Although the Arctic Ocean is relatively small in volume, its extensive coastline delivers large quantities of terrigenous material from rivers and coastal erosion. As a result, the Arctic Ocean is impacted more strongly by terrigenous material than most other parts of the global ocean. Yet the effect of this material on carbon cycling and ocean acidification remains poorly quantified. In this study, we use an ocean biogeochemical model driven by observation-based estimates of terrigenous carbon, alkalinity, and nutrients to evaluate their contribution to the mean state, depth pattern, and seasonal cycle of ocean acidification, as measured by the aragonite saturation state. Riverine alkalinity generally mitigates acidification, whereas organic carbon from coastal erosion intensifies it. Nutrients from both sources mitigate ocean acidification at the surface by stimulating primary production, but intensify it at depth through subsequent remineralisation. Together, riverine and erosion-derived inputs account for about 20–40 % of the seasonal variability in the saturation state of the surface ocean. This amplification of the natural seasonal cycle is primarily caused by an increase in the summertime maximum of the saturation state. Terrigenous inputs also reduce the Arctic Ocean’s capacity to absorb atmospheric CO2 by 17–25 %. Accurately representing carbon and nutrient inputs from rivers and coastal erosion in biogeochemical models is therefore important for reliable assessments of ocean acidification, ecosystem health, and carbon budgets in the Arctic Ocean.
Continue reading ‘Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification’Posts Tagged 'Arctic'
Contrasting effects of river and erosion-derived inputs on Arctic Ocean acidification
Published 18 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, modeling, regionalmodeling
High vertical resolution measurements of pH, pCO2, total alkalinity, and dissolved inorganic carbon using a new approach: the carbonate profiler
Published 4 March 2026 Science ClosedTags: Arctic, Baltic, chemistry, field, methods
The equilibrium between the different parameters of the marine carbonate system–dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2, and pH–is the core of ocean acidification studies, evaluation of inorganic carbon inventory, and air-sea CO2 fluxes. To date, it has been challenging to simultaneously measure all those components in the water column due to different sampling methodologies, and especially in stratified waters, where sharp vertical biogeochemical gradients may occur. In this study, we designed a low-cost and easy-to-assemble pumping system, which, combined with a CTD profiler, makes a PUMP-CTD system that can efficiently serve as a precise water column sampler, allowing for simultaneous measurements and sampling of dissolved inorganic carbon, total alkalinity, partial pressure of CO2, and pH with high vertical resolution. Importantly, this water sampler (denoted as the carbonate profiler) can be easily integrated with equilibrator-based continuous pCO2 measurement systems, which are routinely used for underway data acquisition, making them suitable for water column sampling as well. We tested the carbonate profiler in the open ocean water column, where we obtained excellent consistency between measured pCO2 and calculated values based on pH and DIC. Afterwards, we tested the operability of the system by measuring the vertical variability of all the components of the marine carbonate system in the Vistula River estuarine waters (southern Baltic Sea) and within the Arctic fjords affected by continental freshwater runoff. Overall, this system performed outstandingly, with a vertical resolution of half a meter, proving its utility in accurately measuring steep biogeochemical changes in the water column regardless of the analytical method used.
Continue reading ‘High vertical resolution measurements of pH, pCO2, total alkalinity, and dissolved inorganic carbon using a new approach: the carbonate profiler’Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations
Published 3 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, methods
While total alkalinity (AT) is traditionally attributed to dissolved inorganic constituents, dissolved organic matter (DOM) can significantly contribute to AT as organic alkalinity (OrgAlk), introducing errors in calculated carbonate parameters, such as the CaCO3 saturation state (Ω) and partial pressure of CO2 (pCO2). This study presents measurements of OrgAlk in the Arctic Ocean sea ice system and assesses its influence on carbonate speciation, with OrgAlk contributing 0.1–1.0% to AT. Sea ice brine exhibited elevated DOM and OrgAlk, with an OrgAlk/DOC ratio of 0.13 ± 0.06 µmol kg− 1 µM− 1, consistent with global ocean values. Correcting AT for OrgAlk increased computed pCO2 up to 84 µatm and decreased Ω ≤ 0.2 for aragonite and ≤ 0.3 for calcite compared to un-adjusted values. Elevated brine pCO2 suggests that conventional estimates of Arctic sea ice CO2 uptake may be overestimated when AT is used as an input parameter, particularly in spring as OrgAlk is released. The omission of OrgAlk contributed greater errors to calculated carbonate parameters than the differences in boron from using direct measurements versus salinity based ratios, highlighting the necessity of accounting for even minor OrgAlk to refine predictions of surface pCO2, net air-sea CO2 flux, and the fate of CaCO3 minerals.
Continue reading ‘Neglecting organic alkalinity introduces greater error than assuming boron to salinity ratios in Arctic sea ice brine carbonate system calculations’Ocean acidification and changes in biological production in the western subarctic region of the North Pacific over the quarter century, 1999–2023
Published 2 March 2026 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, North Pacific
Changes in the physical and biogeochemical conditions of the ocean over time can affect marine ecosystems. In this study, we use biogeochemical observational data for the past 25 years (1999–2023) to investigate ocean acidification and changes in biological production at site K2 (47˚ N, 160˚ E) in the western subarctic region of the North Pacific Ocean. During this period, satellite-derived sea surface temperatures increased at a rate of 0.056 °C yr–1, while the surface mixed-layer salinity decreased by 0.004 yr−1. As a result of the oceanic uptake of anthropogenic CO2 from the atmosphere, the deseasonalized annual mean surface mixed-layer pH and saturation states of calcium carbonate minerals of calcite and aragonite decreased at rates of 0.0013 ± 0.0004, 0.007 ± 0.003, and 0.004 ± 0.002 yr−1, respectively. These rates are consistent with those calculated for winter. Under these acidification conditions, no significant trends were observed in either the annual mean or winter concentrations of nutrients (phosphate, nitrate, and silicate), or in total alkalinity in the surface mixed layer. However, the decadal trends in nutrient concentrations show a significant increase in May and decrease in July. Net community production (NCP), which is an index of biological production, was estimated from differences in nutrient concentrations between winter and May or July. This analysis revealed significant decreasing trends in NCP from winter to May, followed by increasing trends from winter to July. The stoichiometric molar ratio of Si associated with the July NCP increase (P:N:Si = 1:15:55) is higher than the previously reported ratio (1:16:40). A significant decreasing trend in satellite-derived photosynthetically active radiation (PAR) was observed in May (0.20 ± 0.08 yr−1), which may be linked to reduced biological production during that month. This decrease may be offset by increased production in summer that is likely due to a shift in the timing of the diatom bloom. These findings highlight the effects of long-term changes of potential drivers of both atmospheric and deep oceanic origin on oceanic biological production.
Continue reading ‘Ocean acidification and changes in biological production in the western subarctic region of the North Pacific over the quarter century, 1999–2023’The internal consistency between calculated and measured variables of the marine carbonate system in Arctic open and coastal waters, case study: Atlantic Arctic
Published 21 January 2026 Science ClosedTags: Arctic, chemistry, field, methods
Highlights
- Good consistency between calculated and measured variables of the marine carbonate system in Oceanic waters.
- Only pH and pCO2 can be calculated with good accuracy in coastal waters.
- The nutrient data are not required to calculate accurate marine carbonate system data in this region.
- Total Alkalinity and pH (or pCO2) can be used to obtain good quality pCO2 (or pH) data.
Abstract
The Arctic Ocean plays a crucial role in anthropogenic carbon sequestration, while also being among the regions most susceptible to Ocean Acidification (OA). To understand, quantify, and monitor the rapid biogeochemical changes in the Arctic shelves and coastal waters, it is necessary to accurately determine the complete marine carbonate system. However, the uncertainty range in the calculated values is still unclear, fogging our ability to properly estimate carbon inventory and OA. In this study, we collected samples in the Arctic open and coastal waters to estimate the internal consistency of total alkalinity (TA), pH, partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) when only two of them are measured and the other two calculated. In open ocean waters, calculated values generally show good consistency with observations, whereas in coastal areas, it was only possible to accurately calculate two variables: 1) pH using as input parameters pCO2 together with either TA or DIC, and 2) pCO2 using DIC and pH. Furthermore, we found that, in this dataset, using the TA estimated from its correlation with salinity together with pCO2 also allowed obtaining accurate pH values in both coastal and ocean waters. This opens a new possibility of monitoring changes in the carbon cycle by measuring only salinity and pCO2 in areas where its consistency has been evaluated. Finally, in this study, we provide guidelines for obtaining and reporting good-quality carbonate system data in Arctic coastal areas.
Continue reading ‘The internal consistency between calculated and measured variables of the marine carbonate system in Arctic open and coastal waters, case study: Atlantic Arctic’Combined effects of ocean acidification, warming, and salinity on the fertilization success in an Arctic population of sea urchins
Published 9 January 2026 Science ClosedTags: Arctic, biological response, echinoderms, laboratory, multiple factors, reproduction, salinity, temperature
Anthropogenic stressors, including ocean acidification (OA), ocean warming (OW), and salinity changes, are rapidly altering marine ecosystems, with Arctic regions being particularly vulnerable. This study investigates the combined effects of these stressors on the fertilization success of the green sea urchin (Strongylocentrotus droebachiensis) from Kongsfjorden, Svalbard. We exposed gametes to various levels of pH, temperature, and salinity to assess their individual and combined impacts on fertilization performance. Our results show that temperature and pH significantly influenced fertilization success, with temperature having the strongest effect, while salinity had no significant impact. A significant statistical interaction between temperature and pH indicated that warming enhanced fertilization more effectively at higher pH levels, while low pH suppressed this increase. To compare the relative influence of each stressor, we used a conceptual model based on standardized slopes, which supported temperature as the dominant driver, followed by pH. These findings highlight the importance of considering the effects of combined stressors when assessing marine organism responses to climate change, especially in polar ecosystems. Our study underscores the need for further research into the mechanisms driving these combined effects, given that Arctic ecosystems face accelerated environmental changes.
Continue reading ‘Combined effects of ocean acidification, warming, and salinity on the fertilization success in an Arctic population of sea urchins’Stressed overwintering bottleneck hypothesis: ocean warming and acidification synergistically disrupt Arctic zooplankton overwintering
Published 1 December 2025 Science ClosedTags: Arctic, biological response, crustaceans, laboratory, molecular biology, mortality, multiple factors, physiology, reproduction, respiration, temperature, zooplankton
Ocean warming (OW), driven by the influx of warm Atlantic water masses, and acidification (OA) are threatening Arctic marine ecosystems. However, their potential synergistic effects are poorly understood, especially during the Polar Night when marine species are particularly vulnerable to stressors. Here, we tested our novel Stressed Overwintering Bottleneck Hypothesis (SOBH): warming will disrupt the overwintering of the keystone pan-Arctic copepod Calanus glacialis, a pivotal secondary producer, by impairing fitness-related traits underpinning survival and reproduction. We exposed C. glacialis to current and projected future OW levels (0 °C and 4 °C) and OA levels (pH 8.0 and 7.4-7.3) for 53 days during the mid-Arctic Polar Night. We assessed survival, development, and physiological and molecular mechanisms (oxygen consumption, lipid depletion, the expression of nine targeted genes related to oxidative stress and damage repair, and DNA damage). OW alone did not affect C. glacialis mortality; however, OA increased copepod survival at 0 °C. Notably, their combined effects (OWA) synergistically doubled mortality, as predicted by SOBH. Warming also accelerated moulting from copepodite stage V to adulthood in December, and increased respiration, exhausted lipid reserves entirely by early March, approximately one to four months before the spring algal bloom, further supporting SOBH. DNA damage and gene expression patterns indicated low investment in maintenance and damage repair. Collectively, these findings reveal hidden mechanisms by which OW and OA synergistically threaten overwintering Calanus copepods by drastically increasing mortality, accelerating moulting, raising metabolic rates, and causing early lipid depletion. These effects generate cross-seasonal phenological mismatches among overwintering survival, energy reserves, reproduction, and primary production. Such stressed overwintering bottlenecks in foundational secondary producers like Calanus copepods provide novel explanations for how OW and OA can constrict Arctic marine food webs. At a broader perspective, SOBH highlights how multiple stressors induced overwintering disruption could reshape pan-Arctic and global biodiversity.
Continue reading ‘Stressed overwintering bottleneck hypothesis: ocean warming and acidification synergistically disrupt Arctic zooplankton overwintering’Model based analysis of the methane seeping influence on the acidification in the East Siberian Arctic Shelf waters
Published 4 September 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, modeling, regionalmodeling
A giant Arctic subsea permafrost reservoir of methane (CH4) in different forms (hydrates, free gas) is leaking, likely at an increasing rate under climate warming. This is causing a massive CH4 release from sediments into the water column and atmosphere. A part of the released CH4 is oxidized in the water column to CO2. In this work we applied a model for analyzing of consequences for the water column carbonate system of excessive production of CO2 during the aerobic oxidation of CH4 in an area of its intensive seeping in the East Siberian Arctic Shelf (ESAS). The model system comprised a 2-Dimensional vertical Benthic Pelagic transport Model 2DBP, principal biogeochemistry and carbonate system modules from the biogeochemical model BROM (Bottom RedOx Model), and a gas bubble fate module that parameterizes bubbles rising and dissolution. The simulations showed that consumption of oxygen and production of carbon dioxide via aerobic oxidation of methane results in spatial anomalies of pH and dissolved oxygen concentration that are consistent with the field observations. We hypothesize that aerobic oxidation of methane in the regions of intensive seeping leads to production of CO2, with associated decrease of pH and lowering of aragonite saturation to less than 1, therefore contributing to the extreme acidification states that are observed on the East Siberian Arctic Shelf.
Continue reading ‘Model based analysis of the methane seeping influence on the acidification in the East Siberian Arctic Shelf waters’Glacial meltwater increases coastal carbon dioxide uptake and sensitivity to biogeochemical change
Published 28 August 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, modeling, regionalmodeling
The accelerating melt of the Greenland Ice Sheet is releasing large volumes of freshwater into the coastal ocean, diluting seawater alkalinity. Biogeochemical processes such as photosynthesis, respiration, and sediment mineral dissolution also shape carbon dynamics in these freshened waters, but their combined influence on the ocean’s carbon pump remains unresolved. Here we isolate the chemical effects of meltwater dilution through a controlled seawater-freshwater mixing experiment, providing empirical evidence for nonlinear reduction in the partial pressure of carbon dioxide (pCO2). Carbonate system modeling revealed the mechanisms behind this nonlinearity, helping to explain 17 years of low pCO2 in a Greenlandic fjord. Sensitivity analysis shows that the influence of biogeochemical processes is fundamentally shaped by the chemical environment in which they operate. Freshwater input reduces buffering capacity and therefore amplifies the system’s sensitivity to biological activity and acidification. Our findings highlight how meltwater amplifies biogeochemical control of pCO2 in Arctic coastal systems.
Continue reading ‘Glacial meltwater increases coastal carbon dioxide uptake and sensitivity to biogeochemical change’Temperature and CO2 alter trophic structure of Arctic plankton assemblages
Published 27 August 2025 Science ClosedTags: Arctic, biological response, BRcommunity, growth, laboratory, multiple factors, performance, phytoplankton, temperature, zooplankton
Driven by increasing anthropogenic CO2, the impact of ongoing climate change on the marine plankton ecosystem ultimately extends to higher trophic levels and the biogeochemical cycling of carbon and nutrients. However, the impacts of multiple environmental changes on trophic interactions between predator and prey have still not been fully explored. Here we conducted incubation experiments to determine the temperature and CO2 sensitivities of marine phytoplankton growth and microzooplankton grazing in the western Arctic Ocean, where rapid climate change is taking place. The temperature sensitivity of the growth of larger phytoplankton decreased owing to the increase in CO2 levels, whereas that of the growth of smaller phytoplankton increased under higher CO2 levels. Notably, the temperature sensitivity of Arctic phytoplankton is at least two times higher than the canonical estimates irrespective of size classes, highlighting the uniqueness of the Arctic ecosystem’s response to warming. Microzooplankton grazing was closely coupled with, but did not exceed, the growth rates of their prey, suggesting that microzooplankton behavior is mainly regulated by prey availability rather than the ambient environment. The higher competitiveness of smaller phytoplankton under higher temperatures and CO2 conditions might lead to a less productive Arctic Ocean ecosystem for higher trophic-level organisms in the future.
Continue reading ‘Temperature and CO2 alter trophic structure of Arctic plankton assemblages’Unraveling ocean pCO2 dynamics in northwest Greenland fjords
Published 19 August 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field
We investigated the relative contributions of various factors that influence seasonal changes in sea surface partial pressure of CO2 (pCO2, calculated from the measured pH and total alkalinity) in four regions of northwestern Greenland: Nares Strait, Lincoln Sea, Sherard Osborn and Petermann fjords. Using the temperature minimum layer as a proxy for winter conditions, we examined pCO2 dynamics from the onset of sea-ice melt to summer. Our findings revealed significant spatial variability in pCO2, driven by differences in temperature, freshwater inputs, and biological activity. In particular, in Sherard Osborn Fjord substantial freshwater inputs and strong stratification were found to enhance pCO2 accumulation, while in Petermann Fjord biological CO2 uptake was the main driver. This study, conducted in summer 2019, underscores the critical role of northwest Greenland’s coastal waters as a summer CO2 sink. It highlights the complex interplay of physical and biogeochemical processes in modulating pCO2, suggesting significant regional differences in CO2 dynamics between two neighboring fjords.
Continue reading ‘Unraveling ocean pCO2 dynamics in northwest Greenland fjords’Assessing vulnerability of Arctic fish species to climate change
Published 12 August 2025 Science ClosedTags: Arctic, biological response, communitymodeling, fish, modeling, review
Climate change is impacting Arctic marine ecosystems at faster rates than the global average, challenging the management and conservation of biodiversity and living marine resources. This study examined the climate risks and vulnerabilities of 21 Arctic fish species occurring in the western Canadian Arctic using a fuzzy logic approach. Identified climatic hazards to marine species and their habitats are increasing temperature, decreasing sea ice cover, freshening, decreasing oxygen concentration, and acidification. The nature of these hazards included changes in mean conditions by 2050 (2041–2060), compared to the historical period (1979–2015 average) simulated from a regional coupled ice-ocean biogeochemical model and two coupled Earth system models under low and high emissions scenarios. A spatially-explicit algorithm was used to assess the risk and vulnerability in the Beaufort Sea shelf and slope and Amundsen Gulf (BS–AG) based on the species’ biological traits, biogeography and their exposure to climatic hazards. The results indicated high to very high exposure and risk of climate impacts across the ecosystem variables. Specifically, shallow areas were projected to be simultaneously exposed to more intense warming, reduced sea ice coverage, freshening, and acidification relative to the regional averages. In addition, for species occurring in the BS–AG, low adaptability and high sensitivity to climate hazards was identified. These applied tools and evaluations can inform marine spatial planning and climate adaptation efforts to help achieve conservation objectives and sustain ecosystem and community health in a changing Arctic climate.
Continue reading ‘Assessing vulnerability of Arctic fish species to climate change’Larval Arctic cod (Boreogadus saida) exhibit stronger developmental and physiological responses to temperature than to elevated pCO2
Published 10 July 2025 Science ClosedTags: Arctic, biological response, fish, growth, laboratory, morphology, mortality, multiple factors, physiology, reproduction, temperature
High-latitude ecosystems are simultaneously warming and acidifying under ongoing climate change. Arctic cod (Boreogadus saida) are a key species in the Arctic Ocean and have demonstrated sensitivity to ocean warming and acidification as adults and embryos, but their larval sensitivity to the combined stressors is unknown. In a laboratory multistressor experiment, larval Arctic cod were exposed to a combination of three temperatures (1.8, 5 and 7.3°C) and two carbon dioxide (pCO2) levels (ambient: 330 μatm, high: 1470 μatm) from hatching to 6-weeks of growth. Mortality rates were highest at 7.3°C (5% day°1); however, both growth and morphometric-based condition were also highest at this temperature. When these metrics were assessed via a mortality: growth (M:G) ratio, 5°C appeared to be an optimal temperature for net population biomass, as faster growth at 7.3°C did not fully compensate for higher mortality. In contrast, although morphometric-based condition was lowest at 1.8°C, lipid-based condition was highest, which may reflect prioritization of lipid storage at cold temperatures. The capacity of larval Arctic cod to acclimate to a range of temperatures was exhibited by two lipid-based indicators of membrane fluidity, including a ratio of unsaturated to saturated fatty acids and a ratio of polar lipids to sterols. The effects of elevated pCO2 were subtle, as well as temperature- and metric dependent. When exposed to elevated pCO2 levels, Arctic cod at 1.8°C exhibited signs of lipid dysregulation, suggesting potential interference with membrane acclimation; larvae at 5°C were in lower morphometric-based condition; and larvae at 7.3°C had higher activity eicosanoid substrates, indicating possible physiological stress. Overall, Arctic cod physiological response to temperature variation was more pronounced than their response to elevated pCO2. Future projections of pCO2 effects on Arctic cod health in a warming ecosystem will need to consider the complexity of temperature-dependence and the specificity of multiple physiological responses.
Continue reading ‘Larval Arctic cod (Boreogadus saida) exhibit stronger developmental and physiological responses to temperature than to elevated pCO2’Current state of ocean acidification in surface waters of the western Arctic Ocean from 2020 to 2022
Published 6 June 2025 Science ClosedTags: Arctic, chemistry, field
The aragonite saturation state (Ωarag) was determined for surface waters of the western Arctic Ocean over 3 years, from 2020 to 2022, to investigate the current state of ocean acidification and to assess the interannual variation in surface Ωarag. In the Chukchi marginal area (CMA), surface Ωarag ranged from 0.97 to 1.86 over 3 years, with an average value of 1.20, indicating near-saturated conditions with respect to aragonite. In the East Siberian marginal area (ESMA), surface Ωarag varied from 0.88 to 1.47, with an average value of 1.12, which was slightly lower than levels in the CMA. The ESMA experienced significant changes in environmental conditions and seawater carbonate chemistry during 2020–2022 compared to 2016–2018. These notable changes in the ESMA during 2020–2022 were attributed to the influence of the Beaufort Gyre. In contrast, the CMA showed little interannual variation in environmental conditions and seawater carbonate chemistry from 2016 to 2022. In the ESMA, the progression of ocean acidification depends on the Arctic Oscillation (AO) state; ocean acidification improves with a positive AO state and worsens when the AO state is negative.
Continue reading ‘Current state of ocean acidification in surface waters of the western Arctic Ocean from 2020 to 2022’Influences of global warming and upwelling on the acidification in the Beaufort Sea
Published 7 March 2025 Science ClosedTags: Arctic, chemistry, modeling, regionalmodeling
Over the past three decades, increasing atmospheric CO2 (AtmCO2) has led to climate warming, sea ice reduction and ocean acidification in the Beaufort Sea (BS). Additionally, the effects of upwelling on the carbon cycle and acidification in the BS are still unknown. The Regional Arctic System Model (RASM) adequately reflects the observed long-term trends and interannual variations in summer sea ice concentration (SIC), temperature, partial pressure of CO2 (pCO2) and pH from 1990 to 2020. Multiple linear regression results from a control case show that surface (0–20 m) pH decline is significantly driven by AtmCO2 and SIC, while AtmCO2 dominates in subsurface (20–50 m) and deep layers (50–120 m). Regression results from a sensitivity case show that even if the AtmCO2 concentration remained at 1990 levels, the pH would still exhibit a long-term decline trend, being significantly driven by SIC only in the surface layers and by SIC and net primary production (NPP) in the subsurface layers. In contrast to the nearly linearly increasing AtmCO2 over the last three decades, the ocean pH shows more interannual variations that are significantly affected by SIC and mixed layer depth (MLD) in the surface, NPP and Ekman pumping velocity (EPV) in the subsurface and EPV only in the deep layer. The comparison of results from high and low SIC years reveals that areas with notable pH differences are overlapping regions with the largest differences in both SIC and MLD, and both cause a statistically significant increase in pCO2 and decrease in pH. Comparison of results from high and low EPV years reveals that although stronger upwelling can lift up more nutrient-rich seawater in the subsurface and deep layers and lead to higher NPP and pH, this effect is more than offset by the higher DIC lifted up from deep water, leading to generally lower pH in most regions.
Continue reading ‘Influences of global warming and upwelling on the acidification in the Beaufort Sea’Pacific-Arctic ocean acidification: decadal trends and drivers
Published 28 February 2025 Science ClosedTags: Arctic, chemistry, field, review
This study presents the first regional-scale analysis to quantify decadal trends and drivers of surface ocean acidification (OA) across the highly sensitive Pacific-Arctic Region (PAR) using a consistent trend methodology. From 1993 to 2021, the Southern PAR acidified at rates comparable to the global average, with pHT declining by 0.018 units dec−1 and aragonite saturation state (ΩAr) decreasing by 0.063 units dec−1, primarily driven by anthropogenic CO2 uptake. In contrast, the Bering Strait exhibited slower acidification, with pHT declining by 0.011 units dec−1 and ΩAr decreasing by 0.020 units dec−1 — substantially lower than previously reported — likely due to increased primary productivity. The Northern PAR experienced the most rapid acidification: pHT decreased by 0.028 units dec−1 and ΩAr by 0.078 units dec−1, with the Beaufort Gyre acidifying 2–4 times faster than the global mean. This rapid change was driven by rising atmospheric CO2 and significant freshening linked to sea ice melt and increased riverine input, which reduced the ocean’s buffering capacity. Continued warming will likely exacerbate acidification in regions transitioning from multi-year to seasonal ice. While local processes such as primary productivity can temporarily counteract OA, whether they can offset rising anthropogenic CO2 levels remains unclear. This underscores the importance of biogeochemical models that integrate climatic and biological feedbacks, enabling accurate forecasts of OA changes and their impacts on marine ecosystems. These findings highlight the urgent need for sustained monitoring in the PAR, where accelerating changes threaten critical ecosystems.
Continue reading ‘Pacific-Arctic ocean acidification: decadal trends and drivers’Vertical expansion of aragonite undersaturated waters in the Canada Basin of the Arctic Ocean from 2003 to 2019
Published 25 February 2025 Science ClosedTags: Arctic, chemistry, field
Abstract
The Canada Basin of the Arctic Ocean is considered the region of the world’s open ocean most susceptible to the Ocean Acidification (OA). This study examines progression of OA in the Canada Basin, focusing on expansion of surface and subsurface aragonite undersaturated waters (USW). Surface USW thickness increased from 0 m in 2003 to 19 ± 2 m in 2019. This change was due to freshening until 2012, and then due to increased uptake of anthropogenic CO2 after 2012. In the subsurface layer, USW thickness increased from 94 ± 6 m in 2003 to 136 ± 11 m in 2019. This change is primarily attributed to OA in upstream shelf regions, driven by increased CO2 uptake and respiration, with some contribution from thickening in the Pacific Winter Water layer. The combined thickening of surface and subsurface USW layers increased the percentage of USW in the 0–250 m water column from 38 ± 3% in 2003 to 62 ± 5% in 2019. Because of the concurrent deepening of the water masses due to the enhanced Beaufort Gyre, the replacement of oversaturated water to USW occurred mostly at the subsurface layer below 190 m. The thickness of the oversaturated layer between surface and subsurface USWs remained almost unchanged. If Beaufort Gyre weakens in the future, it would bring subsurface USW shallower, potentially affecting marine life.
Key Points
- Long-term observations revealed expansion of aragonite undersaturated waters (USW) in the Canada Basin of the Arctic Ocean
- Increase in USW thickness was mainly due to physical processes in the earlier period and biogeochemical processes in the later period
- Although USW thickened in surface and subsurface layers, the thickness of the oversaturated layer between them did not change
Plain Language Summary
The Canada Basin of the Arctic Ocean is particularly vulnerable to a process called Ocean Acidification (OA), which makes the water less suitable for marine life. This study focuses on how OA has been changing in this area, especially the expansion of certain types of problematic water (called “aragonite undersaturated waters” or USW) in the surface and subsurface layers. At the surface, this less hospitable USW has become thicker, going from essentially nothing in 2003 to 19 ± 2 m deep in 2019. This change was due to the water becoming less salty (freshening) and increased absorption of carbon dioxide (CO2). In the subsurface layer, USW also got thicker, increasing from 94 ± 6 m in 2003 to 136 ± 11 m in 2019. This happened because of OA driven by more atmospheric CO2 absorption and increased respiration in the upstream shallow shelf areas. The combined increase in the thickness of these surface and subsurface USW layers means that a larger portion of the water now consists of this less hospitable USW, going from 38 ± 3% in 2003 to 62 ± 5% in 2019. If physical conditions change in the future, the less suitable subsurface water would be brought closer to the surface, potentially impacting marine life.
Continue reading ‘Vertical expansion of aragonite undersaturated waters in the Canada Basin of the Arctic Ocean from 2003 to 2019’Influences on chemical distribution patterns across the west Greenland shelf: the roles of ocean currents, sea ice melt, and freshwater runoff
Published 19 February 2025 Science ClosedTags: Arctic, chemistry
The west Greenland shelf is a dynamic marine environment influenced by various physicochemical and biological processes. This study provides an overview of the main factors affecting the distribution of macronutrients, carbonate system parameters, and dissolved trace elements during late summer. Key drivers include major ocean currents, melting sea ice, and terrestrial freshwater runoff, each uniquely contributing to the cycling and spatial distribution of chemical constituents. Major ocean currents, such as the southward-moving Baffin Island Current (BIC) and the northward-moving West Greenland Current (WGC), shape the chemical composition of shelf waters by introducing water masses with distinct chemical signatures. Melting sea ice is an important source of freshwater and dissolved constituents for the marine environment. The east-to-west direction of sea ice retreat creates nutrient gradients, with low nutrient levels in highly productive shelf waters and high nutrient levels in areas with prolonged ice cover. This process also affects the carbonate system, leading to changes in pH and aragonite saturation states, which is critical for the health of marine organisms. Terrestrial freshwater runoff, particularly from the Greenland Ice Sheet (GIS), replenishes macronutrients in the photic zone, stimulating primary production and creating important CO2 sinks. However, surface waters become more susceptible to acidification by the input of poorly buffered glacial freshwater. Understanding these key drivers is essential for forecasting future changes in the marine chemistry and biology of the west Greenland shelf, especially in the context of ongoing climate change within this high-latitude region.
Continue reading ‘Influences on chemical distribution patterns across the west Greenland shelf: the roles of ocean currents, sea ice melt, and freshwater runoff’Carbon cycling and ocean acidification studies in Baffin Bay and Nares Strait
Published 20 January 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field, modeling, regionalmodeling
The marine carbon cycle in Canadian Arctic waters, particularly in Nares Strait and Baffin Bay, is undergoing rapid change due to a shifting climate. Despite this, there’s been a paucity of research into the carbonate chemistry and biogeochemical processes in these regions. This thesis addresses this gap by investigating the complex carbon dynamics in these waters, critical for understanding their role in the global carbon cycle. The first research chapter evaluates the strength of the biological carbon pump during the spring ice-edge bloom in Baffin Bay. We found stark differences in springtime net community production (NCP) between Arctic and Atlantic water domains, in western and eastern Baffin Bay, respectively. Arctic outflow waters exhibited low spring NCP (< 1 mol C m-2) due to persistent sea-ice cover and strong stratification of the upper water column, whereas the Atlantic water domain displayed high NCP rates (up to 5.7 mol C m-2). The first comprehensive examination of the marine carbon dynamics in Nares Strait is also presented. Using a multi-tracer linear mixing model, we distinguished the role of physical and biological processes on the distribution of dissolved inorganic carbon in Nares Strait. We identified water mass mixing as the dominant control on marine carbon dynamics, with primary production also playing an important role in decreasing surface pCO2. Importantly, this investigation also provided the first documented evidence of Siberian river waters arriving in Nares Strait. The final research chapter of this thesis investigates the biogeochemical processes affecting aragonite saturation states (ΩAr), and the state of ocean acidification in Baffin Bay, with a focus on the west Greenland continental shelf region, which has remained under-studied in terms of its marine biogeochemistry. We identify two main depth-dependent processes shaping the ΩAr distribution throughout Baffin Bay; within the upper 200 metres, lower ΩAr coincides with increasing fractions of Arctic-outflow waters, while below 200 metres organic matter respiration is responsible for decreasing ΩAr. Surprisingly, substantial Arctic-outflow waters were identified on the west Greenland shelf, challenging what is currently known of circulation patterns in the bay, and underscoring the need for further research.
Continue reading ‘Carbon cycling and ocean acidification studies in Baffin Bay and Nares Strait’The contrasting role of marine- and land-terminating glaciers on biogeochemical cycles in Kongsfjorden, Svalbard
Published 15 January 2025 Science ClosedTags: Arctic, biogeochemistry, chemistry, field
This case study of Kongsfjorden, western coastal Svalbard, provides insights on how freshwater runoff from marine- and land-terminating glaciers influences the biogeochemical cycles and distribution patterns of carbon, nutrients, and trace elements in an Arctic fjord system. We collected samples from the water column at stations along the fjord axis and proglacial river catchments, and analyzed concentrations of dissolved trace elements, together with dissolved nutrients, as well as alkalinity and dissolved inorganic carbon. Statistical tools were applied to identify and quantify biogeochemical processes within the fjord that govern the constituent distributions. Our results suggest that the glacier type affects nutrient availability and, therefore, primary production. Glacial discharge from both marine-terminating glaciers and riverine discharge from land-terminating glaciers are important sources of dissolved trace elements (dAl, dMn, dCo, dNi, dCu, and dPb) that are involved in biological and scavenging processes within marine systems. We identified benthic fluxes across the sediment-water interface to supply fjord waters with silicate, dFe, dCu, and dZn. Our data show that intensive carbonate weathering in proglacial catchments supplies fjord waters with additional dissolved carbonates and, therefore, attenuates reduced buffering capacities caused by glacial runoff. Our study provides valuable insight into biogeochemical processes and carbon cycling within a climate-sensitive, high-latitude fjord region, which may help predict Arctic ecosystem changes in the future.
Key Points
- Nutrient, trace element, and carbon species distributions are influenced by glacial discharge of land- and marine-terminating glaciers
- Discharge of marine- and land-terminating glaciers is an important source of bio-essential trace elements
- Progressive glacier retreat will likely impact biotic and abiotic carbon uptake in the future
Plain Language Summary
Arctic regions are particularly vulnerable to climate change and are considerably influenced by anthropogenic impacts. However, the scientific community currently lacks sufficient information on the mechanisms and drivers of these environmental changes, and the consequences that may arise for Arctic ecosystems. Our study provides insights into the distribution patterns of carbon, nutrients, and trace elements in fjord systems influenced by freshwater supply from melting glaciers. We collected water samples from the water column of Kongsfjorden (Svalbard, Norway) and from glacier-fed rivers draining into the fjord. Our results show that freshwater from glaciers is an important source of nutrients, and trace elements that are involved in biological processes within coastal areas. In the future, we predict Arctic fjords will become less productive ecosystems, as a result of the progressive melting and glacier retreat. Ultimately, this has the potential to alter the circulation of water masses and consequently change the redistribution of nutrients and essential trace elements in the water column.
Continue reading ‘The contrasting role of marine- and land-terminating glaciers on biogeochemical cycles in Kongsfjorden, Svalbard’
