Posts Tagged 'Indian'

Climatic projections of Indian Ocean during 2030, 2050, 2080 with implications on fisheries sector

Climatic projections are essential to frame resilient strategies towards futuristic impacts of climate changes on fish species and habitat. The present study projects the variations of climatic variables such as Sea Surface Temperature (SST), Sea Surface Salinity (SSS), Sea Level Rise (SLR), Precipitation (Pr), and pH along the Indian Ocean. Climate projections for 2030, 2050 and 2080 were obtained as MIROC-ESM-CHEM, CMIP5 model output for each Representative Concentration Pathways (RCP) scenarios. Each climatic variable was assessed for any change against the reference year of 2015. The RCP scenarios showed an increasing trend for SLR and SST while a decreasing trend for SSS and pH. The study focuses on assessing the impacts of projected variations on marine and aquaculture system. The climate model projections show that the SST during 2080 is likely to rise by 0.69°C for the lowest emissions scenario and 2.6°C for the highest emissions scenario. Elevated temperature disturbs the homeostasis of fish and subjects to physiological stress in the habitat resulting in mortality. These thermal limits can predict distributional changes of marine species in response to climate change. Projections showed no significant changes in the pattern of precipitation. Changes in sea level rise and sea surface salinity reduce water quality, spawning and seed availability, increased disease incidence and damage to freshwater aquaculture system by salinization of groundwater. The results show that variation in SST and pH have a potential impact on marine fisheries while SSS, SLR, Precipitation affects the aquaculture systems. The synergic effects of climatic variations are found to have negative implications on capture fisheries as well as aquaculture system and are elucidated through this work.

Continue reading ‘Climatic projections of Indian Ocean during 2030, 2050, 2080 with implications on fisheries sector’

Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal

Highlights

• Satellite salinity measurements enable estimation of surface carbonate parameters.

• Uncertainties within these observation-based estimates are well characterized.

• Monthly satellite salinity and temperature allows synoptic monitoring.

• Satellite observations allow study of seasonal, interannual and episodic variations.

Abstract

Improving our ability to monitor ocean carbonate chemistry has become a priority as the ocean continues to absorb carbon dioxide from the atmosphere. This long-term uptake is reducing the ocean pH; a process commonly known as ocean acidification. The use of satellite Earth Observation has not yet been thoroughly explored as an option for routinely observing surface ocean carbonate chemistry, although its potential has been highlighted. We demonstrate the suitability of using empirical algorithms to calculate total alkalinity (AT) and total dissolved inorganic carbon (CT), assessing the relative performance of satellite, interpolated in situ, and climatology datasets in reproducing the wider spatial patterns of these two variables. Both AT and CT in situ data are reproducible, both regionally and globally, using salinity and temperature datasets, with satellite observed salinity from Aquarius and SMOS providing performance comparable to other datasets for the majority of case studies. Global root mean squared difference (RMSD) between in situ validation data and satellite estimates is 17 μmol kg−1 with bias  < 5 μmol kg−1 for AT and 30 μmol kg−1 with bias  < 10 μmol kg−1 for CT. This analysis demonstrates that satellite sensors provide a credible solution for monitoring surface synoptic scale AT and CT. It also enables the first demonstration of observation-based synoptic scale AT and CT temporal mixing in the Amazon plume for 2010–2016, complete with a robust estimation of their uncertainty.

Continue reading ‘Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal’

Influence of physico-chemical parameters and pCO2 concentration on mangroves-associated polychaetes at Pichavaram, southeast coast of India

Studies related to partial pressure of carbon dioxide (pCO2) concentration linking with polychaete diversity in mangrove ecosystems are limited in time and space. Therefore, the present study was conducted during July 2017–June 2018 on a monthly interval and reported the concentration of pCO2 coupled with physico-chemical parameters in relation to polychaetes diversity in Pichavaram mangroves ecosystem, southeast coast of India. Totally, 41 species were identified and the most dominant species were Prionospio cirrifera, P. cirrobranchiata, P. sexoculata, Prionospio sp. and Capitella capitata. Among the stations, higher polychaete diversity was found in marine zone compared to other zones. The correlation reflected a significant positive linear relationship between dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate organic carbon (POC) and CO2 versus pCO2. The carbon species DIC, DOC, POC and pCO2 concentration ranged from 1100.1 to 2053.3(µmol/kg), 165.7–1954.0(µmol/kg), 4.5–89.2(µmol/kg) and 184.7–3763.1(µatm), respectively. Further, the statistical analyses revealed that there was a strong correlation among carbon species with distribution of polychaete species in various zones of mangroves and thus indicating pivotal role in occurrence of polychaetes in mangroves.

Continue reading ‘Influence of physico-chemical parameters and pCO2 concentration on mangroves-associated polychaetes at Pichavaram, southeast coast of India’

Ocean acidification during prefertilization chemical communication affects sperm success

Ocean acidification (OA) poses a major threat to marine organisms, particularly during reproduction when externally shed gametes are vulnerable to changes in seawater pH. Accordingly, several studies on OA have focused on how changes in seawater pH influence sperm behavior and/or rates of in vitro fertilization. By contrast, few studies have examined how pH influences prefertilization gamete interactions, which are crucial during natural spawning events in most externally fertilizing taxa. One mechanism of gamete interaction that forms an important component of fertilization in most taxa is communication between sperm and egg‐derived chemicals. These chemical signals, along with the physiological responses in sperm they elicit, are likely to be highly sensitive to changes in seawater chemistry. In this study, we experimentally tested this possibility using the blue mussel, Mytilus galloprovincialis, a species in which females have been shown to use egg‐derived chemicals to promote the success of sperm from genetically compatible males. We conducted trials in which sperm were allowed to swim in gradients of egg‐derived chemicals under different seawater CO2 (and therefore pH) treatments. We found that sperm had elevated fertilization rates after swimming in the presence of egg‐derived chemicals in low pH (pH 7.6) compared with ambient (pH 8.0) seawater. This observed effect could have important implications for the reproductive fitness of external fertilizers, where gamete compatibility plays a critical role in modulating reproduction in many species. For example, elevated sperm fertilization rates might disrupt the eggs’ capacity to avoid fertilizations by genetically incompatible sperm. Our findings highlight the need to understand how OA affects the multiple stages of sperm‐egg interactions and to develop approaches that disentangle the implications of OA for female, male, and population fitness.

Continue reading ‘Ocean acidification during prefertilization chemical communication affects sperm success’

Control of CaCO3 dissolution at the deep seafloor and its consequences

Prediction of the neutralization of anthropogenic CO2 in the oceans and the interpretation of the calcite record preserved in deep-sea sediments requires the use of the correct kinetics for calcite dissolution. Dissolution rate information from suspended calcite-grain experiments consistently indicates a high-order nonlinear dependence on undersaturation, with a well-defined rate constant. Conversely, stirred-chamber and rotating-disc dissolution experiments consistently indicate linear kinetics of dissolution and a strong dependence on the fluid flow velocity. Here, we resolve these seeming incongruities and establish reliably the kinetic controls on deep-sea calcite dissolution. By equating the carbonate-ion flux from a dissolving calcite bed, governed by laboratory-based nonlinear kinetics, to the flux across typical diffusive boundary layers (DBL) at the seafloor, we show that the net flux is influenced both by boundary layer and bed processes, but that flux is strongly dominated by the rate of diffusion through the DBL. Furthermore, coupling that calculation to an equation for the calcite content of the seafloor, we show that a DBL-transport dominated model adeptly lysoclines adeptly, i.e., CaCO3 vs ocean depth profiles, observed across the oceans. Conversely, a model with only sediment-side processes fails to predict lysoclines in all tested regions. Consequently, the past practice of arbitrarily altering the calcite-dissolution rate constant to allow sediment-only models to fit calcite profiles constitutes confirmation bias. From these results, we hypothesize that the reason suspended-grain experiments and bed experiments yield different reaction orders is that dissolution rates of individual grains in a bed are fast enough to maintain porewaters at or close to saturation, so that the exact reaction order cannot be measured and dissolution appears to be linear. Finally, we provide a further test of DBL-transport dominated calcite dissolution by successfully predicting, not fitting, the in-situ pH profiles observed at four stations reported in the literature.

Continue reading ‘Control of CaCO3 dissolution at the deep seafloor and its consequences’

Low CO2 evasion rate from the mangrove surrounding waters of Sundarban

Globally, water bodies adjacent to mangroves are considered sources of atmospheric CO2. We directly measured the partial pressure of CO2 in water, pCO2(water), and other related biogeochemical parameters with very high (1-min) temporal resolution at Dhanchi Island in India’s Sundarbans during the post-monsoon season. We used elemental, stable isotopic, and optical signatures to investigate the sources of dissolved inorganic carbon (DIC) and organic matter (OM) in these waters. Diel mean pCO2(water) was marginally oversaturated in creeks (efflux, 69 ± 180 µmol m−2 h−1) and undersaturated along the island boundary and in the main river (influx, −17 ± 53 and −31 ± 73 µmol m−2 h−1, respectively) compared to the atmospheric CO2 concentration. The possibility in earlier studies of over- or underestimating the CO2 flux because of an inability to capture tidal minima and maxima was minimized in the present study, which confirmed that the waters surrounding mangroves in this region can act as a sink or a very weak source of atmospheric CO2. δ13C values for DIC suggest a mixed DIC source, and a three-end-member stable isotope mixing model and optical signatures of OM suggest negligible riverine contribution of freshwater to OM. We conclude that the CO2 sink or weak source character was due to a reduced input of riverine freshwater [which usually has high pCO2(water)] and the predominance of pCO2-lean water from the coastal sea, which eventually increases the buffering capacity of the water as evidenced by the Revelle factor. Up-scaling the CO2 flux data for all seasons and the entire estuary, we propose that the CO2 evasion rate observed in this study is much lower than the recently estimated world average. Mangrove areas having such low emissions should be given due emphasis when up-scaling the global mangrove carbon budget from regional observations.

Continue reading ‘Low CO2 evasion rate from the mangrove surrounding waters of Sundarban’

Role of seaweeds in neutralizing the impact of seawater acidification- A laboratory study with beached shells of certain bivalves and spines of a sea urchin

Ocean acidification is one of the major impacts of climate change in sea which is manifested by the decrease in hydrogen ion concentration (pH) of seawater mainly due to increased uptake of CO2 and reduction in carbonate ions. This is a report on the dissolution rate of dead shells of four marine bivalves and spines of a sea urchin when treated with different levels of CO2 dissolved in seawater for 48 hours which was measured gravimetrically. Dissolution of dead shells expressed as reduction in shell weight was directly proportional to the concentration of dissolved CO2. Live thallus of green seaweed Chaetomorpha antennina did reduce the magnitude of dissolution rates (P<0.05) of all the shells and spines considerably as well as the change in pH of ambient seawater due to the addition of CO2. The remedial property of seaweeds was more effective at lower concentrations of dissolved CO2. The induced change in pH was restored by green seaweed only at concentrations above 250 ppm. Although we noticed strong impact of dissolved CO2 on the dead shells of Mactrinula plicataria even at 100 ppm level, the remedial action by the green seaweed was maximum in Siliqua radiata followed by Perna viridis. Results of this laboratory study shows the positive role of seaweeds in neutralizing the acidification impacts.

Continue reading ‘Role of seaweeds in neutralizing the impact of seawater acidification- A laboratory study with beached shells of certain bivalves and spines of a sea urchin’


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Ocean acidification in the IPCC AR5 WG II

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