Posts Tagged 'Arctic'

Author correction: contrasting drivers and trends of ocean acidification in the subarctic Atlantic

The Original Article was published on 07 July 2021

Correction to: Scientific Reports https://doi.org/10.1038/s41598-021-93324-3, published online 07 July 2021

The original version of this Article contained errors.

In Table 2 legend, the symbol of “picomol” was incorrectly given as “nanomol”.

“Average trends obtained with the seasonally detrended data the in situ temperature (T in °C yr−1), salinity (S in yr−1), Total Alkalinity (TA in µmol kg−1 yr−1), salinity-normalized alkalinity (nTA in µmol kg−1 yr−1), total dissolved inorganic carbon (DIC in µmol kg−1 yr−1), salinity-normalized dissolved inorganic carbon (nDIC in µmol kg−1 yr−1), in situ pH in total scale (pHT yr−1), total hydrogen ion concentrations ([H+]T in nanomol kg−1 yr−1), ion carbonate concentration excess over aragonite saturation (exCO3 = in µmol kg−1 yr−1), and anthropogenic CO2.”

now reads:

“Average trends obtained with the seasonally detrended data the in situ temperature (T in °C yr−1), salinity (S in yr−1), Total Alkalinity (TA in µmol kg−1 yr−1), salinity-normalized alkalinity (nTA in µmol kg−1 yr−1), total dissolved inorganic carbon (DIC in µmol kg−1 yr−1), salinity-normalized dissolved inorganic carbon (nDIC in µmol kg−1 yr−1), in situ pH in total scale (pHT yr−1), total hydrogen ion concentrations ([H+]T in picomol kg−1 yr−1), ion carbonate concentration excess over aragonite saturation (exCO3 = in µmol kg−1 yr−1), and anthropogenic CO2.”

Additionally, the article contains a repeated error where the symbol for “pmol” was incorrectly given as “nmol” in the Results section, under the subheading ‘Acidifcation drivers’, in Figure 6 legend, and in the Conclusions.

Furthermore, in Figure 6A and Supplementary Figure S5A “pmol” was incorrectly given as “nmol” in the y-axis. The original Figure 6 and accompanying legend, and Supplementary Information file appear below.

Acidification trends and drivers decomposition (T,S, nDIC and nTA) for the seasonally detrended average time series of total hydrogen ions concentration in pmol/kg/yr (Δ[H+]TA) and for excess of [CO3= ] over the [CO3= ] at aragonite saturation in µmol/kg/yr (Δex[CO3=]B). The nDIC driver trends is split in natural (nCnat) and anthropogenic components (nCanth). The colour code is shown on both panels.

The original Article and accompanying Supplementary Information file have been corrected.

Continue reading ‘Author correction: contrasting drivers and trends of ocean acidification in the subarctic Atlantic’

Ichnodiversity in the eastern Canadian Arctic in the context of polar microbioerosion patterns

Studies of marine microbioerosion in polar environments are scarce. They include our recent investigations of bioerosion traces preserved in sessile balanid skeletons from the Arctic Svalbard archipelago and the Antarctic Ross Sea. Here, we present results from a third study site, Frobisher Bay, in the eastern Canadian Arctic, together with a synthesis of our current knowledge of polar bioerosion in both hemispheres. Barnacles from 62 to 94 m water depth in Frobisher Bay were prepared using the cast-embedding technique to enable visualization of microboring traces by scanning electron microscopy. In total, six ichnotaxa of traces produced by organotrophic bioeroders were found. All recorded ichnotaxa were also present in Mosselbukta, Svalbard, and most in the Ross Sea. Frobisher Bay contrasts with Mosselbukta in that it is a siliciclastic-dominated environment and shows a lower ichnodiversity, which may be accounted for by the limited bathymetrical range and a high turbidity and sedimentation rate. We evaluate potential key ichnotaxa for the cold-temperate and polar regions, of which the most suitable are Flagrichnus baiulus and Saccomorpha guttulata, and propose adapted index ichnocoenoses for the interpretation of palaeobathymetry accordingly. Together, the three studies allow us to make provisional considerations about the biogeographical distribution of polar microbioerosion traces reflecting the ecophysiological limits of their makers.

Continue reading ‘Ichnodiversity in the eastern Canadian Arctic in the context of polar microbioerosion patterns’

Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning

Ocean acidification is a consequence of the absorption of anthropogenic carbon emissions and it profoundly impacts marine life. Arctic regions are particularly vulnerable to rapid pH changes due to low ocean buffering capacities and high stratification. Here, an unsupervised machine learning methodology is applied to simulations of surface Arctic acidification from two state-of-the-art coupled climate models. We identify four sub-regions whose boundaries are influenced by present-day and projected sea ice patterns. The regional boundaries are consistent between the models and across lower (SSP2-4.5) and higher (SSP5-8.5) carbon emissions scenarios. Stronger trends toward corrosive surface waters in the central Arctic Ocean are driven by early summer warming in regions of annual ice cover and late summer freshening in regions of perennial ice cover. Sea surface salinity and total alkalinity reductions dominate the Arctic pH changes, highlighting the importance of objective sub-regional identification and subsequent analysis of surface water mass properties.

Continue reading ‘Regional sensitivity patterns of Arctic Ocean acidification revealed with machine learning’

Editorial: acidification and hypoxia in marginal seas

Editorial on the Research Topic
Acidification and Hypoxia in Marginal Seas

Ocean acidification and hypoxia (dissolved oxygen <2 mg L−1 or <62 μmol L−1) are universal environmental concerns that can impact ecological and biogeochemical processes, including element cycling, carbon sequestration, community shifts, contributing to biodiversity reduction, and reducing marine ecosystem services (Riebesell et al., 2000Feely et al., 20042009Andersson et al., 2005Doney, 2006Cohen and Holcomb, 2009Doney et al., 20092020Kleypas and Yates, 2009Ekstrom et al., 2015Gattuso et al., 2015). While the stressors are global in their occurrence, local and regional impacts might be enhanced and even more accelerated, thus requiring even greater and faster consideration (Doney et al., 2020).

The driving mechanisms of acidification and hypoxia are inextricably linked in near-shore and coastal habitats. Along coastal shelf and its adjacent marginal seas, where the natural variability of multiple stressors is high, human-induced eutrophication is additionally enhancing both local acidification and hypoxia. For example, the well-known eutrophication of surface waters in the northern Gulf of Mexico caused hypoxic conditions that result in a pH decrease by 0.34 in the oxygen-depleted bottom water, which is significantly more than the pH decrease via atmospheric CO2 sequestration alone (pH decrease by 0.11; Cai et al., 2011). Similar changes in coastal conditions involving biological respiration and atmospheric CO2 invasion have also been observed in other marginal seas, urbanized estuaries, salt marshes and mangroves (Feely et al., 200820102018Cai et al., 2011Howarth et al., 2011). Other natural and anthropogenic processes, such as increased wind intensity and coastal upwelling, enhanced stratification due to global warming, along with more intense benthic respiration, more frequent extreme events, oscillation of water circulations, and variations in the terrestrial carbon and/or alkalinity fluxes, etc., all influence the onset and maintenance of acidification and/or hypoxia. For example, coastal upwelling brings both low pH and hypoxic water from below and enhances acidification and hypoxia in the coastal regions (Feely et al., 2008). Although acidification and hypoxia in the open oceans have received considerable attention already, the advances in our understanding of the driving mechanisms and the temporal evolution under global climate change is still poorly understood, particularly with respect to the region-specific differences, various scales of temporal and spatial variability, predictability patterns, and interactive multiple stressor impacts. Therefore, coastal ecosystems have a much broader range of rates of change in pH than the open ocean does (Carstensen and Duarte, 2019). The importance of understanding acidification and hypoxia for the biogeochemical and ecosystem implications in marginal seas is essential for climate change mitigation and adaptation strategy implementations in the future.

The scope of this Research Topic is to cover the most recent advances related to the status of acidification and hypoxia in marginal seas, the coupling mechanisms of multi-drivers and human impacts, ecosystem responses, prediction of their evolution over space and time, and under future climate change scenarios. The authors of this Research Topic contributed a total of 35 papers covering a wide variety of subjects spanning from acidification and/or hypoxia (OAH) status, the carbonate chemistry baseline and trends, the impacts of OAH on the habitat suitability and ecosystem implications, and the long-term changes and variability of OAH in marginal seas.

Continue reading ‘Editorial: acidification and hypoxia in marginal seas’

Impact of sea ice melting on summer air-sea CO2 exchange in the East Siberian Sea

The role of sea ice melting on the air-sea CO2 flux was investigated at two ice camps in the East Siberian Sea of the Arctic Ocean. On average, sea ice samples from the two ice camps had a total alkalinity (TA) of ∼108 and ∼31 μmol kg–1 and a corresponding salinity of 1.39 and 0.36, respectively. A portion (18–23% as an average) of these sea ice TA values was estimated to exist in the sea ice with zero salinity, which indicates the excess TA was likely attributed to chemical (CaCO3 formation and dissolution) and biological processes in the sea ice. The dilution by sea ice melting could increase the oceanic CO2 uptake to 11–12 mmol m–2 d–1 over the next 21 days if the mixed layer depth and sea ice thickness were assumed to be 18.5 and 1.5 m, respectively. This role can be further enhanced by adding TA (including excess TA) from sea ice melting, but a simultaneous release of dissolved inorganic carbon (DIC) counteracts the effect of TA supply. In our study region, the additional impact of sea ice melting with close to unity TA:DIC ratio on air-sea CO2 exchange was not significant.

Continue reading ‘Impact of sea ice melting on summer air-sea CO2 exchange in the East Siberian Sea’

A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans

We have estimated global air–sea CO2 fluxes (fgCO2) from the open ocean to coastal seas. Fluxes and associated uncertainty are computed from an ensemble-based reconstruction of CO2 sea surface partial pressure (pCO2) maps trained with gridded data from the Surface Ocean CO2 Atlas v2020 database. The ensemble mean (which is the best estimate provided by the approach) fits independent data well, and a broad agreement between the spatial distribution of model–data differences and the ensemble standard deviation (which is our model uncertainty estimate) is seen. Ensemble-based uncertainty estimates are denoted by ±1σ. The space–time-varying uncertainty fields identify oceanic regions where improvements in data reconstruction and extensions of the observational network are needed. Poor reconstructions of pCO2 are primarily found over the coasts and/or in regions with sparse observations, while fgCO2 estimates with the largest uncertainty are observed over the open Southern Ocean (44 S southward), the subpolar regions, the Indian Ocean gyre, and upwelling systems.

Our estimate of the global net sink for the period 1985–2019 is 1.643±0.125 PgC yr−1 including 0.150±0.010 PgC yr−1 for the coastal net sink. Among the ocean basins, the Subtropical Pacific (18–49 N) and the Subpolar Atlantic (49–76 N) appear to be the strongest CO2 sinks for the open ocean and the coastal ocean, respectively. Based on mean flux density per unit area, the most intense CO2 drawdown is, however, observed over the Arctic (76 N poleward) followed by the Subpolar Atlantic and Subtropical Pacific for both open-ocean and coastal sectors. Reconstruction results also show significant changes in the global annual integral of all open- and coastal-ocean CO2 fluxes with a growth rate of  PgC yr−2 and a temporal standard deviation of 0.526±0.022 PgC yr−1 over the 35-year period. The link between the large interannual to multi-year variations of the global net sink and the El Niño–Southern Oscillation climate variability is reconfirmed.

Continue reading ‘A seamless ensemble-based reconstruction of surface ocean pCO2 and air–sea CO2 fluxes over the global coastal and open oceans’

Particulate iron bioavailability to phytoplankton in Antarctic and Arctic waters: effects of ocean acidification and the organic ligand EDTA

Particulate iron (PFe) usually is not considered as a bioavailable iron fraction to phytoplankton. In this study we tested the bioavailability of one PFe species, goethite (α-FeO(OH)), to phytoplankton community in Southern Ocean under the effect of ocean acidification (OA) (pHT ca. 7.5) and representative concentration pathways (RCP) 8.5 condition (pCO2 ca. 1300 µatm), and to an Arctic diatom species, Nitzschia frigida, under the effect of the organic ligand, EDTA (using the commercially available salt disodium ethylenediaminetetraacetate dihydrate), as a chelator, respectively.

In March 2019, a natural phytoplankton community was sampled and used for the deck incubation experiment in the Southern Ocean. The sampling site was 68.10°S, 6.00° W, which was in the region of Queen Maud Land (Norwegian: Dronning Maud Land, DML). We observed marine biogeochemical performance of the phytoplankton community under OA. Different chemical and biological parameters during the incubation were determined, including dissolved iron (DFe), total acid leachable iron (TaLFe), macronutrients including nitrate (NO3-), phosphate (PO43-) and silicate, total pH (pHT), dissolved inorganic carbon (DIC), the concentration & fugacity of carbon dioxide (fCO2), chlorophyll a (Chla) concentration & in vivo fluorescence. The results show that the tested phytoplankton assemblage was more severely influenced by OA than iron bioavailability, especially under severe OA. Goethite, as one type of PFe, is insoluble under the tested OA scenarios. There could be PO43- remineralization in all treatments but species shift to diatoms only in ambient pH treatments (mild OA), which coincides with the judgement that OA impact is predominant in comparison to iron enrichment in this experiment. We should analyze phytoplankton species to test this hypothesis. OA can result in that phytoplankton launches Hv channel-mediated H+ efflux mechanism, carbon concentration mechanism (CCM) down-regulation of phytoplankton and the thriving of more tolerant species with more efficient CCM.

In April 2021, using an Arctic diatom species, Nitzschia frigida, we investigated the possibility of EDTA increasing goethite bioavailability to phytoplankton and photosynthetic performance by measuring relative electron transport rate (rETR) in the experiment performed at Trondheim Biological Station (Norwegian: Trondheim Biologiske Stasjon, TBS). The results show that elevating EDTA concentration can increase the bioavailability of goethite while decrease that of ferric chloride (FeCl3). This is inconclusive according to possibly negatively biased α (the slope of a typical P/E (photosynthesis/irradiance) curve), because it results in underestimation of goethite bioavailability under the influence of EDTA.

Further research regarding the combined effect of OA and EDTA on PFe bioavailability to phytoplankton is recommended.

Continue reading ‘Particulate iron bioavailability to phytoplankton in Antarctic and Arctic waters: effects of ocean acidification and the organic ligand EDTA’

Rapid acidification of the Arctic Chukchi Sea waters driven by anthropogenic forcing and biological carbon recycling

Abstract

The acidification of coastal waters is distinguished from the open ocean because of much stronger synergistic effects between anthropogenic forcing and local biogeochemical processes. However, ocean acidification research is still rather limited in polar coastal oceans. Here, we present a 17-year (2002-2019) observational dataset in the Chukchi Sea to determine the long-term changes in pH and aragonite saturation state (Ωarag). We found that pH and Ωarag declined in different water masses with average rates of -0.0047 ± 0.0026 year-1 and -0.017 ± 0.009 year-1, respectively, and are ∼2-3 times faster than those solely due to increasing atmospheric CO2. We attributed the rapid acidification to the increased dissolved inorganic carbon owing to a combination of ice melt-induced increased atmospheric CO2 invasion and subsurface remineralization induced by a stronger surface biological production as a result of the increased inflow of the nutrient-rich Pacific water.

Plain Language Summary

Anthropogenic CO2 absorbed by the ocean leads to a lower pH and the calcium carbonate saturation state (Ω) and threatens the marine ecosystems state of healthiness via a process called ocean acidification (OA). The Arctic Ocean is particularly sensitive to OA because more CO2 can be dissolved in cold water. This study used the observations collected over 17 years from 2002 to 2019 to estimate long-term trends of Ωarag and pH in the Chukchi Sea. The results show that rapid acidification occurred throughout all water masses from 2002-2019, leading to or approaching aragonite undersaturation. The rapid acidification is attributed to the enhanced increasing concentration of dissolved inorganic carbon. While sea ice melt induced uptake of anthropogenic CO2 partly explains the long-term acidification, the remainder is due to the increased nutrient-rich Pacific inflow water which promotes the high biological CO2 utilization in the surface waters but leads to stronger subsurface acidification due to the regenerated CO2. We suggest that the acidity in Chukchi Arctic Shelf waters will increase in the future if the increased inflow of Pacific water continues.

Continue reading ‘Rapid acidification of the Arctic Chukchi Sea waters driven by anthropogenic forcing and biological carbon recycling’

The distribution of pCO2W and air-sea CO2 fluxes using FFNN at the continental shelf areas of the Arctic Ocean

A feed-forward neural network (FFNN) was used to estimate the monthly climatology of partial pressure of CO2 (pCO2W) at a spatial resolution of 1° latitude by 1° longitude in the continental shelf of the European Arctic Sector (EAS) of the Arctic Ocean (the Greenland, Norwegian, and Barents seas). The predictors of the network were sea surface temperature (SST), sea surface salinity (SSS), the upper ocean mixed-layer depth (MLD), and chlorophyll-a concentration (Chl-a), and as a target, we used 2 853 pCO2W data points from the Surface Ocean CO2 Atlas. We built an FFNN based on three major datasets that differed in the Chl-a concentration data used to choose the best model to reproduce the spatial distribution and temporal variability of pCO2W. Using all physical–biological components improved estimates of the pCO2W and decreased the biases, even though Chl-a values in many grid cells were interpolated values. General features of pCO2W distribution were reproduced with very good accuracy, but the network underestimated pCO2W in the winter and overestimated pCO2W values in the summer. The results show that the model that contains interpolating Chl-a concentration, SST, SSS, and MLD as a target to predict the spatiotemporal distribution of pCO2W in the sea surface gives the best results and best-fitting network to the observational data. The calculation of monthly drivers of the estimated pCO2W change within continental shelf areas of the EAS confirms the major impact of not only the biological effects to the pCO2W distribution and Air-Sea CO2 flux in the EAS, but also the strong impact of the upper ocean mixing. A strong seasonal correlation between predictor and pCO2W seen earlier in the North Atlantic is clearly a yearly correlation in the EAS. The five-year monthly mean CO2 flux distribution shows that all continental shelf areas of the Arctic Ocean were net CO2 sinks. Strong monthly CO2 influx to the Arctic Ocean through the Greenland and Barents Seas (>12 gC m−2 day−1) occurred in the fall and winter, when the pCO2W level at the sea surface was high (>360 µatm) and the strongest wind speed (>12 ms−1) was present.

Continue reading ‘The distribution of pCO2W and air-sea CO2 fluxes using FFNN at the continental shelf areas of the Arctic Ocean’

Upper environmental pCO2 drives sensitivity to ocean acidification in marine invertebrates

Minimizing the impact of ocean acidification requires an understanding of species responses and environmental variability of population habitats. Whereas the literature is growing rapidly, emerging results suggest unresolved species- or population-specific responses. Here we present a meta-analysis synthesizing experimental studies examining the effects of pCO2 on biological traits in marine invertebrates. At the sampling locations of experimental animals, we determined environmental pCO2 conditions by integrating data from global databases and pCO2 measurements from buoys. Experimental pCO2 scenarios were compared with upper pCO2 using an index considering the upper environmental pCO2. For most taxa, a statistically significant negative linear relationship was observed between this index and mean biological responses, indicating that the impact of a given experimental pCO2 scenario depends on the deviation from the upper pCO2 level experienced by local populations. Our results highlight the importance of local biological adaptation and the need to consider present pCO2 natural variability while interpreting experimental results.

Continue reading ‘Upper environmental pCO2 drives sensitivity to ocean acidification in marine invertebrates’

Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction

The role of ocean acidification in the end-Permian mass extinction is highly controversial with conflicting hypotheses relating to its timing and extent. Observations and experiments on living molluscs demonstrate that those inhabiting acidic settings exhibit characteristic morphological deformities and disordered shell ultrastructures. These deformities should be recognisable in the fossil record, and provide a robust palaeo-proxy for severe ocean acidification. Here, we use fossils of originally aragonitic invertebrates to test whether ocean acidification occurred during the Permian–Triassic transition. Our results show that we can reject a hypothesised worldwide basal Triassic ocean acidification event owing to the absence of deformities and repair marks on bivalves and gastropods from the Triassic Hindeodus parvus Conodont Zone. We could not, however, utilise this proxy to test the role of a hypothesised acidification event just prior to and/or during the mass extinction event. If ocean acidification did develop during the mass extinction event, then it most likely only occurred in the latest Permian, and was not severe enough to impact calcification.

Continue reading ‘Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction’

Arctic planktonic calcifiers in a changing ocean – A study on recent planktonic foraminifera and shelled pteropods in the Fram Strait-Barents Sea region

The Arctic marine realm is being transformed due to the anthropogenically-induced climate change. In the Arctic, the effects of climate change are intensified due to polar amplification and have led to processes in the ocean such as sea-ice retreat, ocean acidification and the increased presence of boreal species referred to as ‘Atlantification’. This thesis presents rare investigations of marine calcifiers in the Fram Strait-Barents Sea region; planktonic foraminifera (Phylum Retaria) and the shelled pteropod Limacina helicina (Phylum Mollusca). There are few previous studies signifying several unknowns pertaining to their ecology and life cycles, and hence how they have and will continue to respond to climate change. The overarching aim of the thesis is to increase the knowledge of living planktonic foraminifera and pteropods in the Arctic, more specifically their distribution patterns, absolute and relative abundance, seasonality, diversity, ontogeny, and calcification. These studies are based on investigations from two dynamic areas; the Bjørnøyrenna Craters in the northern Barents Sea that is a site of intense methane seepage, and the Northeast Greenland Shelf where there is a rapid sea-ice reduction and interplay between Polar and Atlantic water masses. This thesis has shown that the Fram Strait-Barents Sea region is characterized by low species diversity of the planktonic foraminiferal faunas, where Neogloboquadrina pachyderma dominates in Polar Water and Turborotalita quinqueloba dominates in Atlantic Water. Our study areas have low standing stock of both planktonic foraminifera and pteropods in spring and a medium to high standing stock in summer. They have a distinct vertical shell density gradient and are not affected by intense methane seepage even in the relatively shallow Barents Sea. In terms recent impact of climate, there may be a decrease in the relative abundance of N. pachyderma on the Northeast Greenland shelf compared to studies from the 1990s, and sub-tropical species can be found in the Barents Sea. Furthermore, this thesis has helped in filling gaps in research into the impacts of ocean acidification in the Arctic, especially pertaining to methane release from dissociation of methane hydrates. Lastly, we have been able to show that planktonic foraminifera and pteropods in the same size class captured from the same location and depth interval have a wide range of shell densities. The same is also true for planktonic foraminifera found in surface sediments. These two points may complicate modern geochemical or ocean acidification studies as well as paleo-studies.

Continue reading ‘Arctic planktonic calcifiers in a changing ocean – A study on recent planktonic foraminifera and shelled pteropods in the Fram Strait-Barents Sea region’

Near-surface stratification due to ice melt biases Arctic air-sea CO2 flux estimates

Abstract

Air-sea carbon dioxide (CO2) flux is generally estimated by the bulk method using upper ocean CO2 fugacity measurements. In the summertime Arctic, sea-ice melt results in stratification within the upper ocean (top ∼10 m), which can bias bulk CO2 flux estimates when the seawater CO2 fugacity is taken from a ship’s seawater inlet at ∼6 m depth (fCO2w_bulk). Direct flux measurements by eddy covariance are unaffected by near-surface stratification. We use eddy covariance CO2 flux measurements to infer sea surface CO2 fugacity (fCO2w_surface) in the Arctic Ocean. In sea-ice melt regions, fCO2w_surface values are consistently lower than fCO2w_bulk by an average of 39 μatm. Lower fCO2w_surface can be partially accounted for by fresher (≥27%) and colder (17%) melt waters. A back-of-the-envelope calculation shows that neglecting the summertime sea-ice melt could lead to a 6%–17% underestimate of the annual Arctic Ocean CO2 uptake.

Plain Language Summary

The Arctic Ocean is considered to be a strong sink for atmospheric CO2. The air-sea CO2 flux is almost always estimated indirectly using bulk seawater CO2 fugacity measured from the ship’s seawater inlet at typically ∼6 m depth. However, sea-ice melt results in near-surface stratification and can cause a bias in air-sea CO2 flux estimates if the bulk water CO2 fugacity is used. The micrometeorological eddy covariance flux technique is not affected by stratification. Here for the first time, we employ eddy covariance measurements to assess the impact of sea-ice melt on Arctic Ocean CO2 uptake estimates. The results show that the summertime near-surface stratification due to sea-ice melt could lead to an ∼10% (with high uncertainty) underestimation of the annual Arctic Ocean CO2 uptake.

Continue reading ‘Near-surface stratification due to ice melt biases Arctic air-sea CO2 flux estimates’

Carbon dioxide flux at the water–air boundary at the continental slope in the Kara Sea

The values and direction of carbon dioxide flux in the area of the continental slope in the north of the Kara Sea (St. Anna Trough) are calculated based on field studies in 2020 within the Siberian Arctic Sea Ecosystems program. The existence of a stable frontal zone in this area has been confirmed, which is formed by an alongslope current and limits the northward spread of surface waters freshened by the continental runoff. The simultaneous analysis of the carbonate system in the upper sea layer and the CO2 concentration in the surface air layer shows the CO2 flux with a rate of 0.2 to 22 mmol/m2 day to be directed from the atmosphere into the water in the area of the outer shelf, which is affected by the river runoff, and in the area of the continental slope, which is beyond this effect. The highest rates of CO2 absorption by the sea surface layer are localized above the continental slope. Local processes in the area of the slope frontal zone determine the CO2 emission into the atmosphere with a rate of 0.34 mmol/m2 day.

Continue reading ‘Carbon dioxide flux at the water–air boundary at the continental slope in the Kara Sea’

Assessing the state of the Barents Sea using indicators: how, when, and where?

Two end-to-end ecosystem models, NORWECOM.E2E and NoBa Atlantis, have been used to explore a selection of indicators from the Barents Sea Management plans (BSMP). The indicators included in the BSMP are a combination of simple (e.g. temperature, biomass, and abundance) and complex (e.g. trophic level and biomass of functional groups). The abiotic indicators are found to serve more as a tool to report on climate trends rather than being ecological indicators. It is shown that the selected indicators give a good overview of the ecosystem state, but that overarching management targets and lack of connection between indicators and management actions makes it questionable if the indicator system is suitable for direct use in management as such. The lack of socio-economic and economic indicators prevents a holistic view of the system, and an inclusion of these in future management plans is recommended. The evaluated indicators perform well as an assessment of the ecosystem, but consistency and representativeness are extremely dependent on the time and in what area they are sampled. This conclusion strongly supports the inclusion of an observing system simulation experiment in management plans, to make sure that the observations represent the properties that the indicators need.

Continue reading ‘Assessing the state of the Barents Sea using indicators: how, when, and where?’

Ocean acidification state variability of the Atlantic Arctic Ocean around northern Svalbard

Highlights

  • Arctic-like conditions and sea-ice meltwater accelerate surface water acidification.
  • Atlantic-like conditions increased primary production and biological carbon uptake.
  • Alkalinity from Atlantic Water buffers against acidification in ice-free waters.
  • Biological and geochemical “Atlantification” alleviates Arctic Ocean acidification.

Abstract

The Svalbard shelf and Atlantic Arctic Ocean are a transition zone between northward flowing Atlantic Water and ice-covered waters of the Arctic. Effects of regional ocean warming, sea ice loss and greater influence of Atlantic Water or “Atlantification” on the state of ocean acidification, i.e. calcium carbonate (CaCO3) saturation (Ω) are yet to be fully understood. Anomalies in surface layer Ω for the climatically-vulnerable CaCO3 mineral aragonite (ΔΩ) were determined by considering the variability in Ωaragonite during late summer each year from 2014 to 2017 relative to the four-year average. Greatest sea ice extent and more Arctic-like conditions in 2014 resulted in ΔΩ anomalies of −0.05 to −0.01 (up to 45% of total ΔΩ) as a result of lower primary production. Conversely, greater Atlantic Water influence in 2015 supplied the ice-free surface layer with nitrate, which prolonged primary production to drive ΔΩ anomalies of 0.01 to 0.06 (up to 45% of total ΔΩ) in more Atlantic-like conditions. Additionally, dissolution of CaCO3 increased carbonate ion concentrations giving ΔΩ anomalies up to 0.06 (up to 52% of total ΔΩ). These processes enhanced surface water Ω, which ranged between 2.01 and 2.65 across the region. Recent sea ice retreat in 2016 and 2017 (rate of decrease in ice cover of ∼4% in 30 days) created transitional Atlantic-Arctic conditions, where surface water Ω varied between 1.87 and 2.29 driven by ΔΩ anomalies of −0.10-0.01 due to meltwater inputs and influence of Arctic waters. Anomalies as low as −0.12 from reduced CaCO3 dissolution in 2016 further supressed Ω. Wind-driven mixing in 2017 entrained Atlantic Water with low Ω into the surface layer to drive large ΔΩ anomalies of −0.15 (up to 58% of ΔΩ). Sea-ice meltwater provided a minor source of carbonate ions, slightly counteracting dilution effects. Ice-free surface waters were substantial sinks for atmospheric CO2, where uptake of 20.5 mmol m−2 day−1 lowered surface water Ω. “Atlantification” could exacerbate or alleviate acidification of the Arctic Ocean, being highly dependent on the numerous factors examined here that are intricately linked to the sea ice-ocean system variability.

Continue reading ‘Ocean acidification state variability of the Atlantic Arctic Ocean around northern Svalbard’

Spatial and temporal variations of aragonite saturation states in the surface waters of the western Arctic Ocean

Abstract

The aragonite saturation state (Ωarag) was determined for the surface waters of the western Arctic Ocean over three years, from 2016 to 2018, in an investigation of the present state of acidification of its waters and the main factors controlling the spatial and temporal variations in the surface Ωarag. The study area was divided into the Chukchi marginal area (CMA) and the East Siberian marginal area (ESMA) along a longitude of 180°E. In the CMA, the surface Ωarag during the study period ranged from 0.86 to 1.77, with an average of 1.16, indicating near saturation with respect to aragonite. In the ESMA, the surface Ωarag during the study period ranged from 1.01 to 2.21, with a higher average (1.59) than the CMA. Aragonite undersaturation in the ESMA was not observed during any of the measurement periods, so ocean acidification was less serious there than in the CMA. The surface Ωarag of the CMA was mainly determined by the mixing of seawater and freshwater introduced from rivers and/or sea ice, whereas in the ESMA it was influenced by the mixing of seawater and freshwater but also biological production and lateral mixing.

Plain Language Summary

The study was conducted in the western Arctic Ocean and included the Northwind Ridge, Chukchi Plateau, Chukchi Abyssal Plain, Chukchi Sea Slope, East Siberian Sea Slope, and Mendeleyev Ridge. The waters encompassed by these sites are highly vulnerable to acidification because of the inflow of lower-pH water from the Pacific Ocean through the Bering Sea and the current rapid reduction in the amount of sea ice. The study area was divided into the Chukchi marginal area (CMA) and the East Siberian marginal area (ESMA) along a longitude of 180°E. In the CMA, the surface waters were almost saturated with respect to aragonite but in the ESMA they were undersaturated, indicating that oceanic acidification was more serious in the CMA than in the ESMA. In the near future, the aragonite undersaturation in the most of the surface waters of the CMA will prohibit the survival of calcareous organisms and may lead to their extinction from this area. However, a similar short-term scenario is not expected in the ESMA, due to its relatively high biological production, which favors aragonite saturation and will thus delay aragonite undersaturation of the surface water.

Continue reading ‘Spatial and temporal variations of aragonite saturation states in the surface waters of the western Arctic Ocean’

Distribution and abundances of planktic foraminifera and shelled pteropods during the polar night in the sea-ice covered Northern Barents Sea

Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ecosystems. Here we provide, for the first time, information on the under-ice planktic foraminifera and shelled pteropod abundance, species composition and vertical distribution along a transect (82°–76°N) covering the Nansen Basin and the northern Barents Sea during the polar night in December 2019. The two groups of calcifiers were examined in different environments in the context of water masses, sea ice cover, and ocean chemistry (nutrients and carbonate system). The average abundance of planktic foraminifera under the sea-ice was low with the highest average abundance (2 ind. m–3) close to the sea-ice margin. The maximum abundances of planktic foraminifera were concentrated at 20–50 m depth (4 and 7 ind. m–3) in the Nansen Basin and at 80–100 m depth (13 ind. m–3) close to the sea-ice margin. The highest average abundance (13 ind. m–3) and the maximum abundance of pteropods (40 ind. m–3) were found in the surface Polar Water at 0–20 m depth with very low temperatures (–1.9 to –1°C), low salinity (<34.4) and relatively low aragonite saturation of 1.43–1.68. The lowest aragonite saturation (<1.3) was observed in the bottom water in the northern Barents Sea. The species distribution of these calcifiers reflected the water mass distribution with subpolar species at locations and depths influenced by warm and saline Atlantic Water, and polar species in very cold and less saline Polar Water. The population of planktic foraminifera was represented by adults and juveniles of the polar species Neogloboquadrina pachyderma and the subpolar species Turborotalita quinqueloba. The dominating polar pteropod species Limacina helicina was represented by the juvenile and veliger stages. This winter study offers a unique contribution to our understanding of the inter-seasonal variability of planktic foraminfera and shelled pteropods abundance, distribution and population size structure in the Arctic Ocean.

Continue reading ‘Distribution and abundances of planktic foraminifera and shelled pteropods during the polar night in the sea-ice covered Northern Barents Sea’

Nitrous oxide and methane in a changing Arctic Ocean

Human activities are changing the Arctic environment at an unprecedented rate resulting in rapid warming, freshening, sea ice retreat and ocean acidification of the Arctic Ocean. Trace gases such as nitrous oxide (N2O) and methane (CH4) play important roles in both the atmospheric reactivity and radiative budget of the Arctic and thus have a high potential to influence the region’s climate. However, little is known about how these rapid physical and chemical changes will impact the emissions of major climate-relevant trace gases from the Arctic Ocean. The combined consequences of these stressors present a complex combination of environmental changes which might impact on trace gas production and their subsequent release to the Arctic atmosphere. Here we present our current understanding of nitrous oxide and methane cycling in the Arctic Ocean and its relevance for regional and global atmosphere and climate and offer our thoughts on how this might change over coming decades.

Continue reading ‘Nitrous oxide and methane in a changing Arctic Ocean’

Possible future scenarios for two major Arctic Gateways connecting Subarctic and Arctic marine systems: I. climate and physical–chemical oceanography

We review recent trends and projected future physical and chemical changes under climate change in transition zones between Arctic and Subarctic regions with a focus on the two major inflow gateways to the Arctic, one in the Pacific (i.e. Bering Sea, Bering Strait, and the Chukchi Sea) and the other in the Atlantic (i.e. Fram Strait and the Barents Sea). Sea-ice coverage in the gateways has been disappearing during the last few decades. Projected higher air and sea temperatures in these gateways in the future will further reduce sea ice, and cause its later formation and earlier retreat. An intensification of the hydrological cycle will result in less snow, more rain, and increased river runoff. Ocean temperatures are projected to increase, leading to higher heat fluxes through the gateways. Increased upwelling at the Arctic continental shelf is expected as sea ice retreats. The pH of the water will decline as more atmospheric CO2 is absorbed. Long-term surface nutrient levels in the gateways will likely decrease due to increased stratification and reduced vertical mixing. Some effects of these environmental changes on humans in Arctic coastal communities are also presented.

Continue reading ‘Possible future scenarios for two major Arctic Gateways connecting Subarctic and Arctic marine systems: I. climate and physical–chemical oceanography’

  • Reset

Subscribe

OA-ICC Highlights


%d bloggers like this: