Posts Tagged 'Indian'

Variability, trend and controlling factors of ocean acidification over Western Arabian Sea upwelling region

Highlights

  • The factors controlling the seasonal variability and trend in pH over the Western Arabian Sea upwelling region are studied.
  • DIC and SST are the major driving factors of seasonal variability in pH and they act in opposite directions.
  • DIC and ALK contribute up to 73% to the net trend and SST warming alone contributes another 16%.

Abstract

Western Arabian Sea (WAS) is subjected to strong bio-physical forcings which results in significant variability in biological productivity and intense CO2 emission at different timescales. The study aims to understand the major physical factors controlling seasonal variability and trend in pH over WAS. Two sets of sensitivity experiments are carried out in order to delineate the individual factors such as Sea Surface Temperature (SST), Dissolved Inorganic Carbon (DIC), Alkalinity (ALK) and Salinity (S) which control the pH seasonal variability and its trend. The first set of sensitivity experiments extract the major controlling factors of pH seasonal variability and the second set identifies the major contributors to the trend in pH over WAS. The results show that DIC and SST are the principal drivers of seasonal variability of pH and they act in opposite directions. Seasonal warming and cooling have significant effect in pH variability during pre-monsoon and post-monsoon period, respectively. DIC plays a major role in pH seasonality during the monsoon period. WAS has been acidified from a pH of 8.12 (in 1960) to a pH of 8.05 (in 2010). The trend in pH over WAS is due to contributions from DIC and SST of 109% and 16%, respectively. The effect of ALK is to buffer the existing trend in pH by −36% while S contribution is only 7%. Collectively, DIC and ALK contribute up to 73% to the net pH trend. SST warming alone contributes another 16%. pH shows a decreasing trend of −0.0091 for 50 years for October to December and − 0.0039 for July to August with a correlation of 0.374 and 0.244 with increasing trend in SST for the corresponding period, respectively. The study raises a red flag since this region is warming rapidly which is only exacerbating acidification.

Continue reading ‘Variability, trend and controlling factors of ocean acidification over Western Arabian Sea upwelling region’

The ocean-atmospheric condition around Pieh Islands – Western Sumatra, Indonesia and its role on coral reef resilience

Pieh Islands located at the Western Sumatra is one of the most affected areas by massive coral bleaching during 2015-2016. The persistence warming or cooling of sea surface temperature due to regional climate phenomena such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) put the coral reef into stress condition leading into coral bleaching. However, corals have an ability to recover from such bleaching condition into normal state by reducing its stressors. A suitable oceanographic condition such as normal range of temperature and salinity, low nutrient concentration, and low sedimentation rate could support corals recovery process. This study aims to understand the variability of the ocean and atmospheric data and its role in coral reef recovery. Data gained from in situ measurements of water quality at Pieh Marine Conservation Area (PMCA) on June 2018. Several historical ocean-atmospheric data were collected to analyze their temporal variability. It is confirmed that the bleaching event was caused by positive IOD and El Niño condition in 2015-2016. However, there is the sign of coral reef recovery during 2017-2018 which is suggested due to the relatively normal condition of the ocean and atmospheric parameters in Pieh Islands.

Continue reading ‘The ocean-atmospheric condition around Pieh Islands – Western Sumatra, Indonesia and its role on coral reef resilience’

The invisible carbon footprint as a hidden impact of peatland degradation inducing marine carbonate dissolution in Sumatra, Indonesia

In Indonesia, land use change (LUC) in the form of peatland degradation induces carbon loss through direct CO2 emissions, but also via soil leaching of which circa 50% is decomposed and emitted as CO2 from the rivers. However, the fate of the remaining exported leached carbon is uncertain. Here, we show that the majority of this carbon is respired in the estuaries and emitted to the atmosphere. However, a portion is adsorbed into the marine carbon pool where it favors CaCO3 dissolution and can therefore be seen as the invisible carbon footprint. We conclude that the effects of LUC stretch beyond the terrestrial realm and are not limited to CO2 emissions, but also affect marine ecosystems. Considering the ecological and economical importance of these ecosystems, it is important that this so far invisible carbon footprint, as well as the aquatic and marine CO2 emissions, are included in climate mitigation strategies.

Continue reading ‘The invisible carbon footprint as a hidden impact of peatland degradation inducing marine carbonate dissolution in Sumatra, Indonesia’

Performance and herbivory of the tropical topshell Trochus histrio under short-term temperature increase and high CO2

Highlights

• Tropical algae-herbivore interactions were studied under a climate change scenario.

• Survival of topshells did not vary but body fitness declined under high CO2.

• Elevated temperature resulted in better physical condition and stimulated herbivory.

• Dynamic index was temperature- and pCO2-interactively dependent.

• Dominance of bottom-up control (i.e. lower grazing pressure) under high CO2.

Abstract

Within tropical environments, short-term impacts of increased seawater temperature and pCO2 on algae-herbivore interactions remain poorly understood. We investigated the isolated and combined 7-day effects of increased temperature (+4 °C) and pCO2 (~1000 μatm) on the trophic interaction Ulva sp./Trochus histrio, by assessing: i) topshells’ survival and condition index; ii) grazer consumption rates, nutritional composition and interaction strength expressed as a dynamic index. No survival differences were observed whilst body condition varied significantly. Topshells under high pCO2 displayed poor performance, concomitant with lower consumption of macroalgae. Individuals exposed to increased temperature had better physical condition, thus stimulating herbivory, which in turn was negatively correlated with carbon and nitrogen contents. The dynamic index was temperature- and pCO2- interactively dependent, suggesting lower grazing pressure under single acidification. Despite some limitations inherent to a short-term exposure, this study provides new insights to accurately predict tropical species’ phenotypic responses in a changing ocean.

Continue reading ‘Performance and herbivory of the tropical topshell Trochus histrio under short-term temperature increase and high CO2’

Seagrass and macrophyte mediated CO2 and CH4 dynamics in shallow coastal waters

Seagrass meadows are among the most important coastal/ marine ecosystems for long-term carbon storage and conditioning of coastal waters. A combined air-water flux of CO2 and CH4 from the seagrass meadows was studied for the first time from Asia’s largest brackish–water lagoon, Chilika, India. Ecosystem-based comparisons were carried out during two hydrologically different conditions of dry and wet seasons in the seagrass dominated southern sector (SS); macrophyte-dominated northern sector (NS); the largely un-vegetated central sector (CS) and the tidally active outer channel (OC) of the lagoon. The mean fluxes of CO2 from SS, NS, CS and OC were 9.8, 146.6, 48.4 and 33.0mM m-2d-1, and that of CH4 were 0.12, 0.11, 0.05 and 0.07mM m-2d-1, respectively. The net emissions (in terms of CO2 equivalents), considering the global warming potential of CO2 (GWP: 1) and CH4 (GWP: 28) from seagrass meadows were over 14 times lower compared to the macrophyte-dominated sector of the lagoon. Contrasting emissivity characteristics of CO2 and CH4 were observed between macrophytes and seagrass, with the former being a persistent source of CO2. It is inferred that although seagrass meadows act as a weak source of CH4, they could be effective sinks of CO2 if land-based pollution sources are minimized.

Continue reading ‘Seagrass and macrophyte mediated CO2 and CH4 dynamics in shallow coastal waters’

Effect of pH on transport and transformation of Cu-sediment complexes in mangrove systems

Highlights

• Distribution of Cu in different binding phases of sediments changes with changing pH of the surrounding environment.
• Association of Cu organic matter increases at higher pH with sedimentary increases at higher pH.
• Cu-SOM complexes may disaggregate and increase mobility at higher pH.
• Increasing pH decreases lability of Cu complexes and increase mobility of Cu-complexes in sediments.
• Concentration Cu in residual phases remains unchanged under varying pH.

 

Abstract

Impact of pH variation of overlying water column on transport and transformation of Cu-sediment complexes in the bottom mangrove sediments was investigated by using different metal extraction studies. The total Cu concentration in the studied sediments varied from ~64 ± 1 to 78 ± 2 mg·kg−1. The sequential extraction study showed that a major part of the sedimentary Cu (85–90% of the total sedimentary Cu) was present within the structure of the sediments with minimum mobility and bioavailability. The redistribution of non-residual Cu among the different binding phases of the sediments was observed at different pH. It was found that Cu shifted from the different non-residual binding phases to the organic binding phase of the sediments at higher pH. Partial leaching of sedimentary Cu-SOM complexes (with increasing stability as determined by kinetic extraction study) was observed at higher pH. This study infers that increase in pH of overlying water column may release Cu-SOM complexes and increase the mobility of Cu-complexes in mangrove systems.

 

Continue reading ‘Effect of pH on transport and transformation of Cu-sediment complexes in mangrove systems’

Environmental variables and nutrients in selected islands of Lakshadweep Sea; addressing coral bleaching

Highlights

• The present study describes environmental variables and coral bleaching in the Lakshadweep Sea.
• SST (Sea Surface Temperature) and pH were found to be responsible factors for coral bleaching.
• Among the islands studied, Kavaratti and Agatti islands are found with higher levels of NO3 and NO2 due to more anthropogenic activities.
• Narrow range of temperature in the Lakshadweep Sea for about 5 decades was noticed when compared with earlier reports.

Abstract

An observational investigation on the environmental variables in the coral reef ecosystem of the Lakshadweep Sea was made with reference to coral bleaching. The investigation was done during 2014–2015 in selected islands of Lakshadweep Sea. The environmental variables recorded were sea surface temperature (SST; 28.1–31.5 ° C), salinity (34.0–38.36 psu), pH (7.9–8.3), dissolved oxygen (DO; 3.19–7.70 mg/L), total organic carbon of water (WTOC; 1.6–3.20 ppm) and net primary productivity (NPP; 0.440–2.060 mgC/m3/hr). Nutrients of nitrite (NO2; 0.052–1.522μm ol/L), nitrate (NO3; 0.293–14.867μm ol/L), in-organic phosphate (IP; 0.287–2.070μm ol/L), total phosphorous (TP; 1.919–5.200μm ol/L) and reactive silicate (RS; 3.791–19.422μm ol/L) were also recorded. PCA showed positive loadings for salinity, DO, NO2, IP, TP, and RS in the Lakshadweep Sea. Currents and their divergence patterns influencing the upwelling in the nearshore islands might be the sources for the availability of nutrients. Data were treated statistically (linear regression) to understand the interrelationship between the variables. DO was found normal, indicating that the waters of the Lakshadweep Sea are well mixed and aerated. Nutrients such as NO2, NO3, IP and RS in Kavaratti and Agatti islands were found higher indicating that these islands are under the influence of anthropogenic activities. Cluster analysis revealed clear groupings among the islands. Agatti and Kalpetti islands were grouped together indicating more similarity in the values of environmental variables than with other islands. SST was found in the higher range over a study period and also over to the past 5 decades as per records and pH was found at the lower level in majority of the assessments. The unvaried ranges of SST and pH (P >0.01) might have favored bleaching of the corals in the Lakshadweep Sea. The nutrient levels recorded presently besides the other variables will serve as the baseline data for future investigations in the Lakshadweep Sea.

Continue reading ‘Environmental variables and nutrients in selected islands of Lakshadweep Sea; addressing coral bleaching’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book