Climate-enhanced stock assessment models represent potentially vital tools for managing living marine resources under climate change. We present a climate-enhanced stock assessment where environmental variables are integrated within a population dynamics model assessment of biomass, fishing mortality and recruitment that also accounts for process error in demographic parameters. Probability distributions for the impact of the associated environmental factors on recruitment and growth can either be obtained from Bayesian analyses that involve fitting the population dynamics model to the available data or from auxiliary analyses. The results of the assessment form the basis for the calculation of biological and economic target and limit reference points, and projections under alternative harvest strategies. The approach is applied to northern rock sole (Lepidopsetta polyxystra), an important component of the flatfish fisheries in the Eastern Bering Sea. The assessment involves fitting to data on catches, a survey index of abundance, fishery and survey age-compositions and survey weight-at-age, with the relationship between recruitment and cold pool extent and that between growth increment in weight and temperature integrated into the assessment. The projections also allow for an impact of ocean pH on expected recruitment based on auxiliary analyses. Several alternative models are explored to assess the consequences of different ways to model environmental impacts on population demography. The estimates of historical biomass, recruitment and fishing mortality for northern rock sole are not markedly impacted by including climate and environmental factors, but estimates of target and limit reference points are sensitive to whether and how environmental variables are included in stock assessments and projections.
Nitrous oxide (N2O) is a powerful greenhouse gas that degrades ozone. Hypoxia and ocean acidification are becoming more intense as a result of climate change. The former stimulates N2O emissions, whereas the effects of the latter on N2O production vary by the ocean. Hypoxia and ocean acidification may play a critical role in the evolution of future oceanic N2O production. However, the interactive effects of hypoxia and ocean acidification on N2O production remain unclear. We conducted a research cruise in the Bohai Sea of China to assess the occurrence of ocean acidification in the seasonal oxygen minimum zone of the sea and further conducted laboratory incubation experiments to determine the effects of ocean acidification and hypoxia on N2O production. When pH decreased by 0.25, N2O production decreased by 50.77 and 72.38%, respectively. In contrast, hypoxia had a positive impact; when dissolved oxygen (DO) decreased to 3.7 and 2.4 mg L−1, N2O production increased by 49.72 and 278.68%, respectively. The incubation experiments demonstrated that the coupling of ocean acidification and hypoxia significantly increased N2O production, but, individually, there was an antagonistic relationship between the two. Structural equation modeling showed that the total effects of hypoxia treatment on N2O production changes weakened the effects of ocean acidification, with overall positive effects. Generally speaking, our results suggest that N2O production from the coastal waters of the Bohai Sea may increase under future climate change scenarios due to increasingly serious ocean acidification and hypoxia working in combination.
Understanding decadal changes in the coastal carbonate system is essential for predicting how the health of these waters responds to anthropogenic drivers, such as changing atmospheric conditions and riverine inputs. However, studies that quantify the relative impacts of these drivers are lacking. In this study, the primary drivers of decadal trends in the surface carbonate system, and the spatiotemporal variability in these trends, are identified for a large coastal plain estuary: the Chesapeake Bay. Experiments using a coupled three-dimensional hydrodynamic-biogeochemical model highlight that, over the past three decades, the changes in the surface carbonate system of Chesapeake Bay have strong seasonal and spatial variability. The greatest surface pH and aragonite saturation state (ΩAR) reductions have occurred in the summer in the middle (mesohaline) Bay: −0.24 and −0.9 per 30 years, respectively, with increases in atmospheric CO2 and reductions in nitrate loading both being primary drivers. Reductions in nitrate loading have a strong seasonal influence on the carbonate system, with the most pronounced decadal decreases in pH and ΩAR occurring during the summer when primary production is strongly dependent on nutrient availability. Increases in riverine total alkalinity and dissolved inorganic carbon have raised surface pH in the upper oligohaline Bay, while other drivers such as atmospheric warming and input of acidified ocean water through the Bay mouth have had comparatively minor impacts on the estuarine carbonate system. This work has significant implications for estuarine ecosystem services, which are typically most sensitive to surface acidification in the spring and summer seasons.
Plain Language Summary
Seawater pH, a measure of how acidic or basic water is, is a crucial water quality parameter influencing the growth and health of marine organisms, such as oysters, fishes and crabs. Decreasing pH, commonly referred to as acidification, is a severe environmental issue that has been exacerbated by human activities since the industrial revolution. In the open ocean, elevated atmospheric carbon dioxide is the key driver of acidification. However, in coastal environments the drivers are particularly complex due to changing human influences on land. In this study the primary drivers of acidification in the Chesapeake Bay over the past three decades are identified via the application of a three-dimensional ecosystem model. Increased atmospheric CO2 concentrations and decreased terrestrial nutrient inputs are two primary drivers causing nearly equal reductions in pH in surface waters of the Bay. The pH reductions resulting from decreased nutrient loads indicate that the system is reverting back to more natural conditions when human-induced nutrient inputs to the Bay were lower. As nutrient reduction efforts to improve coastal water quality continue in the future, controlling the emissions of anthropogenic CO2 globally becomes increasingly important for the shellfish industry and the ecosystem services it provides.
Ocean thermal energy conversion (OTEC) is a power generation technology that extracts energy from the temperature difference between deep seawater and surface water in the ocean. Currently, a 100 kW class OTEC demonstration project is underway on Kume Island, Okinawa, and a plan to increase water intake and introduce a 1 MW class OTEC plant is under consideration. Year-round generation of electricity by an OTEC plant requires that it be installed in tropical and subtropical regions, where the surface water has a high temperature and low nutrient content. However, the water discharged from an OTEC plant will have the opposite characteristics of low water temperature and high nutrients, as well as a low pH. One of the most concerning environmental impacts of this discharged water is its influence on corals, which are important species in tropical and subtropical marine ecosystems. In this study, we developed an ecosystem model for a subtropical shallow-water region; the model combines a pelagic submodel, a chemical equilibrium submodel, and a benthic submodel, and successfully reproduces the observed variation in pH. The model was used to predict the environmental impact of water discharged from OTEC plant. The simulation results suggest that a 1 MW class OTEC plant would cause few environmental changes that would affect corals.
Ocean Alkalinity Enhancement (OAE) simultaneously mitigates atmospheric concentrations of CO2 and ocean acidification; however, no previous studies have investigated the response of the non-linear marine carbonate system sensitivity to alkalinity enhancement on regional scales. We hypothesise that regional implementations of OAE can sequester more atmospheric CO2 than a global implementation. To address this, we investigate physical regimes and alkalinity sensitivity as drivers of the carbon-uptake potential response to global and different regional simulations of OAE. In this idealised ocean-only set-up, total alkalinity is enhanced at a rate of 0.25 Pmol a-1 in 75-year simulations using the Max Planck Institute Ocean Model coupled to the HAMburg Ocean Carbon Cycle model with pre-industrial atmospheric forcing. Alkalinity is enhanced globally and in eight regions: the Subpolar and Subtropical Atlantic and Pacific gyres, the Indian Ocean and the Southern Ocean. This study reveals that regional alkalinity enhancement has the capacity to exceed carbon uptake by global OAE. We find that 82–175 Pg more carbon is sequestered into the ocean when alkalinity is enhanced regionally and 156 PgC when enhanced globally, compared with the background-state. The Southern Ocean application is most efficient, sequestering 12% more carbon than the Global experiment despite OAE being applied across a surface area 40 times smaller. For the first time, we find that different carbon-uptake potentials are driven by the surface pattern of total alkalinity redistributed by physical regimes across areas of different carbon-uptake efficiencies. We also show that, while the marine carbonate system becomes less sensitive to alkalinity enhancement in all experiments globally, regional responses to enhanced alkalinity vary depending upon the background concentrations of dissolved inorganic carbon and total alkalinity. Furthermore, the Subpolar North Atlantic displays a previously unexpected alkalinity sensitivity increase in response to high total alkalinity concentrations.
Surface ocean CO2 measurements are used to compute the oceanic air–sea CO2 flux. The CO2 flux component from rivers and estuaries is uncertain. Estuarine and coastal water carbon dioxide (CO2) observations are relatively few compared to observations in the open ocean. The contribution of these regions to the global air–sea CO2 flux remains uncertain due to systematic under-sampling. Existing high-quality CO2 instrumentation predominantly utilise 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 end members determines the variations in fCO2. 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 dominated 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 bias 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.
The United States Department of Energy (DOE)’s Ocean Margins Program (OMP) cruise EN279 in March 1996 provides an important baseline for assessing long-term changes in the carbon cycle and biogeochemistry in the Mid-Atlantic Bight (MAB) as climate and anthropogenic changes have been substantial in this region over the past two decades. The distributions of O2, nutrients, and marine inorganic carbon system parameters are influenced by coastal currents, temperature gradients, and biological production and respiration. On the cross-shelf direction, pH decreases seaward, but carbonate saturation state (ΩArag) does not exhibit a clear trend. In contrast, ΩArag increases from north to south, while pH has no clear spatial patterns in the along-shelf direction. In order to distinguish between the effects of physical mixing of various water masses and those of biological activities on the marine inorganic carbon system, we use the potential temperature-salinity diagram to identify water masses, and differences between observations and theoretical mixing concentrations to measure the non-conservative (primarily biological) effects. Our analysis clearly shows the degree to which ocean margin pH and ΩArag are regulated by biological activities in addition to water mass mixing, gas exchange, and temperature. The correlations among anomalies in dissolved inorganic carbon, phosphate, nitrate, and apparent oxygen utilization agree with known biological stoichiometry. Biological uptake is substantial in nearshore waters and in shelf-slope mixing areas. This work provides valuable baseline information to assess the more recent changes in the marine inorganic carbon system and the status of coastal ocean acidification.
Our understanding of eutrophication-induced acidification in estuaries and coastal oceans is complicated by the seasonally and spatially changing interactions between physical and biochemical drivers. By combining the conservative mixing method and a physical-biogeochemical model, we present the seasonal and spatial dynamical analysis of eutrophication-induced acidification in the Pearl River Estuary in the northern South China Sea. In summer, the widespread eutrophication-induced acidification is regulated by two distinct physical drivers, which are the strengthened stratification in the hypoxia zone and the high turbidity in the Lingdingyang Bay. In the hypoxia zone, eutrophication-induced acidification is controlled by the combined effect of benthic remineralization and stratification, while it is dominantly regulated by local biochemical processes (nitrification and respiration) of the whole water column in other regions of the estuary. In winter with the enhanced vertical mixing, the eutrophication-induced acidification is still active in the Lingdingyang Bay, and its strength has largely decreased compared with summer condition. While for the hypoxia zone, the eutrophication-induced acidification peaks in summer and disappears in winter.
Plain Language Summary
Eutrophication in estuaries has accelerated the ocean acidification, which induced a negative impact on marine ecosystem. In the estuary, physical and biochemical processes lead to difficulties in understanding and evaluating the impact of eutrophication-induced acidification. High-resolution and coupled oceanographic models can reproduce the biogeochemical cycles in the marine system and present an integrated framework to understand ocean acidification. We revealed two distinct types of eutrophication-induced acidification in the estuary by using an oceanographic model. The model results show that these two types of eutrophication-induced acidification are regulated by different physical processes that are water stratification and turbidity, which result in their unique seasonal evolution patterns.
This research is conducted to assess the accuracy of spline interpolation methods to predict and model the surface water pH of Pulau Tuba, Langkawi, Kedah, Malaysia. In-situ sampling activities using pH-meter and Geographic Positioning Systems (GPS) were carried out during high tides and at noon in November 2018. The development of spatial models were constructed using the Regularized and Tension spline methods. Then, validation of models was carried out to compare the observed and predicted values of pH using correlation analysis, regression analysis, and error analysis. The accuracy of the developed map was calculated using the overall accuracy equation. The research found that the regularized spline method had more accuracy in estimating surface water pH variability than the tension spline method. The Pearson correlation coefficient (r), Coefficient of determination (R2), Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) were reported at 0.896, 0.803, 0.0265 and 0.0344 for the regularized spline method, respectively. The developed spatial model was then transformed into a map by adding map elements such as legend, title, north arrow, and scales for effective visualization. The developed map has an accuracy of 87.50%. The surface water pH was found at the range of 7-8. The low reading of pH is expected due to the addition of rainwater that lowered the pH of the coastal water of Pulau Tuba, Langkawi, Kedah. The research outcomes would benefit the government and non-government agencies to monitor the coastal and ocean acidification and the development of strategic policies and rules to reduce the impact of anthropogenic activities and climate change for this area.
The seasonal variability of the lateral flux of total alkalinity (TAlk) and dissolved inorganic carbon (DIC) of the tropical Hooghly estuary is analyzed in this work. In situ observations of water temperature, salinity, dissolved oxygen, TAlk, and pH were measured in four different stations of the Hooghly estuary. It was measured once every month during 2015–2016, and subsequently, DIC was estimated. A carbon budget was constructed to quantify carbon flows through the freshwater-marine continuum of the Hooghly estuary, and plausible impacts on the adjacent coastal ocean, the northern Bay of Bengal, were examined. The biogeochemical mass balance box model was used to compute the seasonal flow of carbon flux, and subsequently, the annual budgeting of lateral fluxes of TAlk and DIC to the adjacent coastal ocean was carried out. The net annual TAlk and DIC flux from the Hooghly estuary to the adjacent coastal ocean were 4.45 ± 1.90 × 1011 mol and 4.59 ± 1.70 × 1011 mol, respectively. The net annual DIC flux of the Hooghly estuary is about 30 to 60 times higher than surface area integrated air–water CO2 flux, which is an indication of promoting acidification in the adjacent coastal ocean. The present study indicates that the lateral DIC flux has increased substantially in the Hooghly estuary during the last two decades. The increase in inorganic carbon load in the Hooghly estuary due to the enhanced discharge of inorganic and organic matter load in the upper reaches of the estuary led to this increase in lateral DIC flux. The results strongly establish the need of having such regional studies for better understanding the estuarine carbon dynamics, and its role in controlling the adjacent coastal ocean dynamics.
The multi-decadal variation in ocean acidification indices in the Northwest Pacific was examined using a biogeochemical model with an operational ocean model product for the period 1993–2018. We found that ocean acidification varied regionally in the Northwest Pacific. The surface ocean (above 100 m depth) underwent acidification that progressed more quickly in the subtropical region and the Kuroshio extension than in the subarctic region due to vertical mixing of the dissolved inorganic carbon (DIC) supply exceeding DIC release by air–sea exchange. Below 100 m depth, acidification and alkalinization occurred in the subtropical and subarctic regions, respectively. We attribute these regional differences in acidification and alkalinization to spatially variable biological processes in the upper layer and physical redistribution of DIC, both horizontally and vertically.
We conduct a modeling study of the effects of enhanced coastal nutrient export from human activities on the carbon, nitrogen, and oxygen cycles of the Southern California Bight, in the context of emerging global climate change. The modeling approach used is innovative in the breadth of its scope, and simulations are generally consistent with local measurements. The human effects on the regional ecosystem from coastal nitrogen inputs of 23 million people are substantial, leading to significant increases in the photosynthesis and biomass of phytoplankton and increased oxygen loss and acidification of the water column. These changes are likely to compress habitat for a variety of marine organisms, with cascading ecological effects and implications for marine resources and water-quality management.
Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical–biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m−3, 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.
Global projections for ocean conditions in 2100 predict that the North Pacific will experience some of the largest changes. Coastal processes that drive variability in the region can alter these projected changes but are poorly resolved by global coarse-resolution models. We quantify the degree to which local processes modify biogeochemical changes in the eastern boundary California Current System (CCS) using multi-model regionally downscaled climate projections of multiple climate-associated stressors (temperature, O2, pH, saturation state (Ω), and CO2). The downscaled projections predict changes consistent with the directional change from the global projections for the same emissions scenario. However, the magnitude and spatial variability of projected changes are modified in the downscaled projections for carbon variables. Future changes in pCO2 and surface Ω are amplified, while changes in pH and upper 200 m Ω are dampened relative to the projected change in global models. Surface carbon variable changes are highly correlated to changes in dissolved inorganic carbon (DIC), pCO2 changes over the upper 200 m are correlated to total alkalinity (TA), and changes at the bottom are correlated to DIC and nutrient changes. The correlations in these latter two regions suggest that future changes in carbon variables are influenced by nutrient cycling, changes in benthic–pelagic coupling, and TA resolved by the downscaled projections. Within the CCS, differences in global and downscaled climate stressors are spatially variable, and the northern CCS experiences the most intense modification. These projected changes are consistent with the continued reduction in source water oxygen; increase in source water nutrients; and, combined with solubility-driven changes, altered future upwelled source waters in the CCS. The results presented here suggest that projections that resolve coastal processes are necessary for adequate representation of the magnitude of projected change in carbon stressors in the CCS.
Quantifying the spatial and temporal footprint of multiple environmental stressors on marine fisheries is imperative to understanding the effects of changing ocean conditions on living marine resources. Pacific Cod (Gadus macrocephalus), an important marine species in the Gulf of Alaska ecosystem, has declined dramatically in recent years, likely in response to extreme environmental variability in the Gulf of Alaska related to anomalous marine heatwave conditions in 2014–2016 and 2019. Here, we evaluate the effects of two potential environmental stressors, temperature variability and ocean acidification, on the growth of juvenile Pacific Cod in the Gulf of Alaska using a novel machine-learning framework called “stress-scapes,” which applies the fundamentals of dynamic seascape classification to both environmental and biological data. Stress-scapes apply a probabilistic self-organizing map (prSOM) machine learning algorithm and Hierarchical Agglomerative Clustering (HAC) analysis to produce distinct, dynamic patches of the ocean that share similar environmental variability and Pacific Cod growth characteristics, preserve the topology of the underlying data, and are robust to non-linear biological patterns. We then compare stress-scape output classes to Pacific Cod growth rates in the field using otolith increment analysis. Our work successfully resolved five dynamic stress-scapes in the coastal Gulf of Alaska ecosystem from 2010 to 2016. We utilized stress-scapes to compare conditions during the 2014–2016 marine heatwave to cooler years immediately prior and found that the stress-scapes captured distinct heatwave and non-heatwave classes, which highlighted high juvenile Pacific Cod growth and anomalous environmental conditions during heatwave conditions. Dominant stress-scapes underestimated juvenile Pacific Cod growth across all study years when compared to otolith-derived field growth rates, highlighting the potential for selective mortality or biological parameters currently missing in the stress-scape model as well as differences in potential growth predicted by the stress-scape and realized growth observed in the field. A sensitivity analysis of the stress-scape classification result shows that including growth rate data in stress-scape classification adjusts the training of the prSOM, enabling it to distinguish between regions where elevated sea surface temperature is negatively impacting growth rates. Classifications that rely solely on environmental data fail to distinguish these regions. With their incorporation of environmental and non-linear physiological variables across a wide spatio-temporal scale, stress-scapes show promise as an emerging methodology for evaluating the response of marine fisheries to changing ocean conditions in any dynamic marine system where sufficient data are available.
- The seasonal upwelling transport has increased by as much as 25% in 1996–2018.
- Spatially structured trends in pH and Chl-a are observed for the same period.
- Results from satellite analysis and model reanalysis products diverge locally.
Long-term changes in the marine ecosystems of the Eastern Boundary Upwelling Systems (EBUS) are predicted due to anthropogenic climate change. In particular, global ocean acidification is having a profound effect on the coastal waters of the EBUS, affecting the entire trophic chain, net primary production (NPP) and related economic activities such as fisheries. Another predicted change related to human activity is that of upwelling dynamics with expected long-term changes in upwelling winds as proposed by Bakun (1990), Bakun et al. (2015) and Rykaczewski et al. (2015). Although these predicted long-term changes may emerge only later in the 21st century, this has fueled many studies using historical data. Long-term increase in upwelling winds has thus been a much debated topic, showing that there is considerable uncertainty depending on the EBUS considered, the effect of natural climate fluctuations, the choice of wind dataset, the time period considered, and the methodologies and significance tests applied. Therefore, there is an immediate interest in being able to monitor upwelling using verified and self-consistent wind data sets. This work focused on a sensitivity study of the estimated trends in upwelling winds in the California Current Upwelling System (CCUS), for the most recent period 1996–2018, using the two state-of-the-art satellite wind analyses and two atmospheric model re-analyses. Embedded into the strong modulation by natural climate fluctuations on interannual and decadal time scales, we do see an increase in upwelling-favorable winds in the core of the CCUS, with a local increase of more than 25% in seasonal upwelling transport for the period considered. In this central upwelling zone, a good agreement on stronger equatorward winds for the winter and spring seasons is found between the different datasets, although with different significance levels. Conversely, conflicting results are found in the southernmost part of the CCUS between the satellite analyses and the model reanalyses. Systematic, time-dependent differences are found between the wind products, highlighting the need to further investigate the poorly documented temporal stability of these widely used wind long-term climatology products. The observed spatial structuring of the estimated wind trends is consistent with the trend analysis of water chlorophyll-a, partial pressure of CO2, and basity (pH) analysis products. This result is consistent with changes being important for modulating the carbonate system within the CCUS.
The uptake of anthropogenic carbon (Cant) by the ocean leads to ocean acidification, causing the reduction of pH and the saturation states of aragonite (Ωarag) and calcite (Ωcalc). The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states and due to ongoing freshening and the concurrent reduction in total alkalinity in this region. Here, we analyse ocean acidification in the Arctic Ocean over the 21st century across 14 Earth system models (ESMs) from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of Cant into the Arctic Ocean interior, with simulated historical increases in Cant in improved agreement with observational products. Moreover, in CMIP6 the inter-model uncertainty of projected changes over the 21st century in Arctic Ocean Ωarag and Ωcalc averaged over the upper 1000 m is reduced by 44–64 %. The strong reduction in projection uncertainties of Ωarag and Ωcalc can be attributed to compensation between Cant uptake and total alkalinity reduction in the latest models. Specifically, ESMs with a large increase in Arctic Ocean Cant over the 21st century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in Cant simulate a relatively strong freshening and concurrent total alkalinity reduction. Although both mechanisms contribute to Arctic Ocean acidification over the 21st century, the increase in Cant remains the dominant driver. Even under the low-emissions Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6), basin-wide averaged Ωarag undersaturation in the upper 1000 m occurs before the end of the century. While under the high-emissions pathway SSP5-8.5, the Arctic Ocean mesopelagic is projected to even become undersaturated with respect to calcite. An emergent constraint identified in CMIP5 which relates present-day maximum sea surface densities in the Arctic Ocean to the projected end-of-century Arctic Ocean Cant inventory is found to generally hold in CMIP6. However, a coincident constraint on Arctic declines in Ωarag and Ωcalc is not apparent in the new generation of models. This is due to both the reduction in Ωarag and Ωcalc projection uncertainty and the weaker direct relationship between projected changes in Arctic Ocean Cant and changes in Ωarag and Ωcalc.
The Arctic may be particularly vulnerable to the consequences of both ocean acidification (OA) and global warming, given the faster pace of warming and acidification. Here, we use the Atlantis ecosystem model to assess how the trophic network of marine fishes and invertebrates in the Icelandic waters is responding to the combined pressures of OA and warming. We develop an approach which allows us to focus on species of economic (catch-value), social (number of participants in fisheries), or ecological (keystone species) importance. We parameterize the model with literature-determined ranges of sensitivity to OA and warming for different species and functional groups in the Icelandic waters. We found divergent species responses to warming and acidification levels; (mainly) planktonic groups and forage fish benefited while (mainly) benthic groups and predatory fish decreased under warming and acidification scenarios. Assuming conservative harvest rates for the largest catch-value species, Atlantic cod, we see that the population is projected to remain stable under even the harshest acidification and warming scenario. Further, for the scenarios where the model projects reductions in biomass of Atlantic cod, other species in the ecosystem increase, likely due to a reduction in competition and predation. These results highlight the interdependencies of multiple global change drivers and their cascading effects on trophic organization, and the supply of an important species from a socio-economic perspective in the Icelandic fisheries.
- A real-time environmental forecast system of the Chesapeake Bay has run since 2017.
- Forecast includes salinity, temperature, oxygen, and acidification metrics.
- Current conditions and 2-day forecasts are available on a mobile-friendly website.
- Visualizations are updated regularly based on stakeholder feedback.
- Model output is available on a THREDDS server for use by others via MARACOOS.
Daily real-time nowcasts (current conditions) and 2-day forecasts of environmental conditions in the Chesapeake Bay have been continuously available for 4 years. The forecasts use a 3-D hydrodynamic-biogeochemical model with 1 to 2 km resolution and 3-D output every 6 hours that includes salinity, water temperature, pH, aragonite saturation state, alkalinity, dissolved oxygen, and hypoxic volume. Visualizations of the forecasts are available through a local institutional website (www.vims.edu/hypoxia) and the MARACOOS Oceans Map portal (https://oceansmap.maracoos.org/chesapeake-bay/). Modifications to real-time graphics on the local website are routinely made based on stakeholder input and are formatted for use on a mobile device. Continuous model input files were developed from daily real-time forecast input files, for hindcast simulations and efficient evaluation and improvement of the real-time model. This manuscript describes the setup of the environmental forecasting system, how the model accuracy has been improved, and the revision of online graphics based on stakeholder feedback.
Despite the well-recognized importance in understanding the long term impact of anthropogenic release of atmospheric CO2 (its partial pressure named as pCO2air) on surface seawater pCO2 (pCO2sw), it has been difficult to quantify the trends or changing rates of pCO2sw driven by increasing atmospheric CO2 forcing (pCO2swatm_forced) due to its combination with the natural variability of pCO2sw (pCO2swnat_forced) and the requirement of long time series data records. Here, using a novel satellite-based pCO2sw model with inputs of ocean color and other ancillary data between 2002 and 2019, we address this challenge for a mooring station at the Hawaii Ocean Time-series Station in the North Pacific subtropical gyre. Specifically, using the developed pCO2sw model, we differentiated and separately quantified the interannual-decadal trends of pCO2swnat_forced and pCO2swatm_forced. Between 2002 and 2019, both pCO2sw and pCO2air show significant increases at rates of 1.7 ± 0.1 μatm yr–1 and 2.2 ± 0.1 μatm yr–1, respectively. Correspondingly, the changing rate in pCO2swnat_forced is mainly driven by large scale forcing such as Pacific Decadal Oscillation, with a negative rate (-0.5 ± 0.2 μatm yr–1) and a positive rate (0.6 ± 0.3 μatm yr–1) before and after 2013. The pCO2swatm_forced shows a smaller increasing rate of 1.4 ± 0.1 μatm yr–1 than that of the modeled pCO2sw, varying in different time intervals in response to the variations in atmospheric pCO2. The findings of decoupled trends in pCO2swatm_forced and pCO2swnat_forced highlight the necessity to differentiate the two toward a better understanding of the long term oceanic absorption of anthropogenic CO2 and the anthropogenic impact on the changing surface ocean carbonic chemistry.
Model projections of ocean circulation and biogeochemistry are used to investigate large scale climate changes under moderate mitigation (RCP 4.5) and high emissions (RCP 8.5) scenarios along the continental shelf of the Canadian Pacific Coast. To reduce computational cost, an approach for dynamical downscaling of climate projections was developed that uses atmospheric climatologies with augmented winds to simulate historical (1986–2005) and future (2046–2065) periods separately. The two simulations differ in initial and lateral open boundary conditions. For each simulation, the daily climatology of surface winds in the driving model was augmented with high-frequency variability from an atmospheric reanalysis product. The “time-slice” approach was able to reproduce the observed climate state for the historical period. Sensitivity tests confirmed that the high frequency wind variability plays an essential role in freshwater distribution in this region. Projections suggest that sea surface temperature will increase by 1.8–2.4°C and surface salinity will decrease between −0.08 and −0.23 depending on whether a moderate or high emissions scenario is used. Stratification increases throughout the region and there is some evidence of nutrient limitation near the surface. Primary production and phytoplankton productivity (chlorophyll) also increase. Density surfaces are relocated deeper in the water column and this change is mainly driven by surface heating and freshening. Changes in saturation state are mainly due to anthropogenic CO2 with minor contributions from solubility, remineralization and advection. There is little difference between RCP 4.5 and RCP 8.5 with regard to projections of deoxygenation and acidification. The depths of the aragonite saturation state and the oxygen minimum zone are projected to become shallower by ≃ 100 and ≃ 75 m respectively. Extreme states of temperature, oxygen and acidification are projected to become more frequent and more extreme, with the frequency of occurrence of [O2]<60 mmolm−3[O2]<60 mmolm-3 expected to approximately double under either scenario.