Low–lying coral islands are susceptible to rising sea levels and climate change, posing risks to island habitability over the next century. The decadal timescale evolution of the islands can provide an understanding of the governing controls of change and island response. This study investigates variations in the shoreline morphology of the Lakshadweep coral islands (Northern Indian Ocean/Arabian Sea) using satellite datasets (2003–2022; CNES/Airbus;0.3m – 0.7m resolution) and sedimentological data. Of the thirty islands (ten inhabited), six islands (Bangaram, Thinnakara, Suheli, Minicoy, Androth and Bitra) have been studied. Most of these islands are less than 1 km2 in size except Androth and Minicoy (>4 km2). While the data is discontinuous for the islands due to cloud obscuring, the shoreline morphology depicts variations for all the islands’ studied, irrespective of habitation and size. Larger islands have undergone consistent erosion since 2007 (total land loss is approximately 3 – 5% cumulatively). Smaller islands have undergone lateral migration, with sediment erosion usually along the southern edge and sediment migration and accumulation northwards, however, overall, their size remains consistently stable. The migration of sediments is observed only from 2007–2017, which coincides with severe El–Nino Southern Oscillation (ENSO) and low amplitude positive Indian Ocean Dipole (IOD) events. Furthermore, sedimentological analysis along Bangaram’s (small island) accreting margin reveals unconsolidated bio-detrital grainstones with predominant sand-sized fractions (2 – 0.25mm). Corals (43%), molluscs (33%), forams (13%), and algae (8%) are the major sediment producers (with 3% unidentified bioclasts). The ongoing climate warming and ocean acidification will influence the carbonate sediment budget in addition to the changing hydrodynamics owing to monsoons, cyclones, and coupled ocean-atmospheric regional phenomenon, altering the sediment production, transport and accumulation on these islands. Furthermore, rising sea levels and consequent erosion by wave action might lead to rapid drowning in the next few centuries. Our study identifies the current status of the island size variability in the Lakshadweep Archipelago and how site-specific and global factors influence them, thus providing insights into assessing the habitability within these low-lying coral islands.
Continue reading ‘Decadal timescale evolution of coral islands: insights from Lakshadweep Archipelago’Posts Tagged 'Indian'
Decadal timescale evolution of coral islands: insights from Lakshadweep Archipelago
Published 29 July 2024 Science ClosedTags: Indian, laboratory, paleo, sediment
Temperate coastal fish shows resilience to extreme low pH in early larval stages
Published 11 July 2024 Science ClosedTags: biological response, chemistry, fish, Indian, laboratory, performance, physiology, reproduction, respiration
Highlights
- Coastal species is tolerant short term, acute low pH conditions in dynamic coastal habitats.
- Tolerance exceeds projected ocean acidification for local coastal habitat.
- Physiological capacity sufficient to compensate for low pH conditions even in the early post-flexion stage of Diplodus capensis.
- Diplodus capensis shows potential for behavioural plasticity at low pH.
Abstract
Fishes have shown varying responses to the decline in seawater pH associated with ocean acidification. Coastal marine species inhabit characteristically dynamic environments which requires physiological adaptation to variability, including fluctuations in pH and associated carbonate chemistry parameters. Our study assessed the response of the early life stages (postflexion) of a common coastal fish species (Diplodus capensis) that is found in coastal nearshore and estuarine habitats along the South African coastline. We assessed their metabolic and behavioural response to a range of pH conditions which covered a high pH (8.02), the lowest pH that they are naturally exposed to (7.75) as well as extremely low pH levels (∼7.75–7.27) exceeding their current range of exposure, which may occur with future coastal acidification. Our findings suggest that this species is metabolically tolerant of acute low pH conditions (down to 7.27 pH) showing no changes in either routine or active metabolic rates. Although our study identified a slight increase in swimming activity in D. capensis larvae exposed to low pH, there was no change in feeding activity. These results suggest that this species may have the physiological capacity to withstand the present and future high pH variability associated with its environments, in the absence of other stressors and ecological interactions. However, the increased swimming activity at low pH may translate into downstream ecological impacts, for which the mechanisms need to be assessed with further research.
Continue reading ‘Temperate coastal fish shows resilience to extreme low pH in early larval stages’Ocean acidification in the tropical Indian Ocean over the past 37 years: insights from 𝛿11B and B/Ca records in a Maldives coral
Published 1 July 2024 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, Indian, laboratory, modeling, paleo, regionalmodeling
Highlights
- This is the first coral’s carbonate chemistry record in the tropical Indian Ocean.
- Porites calcification pH is sensitive to ocean acidification, but the transfer function to seawater pH needs re-evaluation.
- A different internal energy/dissolved inorganic carbon (DIC) supply might explain the lower [DIC] CF observed in Maldives corals.
- Data from a wider geographic range is required to constrain the impacts of ocean acidification on corals.
Abstract
Boron isotopes (𝛿11B) in coral skeletons of Porites have been widely applied to reconstruct past seawater pH (pHSW) on decadal to centennial timescales. However, due to biological regulation within corals, an additional transfer function is required to estimate ambient seawater chemistry during the skeleton growth under the calcification site fluid pH. Temperature may also interfere with coral calcification fluid pH (pHCF) due to changes in kinetics of coral aragonite precipitation, or buffering capacity in coral calcification fluid. To decipher how coral Porites adjusts pHCF in response to pHSW from complex environmental controls, long-term records from sites with least fluctuations in environmental conditions other than pHSW are essential. Here we present a 37-year record of coral 𝛿11B and B/Ca ratios derived from a coral core collected from southern Maldives, the tropical Indian Ocean. Our results show no clear seasonality in the coral 𝛿11B and B/Ca ratios between monsoons, but a long-term decline in coral pHCF is evident across the entire record. When applying different existing transfer functions, we also observe discrepancies among the calculated pHCF values, model results and short-term instrumental data. Calculated calcification fluid dissolved inorganic carbon concentration ([DIC]CF) values are relatively low compared to literature, suggesting that coral calcification fluid carbonate chemistry may be under different levels of control, even within the same coral taxa. Thus, coral records from a wider geographic range are required to better quantify coral response to ocean acidification, and our results can serve as a baseline for future comparisons.
Continue reading ‘Ocean acidification in the tropical Indian Ocean over the past 37 years: insights from 𝛿11B and B/Ca records in a Maldives coral’Patterns of carbonate chemistry in mangroves of the Northern Persian Gulf
Published 27 June 2024 Science ClosedTags: chemistry, Indian
Highlights
- Pattern of carbonate chemistry in mangroves of the northern Persian Gulf was examined for the first time.
- The Nayband surface waters were undersaturated with respect to aragonite.
- Anthropogenic CO2 emission from PSEEZ has affected the Nayband mangrove ecosystem.
- Higher TA in the Nayband site compared to the other two sites, might be due to the presence of denser mangrove forest in this site.
Abstract
The mangroves located in the Northern Persian Gulf are reeling from anthropogenic pressures including from intense industrial activities (Pars Special Economic Energy Zone-PSEEZ). Given the unique geographical location of these mangroves, understanding the initial basis of seawater carbonate chemistry is key to link with global patterns of coastal ocean carbonate dynamics. In this study, water samples were collected from pre-designated stations representing the mangrove forest and nearshore water namely Nayband, Mel-e-Gonzeh and Bardestan of the Persian Gulf in September of 2016. Based on extensive carbonate chemistry measurements, the results show that the pCO2 at the Nayband site (13217.9±5841.5 µatm) was significantly higher than the other two sites (Mel-e-Gonzeh: 416.4±49.3 µatm and Bardestan: 294.3±95.0 µatm) while pH (6.92±0.18) was significantly lower than the two other sites (Mel-e-Gonzeh: 8.18±0.02, Bardestan: 8.26±0.04). The observed increase of pCO2 and decrease of surface water pH at the Nayband site compared to other two sites may have due to the emission of CO2 originating from oil and gas refining facilities located PSEEZ. Moreover, surface water in Nayband was undersaturated with respect to aragonite (Ωarg<1) and supersaturated (Ωarg>1) in case of the Mel-e-Gonzeh and Bardestan sites. This study although preliminary provides much-needed baseline information to address issues of changing carbonate chemistry and can help towards understanding the basis of coastal ocean acidification.
Continue reading ‘Patterns of carbonate chemistry in mangroves of the Northern Persian Gulf’Shell size variation of pteropod Heliconoides inflatus: inferences on Indian Ocean carbonate chemistry during late Quaternary
Published 30 May 2024 Science ClosedTags: biological response, chemistry, Indian, laboratory, mollusks, morphology, sediment
The current study is an effort to understand the relationship between the average shell size and Limacina Dissolution Index (LDX) of pteropod species, Heliconoides inflatus as a metric for shell calcification using several cores, ranging in age from recent to 1.2 Myr. The current study is based on the variability of H. inflatus average shell size, LDX, and fragmentation ratio (FR) and their correlation among different spatial and temporal sediment core records from the Northern Indian Ocean. Results suggest that in the cores collected above the Aragonite lysocline (Aly) and the Aragonite Compensation Depth (ACD) (SPC 05, 06, 09, 11, 12, 13, 14, and NGHP-17), the average shell size values exhibited larger shells during the stadials/glacial periods (Little Ice Age (LIA), Marine Isotope Stages (MIS) 3, 6, 10 − 9 transition etc.) which corresponds to lower LDX values. However, the cores beyond the ACD (SK168, AAS11, and RVS2) show larger shell size values during the warm interstadials (e.g., Bølling–Allerød) with higher FR. The variability in shell size and LDX shows an indication of the carbonate ion saturation in the water column over glacial/interglacial time scales and the impact of changing atmospheric CO2 in the atmosphere. However, the factors adding to the carbonate ion saturation within the water column could be varied physiographically. The calcification proxy complements the dissolution proxies and reveals that the most intense aragonite dissolution occurred during the Holocene and interstadials/interglacials.
Continue reading ‘Shell size variation of pteropod Heliconoides inflatus: inferences on Indian Ocean carbonate chemistry during late Quaternary’Time series (2003–15) analysis of selected physicochemical parameters in Indian Ocean: cumulative impacts prediction on coral bleaching using machine learning
Published 7 May 2024 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling, review
Highlights
- Long term prediction of coral bleaching in Indian Ocean
- Cumulative impacts of selected physico chemicals parameters on bleaching
- Application of machine learning in environmental impacts study
- Salinity fCO2 and pH have positive impacts on coral bleaching.
Abstract
Coral bleaching is an important ecological threat worldwide, as the coral ecosystem supports a rich marine biodiversity to survive. Sea surface temperature was considered a major culprit; however, later it was observed that other water parameters like pH, tCO2, fCO2, salinity, dissolved oxygen, etc. also play a significant role in bleaching. In the present study, all these parameters of the Indian Ocean area for 15 years (2003–2017) were collected and analysed using machine learning language. The main aim is to see the cumulative impacts of various ocean parameters on coral bleaching. Introducing machine learning in environmental impact assessment studies is a new approach, and the prediction of coral bleaching using simulation of physico-chemical parameters interactions shows 70 % accuracy for the prediction of the future bleaching event. This study can be probably the first step in the application of the machine learning language for the prediction of coral bleaching in the field of marine science.
Continue reading ‘Time series (2003–15) analysis of selected physicochemical parameters in Indian Ocean: cumulative impacts prediction on coral bleaching using machine learning’Influencing intertidal food web: implications of ocean acidification on the physiological energetics of key species the ‘wedge’ clam Donax faba
Published 26 April 2024 Science ClosedTags: biological response, chemistry, growth, Indian, laboratory, mollusks, morphology, physiology
Highlights
- Daily growth rate & calcium concentration have significantly decreased in acidified condition.
- Total antioxidants and antioxidant enzymes showed an upward tendency.
- Nutrient composition in clams has altered in acidified condition compared to control.
- Prolonged exposure to OA will cause deleterious effects on clams thereby upsetting the intertidal food chain.
Abstract
Ocean acidification has become increasingly severe in coastal areas. It poses emerging threats to coastal organisms and influences ecological functioning. Donax faba, a dominant clam in the intertidal zone of the Bay of Bengal, plays an important role in the coastal food web. This clam has been widely consumed by the local communities and also acts as a staple diet for shorebirds and crustaceans. In this paper, we investigated how acidified conditions will influence the physiology, biochemical constituents, and energetics of Donax faba. Upon incubation for 2 months in lowered pH 7.7 ± 0.05 and control 8.1 ± 0.05 conditions, we found a delayed growth in the acidified conditions followed by decrease in calcium ions in the clam shell. Although not significant, we found the digestive enzymes showed a downward trend. Total antioxidant was significantly increased in the acidified condition compared to the control. Though not significant, the expression level of MDA and antioxidant enzymes (SOD, CAT, GST, GPX, and APX) showed increasing trend in acidified samples. Among nutrients such as amino acids and fatty acids, there was no significant difference between treatments, however, showed a downward trend in the acidified conditions compared to control. Among the minerals, iron and zinc showed significant increase in the acidified conditions. The above results suggest that the clam growth, and physiological energetics may have deleterious effects if exposed for longer durations at lowered pH condition thereby affecting the organisms involved in the coastal food web.
Continue reading ‘Influencing intertidal food web: implications of ocean acidification on the physiological energetics of key species the ‘wedge’ clam Donax faba’Sea-surface pCO2 maps for the Bay of Bengal based on advanced machine learning algorithms
Published 23 April 2024 Science ClosedTags: chemistry, Indian, modeling, regionalmodeling
Lack of sufficient observations has been an impediment for understanding the spatial and temporal variability of sea-surface pCO2 for the Bay of Bengal (BoB). The limited number of observations into existing machine learning (ML) products from BoB often results in high prediction errors. This study develops climatological sea-surface pCO2 maps using a significant number of open and coastal ocean observations of pCO2 and associated variables regulating pCO2 variability in BoB. We employ four advanced ML algorithms to predict pCO2. We use the best ML model to produce a high-resolution climatological product (INCOIS-ReML). The comparison of INCOIS-ReML pCO2 with RAMA buoy-based sea-surface pCO2 observations indicates INCOIS-ReML’s satisfactory performance. Further, the comparison of INCOIS-ReML pCO2 with existing ML products establishes the superiority of INCOIS-ReML. The high-resolution INCOIS-ReML greatly captures the spatial variability of pCO2 and associated air-sea CO2 flux compared to other ML products in the coastal BoB and the northern BoB.
Continue reading ‘Sea-surface pCO2 maps for the Bay of Bengal based on advanced machine learning algorithms’Seasonally varying biogeochemical regime around the coral habitats off central west coast of India
Published 9 April 2024 Science ClosedTags: biogeochemistry, biological response, chemistry, corals, field, Indian
Highlights
- Waters around the Grande Island (harboring patchy coral growth) along the central west coast of India experience low- O2, pH, and temperature during seasonal upwelling, while episodes of low- O2 and pH are observed during plankton blooms in the summer season.
- Changes in benthic communities and a steady decline in coral cover associated with a sharp increase in the macro-algae and rubble were observed at the Grande Island.
- Angria Bank, the offshore coral site, does not show extreme seasonal change in the environmental conditions, rather it shows open ocean biogeochemical characyteristics.
Abstract
The Western Indian Continental Shelf (WICS) experiences upwelling during the Southwest Monsoon (SWM), leading to deoxygenation and acidification of subsurface waters. The region has patchy growth of corals, e.g. in the Grande Island and Angria Bank. Measurements made during the late SWM of 2022 reveal that the shelf waters around the Grande Island were subject to varying environmental conditions, viz. lower temperature (21.3–26.1°C), oxygen (0–4.9 mL L−1) and pHT (7.506–7.927). Complete anoxia was associated with sulphide build-up to a maximum of 5.9 μmol L−1 at 17 m depth. An additional episodic condition (high temperature, low oxygen and pH) also occurred associated presumably with a plankton bloom in April 2017. Hence, unlike the offshore coral site Angria Bank, waters around the Grande Island experiences extreme changes in physico-chemical conditions (e.g. Ωarg ∼1.2–1.8 during October 2022) seasonally as reported here. The biogeochemical conditions are however not as intense (Ωarg = 0.6) as observed along the eastern boundary upwelling system of the Pacific Ocean.
Continue reading ‘Seasonally varying biogeochemical regime around the coral habitats off central west coast of India’Adaptive mechanism of the marine bacterium Pseudomonas sihuiensis-BFB-6S towards pCO2 variation: insights into synthesis of extracellular polymeric substances and physiochemical modulation
Published 26 February 2024 Science ClosedTags: biological response, BRcommunity, Indian, laboratory, physiology, primary production, prokaryotes
Highlights
- Optimal biofilm modulation can provide the adaptive response of bacteria.
- Potential characterization of EPS explored by microscopic and spectroscopic annotation.
- Modulation of EPS is a hallmark of the protection barrier.
- High concentration of pCO2 can trigger protein-less EPS release.
Abstract
Marine bacteria can adapt to various extreme environments by the production of extracellular polymeric substances (EPS). Throughout this investigation, impact of variable pCO2 levels on the metabolic activity and physiochemical modulation in EPS matrix of marine bacterium Pseudomonas sihuiensis – BFB-6S was evaluated using a fluorescence microscope, excitation-emission matrix (EEM), 2D-Fourier transform infrared correlation spectroscopy (2D-ATR-FTIR-COS), FT-NMR and TGA-DSC. From the results at higher pCO2 levels, there was a substantial reduction in EPS production by 58–62.8 % (DW). In addition to the biochemical composition of EPS, reduction in carbohydrates (8.7–47.6 %), protein (7.1–91.5 %), and lipids (16.9–68.6 %) content were observed at higher pCO2 levels. Functional discrepancies of fluorophores (tyrosine and tryptophan-like) in EPS, speckled differently in response to variable pCO2. The 2D-ATR-FTIR-COS analysis revealed functional amides (C
N, CC, C
O bending, -NH bending in amines) of EPS were preferentially altered, which led to the domination of polysaccharides relevant functional groups at higher pCO2. 1H NMR analysis of EPS confirmed the absence of chemical signals from H-C-COOH of proteins, α, β anomeric protons, and acetyl group relevant region at higher pCO2 levels. These findings can contribute new insights into the influence of pCO2 on the adaptation of marine microbes in future ocean acidification scenarios.
A review of the Indian Ocean carbon dynamics, acidity, and productivity in a changing environment
Published 22 February 2024 Science ClosedTags: biogeochemistry, chemistry, field, Indian
Highlights
- Current understanding of Indian Ocean carbon fluxes, acidity, and productivity from observations and model simulations.
- Recapitulation of the functioning of air-sea exchange of CO2 in the Indian Ocean and its potential impact on climate change.
- Recent developments in understanding the Indian Ocean acidification and Aerosol optical depth variability.
- Highlighting grey areas of the Indian Ocean biogeochemical dynamics that need to be understood.
Abstract
The Indian Ocean dynamics is governed by the seasonal reversal of monsoon winds and the associated ocean currents. The relatively deep thermocline along the equator due to a lack of steady easterlies, low-latitude connection to the neighbouring Pacific, and a lack of northward heat export due to the position of the Asian continent are important factors in regulating the ocean state. These features make it a unique ecosystem among the world’s tropical oceans and determine key features of potential air-sea interaction at different time scales. The pCO2 shows a large seasonal variation linked with monsoon circulation. The Indian Ocean’s northwestern part acts as an atmospheric CO2 source, whereas the northeastern part acts as a net atmospheric CO2 sink. The region between the latitudes of 15°S-50°S in the Indian Ocean is a major subduction zone because of positive wind stress curl. The subducted water masses are transported to the northern Indian Ocean by the cross-equatorial cell (a shallow meridional overturning circulation). Based on the regional studies carried out on the carbonate system in the Indian Ocean, the area north of 15°S is a source of atmospheric CO2, while the area between 15°S and 50°S is a sink. A recent synthesis of models (observational climatology) over different spatial scales provides an estimate of the mean value of CO2 in the north of 37.5°S of the Indian Ocean as − 0.19 ± 0.1 PgC/yr (−0.07 ± 0.14 PgC/yr) during 1985–2018. The estimated decrease in pH (acidification) using model outputs in the Indian Ocean basin is 0.0675 units during 1961–2010, in which the contribution of dissolved inorganic carbon and surface temperature is 69.3 % and 13.8 %, respectively. The range of the Indian Ocean’s annual primary production based on satellite estimates over the last two decades (1998–2018) is 7.72–8.70 Gt C/yr, whereas the climatological mean is 8.24 ± 0.30 Gt C/yr. This paper consolidates the current state of understanding of the Indian Ocean carbon fluxes, acidification, and productivity using available field and satellite-based measurements, model simulations, and re-constructed datasets. It provides an overview of the functioning of the Indian Ocean’s air-to-sea CO2 exchange and highlights its influence on global climate. Finally, it aims to highlight the grey areas of the Indian Ocean carbon cycle that need to be understood.
Continue reading ‘A review of the Indian Ocean carbon dynamics, acidity, and productivity in a changing environment’Contrasting patterns in pH variability in the Arabian Sea and Bay of Bengal
Published 22 February 2024 Science ClosedTags: chemistry, field, Indian
Continuous understanding of the ongoing ocean acidification (OA) is essential for predicting the future impact of OA on marine ecosystems. Here we report the results of open ocean time-series measurements (19 cruises) of seawater pH in total hydrogen ion scale (pHT) and associated parameters in the Arabian Sea (AS) and the Bay of Bengal (BoB). During southwest monsoon (SWM), the pHT within the 30 to 100 m water column shows the maximum difference between the two basins with BoB pHT being lower (up to ~0.39 units) than AS which could be due to freshwater influx from rivers, mixed layer dynamics, and cold-core eddies. However, during Spring inter-monsoon (SIM), the pHT of BoB follows the trend of AS. A contrasting finding is that the lowest pHT occurs at 350 to 500 m in the BoB while it is ~1000 m in the AS. The pHT within the 150 to 1500 m layer of these two basins shows lower values by 0.03 (±0.02) in the BoB as compared to the AS. The possible reasons for the low pHT within the BoB oxygen minimum zone (OMZ) could be due to intrusion of western Pacific water in the BoB, freshwater influx from rivers, variations in OMZ of the two basins, higher temperature (~2°C) within the OMZ of the AS, and denitrification in the AS. The pHT in both the basins (500 to 1000 m) is lower than in the North Atlantic and higher than in the North Pacific waters; however, the pHT in the 200 to 500 m is lower in the BoB than in all these basins. This study highlights the under-saturation of calcium carbonate at very shallow depths (~ 100 m) in the BoB, indicating that the plankton in the BoB are facing a major risk from OA compared to the AS and need further investigation.
Continue reading ‘Contrasting patterns in pH variability in the Arabian Sea and Bay of Bengal’Spatial variability of aragonite saturation state (Ωarag) in Indonesian coastal waters
Published 15 February 2024 Science ClosedTags: chemistry, field, Indian, South Pacific
Highlights
- Regional disparities reveal lower Ωarag in Pari, Lombok; higher levels in Selayar, Flores.
- Salinity impact ranges 24.13%–52.92%, showing a negative sea surface temperature-Ωarag correlation.
- Climate change projections for 2100 predict substantial Ωarag reduction in Indonesian coastal waters.
- The susceptibility to ocean acidification suggests coral reefs deteriorate by 2100, except for those in the coastal waters of Selayar Island.
Abstract
The effects of Ocean acidification (OA) on the coastal waters of small islands in Indonesia have yet to be extensively studied. This research aims to investigate the process of OA in the coastal waters of small Indonesian islands and examine how land-sea interactions impact carbonate mineral saturation. We collected seawater samples from seven locations on small islands in Indonesia between 2015 and 2021 to analyze the aragonite saturation state. The result shows that most of Indonesia’s coastal waters are accompanied by supersaturation of aragonite saturation state (Ωarag>1). Selayar Island’s waters had the highest aragonite saturation, averaging 4.96 ± 0.48, while Pari Island’s coastal waters had the lowest, averaging 2.49 ± 0.50. Salinity had the greatest effect on Ωarag in all of the sampling sites, ranging from 24.13% to 52.92%, except Aceh Island, where temperature had a greater impact (34.35%) than salinity (26.99%). By the end of this century, Ωarag is predicted to decline based on projections related to climate change. Small island coastal waters are expected to experience a more substantial decline compared to those near the mainland, ranging from 4.71% to 79.58%. The coastal waters of Weh and Selayar Island are probably going to decline the greatest, while the coastal waters of Sorong (mainland) are probably going to decline the least. All seven sampling locations are expected to observe the decrease. This decline will be observed at all seven sampling locations, with Ωarag values ranging from 1.91 to 3.35.
Continue reading ‘Spatial variability of aragonite saturation state (Ωarag) in Indonesian coastal waters’A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)
Published 31 January 2024 Science ClosedTags: Antarctic, chemistry, field, Indian, Mediterranean, North Atlantic, North Pacific, South Atlantic, South Pacific
Total alkalinity (AT) and dissolved inorganic carbon (CT) in the oceans are important properties with respect to understanding the ocean carbon cycle and its link to global change (ocean carbon sinks and sources, ocean acidification) and ultimately finding carbon-based solutions or mitigation procedures (marine carbon removal). We present a database of more than 44 400 AT and CT observations along with basic ancillary data (spatiotemporal location, depth, temperature and salinity) from various ocean regions obtained, mainly in the framework of French projects, since 1993. This includes both surface and water column data acquired in the open ocean, coastal zones and in the Mediterranean Sea and either from time series or dedicated one-off cruises. Most AT and CT data in this synthesis were measured from discrete samples using the same closed-cell potentiometric titration calibrated with Certified Reference Material, with an overall accuracy of ±4 µmol kg−1 for both AT and CT. The data are provided in two separate datasets – for the Global Ocean and the Mediterranean Sea (https://doi.org/10.17882/95414, Metzl et al., 2023), respectively – that offer a direct use for regional or global purposes, e.g., AT–salinity relationships, long-term CT estimates, and constraint and validation of diagnostic CT and AT reconstructed fields or ocean carbon and coupled climate–carbon models simulations as well as data derived from Biogeochemical-Argo (BGC-Argo) floats. When associated with other properties, these data can also be used to calculate pH, the fugacity of CO2 (fCO2) and other carbon system properties to derive ocean acidification rates or air–sea CO2 fluxes.
Continue reading ‘A synthesis of ocean total alkalinity and dissolved inorganic carbon measurements from 1993 to 2022: the SNAPO-CO2-v1 dataset (update)’The correlation between echinoderms diversity and physicochemical parameters in marine pollution: a case study of the Persian Gulf coastline
Published 24 January 2024 Science ClosedTags: abundance, biological response, echinoderms, field, Indian, morphology, otherprocess
This study was conducted with the aim of investigating the correlation between echinoderms diversity and physicochemical parameters in the Persian Gulf coastline in Bushehr province in 4 seasons from March to December 2017. The physicochemical parameters including water temperature, dissolved oxygen (DO), electrical conductivity (EC), salinity, pH and turbidity were measured at each sampling location. The results showed a significant correlation between echinoderms diversity and physicochemical parameters. The correlation coefficient of the Astropecten polyacanthus species with the parameters of temperature, DO, EC, salinity and turbidity was reported as -0.41, 0.64, -0.25, -0.44 and 0.60 respectively. This coefficient for the Ophiothrix fragilis species was reported as -0.68, 0.70, -0.21, -0.36 and -0.55 respectively. The results demonstrated that the most sensitive species were Astropecten polyacanthus and Ophiothrix fragilis respectively. The different species of echinoderms can be used as biological indicators of pollution in evaluating the physicochemical quality of marine environments.
Paleoceanographic importance of tri- and di-unsaturated alkenones through the early phase of Cretaceous Oceanic Anoxic Event 2 from southern high latitudes of the proto-Indian Ocean
Published 17 January 2024 Science ClosedTags: algae, biological response, field, Indian, paleo, physiology, sediment
Alkenones are biomarkers derived exclusively from species of haptophyte algae. The relative abundance of di- to tri-unsaturated C37 alkenones expressed as UK’37 is widely applied as a sea surface paleotemperature proxy for Cenozoic marine sediments. However, the absence of alkatrienones prior to the Eocene has precluded application of the UK’37 proxy for assessment of Cretaceous paleoclimates. Herein, we report a C40 alkatrienone (tetraconta-9E, 16E, 23E-trien-3-one; C40:3 Et) in deep-sea sediments from southern high latitudes (International Ocean Discovery Program: IODP site U1516). This discovery extends the geologic record of alkatrienones to the late Cenomanian, ∼70 million years earlier than previous reports. The parallel occurrence of higher abundances of a C40 alkadienone (tetraconta-16E, 23E-dien-3-one; C40:2 Et) allowed calculation of the UK’40 unsaturation index, comparable to UK’37. Stratigraphic variations in the δ13C of C40:2 Et revealed an elevated (∼1.5 ‰) positive carbon isotope excursion (CIE) relative to those observed in carbonate from other OAE2 sequences likely reflecting a decrease in global pCO2. The UK’40 profile suggests a concurrent drop in sea surface temperature associated with the decline in pCO2 during the early phase of OAE2. The timing of these environmental perturbations in the southern high latitude of the proto-Indian Ocean suggests they were triggered by volcanism associated with large igneous province (LIP) formation.
Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes
Published 2 January 2024 Science ClosedTags: Arctic, chemistry, field, Indian, North Atlantic, North Pacific, South Atlantic, South Pacific
Mangroves and saltmarshes are biogeochemical hotspots storing carbon in sediments and in the ocean following lateral carbon export (outwelling). Coastal seawater pH is modified by both uptake of anthropogenic carbon dioxide and natural biogeochemical processes, e.g., wetland inputs. Here, we investigate how mangroves and saltmarshes influence coastal carbonate chemistry and quantify the contribution of alkalinity and dissolved inorganic carbon (DIC) outwelling to blue carbon budgets. Observations from 45 mangroves and 16 saltmarshes worldwide revealed that >70% of intertidal wetlands export more DIC than alkalinity, potentially decreasing the pH of coastal waters. Porewater-derived DIC outwelling (81 ± 47 mmol m−2 d−1 in mangroves and 57 ± 104 mmol m−2 d−1 in saltmarshes) was the major term in blue carbon budgets. However, substantial amounts of fixed carbon remain unaccounted for. Concurrently, alkalinity outwelling was similar or higher than sediment carbon burial and is therefore a significant but often overlooked carbon sequestration mechanism.
Continue reading ‘Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes’Systems thinking approach to understand Indonesia’s ocean acidification
Published 20 December 2023 Science ClosedTags: education, Indian, South Pacific
Establishing a proper connection between content and context is essential to infusing Systems Thinking (ST) into sustainable chemistry learning. Several efforts have been made to realize ST in chemistry in the context of coping with climate change through chemistry education. One potential model is connecting the interpretation of chemical reactions at the molecular level to local phenomena such as Indonesia’s ocean acidification (IOA). As citizens of an archipelagic country, Indonesian students should understand the fundamental nature of particles that cause ocean acidification. In this work, we offer the perspective on scaffolding the ST competencies using the iterative cycle of Design-Based Research, particularly in the preparation and design stages. The developed ST sequences appear from identifying system components via history; relationship between component and natural world; identifying dynamic interaction and cyclic behavior; application and ownership in sustainability action. All stages above focused on carbonate and hydrogen carbonate ions as central particles in the ocean acidification context. To sum up, the current Indonesian curriculum need to apply the ST approach to equip students as climate-literate citizens of science with adequate knowledge and skills.
Continue reading ‘Systems thinking approach to understand Indonesia’s ocean acidification’Physio-biochemical and metabolomic analyses of the agarophyte Gracilaria salicornia indicates its tolerance to elevated pCO2 levels
Published 14 December 2023 Science ClosedTags: abundance, algae, biological response, growth, Indian, laboratory, otherprocess, photosynthesis, physiology
Gracilaria salicornia is an agar-producing red macroalga commonly found growing in the intertidal and upper subtidal on various substrates with distribution across the Indo-Pacific. The ability of G. salicornia to survive under harsh conditions suggests potential use as a candidate for sustainable farming and alternative source of livelihood for the local coastal communities under future climate conditions. An earlier study investigated the effects of future predicted pCO2 level on the photosynthesis and respiration of G. salicornia but studies on the metabolomic responses of this alga to constant elevated pCO2 level is lacking. Here, elevated pCO2 level was simulated on G. salicornia for 14 days to compare its growth, photosynthetic efficiency, pigment content, agar properties and metabolite composition under current pCO2 level (∼pH 8.1) and end-of-century future-predicted (∼pH 7.8) pCO2 level. The observed biomass growth, coupled with unaffected photosynthetic parameters and agar-related properties underscore G. salicornia’s ability to adapt to higher pCO2 levels. The modulation of metabolites showcases the alga’s adaptive strategies at elevated pCO2 whereby stress-mediating compounds such as gallic acid and oxalic acid were increased while stress-indicating metabolites such as serine, glycine, and ascorbic acid did not show significant changes. Interestingly, the metabolome profile imply that the alga regulates its metabolism according to culture duration rather than the pCO2 level.
Continue reading ‘Physio-biochemical and metabolomic analyses of the agarophyte Gracilaria salicornia indicates its tolerance to elevated pCO2 levels’Porcelaneous larger foraminiferal responses to Oligocene–Miocene global changes
Published 1 December 2023 Science ClosedTags: biological response, BRcommunity, community composition, Indian, Mediterranean, North Pacific, otherprocess, paleo, protists, review, sediment, South Pacific
Highlights
- Porcelaneous large foraminifera diversified during the Oligocene–Miocene.
- The Aquitanian and Langhian–Serravallian peaks in richness occurred when SST ∼ 29 °C.
- Detrimental effects of high pCO2 (> 600 ppm) in the Rupelian–early Chattian.
- Detrimental effects of high tropical SST (> 31 °C) during the beginning of MCO
- Detrimental effects of low tropical SST (< 26 °C) in the Tortonian
- Sea-level highstands affected diversification of Oligocene–Miocene pLBF
Abstract
Sea surface temperatures (SST) have been identified as a main controlling factor on larger benthic foraminifera (LBF) living in tropical to sub-tropical shallow-water carbonate and mixed siliciclastic‑carbonate platforms. Changes in SST, along with those in ocean acidification and nutrient content recorded in the global oceans throughout their history will not only continue but also be amplified in the future at an unprecedented rate of change possibly reaching levels recorded in the geological record. This study focuses on the Oligocene (mean SST 8 °C higher than present) and the Miocene (SST 5–8 °C higher than present) epochs which were characterized by a higher richness in porcelaneous LBF (pLBF) than today. A systematic re-assessment and comprehensive literature survey of stratigraphic ranges and palaeogeographic distribution in the Western Tethyan (Mediterranean) and Indo-Pacific regions are used to evaluate the impact of changes in SST, seawater pCO2 and pH on the biodiversity of the Oligocene–Miocene pLBF Alveolinella, Austrotrillina, Borelis, Bullalveolina, Flosculinella and Praebullalveolina. Two peaks in species richness were identified during the Aquitanian and Langhian–Serravallian. These peaks occurred when SST was ∼29 °C, with pCO2 of ∼400 ppm and pH > 7.8. These values are comparable to those of today. The minima in species richness recorded in the Rupelian–early Chattian, in the Burdigalian and from the Tortonian onward can be correlated to the detrimental effects of both minima (< 26 °C) and maxima (> 31 °C) SST thresholds. High pCO2 (> 600 ppm) values, which are limited to the Rupelian–early Chattian, are also detrimental to species richness. Seawater pH higher than 7.7 did not negatively affect species richness. These historical trends have serious implications for the future diversity of pLBFs with the increasing likely scenario of rising SST and pCO2 and lowering of pH values in the near future. These developments can potentially lead to diversity decrease and even extinction of pLBFs. However, the resilience of present-day pLBF species to rising SST and pCO2 levels is underpinned by the evolutionary histories of their fossil counterparts during climate variations, albeit at much different rates of change.
Continue reading ‘Porcelaneous larger foraminiferal responses to Oligocene–Miocene global changes’
