Search Results (29)

Massachusetts Bay in the northeastern United States is highly vulnerable to ocean acidification (OA) due to reduced buffering capacity from significant freshwater inputs. We hypothesize that acidification varies across temporal and spatial scales, with short-term variability driven by seasonal biological respiration, precipitation–evaporation balance, and river discharge, and long-term changes linked to global warming and river flux shifts. These patterns arise from complex nonlinear interactions between physical and biogeochemical processes. To investigate OA variability, we applied the Northeast Biogeochemistry and Ecosystem Model (NeBEM), a fully coupled three-dimensional physical–biogeochemical system, to Massachusetts Bay and Boston Harbor. Numerical simulation was performed for 2016. Assimilating satellite-derived sea surface temperature and sea surface height improved NeBEM’s ability to reproduce observed seasonal and spatial variability in stratification, mixing, and circulation. The model accurately simulated seasonal changes in nutrients, chlorophyll-a, dissolved oxygen, and pH. The model results suggest that nearshore areas were consistently more susceptible to OA, especially during winter and spring. Mechanistic analysis revealed contrasting processes between shallow inner and deeper outer bay waters. In the inner bay, partial pressure of pCO₂ (pCO₂) and aragonite saturation (Ω_a) were influenced by sea temperature, dissolved inorganic carbon (DIC), and total alkalinity (TA). TA variability was driven by nitrification and denitrification, while DIC was shaped by advection and net community production (NCP). In the outer bay, pCO₂ was controlled by temperature and DIC, and Ω_a was primarily determined by DIC variability. TA changes were linked to NCP and nitrification–denitrification, with DIC also influenced by air–sea gas exchange. Full article

The ocean is one of the world’s largest anthropogenic carbon dioxide (CO₂) sinks, but closing the carbon budget is logistically difficult and expensive, and uncertainties in carbon fluxes and reservoirs remain. One specific challenge is that measuring the CO₂ flux at the air–sea interface usually requires costly sensors or analyzers (USD > 30,000), which can limit observational capacity. Our group has developed and validated a low-cost ΔpCO₂ system, able to measure both pCO₂^water and pCO₂^air, for USD ~1400 to combat this limitation. The device is equipped with Internet of Things (IoT) capabilities and built around a USD ~100 pCO₂ K30 sensor at its core. Our Sensor for the Exchange of Atmospheric CO₂ with Water (SEACOW) may be placed in an observational network with traditional pCO₂ sensors or ∆pCO₂ sensors to extend the spatial coverage and resolution of monitoring systems. After calibration, the SEACOW reports atmospheric pCO₂ measurements that are within 2–3% of the measurements made with a calibrated LI-COR LI-850. We also demonstrate the SEACOW’s ability to capture diel pCO₂ cycling in seagrass, provide recommendations for SEACOW field deployments, and provide additional technical specifications for the SEACOW and for the K30 itself (e.g., air- and water-side 99.3% response time; 5.7 and 29.6 min, respectively). Full article

The Southern Ocean (SO) is crucial for global climate regulation by absorbing excess heat and anthropogenic CO₂. However, representing air-sea heat fluxes in climate models remains a challenge, particularly in regions characterised by strong ocean–atmosphere–sea ice interactions. This study analysed air–sea heat fluxes over the SO using four products and seven CMIP6 HighResMIP pairs, comparing the mean state and trends (1985–2014) of sensible and latent heat fluxes (SHF and LHF, respectively) and the impact of grid resolution refinement on their estimation. Our results revealed significant discrepancies across datasets and SO sectors, with LHF showing more consistent seasonal performance than SHF. High-resolution models better capture air–sea heat flux variability, particularly in eddy-rich regions, with climatological mean differences reaching ±20 W.m⁻² and air–sea exchange variations spreading up to 30%. Most refined models exhibited enhanced spatial detail, amplifying trend magnitudes by 30–50%, with even higher values observed in some regions. Furthermore, the trend analysis showed significant regional differences, particularly in the Pacific sector, where air–sea heat fluxes showed heightened variability. Despite modelling advances, discrepancies between datasets revealed uncertainties in climate simulations, highlighting the critical need for continued improvements in climate modelling and observational strategies to accurately represent SO air–sea heat fluxes. Full article

The chemistry of atmospheric precipitation serves as an important proxy for discriminating the source(s) of air contaminants in urban environments as well as to discuss the dynamic of atmospheric chemistry exchanges. This approach can be undertaken at time scales varying from single events to seasonal and yearly time frames. Here, we characterized the chemical composition of two single rain episodes (18 July 2018 and 21 February 2019) collected in Wrocław (SW Poland). Our results demonstrated inner variations and seasonality (within the rain event as well as between summer and winter), both in ion concentrations as well as in their potential relations with local air contaminants and scavenging processes. Coupling statistical analysis of chemical parameters with meteorological/synoptic conditions and HYSPLIT back trajectories allowed us to identify three main factors (i.e., principal components; PC) controlling the chemical composition of precipitation, and that these fluctuated during each event: (i) PC1 (40%) was interpreted as reflecting the long-range transport and/or anthropogenic influences of emission sources that included biomass burning, fossil fuel combustion, industrial processes, and inputs of crustal origin; (ii) PC2 (20%) represents the dissolution of atmospheric CO₂ and HF into ionic forms; and (iii) PC3 (20%) originates from agricultural activities and/or biomass burning. Time variations during the rain events showed that each factor was more important at the start of the event. The study of both SO₄²⁻ and Ca²⁺ concentrations showed that while sea spray inputs fluctuated during both rain events, their overall impact was relatively low. Finally, below-cloud particle scavenging processes were only observed for PM₁₀ at the start of the winter rain episode, which was probably explained by the corresponding low rain intensity and an overlap from local aerosol emissions. Our study demonstrates the importance of multi-time scale approaches to explain the chemical variability in rainwater and both its relation to emission sources and the atmosphere operating processes. Full article

The El Niño-Southern Oscillation (ENSO) alters ocean–atmosphere carbon exchange, but the mechanisms by which it affects the air–sea carbon flux (FCO₂) remain unclear. Here, we used gridded FCO₂ data from 2003 to 2021 to elucidate the control processes and regional differences in the influence of the ENSO on FCO₂ in the mid–low latitude Pacific Ocean. Overall, the mid–low latitude Pacific Ocean region was a net sink for CO₂, with an average uptake rate of −0.39 molC·m⁻²·year⁻¹. Specifically, during the La Niña period in 2010–2012, the absorption rate decreased by 15.38%, while during the El Niño period in 2015–2016, it increased by 30.77%. El Niño (La Niña) suppressed (promoted) biological primary production in the North Pacific, leading to reduced (enhanced) carbon uptake. El Niño (La Niña) also inhibited (promoted) physical vertical mixing in the Equatorial Pacific, leading to reduced (enhanced) carbon emissions. In the South Pacific, however, El Niño increased carbon uptake and La Niña decreased carbon uptake; although, not by these two processes. More frequent El Niño in the future will further reduce carbon absorption in the North Pacific and carbon emission in the Equatorial Pacific but increase carbon absorption in the South Pacific. Full article

The air–sea exchange of carbon dioxide (CO₂) on a global scale is a key factor in understanding climate change and predicting its effects. The magnitude of sea spray’s contribution to this flux is currently highly uncertain. Constraining CO₂’s diffusion in sea spray droplets is important for reducing error margins in global estimates of oceanic CO₂ uptake and release. The timescale for CO₂ gas diffusion within sea spray is known to be shorter than the timescales for the droplets’ physical changes to take place while aloft. However, the rate of aqueous carbonate reactions relative to these timescales has not been assessed. This study investigates the timescales of droplet physical changes to those of chemical transformations across the H₂CO₃/HCO₃⁻/CO₃²⁻ sequence. We found that physical timescales are rate limiting and that evaporation drives carbonate species into gaseous CO₂, promoting the production and evasion of CO₂ from sea spray droplets. This has important implications for carbon cycling and feedback in the surface ocean. Full article

Against the background of climate warming, marine heatwaves (MHWs) and terrestrial drought events have become increasingly frequent in recent decades. However, the combined effects of MHWs and terrestrial drought on CO₂ uptake in marginal seas are still unclear. The East China Sea (ECS) experienced an intense and long-lasting MHW accompanied by an extreme terrestrial drought in the Changjiang basin in the summer of 2022. In this study, we employed multi-source satellite remote sensing products to reveal the patterns, magnitude, and potential drivers of CO₂ flux changes in the ECS resulting from the compounding MHW and terrestrial drought extremes. The CO₂ uptake of the ECS reduced by 17.0% (1.06 Tg C) in the latter half of 2022 and the Changjiang River plume region shifted from a CO₂ sink to a source (releasing 0.11 Tg C) in July-September. In the majority of the ECS, the positive sea surface temperature (SST) anomaly during the MHW diminished the solubility of CO₂ in seawater, thereby reducing CO₂ uptake. Moreover, the reduction in nutrient input associated with terrestrial drought, which is unfavorable to phytoplankton growth, further reduced the capacity of CO₂ uptake. Meanwhile, the CO₂ sink doubled for the offshore waters of the ECS continental shelf in July-September 2022, indicating the complexity and heterogeneity of the impacts of extreme climatic events in marginal seas. This study is of great significance in improving the estimation results of CO₂ fluxes in marginal seas and understanding sea–air CO₂ exchanges against the background of global climate change. Full article

In situ field investigations coupled with coral culture experiments were carried out in the coral reef waters of the eastern coast of Shenzhen, Da’ao Bay (DAB), Dalu Bay (DLB), and Yangmeikeng Sea Area (YMKSA) to study the dynamics of the carbon dioxide (CO₂) system in seawater and its controlling factors. The results indicated that the CO₂ parameters were highly variable over a range of spatiotemporal scales, forced by various physical and biochemical processes. Comprehensively, DAB acted as a sink for atmospheric CO₂ with exchange flux of –1.51 ± 0.31 to 0.27 ± 0.50 mmol C m⁻² d⁻¹, while DLB and YMKSA acted as a CO₂ source with exchange fluxes of –0.42 ± 0.36 to 1.69 ± 0.74 mmol C m⁻² d⁻¹ and –0.58 ± 0.48 to 1.69 ± 0.41 mmol C m⁻² d⁻¹, respectively. The biological process and mixing effect could be the most important factor for the seasonal variation in total alkalinity (TA). In terms of dissolved inorganic carbon (DIC), in addition to biological process and mixing, its seasonal variation was affected by air–sea exchange and coral metabolism to some extent. Different from the former, the other CO₂ parameters, total scale pH (pH_T), partial pressure of CO₂ (pCO₂), and aragonite saturation state (Ω_A), were mainly controlled by a combination of the temperature change, biochemical processes, air–sea exchange, and coral metabolism, while water mixing has little effect on them. In addition, our results indicated that coral communities could significantly increase the DIC/TA ratio by reducing the TA concentration and increasing the DIC in the reef waters, which may promote the acidification of local seawater and need attention. Full article

Near-surface oceanic turbulence plays an important role in the exchange of mass, momentum, and energy between the atmosphere and the ocean. The climate modifying the air–sea CO${}_2$ transfer rate varies linearly with the surface turbulent kinetic energy dissipation rate to the $1/4$ power in a range of systems with different types of forcing, such as coastal oceans, river estuaries, large tidal freshwater rivers, and oceans. In the first part of this paper, we present a numerical study of the near-surface turbulent kinetic energy spectra deduced from a direct numerical simulation (DNS) compared to turbulent kinetic energy spectra deduced from idealized infrared (IR) images. The DNS temperature fields served as a surrogate for IR images from which we have calculated the underlying kinetic energy spectra. Despite the near-surface flow region being highly anisotropic, we demonstrated that modeled isotropic and homogeneous turbulence spectra can serve as an approximation to observed near-surface spectra within the inertial and dissipation ranges. The second part of this paper validates our numerical observations in a laboratory experiment. In this experiment, we compared the turbulent kinetic energy spectra near the surface, as measured using a submerged shear sensor with the spectra derived from infrared images collected from above the surface. The energy dissipation measured by the shear sensor was found to be within 20% of the dissipation value derived from the IR images. Numerically and experimentally, we have demonstrated that IR-based and remote measurement techniques of the aquatic near surface offer a potentially accurate and non-invasive way to measure near-surface turbulence, which is needed by the community to improve models of oceanic air–sea heat, momentum, and gas fluxes. Full article

Near Inertial Oscillations (NIOs) are ocean oscillations forced by intermittent winds. They are most energetic at mid-latitudes, particularly in regions with atmospheric storm tracks. Wind-driven, large-scale NIOs are quickly scattered by ocean mesoscale eddies (with sizes ranging from 100 to 400 km), causing a significant portion of the NIO energy to propagate into the subsurface ocean interior. This kinetic energy pathway illustrates that the wind energy input to NIO is critical for maintaining deep ocean stratification and thus closing the total energy budget, as emphasised by numerous modelling studies. However, this wind energy input to NIO remains poorly observed on a global scale. A remote sensing approach that observes winds and ocean currents co-located in time and space with high resolution is necessary to capture the intermittent air-sea coupling. The current satellite observations do not meet these requirements. This study assesses the potential of a new satellite mission concept, Ocean DYnamics and Surface Exchange with the Atmosphere (OSYSEA), to recover wind-forced NIOs from co-located winds and currents. To do this, we use an Observation System Simulation Experiment (OSSE) based on hourly observations of ocean surface currents and surface winds from five surface moorings covering latitudes from ${15}^{°}$ to ${50}^{°}$. ODYSEA wind and current observations are expected to have a spatial resolution of 10 km with about a 12 h sampling frequency in mid-latitudes. Results show that NIOs can be recovered with high accuracy using the ODYSEA spatial and temporal resolution, but only if observations are made over a wide area of 1800 km. A narrower swath (1000 km) may lead to significant aliasing. Full article

The carbon dioxide concentration in the atmosphere has progressively risen since pre-industrial times. About one-third of the anthropogenically generated CO₂ is absorbed by the waters of the World Ocean, whereas the waters of the Southern Ocean take up about 40% of this CO₂. The concentrations of oxygen and carbon dioxide dissolved in seawater are sensitive to climate changes, transferring anthropogenic pressures with consequences for the biogeochemical cycles in the World Ocean. The Southern Ocean is a key region for the exchange of oxygen and carbon between the surface water and the atmosphere and for their transfer with cold water masses to the deep layers of the Ocean. In this paper, we discuss the dynamics of the carbon dioxide partial pressure (pCO₂) and dissolved oxygen (O₂) in the surface waters of the Atlantic Southern Ocean based on data collected during the 87th cruise of the R/V “Academik Mstislav Keldysh”. The study area includes the Bransfield Strait, Antarctic Sound, the Powell Basin, the Weddell, and Scotia Seas. We have analyzed the spatial distribution of pCO₂ and oxygen for the areas of transformation of water masses and changes in biogeochemical processes. In the zone of Scotia and Weddell Seas, we have observed an increase in pCO₂ and a decrease in oxygen concentrations at the transect from the Weddell Sea at 56° W to the Powell Basin. From the Antarctic Sound to the Bransfield Strait, a decrease in oxygen saturation and an increase in pCO₂ has been traced. The surface waters of the Bransfield Strait have revealed the greatest variability of hydrochemical characteristics due to a complex structure of currents and intrusions of different water masses. In general, this area has been characterized by the maximum pCO₂, while the surface waters are undersaturated with oxygen. The variability of the AOU/ΔpCO₂ (w-a) ratio has revealed a pCO₂ oversaturation and an O₂ undersaturation in the waters of the Bransfield Strait. It is evidence of active organic carbon decomposition as the major controlling process. Yet, photosynthesis is the major biogeochemical process in the studied areas of the Weddell and Scotia seas, and their waters have been undersaturated with pCO₂ and oversaturated with O₂. As it comes from the analysis of the distribution and correlation coefficients of AOU and the sea-air gradient of pCO₂ with other physical and biogeochemical properties, the predominance of the biotic processes to the dynamics of O₂ and pCO₂ in the surface water layer has been demonstrated for the studied areas. Yet, there is evidence of additional sources of CO₂ not associated with the production and destruction processes of organic matter. Full article

In the recent significant rise in atmospheric CO₂, seawater’s continuous acidification is altering the marine environment’s chemical structure at an unprecedented rate. Due to its potential socioeconomic impact, this subject attracted significant research interest. This study used traditional linear regression, nonlinear regression random forest, and the BP neural network algorithm to establish a prediction model for surface seawater pH based on data of North Pacific sea surface temperature (SST), salinity (SSS), chlorophyll-a concentration (Chl-a), and pressure of carbon dioxide on the sea surface (pCO₂) from 1993 to 2018. According to existing research, three approaches were found to be highly accurate in reconstructing the surface seawater pH of the North Pacific. The highest-performing models were the linear regression model using SSS, Chl-a, and pCO₂, the random forest model using SST and pCO₂, and the BP neural network model using SST, SSS, Chl-a, and pCO₂. The BP neural network model outperformed the linear regression and random forest model when comparing the root mean square error and fitting coefficient of the three best models. In addition, the best BP neural network model had substantially higher seasonal applicability than the best linear regression and the best random forest model, with good fitting effects in all four seasons—spring, summer, autumn, and winter. The process of CO₂ exchange at the sea–air interface was the key factor affecting the pH of the surface seawater, which was found to be negatively correlated with pCO₂ and SST, and positively correlated with SSS and Chl-a. Using the best BP neural network model to reconstruct the surface seawater pH over the North Pacific, it was found that the pH exhibited significant temporal and spatiotemporal variation characteristics. The surface seawater pH value was greater in the winter than the summer, and the pH decline rate over the past 26 years averaged 0.0013 yr⁻¹, with a general decreasing tendency from the northwest to the southeast. The highest value was observed in the tropical western Pacific, while the lowest value was observed in the eastern equatorial region with upwelling, which is consistent with the findings of previous studies. Full article

Based on case studies, the development of low-pressure systems leading to extreme precipitation events reveals common characteristics. They highlight the co-evolution of sea surface temperature (SST) anomalies and the clustering of mesoscale convective systems in characteristic period ranges according to harmonic modes of the annual declination of the sun. This suggests a quasi-resonance of the heat exchanges of the ocean and the atmosphere during cyclogenesis. The formation of coherent extensive positive SST anomalies in characteristic period ranges, which reflects various interactions from baroclinic waves at mid-latitudes, i.e., Rossby waves especially present where the western boundary currents move away from the continents, may be a precursor of an extreme heavy rainfall event. Fed by warm and humid air coming from coherent SST anomalies, the convective cyclonic system strengthens concomitantly with the formation of cut-off lows, favoring blocks. However, the concentration in space and time of large-amplitude rainfall anomalies requires a relative stability of the atmospheric blocking circulation during the slow maturation processes. Intensification of extratropical cyclones is presumably the consequence of natural and anthropogenic warming, which strengthens the mechanisms leading to the clustering of mesoscale convective systems. The present study should help to refine the prediction of these extreme events while contributing to enrich our understanding of their presumed link with global warming. Full article

Air–sea fluxes are greatly enhanced by the winds and vertical exchanges generated by mesoscale convective systems (MCSs). In contrast to global numerical weather prediction models, space-borne scatterometers are able to resolve the small-scale wind variability in and near MCSs at the ocean surface. Downbursts of heavy rain in MCSs produce strong gusts and large divergence and vorticity in surface winds. In this paper, 12.5 km wind fields from the ASCAT-A and ASCAT-B tandem mission, collocated with short time series of Meteosat Second Generation 3 km rain fields, are used to quantify correlations between wind divergence and rain in the Inter-Tropical Convergence Zone (ITCZ) of the Atlantic Ocean. We show that when there is extreme rain, there is extreme convergence/divergence in the vicinity. Probability distributions for wind divergence and rain rates were found to be heavy-tailed: exponential tails for wind divergence (P∼$e^{-\alpha \delta }$ with slopes that flatten with increasing rain rate), and power-law tails for rain rates (P∼${\left(R^{*}\right)}^{-\beta }$ with a slower and approximately equal decay for the extremes of convergence and divergence). Co-occurring points are tabulated in two-by-two contingency tables from which cross-correlations are calculated in terms of the odds and odds ratio for each time lag in the collocation. The odds ratio for extreme convergence and extreme divergence both have a well-defined peak. The divergence time lag is close to zero, while it is 30 min for the convergence peak, implying that extreme rain generally appears after (lags) extreme convergence. The temporal scale of moist convection is thus determined by the slower updraft process, as expected. A structural analysis was carried out that demonstrates consistency with the known structure of MCSs. This work demonstrates that (tandem) ASCAT winds are well suited for air–sea exchange studies in moist convection. Full article

The traditional field-based measurements of carbon dioxide (pCO₂) for inland waters are a snapshot of the conditions on a particular site, which might not adequately represent the pCO₂ variation of the entire lake. However, these field measurements can be used in the pCO₂ remote sensing modeling and verification. By focusing on inland waters (including lakes, reservoirs, rivers, and streams), this paper reviews the temporal and spatial variability of pCO₂ based on published data. The results indicate the significant daily and seasonal variations in pCO₂ in lakes. Rivers and streams contain higher pCO₂ than lakes and reservoirs in the same climatic zone, and tropical waters typically exhibit higher pCO₂ than temperate, boreal, and arctic waters. Due to the temporal and spatial variations of pCO₂, it can differ in different inland water types in the same space-time. The estimation of CO₂ fluxes in global inland waters showed large uncertainties with a range of 1.40–3.28 Pg C y⁻¹. This paper also reviews existing remote sensing models/algorithms used for estimating pCO₂ in sea and coastal waters and presents some perspectives and challenges of pCO₂ estimation in inland waters using remote sensing for future studies. To overcome the uncertainties of pCO₂ and CO₂ emissions from inland waters at the global scale, more reliable and universal pCO₂ remote sensing models/algorithms will be needed for mapping the long-term and large-scale pCO₂ variations for inland waters. The development of inverse models based on dissolved biogeochemical processes and the machine learning algorithm based on measurement data might be more applicable over longer periods and across larger spatial scales. In addition, it should be noted that the remote sensing-retrieved pCO₂/the CO₂ concentration values are the instantaneous values at the satellite transit time. A major technical challenge is in the methodology to transform the retrieved pCO₂ values on time scales from instant to days/months, which will need further investigations. Understanding the interrelated control and influence processes closely related to pCO₂ in the inland waters (including the biological activities, physical mixing, a thermodynamic process, and the air–water gas exchange) is the key to achieving remote sensing models/algorithms of pCO₂ in inland waters. This review should be useful for a general understanding of the role of inland waters in the global carbon cycle. Full article