Posts Tagged 'Indian'

First ROV exploration of the Perth Canyon: canyon setting, faunal observations, and anthropogenic impacts

This study represents the first ROV-based exploration of the Perth Canyon, a prominent submarine valley system in the southeast Indian Ocean offshore Fremantle (Perth), Western Australia. This multi-disciplinary study characterizes the canyon topography, hydrography, anthropogenic impacts, and provides a general overview of the fauna and habitats encountered during the cruise. ROV surveys and sample collections, with a specific focus on deep-sea corals, were conducted at six sites extending from the head to the mouth of the canyon. Multi-beam maps of the canyon topography show near vertical cliff walls, scarps, and broad terraces. Biostratigraphic analyses of the canyon lithologies indicate Late Paleocene to Late Oligocene depositional ages within upper bathyal depths (200–700 m). The video footage has revealed a quiescent ‘fossil canyon’ system with sporadic, localized concentrations of mega- and macro-benthos (∼680–1,800 m), which include corals, sponges, molluscs, echinoderms, crustaceans, brachiopods, and worms, as well as plankton and nekton (fish species). Solitary (Desmophyllum dianthus, Caryophyllia sp., Vaughanella sp., and Polymyces sp.) and colonial (Solenosmilia variabilis) scleractinians were sporadically distributed along the walls and under overhangs within the canyon valleys and along its rim. Gorgonian, bamboo, and proteinaceous corals were present, with live Corallium often hosting a diverse community of organisms. Extensive coral graveyards, discovered at two disparate sites between ∼690–720 m and 1,560–1,790 m, comprise colonial (S. variabilis) and solitary (D. dianthus) scleractinians that flourished during the last ice age (∼18 ka to 33 ka BP). ROV sampling (674–1,815 m) spanned intermediate (Antarctic Intermediate Water) and deep waters (Upper Circumpolar Deep Water) with temperatures from ∼2.5 to 6°C. Seawater CTD profiles of these waters show consistent physical and chemical conditions at equivalent depths between dive sites. Their carbonate chemistry indicate supersaturation (Ωcalcite ∼ 1.3–2.2) with respect to calcite, but mild saturation to undersaturation (Ωaragonite ∼ 0.8–1.4) of aragonite; notably some scleractinians were found living below the aragonite saturation horizon (∼1,000 m). Seawater δ13C and nuclear bomb produced Δ14C compositions decrease in the upper canyon waters by up to ∼0.8‰ (<800 m) and 95‰ (<500 m), respectively, relative to measurements taken nearby in 1978, reflecting the ingress of anthropogenic carbon into upper intermediate waters.

Continue reading ‘First ROV exploration of the Perth Canyon: canyon setting, faunal observations, and anthropogenic impacts’

Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy

Ocean acidification poses a serious threat to marine calcifying organisms, yet experimental and field studies have found highly diverse responses among species and environments. Our understanding of the underlying drivers of differential responses to ocean acidification is currently limited by difficulties in directly observing and quantifying the mechanisms of bio‐calcification. Here, we present Raman spectroscopy techniques for characterizing the skeletal mineralogy and calcifying fluid chemistry of marine calcifying organisms such as corals, coralline algae, foraminifera, and fish (carbonate otoliths). First, our in vivo Raman technique is the ideal tool for investigating non‐classical mineralization pathways. This includes calcification by amorphous particle attachment, which has recently been controversially suggested as a mechanism by which corals resist the negative effects of ocean acidification. Second, high‐resolution ex vivo Raman mapping reveals complex banding structures in the mineralogy of marine calcifiers, and provides a tool to quantify calcification responses to environmental variability on various timescales from days to years. We describe the new insights into marine bio‐calcification that our techniques have already uncovered, and we consider the wide range of questions regarding calcifier responses to global change that can now be proposed and addressed with these new Raman spectroscopy tools.

Continue reading ‘Investigating marine bio‐calcification mechanisms in a changing ocean with in vivo and high‐resolution ex vivo Raman spectroscopy’

Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia

Highlights

• Ocean warming has accelerated since the 1970s in the nearshore Kimberley.

• Coral calcification remains less affected and ‘normal’ seasonal coral internal carbonate chemistry is observed.

• Under intensified warming, coral’s ability to concentrate metabolic DIC has been reduced.

• Ocean acidification has led to the secular reduction of pHcf.

Abstract

The impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer-term sustainability of coral reefs. Here we report century-long temperature (Sr/Ca and Li/Mg) and calcifying fluid (CF) carbonate chemistry (δ11B and B/Ca) records for a long-lived (1919 to 2016) Porites coral from the high thermally variable Kimberley region of northwestern Australia. We investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral’s CF and impacts of climate change on calcification. Using Sr/Ca and Li/Mg multiproxy we show that annual temperature in the nearshore Kimberley exhibited a gradual increase (0.009 ± 0.003 °C/yr) from the 1920s onward. However for the most recent years (2000–2015) more rapid summer warming (0.05 ± 0.01 °C/yr) are registered, indicative of intensified warming. Despite that, we find no significant trend for calcification rate of this coral over the past century, as well as ‘normal’ seasonal variability in coral’s CF carbonate chemistry. Importantly, the coral’s ability to concentrate inorganic carbon seems to be affected by recent warming, with reduced DICcf observed during 2008 to 2015, while the minimally-affected pHcf acts to compensate the decreases of DICcf with the calcification rate showing only slight decrease. Additionally, we also find that ocean acidification has clearly led to the long-term reduction in the pH of the CF.

Continue reading ‘Anthropogenic ocean warming and acidification recorded by Sr/Ca, Li/Mg, δ11B and B/Ca in Porites coral from the Kimberley region of northwestern Australia’

Dealing with the effects of ocean acidification on coral reefs in the Indian Ocean and Asia

Shallow coral reefs provide food, income, well-being and coastal protection to countries around the Indian Ocean and Asia. These reefs are under threat due to many anthropogenic stressors including pollution, sedimentation, overfishing, sea surface warming and habitat destruction. Ocean acidification interacts with these factors to exacerbate stress on coral reefs. Effective solutions in tackling the impact of ocean acidification require a thorough understanding of the current adaptive capacity of each nation to deal with the consequences. Here, we aim to help the decision-making process for policy makers in dealing with these future challenges at the regional and national levels. We recommend that a series of evaluations be made to understand the current status of each nation in this region in dealing with ocean acidification impacts by assessing the climate policy, education, policy coherence, related research activities, adaptive capacity of reef-dependent economic sectors and local management. Indonesia and Thailand, are selected as case studies. We also highlight general recommendations on mitigation and adaptation to ocean acidification impacts on coral reefs and propose well-designed research program would be necessary for developing a more targeted policy agenda in this region.

Continue reading ‘Dealing with the effects of ocean acidification on coral reefs in the Indian Ocean and Asia’

Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia

The processes that occur at the micro‐scale site of calcification are fundamental to understanding the response of coral growth in a changing world. However, our mechanistic understanding of chemical processes driving calcification is still evolving. Here, we report the results of a long‐term in situ study of coral calcification rates, photo‐physiology, and calcifying fluid (cf) carbonate chemistry (using boron isotopes, elemental systematics, and Raman spectroscopy) for seven species (four genera) of symbiotic corals growing in their natural environments at tropical, subtropical, and temperate locations in Western Australia (latitudinal range of ~11°). We find that changes in net coral calcification rates are primarily driven by pHcf and carbonate ion concentration []cf in conjunction with temperature and DICcf. Coral pHcf varies with latitudinal and seasonal changes in temperature and works together with the seasonally varying DICcf to optimize []cf at species‐dependent levels. Our results indicate that corals shift their pHcf to adapt and/or acclimatize to their localized thermal regimes. This biological response is likely to have critical implications for predicting the future of coral reefs under CO2‐driven warming and acidification.

Continue reading ‘Environmental and physiochemical controls on coral calcification along a latitudinal temperature gradient in Western Australia’

Physical factors affecting oyster diversity and distribution in southern Thailand

Aim : Studies on oyster population dynamic is essential for effective oyster aquaculture.Bandon Bay in Southern Thailand is a major shellfish aquaculture site of high commercial value. The aim of this study was to evaluate the influence of environmental factors on oyster diversity and their distribution in Bandon Bay. Methodology: Adult oysters were collected from eight aquaculture sites during low tide and their body sizes were measured. Monthly, transparency, salinity, pH, dissolved oxygen, biochemical oxygen demand, alkalinity, ammonium (NH4-N),nitrite, nitrate and phosphate were recorded from Surat Thani Coastal Fisheries Research and Development Centre, Department of Fisheries. Results : Three oyster species were observed: Crassostrea belcheri, Crassostrea lugubris and Saccostrea forskalii, however, C. belcheri was most abundant at most locations. Oyster density in Bandon Bay was mostly influenced by alkalinity, followed by salinity, pH, NO3and NH4-N. Interpretation : Since oyster reproduction, survival and shell development depend on environmental factors, thus studies on relationships between environmental factors and oyster occurrence/density may provide a better understanding about the community structures and spatial dynamics of oysters, as well as how oysters respond to environmental changes.

Continue reading ‘Physical factors affecting oyster diversity and distribution in southern Thailand’

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’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,242,876 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book