Posts Tagged 'modeling'

Assessing the effects of ocean warming and acidification on the seagrass Thalassia hemprichii

Seagrass beds serve as important carbon sinks, and it is thought that increasing the quantity and quality of such sinks could help to slow the rate of global climate change. Therefore, it will be important to (1) gain a better understanding of seagrass bed metabolism and (2) document how these high-productivity ecosystems are impacted by climate change-associated factors, such as ocean acidification (OA) and ocean warming (OW). A mesocosm-based approach was taken herein in which a tropical, Western Pacific seagrass species Thalassia hemprichii was cultured under either control or OA-simulating conditions; the temperature was gradually increased from 25 to 31 °C for both CO2 enrichment treatments, and it was hypothesized that this species would respond positively to OA and elevated temperature. After 12 weeks of exposure, OA (~1200 ppm) led to (1) increases in underground biomass and root C:N ratios and (2) decreases in root nitrogen content. Rising temperatures (25 to 31 °C) increased the maximum quantum yield of photosystem II (Fv:Fm), productivity, leaf growth rate, decomposition rate, and carbon sequestration, but decreased the rate of shoot density increase and the carbon content of the leaves; this indicates that warming alone does not increase the short-term carbon sink capacity of this seagrass species. Under high CO2 and the highest temperature employed (31 °C), this seagrass demonstrated its highest productivity, Fv:Fm, leaf growth rate, and carbon sequestration. Collectively, then, it appears that high CO2 levels offset the negative effects of high temperature on this seagrass species. Whether this pattern is maintained at temperatures that actually induce marked seagrass stress (likely beginning at 33–34 °C in Southern Taiwan) should be the focus of future research.

Continue reading ‘Assessing the effects of ocean warming and acidification on the seagrass Thalassia hemprichii’

Enhanced silica export in a future ocean triggers global diatom decline

Diatoms account for up to 40% of marine primary production and require silicic acid to grow and build their opal shell3. On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification. Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 ± 6 per cent under pCO2 conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13–26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system.

Continue reading ‘Enhanced silica export in a future ocean triggers global diatom decline’

Sinking diatoms trap silicon in deep seawater of acidified oceans

The seas are acidifying as a result of carbon dioxide emissions. It now emerges that this will alter the solubility of the shells of marine organisms called diatoms — and thereby change the distribution of nutrients and plankton in the ocean.

The ecologically dominant phytoplankton in much of the ocean are a group of unicellular organisms known as diatoms. Writing in Nature, Taucher et al. present a study that uses a combination of experimental, observational and modelling approaches to examine how the diatom-driven effects of ocean acidification — a consequence of rising carbon dioxide concentrations in seawater — will affect biogeochemical cycles. The separate lines of evidence suggest that ocean acidification will have far-reaching effects on the export of elements to the deep ocean.

Diatoms are highly efficient at converting dissolved CO2 into organic carbon through photosynthesis, whereupon this organic carbon becomes incorporated into particles that sink rapidly to the deep ocean. Diatoms therefore serve as primary engines of a ‘biological pump’ that exports carbon to the deep ocean for sequestration. Each diatom cell is enclosed in a shell of silica (SiO2, where Si is silicon), and the solubility of the silicon in this biomineral is pH-sensitive — it becomes less soluble as seawater acidity rises. Although these features of diatoms are familiar to marine scientists, their combined implications for future biogeochemical cycles in the context of ocean acidification had not been explored.

Enter Taucher and colleagues. They carried out a series of five experiments in various parts of the ocean in which natural phytoplankton communities were grown in large enclosures (with volumes of 35–75 cubic metres) known as mesocosms, which simulated future ocean acidification. When the authors measured the elemental composition of the diatom-derived debris at the bottom of the mesocosms, they observed much higher ratios of silicon to nitrogen than the ratios of particles suspended near the surface. This suggested that, at low seawater pH, diatom silica shells were dissolving much more slowly than nitrogen-containing compounds in the same sinking material. In other words, silicon was being exported from the surface to deeper waters preferentially to nitrogen. The authors validated this finding using records of silicon-to-nitrogen ratios in sinking biological detritus in the open ocean, measured as a function of seawater pH, and obtained from particle-collecting sediment traps deployed by research vessels.

Continue reading ‘Sinking diatoms trap silicon in deep seawater of acidified oceans’

Cessation of hardground accretion by the cold-water coralline algae Clathromorphum compactum and Clathromorphum nereostratum predicted within two centuries

Ocean acidification and warming are expected to disproportionately affect high-latitude calcifying species, such as crustose coralline algae. Clathromorphum nereostratum and Clathromorphum compactum are the primary builders of carbonate-hardgrounds in the Aleutians Islands of Alaska and North Atlantic shelf, respectively, providing habitat and settlement substrates for a large number of species. We exposed wild-collected specimens to 12 pCO2/T treatments (344–3322 μatm; 6.38–12.40°C) for 4 months in a factorially crossed, replicated laboratory experiment. Impacts of pCO2/T on algal calcification were quantified from linear extension and buoyant weight. Here we show that, despite belonging to the same genus, Cnereostratum exhibited greater sensitivity to thermal stress, while Ccompactum exhibited greater sensitivity to pH stress. Furthermore, multivariate models of algal calcification derived from the experiment indicate that both Cnereostratum and Ccompactum will commence net dissolution as early as 2120 and 2200 AD, respectively. Our results therefore indicate that near-term climate change may lead to substantial degradation of these species and loss of the critical hardground habitats that they form.

Continue reading ‘Cessation of hardground accretion by the cold-water coralline algae Clathromorphum compactum and Clathromorphum nereostratum predicted within two centuries’

Individual-based modeling of shelled pteropods

Highlights

  • First shelled pteropod individual-based model (IBM) based on Limacinidae species.
  • Shelled pteropod IBM reproduces the abundance signal measured at temperate latitudes.
  • The pteropod IBM provides the life-stage composition, and life-stage progression of populations.
  • IBM might be used for quantifying ongoing and future effects of climate change.

Abstract

Shelled pteropods are cosmopolitan, free-swimming organisms of biogeochemical and commercial importance. They are widely used as sentinel species for the overall response of marine ecosystems to environmental stressors associated with climate change and changes in ocean chemistry. However, currently we are unable to project the effects of climate change on shelled pteropods at the population level, due to the missing spatio-temporal characterization of the response of pteropods to environmental stressors, and the limited information on the pteropod life history and life-cycle. In this study, we implement a shelled pteropod Individual-Based Model (IBM), i.e. we simulate a pteropod population as a set of discrete individuals over several generations, life-stages (eggs, larvae, juveniles and adults) and as a function of temperature, food availability, and aragonite saturation state. The model is able to provide an abundance signal that is consistent with the abundance signal measured in the temperate region. In addition, the modeled life-stage progression matches the reported size spectrum across the year, with two major spawning periods in spring and fall, and maturation in March and September. Furthermore, our IBM correctly predicts the abundance maxima of younger, smaller and potentially more susceptible life-stages in spring and winter. Thus, our model provides a tool for advancing our understanding of the response of pteropod populations to future environmental changes.

Continue reading ‘Individual-based modeling of shelled pteropods’

A competitive advantage of middle-sized diatoms from increasing seawater CO2

Diatoms, one of the most important phytoplankton groups, fulfill their carbon demand from seawater mainly by obtaining passively diffused carbon dioxide (CO2) and/or actively consuming intracellular energy to acquire bicarbonate (HCO3). An anthropogenically induced increase in seawater CO2 reduces the HCO3 requirement of diatoms, potentially saving intracellular energy and benefitting their growth. This effect is commonly speculated to be most remarkable in larger diatoms that are subject to a stronger limitation of CO2 supply because of their smaller surface-to-volume ratios. However, we constructed a theoretical model for diatoms and revealed a unimodal relationship between the simulated growth rate response (GRR, the ratio of growth rates under elevated and ambient CO2) and cell size, with the GRR peaking at a cell diameter of ∼7 μm. The simulated GRR of the smallest diatoms was low because the CO2 supply was nearly sufficient at the ambient level, while the decline of GRR from a cell diameter of 7 μm was simulated because the contribution of seawater CO2 to the total carbon demand greatly decreased and diatoms became less sensitive to CO2 increase. A collection of historical data in CO2 enrichment experiments of diatoms also showed a roughly unimodal relationship between maximal GRR and cell size. Our model further revealed that the “optimal” cell size corresponding to peak GRR enlarged with the magnitude of CO2 increase but diminished with elevating cellular carbon demand, leading to projection of the smallest optimal cell size in the equatorial Pacific upwelling zone. Last, we need to emphasize that the size-dependent effects of increasing CO2 on diatoms are multifaceted, while our model only considers the inorganic carbon supply from seawater and optimal allocation of intracellular energy. Our study proposes a competitive advantage of middle-sized diatoms and can be useful in projecting changes in the diatom community in the future acidified high-CO2 ocean.

Continue reading ‘A competitive advantage of middle-sized diatoms from increasing seawater CO2’

Towards a digital twin of the Italian coast

In the framework of the Destination Earth initiative, a long-term project to take advantage of the great amount of data produced by European agencies and scientific organizations around the world, the goal of building a Digital Twin of the Earth was born. The Digital Twin Earth is a highprecision digital model of the Earth that integrates various aspects of the Earth’s system in order to monitor and simulate natural phenomena and related human activities, and that is able to explore the past and present and predict the future.

To build a Digital Twin Earth it is required the scientific cooperation of European institutions, alongside with a set of technological tools such as High-Performance Computing (HPC), Cloud Computing and connectivity, Big Data, interoperable data and data standards, and Artificial Intelligence (AI) to simulate and model the Earth’s systems processes.

On this work it is presented a web platform that uses open-source technologies to integrate a wide set of more than 60 geospatial layers of environmental data, provided openly and for free by Copernicus Marine Service, and Copernicus Land Monitoring Service, in addition to demographics data provided also open and free by WorldPop. With the data integrated on this platform a user is able to explore and analyze many land and sea layers. This platform is focused solely on the coastal areas of Italy, but its modular and extensible design is suitable for extending it and replicating it to other parts of the world.

The platform addresses the Digital Twin Earth’s Big Data and interoperability component by integrating several geospatial data sources using a mediator-wrapper integration architecture that leverages the Open Geospatial Consortium (OGC) standards for geospatial data, the Cloud Computing and connectivity component by providing a web-based interface to explore and analyze the integrated data, and the scientific cooperation component by enabling the possibility to save and share the analysis and discoveries made through the platform.

This work constitutes a proof of concept and an approach of what a Digital Twin of the Earth is capable of. To show it, a case study is presented analyzing ocean acidification on Genova and is whereabouts.

The development of the platform is a work in progress, which means that many more features and functionalities are to be included in following versions, having in mind a tool that is open, data-centric, and a good example of a Digital Twin Earth.

Continue reading ‘Towards a digital twin of the Italian coast’

Multiscale mechanical consequences of ocean acidification for cold-water corals

Ocean acidification is a threat to deep-sea corals and could lead to dramatic and rapid loss of the reef framework habitat they build. Weakening of structurally critical parts of the coral reef framework can lead to physical habitat collapse on an ecosystem scale, reducing the potential for biodiversity support. The mechanism underpinning crumbling and collapse of corals can be described via a combination of laboratory-scale experiments and mathematical and computational models. We synthesise data from electron back-scatter diffraction, micro-computed tomography, and micromechanical experiments, supplemented by molecular dynamics and continuum micromechanics simulations to predict failure of coral structures under increasing porosity and dissolution. Results reveal remarkable mechanical properties of the building material of cold-water coral skeletons of 462 MPa compressive strength and 45–67 GPa stiffness. This is 10 times stronger than concrete, twice as strong as ultrahigh performance fibre reinforced concrete, or nacre. Contrary to what would be expected, CWCs retain the strength of their skeletal building material despite a loss of its stiffness even when synthesised under future oceanic conditions. As this is on the material length-scale, it is independent of increasing porosity from exposure to corrosive water or bioerosion. Our models then illustrate how small increases in porosity lead to significantly increased risk of crumbling coral habitat. This new understanding, combined with projections of how seawater chemistry will change over the coming decades, will help support future conservation and management efforts of these vulnerable marine ecosystems by identifying which ecosystems are at risk and when they will be at risk, allowing assessment of the impact upon associated biodiversity.

Continue reading ‘Multiscale mechanical consequences of ocean acidification for cold-water corals’

Influence of climate on seawater quality and green mussel production

This study aimed to investigate the relationships between atmospheric parameters, seawater quality and green mussel production which were cultured in pond, estuary and coastal areas. Seawater and mussel samples were collected from mussel farms in the inner Gulf of Thailand from January to December 2019. Climate data were obtained from the Thai Meteorological Department. The correlations between selected atmospheric and seawater parameters were developed using linear and non-linear models. The influence of seawater quality on mussel production was evaluated using principal component analysis and stepwise multiple linear regression. The effects of atmospheric variation on green mussel productivity were simulated. The results showed that high air temperature and rainfall caused an increase in seawater temperature and a decrease in salinity, respectively. It was observed that the most influential factors affecting mussel production were nutrients and dissolved oxygen in ponds, temperature and salinity in estuaries, and nutrients and pH in coastal areas. The simulation indicated that mussel production can deteriorate when air temperature reaches 34°C and rainfall is higher than 200 mm per month. Our results suggest that under climate change events, locations with less riverine influence can provide higher mussel productivity. These results can be used as a guideline for farmers during a climate change event.

Continue reading ‘Influence of climate on seawater quality and green mussel production’

Coral symbiosis carbon flow: a numerical model study spanning cellular to ecosystem levels

Corals rely on a symbiotic relationship with algae (zooxanthellae), which reside in the host tissue and play a critical role for host metabolism through photosynthesis, respiration, carbon translocation, and calcification. These processes affect coral reefs on different scales from cellular to organismal and ecosystem levels. A process-based dynamic model was developed and coupled with a one-dimensional (1-D) biogeochemical model to describe coral photosynthesis, respiration, and carbon translocation at the cellular level, calcification and ion transport in different coral polyp components (i.e., coelenteron, calcifying fluid) at the organismal level; and the exchange of material between corals and the ambient seawater at the ecosystem level. Major processes controlling the carbon budget in internal symbiosis were identified. For the symbiont, photosynthesis is the primary carbon source and translocation to the host is the major sink. For the host, most of the carbon translocated from the symbiont is lost through mucus leakage. In the host dissolved inorganic carbon (DIC) pool, most of the carbon is obtained from the surrounding seawater through uptake; photosynthesis and calcification are the major sinks of DIC. Based on a series of scenario studies, the model produced increase of photosynthesis rate with decline of calcification rate under higher air pCO2 and associated carbonate chemistry variabilities in different polyp components. The model results support the hypothesis that elevated pCO2 stimulates photosynthesis, resulting in a reduced supply of DIC to calcification. Such coupled models allow the exploration of process-based mechanisms, complementing laboratory and field studies.

Continue reading ‘Coral symbiosis carbon flow: a numerical model study spanning cellular to ecosystem levels’

Ocean biogeochemical signatures of the North Pacific Blob

Abstract

The Blob was the early manifestation of the Northeast Pacific marine heat wave from 2013 to 2016. While the upper ocean temperature in the Blob has been well described, the impacts on marine biogeochemistry have not been fully studied. Here, we characterize and develop understanding of Eastern North Pacific upper ocean biogeochemical properties during the Winter of 2013-14 using in situ observations, an observation-based product, and reconstructions from a collection of ocean models. We find that the Blob is associated with significant upper ocean biogeochemical anomalies: a 5% increase in aragonite saturation state (temporary reprieve of ocean acidification) and a 3% decrease in oxygen concentration (enhanced deoxygenation). Anomalous advection and mixing drive the aragonite saturation anomaly, while anomalous heating and air-sea gas exchange drive the oxygen anomaly. Marine heatwaves do not necessarily serve as an analog for future change as they may enhance or mitigate long-term trends.

Plain Language Summary

The global ocean is experiencing major changes due to human-made carbon emissions and climate change, leading to a warming ocean with increasing acidity and declining oxygen. On top of these long-term changes in the ocean are short-term extreme events, such as marine heatwaves. These extreme events quickly change the ocean state and can stress marine ecosystems in multiple ways. The Northeast Pacific marine heat wave (2013-2016) was one such marine heatwave. Here we focus on the early portion of this marine heatwave, called the Blob. While the ocean temperature changes during the event are well understood, the effects on ocean biogeochemistry have not been fully examined. In this study, we use an earth system model that accurately simulates the Blob to examine short-term changes in oxygen and acidity. We find that the warming signal leads to a decline in the effects of ocean acidification, mainly due to changes in the movement of carbon, and lowers the amount of oxygen, due primarily to temperature-driven effects. These results suggest that some effects of climate change may be exacerbated (warming) or mitigated (ocean acidification) by marine heatwaves.

Continue reading ‘Ocean biogeochemical signatures of the North Pacific Blob’

Ocean futures for the world’s largest yellowfin tuna population under the combined effects of ocean warming and acidification

The impacts of climate change are expected to have profound effects on the fisheries of the Pacific Ocean, including its tuna fisheries, the largest globally. This study examined the combined effects of climate change on the yellowfin tuna population using the ecosystem model SEAPODYM. Yellowfin tuna fisheries in the Pacific contribute significantly to the economies and food security of Pacific Island Countries and Territories and Oceania. We use an ensemble of earth climate models to project yellowfin populations under a high greenhouse gas emissions (IPCC RCP8.5) scenario, which includes, the combined effects of a warming ocean, increasing acidification and changing ocean chemistry. Our results suggest that the acidification impact will be smaller in comparison to the ocean warming impact, even in the most extreme ensemble member scenario explored, but will have additional influences on yellowfin tuna population dynamics. An eastward shift in the distribution of yellowfin tuna was observed in the projections in the model ensemble in the absence of explicitly accounting for changes in acidification. The extent of this shift did not substantially differ when the three-acidification induced larval mortality scenarios were included in the ensemble; however, acidification was projected to weaken the magnitude of the increase in abundance in the eastern Pacific. Together with intensive fishing, these potential changes are likely to challenge the global fishing industry as well as the economies and food systems of many small Pacific Island Countries and Territories. The modelling framework applied in this study provides a tool for evaluating such effects and informing policy development.

Continue reading ‘Ocean futures for the world’s largest yellowfin tuna population under the combined effects of ocean warming and acidification’

Tracking the space-time evolution of ocean acidification extremes in the California Current System and Northeast Pacific

Abstract

Ocean acidification is punctuated by episodic extremes of low pH and saturation state with regard to aragonite (ΩA). Here, we use a hindcast simulation from 1984 to 2019 with a high-resolution regional ocean model (ROMS-BEC) to identify and track ocean acidification extremes (OAX) in the Northeast Pacific and the California Current System (CCS). In the first step, we identify all grid cells whose pH and ΩA are simultaneously below their first percentile over the analysis period (1984-2019). In the second step, we aggregate all neighboring cells with extreme conditions into three-dimensional time evolving events, permitting us to track them in a Lagrangian manner over their lifetime. We detect more than twenty-two thousand events that occur at least once in the upper 100 m during their lifetime, with broad distributions in terms of size, duration, volume and intensity, and with 26% of them harboring corrosive conditions (ΩA < 1). By clustering the OAXs, we find three types of extremes in the CCS. Near the coast, intense, shallow, and short-lasting OAXs dominate, caused by strong upwelling. A second type consists of large and long-lasting OAX events that are associated with westward propagating cyclonic eddies. They account for only 3% of all extremes, but are the most severe events. The third type are small extremes at depth arising from pycnocline heave. OAX potentially have deleterious effects on marine life. Marine calcifiers, such as pteropods, might be especially impacted by the long-lasting events with corrosive conditions.

Plain Language Summary

The emission of carbon dioxide by human activities causes ocean acidification, i.e., the decrease of the pH and saturation level of seawater with respect to the carbonate mineral aragonite. Episodic events of unusually low pH and aragonite saturation level punctuate these long-term declines, potentially intensifying stress on marine plankton. Particularly prone to extremes is the California Current System off the U.S. West coast due to its naturally low pH-aragonite waters and its strong variability. We use a high-resolution numerical model to identify and characterize extreme events associated with ocean acidification in this region, and understand their drivers. We find extremes to have a broad range of volumes, durations and strengths, with a quarter of them carrying corrosive conditions for shelled organisms, i.e., aragonite saturation levels below 1. The largest and longest-lived events are associated with cyclonic eddies (whirls of approximately 50 to 100 km in diameter) that trap upwelled low pH-aragonite waters near the coast. Although representing only 3% of the events, they cause most of the total excess of acidity induced by all identified extremes. The vertical extent and duration of extremes with corrosive mean conditions are expected to impact calcifying organisms, such as pteropods.

Continue reading ‘Tracking the space-time evolution of ocean acidification extremes in the California Current System and Northeast Pacific’

Comprehending the role of different mechanisms and drivers affecting the sea-surface pCO2 and the air-sea CO2 fluxes in the Bay of Bengal: a modeling study

We apply a coupled physical and biogeochemical (ROMS+PISCES) to understand the influence of distinct drivers and mechanisms on the sea-surface pCO2 and the air-sea CO2 flux of the Bay of Bengal (BoB). The model evaluation suggests that the model simulated sea-surface pCO2 is in accord with the observations. The north of BoB is found to be a sink for the atmospheric CO2, whereas the rest of the region acts as a source. The effect of dissolved inorganic carbon (DIC) and the total alkalinity (TALK) is found to be predominant but is contrasting in nature. Mixing-induced changes in DIC and TALK results in high pCO2 (+570μatm) and, consequently, the positive CO2 flux. The biological activity does draw down the surface pCO2 (−120μatm) but is insufficient in completely opposing the effect of mixing. The uptake of CO2 in the north is due to the CO2 solubility, which is a function of salinity and temperature. The northern rivers, having a high discharge rate, reduce the salinity and temperatures in the north, which possibly aids in this region to be a sink. In the northeast monsoon season, the impact of temperature and DIC is high and opposing. The TALK reduces the pCO2 in the northeast monsoon, but the magnitude is low. The pCO2 in the southwest monsoon is influenced primarily by temperature, whereas in the postmonsoon monsoon, the freshwater dominates. The pre-monsoon season experiences the TALK, temperature, and freshwater increase the pCO2 anomalies, and only the DIC reduces pCO2 anomalies.

Continue reading ‘Comprehending the role of different mechanisms and drivers affecting the sea-surface pCO2 and the air-sea CO2 fluxes in the Bay of Bengal: a modeling study’

Controls on buffering and coastal acidification in a temperate estuary

Estuaries may be uniquely susceptible to the combined acidification pressures of atmospherically driven ocean acidification (OA), biologically driven CO2 inputs from the estuary itself, and terrestrially derived freshwater inputs. This study utilized continuous measurements of total alkalinity (TA) and the partial pressure of carbon dioxide (pCO2) from the mouth of Great Bay, a temperate northeastern U.S. estuary, to examine the potential influences of endmember mixing and biogeochemical transformation upon estuary buffering capacity (βH). Observations were collected hourly over 28 months representing all seasons between May 2016 and December 2019. Results indicated that endmember mixing explained most of the observed variability in TA and dissolved inorganic carbon (DIC), concentrations of which varied strongly with season. For much of the year, mixing dictated the relative proportions of salinity-normalized TA and DIC as well, but a fall season shift in these proportions indicated that aerobic respiration was observed, which would decrease βH by decreasing TA and increasing DIC. However, fall was also the season of weakest statistical correspondence between salinity and both TA and DIC, as well as the overall highest salinity, TA and βH. Potential biogeochemically driven βH decreases were overshadowed by increased buffering capacity supplied by coastal ocean water. A simple modeling exercise showed that mixing processes controlled most monthly changes in TA and DIC, obscuring impacts from air–sea exchange or metabolic processes. Advective mixing contributions may be as important as biogeochemically driven changes to observe when evaluating local estuarine and coastal OA.

Continue reading ‘Controls on buffering and coastal acidification in a temperate estuary’

Understanding the seasonality, trends and controlling factors of Indian ocean acidification over distinctive bio-provinces

The Indian Ocean (IO) is witnessing acidification as a direct consequence of the continuous rising of atmospheric CO2 concentration and indirectly due to the rapid ocean warming, which disrupts the pH of the surface waters. This study investigates the pH seasonality and trends over various bio-provinces of the IO and regionally assesses the contribution of each of its controlling factors. Simulations from a global and a regional ocean model coupled with biogeochemical modules were validated with pH measurements over the basin, and used to discern the regional response of pH seasonality (1990-2010) and trend (1961-2010) in response to changes in Sea Surface Temperature (SST), Dissolved Inorganic Carbon (DIC), Total Alkalinity (ALK) and Salinity (S). DIC and SST are significant contributors to the seasonal variability of pH in almost all bio-provinces. Total acidification in the IO basin was 0.0675 units from 1961 to 2010, with 69.3% contribution from DIC followed by 13.8% contribution from SST. For most of the bio-provinces, DIC remains a dominant contributor to changing trends in pH except for the Northern Bay of Bengal and Around India (NBoB-AI) region, wherein the pH trend is dominated by ALK (55.6%) and SST (16.8%). Interdependence of SST and S over ALK is significant in modifying the carbonate chemistry and biogeochemical dynamics of NBoB-AI and a part of tropical, subtropical IO bio-provinces. A strong correlation between SST and pH trends infers an increasing risk of acidification in the bio-provinces with rising SST and points out the need for sustained monitoring of IO pH in such hotspots.

Continue reading ‘Understanding the seasonality, trends and controlling factors of Indian ocean acidification over distinctive bio-provinces’

Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning

Ocean acidification is a consequence of the absorption of anthropogenic carbon emissions and it profoundly impacts marine life. Arctic regions are particularly vulnerable to rapid pH changes due to low ocean buffering capacities and high stratification. Here, an unsupervised machine learning methodology is applied to simulations of surface Arctic acidification from two state-of-the-art coupled climate models. We identify four sub-regions whose boundaries are influenced by present-day and projected sea ice patterns. The regional boundaries are consistent between the models and across lower (SSP2-4.5) and higher (SSP5-8.5) carbon emissions scenarios. Stronger trends toward corrosive surface waters in the central Arctic Ocean are driven by early summer warming in regions of annual ice cover and late summer freshening in regions of perennial ice cover. Sea surface salinity and total alkalinity reductions dominate the Arctic pH changes, highlighting the importance of objective sub-regional identification and subsequent analysis of surface water mass properties.

Continue reading ‘Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning’

Eelgrass beds can mitigate local acidification and reduce oyster malformation risk in a subarctic lagoon, Japan: a three-dimensional ecosystem model study

Highlights

  • An ecosystem model representing carbonate systems in a lagoon was developed.
  • The effect of ocean acidification on oyster malformation was evaluated.
  • Simulation under the absence of eelgrass bed was also performed.
  • The model could reproduce the spatiotemporal variations of the observed values.
  • Eelgrass beds mitigate the adverse effects of acidification on oyster growth.

Abstract

It is well known that ocean acidification (OA) inhibits growth of marine calcifying organisms. Therefore, the adverse effects of acidification on marine ecosystems and aquaculture, such as oyster farming, are of concern. Since eelgrass beds in neritic areas have a high potential for carbon assimilation, this study focuses on local scale mitigation of OA effects. Using a three-dimensional lower-trophic system ecosystem model, we modeled nitrogen and carbon cycles, and the dynamics of carbonate parameters in a subarctic shallow lagoon and bay, where nitrogen availability limits the photosynthesis of primary producers. Simulation of the present conditions allowed reproduction of spatiotemporal variations in water quality and, by assuming future environmental changes quantitatively, revealed that the progress of OA significantly elevated the probability of shell malformation in juvenile oysters. The results represent the spatiotemporal variations in carbonate parameters inside and outside eelgrass beds and enable the evaluation of the alleviation effect on local acidification by the presence of a dense eelgrass bed. Our study shows that in the absence of the eelgrass bed scenario, the effect of OA on oysters became more remarkable. The simulations revealed that maintaining eelgrass beds is essential to mitigate the effects of acidification on oysters.

Continue reading ‘Eelgrass beds can mitigate local acidification and reduce oyster malformation risk in a subarctic lagoon, Japan: a three-dimensional ecosystem model study’

Dynamic energy budget modeling of Atlantic surfclam, Spisula solidissima, under future ocean acidification and warming

Highlights

  • Surfclams were exposed to OA levels inducing effects on physiological rates
  • A DEB model was calibrated integrating effects on ingestion and maintenance costs
  • The model was validated on Georges Bank and Mid-Atlantic Bight population data
  • Effects of future OA and warming conditions projected by RCP scenarios were simulated
  • Under high pCO2 emissions, DEB projects effects on growth and reproduction by 2100

Abstract

A dynamic energy budget (DEB) model integrating pCO2 was used to describe ocean acidification (OA) effects on Atlantic surfclam, Spisula solidissima, bioenergetics. Effects of elevated pCO2 on ingestion and somatic maintenance costs were simulated, validated, and adapted in the DEB model based upon growth and biological rates acquired during a 12-week laboratory experiment. Temperature and pCO2 were projected for the next 100 years following the intergovernmental panel on climate change representative concentration pathways scenarios (2.6, 6.0, and 8.5) and used as forcing variables to project surfclam growth and reproduction. End-of-century water warming and acidification conditions resulted in simulated faster growth for young surfclams and more energy allocated to reproduction until the beginning of the 22nd century when a reduction in maximum shell length and energy allocated to reproduction was observed for the RCP 8.5 scenario.

Continue reading ‘Dynamic energy budget modeling of Atlantic surfclam, Spisula solidissima, under future ocean acidification and warming’

Tidal mixing of estuarine and coastal waters in the western English Channel is a control on spatial and temporal variability in seawater CO2 (update)

Surface ocean carbon dioxide (CO2) measurements are used to compute the oceanic air–sea CO2 flux. The CO2 flux component from rivers and estuaries is uncertain due to the high spatial and seasonal heterogeneity of CO2 in coastal waters. Existing high-quality CO2 instrumentation predominantly utilises showerhead and percolating style equilibrators optimised for open-ocean observations. The intervals between measurements made with such instrumentation make it difficult to resolve the fine-scale spatial variability of surface water CO2 at timescales relevant to the high frequency variability in estuarine and coastal environments. Here we present a novel dataset with unprecedented frequency and spatial resolution transects made at the Western Channel Observatory in the south-west of the UK from June to September 2016, using a fast-response seawater CO2 system. Novel observations were made along the estuarine–coastal continuum at different stages of the tide and reveal distinct spatial patterns in the surface water CO2 fugacity (fCO2) at different stages of the tidal cycle. Changes in salinity and fCO2 were closely correlated at all stages of the tidal cycle and suggest that the mixing of oceanic and riverine endmembers partially determines the variations in fCO2. The correlation between salinity and fCO2 was different in Cawsand Bay, which could be due to enhanced gas exchange or to enhanced biological activity in the region. The observations demonstrate the complex dynamics determining spatial and temporal patterns of salinity and fCO2 in the region. Spatial variations in observed surface salinity were used to validate the output of a regional high-resolution hydrodynamic model. The model enables a novel estimate of the air–sea CO2 flux in the estuarine–coastal zone. Air–sea CO2 flux variability in the estuarine–coastal boundary region is influenced by the state of the tide because of strong CO2 outgassing from the river plume. The observations and model output demonstrate that undersampling the complex tidal and mixing processes characteristic of estuarine and coastal environment biases quantification of air–sea CO2 fluxes in coastal waters. The results provide a mechanism to support critical national and regional policy implementation by reducing uncertainty in carbon budgets.

Continue reading ‘Tidal mixing of estuarine and coastal waters in the western English Channel is a control on spatial and temporal variability in seawater CO2 (update)’

  • Reset

Subscribe

OA-ICC Highlights


%d bloggers like this: