For open ocean environments, it is rare to find continuous, simultaneous air and sea observation records due to the challenges of instrument installation and maintenance. The Ieodo Ocean Research Station (Ieodo ORS), a remote ocean site located in the northern East China Sea with its harsh oceanic and atmospheric environment, provides a platform for the concurrent monitoring of air and sea environments. Since 2014, the Korea Hydrographic and Oceanographic Agency has run the “Ieodo ORS field trip program,” via which researchers are able to stay at the station for a week or more. This work reports technical lessons learned over 5 years from five Ieodo ORS research projects launched in 2016. Over the course of these projects, Ieodo ORS has monitored sea surface temperature, temperature and salinity in the water column, seawater pH, air pollutants, and solar radiation. The purpose of this paper is to facilitate the success of future research activities in similar environments by sharing our experiences and “best practices.”
Continue reading ‘Ocean and atmospheric observations at the remote Ieodo Ocean Research Station in the Northern East China Sea’Posts Tagged 'methods'
Ocean and atmospheric observations at the remote Ieodo Ocean Research Station in the Northern East China Sea
Published 9 July 2021 Science ClosedTags: chemistry, field, methods, North Pacific
Technical note: stability of tris pH buffer in artificial seawater stored in bags
Published 2 July 2021 Science ClosedTags: laboratory, methods
Equimolal tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer in artificial seawater is a well characterized and commonly used standard for oceanographic pH measurements. We evaluated the stability of tris pH when stored in purportedly gas-impermeable bags across a variety of experimental conditions, including bag type and storage in air vs. seawater over 300 d. Bench-top spectrophotometric pH analysis revealed that the pH of tris stored in bags decreased at a rate of 0.0058±0.0011 yr−1 (mean slope ±95 % confidence interval of slope). The upper and lower bounds of expected pH change at t=365 d, calculated using the averages and confidence intervals of slope and intercept of measured pH change vs. time data, were −0.0042 and −0.0076 from initial pH. Analyses of total dissolved inorganic carbon confirmed that a combination of CO2 infiltration and/or microbial respiration led to the observed decrease in pH. Eliminating the change in pH of bagged tris remains a goal, yet the rate of pH change is lower than many processes of interest and demonstrates the potential of bagged tris for sensor calibration and validation of autonomous in situ pH measurements.
Continue reading ‘Technical note: stability of tris pH buffer in artificial seawater stored in bags’Seasonal and spatial controls on the eutrophication-induced acidification in the Pearl River Estuary
Published 25 June 2021 Science ClosedTags: biogeochemistry, chemistry, field, methods, modeling, North Pacific, regionalmodeling
Abstract
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.
Continue reading ‘Seasonal and spatial controls on the eutrophication-induced acidification in the Pearl River Estuary’Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage
Published 24 June 2021 Science ClosedTags: laboratory, methods, South Pacific
We compared the effects of preservation and storage methods on total alkalinity (AT) of seawater, estuarine water, freshwater, and groundwater samples stored for 0–6 months. Water samples, untreated or treated with HgCl2, 0.45 µm filtration, or filtration plus HgCl2, were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean AT of samples treated with HgCl2 was reduced by as much as 49.1 µmol kg−1 (1.3%). Borosilicate glass elevated AT, possibly due to dissolving silicates. There was little change in AT of control and filtered samples stored in polypropylene, except for untreated groundwater (~ 4.1% reduction at 6 months). HgCl2 concentrations of 0.02–0.05% reduced the AT of fresh, estuarine, and ground water samples by as much as 35.5 µmol kg−1 after 1 month, but had little effect on the AT of seawater. Adding glucose as a carbon source for microbial growth resulted in no AT changes in 0.45 µm-filtered samples. We suggest water samples intended for AT analyses can be filtered to 0.45 µm, and stored in polypropylene vials at 4 °C for at least 6 months. Borosilicate glassware and HgCl2 can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg2+.
Continue reading ‘Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage’Coastal Ocean Data Analysis Product in North America (CODAP-NA) – an internally consistent data product for discrete inorganic carbon, oxygen, and nutrients on the North American ocean margins (update)
Published 16 June 2021 Science ClosedTags: biogeochemistry, chemistry, methods, North Atlantic, North Pacific
Internally consistent, quality-controlled (QC) data products play an important role in promoting regional-to-global research efforts to understand societal vulnerabilities to ocean acidification (OA). However, there are currently no such data products for the coastal ocean, where most of the OA-susceptible commercial and recreational fisheries and aquaculture industries are located. In this collaborative effort, we compiled, quality-controlled, and synthesized 2 decades of discrete measurements of inorganic carbon system parameters, oxygen, and nutrient chemistry data from the North American continental shelves to generate a data product called the Coastal Ocean Data Analysis Product in North America (CODAP-NA). There are few deep-water (> 1500 m) sampling locations in the current data product. As a result, crossover analyses, which rely on comparisons between measurements on different cruises in the stable deep ocean, could not form the basis for cruise-to-cruise adjustments. For this reason, care was taken in the selection of data sets to include in this initial release of CODAP-NA, and only data sets from laboratories with known quality assurance practices were included. New consistency checks and outlier detections were used to QC the data. Future releases of this CODAP-NA product will use this core data product as the basis for cruise-to-cruise comparisons. We worked closely with the investigators who collected and measured these data during the QC process. This version (v2021) of the CODAP-NA is comprised of 3391 oceanographic profiles from 61 research cruises covering all continental shelves of North America, from Alaska to Mexico in the west and from Canada to the Caribbean in the east. Data for 14 variables (temperature; salinity; dissolved oxygen content; dissolved inorganic carbon content; total alkalinity; pH on total scale; carbonate ion content; fugacity of carbon dioxide; and substance contents of silicate, phosphate, nitrate, nitrite, nitrate plus nitrite, and ammonium) have been subjected to extensive QC. CODAP-NA is available as a merged data product (Excel, CSV, MATLAB, and NetCDF; https://doi.org/10.25921/531n-c230, https://www.ncei.noaa.gov/data/oceans/ncei/ocads/metadata/0219960.html, last access: 15 May 2021) (Jiang et al., 2021a). The original cruise data have also been updated with data providers’ consent and summarized in a table with links to NOAA’s National Centers for Environmental Information (NCEI) archives (https://www.ncei.noaa.gov/access/ocean-acidification-data-stewardship-oads/synthesis/NAcruises.html).
Continue reading ‘Coastal Ocean Data Analysis Product in North America (CODAP-NA) – an internally consistent data product for discrete inorganic carbon, oxygen, and nutrients on the North American ocean margins (update)’Hands-on exploration of ocean acidification with a living calcifier
Published 14 June 2021 Science ClosedTags: algae, biological response, calcification, education, laboratory, methods
This hands-on lab allows students to explore concepts and quantify effects of ocean acidification. Many laboratory activities simplify ocean acidification through computer simulations or dripping acid on nonliving materials (e.g., sea shells) but do not provide adequate opportunities for students to measure, inquire, or see real consequences for living organisms. Thus, we developed this low-cost, easily accessible experiment to imitate ocean acidification on living, calcifying organisms.
Continue reading ‘Hands-on exploration of ocean acidification with a living calcifier’Online-coupling of widely-ranged timescales to model coral reef development
Published 4 June 2021 Science ClosedTags: biological response, calcification, corals, individualmodeling, light, methods, modeling, morphology, mortality, multiple factors, photosynthesis, physiology, policy, temperature
Highlights
- A biophysical model framework for coral reef evolution is developed.
- The model can be used to predict the coral response to the environment via process-based relations.
- The model bridges the gap in timescales of processes from seconds to millennia.
- Model predictions are within the accuracy of climate projections.
- The model is an efficient tool for forecasting coral reef development to inform policy makers.
Abstract
The increasing pressure on Earth’s ecosystems due to climate change is becoming more and more evident and the impacts of climate change are especially visible on coral reefs. Understanding how climate change interacts with the physical environment of reefs to impact coral growth and reef development is critically important to predicting the persistence of reefs into the future. In this study, a biophysical model was developed including four environmental factors in a feedback loop with the coral’s biology: (1) light; (2) hydrodynamics; (3) temperature; and (4) pH. The submodels are online coupled, i.e. regularly exchanging information and feedbacks while the model runs. This ensures computational efficiency despite the widely-ranged timescales. The composed biophysical model provides a significant step forward in understanding the processes that modulate the evolution of coral reefs, as it is the first construction of a model in which the hydrodynamics are included in the feedback loop.
Continue reading ‘Online-coupling of widely-ranged timescales to model coral reef development’Accurate pH and O2 measurements from spray underwater gliders
Published 31 May 2021 Science ClosedTags: chemistry, field, methods, North Pacific
The California Current System is thought to be particularly vulnerable to ocean acidification, yet pH remains chronically undersampled along this coast, limiting our ability to assess the impacts of ocean acidification. To address this observational gap, we integrated the Deep-Sea-DuraFET, a solid-state pH sensor, onto a Spray underwater glider. Over the course of a year starting in April 2019, we conducted seven missions in central California that spanned 161 glider days and >1600 dives to a maximum depth of 1000 m. The sensor accuracy was estimated to be ± 0.01 based on comparisons to discrete samples taken alongside the glider (n = 105), and the precision was ±0.0016. CO2 partial pressure, dissolved inorganic carbon, and aragonite saturation state could be estimated from the pH data with uncertainty better than ± 2.5%, ± 8 μmol kg−1, and ± 2%, respectively. The sensor was stable to ±0.01 for the first 9 months but exhibited a drift of 0.015 during the last mission. The drift was correctable using a piecewise linear regression based on a reference pH field at 450 m estimated from published global empirical algorithms. These algorithms require accurate O2 as inputs; thus, protocols for a simple predeployment air calibration that achieved accuracy of better than 1% were implemented. The glider observations revealed upwelling of undersaturated waters with respect to aragonite to within 5 m below the surface near Monterey Bay. These observations highlight the importance of persistent observations through autonomous platforms in highly dynamic coastal environments.
Continue reading ‘Accurate pH and O2 measurements from spray underwater gliders’Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system
Published 19 May 2021 Science ClosedTags: abundance, biogeochemistry, biological response, chemistry, methods, modeling, North Pacific, otherprocess, photosynthesis, phytoplankton, primary production, regionalmodeling, respiration
Significance
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.
Abstract
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.
Continue reading ‘Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system’A dynamic stress-scape framework to evaluate potential effects of multiple environmental stressors on Gulf of Alaska juvenile Pacific cod
Published 13 May 2021 Science ClosedTags: biological response, chemistry, field, fish, fisheries, methods, modeling, morphology, North Pacific, regionalmodeling
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.
Continue reading ‘A dynamic stress-scape framework to evaluate potential effects of multiple environmental stressors on Gulf of Alaska juvenile Pacific cod’Calcium carbonate dissolution patterns in the ocean
Published 12 May 2021 Science ClosedTags: chemistry, dissolution, globalmodeling, methods
Calcium carbonate (CaCO3) minerals secreted by marine organisms are abundant in the ocean. These particles settle and the majority dissolves in deeper waters or at the seafloor. Dissolution of carbonates buffers the ocean, but the vertical and regional distribution and magnitude of dissolution are unclear. Here we use seawater chemistry and age data to derive pelagic CaCO3 dissolution rates in major oceanic regions and provide the first data-based, regional profiles of CaCO3 settling fluxes. We find that global CaCO3 export at 300 m depth is 76 ± 12 Tmol yr−1, of which 36 ± 8 Tmol (47%) dissolves in the water column. Dissolution occurs in two distinct depth zones. In shallow waters, metabolic CO2 release and high-magnesium calcites dominate dissolution while increased CaCO3 solubility governs dissolution in deeper waters. Based on reconstructed sinking fluxes, our data indicate a higher CaCO3 transfer efficiency from the surface to the seafloor in high-productivity, upwelling areas than in oligotrophic systems. These results have implications for assessments of future ocean acidification as well as palaeorecord interpretations, as they demonstrate that surface ecosystems, not only interior ocean chemistry, are key to controlling the dissolution of settling CaCO3 particles.
Continue reading ‘Calcium carbonate dissolution patterns in the ocean’A critical analysis of the ocean effects of carbon dioxide removal via direct air and ocean capture – is it a safe and sustainable solution?
Published 14 April 2021 Newsletters and reports ClosedTags: methods, mitigation, review
Executive Summary
Catalyzed by the 2015 Paris Agreement, there are numerous initiatives for policies and sciencebased solutions to reduce greenhouse gas emissions and to achieve net-zero emissions internationally. President Biden plans to achieve net-zero in the United States no later than 2050. Despite forward-moving initiatives, the Intergovernmental Panel on Climate Change (IPCC) recently reported that two-thirds of the countries that have pledged to reduce greenhouse gas emissions have committed to levels that remain insufficient in meeting vital international climate targets [1]. The overarching goal to reduce greenhouse gas (GHG) emissions must be accomplished by transitioning to a more equitable and environmentally just energy system that reduces pollution while meeting global food, transportation, and energy needs. Carbon dioxide removal (CDR) is at the forefront of policy change, investments, and technology to reduce the amount of CO2 in the atmosphere and the ocean. We must respond quickly, yet carefully, to the considerable pressure to remove carbon dioxide from the atmosphere even as we transition away from burning fossil fuels and other anthropogenic CO2-emitting activities. There are a number of emerging technologies based on direct air capture (DAC) and direct ocean capture (DOC) which use machines to extract CO2 directly from the atmosphere or the ocean and move the CO2 underground to storage facilities or utilize the CO2 to enhance oil recovery from commercially-depleted wells. These technological interventions are in contrast to nature-based solutions. These include restoring mangroves and other coastal and marine ecosystems, regenerative agriculture, and reforestation to remove and store carbon dioxide in plants and soils. These nature-based strategies can offer multiple community benefits, biodiversity benefits, and long-term carbon storage, a global benefit.2 This report mainly focuses on the viability and consequences, including potential harm to the environment and livelihoods of the direct air capture and direct ocean capture approaches.
Continue reading ‘A critical analysis of the ocean effects of carbon dioxide removal via direct air and ocean capture – is it a safe and sustainable solution?’Technical note: excess alkalinity in carbonate system reference materials
Published 7 April 2021 Science ClosedTags: chemistry, field, methods, North Atlantic
Certified reference materials (CRMs) for oceanic carbonate system measurements are critical for verifying the accuracy of laboratory protocols and the reliability of field sensors. CRMs are certified for total alkalinity and dissolved inorganic carbon, parameters that are (1) stable for a long period of time when a sample is properly stored and (2) not affected by changes in temperature and pressure. In experimentation initially designed to measure the total boron to salinity ratio of seawater, an interesting result has emerged regarding CRMs. A unique acidimetric titration method has indicated that three different batches of CRM contain excess alkalinity (i.e., alkalinity that is not attributable to inorganic bases included in the traditional definition of seawater total alkalinity) that is statistically greater than the excess alkalinity measured in open-ocean water from the Gulf of Mexico. Further, the amount of excess alkalinity appears to differ in certain CRM batches. Excess alkalinity in CRMs is likely caused by organic proton acceptors that are not completely oxidized by the ultraviolet sterilization procedure that CRMs undergo. The primary use of CRMs — to maintain the accuracy and consistency of carbonate system measurements — may be inhibited by excess alkalinity, which can cause differences in total alkalinity values determined by different titration methods. Excess alkalinity also invalidates the assumptions applied to CO2 system calculations, and so would produce incorrect values of CO2 system parameters calculated from certified total alkalinity and dissolved inorganic carbon values of CRMs. Finally, excess alkalinity analyses highlight the urgent need for the marine chemistry community to establish a universally agreed upon total boron to salinity ratio.
Continue reading ‘Technical note: excess alkalinity in carbonate system reference materials’Seasonal marine carbon system processes in an Arctic coastal landfast sea ice environment observed with an innovative underwater sensor platform
Published 7 April 2021 Science ClosedTags: biogeochemistry, biological response, chemistry, field, methods, photosynthesis, phytoplankton, respiration
Studying carbon dioxide in the ocean helps to understand how the ocean will be impacted by climate change and respond to increasing fossil fuel emissions. The marine carbonate system is not well characterized in the Arctic, where challenging logistics and extreme conditions limit observations of atmospheric CO2 flux and ocean acidification. Here, we present a high-resolution marine carbon system data set covering the complete cycle of sea-ice growth and melt in an Arctic estuary (Nunavut, Canada). This data set was collected through three consecutive yearlong deployments of sensors for pH and partial pressure of CO2 in seawater (pCO2sw) on a cabled underwater observatory. The sensors were remarkably stable compared to discrete samples: While corrections for offsets were required in some instances, we did not observe significant drift over the deployment periods. Our observations revealed a strong seasonality in this marine carbon system. Prior to sea-ice formation, air–sea gas exchange and respiration were the dominant processes, leading to increasing pCO2sw and reduced aragonite saturation state (ΩAr). During sea-ice growth, water column respiration and brine rejection (possibly enriched in dissolved inorganic carbon, relative to alkalinity, due to ikaite precipitation in sea ice) drove pCO2sw to supersaturation and lowered ΩAr to < 1. Shortly after polar sunrise, the ecosystem became net autotrophic, returning pCO2sw to undersaturation. The biological community responsible for this early switch to autotrophy (well before ice algae or phytoplankton blooms) requires further investigation. After sea-ice melt initiated, an under-ice phytoplankton bloom strongly reduced aqueous carbon (chlorophyll-a max of 2.4 µg L–1), returning ΩAr to > 1 after 4.5 months of undersaturation. Based on simple extrapolations of anthropogenic carbon inventories, we suspect that this seasonal undersaturation would not have occurred naturally. At ice breakup, the sensor platform recorded low pCO2sw (230 µatm), suggesting a strong CO2 sink during the open water season.
Continue reading ‘Seasonal marine carbon system processes in an Arctic coastal landfast sea ice environment observed with an innovative underwater sensor platform’Change of coral carbon isotopic response to anthropogenic Suess effect since around 2000s
Published 7 April 2021 Science ClosedTags: chemistry, corals, field, methods
Highlights
- The declining trend in the coral δ13C time series slowed or reversed after 2000.
- The change of the declining rate in coral δ13C is not due to seawater chemistry.
- The response of coral δ13C to Suess effect has changed since around 2000s.
- The change results from coral acclimatization to external environmental stressors.
Abstract
The stable carbon isotope composition (δ13C) in coral skeletons can be used to reconstruct the evolution of the dissolved inorganic carbon (DIC) in surface seawater, and its long-term declining trend during the past 200 years (∼1800-2000) reflects the effect of anthropogenic Suess effect on carbonate chemistry in surface oceans. The global atmospheric CO2 concentration still has been increasing since 2000, and the Suess effect is intensifying. Considering the coral’s ability of resilience and acclimatization to external environmental stressors, the response of coral δ13C to Suess effect may change and needs to be re-evaluated. In this study, ten long coral δ13C time series synthesized from different oceans were used to re-evaluate the response of coral carbonate chemistry to Suess effect under the changing environments. These δ13C time series showed a long-term declining trend since 1960s, but the declining rates slowed in eight time series since around 2000s. Considering that the declining rates of the DIC-δ13C in surface seawater from the Hawaii Ocean Time-series Station and Bermuda Atlantic Time-series Station has not changed since 2000 compared with those during 1960-1999, the change in the coral δ13C trends at eight of ten locations may indicate that the response of coral δ13C to the anthropogenic Suess effect has changed since around 2000s. This change may have resulted from coral acclimatization to external environmental stressors. To adapt to acidifying oceans, coral may have the ability to regulate the source of DIC in extracellular calcifying fluid and/or the utilization way of DIC, therefore the response of coral δ13C to anthropogenic Suess effect will change accordingly.
Continue reading ‘Change of coral carbon isotopic response to anthropogenic Suess effect since around 2000s’On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean
Published 6 April 2021 Science ClosedTags: chemistry, field, Indian, methods, North Pacific
An important factor for predicting the effect of increased CO2 on future acidification of the ocean is a proper understanding of the interactions controlling production and dissolution of calcium carbonate minerals (CaCO3). The production and dissolution of CaCO3 in the ocean can be assessed over large spatial scales by measuring seawater calcium concentrations and total alkalinity (AT), yet past studies suggest that there could be large discrepancies between calcium and AT-based balances of the CaCO3 cycle in the North Pacific and Indian Oceans. Here, we analyse water column samples collected along transects in the North Pacific, Southern Ocean, tropical Indian Ocean and Red Sea for their concentrations of calcium, nutrients, and AT. We find that there is an excess calcium over AT anomaly in the top 1000 m of the tropical Indian Ocean water-column. The source of this anomaly is the dissolution of subsurface gypsum deposits in the Red Sea. We find no evidence for calcium-over-AT anomalies in the North Pacific, in contrast to previous studies. Our results show that, in most cases, calcium and AT data agree well and can be used to reconstruct the marine CaCO3 cycle.
Continue reading ‘On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean’Ideas and perspectives: when ocean acidification experiments are not the same, repeatability is not tested (update)
Published 15 March 2021 Science ClosedTags: biological response, fish, methods, performance
Can experimental studies on the behavioural impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously observed responses of coral reef fish to high CO2. New information on the methodologies used in the “replicated” studies now provides a plausible explanation: the experimental conditions were substantially different. High sensitivity to test conditions is characteristic of ocean acidification research; such response variability shows that effects are complex, interacting with many other factors. Open-minded assessment of all research results, both negative and positive, remains the best way to develop process-based understanding. As in other fields, replication studies in ocean acidification are most likely to contribute to scientific advancement when carried out in a spirit of collaboration rather than confrontation.
Continue reading ‘Ideas and perspectives: when ocean acidification experiments are not the same, repeatability is not tested (update)’Variability of USA East Coast surface total alkalinity distributions revealed by automated instrument measurements
Published 12 March 2021 Science ClosedTags: chemistry, field, methods, North Atlantic
Highlights
• Automated total alkalinity (TA) analyses greatly expanded spatiotemporal coverage
• Regional distributions of TA relative to salinity changed between seasons and years
• Seasonal changes were sometimes inconsistent with a new historical dataset
Abstract
Seawater total alkalinity (TA) is one important determinant used to monitor the ocean carbon cycle, whose spatial distributions have previously been characterized along the United States East Coast via discrete bottle samples. Using these data, several regional models for TA retrievals based on practical salinity (S) have been developed. Broad-scale seasonal or interannual variations, however, are not well resolved in these models and existing data are highly seasonally biased. This study reports findings from the first long duration deployment of a new, commercially available TA titrator aboard a research vessel and the continuous underway surface TA measurements produced. The instrument, operated on seven East Coast USA cruises during six months in 2017 and for two months in 2018 on the summertime East Coast Ocean Acidification survey (ECOA-2), collected a total of nearly 11,000 surface TA measurements. Data from these efforts, along with a newly synthesized set of more than 11,000 regional surface TA observations, are analyzed to re-examine distributions of TA and S along the United States East Coast. Overall, regional distributions of S and TA generally agreed with prior findings, but linear TA:S regressions varied markedly over time and deviated from previously developed models. This variability is likely due to a combination of biological, seasonal, and episodic influences and indicates that substantial errors of ±10–20 μmol kg−1 in TA estimation from S can be expected due to these factors. This finding has likely implications for numerical ecosystem modeling and inorganic carbon system calculations. New results presented in this paper provide refined surface TA:S relationships, present more data in space and time, and improve TA modeling uncertainty.
Continue reading ‘Variability of USA East Coast surface total alkalinity distributions revealed by automated instrument measurements’A portable tunable diode laser absorption spectroscopy system for dissolved CO2 detection using a high-efficiency headspace equilibrator
Published 9 March 2021 Science ClosedTags: chemistry, methods
Continuous observation of aquatic pCO2 at the ocean surface, with a sensitive response time and high spatiotemporal resolution, is essential for research into the carbon biogeochemical cycle. In this work, a portable tunable diode laser absorption spectroscopy (TDLAS) system for dissolved CO2 detection in surface seawater, coupled with a home-made headspace equilibrator, allowing real time underway measurements, is described. Both the optical detection part and sample extraction part were integrated together into a compact chamber. An empirical equation suitable for this system was acquired, which can convert the concentration from the gas-phase to the aqueous-phase. A monitoring precision of 0.5% was obtained with time-series measurement, and the detection limits of 2.3 ppmv and 0.1 ppmv were determined with 1 s and 128 s averaging time, respectively. Sampling device used in this work was ameliorated so that the response time of system reduced by about 50% compared to the traditional ‘shower head’ system. The fast response time reached the order of 41 s when the final concentration span was 3079 ppmv. For1902 ppmv, this figure was as short as 20 s. Finally, a field underway measurement campaign was carried out and the results were briefly analyzed. Our work proved the feasibility of the TDLAS system for dissolved CO2 rapid detection.
Continue reading ‘A portable tunable diode laser absorption spectroscopy system for dissolved CO2 detection using a high-efficiency headspace equilibrator’Technical note: interpreting pH changes (update)
Published 26 February 2021 Science ClosedTags: chemistry, methods
The number and quality of ocean pH measurements have increased substantially over the past few decades such that trends, variability, and spatial patterns of change are now being evaluated. However, comparing pH changes across domains with different initial pH values can be misleading because a pH change reflects a relative change in the hydrogen ion concentration ([H+], expressed in mol kg−1) rather than an absolute change in [H+]. We recommend that [H+] be used in addition to pH when describing such changes and provide three examples illustrating why.
Continue reading ‘Technical note: interpreting pH changes (update)’
