Ocean acidification, driven by rising atmospheric carbon dioxide levels, poses a significant threat to the health of marine ecosystems, particularly in the Pacific Ocean. This study employs a multi-variate hybrid machine learning approach to predict future pH trends within the Pacific and to analyze the influence of key biogeochemical drivers on these trends. Hybrid models, strategically combining the strengths of individual algorithms, were developed for predicting several ocean acidification parameters. A performance analysis demonstrated the superior accuracy of hybrid models compared to their counterparts. The predicted pH trends reveal a concerning shift towards increased acidity within the Pacific Ocean, highlighting the urgency of understanding and mitigating its impacts. In-depth analysis was conducted to identify the relative influence of key biogeochemical factors on the changing pH dynamics. This research aims to provide crucial insights for developing targeted mitigation strategies and protecting the vulnerable ecosystems of the Pacific Ocean from the escalating consequences of ocean acidification.
Continue reading ‘Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers’Posts Tagged 'regionalmodeling'
Multi-variate hybrid modeling for pacific ocean acidification: predicting future pH trends and analyzing key biogeochemical drivers
Published 7 January 2025 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling, South Pacific
Acceleration of warming, deoxygenation, and acidification in the Arabian Gulf driven by weakening of summer winds
Published 1 January 2025 Science ClosedTags: biogeochemistry, modeling, regionalmodeling
The Arabian Gulf (AG) exports hypersaline, dense waters into the Sea of Oman (SOO), replaced by fresher inflowing surface waters from the Indian Ocean. We investigate the impact of recent AG warming on its exchange with the SOO and the implications this has on the AG biogeochemistry. Using an eddy-resolving hindcast model simulation, we analyze the hydrography and biogeochemistry of the AG and the SOO from 1980 to 2018. Our study reveals that changes in summer surface winds have accelerated AG warming and weakened it in the SOO, reducing the density gradient and water exchange between the two seas during late summer. This has led to nutrient buildup, increased productivity, and heightened deoxygenation and acidification in the AG. These findings underscore how subtle wind changes can exacerbate the vulnerability of marginal seas to climate change and stress the need to properly represent regional winds in global climate models.
Continue reading ‘Acceleration of warming, deoxygenation, and acidification in the Arabian Gulf driven by weakening of summer winds’Arctic Ocean acidification and carbonate undersaturation enhanced by coastal permafrost erosion
Published 31 December 2024 Science ClosedTags: Arctic, biogeochemistry, modeling, regionalmodeling
Increasing atmospheric CO2 drives ocean acidification, with some of the fastest rates observed on Arctic shelves. Lowest pH levels occur near the coasts due to the additional effects of land-derived carbon sources. However, the impact of anthropogenic climate change on seawater acidity mediated by increasing permafrost thaw and coastal erosion remains unknown. Here, we find that the increase in organic matter release by coastal permafrost erosion over the 20th century enhances the interannual variability of seawater pH in Arctic near-shore areas. As a consequence, carbonate undersaturation events, stressing marine ecosystems, become more frequent, intense, and longer-lasting. We account for synergistic effects of anthropogenic climate change by combining increasing atmospheric CO2 levels and coastal erosion rates, utilizing a novel global model with high-resolution grid refinement towards coastal regions and improved process representation of shelf-specific carbon dynamics. By considering the role of coastal permafrost erosion, we conclude that critical Arctic Ocean acidification states will emerge earlier than simulated by the current generation of Earth system models. Our results emphasize the importance of understanding permafrost-ocean interactions and their increasing impact on marine ecosystems, especially in the rapidly changing Arctic region.
Continue reading ‘Arctic Ocean acidification and carbonate undersaturation enhanced by coastal permafrost erosion’Regional relationship between total alkalinity and salinity in the surface waters of the western South Atlantic margin
Published 30 December 2024 Science ClosedTags: chemistry, field, modeling, regionalmodeling, South Atlantic
Highlights
- Surface AT and SSS patterns show a decreasing pattern from north to south along the southwestern South Atlantic margin.
- The relationship found between surface AT and SSS reveals that salinity explains ∼ 80 % of AT variability.
- The estimated AT values reflect both current-dominated and freshwater mixing processes along the southwestern SAO margin.
Abstract
We examined the surface total alkalinity (AT) and salinity (SSS) distributions and their relationship along the southwestern South Atlantic Ocean margin off the Brazilian coast. In situ hydrographic data from shelf and slope stations were measured during three oceanographic cruises in October 2014 (austral spring), April 2018 (austral autumn) and June 2019 (austral winter). The northern portion of the study area lies within the Brazil Current domain, transporting warm and salty Tropical Water, while further south the Subtropical Shelf Water and the freshwater plume derived from the Patos Lagoon and Plata River influence the temperature, salinity, and AT distribution. The present study aimed to determine the relationship between AT and SSS to establish a model for reconstructing a surface time series for the marine carbonate system in the undersampled region of the subtropical southwestern South Atlantic Ocean margin. The AT – SSS relationship showed a significant positive linear relationship (r2=0.76), reflecting both current-dominated (i.e., outer and northernmost stations) and freshwater mixing processes (i.e., inner and southernmost stations and continental inputs). The observed AT values were well correlated with the reported ranges for the tropical and subtropical South Atlantic Ocean, and the predicted AT obtained from the Global Ocean Data Analysis Project and the World Ocean Database 2013 SSS data confirmed lower AT in shelf waters under the influence of continental inputs, which increased towards the outer shelf and slope. Finally, the newly proposed regional AT – SSS relationship improves previous linear regressions for the southwestern Atlantic Ocean margin.
Continue reading ‘Regional relationship between total alkalinity and salinity in the surface waters of the western South Atlantic margin’Development of a high-resolution ocean ensemble future projection dataset for the North Pacific incorporating simple biogeochemical processes
Published 27 December 2024 Science ClosedTags: biogeochemistry, modeling, North Pacific, regionalmodeling
In this study, we developed a new version of the future ocean regional projection dataset in the North Pacific (FORP-NP10) by performing an ensemble of historical and multi-scenario future projection simulations from 1960 to 2100 using a high-resolution ocean downscaling model system driven by surface forcings based on the atmospheric data of the Coupled Model Intercomparison Project (Phase 5). This version is characterized by the inclusion of simple biogeochemical processes within the simulations of the multi-case (four forcing cases) and multi-future projection scenarios (representative concentration pathway 2.6 and 8.5) using a mesoscale eddy-resolving (approximately 10 km) horizontal resolution. The dataset reasonably represented the main biogeochemical properties in the North Pacific and around Japan, such as surface CO2 flux, pH, subsurface oxygen, surface nitrate, and chlorophyll, as well as the ocean physics of the regions, including the mesoscale/frontal structures of the Kuroshio, Kuroshio Extension, and mixed layer depth. We assessed the bias tendencies and structures of these properties by comparing them with observational reference data and the low-resolution model results. Our ensemble dataset consistently projected future upper-ocean warming, acidification, deoxygenation, and changes in nutrient and primary production in the twenty-first century (reported as global analyses in recent reports of the Intergovernmental Panel on Climate Change) in the regions surrounding Japan, revealing that the future changes exhibited spatial contrasts or varying tendencies in the regions.
Continue reading ‘Development of a high-resolution ocean ensemble future projection dataset for the North Pacific incorporating simple biogeochemical processes’Climate covariate choice and uncertainty in projecting species range shifts: a case study in the Eastern Bering Sea
Published 26 December 2024 Science ClosedTags: Arctic, biological response, crustaceans, field, fish, fisheries, modeling, multiple factors, oxygen, regionalmodeling, temperature
Species distribution models (SDMs) are critical to the adaptive management of fisheries under climate change. While many approaches projecting marine species range shifts have incorporated the effects of temperature on movement, there is a need to incorporate a wider suite of ecologically relevant predictors as temperature-based SDMs can considerably under- or over-estimate the rate of species responses to climate shocks. As a subarctic ecosystem at the sea ice margin, the Eastern Bering Sea (EBS) is warming faster than much of the global ocean, resulting in the rapid redistribution of key fishery and subsistence resources. To support long-term planning and adaptation, we combine 40 years of scientific surveys with a high-resolution oceanographic model to examine the effects of bottom temperature, oxygen, pH and a regional climate index (the extent of the EBS ‘cold pool’) on range projections through the end of the century. We use multimodel inference to partition uncertainty among earth systems models, climate scenarios and distribution model parameterizations for several ecologically and economically important EBS groundfish and crabs. Covariate choice is the primary source of uncertainty for most species, with models that account for spatial responses to the cold pool performing better and suggesting more extensive northward movements than alternative models. Models suggest declines in the probability of occurrence at low pH and oxygen concentrations for most species. We project shifts that are directionally consistent with, yet larger than those previously estimated for most species, suggesting that accounting for large-scale climate variability in species distribution models may substantially alter range projections.
Continue reading ‘Climate covariate choice and uncertainty in projecting species range shifts: a case study in the Eastern Bering Sea’A regional physical-biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)
Published 25 December 2024 Science ClosedTags: Arctic, biogeochemistry, biological response, field, modeling, North Pacific, regionalmodeling, zooplankton
Regional ocean models enable generation of computationally-affordable and regionally-tailored \ ensembles of near-term forecasts and long-term projections of sufficient resolution to serve marine resource management. Climate change, however, has created marine resource challenges, such as shifting stock distributions, that cut across domestic and international management boundaries and have pushed regional modeling efforts toward “coastwide” approaches. Here we present and evaluate a multidecadal hindcast with a Northeast Pacific (NEP) regional implementation of the Modular Ocean Model version 6 with sea ice and biogeochemistry that extends from the Chukchi Sea to the Baja California Peninsula at 10-km horizontal resolution (MOM6-COBALT-NEP10k, or “NEP10k”). This domain includes an Arctic-adjacent system with a broad shallow shelf seasonally covered by sea ice (the Eastern Bering Sea, EBS), a sub-Arctic system with upwelling in the Alaska Gyre and predominant downwelling winds and large freshwater forcing along the coast (the Gulf of Alaska, GoA), and a temperate, eastern boundary upwelling ecosystem (the California Current Ecosystem, CCE). The coastwide model was able to recreate seasonal and cross-ecosystem contrasts in numerous ecosystem-critical properties including temperature, salinity, inorganic nutrients, oxygen, carbonate saturation states, and chlorophyll. Spatial consistency between modeled quantities and observations generally extended to plankton ecosystems, though small to moderate biases were also apparent. Fidelity with observed zooplankton biomass, for example, was limited to first-order seasonal and cross-system contrasts. Temporally, simulated monthly surface and bottom temperature anomalies in coastal regions (< 500m deep) closely matched estimates from data-assimilative ocean reanalyses. Performance, however, was reduced in some nearshore regions coarsely resolved by the model’s 10-km resolution grid, and the time series of satellite-based chlorophyll anomaly estimates proved more difficult to match than temperature. System-specific ecosystem indicators were also assessed. In the EBS, NEP10k robustly matched observed variations, including recent large declines, in the area of the summer bottom water “cold pool” (< 2 °C) which exerts a profound influence on EBS fisheries. In the GoA, the simulation captured patterns of sea surface height variability and variations in thermal, oxygen and acidification risk associated with local modes of inter-annual to decadal climate variability. In the CCE, the simulation robustly captured variations in upwelling indices and coastal water masses, though discrepancies in the latter were evident in the Southern California Bight. Enhanced model resolution may reduce such discrepancies, but any benefits must be carefully weighed against computational costs given the intended use of this system for ensemble predictions and projections. Meanwhile, the demonstrated NEP10k skill level herein, particularly in recreating cross-ecosystem contrasts and the time variation of ecosystem indicators over multiple decades, suggests considerable immediate utility for coastwide retrospective and predictive applications.
Continue reading ‘A regional physical-biogeochemical ocean model for marine resource applications in the Northeast Pacific (MOM6-COBALT-NEP10k v1.0)’Sensitivity of pteropod calcification to multi stressor variability in coastal habitats
Published 18 December 2024 Science , Uncategorized ClosedTags: biological response, field, modeling, mollusks, morphology, multiple factors, North Pacific, regionalmodeling, temperature, zooplankton
Highlights
- Pteropod calcification under coastal multiple stressors was investigated.
- Shell morphometrics and high-resolution model outputs was combined.
- Saturation state, temperature and food are drivers of calcification.
- Different calcification modes are dependent on the type of environment.
- Stable vs dynamic conditions induce different calcification strategy.
Abstract
Comprehensive understanding of environmental multiple stressors on calcification in marine calcifiers remains an important topic of study, especially under ocean global change associated with multiple stressors. We explore the impact of multiple stressor variability on pteropod calcification in the southern Salish Sea (Washington, U.S.), a coastal estuarine system that exhibits a high degree of spatial and temporal variability in multiple environmental parameters across sampling locations. We hypothesized that such variability is associated with differences in pteropod calcification. Shell thickness and shell density across pteropod life history stages was compared with high-resolution outputs from a realistic model of regional circulation and biogeochemistry to explore how the mean and variability of multiple stressors (aragonite saturation state (Ωar), temperature, food availability) influence calcification. We found that both the mean and variability in multiple stressors play a major role in calcification in pteropods, with a generalized linear model explaining more than 60% of the variance in calcification. We suggest two different modes of shell building: stable conditions of lower mean Ωar trigger the loss of shell thickness and density. In the more variable habitats, i.e., where the variability occurs over diel and seasonal scales, shell thickness increases at higher Ωar variability and greater food availability, which might partially compensate for the loss of shell density. This plastic response appears to be consistent across life stages and could represent a response mechanism that allows some compensatory calcification under less favourable conditions. However, compensation is very limited, as evident by lower shell growth resulting in lower shell sizes comparable to early life stages. These results substantially improve the understanding of the variability in multiple stressors on the calcification process under multiple stressors and provide a foundation for the development of two new proxies for calcification monitoring, and with implications for marine carbon dioxide removal strategies.
Continue reading ‘Sensitivity of pteropod calcification to multi stressor variability in coastal habitats’Hindcast (back to 1955) and forecast (up to 2100) of sea-surface pH at BATS and Hydrostation S (Bermuda area)
Published 9 December 2024 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
Time-series measurements in the North Atlantic Ocean at the Hydrostation S site (32°10′N, 64°30′W), started in 1954. At that time, it was not yet possible to measure all the properties of the oceanic carbon cycle. However temperature and salinity were measured. We use these important hydrographic data with the knowledge acquired from more recent measurements (since 1989) of the CO2/carbonate properties at the near-by Bermuda Atlantic Time Series Study (BATS; 31°40′N, 64°10′W), to reconstruct, using two different approaches based upon multi-linear-regressions, the pH at this hydrostation S since its beginning. The results provide good estimates of the ocean acidification in the ocean surface of the area of stations S and BATS since the mid 1950’s, an unprecedented near 70-year trend of ocean acidification, as well as a simple way to forecast to 2100 its variations according to the various scenarios of atmospheric CO2 fugacity increase. The simplest approach shown here, further provides an easy way to estimate surface ocean acidification from satellite sea surface temperature measurements.
Continue reading ‘Hindcast (back to 1955) and forecast (up to 2100) of sea-surface pH at BATS and Hydrostation S (Bermuda area)’Sensitivity of the Southern Ocean CO2 sink to a rapid increase and subsequent decrease of atmospheric CO2
Published 28 November 2024 Science ClosedTags: Antarctic, chemistry, modeling, regionalmodeling
Despite the importance of the Southern Ocean carbon sink, its response to future atmospheric CO2 perturbations and warming remains highly uncertain. In this study, we use six state-of-the-art Earth system models to assess the response of Southern Ocean air-sea CO2 fluxes (FCO2) to a rapid atmospheric forcing increase and subsequent negative emissions in an idealized carbon dioxide removal reversibility experiment. We find that during positive emissions, the region north of the Polar Front only takes up atmospheric CO2 for 30-50 years before reaching equilibrium; surface stratification and reduction of CO2 solubility with warming diminishes ocean CO2 uptake in this region. In contrast, south of the Polar Front, the upper ocean continues to take up CO2 until the end of positive emissions at 140 years. Sea-ice loss and the accumulation of anthropogenic dissolved inorganic carbon in the upper ocean reduce the upwelling-driven seasonal CO2 outgassing, leading to a stronger Antarctic CO2 sink. CO2 removal triggers a CO2 uptake reduction that slowly converts the Southern Ocean into a CO2 source which persists for at least 50 years post-mitigation. Furthermore, we find that model sensitivity to atmospheric perturbation is closely linked to seasonal FCO2 dynamics. Specifically, models with a thermally dominated pCO2 seasonal cycle exhibit nearly twice the sensitivity to atmospheric perturbations compared to non-thermal models. Our findings further emphasize the necessity of accurate model representation of the seasonal CO2 dynamics for appropriately simulating the future Southern Ocean carbon sink.
Continue reading ‘Sensitivity of the Southern Ocean CO2 sink to a rapid increase and subsequent decrease of atmospheric CO2’Hydrological cycle amplification imposes spatial patterns on the climate change response of ocean pH and carbonate chemistry
Published 31 October 2024 Science ClosedTags: chemistry, modeling, regionalmodeling
Ocean CO2 uptake and acidification in response to human activities are driven primarily by the rise in atmospheric CO2 but are also modulated by climate change. Existing work suggests that this “climate effect” influences the uptake and storage of anthropogenic carbon and acidification via the global increase in ocean temperature, although some regional responses have been attributed to changes in circulation or biological activity. Here, we investigate spatial patterns in the climate effect on surface ocean acidification (and the closely related carbonate chemistry) in an Earth system model under a rapid CO2-increase scenario and identify a different driving process. We show that the amplification of the hydrological cycle, a robustly simulated feature of climate change, is largely responsible for the spatial patterns in this climate effect at the sea surface. This “hydrological effect” can be understood as a subset of the total climate effect, which includes warming, hydrological cycle amplification, circulation, and biological changes. We demonstrate that it acts through two primary mechanisms: (i) directly diluting or concentrating dissolved ions by adding or removing freshwater and (ii) altering the sea surface temperature, which influences the solubility of dissolved inorganic carbon (DIC) and acidity of seawater. The hydrological effect opposes acidification in salinifying regions, most notably the subtropical Atlantic, and enhances acidification in freshening regions such as the western Pacific. Its single strongest effect is to dilute the negative ions that buffer the dissolution of CO2, quantified as alkalinity. The local changes in alkalinity, DIC, and pH linked to the pattern of hydrological cycle amplification are as strong as the (largely uniform) changes due to warming, explaining the weak increase in pH and DIC seen in the climate effect in the subtropical Atlantic Ocean.
Continue reading ‘Hydrological cycle amplification imposes spatial patterns on the climate change response of ocean pH and carbonate chemistry’The role of benthic fluxes in acidifying the bottom waters in the Northern Gulf of Mexico hypoxic zone based on an updated water column biogeochemical-seabed diagenetic and sediment transport model
Published 23 October 2024 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling, sediment
The seabed and the water column are tightly coupled in shallow coastal environments. Numerical models of seabed-water interaction provide an alternative to observational studies that require concurrent measurements in both compartments, which are hard to obtain and rarely available. Here, we present a coupled model that includes water column biogeochemistry, seabed diagenesis, sediment transport and hydrodynamics. Our model includes realistic representations of biogeochemical reactions in both seabed and water column, and fluxes at their interface. The model was built on algorithms for seabed-water exchange in the Regional Ocean Modeling System and expanded to include carbonate chemistry in seabed. The updated model was tested for two sites where benthic flux and porewater concentration measurements were available in the northern Gulf of Mexico hypoxic zone. The calibrated model reproduced the porewater concentration-depth profiles and benthic fluxes of O2, dissolved inorganic carbon (DIC), TAlk, NO3 and NH4. We used the calibrated model to explore the role of benthic fluxes in acidifying bottom water during fair weather and resuspension periods. Under fair weather conditions, model results indicated that bio-diffusion in sediment, labile material input and sediment porosity have a large control on the importance of benthic flux to bottom water acidification. During resuspension, the model indicated that bottom water acidification would be enhanced due to the sharp increase of the DIC/TAlk ratio of benthic fluxes. To conclude, our model reproduced the seabed-water column exchange of biologically important solutes and can be used for quantifying the role of benthic fluxes in driving bottom water acidification over continental shelves.
Key Points
- A coupled water column biogeochemical-seabed diagenetic model is updated to include dissolved inorganic carbon (DIC) and TAlk for ocean acidification
- The modeled impact of benthic fluxes on bottom water acidification during quiescent periods is impacted by the intensity of bio-diffusion
- Resuspension enhances bottom water acidification by increasing the benthic flux DIC/TAlk ratio
Plain Language Summary
In coastal environments where water is shallow, significant interactions occur between the seabed and the overlying water column. In the Northern Gulf of Mexico (NGoM) hypoxic zone, the seabed is believed to play an important role in the acidification of bottom ocean water. In this study we use a numerical model to understand how the seabed can affect bottom water acidification over the NGoM hypoxic zone. We found that during fair weather periods, mixing in the sediment bed due to biological activity, organic matter supply from the water column to the sediment, and the porosity of sediment itself can largely affect the role of the seabed in acidifying the bottom water. When the ocean condition is highly dynamic and resuspension occurs, the contribution of the seabed to bottom water acidification will likely be enhanced.
Continue reading ‘The role of benthic fluxes in acidifying the bottom waters in the Northern Gulf of Mexico hypoxic zone based on an updated water column biogeochemical-seabed diagenetic and sediment transport model’Linking cumulative carbon emissions to observable climate impacts
Published 10 October 2024 Science ClosedTags: globalmodeling, mitigation, modeling, policy, regionalmodeling, review
Anthropogenic CO2 emissions are causing climate change, and impacts of climate change are already affecting every region on Earth. The purpose of this review is to investigate climate impacts that can be linked quantitatively to cumulative CO2 emissions (CE), with a focus on impacts scaling linearly with CE. The reviewed studies indicate a proportionality between CE and various observable climate impacts such as regional warming, extreme daily temperatures, heavy precipitation events, seasonal changes in temperature and precipitation, global mean precipitation increase over ocean, sea ice decline in September across the Arctic Ocean, surface ocean acidification, global mean sea level rise, different marine heatwave characteristics, changes in habitat viability for non-human primates, as well as labour productivity loss due to extreme heat exposure. From the reviewed literature, we report estimates of these climate impacts resulting from one trillion tonne of CE (1 Tt C). These estimates are highly relevant for climate policy as they provide a way for assessing climate impacts associated with every amount of CO2 emitted by human activities. With the goal of expanding the number of climate impacts that could be linked quantitatively to CE, we propose a framework for estimating additional climate impacts resulting from CE. This framework builds on the transient climate response to cumulative emissions (TCRE), and it is applicable to climate impacts that scale linearly with global warming. We illustrate how the framework can be applied to quantify physical, biological, and societal climate impacts resulting from CE. With this review, we highlight that each tonne of CO2 emissions matters in terms of resulting impacts on natural and human systems.
Continue reading ‘Linking cumulative carbon emissions to observable climate impacts’Impact of Alaska atmospheric blocking on the carbon flux in the Northeast Pacific Ocean
Published 1 October 2024 Science ClosedTags: modeling, North Pacific, regionalmodeling
Highlights
- An machine learning based model was developed to retrieval pCO2 from satellite obsevations.
- A long-term time series record of carbon flux was constructed for the NEP.
- The linkage between regional carbon flux variability and large scale atmospheric dynamic was disclosed.
Abstract
The Northeast Pacific Ocean (NEP) is one of the important carbon sinks in the global ocean. The causes of carbon flux changes in this region have been widely studied, but the physical processes associated with large scale climate variability remain controversial primarily due to scarcity of spatially and temporally continuous observations. In this study, we constructed a high-resolution sea surface partial pressure of CO2 (pCO2) from satellite observations for the NEP from 2003 to 2020 using the machine learning based XGBoost model. By analyzing the interannual large-scale high-latitude atmospheric dynamics and ocean physical conditions over the NEP, we find that the CO2 flux density (FCO2) anomalies have a strong correlation with the Alaskan atmospheric blocking events. In the region north of 48°N, anomalous cyclones triggered by atmospheric blocking increased sea surface height (SSH), which reduced the replenishment of dissolved inorganic carbon (DIC) from deep seawater, leading to enhanced carbon uptake. By contrast, in the region south of 48°N, the increase in sea surface temperature (SST) triggered by atmospheric blocking reduced the solubility of CO2 in seawater, resulting in a decrease in regional carbon flux. These results provide new perspectives for better understanding and predicting the effects of high-latitude atmospheric dynamics on regional ocean carbon fluxes.
Continue reading ‘Impact of Alaska atmospheric blocking on the carbon flux in the Northeast Pacific Ocean’Influence of rivers, tides, and tidal wetlands on estuarine carbonate system dynamics
Published 26 September 2024 Science ClosedTags: biogeochemistry, chemistry, field, modeling, North Atlantic, regionalmodeling
Variations in estuarine carbonate chemistry can have critical impacts on marine calcifying organisms, yet the drivers of this variability are difficult to quantify from observations alone, due to the strong spatiotemporal variability of these systems. Terrestrial runoff and wetland processes vary year to year based on local precipitation, and estuarine processes are often strongly modulated by tides. In this study, a 3D-coupled hydrodynamic-biogeochemical model is used to quantify the controls on the carbonate system of a coastal plain estuary, specifically the York River estuary. Experiments were conducted both with and without tidal wetlands. Results show that on average, wetlands account for 20–30% of total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes into the estuary, and double-estuarine CO2 outgassing. Strong quasi-monthly variability is driven by the tides and causes fluctuations between net heterotrophy and net autotrophy. On longer time scales, model results show that in wetter years, lower light availability decreases primary production relative to biological respiration (i.e., greater net heterotrophy) resulting in substantial increases in CO2 outgassing. Additionally, in wetter years, advective exports of DIC and TA to the Chesapeake Bay increase by a factor of three to four, resulting in lower concentrations of DIC and TA within the estuary. Quantifying the impacts of these complex drivers is not only essential for a better understanding of coastal carbon and alkalinity cycling, but also leads to an improved assessment of the health and functioning of coastal ecosystems both in the present day and under future climate change.
Continue reading ‘Influence of rivers, tides, and tidal wetlands on estuarine carbonate system dynamics’Long-term trends of pH, alkalinity, and hydrogen ion concentration in an upwelling-dominated coastal ecosystem: Ría de Vigo, NW Spain
Published 12 August 2024 Science ClosedTags: chemistry, methods, modeling, North Atlantic, regionalmodeling
The present study focuses on the Ría de Vigo (NW Spain), a coastal embayment influenced by the Canary Current Upwelling System, which is among the world’s significant Eastern Boundary Upwelling Ecosystems. The research assesses historical changes in the marine carbonate system by generating 25-year weekly time series at six stations . Assessing ocean acidification in the region is complex due to diverse factors influencing coastal carbon dynamics, making predictions more challenging. To capture the specific dynamics in Ría de Vigo, ensembles of Neural Networks were applied. These networks were trained with a data set obtained in several oceanographic cruises, in order to retrieve pH, hydrogen ion concentration and alkalinity, achieving a root mean square error of 0.0272 pH units, 0.588 nmol Kg-1, and 10.6 μμmol kg−1, respectively. Subsequently, time series of the selected variables were generated, applying data of predictors measured at the aforementioned stations . An increase in normalized alkalinity was observed for all stations, except in the surface layer at the innermost location. A decrease in pH and an increase in hydrogen ion concentration were observed for all points, with trends that exceed reported rates of ocean acidification in the open ocean.
Continue reading ‘Long-term trends of pH, alkalinity, and hydrogen ion concentration in an upwelling-dominated coastal ecosystem: Ría de Vigo, NW Spain’Climatological distribution of ocean acidification variables along the North American ocean margins
Published 31 July 2024 Science ClosedTags: chemistry, methods, modeling, North Atlantic, regionalmodeling
Climatologies, which depict mean fields of oceanographic variables on a regular geographic grid, and atlases, which provide graphical depictions of specific areas, play pivotal roles in comprehending the societal vulnerabilities linked to ocean acidification (OA). This significance is particularly pronounced in coastal regions where most economic activities, such as commercial and recreational fisheries and aquaculture industries, occur. In this paper, we unveil a comprehensive data product featuring coastal ocean acidification climatologies and atlases, encompassing the fugacity of carbon dioxide, pH on the total scale, total hydrogen ion content, free hydrogen ion content, carbonate ion content, aragonite saturation state, calcite saturation state, Revelle factor, total dissolved inorganic carbon content, and total alkalinity content. These variables are provided on 1° × 1° spatial grids at 14 standardized depth levels, ranging from the surface to a depth of 500 m, along the North American ocean margins, defined as the region between the coastline and a distance of 200 nautical miles (∼370 km) offshore. The climatologies and atlases were developed using the World Ocean Atlas (WOA) gridding methods of the NOAA National Centers for Environmental Information (NCEI) based on the recently released Coastal Ocean Data Analysis Product in North America (CODAP-NA), along with the 2021 update to the Global Ocean Data Analysis Project version 2 (GLODAPv2.2021) data product. The relevant variables were adjusted to the index year of 2010. The data product is available in NetCDF (https://doi.org/10.25921/g8pb-zy76, Jiang et al., 2022b) on the NOAA Ocean Carbon and Acidification Data System: https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0270962.html (last access: 15 July 2024). It is recommended to use the objectively analyzed mean fields (with “_an” suffix) for each variable. The atlases can be accessed at https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/synthesis/nacoastal.html (last access: 15 July 2024).
Continue reading ‘Climatological distribution of ocean acidification variables along the North American ocean margins’The Southern Ocean carbon sink has been overestimated in the past three decades
Published 29 July 2024 Science ClosedTags: Antarctic, chemistry, methods, modeling, regionalmodeling
Employing machine learning methods for mapping surface ocean pCO2 has reduced the uncertainty in estimating sea-air CO2 flux. However, a general discrepancy exists between the Southern Ocean carbon sinks derived from pCO2 products and those from biogeochemistry models. Here, by performing a boosting ensemble learning feed-forward neural networks method, we have identified an underestimation of the surface Southern Ocean pCO2 due to notably uneven density of pCO2 measurements between summer and winter, which resulted in about 16% overestimating of Southern Ocean carbon sink over the past three decades. In particular, the Southern Ocean carbon sink since 2010 was notably overestimated by approximately 29%. This overestimation can be mitigated by a winter correction in algorithms, with the average Southern Ocean carbon sink during 1992-2021 corrected to −0.87 PgC yr−1 from the original −1.01 PgC yr−1. Furthermore, the most notable underestimation of surface ocean pCO2 mainly occurred in regions south of 60°S and was hiding under ice cover. As the surface ocean pCO2 under sea ice coverage in the winter is much higher than the atmosphere, if sea ice melts completely, there could be a further reduction of about 0.14 PgC yr−1 in the Southern Ocean carbon sink.
Continue reading ‘The Southern Ocean carbon sink has been overestimated in the past three decades’Climate projections of oceanographic variables in the Exclusive Economic Zone of Ecuador: a 21st century perspective to inform impact and adaptation assessment
Published 17 July 2024 Science ClosedTags: chemistry, modeling, regionalmodeling, socio-economy
Highlights
- A statistically robust increase in SST is expected in the EEEZ for the 21st Century.
- A statistically robust reduction in pH is expected in the EEEZ for the 21st Century.
- DO climate projections are not robust in the EEEZ for the 21st Century.
- Flood events historically occurring once every 100 years would occur annually by the end-of-century.
- Possible coastal impacts within the biodiverse equatorial upwelling system are discussed.
Abstract
Climate projections of ocean variables are essential to inform adaptation strategies and plans involving open and coastal oceanic regions. Assessment of baseline and projections of sea surface temperature (SST), pH, dissolved oxygen (DO), mean sea level (MSL), waves coastal flooding within Ecuador’s Exclusive Economic Zone, including Galapagos Islands are reported herein. With different magnitudes of change, both near-future (2021–2050) and far-future projections (2051–2080) show a statistically robust increase in SST, MSL rise and a reduction in pH, a proxy for acidification. In contrast, DO decrease is only observed in surface (0–100 m) but not in subsurface waters (100–400 m). The likelihood of extreme sea level events in the coastal cities of La Libertad, Manta and Esmeraldas would remain almost unchanged for near-future projections (2026–2045) whereas, for end-of-century projections (2081–2100), historical 1 in a 100-year extreme flooding events would become yearly occurrences. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change. Since the eastern Tropical Pacific Ocean is one of the most productive and biodiverse worldwide due to the equatorial upwelling system, possible impacts on marine biodiversity, social, and economic systems are discussed.
Continue reading ‘Climate projections of oceanographic variables in the Exclusive Economic Zone of Ecuador: a 21st century perspective to inform impact and adaptation assessment’Nutrient limitation dampens the response of a harmful algae to a marine heatwave in an upwelling system
Published 15 July 2024 Science ClosedTags: chemistry, methods, modeling, North Pacific, regionalmodeling
Harmful algal blooms caused by toxin-producing species of the diatom genus Pseudo-nitzschia have been linked to anomalously warm ocean conditions in the Northern California Current System. This study compares summertime concentrations of Pseudo-nitzschia spp. and the toxin they produce, domoic acid, during a marine heatwave year (2019) and a climatologically neutral year (2021). An Imaging FlowCytobot was installed on a fishery survey vessel alongside environmental sensors to continuously sample phytoplankton and oceanographic parameters. This was paired with targeted manual sample collections for nutrients, chlorophyll, and domoic acid. Accumulations of Pseudo-nitzschia spp. were associated with upwelling zones and established hotspot regions: the Juan de Fuca Eddy, Heceta Bank, and Trinidad Head. Overall, however, Pseudo-nitzschia spp. and domoic acid concentrations were low during both summers and appear to have been limited by nitrate. Nutrient availability may therefore modulate the response of Pseudo-nitzschia spp. to warm anomalies. Comparison of these results with 2015, another marine heatwave year but one that produced record concentrations of Pseudo-nitzschia spp. and domoic acid, suggests that the timing of marine heatwave conditions in the nearshore relative to seasonal upwelling plays a key role in determining whether a Pseudo-nitzschia spp. harmful algal bloom will occur.
Continue reading ‘Nutrient limitation dampens the response of a harmful algae to a marine heatwave in an upwelling system’
