Posts Tagged 'modeling'

The combined effects of ocean acidification and respiration on habitat suitability for marine calcifiers along the West coast of North America

Published 24 April 2024 Science Leave a Comment
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Abstract

The California Current Ecosystem (CCE) is a natural laboratory for studying the chemical and ecological impacts of ocean acidification. Biogeochemical variability in the region is due primarily to wind-driven near-shore upwelling of cold waters that are rich in re-mineralized carbon and poor in oxygen. The coastal regions are exposed to surface waters with increasing concentrations of anthropogenic CO2 (Canth) from exchanges with the atmosphere and the shoreward transport and mixing of upwelled water. The upwelling drives intense cycling of organic matter that is created through photosynthesis in the surface ocean and degraded through biological respiration in subsurface habitats. We used an extended multiple linear-regression approach to determine the spatial and temporal concentrations of Canth and respired carbon (Cbio) in the CCE based on cruise data from 2007, 2011, 2012, 2013, 2016, and 2021. Over the region, the Canth accumulation rate increased from 0.8 ± 0.1 μmol kg−1 yr−1 in the northern latitudes to 1.1 ± 0.1 μmol kg−1 yr−1 further south. The rates decreased to values of about ∼0.3 μmol kg−1 yr−1 at depths near 300 m. These accumulation rates at the surface correspond to total pH decreases that averaged about 0.002 yr-1; whereas, decreases in aragonite saturation state ranged from 0.006 to 0.011 yr-1. The impact of the Canth uptake was to decrease the amount of oxygen consumption required to cross critical biological thresholds (i.e., calcification, dissolution) for marine calcifiers and are significantly lower in the recent cruises than in the pre-industrial period because of the addition of Canth.

Key Points

  • In the California Current Ecosystem the anthropogenic carbon (Canth) uptake rate at the surface ranges from 0.8 to 1.1 μmol kg−1 yr−1
  • This corresponds to a total pH decrease of about 0.002 yr−1, whereas the decrease in aragonite saturation ranges from 0.006 to 0.011 yr−1
  • Dissolved oxygen consumptions required to cross critical biological thresholds are significantly lower in 2021 than in the pre-industrial

Plain Language Summary

The combined effect of ocean acidification and respiration in the California Current Ecosystem is to reduce water column pH and aragonite saturation state, resulting in a compression of the overall size of suitable habitat for marine calcifiers. The addition of excess anthropogenic CO2 also makes it more likely that critical biological thresholds are crossed and shell dissolution begins to occur. Consequently, the addition of the excess CO2 also has the added effect of reducing the amount of biological consumption of oxygen that is required to drop the ecosystem below these thresholds.

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Sea-surface pCO2 maps for the Bay of Bengal based on advanced machine learning algorithms

Published 23 April 2024 Science Leave a Comment
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Lack of sufficient observations has been an impediment for understanding the spatial and temporal variability of sea-surface pCO2 for the Bay of Bengal (BoB). The limited number of observations into existing machine learning (ML) products from BoB often results in high prediction errors. This study develops climatological sea-surface pCO2 maps using a significant number of open and coastal ocean observations of pCO2 and associated variables regulating pCO2 variability in BoB. We employ four advanced ML algorithms to predict pCO2. We use the best ML model to produce a high-resolution climatological product (INCOIS-ReML). The comparison of INCOIS-ReML pCO2 with RAMA buoy-based sea-surface pCO2 observations indicates INCOIS-ReML’s satisfactory performance. Further, the comparison of INCOIS-ReML pCO2 with existing ML products establishes the superiority of INCOIS-ReML. The high-resolution INCOIS-ReML greatly captures the spatial variability of pCO2 and associated air-sea CO2 flux compared to other ML products in the coastal BoB and the northern BoB.

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The combined effects of warming, ocean acidification, and fishing on the northeast Atlantic cod (Gadus morhua) in the Barents Sea

Published 19 April 2024 Science Leave a Comment
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With a biomass of ∼4 million tonnes, and annual catches of 900 000 tonnes, the northeast Atlantic (NEA) cod stock in the Barents Sea is the world’s largest. Scientists have been trying to explain the variability in recruitment of this stock for over 100 years, in particular connecting it to spawning stock biomass and environmental factors such as temperature. It has been suggested that the combination of ocean acidification and global warming will lead to a significant decrease in the spawning stock biomass and an eventual (end of this century) collapse of the NEA cod stock in the Barents Sea. We show that a temperature- and OA-driven decline in recruits will likely lead to a smaller cod stock, but not to a collapse. Instead, the level of fishing pressure and, not least, the choice of the recruitment function applied in simulations and how it relates to temperature, is extremely important when making such forecasts. Applying a non-linear relationship between temperature and spawning stock biomass—as has been done in studies that predict a collapse of the NEA cod stock—does not improve accuracy and, in addition, adds a large decrease in number of recruits that is not biologically supported.

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Water pollution is fueling ocean acidification. Environmentalists urge California to act

Published 19 April 2024 Press releases Leave a Comment
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The Hyperion Water Reclamation Plant in Playa del Rey is one of a number of wastewater treatment plants that send treated effluent into the waters off California’s coast. (Gary Coronado / Los Angeles Times)

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As the burning of fossil fuels and other human activities continue to increase the levels of carbon dioxide in the atmosphere, the ocean is absorbing a large portion of the CO2, which is making seawater more acidic.

The changing water chemistry in the ocean has far-reaching effects for plankton, shellfish and the entire marine food web.

And here’s one important fact about ocean acidification: It’s not happening at the same rate everywhere.

The California coast is one of the regions of the world where ocean acidification is occurring the fastest. And researchers have found that local sources of pollution are part of the problem.

In particular, effluent discharged from coastal sewage treatment plants, which has high nitrogen levels from human waste, has been shown to significantly contribute to ocean acidification off the Southern California coast. These nitrogen-filled discharges also periodically contribute to algae blooms, leading to hypoxia, or oxygen-deprived water that is inhospitable for marine life.

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Seasonal variability of coastal pH and CO2 using an oceanographic buoy in the Canary Islands

Published 17 April 2024 Science Closed
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Ocean acidification, caused by the absorption of carbon dioxide (CO2) from the atmosphere into the ocean, ranks among the most critical consequences of climate change for marine ecosystems. Most studies have examined pH and CO2 trends in the open ocean through oceanic time-series research. The analysis in coastal waters, particularly in island environments, remains relatively underexplored. This gap in our understanding is particularly important given the profound implications of these changes for coastal ecosystems and the blue economy. The present study focuses on the ongoing monitoring effort that started in March 2020 along the east coast of Gran Canaria, within the Gando Bay, by the CanOA-1 buoy. This monitoring initiative focuses on the systematic collection of multiple variables within the CO2 system, such as CO2 fugacity (fCO2), pH (in total scale, pHT), total inorganic carbon (CT), and other hydrographic variables including sea surface salinity (SSS), sea surface temperature (SST) and wind intensity and direction. Accordingly, the study allows the computation of the CO2 flux (FCO2) between the surface waters and the atmosphere. During the study period, stational (warm and cold periods) behavior was found for all the variables. The lowest SST values were recorded in March, with a range of 18.8-19.3°C, while the highest SST were observed in September and October, ranging from 24.5-24.8°C. SST exhibited an annual increase with a rate of 0.007°C yr-1. Warmer months increased SSS, while colder periods, influenced by extreme events like tropical storms, led to lower salinity (SSS=34.02). The predominant Trade Winds facilitated the arrival of deeper water, replenishing seawater. The study provided insights into atmospheric CO2. Atmospheric fCO2 averaged 415 ± 4 µatm (2020-2023). Surface water fCO2sw presented variability, with the highest values recorded in September and October, peaking at 437 µatm in September 2021. The lowest values for fCO2sw were found in February 2021 (368 µatm). From 2020 to 2023, surface water fCO2sw values displayed an increasing rate of 1.9 µatm yr-1 in the study area. The assessment of fCO2sw decomposition into thermal and non-thermal processes revealed the importance of SST on the fCO2sw. Nevertheless, in the present study, it is crucial to remark the impact of non-thermal factors on near-shallow coastal regions. Our findings highlight the influence of physical factors such as tides, and wind effect to horizontal mixing in these areas. The CT showed a mean concentration of 2113 ± 8 μmol kg-1 and pH at in-situ temperature (pHT,IS) has a mean value of 8.05 ± 0.02. The mean FCO2 from 2020 to 2023 was 0.34 ± 0.04 mmol m-2 d-1 (126 ± 13 mmol m-2 yr-1) acting as a slight CO2 source. In general, between May and December were the months when the area was a source of CO2. Extrapolating to the entire 6 km2 of Gando Bay, the region sourced 33 ± 4 Tons of CO2 yr-1.

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Countering the effect of ocean acidification in coastal sediments through carbonate mineral additions

Published 4 April 2024 Science Closed
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Along with its impact on calcifying plankton, ocean acidification also affects benthic biogeochemistry and organisms. Compared to the overlying water, fluid composition in sediments is altered through the effect of the mineralization of organic matter, which can further lower both pH and the carbonate saturation state. This can potentially be counteracted by the addition of carbonate minerals to the sediment surface. To explore the biogeochemical effects of mineral additions to coastal sediments, we experimentally quantified carbonate mineral dissolution kinetics, and then integrated this data into a reactive transport model that represents early diagenetic cycling of C, O, N, S and Fe, and traces total alkalinity, pH and saturation state of CaCO3. Model simulations were carried out to delineate the impact of mineral type and amount added, porewater mixing and organic matter mineralization rates on sediment alkalinity and its flux to the overlying water. Model results showed that the added minerals undergo initial rapid dissolution and generate saturated conditions. Aragonite dissolution led to higher alkalinity concentrations than calcite. Simulations of carbonate mineral additions to sediment environments with low rates of organic matter mineralization exhibited a significant increase in mineral saturation state compared to sediments with high CO2 production rates, highlighting the environment-specific extent of the buffering effect. Our work indicates that carbonate additions have the potential to effectively buffer surficial sediments over multiple years, yielding biogeochemical conditions that counteract the detrimental effect of OA conditions on larval recruitment, and potentially increase benthic alkalinity fluxes to support marine carbon dioxide removal (mCDR) in the overlying water.

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Response of ocean acidification to atmospheric carbon dioxide removal

Published 28 March 2024 Science Closed
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Artificial CO2 removal from the atmosphere (also referred to as negative CO2 emissions) has been proposed as a potential means to counteract anthropogenic climate change. Here we use an Earth system model to examine the response of ocean acidification to idealized atmospheric CO2 removal scenarios. In our simulations, atmospheric CO2 is assumed to increase at a rate of 1% per year to four times its pre-industrial value and then decreases to the pre-industrial level at a rate of 0.5%, 1%, 2% per year, respectively. Our results show that the annual mean state of surface ocean carbonate chemistry fields including hydrogen ion concentration ([H+]), pH and aragonite saturation state respond quickly to removal of atmospheric CO2. However, the change of seasonal cycle in carbonate chemistry lags behind the decline in atmospheric CO2. When CO2 returns to the pre-industrial level, over some parts of the ocean, relative to the pre-industrial state, the seasonal amplitude of carbonate chemistry fields is substantially larger. Simulation results also show that changes in deep ocean carbonate chemistry substantially lag behind atmospheric CO2 change. When CO2 returns to its pre-industrial value, the whole-ocean acidity measured by [H+] is 15%-18% larger than the pre-industrial level, depending on the rate of CO2 decrease. Our study demonstrates that even if atmospheric CO2 can be lowered in the future as a result of net negative CO2 emissions, the recovery of some aspects of ocean acidification would take decades to centuries, which would have important implications for the resilience of marine ecosystems.

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Trends and drivers of CO2 parameters, from 2006 to 2021, at a time-series station in the Eastern Tropical Atlantic (6°S, 10°W)

Published 27 March 2024 Science Closed
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The seawater fugacity of CO2 (fCO2) has been monitored hourly at an instrumented mooring at 6°S, 10°W since 2006. The mooring is located in the South Equatorial Current and is affected by the equatorial Atlantic cold tongue. This site is characterized by large seasonal sea surface temperature variations (>4°C). The fCO2 is measured by a spectrophotometric sensor deployed at about 1.5 meters deep. Measurements of seawater fCO2, sea surface temperature (SST) and sea surface salinity (SSS) are used to calculate total dissolved inorganic carbon (TCO2) and pH. Total alkalinity (TA) is calculated using an empirical relationship with SSS determined for this region. Satellite chlorophyll-a concentrations at 6°S, 10°W are low (<0.2 mg m-3) but some peaks over 0.8 mg m-3 are sometimes detected in August. Nevertheless, the site is a permanent source of CO2 to the atmosphere, averaging 4.7 ± 2.4 mmol m-2d-1 over 2006-2021. Despite the weakening of the wind, the CO2 flux increases significantly by 0.20 ± 0.05 mmol m-2d-1 yr-1. This suggests that the source of CO2 is increasing in this region. This is explained by seawater fCO2 increasing faster than the atmospheric increase during 2006-2021. Most of the seawater fCO2 increase is driven by the increase of TCO2, followed by SST. The fCO2 increase leads to a pH decrease of -0.0030 ± 0.0004 yr-1. The SST anomalies (SSTA) at 6°S, 10°W are correlated to the Tropical Southern Atlantic (TSA) index and to the Atlantic 3 region (ATL3) index with a correlation coefficient higher than 0.75. The strong positive phase of both ATL3 and TSA, observed towards the end of the time-series, is likely contributing to the strong increase of seawater fCO2.

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Anthropogenic climate change drives non-stationary phytoplankton internal variability

Published 19 March 2024 Science Closed
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Earth system models suggest that anthropogenic climate change will influence marine phytoplankton over the coming century with light-limited regions becoming more productive and nutrient-limited regions less productive. Anthropogenic climate change can influence not only the mean state but also the internal variability around the mean state, yet little is known about how internal variability in marine phytoplankton will change with time. Here, we quantify the influence of anthropogenic climate change on internal variability in marine phytoplankton biomass from 1920 to 2100 using the Community Earth System Model 1 Large Ensemble (CESM1-LE). We find a significant decrease in the internal variability of global phytoplankton carbon biomass under a high emission (RCP8.5) scenario and heterogeneous regional trends. Decreasing internal variability in biomass is most apparent in the subpolar North Atlantic and North Pacific. In these high-latitude regions, bottom-up controls (e.g., nutrient supply, temperature) influence changes in biomass internal variability. In the biogeochemically critical regions of the Southern Ocean and the equatorial Pacific, bottom-up controls (e.g., light, nutrients) and top-down controls (e.g., grazer biomass) affect changes in phytoplankton carbon internal variability, respectively. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries, marine carbon cycling) should also consider changes in phytoplankton internal variability driven by anthropogenic warming, particularly on regional scales.

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Feedbacks between estuarine metabolism and anthropogenic CO2 accelerate local rates of ocean acidification and hasten threshold exceedances

Published 14 March 2024 Science Closed
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Attribution of the ocean acidification (OA) signal in estuarine carbonate system observations is necessary for quantifying the impacts of global anthropogenic CO2 emissions on water quality, and informing managers of the efficacy of potential mitigation options. We present an analysis of observational data to characterize dynamics and drivers of seasonal carbonate system variability in two seagrass habitats of Puget Sound, WA, USA, and estimate how carbon accumulations due to anthropogenic CO2 emissions (Canth) interact with these drivers of carbonate chemistry to determine seasonally resolved rates of acidification in these habitats. Three independent simulations of Canth accumulation from 1765 to 2100 were run using two previously published methods and one novel method for Canth estimation. Our results revealed persistent seasonal differences in the magnitude of carbonate system responses to anthropogenic CO2 emissions caused by seasonal metabolic changes to the buffering capacity of estuarine waters. The seasonal variability of pHT and pCO2 is increased (while that of Ωaragonite is decreased) and acidification rates are accelerated when compared with open-ocean estimates, highlighting how feedbacks between local metabolism and Canth can control the susceptibility of estuarine habitats to OA impacts. The changes in seasonal variability can shorten the timeline to exceedance of established physiological thresholds for endemic organisms and existing Washington State water quality criteria for pH. We highlight how Canth estimation uncertainties manifest in shallow coastal waters and limit our ability to predict impacts to coastal organisms and ecosystems from anthropogenic CO2 emissions.

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Quantifying the impacts of multiple stressors on the production of marine benthic resources

Published 11 March 2024 Science Closed
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Coastal ecosystems are among the most heavily affected by climate change and anthropogenic activities, which impacts their diversity, productivity and functioning and puts many of the key ecosystem services that they provide at risk. Although empirical studies have moved beyond single-stressor-single-species experiments with limited extrapolation potential and have increasingly investigated the cumulative effects of simultaneously occurring multiple stressors, consistent generalities have not yet been identified. Upscaling from controlled experiments to natural ecosystems, therefore, remains an unsolved challenge. Disentangling the independent and cumulative effects of multiple stressors across different levels of biological complexity, revealing the underlying mechanisms and understanding how coastal ecosystems may respond to predicted scenarios of global change is critical to manage and protect our natural capital.

In this thesis, I advance multiple stressor research by applying complementary approaches to quantify the impact of multiple stressors on marine benthic resources and thereby help predict the consequences of expected climate change for coastal habitats. First, I present the newly developed experimental platform QIMS (Quantifying the Impacts of Multiple Stressors) that overcomes some of the shortfalls of previous multiple stressor research (Chapter 2). Second, in a novel empirical study, I investigate the independent and combined effects of moderate ocean warming and acidification on the functioning and production of mussels and algae, considering the effects of interspecific interactions in the presence or absence of the respective other species (Chapter 3). Third, I synthesise monitoring data from Dublin Bay (representative of a typical metropolitan estuary) using conditional interference and a Bayesian Network model and provide alternative system trajectories according to different climate change scenarios. From this new model, I deepen the understanding of the complex linkages between environmental conditions and the diversity and functioning of Dublin Bay to support local decision making and management (Chapter 4).

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Remotely sensed retrieval of air-sea carbon flux and acidification risk in Chinese Bohai Sea based on a semi-analytical mechanism model with hour-level GOCI image and ERA5 reanalysis data

Published 8 March 2024 Science Closed
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Highlights

  • We proposed a local MeSAA algorithm to gain pCO2sw in the Chinese Bohai Sea
  • The diurnal, daily, and monthly changes of pCO2sw, fCO2, pH, and Ωarag were gained
  • Bohai Sea was a carbon source with positive fCO2 values (0.5–6 mmol C·m−2·day−1)
  • Three bays of Bohai Sea were in a high acidification risk with low Ωarag(1.15–1.3)
  • Uncertainty of mapping at different time scales(hourly and daily) were analyzed
  • Advantage of hour-level GOCI imagery in improving assessment accuracies was verified

Abstract

Marine carbon sinks act as a buffer against global warming, but raise the risk of acidification, especially in the marginal shelf seas which are rich in terrigenous carbon input. The Chinese Bohai Sea performs generally as a weak carbon source while carbon fluxes (fCO2), pH, and aragonite saturation states (Ωarag) vary in time and space under intensive land-sea interaction. However, there are still 1) insufficient spatiotemporal resolution in existing remotely sensed retrieval of carbon flux, 2) inadequate analytic mechanism for existing empirical models, which are not suitable for case II waters in Bohai Sea, and 3) limited research on remotely sensed retrieval of acidification risk expressed as pH and Ωarag. Thus, we proposed a semi-analytical mechanism algorithm (MeSAA) to gain seawater partial pressure of CO2 (pCO2sw) with hour-level GOCI imagery and seawater carbonate equilibrium equation (CO2SYS). With the assistance of ERA5 reanalysis data, the gained pCO2sw was then used to obtain fCO2 by using the sea-air CO2 partial pressure difference (ΔpCO2) method. Similarly, with the assistance of remotely sensed retrieval, two indices, pH and Ωarag were also gained from CO2SYS to identify the acidification risk. The results showed that Bohai Sea was a weak carbon source with the positive values of fCO2 (0.5–6 mmol C·m−2·day−1) and total emission (0.956 Tg C·yr−1). It suffered from a high acidification risk, especially in three bays with low values of Ωarag (1.15–1.3) from May to September 2011. Although photosynthetic carbon sequestration was intensive near shore, it could not consume the large amount of the rich carbon input, and resulting a monthly increase for pCO2sw and fCO2 and a monthly decrease for pH and Ωarag from May to September. The distribution of pCO2sw was in accord with a former study, but the values were not. The local parameter adjustment of MeSAA in the Bohai Sea was analyzed for this issue, so did the effect of uncertainty analysis of mapping at different time scales (hourly and daily). Moreover, the contrast of absolute deviation and relative deviation on different time scales verified the advantage of hour-level GOCI imagery in improving assessment accuracies. This study gained a more precise change trend of pCO2sw, fCO2, pH, and Ωarag in the Bohai Sea from May to September 2011, which would be beneficial to the study of the carbon cycle in the marginal sea of the shelf under the conditions of climate change.

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Multi-Decadal Coastal Acidification in the Northern Gulf of Mexico Driven by Climate Change and Eutrophication

Published 8 March 2024 Science Closed
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Coastal waters often experience enhanced ocean acidification due to the combined effects of climate change and regional biological and anthropogenic activities. Through reconstructing summertime bottom pH in the northern Gulf of Mexico from 1986 to 2019, we demonstrated that eutrophication-fueled respiration dominated bottom pH changes on intra-seasonal and interannual timescales, resulting in recurring acidification coinciding with hypoxia. However, the multi-decadal acidification trend was principally driven by rising atmospheric CO2 and ocean warming, with more acidified and less buffered hypoxic waters exhibiting a higher rate of pH decline (−0.0023 yr−1) compared to non-hypoxic waters (−0.014 yr−1). The cumulative effect of climate-driven decrease in pH baseline is projected to become more significant over time, while the potential eutrophication-induced seasonal exacerbation of acidification may lessen with decreasing oxygen availability resulting from ocean warming. Mitigating coastal acidification requires both global reduction in CO2 emissions and regional management of riverine nutrient loads.

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Potential distribution of Crassostrea sikamea (Amemiya, 1928) along coastal China under global climate change

Published 7 March 2024 Science Closed
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Highlights

  • The salinity and temperature primarily dictate the distribution of C. sikamea.
  • C. sikamea exhibits a south-to-north future migration pattern due to rising sea temperatures.
  • By 2100s, C. sikamea’s northern boundary is expected to surpass 33–34°N.
  • C. sikamea’s habitat suitability may decline by 2050s but recover gradually by 2100s.

Abstract

Global climate change has led to ocean warming, acidification, hypoxia, and alterations in the biogeochemical circulation, thereby influencing the distribution, abundance, and population patterns of marine organisms. Particularly, oysters, which tend to attach to rocks in intertidal zones, may be more vulnerable to climate change. The Kumamoto oyster, Crassostrea sikamea (Amemiya, 1928), is renowned for its nutritional content, breeding benefits, and ecosystem restoration abilities. Previous research has demonstrated that the geographical range of C. sikamea in China has gradually shifted. In this study, the Maximum Entropy (MaxEnt) model was employed to predict the suitability for C. sikamea under different climate scenarios. We utilized first-hand data collected by our research team over the past 14 years, which consisted of 3030 C. sikamea samples from seven provinces in China. The contribution rate of the environmental variables and the jackknife test revealed that salinity (13–21PSS) and temperature (24.6–25.5 °C) are the primary factors influencing the distribution of C. sikamea. The future distribution shows a south-to-north migration pattern triggered by increased sea temperature, resulting in increased suitability at higher latitudes. The migratory effect is more dramatic under the high-emission scenario (Representative Concentration Pathways 8.5 (RCP8.5)) compared to medium-(RCP4.5/RCP6.0) and low-emission scenarios (RCP2.6) and becomes increasingly evident over time. Model predictions indicated that C. sikamea could maintain its suitability under all climate scenarios until the 2050s. However, by the 2100s, the suitability is expected to shift northward beyond the 33–34°N boundary under RCP2.6, RCP6.0, and RCP8.5, extending to the northern coast of Jiangsu. The suitability of C. sikamea within its habitat may experience a significant decline by the 2050s, followed by a gradual recovery over the next 50 years. The potential northward migration of C. sikamea presents new prospects for oyster aquaculture and artificial reefs establishment in China. However, this migration will inevitably lead to significant impacts on the invaded ecosystems and overall biodiversity.

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Trends and projections in climate-related stressors impacting Arctic marine ecosystems – a CMIP6 model analysis

Published 4 March 2024 Science Closed
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Eleven Earth System Models (ESMs) contributing to the Coupled Model Intercomparison Project (CMIP6) were evaluated with respect to climate-related stressors impacting Arctic marine ecosystems (temperature, sea ice, oxygen, ocean acidification). Stressors show regional differences and varying differences over time and space among models. Trend magnitudes increase over time and are highest by end-of-century for temperature and O2. Differences between scenarios SSP2-4.5 and SSP5-8.5 for these variables vary among models and regions, mainly driven by sea-ice retreat. Differences in biogeochemical parameterizations contribute to acidification differences. Projections indicate consistent ocean acidification until 2040 and faster progression for the higher emission scenario thereafter. For SSP5-8.5 all Arctic regions show aragonite undersaturation by 2080, and calcite undersaturation for all but two regions by 2100 for all models. Most regions can avoid calcite undersaturation with lower emissions (SSP2-4.5). All variables show increases in seasonal amplitude, most prominently for temperature and oxygen. Calcium carbonate saturation state (Ω) shows little change to the seasonal range and a suggestion of temporal shifts in extrema. Seasonal changes in Ω may be underestimated due to lacking carbon cycle processes within sea ice in CMIP6 models. The analysis emphasizes regionally varying threats from multiple stressors on Arctic marine ecosystems and highlights the propagation of uncertainties from sea ice to temperature and biogeochemical variables. Large model differences in seasonal cycles emphasize the need for improved model constraints, predominantly the representation of sea-ice decline, to enhance the applicability of CMIP models in multi-stressor impacts assessments.

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Policy analysis of coastal-based special economic zone development using system dynamics

Published 28 February 2024 Science Closed
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Special Economic Zone (SEZ) development is becoming a preferable policy by the Indonesian government to boost economic growth in less-developed local regions. This is because of the promise that SEZ could attract investment and job creation based on local competitive commodities. One of these areas is Bitung SEZ, North Sulawesi – Indonesia, a coastal-based SEZ, as its strategic position for logistics, fishery resources, and coconut plantation. To explore the promise of growth proposed by developing SEZ in Bitung, we developed a Systems Dynamics model of the interaction between economic growth, social development, and environmental impacts. Based on the model understanding and development, we identified three factors the Indonesian government should improve: coconut plantation productivity, fisheries ship management, and education index. With these three factors in mind, several policy options were tested in the model, resulting in a more substantial impact than the business-as-usual condition.

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Modeling of ocean acidification in the Massachusetts Bay and Boston Harbor: 1-D experiments

Published 27 February 2024 Science Closed
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The U.S. Northeast Biogeochemistry Ecosystem Model (NeBEM) was developed based on the modified version of the European Regional Seas Ecosystem Model (ERSEM). NeBEM was applied to examine the ocean acidification (OA) in Massachusetts Bay (Mass Bay) through one- and three-dimensional (1-D and 3-D) experiments. This paper focuses on the 1-D investigation made at the outer and inner bay sites, aiming to a) demonstrate NeBEM’s capability of simulating the observed seasonal cycles for the OA-related variables under near-actual physical conditions,  especially pCO2 and pH in shallow and deep areas of the Mass Bay, and b) examine the sensitivity of the model performance to parameterizations and evaluate the various algorithms to calculate dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, and pH in ERSEM. Model skill assessments were done for physical and biogeochemical variables, and the mechanisms driving the changes in DIC and TA were discussed. Experiment results show that the 1-D NeBEM was robust enough to capture seasonal and interannual variability of nutrients, dissolved oxygen (DO), and chlorophyll a, pCO2, and pH at the deep outer bay site, where the surface meteorological forcing dominantly drove the ecosystem. However, it failed at the shallow inner bay site due to an inadequate characterization of river discharge-induced advection. Calculating pCO2 and pH via diagnostic, prognostic, and semi-diagnostic TA algorithms suggests that the semi-diagnostic method performed better to resolve the observed seasonal variation of pCO2 and has the highest correlation and most minor root mean square error, although all three methods show an insignificant difference in pH simulation. The semi-diagnostic algorithm was also compared with the data-fitting-based BGC+/BGC+* model and T/S-fitting methods. The performances of all three empirical models rely substantially on their calibration set. In this region, NeBEM showed the change in TA (even though underestimated due to 1-D limitation) was dominantly modulated by nitrification and net community production (NCP), while the benthic remineralization was not a significant driver. NCP primarily controlled the change in DIC, and the atmospheric CO2 loading played as the first-order contributor compared to NCP.

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Multi-month forecasts of marine heatwaves and ocean acidification extremes

Published 21 February 2024 Science Closed
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Marine heatwaves (MHW) and ocean acidification extreme events (OAX) are periods during which temperature and acidification reach extreme levels, endangering ecosystems. As the threats from MHW and OAX grow with climate change, there is need for skillful predictions of events months-to-years in advance. Previous work has demonstrated that climate models can predict marine heatwaves up to 12 months in advance in key regions, but no studies have attempted to predict OAX. Here we use the Community Earth System Model (CESM) Seasonal-to-Multiyear Large Ensemble (SMYLE) to make predictions of both MHW and OAX events. We find that CESM SMYLE skillfully predicts discrete MHW and OAX events up to 1 year in advance. Skill is highest in the tropical and northeast Pacific, reflecting the contribution of El Niño-Southern Oscillation. A forecast generated in late 2023 during the 2023-24 ENSO event finds high likelihood for widespread MHWs and OAX in 2024.

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More frequent abrupt marine environmental changes expected

Published 16 February 2024 Science Closed
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Abstract

We quantify an elevated occurrence of abrupt changes in ocean environmental conditions under human-induced climate forcing using Earth system model output through a novel analysis method that compares the temporal evolution of the forcings applied with the development of local ocean state changes for temperature, oxygen concentration, and carbonate ion concentration. Through a multi-centennial Earth system model experiment, we show that such an increase is not fully reversible after excess greenhouse gas emissions go back to zero. The increase in occurrence of regional abrupt changes in marine environmental conditions has not yet been accounted for adequately in climate impact analyses that usually associate ecosystem shifts large-scale variability or extreme events. Estimates for remaining greenhouse gas emission targets need thus to be more conservative.

Key Points

  • There is an elevated occurrence of abrupt changes in key ocean state variables under human-induced climate forcing
  • The occurrence of abrupt changes in the upper ocean peaks around the maximum of the rate of change in human-induced forcing
  • A multi-centennial legacy is expected for abrupt shifts in environmental conditions, long after a stop of anthropogenic CO2 emissions
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From models to management: oceanographic processes shaping the spatial patterns and progression of ocean acidification and hypoxia in the California Current System

Published 13 February 2024 Science Closed
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The California Current System, situated off the US West Coast, experiences natural exposure to acidified and oxygen-poor conditions due to coastal upwelling, which brings low pH, low oxygen water from depth to the nearshore environment. The addition of anthropogenic ocean acidification and hypoxia (OAH) is therefore pushing conditions below biological thresholds, resulting in a variety of harmful effects ranging from behavior impacts to shell dissolution and mortality. It is therefore important to characterize the progression of ocean acidification and hypoxia in the California Current, where exposure to corrosive and hypoxic conditions is spatially variable and episodic in nature, making it a challenge to describe these patterns and their biophysical drivers through observational data alone. Here, a high resolution (~3 km) coupled physical-biogeochemical model is used to characterize the recent and projected spatial and temporal patterns in exposure to reduced pH and oxygen conditions, along with their physical and biogeochemical drivers. Results from Chapter 1 demonstrate that historical (1988-2010) alongshore variability in pH and oxygen is driven by a complex interplay of upwelling and primary production, modulated by the alongshore and cross-shore regional circulation. Results from Chapter 2 establish that historical variability in the interannual severity of exposure to corrosive conditions is driven by combined changes in source water properties and upwelling intensity, respectively associated with decadal basin scale variability and interannual regional scale forcing. Chapters 3 and 4 utilize downscaled regional climate projections to investigate the future (2000-2100) progression of ocean acidification and hypoxia hot spots, the emergence of these features, and their implications for marine resource management. Results from Chapter 3 highlight that where and when hot spots and refugia for pH and oxygen emerge depends on the metrics used to quantify them. If one is managing for OAH and cares about where and when conditions become distinct from their historical range, the projections suggest hot spots will be located in areas of historically weaker upwelling due to their narrow range of variability. In contrast, if one is managing for OAH and cares about where and when conditions will drop below specific biological thresholds, the projections suggest hot spots will be located in areas of historically stronger upwelling due to their lower baseline pH and oxygen conditions. Chapter 4 synthesizes information from the projections and displays it in an online interactive management tool, where users can explore future OAH change based on their species or region of interest. As a whole, these four chapters provide the first comprehensive mechanistic description of the physical and biogeochemical drivers shaping historical and future alongshore and interannual OAH variability in the central California Current region, while disseminating this information to marine resource managers in an accessible format.

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