Undersaturated Water Research Articles

Seafloor alkalinity enhancement as a carbon dioxide removal strategy in the Baltic Sea

Carbon dioxide removal from the atmosphere and storage over long times scales in terrestrial and marine reservoirs is urgently needed to limit global warming and for sustainable management of the global carbon cycle. Ocean alkalinity enhancement by the artificial addition of carbonate minerals to the seafloor has been proposed as a method to sequester atmospheric CO2 and store it in the ocean as dissolved bicarbonate. Here, a reaction-transport model is used to scrutinize the efficacy of calcite addition and dissolution at a well-studied site in the southwestern Baltic Sea – a brackish coastal water body in northern Europe. We find that most calcite is simply buried without dissolution under moderate addition rates. Applying the model to other sites in the Baltic Sea suggests that dissolution rates and efficiencies are higher in areas with low salinity and undersaturated bottom waters. A simple box model predicts a tentative net CO2 uptake rate from the atmosphere of 3.2 megatonnes of carbon dioxide per year for the wider Baltic Sea after continually adding calcite to muddy sediments for 10 years. More robust estimates now require validation by field studies.

Sources of limestone dissolution from surface water-groundwater interaction in the carbonate critical zone

Dissolution of carbonate minerals in karst aquifers has long been recognized to result from recharge of surface water undersaturated with respect to calcite from carbonic acid produced by hydration of dissolved atmospheric and respired CO2. However, dissolution also results from additional acids produced by reactions of redox sensitive solutes in the subsurface, which may represent a source of CO2 to Earth's atmosphere. Because the magnitude of dissolution by these additional acids is poorly constrained, we compare here fractions of dissolution from initial surface water undersaturation and subsurface redox reactions. Estimates are based on chemical mixing and geochemical (PHREEQC) modeling of time series measurements of water compositions at a spring vent that receives surface water during stream flooding and a stream sink-rise system in north-central Florida. During a single spring reversal, 9.2 × 105 kg of limestone dissolved. At the stream sink-rise system, where subsurface residence times are shorter than during the spring reversal, both limestone dissolution (102–104 kg) and precipitation (102–105 kg) occur as water flows through the conduits with residence times ranging from 10 to 70 h. At both sites, maximum calcite dissolution rates of ∼10 μM hr−1 occurs at subsurface residence times between 30 and 50 h. For subsurface residence time > ∼20–60 h, the models indicate that production of additional acid in the subsurface is required for ∼53 ± 7% of dissolution. Oxidation of organic carbon, ammonium, pyrite, iron, and/or manganese produce sufficient acid for additional dissolution, but dissolved oxygen is insufficient for these reactions, indicating some acidity is generated under anerobic conditions. Dissolution caused by subsurface reactions in our samples represents mobilization of 20 × 104-30 × 104 kg of CO2 via remineralization of organic carbon or carbonate dissolution by nitric and sulfuric acids. Acid produced by subsurface redox reactions during surface water-groundwater interactions, including non‑carbonic acids, are important in conduit development and carbon cycling in the carbonate critical zone.

The effect of cave ventilation on carbon and oxygen isotopic fractionation between calcite and drip water

Rapid CO2 degassing and calcite precipitation driven by cave ventilation influence the speleothem δ18O and δ13C. However, the drivers of cave ventilation are not completely understood due to the lack of monitoring of multiple environmental factors. Furthermore, the understanding of isotope fractionation caused by the dissolution of speleothem in undersaturated drip water is limited during the cave air stagnation. In this study, we displayed four years of cave microenvironment monitoring in Shawan Cave, Southwestern China, and analyzed the δ13CDIC and δ18O of drip water, and calcite precipitation δ18O and δ13C. The results show that the ventilation process is attributed to buoyancy airflow between external atmosphere, fissure air, and cave air. This causes that the higher (lower) cave air pCO2 in the summer (winter) is associated with upward airflow mode (downward airflow mode). Furthermore, cave ventilation could control the isotopic fractionation. Specifically, when cave air pCO2 is lower, the carbon isotopic disequilibrium between calcite and dissolved inorganic carbon (DIC) is controlled by the degassing of CO2 associated with calcite precipitation. The disequilibrium fractionation in carbon isotopes is less pronounced at slower drip-rate sites. The oxygen isotope fractionation between calcite and the drip water is found to be close to equilibrium. However, the high cave air pCO2 (exceeding 10,000 ppm) may result in drip water undersaturation to drive the dissolution of speleothem calcite. The δ18O values of drip water are pulled away from their original values to disequilibrate to the calcite because the exchange time of oxygen in the dissolved carbonates with the oxygen in the water is sufficiently long. Hence, the dissolution of speleothems may be a new mechanism to explain the oxygen isotopic disequilibrium between the calcite and drip water during the cave air stagnation. The carbon isotope fractionation between calcite and drip water is close to equilibrium.

Subsurface oxygen maximum in oligotrophic marine ecosystems: mapping the interaction between physical and biogeochemical processes

Abstract. The subsurface oxygen maximum (SOM) is observed in oligotrophic oceans and is associated with different physical and biological processes. This study characterizes the SOM in the Mediterranean Sea at the basin scale and investigates its driving mechanisms by analysing the output of the 1/24∘ resolution biogeochemical reanalysis provided by the Copernicus Marine Service for the 1999–2019 time period. We validated the model-derived oxygen concentration in the epipelagic layer at different spatial and temporal scales, including novel process comparisons with estimates from in situ observations. Moreover, using Biogeochemical Argo (BGC-Argo) float observations, we estimated the model uncertainty in reproducing the SOM concentration and depth in summer (13 mmol O2 m−3 and 13 m, respectively). The western and eastern Mediterranean Sea depicts different SOM signatures in summer, with higher oxygen values and shallower depths in the western Mediterranean. The concentrations and depths (in the ranges of 230–250 mmol O2 m−3 and 30–100 m, respectively) are in agreement with the estimations from the literature and show mesoscale variability patterns. The western Mediterranean also shows a stronger biological activity, specifically oxygen production and consumption, along the whole epipelagic layer and higher oxygen concentrations at the surface throughout the year, but heavy undersaturated waters are associated with winter deep convection in the northwestern Mediterranean Sea. A 1-year analysis conducted on selected areas that are representative of the heterogeneity of summer SOM highlighted that the SOM can actually be sustained by biological production (as in northwestern Mediterranean areas), or it can be a residual of the confinement of spring production (as in the central Ionian area) and vertical motions influence its depth (as in the Levantine subduction area).

The emergence of drop-type and thin-layer-type quasi-liquid layers on ice crystal surfaces and their thermodynamic origin

Ice crystals play crucially important roles in wide variety of natural phenomena on the earth’s surface. However, in-situ optical observation of quasi-liquid layers (QLLs), which governs properties of ice crystal surfaces at temperature close to 0 °C, has been an experimental challenge. In this review, we show our recent studies on the in-situ observation of QLLs formed by the surface melting of ice crystals at temperatures below 0 °C. We first show our advanced optical microscopy that can directly visualize individual elementary steps (0.4 nm in thickness) on ice crystal surfaces. Then we next demonstrate the emergence of two kinds of QLLs with different morphologies (droplets and thin layers) on basal and prism faces of ice crystals. We also determined the surface tension-to-shear viscosity ratio (the so-called characteristic velocity) of both QLLs, indicating that the drop-type and thin-layer-type QLLs are 20- and 200-times less fluidic than bulk water, respectively. In addition, we measured the contact angles of drop-type QLLs on ice crystal surfaces and found that the formation of the drop-type and thin-layer-type QLLs can be explained by the wetting transition of QLLs on ice crystal surfaces. Furthermore, we determined the water vapor pressure–temperature ranges, in which both QLLs can present, and found that both QLLs are formed kinetically only in supersaturated or undersaturated water vapor. Our findings show a novel picture of surface melting that were significantly different from the conventional picture in which one QLL phase appear uniformly on ice crystal surfaces.

Stylasterid corals build aragonite skeletons in undersaturated water despite low pH at the site of calcification

Anthropogenic carbon emissions are causing seawater pH to decline, yet the impact on marine calcifiers is uncertain. Scleractinian corals and coralline algae strongly elevate the pH of their calcifying fluid (CF) to promote calcification. Other organisms adopt less energetically demanding calcification approaches but restrict their habitat. Stylasterid corals occur widely (extending well below the carbonate saturation horizon) and precipitate both aragonite and high-Mg calcite, however, their mode of biocalcification and resilience to ocean acidification are unknown. Here we measure skeletal boron isotopes (δ11B), B/Ca, and U/Ca to provide the first assessment of pH and rate of seawater flushing of stylasterid CF. Remarkably, both aragonitic and high-Mg calcitic stylasterids have low δ11B values implying little modification of internal pH. Collectively, our results suggest stylasterids have low seawater exchange rates into the calcifying space or rely on organic molecule templating to facilitate calcification. Thus, despite occupying similar niches to Scleractinia, Stylasteridae exhibit highly contrasting biocalcification, calling into question their resilience to ocean acidification.

Intermolecular forces at ice and water interfaces: Premelting, surface freezing, and regelation.

Using Lifshitz theory, we assess the role of van der Waals forces at interfaces of ice and water. The results are combined with measured structural forces from computer simulations to develop a quantitative model of the surface free energy of premelting films. This input is employed within the framework of wetting theory and allows us to predict qualitatively the behavior of quasi-liquid layer thickness as a function of ambient conditions. Our results emphasize the significance of vapor pressure. The ice-vapor interface is shown to exhibit only incomplete premelting, but the situation can shift to a state of complete surface melting above water saturation. The results obtained serve also to assess the role of subsurface freezing at the water-vapor interface, and we show that intermolecular forces favor subsurface ice nucleation only in conditions of water undersaturation. We show that ice regelation at ambient pressure may be explained as a process of capillary freezing, without the need to invoke the action of bulk pressure melting. Our results for van der Waals forces are exploited in order to gauge dispersion interactions in empirical point charge models of water.

Environmental stability and phenotypic plasticity benefit the cold-water coral Desmophyllum dianthus in an acidified fjord

The stratified Chilean Comau Fjord sustains a dense population of the cold-water coral (CWC) Desmophyllum dianthus in aragonite supersaturated shallow and aragonite undersaturated deep water. This provides a rare opportunity to evaluate CWC fitness trade-offs in response to physico-chemical drivers and their variability. Here, we combined year-long reciprocal transplantation experiments along natural oceanographic gradients with an in situ assessment of CWC fitness. Following transplantation, corals acclimated fast to the novel environment with no discernible difference between native and novel (i.e. cross-transplanted) corals, demonstrating high phenotypic plasticity. Surprisingly, corals exposed to lowest aragonite saturation (Ωarag < 1) and temperature (T < 12.0 °C), but stable environmental conditions, at the deep station grew fastest and expressed the fittest phenotype. We found an inverse relationship between CWC fitness and environmental variability and propose to consider the high frequency fluctuations of abiotic and biotic factors to better predict the future of CWCs in a changing ocean.

Water storage in cratonic mantle

AbstractKnowledge of the water capacity of the deep lithosphere is crucial for validating models of craton growth and for constraining solid earth volatile cycles over geologic time. However, experimental constraints on water solubility and partitioning often disagree with natural rock data. We present a bulk compositionally dependent model of water storage capacity in pyrolite over a range of lithospheric mantle pressures and temperatures. Models are compared against published xenolith nominally anhydrous mineral (NAM) water contents, which have been recalculated to reflect the last water content of the mantle lithosphere by using coexisting pyroxene water contents in the same samples. Our main findings are that (1) regardless of tectonic setting, olivine records similar recalculated water contents, suggesting a common level of water undersaturation in the lithospheric mantle, and (2) equilibrium water partitioning between clinopyroxene and orthopyroxene (Dcpx/opx) increases down‐temperature. We propose these trends may be explained by re‐hydration/re‐fertilization of cratonic mantle early during coalescence, followed by cooling‐induced water exsolution from orthopyroxene and garnet formation as cratons thicken and stabilize.

Evolution of fracture aperture and thermal productivity influenced by chemical reaction in enhanced geothermal system

Geothermal reservoir scaling controlled by reactive flow is a common phenomenon during geothermal development, which might lead to the decline of geothermal productivity and abandonment of geothermal projects. It is significant to reveal chemical influence on the geothermal reservoir characteristics and production performance to provide the reference for geothermal sustainable development. In this work, a thermal-hydraulic-chemical coupling model is developed for a triple-well fractured enhanced geothermal system considering the silica dissolution and precipitation at the fracture surface. It is focused on the evolution of fracture aperture and geothermal productivity. The results indicate that undersaturated injection will cause mineral dissolution which leads to the rise of fracture transmissibility and a thermal break. The fracture width is enhanced by 0.093 mm, and the permeability is 8 times the initial value after 20-year production. The oversaturated injection will cause mineral precipitation which leads to the reduction of fracture aperture and the increase of pressure difference. The opening is reduced by 0.041 mm and the permeability goes down by 2 orders of magnitude. The maximum increases of average production temperature and differential pressure are 10 °C and 13.5 MPa respectively in the 20th year from undersaturation to supersaturation. Besides, it is figured out that reaction rate denotes the evolution of fracture aperture. Both of them are distributed as a band at a fracture plane, which is determined by saturation index and temperature together. The former controls the reaction pattern (dissolution/precipitation) while the latter controls the reaction speed. Furthermore, the evolution of opening is uneven around the production well at different exploitation stages. Fracture width is higher on the strong side in the first 8.7 years but is higher on the weak side in later development when undersaturated water (0 mol/kg) is injected. The phenomenon can be employed to judge the production status, guide the descaling, etc. Production analysis indicates that oversaturation delays the heat breakthrough and undersaturation reduces the surface pump input. This study will provide a significant reference for the geothermal sustainable production influenced by chemical reactions in an enhanced geothermal system.

Contrasts in calcium carbonate dissolution above the lysocline in the equatorial Indian Ocean over the last ~40 ka

Understanding calcite dissolution above the lysocline is crucial to comprehend the oceanic calcium carbonate cycle. To understand past calcite dissolution in sediments from above the lysocline, we use multiple dissolution proxies in a gravity core SSD-44/GC-01 from the central equatorial Indian Ocean, which spans a period of 43 ka. Our results suggest that calcite dissolution occurred during marine isotope stage −3 (MIS-3) and the last glacial maximum (LGM). Furthermore, dissolution of carbonate with increasing intensity occurred during the Holocene. Calcite dissolution above the lysocline is probably a result of pore water undersaturation in carbonate ion, which is in line with increased productivity during MIS-3 and the LGM. Furthermore, decreased sedimentation rate and increased exposure time of foraminifera during the Holocene may have led to efficient organic matter degradation and pore water undersaturation in carbonate ion. However, better preservation of calcite observed during the last deglacial period is probably due to increased deep-sea carbonate ion concentration, related to outgassing of CO2 to the atmosphere, stored during the LGM in the deep sea.

Assessment of the seasonal variations in hydrochemistry of Oued Fodda dam, Algeria

Abstract This study was carried out on the surface water of Oued Fodda dam in western Algeria, and aimed to evaluate the seasonal variations of chemical characteristics with the aim to define the processes controlling the mineralization of surface water in this dam. The results showed significant variations in the majority of parameters during the study period from 2009 to 2013, indicating slightly alkaline water, and a SO4-Cl-Ca-Mg water type. Principal component analysis (PCA) and cluster analysis (CA) were used to explain the correlations between the parameters analysed, and the probable sources of surface water contamination. The calculation of saturation indices (SI) of water indicated undersaturated water with respect to halite (NaCl), and equilibrium with respect to the other minerals. While, the temporal variation of physico-chemical parameters such as EC, TDS, SO4 2-, Cl-, Ca2+, Mg2+ indicated a reverse adjustment between physico-chemical parameters and water volumes (WV) in this dam, which can be explained by the weathering of silicate and carbonate minerals, these were justified by the use of ionic ratios, diagrams and scatter plots and multivariate statistical techniques. Conversely, evaluation of the organic water pollution level in this dam showed a water quality from moderately to severely polluted.

Elimination of wetting study flaws in unsaturated vapors based on Laplace fit parameters

Performing digital video image processing of sessile droplets and Laplace fit optimization is one of the most widely used modern techniques to measure the contact angle. The attractive feature of this approach is related to the possibility of simultaneous determination of numerous droplet parameters, such as contact angles, droplet surface tension, droplet surface area and droplet volume. However, lately in the literature, the analysis of the droplet shape is usually restricted by the contact angle determination, and the experiments are performed under open atmospheric conditions without simultaneous monitoring of the other droplet parameters. In this brief note, it is shown how wettability measurements under conditions of undersaturated water vapor affect the observed water droplet parameters.

Southern Ocean carbonate dissolution paced by Antarctic Ice-Sheet expansion in the early Miocene

The preservation of calcium carbonate deposits on the seafloor is one of the factors that regulates Earth's carbon cycle over longer timescales. Fluctuations in the carbonate compensation depth (CCD), the depth below which calcium carbonate is completely dissolved, can therefore significantly alter the ocean's capacity to sequester or release atmospheric carbon. High-latitude deep oceans are particularly important to the carbon cycle given their large capacity to store carbon dioxide. Here we present carbonate content results from an abyssal Subantarctic record (Site U1514) that spans the early Miocene and the onset of the Miocene Climatic Optimum. We show that carbonate preservation was highly variable from 19.9 to 17 Ma, with multiple episodes of total carbonate dissolution. Carbonate preservation then improved gradually after 17 Ma following the onset of the Miocene Climatic Optimum. Episodes of carbonate dissolution occurred preferentially at long eccentricity minima while periods of long eccentricity maxima improved carbonate preservation. These patterns of carbonate accumulation are in opposite phase to lower latitude Atlantic and Pacific records, which suggests that different mechanisms of carbonate accumulation/preservation were in place in high and low-latitude oceans. Comparison of Site U1514 with Antarctic records indicates an influence of ice sheet oscillations on carbonate preservation at the Subantarctic seafloor. We propose that carbonate dissolution occurred via the northward expansion of southern-derived undersaturated waters during periods of Antarctic ice sheet expansion. These findings indicate that the Subantarctic Southern Ocean was highly sensitive to Antarctic ice sheet fluctuations during the early Miocene, consistent with observations from Antarctica that show intensified polar amplification under a warmer climate.

Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Halite formations are attractive geothermal reservoirs due to their high heat conductivity, resulting in higher temperatures than other formations at similar depths. However, halite formations are highly reactive with undersaturated water. An understanding of the geochemical reactions that occur within halite-saturated formation waters can inform decision making regarding well construction, prevention of well clogging, formation dissolution, and thermal short-circuiting. Batch reaction and numerical 3-D flow and equilibrium reactive transport modeling were used to characterize the produced NaCl-brine in a well targeting a halite-saturated formation. The potential for inhibition of precipitation and dissolution using an MgCl2-brine and NaCl + MgCl2-brine were also investigated. Within the injection well, heating of an NaCl-brine from 70 to 120 °C caused the solubility of halite to decrease, resulting in the potential dissolution of 0.479 mol kg−1 halite at the formation. Conversely, cooling from 120 to 100 °C in the production well resulted in potential precipitation of 0.196 mol kg−1 halite. Concurrent precipitation of anhydrite is also expected. Introduction of MgCl2 into the heat exchange brine, which has a common Cl− ion, resulted in a decreased potential for dissolution by 0.290 mol kg−1 halite within the formation, as well as decreased precipitation within the production well, compared to the NaCl-brine. The halite solubility was altered by changes in pressure up to 0.045 mol kg−1. This indicates that designing and monitoring the composition of heat exchange fluids in highly saline environments is an important component in geothermal project design.

Accurate pH and O2 Measurements from Spray Underwater Gliders

AbstractThe 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 &gt;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.

Direct Imaging of Bubble Ripening in Two-dimensional Porous Media Micromodels

Carbon geo-sequestration technology is expected to play a significant role to reduce anthropogenic emission and achieve negative emission in the long term. The subsurface storage potential of CO2 is largely dominated by capillary action that generates a so-called residual phase in the pores of the rock in the form of disconnected bubbles. Understanding the temporal and spatial evolution of this residual phase is key to ensure the long-term storage security of CO2. To understand the factors affecting the stability of residually trapped CO2, we make direct observations of the interactions of a population of air bubbles surrounded by undersaturated water in a regular 2D porous medium micromodel at isothermal conditions. Mass transfer between neighbouring bubbles is shown to start at ~10 times bulk diffusive time scale and to correlate with the capillary pressure gradient between bubbles.

Subaerial morphology affected by groundwater aggressiveness: Sinkhole susceptibility above karstified salt, Dead Sea

Evaporite karst is intensively developing at the Dead Sea (DS), both along its western and eastern shores. The collapse of overlying sediments into evaporite karst cavities results in sinkhole formation. The dissolution is produced by undersaturated water, aggressive concerning halite. The evaporite karst is developing rapidly, in the time scale of months to years, so groundwater aggressiveness is a relevant factor for sinkhole susceptibility assessment. The present study analyzes sinkhole development concerning groundwater aggressiveness. The aggressiveness is evaluated from bulk resistivity (ρx) of the aquifer, measured from the surface using the Transient Electromagnetic (TEM) method, and from resistivity (ρw) of groundwater filling its pores. We suggest a methodology for water aggressiveness determination and its classification concerning salt. We then demonstrate a significant correlation between water aggressiveness and the actual distribution of sinkholes in five study areas along the Dead Sea. Conversely, we show that the timing of sinkholes occurrence within recent decades does not correlate with water aggressiveness. The timing is attributed to the multiple factors that control the dissolution of salt and consequent collapse. Acknowledging that the real hydrogeological conditions involve multifactorial processes, we shortly analyze other concurrent factors, including water table depth, existing salt karstification east of the salt edge, and site location relative to the salt edge.

Carbonate chemistry dynamics in shellfish farming areas along the Chilean coast: natural ranges and biological implications

AbstractThe increasing shellfish aquaculture requires knowledge about nearshore environmental variability to manage sustainably and create climate change adaptation strategies. We used data from mooring time series and in situ sampling to characterize oceanographic and carbonate system variability in three bivalve aquaculture areas located along a latitudinal gradient off the Humboldt Current System. Our results showed pHT &amp;lt;8 in most coastal sites and occasionally below 7.5 during austral spring–summer in the lower (−30°S) and central (−37°S) latitudes, related to upwelling. Farmed mussels were exposed to undersaturated (Ωarag &amp;lt; 1) and hypoxic (&amp;lt;2 ml l−1) waters during warm seasons at −37°S, while in the higher latitude (43°S) undersaturated waters were only detected during colder seasons, associated with freshwater runoff. We suggest that both Argopecten purpuratus farmed at −30°S and Mytilus chilensis farmed at −43°S may enhance their growth during summer due to higher temperatures, lower pCO2, and oversaturated waters. In contrast, Mytilus galloprovincialis farmed at 37°S grows better during spring–summer, following higher temperatures and high pCO2. This knowledge is relevant for aquaculture, but it must be improved using high-resolution time series and in situ experimentation with farmed species to aid their adaptation to climate change and ocean acidification.

The recent state and variability of the carbonate system of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidification

Abstract. Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA&lt;1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area.