combination with habitat and type of fishing craft showed higher diversity for Ngomeni in the marine habitat with mashua fishing crafts than in Kipini. Significantly different catch rates (Df = 2, F = 10.43, p<0.001; Df = 1, F = 5.897, p < 0.021) were observed in the three (3) fishing areas and during the NE monsoon and the SE monsoon, respectively. Canoes were the most common fishing craft used, especially in Ngomeni, accounting for 37.1%, and 97.5% in Ozi, while mashua crafts accounted for 44.5% of the total fishing craft in Kipini. Monofilament nets were most common in Ngomeni (34.0%) while basket traps dominated the Ozi site at 63.6%. The Kipini area was dominated by handlines (28.8%). It is therefore evident that the three (3) fishing areas of the Malindi-Ungwana Bay and Lower Tana Delta showed significant differences in catch composition and size of fish caught, attributed partly to the variation in habitat types and fishing methods between the sites. Overall, the Ngomeni area was characterized by more advanced fishing craft with the majority powered by engines, including mashua and FRP boats, compared to Kipini and Ozi fishing areas where canoes were dominant.

Ekman dynamics variability along the southern coast of Java revealed by satellite data

ABSTRACT It has been widely known that the coastal upwelling along the southern coast of Java is generated by southeasterly wind which induces offshore Ekman Mass Transport (EMT) during southeast monsoon. However, the variability of EMT has not been fully described in previous studies. The present study investigated the variability of Ekman dynamics which consist of EMT and Ekman Pumping Velocity (EPV) along the southern coast of Java, based on remotely sensed data. We demonstrated the incongruity between the distribution of southeasterly wind speed and sea surface temperature (SST) during southeast monsoon which is related to the distribution of Ekman dynamics. Offshore EMT at the western region of the southern coast of Java is stronger than offshore EMT at the eastern region. However, stronger offshore EMT at the western part is inhibited by downwelling EPV while weaker offshore EMT at the eastern part is accelerated by upwelling EPV. Consequently, SSTs at the eastern parts are lower than those at the western parts. Thus, the changes of offshore EMT intensity from eastern to western parts are balanced by their EPV distributions which explain the incongruity between the distribution of wind speed and SST during southeast monsoon. On an interannual timescale, the combination of La Niña and negative Indian Ocean Dipole (IOD) events tends to weaken offshore EMT and EPV which reduce the intensity of Chl-a bloom and SST cooling during southeast monsoon season. Furthermore, ENSO has a less significant impact on the Ekman dynamics variability than IOD.

Kehadiran Gelombang Soliter dan Transpor Sesaat Sedimen tersuspensi di Perairan Pantai Bengkulu Tengah

<strong>Existence of Solitary Waves and Transient Suspended Sediment Transport in the Coastal Waters of Central Bengkulu. </strong>Coastal abrasion and suspended sediment transport driven by waves is occurring dreadfully in the coastal waters of Central Bengkulu. The abrasion tends to be accelerated by solitary waves during the southeast monsoon season. The primary data were obtained on 17-26 July 2014, while the secondary data derived from Google Maps imageries obtained on 17 June 2014, representing the southeast monsoon season. The primary data were collected by 1200 KHz Acoustic Doppler Current Profiler (ADCP) for water currents, a single beam Echosounder for depths, Garmin 276C GPS receiver for coordinate positions, RBR-TWR2050 (installed at at a fixed point at 102.2219 °E and 3.6916 °S and depth of 9 m) for height and wave periods, and a compass for the direction of wave propagation. The secondary data included Astrium satellite imageries compiled by Google Earth and displayed as Google Maps images on 17 June 2014. These images were used for identifying the appearance of wave groups and by using a feature in Google Earth, it showed that the estimated distance between wave packets hitting the coast accounted for 147 m. This study showed the existence of solitary waves with height and wave period of 1.02 m and 13.85 seconds respectively, while the wave length reached 147.7 m. The wave energy and wave energy flux were 1123.12 Jm<sup>-2</sup> and 12018.94 Jm<sup>-1</sup>s<sup>-1</sup>, calculated by using the cnoidal wave theory and solved by the KdV equation. These solitary waves have large destructive forces on unstable cliffs along the coasts. Derived from coastal abrasion processes and shown by the ADCP backscatter intensity with the highest of 146 dB, the suspended sediments were likely to be transported by water currents with an average speed of 25.99 cm s<sup>-1</sup> in the dominant direction to the south - southeast; and the sediments were deposited along the coast of Bengkulu City.

Microplastics on the Menu: Plastics Pollute Indonesian Manta Ray and Whale Shark Feeding Grounds

The implications of plastic pollution, including microplastics, on marine ecosystems and species are increasingly seen as an environmental disaster. Yet few reports focus on filter-feeding megafauna in regions heavily impacted by plastic pollution, such as Indonesia in the Coral Triangle, a global marine biodiversity hotspot. Here, we evaluate plastic abundance and characterize debris from feeding grounds for manta rays (Mobula alfredi) and whale sharks (Rhincodon typus) in three coastal locations in Indonesia: Nusa Penida Marine Protected Area, Komodo National Park, and Pantai Bentar, East Java. A 200 µm plankton net was used to sample the top 0.5 m of the water column (‘trawl survey’) and floating plastics were assessed along ~ 440 m long transects (‘visual survey’) during the Indonesian north-west (‘wet’) and south-east (‘dry’) monsoon seasons during 2016 – 2018. Microplastics were identified visually, measured and categorized from trawl samples, and larger floating plastics were counted from vessels in visual transects. Plastic abundance ranged widely from 0.04 to 0.90 pieces m-3 (trawl survey) and 210 to 40,844 pieces km-2 (visual survey). Results from linear models showed significant seasonal and location differences in estimated plastic abundance for trawl and visual surveys in Nusa Penida and Komodo. Plastic abundance was up to ~ 44 times higher in the wet than the dry season, with the largest seasonal effect observed in Nusa Penida. Overall, small pieces 50% combined) were the most prevalent plastics. Theoretical plastic ingestion rates were calculated using estimated filtration volumes of manta rays and whale sharks and the mean plastic abundance in their feeding grounds. Upper plastic ingestion estimates for manta rays were ~ 63 and 25 pieces h-1 for Nusa Penida and Komodo locations, respectively, and ~137 pieces h-1 for whale sharks in Java. Analysis of manta ray egested material confirmed plastic ingestion, the consequences of which might include exposure to toxic plastic additives and adhered persistent organic pollutants. Communicating this information to communities who stand to benefit from healthy megafauna populations might help local governments as they work towards reducing plastics in the marine environment.

The Influence of Seasonal and Interannual Variability on Surface Chlorophyll-a Off the Western Lesser Sunda Islands

Novel and long-term satellite data (2003–2017) are analyzed to investigate the variability of ocean surface chlorophyll-a (Chl-a) concentration off the Western Lesser Sunda Islands (WLSI) under the influence of the Indonesian Australian monsoon, the El Nino-Southern Oscillation, and the Indian Ocean Dipole (IOD). In this article, we first analyzed the seasonal variability of Chl-a, and then describe the relationship among the sea surface Chl-a, sea surface temperature (SST), and sea surface wind stress in the region. Our results demonstrate that prevailing southeasterly wind stress plays a pivotal role in generating the Chl-a maxima off the WLSI. Particularly on seasonal time scale, the strengthening of southeasterly wind stress (up to ∼0.01 N·m−2) during the southeast monsoon season produces enhanced Chl-a concentrations (0.59 mg·m−3) associated with sea surface cooling (∼28.8 °C) in the area of study. In contrast, the Chl-a maxima completely vanished during the northwest monsoon season. On interannual time scale, the largest positive Chl-a and wind stress anomalies and the coolest SST anomaly are observed in 2006 when El Nino and positive IOD events occur at the same time. Meanwhile, the greatest negative Chl-a anomaly is prevailed during the 2016 negative IOD event. This article demonstrates that wind variability is the essential factor in determining the magnitude of the Chl-a maxima off the WLSI.

Spatio-temporal variability of surface chlorophyll-a in the Halmahera Sea and its relation to ENSO and the Indian Ocean Dipole

ABSTRACT Long-term satellite data are used to investigate the variability of ocean surface chlorophyll-a (chl-a) concentration in the Halmahera Sea (HS) under influence of the Australian-Indonesian Monsoon (AIM), the El Niño-Southern Oscillation (ENSO), and the Indian Ocean Dipole (IOD). In this study, we first analysed the seasonal variability of chl-a, and then examine the relationship between surface chl-a, sea surface temperature (SST), and sea surface wind stress in the area. Our results suggest that prevailing southeasterly winds play a fundamental role in generating chl-a blooms in the HS. Particularly on a seasonal timescale, through the mechanism of Ekman mass transport, strengthening of southeasterly wind stress during the Southeast Monsoon season (June – August) produces enhanced chl-a concentrations associated with ocean surface cooling in the area of study. On the other hand, the chl-a bloom completely diminishes during the Northwest Monsoon season (December – February) due to weakening of wind stress and Ekman transport. On an interannual timescale, sea level pressure and wind stress are coherent with ENSO and IOD phases. During El Niño and positive IOD events (La Niña and negative IOD events), both sea level pressure and wind stress greatly increase (decrease) over the HS. These conditions cause an anomaly in southerly (northerly) wind stress, which is favourable to an enhancement (reduction) of the chl-a concentration in the region. This study demonstrates that sea level pressure and wind stress are the critical factors in determining the magnitude of chl-a bloom in the HS.

Distinct Characteristics of SST Variabilities in the Sulawesi Sea and the Northern Part of the Maluku Sea During the Southeast Monsoon

The Sulawesi Sea and the northern part of the Maluku Sea belong to the western equatorial Pacific that is influenced by the Mindanao Current. During the southeast (SE) monsoon, contrasting sea surface temperature (SST) distributions occur between these two seas. The purpose of this research is to investigate the mechanisms of contrasting SST distribution in the Sulawesi Sea and the northern part of the Maluku Sea under the condition of strong southerly wind during the SE monsoon season. Our analysis was based on satellite observations. Warmer (colder) SSTs are identified in the Sulawesi Sea (northern part of the Maluku Sea), which correspond to the weaker (stronger) southerly wind speed. Strong southerly winds in the northern part of the Maluku Sea generate eastward Ekman mass transport (EMT) that carries the water mass away from the coast, inducing upwelling. In contrast, the southerly winds from the Maluku Sea are blocked by the Gorontalo and North Sulawesi Mountains, creating low-wind areas in the Sulawesi Sea that are located on the lee side of those mountains. Furthermore, the existence of a valley between those mountains acts as a wind gap that channels the southerly wind to the Sulawesi Sea. Since the seaward EMT is weak and the latent heat release is not dominant, SSTs in front of the wind gap are only slightly reduced, possibly through the mechanisms of oceanic mixing.

Seasonal and spatial variation of surface current in the Pemba Channel, Tanzania.

The surface current speeds within the Pemba channel were examined using 24 years of drifter data received from the Global Drifter Program. This study aimed to uncover varying surface current in the Pemba Channel in different seasons. The results revealed the Pemba Channel experiences relatively higher median surface current speeds during the southeast (SE) monsoon season compared to the northeast (NE) and inter-monsoon (IN) periods. The strongest current speeds were confined in waters deeper than 200 meters between ~39.4°E and 39.7°E. These results prove that surface currents from the drifters can be used to uncover the patterns of surface circulation even in areas where in-situ measurements are scarce.

The influence of physical-chemical variables on the spatial and seasonal variation of Chlorophyll-a in coastal waters of Unguja, Zanzibar, Tanzania

Chlorophyll-a (Chl-a) concentrations were measured at four sites around Unguja, Zanzibar during the northeast (NE) and southeast (SE) monsoon seasons. Data for Chl- a , nitrate, phosphate, ammonia, dissolved oxygen, sea sur - face temperature, pH and salinity were collected once a month from March 2008 to March 2009. The SE monsoon had insignificantly higher Chl- a compared to the NE monsoon season when Chl- a for Bawe, Chumbe, Pongwe and Mnemba were combined (W = 234, p = 0.93). The drivers of high Chl- a during the SE monsoon were ammonia and nitrate. Results from individual sites showed that Pongwe and Mnemba had higher median Chl- a during the SE- than the NE monsoon season. Temperature, dissolved oxygen and ammonia were the major factors that influenced high Chl- a at these sites. In contrast, Chumbe and Bawe had higher median Chl- a during the NE- than the SE mon- soon season. The major factors influencing high Chl- a in the NE at Chumbe and Bawe were high levels of nutrients, mainly from sewage effluent and various human activities around the coast in Zanzibar town. The interaction of Chl- a between monsoon seasons (NE and SE) and sites (Bawe, Chumbe, Pongwe and Mnemba) was insignificant (F (1,3) = 1.3144, p = 0.2949). The principal component analysis revealed that different physical and chemical environmental variables affect Chl- a concentration over time and location.

On the Influence of Enso And IOD on Rainfall Variability Over The Musi Basin, South Sumatra

The southern Sumatera region experiences one rainy season and one dry season in a year associated with seasonal change in monsoonal winds. The peak of rainy season is occurring in November-December-January during the northwest monsoon season, while the dry season comes in June-July-August during the southeast monsoon season. This study is designed to evaluate possible influence of the coupled ocean-atmospheric modes in the tropical Indo-Pacific region, namely the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) on the rainfall variability over the catchment area of the Music Basin, South Sumatera. The ENSO and IOD occurrences were reflected by the variability of sea surface temperature (SST) in the tropical Pacific and Indian Ocean, respectively. During El Niño and/or positive IOD episode, negative SST anomalies cover the eastern tropical Indian Ocean and western tropical Pacific including the Indonesian seas, leading to suppress convective activities that result in reduce precipitation over the maritime continent. The situation is reversed during La Niña and/or negative IOD event. The results revealed that the high topography area (e.g. Bukit Barisan) was shown to be instrumental to the pattern of rainfall variability. During the 2010 negative IOD co-occurring with La Niña event, the rainfall was significantly increase over the region. This excess rainfall was associated with warm SST anomaly over the eastern tropical Indian Ocean and the Indonesian seas. On the other hand, extreme drought event tends to occur during the 2015 positive IOD simultaneously with the occurrence of the El Niño events Investigation on the SST patterns revealed that cold SST anomalies covered the Indonesian seas during the peak phase of the 2015 positive IOD and El Niño event.

GOATFISH (MULLIDAE) RESOURCES IN VIETNAM SEA BASED ON BOTTOM TRAWL SURVEY IN THE PERIOD 2012 - 2013

During 2012 - 2013, under the project “The current status and movements of fisheries resources in Vietnam sea” two surveys were conducted to investigate bottom fish resources with 494 hauls. Based on the research results, 16 species belonging to 3 genera of goatfishes were analyzed. The goatfish output accounted for 0.34 - 4.31% compared to the total output of bottom fish in the survey time. The species Upeneus japonicus comprised 62 - 94% of the output of the goatfishes. The average exploitation yield of goatfishes in the Northeast monsoon season was 1.035 kg/h and that in the Southwest monsoon season was 1.446 kg/h. The exploitation yield had a tendency of decrease compared with the previous studies. The distribution density was the highest in the Southwestern region areas and the lowest in the Gulf of Tonkin; Meanwhile according to spatial distribution the density of goatfishes was the highest in the depth < 20 m and the lowest in the depth from 30 - 50 m. The estimation for the total biomass of goatfishes in the Northeast monsoon season was 13,450 tons and in the Southeast monsoon season was 15,321 tons.

Wind-Driven Coastal Upwelling in the Southern Coast of Yogyakarta

Satellite measurement provides synoptic view of sea surface wind and can be used to study variability of coastal upwelling. Here we analyzed data of 12 years of satellite-derived sea surface wind, sea surface temperature (SST), and sea surface chlorophyll-a (Chl-a) to examine the spatial and temporal distributions of coastal upwelling off the Yogyakarta waters. Results show that upwelling occurs during the Southeast Monsoon (SEM) season. During this season, the Yogyakarta waters are dominated by strong wind speed (~7 m/s) and SST cooling (25 °C). Whereas during the Northwest Monsoon (NWM) season the low wind speed (<4 m/s) no longer favor upwelling and SST cooling. We suggest that as the Yogyakarta coastline is oriented east-west, northwesterly winds result in downwelling condition at the coast, while southeasterly winds lead to the offshore Ekman transport of surface water and subsequent upwelling.

A NUMERICAL SIMULATION OF THE WIND-DRIVEN WATER CIRCULATION ON THE SUNDA SHELF

A numerical simulation of the barotropic circulation over the Sunda Shelt was carried out for a time-invariant wind field corresponding to (a) the Northwest Monsoon and (b) the Southeast Monsoon seasons. Starting from a state of rest, the current and surface configurations were timestepped until an apparent state of equilibrium was reached. The resulting current pattern and sea-surface topography are in good agreement with observations during those two seasons.

Spatial and temporal variability of surface chlorophyll-a in the Gulf of Tomini, Sulawesi, Indonesia

Sari QW, Siswanto E, Setiabudidaya D, Yustian I, Iskandar I. 2018. Spatial and temporal variability of surface chlorophyll-a in the Gulf of Tomini, Sulawesi, Indonesia. Biodiversitas 19: 793-801. The Gulf of Tomini (GoT) is mostly influenced by seasonal and interannual events. So, the immensive aim of this study is to explore spatial and temporal variations of chlorophyll-a (chl-a) and oceanographic parameters in the GoT under the influences of monsoonal winds, El Niño Southern Oscillation (ENSO), and Indian Ocean Dipole (IOD). The data were collected from the satellite imaging of chl-a and sea and surface temperature (SST) as well as surface wind from the reanalysis data for a period of January 2003 to December 2015. Monthly variations of the chl-a and SST in the GoT reveal chl-a bloom in the center part to the mouth of the GoT during the southeast monsoon season (boreal summer). The chl-a concentrations were relatively higher (>0.1 mg m-3) and distributed throughout most of the areas near the Maluku Sea. The SST in the middle of the GoT was relatively lower than that near the Maluku Sea (the eastern part of the GoT). On the other hand, during the northwest monsoon (boreal winter), the chl-a concentration decreased (<0.1 mg m-3). During this season, the SST was relatively higher (28-29 °C) than that during the boreal summer (27-26 °C) and distributed uniformly. Meanwhile, on interannual timescale, the ENSO and IOD play important role in regulating chl-a distribution in the GoT. High surface chl-a concentration was observed during El Niño and/or positive IOD events. Enhanced surface chl-a concentration during El Niño and/or positive IOD events was associated with the upward Ekman pumping induced by the southeasterly wind anomalies. The situation was reversed during the Niña and/or negative IOD events.

Heat accumulation and soil properties as affected by transparent plastic mulch in Blackgram (Vigna mungo) doubled cropped with Groundnut (Arachis hypogaea) in sequence under rainfed conditions in Tamil Nadu, India

Though plastic film mulch technology has been used widely to increase crop productivity in dryland farming, the economical as well as environmental costs associated with plastic mulches is the major factor limiting the wider adoption of this technology. With the objective of reducing the cost of plastic films by growing more than one crop prior to its disposal, experiments were conducted over 3 years (2012–15) during South West monsoon (SWM) and North East monsoon season (NEM) with four treatments, T1- Transparent plastic mulch maintained for two crops (TPM I), T2- Transparent plastic mulch laid new for each crop(TPM II), T3- Non mulched beds maintained for two crops (NM I) and T4 – Non mulched new beds for each crop (NM II). The crops sown were Blackgram (Vigna mungo) in the first season (SWM) and Groundnut (Arachis hypogaea) in the second season (NEM). Results indicated that soil temperatures appeared highest under transparent mulch in different phenophases of both blackgram and groundnut from sowing to harvest. The mulch film was physically sound even upto the harvest of the second crop (Groundnut) in each year of the study. The light transmission through the transparent mulch maintained for two seasons (TPM I) was also not relatively reduced which has been evidently seen in the soil temperature observed. Both air Degree −Days (DD) and soil Degree –Days (DD) varied between mulched and non- mulched treatments at all the phenophases of observation. The physical properties such as rate of water loss/day, hydraulic conductivity, soil bulk density and percentage of pore space of the soil were also influenced by transparent plastic mulch. Transparent mulch, either newly laid or maintained for two seasons, had an impact on yields of both blackgram and groundnut. As a result the net return was highest with the transparent plastic mulch maintained for both the crops. These results suggest that double-cropping of transparent plastic mulches can be done without loss of crop yield and provide significant savings in cost of land preparation, materials and laying cost, labour and disposal costs.