Posts Tagged 'regionalmodeling'

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’

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’

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’

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)’

Dynamically downscaled projections of ocean acidification for the Bering Sea

A regional ocean biogeochemical model for the Bering Sea is used to dynamically downscale three Earth System Models from the CMIP5 archive under the RCP 8.5 and RCP 4.5 scenarios. These continuous model runs, completed in conjunction with the Alaska Climate Integrated Modeling Project (ACLIM), span the 2006–2100 timeframe and project continued warming, freshening, and ocean acidification (OA) for the Bering Sea shelf region over the 21st Century, with larger magnitude changes in the RCP 8.5 scenario. The downscaled projections suggest that annual average surface seawater aragonite saturation state (Ωarag) for the Bering Sea shelf will decrease by 0.63–0.86 under RCP 8.5 and 0.18–0.43 under RCP 4.5 by 2100. Surface pH values decrease by 0.31–0.35 under RCP 8.5 and 0.07–0.13 under RCP 4.5. Seasonally, Ωarag < 1 conditions start to emerge for ∼2 months per year during winter between 2015-2030 under both climate change scenarios. Under RCP 8.5, the duration of these undersaturated conditions grows to ∼5 months per year by 2100, occurring from mid-October through mid-March. Under RCP 4.5, these conditions remain constrained to 2–3 months per year by 2100. In both scenarios, summer months maintain conditions of Ωarag > 1 due to primary productivity, though the maximum in Ωarag is greatly reduced under RCP 8.5. Spatially, the regions of greatest pH and Ωarag decline are the southeastern Bering Sea shelf and the outer shelf domain near the shelf break. Linear trends in carbonate variables between our downscaled simulations and the Earth System Model (ESM) output are comparable and indistinguishable compared to the model spread. However, bottom water trends differ somewhat between the ESM and our downscaled simulations, with the latter more consistently resolving the different shelf domains. The OA information provided by these downscaled simulations can help inform biological sensitivity experiments and longterm strategic planning for marine fisheries management.

Continue reading ‘Dynamically downscaled projections of ocean acidification for the Bering Sea’

Reoxygenation of the hypoxia in the East China Sea: a ventilation opening for marine life

Hypoxia and upwelling co-occur in the summer, and well-mixed water typically reaches the subsurface in the East China Sea (ECS), especially off the Changjiang River estuary. The impact of upwelling on hypoxia and, therefore, on the ecosystem in the ECS is not known. This study demonstrates both positive and negative effects of upwelling on hypoxia and its impact on the ecosystem. With upwelling, the spatial extent of hypoxic water increases with a lower pH but waters with high regenerated nutrients and fugacity of CO2 (fCO2), which are normally confined to the near-bottom, are found just up to 5–10 m below the surface. This upwelled high nutrient water can enhance phytoplankton growth in this region. On one occasion in August 2014, upwelling reached to the surface and lasted for 3 weeks, with the area of coverage ranging from 326.8 to 24,368.0 km2. During this event, the water was mixed thoroughly throughout the water column, with high concentrations of nutrients, chlorophyll a, and slightly undersaturated dissolved oxygen but saturated fCO2, alongside a normal pH. This event may have served as an important pathway from the ocean to the atmosphere for the regenerated CO2. It also provided a productive and suitable environment for marine life and ventilation to alleviate low-oxygen stress in this hypoxic but upwelling region in the ECS.

Continue reading ‘Reoxygenation of the hypoxia in the East China Sea: a ventilation opening for marine life’

Estimating the carbon content of oceans using satellite sensor data

The impact of chemical processes in ocean surface waters is far-reaching. Recently, increased significance has been placed on the concentration of Carbon and its compounds and the effects these may have on climate change. Remote-sensing enables near real-time measurement of key sea-surface data which can be used to estimate Carbon levels. We illustrate with the use of hybrid Satellite sensor data. To validate our results we use data collected from cruise ships as the ground truth when training our algorithms. The error rate of our predictor is found to be small and hence the proposed approach can be used to estimate Carbon levels in any ocean. This work improves upon previous research in many ways including the use of sea water salinity as a proxy for Carbon estimates. Binary combinations of typically unary predictor attributes are used for the purposes of predicting the Carbon content of surface water and an inherently non-linear model is used to quantify the relationship.

Continue reading ‘Estimating the carbon content of oceans using satellite sensor data’

Evaluating the Arabian Sea as a regional source of atmospheric CO2: seasonal variability and drivers

The Arabian Sea (AS) was confirmed to be a net emitter of CO2 to the atmosphere during the international Joint Global Ocean Flux Study program of the 1990s, but since then few in situ data have been collected, leaving data-based methods to calculate air–sea exchange with fewer and potentially out-of-date data. Additionally, coarse-resolution models underestimate CO2 flux compared to other approaches. To address these shortcomings, we employ a high-resolution () regional model to quantify the seasonal cycle of air–sea CO2 exchange in the AS by focusing on two main contributing factors, pCO2 and winds. We compare the model to available in situ pCO2 data and find that uncertainties in dissolved inorganic carbon (DIC) and total alkalinity (TA) lead to the greatest discrepancies. Nevertheless, the model is more successful than neural network approaches in replicating the large variability in summertime pCO2 because it captures the AS’s intense monsoon dynamics. In the seasonal pCO2 cycle, temperature plays the major role in determining surface pCO2 except where DIC delivery is important in summer upwelling areas. Since seasonal temperature forcing is relatively uniform, pCO2 differences between the AS’s subregions are mostly caused by geographic DIC gradients. We find that primary productivity during both summer and winter monsoon blooms, but also generally, is insufficient to offset the physical delivery of DIC to the surface, resulting in limited biological control of CO2 release. The most intense air–sea CO2 exchange occurs during the summer monsoon when outgassing rates reach ∼ 6  in the upwelling regions of Oman and Somalia, but the entire AS contributes CO2 to the atmosphere. Despite a regional spring maximum of pCO2 driven by surface heating, CO2 exchange rates peak in summer due to winds, which account for ∼ 90 % of the summer CO2 flux variability vs. 6 % for pCO2. In comparison with other estimates, we find that the AS emits ∼ 160 Tg C yr−1, slightly higher than previously reported. Altogether, there is 2× variability in annual flux magnitude across methodologies considered. Future attempts to reduce the variability in estimates will likely require more in situ carbon data. Since summer monsoon winds are critical in determining flux both directly and indirectly through temperature, DIC, TA, mixing, and primary production effects on pCO2, studies looking to predict CO2 emissions in the AS with ongoing climate change will need to correctly resolve their timing, strength, and upwelling dynamics.

Continue reading ‘Evaluating the Arabian Sea as a regional source of atmospheric CO2: seasonal variability and drivers’

Methane hydrate dissociation across the Oligocene–Miocene boundary

Methane hydrate dissociation has long been considered as a mechanism for global carbon cycle perturbations, climate change and even mass extinctions in Earth’s history. However, direct evidence of hydrate destabilization and methane release coinciding with such events is scarce. Here we report the presence of diagnostic lipid biomarkers with depleted carbon isotopes from three sites in the Southern Ocean that are directly linked to methane release and subsequent oxidation across the Oligocene–Miocene boundary (23 million years ago). The biomarker evidence indicates that the hydrate destabilization was initiated during the peak of the Oligocene–Miocene boundary glaciation and sea-level low stand, consistent with our model results suggesting the decrease in hydrostatic pressure eroded the base of global methane hydrate stability zones. Aerobic oxidation of methane in seawater consumes oxygen and acidifies the ocean, acting as a negative feedback that perhaps facilitated the rapid and mysterious termination of glaciation in the early Miocene.

Continue reading ‘Methane hydrate dissociation across the Oligocene–Miocene boundary’

Acidification of the Nordic Seas

Due to low calcium carbonate saturation states, and winter mixing that brings anthropogenic carbon to the deep ocean, the Nordic Seas and their cold-water corals are vulnerable to ocean acidification. Here, we present a detailed investigation of the changes in pH and aragonite saturation in the Nordic Seas from preindustrial times to 2100, by using in situ observations, gridded climatological data, and projections for three different future scenarios with the Norwegian Earth System Model (NorESM1-ME).

During the period of regular ocean biogeochemistry observations from 1981–2019, the pH decreased with rates of 2–3 × 10−3 yr−1 in the upper 200 m of the Nordic Seas. In some regions, the pH decrease can be detected down to 2000 m depth. This resulted in a decrease in the aragonite saturation state, which is now close to undersaturation in the depth layer of 1000–2000 m. The model simulations suggest that the pH of the Nordic Seas will decrease at an overall faster rate than the global ocean from the preindustrial era to 2100, bringing the Nordic Seas’ pH closer to the global average. In the esmRCP8.5 scenario, the whole water column is projected to be undersaturated with respect to aragonite at the end of the 21st century, thereby endangering all cold-water corals of the Nordic Seas. In the esmRCP4.5 scenario, the deepest cold-water coral reefs are projected to be exposed to undersaturation. Exposure of all cold-water corals to corrosive waters can only be avoided with marginal under the esmRCP2.6 scenario.

Over all timescales, the main driver of the pH drop is the increase in dissolved inorganic carbon (CT) caused by the raising anthropogenic CO2, followed by the temperature increase. Thermodynamic salinity effects are of secondary importance. We find substantial changes in total alkalinity (AT) and CT as a result of the salinification, or decreased freshwater content, of the Atlantic water during all time periods, and as a result of an increased freshwater export in polar waters in past and future scenarios. However, the net impact of this decrease (increase) in freshwater content on pH is negligible, as the effects of a concentration (dilution) of CT and AT are canceling.

Continue reading ‘Acidification of the Nordic Seas’

The distribution of pCO2W and air-sea CO2 fluxes using FFNN at the continental shelf areas of the Arctic Ocean

A feed-forward neural network (FFNN) was used to estimate the monthly climatology of partial pressure of CO2 (pCO2W) at a spatial resolution of 1° latitude by 1° longitude in the continental shelf of the European Arctic Sector (EAS) of the Arctic Ocean (the Greenland, Norwegian, and Barents seas). The predictors of the network were sea surface temperature (SST), sea surface salinity (SSS), the upper ocean mixed-layer depth (MLD), and chlorophyll-a concentration (Chl-a), and as a target, we used 2 853 pCO2W data points from the Surface Ocean CO2 Atlas. We built an FFNN based on three major datasets that differed in the Chl-a concentration data used to choose the best model to reproduce the spatial distribution and temporal variability of pCO2W. Using all physical–biological components improved estimates of the pCO2W and decreased the biases, even though Chl-a values in many grid cells were interpolated values. General features of pCO2W distribution were reproduced with very good accuracy, but the network underestimated pCO2W in the winter and overestimated pCO2W values in the summer. The results show that the model that contains interpolating Chl-a concentration, SST, SSS, and MLD as a target to predict the spatiotemporal distribution of pCO2W in the sea surface gives the best results and best-fitting network to the observational data. The calculation of monthly drivers of the estimated pCO2W change within continental shelf areas of the EAS confirms the major impact of not only the biological effects to the pCO2W distribution and Air-Sea CO2 flux in the EAS, but also the strong impact of the upper ocean mixing. A strong seasonal correlation between predictor and pCO2W seen earlier in the North Atlantic is clearly a yearly correlation in the EAS. The five-year monthly mean CO2 flux distribution shows that all continental shelf areas of the Arctic Ocean were net CO2 sinks. Strong monthly CO2 influx to the Arctic Ocean through the Greenland and Barents Seas (>12 gC m−2 day−1) occurred in the fall and winter, when the pCO2W level at the sea surface was high (>360 µatm) and the strongest wind speed (>12 ms−1) was present.

Continue reading ‘The distribution of pCO2W and air-sea CO2 fluxes using FFNN at the continental shelf areas of the Arctic Ocean’

Derivation of seawater pCO2 from net community production identifies the South Atlantic Ocean as a CO2 source

A key step in assessing the global carbon budget is the determination of the partial pressure of CO2 in seawater (pCO2 (sw)). Spatially complete observational fields of pCO2 (sw) are routinely produced for regional and global ocean carbon budget assessments by extrapolating sparse in situ measurements of pCO2 (sw) using satellite observations. As part of this process, satellite chlorophyll a (Chl a) is often used as a proxy for the biological drawdown or release of CO2. Chl a does not, however, quantify carbon fixed through photosynthesis and then respired, which is determined by net community production (NCP).

In this study, pCO2 (sw) over the South Atlantic Ocean is estimated using a feed forward neural network (FNN) scheme and either satellite-derived NCP, net primary production (NPP) or Chl a to compare which biological proxy produces the most accurate fields of pCO2 (sw). Estimates of pCO2 (sw) using NCP, NPP or Chl a were similar, but NCP was more accurate for the Amazon Plume and upwelling regions, which were not fully reproduced when using Chl a or NPP. A perturbation analysis assessed the potential maximum reduction in pCO2 (sw) uncertainties that could be achieved by reducing the uncertainties in the satellite biological parameters. This illustrated further improvement using NCP compared to NPP or Chl a. Using NCP to estimate pCO2 (sw) showed that the South Atlantic Ocean is a CO2 source, whereas if no biological parameters are used in the FNN (following existing annual carbon assessments), this region appears to be a sink for CO2. These results highlight that using NCP improved the accuracy of estimating pCO2 (sw) and changes the South Atlantic Ocean from a CO2 sink to a source. Reducing the uncertainties in NCP derived from satellite parameters will ultimately improve our understanding and confidence in quantification of the global ocean as a CO2 sink.

Continue reading ‘Derivation of seawater pCO2 from net community production identifies the South Atlantic Ocean as a CO2 source’

Net ecosystem dissolution and respiration dominate metabolic rates at two western Atlantic reef sites

Ocean acidification is changing surface water chemistry, but natural variability due to nearshore processes can mask its effects on ecosystem responses. We present an approach of quantitatively resolving net ecosystem metabolism from an array of long-term time series stations, offering perhaps the longest record of such processes over a reef to date. We used 8 and 6 yr of in situ, high-quality frequency observations to characterize the changes in dissolved inorganic carbon and oxygen in La Parguera, Puerto Rico and Cheeca Rocks, Florida, respectively. Net respiration and net dissolution are the dominant metabolic processes at both systems, with a narrow window of ~ 4 months under net calcification. The annual mean net ecosystem calcification (NEC) rates for La Parguera (−0.68 ± 0.91 kg CaCO3 m−2 yr−1) and Cheeca Rocks (−0.48 ± 0.89 kg CaCO3 m−2 yr−1) were on the lower end of typical NEC ranges determined for other reef areas using chemistry- and census-based approaches. At Cheeca Rocks, 53% of the variance in NEC can be explained by net ecosystem production (NEP) and 30% by aragonite saturation state (Ωarag). At La Parguera, NEC is primarily driven by changes in NEP. The linear relationship between NEC and NEP showed a significant slope (± standard error) of 1.00 ± 0.005 and 0.88 ± 0.04 for La Parguera and Cheeca Rocks, respectively. These results suggest that NEP appears to play a prominent role on NEC, and Ωarag probably is not the most informative measure to monitor when attempting to resolve the long-term impacts of ocean acidification.

Continue reading ‘Net ecosystem dissolution and respiration dominate metabolic rates at two western Atlantic reef sites’

Modeling carbon budgets and acidification in the Mediterranean Sea ecosystem under contemporary and future climate

We simulate and analyze the effects of a high CO2 emission scenario on the Mediterranean Sea biogeochemical state at the end of the XXI century, with a focus on carbon cycling, budgets and fluxes, within and between the Mediterranean sub-basins, and on ocean acidification. As a result of the overall warming of surface water and exchanges at the boundaries, the model results project an increment in both the plankton primary production and the system total respiration. However, productivity increases less than respiration, so these changes yield to a decreament in the concentrations of total living carbon, chlorophyll, particulate organic carbon and oxygen in the epipelagic layer, and to an increment in the DIC pool all over the basin. In terms of mass budgets, the large increment in the dissolution of atmospheric CO2 results in an increment of most carbon fluxes, including the horizontal exchanges between eastern and western sub-basins, in a reduction of the organic carbon component, and in an increament of the inorganic one. The eastern sub-basin accumulates more than 85% of the absorbed atmospheric CO2. A clear ocean acidification signal is observed all over the basin, quantitatively similar to those projected in most oceans, and well detectable also down to the mesopelagic and bathypelagic layers.

Continue reading ‘Modeling carbon budgets and acidification in the Mediterranean Sea ecosystem under contemporary and future climate’

Climate change, marine resources and a small Chilean community: making the connections

Climate change is affecting large-scale oceanic processes. How and when these changes will impact those reliant on marine resources is not yet clear. Here we use end-to-end modeling to track the impacts of expected changes through the marine ecosystem on a specific, small community: Cochamó, in the Gulf of Ancud wider area, Chile. This area is important for Chilean fisheries and aquaculture, with Cochamó reliant on both lower and upper trophic level marine resources. We applied the GOTM-ERSEM-BFM coupled hydro-biogeochemical water-column model to gauge lower-trophic level marine ecological community response to bottom-up stressors (climate change, ocean acidification), coupled to an existing Ecopath with Ecosim model for the area, which included top-down stressors (fishing). Social scientists also used participatory modeling (Systems Thinking and Bayesian Belief Networking) to identify key resources for Cochamó residents and to assess the community’s vulnerability to possible changes in key resources. Modeling results suggest that flagellate phytoplankton abundance will increase at the cost of other species (particularly diatoms), resulting in a greater risk of harmful algae blooms. Both climate change and acidification slightly increased primary production in the model. Higher trophic level results indicate that some targeted pelagic resources will decline (while benthic ones may benefit), but that these effects might be mitigated by strong fisheries management efforts. Participatory modeling suggests that Cochamó inhabitants anticipate marine ecosystem changes but are divided about possible adaptation strategies. For climate change impact quantification, detailed experimental studies are recommended based on the dominant threats identified here, with specific local species.

Continue reading ‘Climate change, marine resources and a small Chilean community: making the connections’

  • Reset

Subscribe

OA-ICC Highlights


%d bloggers like this: