Arctic Ocean Water Research Articles

Late-Holocene environment evolution revealed by multi-proxy analyses of peat sequence in the Sawuer Mountains, northern Xinjiang of China

The Sawuer Mountains, located in the western Junggar Basin within northern Xinjiang of China, are considered as a distinct watershed between the Xinjiang inland water system and the Arctic Ocean water system. The suitable climate has fostered the widespread development of peat in the Sawuer Mountains, but our understanding about peat development and their environmental evolution remains limited. This study conducted the detailed investigation of peat developments and their environmental evolution in the Sawuer Mountains inferred from two cores using multi-proxies (peat accumulation rates, loss-on-ignition, total nitrogen, total phosphorus, humification and n-alkanes). The dating results present that peat began to develop at ∼3.1 cal kyr BP. The multi-proxies reveal that the climate exhibited a dry environment at ∼3.1-∼2.24 cal kyr BP and an increasing moisture at ∼2.24-∼1.42 cal kyr BP with the past 1420 years being characterized by an overall drying trend, agreeing well with other records from northern Xinjiang. The moisture reconstruction was both modulated by the NAO (North Atlantic Oscillation) phase and the solar forcing in the late Holocene.

Categorical data analysis using discretization of continuous variables to investigate associations in marine ecosystems

AbstractUnderstanding and predicting interactions between predators and prey and their environment are fundamental for understanding food web structure, dynamics, and ecosystem function in both terrestrial and marine ecosystems. Thus, estimating the conditional associations between species and their environments is important for exploring connections or cooperative links in the ecosystem, which in turn can help to clarify such directional relationships. For this purpose, a relevant and practical statistical method is required to link presence/absence observations with biomass, abundance, and physical quantities obtained as continuous real values. These data are sometimes sparse in oceanic space and too short as time series data. To meet this challenge, we provide an approach based on applying categorical data analysis to present/absent observations and real‐number data. The real‐number data used as explanatory variables for the present/absent response variable are discretized based on the optimal detection of thresholds without any prior biological/ecological information. These discretized data express two different levels, such as large/small or high/low, which give experts a simple interpretation for investigating complicated associations in marine ecosystems. This approach is implemented in the previous statistical method called CATDAP developed by Sakamoto and Akaike in 1979. Our proposed approach consists of a two‐step procedure for categorical data analysis: (1) finding the appropriate threshold to discretize the real‐number data for applying an independent test; and (2) identifying the best conditional probability model to investigate the possible associations among the data based on a statistical information criterion. We perform a simulation study to validate our proposed approach and investigate whether the method's observation includes many zeros (zero‐inflated data), which can often occur in practical situations. Furthermore, the approach is applied to two datasets: (1) one collected during an international synoptic krill survey in the Scotia Sea west of the Antarctic Peninsula to investigate associations among krill, fin whale (Balaenoptera physalus), surface temperature, depth, slope in depth (flatter or steeper terrain), and temperature gradient (slope in temperature); (2) the other collected by ecosystem surveys conducted during August–September in 2014–2017 to investigate associations among common minke whales, the predatory fish Atlantic cod, and their main prey groups (zooplankton, 0‐group fish) in Arctic Ocean waters to the west and north of Svalbard, Norway. The R code summarizing our proposed numerical procedure is presented in S4S1.

Complexity of Arctic Ocean water isotope (δ18O, δ2H) spatial and temporal patterns revealed with machine learning

The stable isotope compositions of water (δ18O, δ2H, deuterium-excess) are important tracers that help illuminate the changing Arctic water cycle and how Arctic-sourced water can influence lower latitudes. We present simultaneous boundary layer water vapor and ocean water isotope data that were measured continuously in the western Arctic Ocean. Sea surface water isotopes varied between the shallower continental Chukchi Shelf and the deeper Chukchi Borderlands to the north. The Chukchi Borderlands surface waters were less saline than the offshore Chukchi Shelf, as the Borderlands are influenced by greater sea ice cover and contribution of sea ice melt to surface freshwater. This greater contribution of sea ice melt resulted in lower deuterium-excess (δ2H − 8*δ18O) in surface water values in the deeper Chukchi Borderlands than on the shallower Chukchi Shelf. Additionally, the sea ice melt contributions to freshwater were less prominent than river runoff, but freshwater from both sources decreased substantially below 70 m depth in the Chukchi Borderlands. Our observed water isotope values provided the foundation for producing water isotope maps (isoscapes) based on remote sensing and machine learning which incorporate parameters that can influence ocean circulation and thus water isotopes (e.g., salinity, sea surface temperature, water depth). These isoscapes suggest spatial complexity in the distribution of stable water isotopes in the Arctic, including sharp gradients in the distribution of the isotopes in seawater that were studied. These isoscapes can be improved in future iterations, for example, with the availability of more spatially continuous, remotely sensed oceanic variables or continuous ship-based measurements to use as additional predictors. As a result, the generation of these isoscapes could become a useful tool for understanding the past, present, and future Arctic water cycle in the context of the global hydrologic cycle.

Distribution of copper-binding ligands in Fram Strait and influences from the Greenland Shelf (GEOTRACES GN05)

The Fram Strait represents the major gateway of Arctic Ocean waters towards the Nordic Seas and North Atlantic Ocean and is a key region to study the impact of climate change on biogeochemical cycles. In the region, information about trace metal speciation, such as copper, is scarce. This manuscript presents the concentrations and conditional stability constants of copper-binding ligands (LCu and log KcondCu2+L) in the water column of Fram Strait and the Greenland shelf (GEOTRACES cruise GN05). Cu-binding ligands were analysed by Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) using salicylaldoxime (SA) as competitive ligand. Based on water masses and the hydrodynamic influences, three provinces were considered (coast, shelf, and Fram Strait) and differences were observed between regions and water masses. The strongest variability was observed in surface waters, with increasing LCu concentrations (mean values: Fram Strait = 2.6 ± 1.0 nM; shelf = 5.2 ± 1.3 nM; coast = 6.4 ± 0.8 nM) and decreasing log KcondCu2+L values (mean values: Fram Strait = 15.7 ± 0.3; shelf = 15.2 ± 0.3; coast = 14.8 ± 0.3) towards the west. The surface LCu concentrations obtained above the Greenland shelf indicate a supply from the coastal environment to the Polar Surface Water (PSW) which is an addition to the ligand exported from the central Arctic to Fram Strait. The significant differences (in terms of LCu and log KcondCu2+L) between shelf and coastal samples were explained considering the processes which modify ligand concentrations and binding strengths, such as biological activity in sea-ice, phytoplankton bloom in surface waters, bacterial degradation, and meltwater discharge from 79NG glacier terminus. Overall, the ligand concentration exceeded those of dissolved Cu (dCu) and kept the free copper (Cu2+) concentrations at femtomolar levels (0.13–21.13 fM). This indicates that Cu2+ toxicity limits were not reached and dCu levels were stabilized in surface waters by organic complexes, which favoured its transport to the Nordic Seas and North Atlantic Ocean and the development of microorganism.

Control of particulate manganese (Mn) cycling in halocline Arctic Ocean waters by putative Mn‐oxidizing bacterial dynamics

AbstractParticulate Mn, given its high adsorptive capacity and oxidation potential, has profound impacts on the cycling of various trace elements and organic matter in the ocean. Moreover, particulate Mn acts as a sink (via oxidation and adsorption) or as a source (via remineralization and photoreduction) term of bioactive dissolved Mn(II). In the Canadian Arctic Ocean, particulate Mn distributions in the water column revealed the presence of distinctively high particulate Mn concentrations and an overwhelming dominance of the non‐lithogenic component to the bulk particulate Mn pool. This phenomenon is of particular importance in halocline waters in the Canada Basin, the Canadian Arctic Archipelago and Baffin Bay, and near‐bottom samples in Baffin Bay. Enhanced microbially‐mediated Mn oxidation in the water column is suggested as the main mechanism driving the non‐lithogenic dominance. Indeed, the microbial community composition data associated with high non‐lithogenic particulate Mn (i.e., Mn oxides) display a high relative abundance of taxa (e.g., f.Pirellulaceae, o.Phycisphaerales, f.Cryomorphaceae, g. Moritella) that have been identified in Mn oxide enriched environments. Furthermore, numerous taxa identified in the Canada Basin halocline water, where non‐lithogenic particulate Mn peaked, are phylogenetically related to known (cultured) Mn‐oxidizing bacteria (MnOB; e.g., Rhodobacteraceae, Oceanospirillaceae, Rhizobiaceae, and other Alphaproteobacteria). Putative MnOB appears to proliferate in certain water masses having a unique set of environmental conditions: low light intensity—alleviating photoinhibition—and high dissolved Mn concentrations, the main drivers known to influence MnOB dynamic, and hence, Mn oxidation.

Meltwater Lenses Over the Chukchi and the Beaufort Seas During Summer 2019: From In Situ to Synoptic View

AbstractWe investigate the Chukchi and the Beaufort seas in the Arctic Ocean, where salty and warm Pacific Water flows in through the Bering Strait and interacts with the sea ice, contributing to its summer melt. Thanks to in situ measurements recorded by two saildrones deployed during summer 2019 and to refined sea ice filtering in satellite L‐band radiometric data, we demonstrate the ability of satellite sea surface salinity (SSS) observed by Soil Moisture and Ocean Salinity and Soil Moisture Active and Passive to capture SSS freshening induced by sea ice melt. We refer to these freshening events as meltwater lenses (MWL). The largest MWL observed by the saildrones during this period occupied a large part of the Chukchi shelf, with a SSS freshening reaching −5 practical salinity scale, persisting for up to 1 month. This MWL restricted the transfer of air‐sea momentum to the upper ocean, as illustrated by measured wind speed and vertical profiles of currents. With satellite‐based sea surface temperature, satellite SSS provides a monitoring of the different water masses encountered in the region during summer 2019. Using sea ice concentration and estimated Ekman transport, we analyze the spatial variability of sea surface properties after the sea ice edge retreat over the Chukchi and the Beaufort seas. The two MWL captured by the saildrones and the satellite measurements resulted from different dynamics. Over the Beaufort Sea, the MWL evolution followed the meridional sea ice retreat whereas, in the Chukchi Sea, a large persisting MWL was generated by advection and subsequent melting of a sea ice filament.

Changes in the oxygen isotope composition of the Bering Sea contribution to the Arctic Ocean are an independent measure of increasing freshwater fluxes through the Bering Strait.

A large volume of freshwater is incorporated in the relatively fresh (salinity ~32–33) Pacific Ocean waters that are transported north through the Bering Strait relative to deep Atlantic salinity in the Arctic Ocean (salinity ~34.8). These freshened waters help maintain the halocline that separates cold Arctic surface waters from warmer Arctic Ocean waters at depth. The stable oxygen isotope composition of the Bering Sea contribution to the upper Arctic Ocean halocline was established as early as the late 1980’s as having a δ18OV-SMOW value of approximately -1.1‰. More recent data indicates a shift to an isotopic composition that is more depleted in 18O (mean δ18O value ~-1.5‰). This shift is supported by a data synthesis of >1400 water samples (salinity from 32.5 to 33.5) from the northern Bering and Chukchi seas, from the years 1987–2020, which show significant year-to-year, seasonal and regional variability. This change in the oxygen isotope composition of water in the upper halocline is consistent with observations of added freshwater in the Canada Basin, and mooring-based estimates of increased freshwater inflows through Bering Strait. Here, we use this isotopic time-series as an independent means of estimating freshwater flux changes through the Bering Strait. We employed a simple end-member mixing model that requires that the volume of freshwater (including runoff and other meteoric water, but not sea ice melt) flowing through Bering Strait has increased by ~40% over the past two decades to account for a change in the isotopic composition of the 33.1 salinity water from a δ18O value of approximately -1.1‰ to a mean of -1.5‰. This freshwater flux change is comparable with independent published measurements made from mooring arrays in the Bering Strait (freshwater fluxes rising from 2000–2500 km3 in 2001 to 3000–3500 km3 in 2011).

Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan-Arctic Synthesis.

Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one‐of‐a‐kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean‐derived waters and Baffin Bay‐derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.

Distribution of total mercury and methylated mercury species in Central Arctic Ocean water and ice

The central Arctic Ocean remains largely unexplored when it comes to the presence and cycling of mercury and its methylated forms including mono- and dimethylmercury (MMeHg and DMeHg, respectively). In this study, we quantified total Hg (HgT) and methylated Hg species in seawater, ice cores, snow, brine, and water from melt ponds collected during the SWEDARCTIC 2016 expedition to the Amerasian and Eurasian side of the Lomonosov Ridge. In the water column, concentrations of HgT, MMeHg and DMeHg ranged from 0.089 to 1.5 pM, <25 to 520 fM and from <1.6 to 160 fM, respectively. HgT was enriched in surface waters while MMeHg and DMeHg were low at the surface (i.e. in the polar mixed layer) and enriched at a water depth of around 200–400 m. A 1:2 ratio of DMeHg to MMeHg was observed in the water column suggesting a lower ratio in the central parts of the Arctic Ocean than what has previously been reported from other parts of the Arctic Ocean. At the ice stations, average HgT ranged from 0.97 ± 1.2 pM in the ice cores to 27 ± 17 pM in melt pond waters and average MeHgT (total MeHg) from 28 ± 15 fM in brine to 130 ± 18 fM in melt pond water. The HgT observed in melt ponds and brine was an order of magnitude greater than HgT observed in surface waters and HgT in the upper part of the ice-cores was ~4–8 times higher HgT in comparison to lower layers. Our study suggests that ice may act as a source of HgT to surface waters but not to be a likely source of the methylated Hg forms. Unlike elemental Hg, DMeHg did not enrich in surface waters covered by ice. Concentrations of DMeHg observed in the ice cores and other samples collected from the ice stations were low, suggesting ice to not act as a source of DMeHg to the atmosphere nor to surface waters.

Comparison of GHRSST SST Analysis in the Arctic Ocean and Alaskan Coastal Waters Using Saildrones

There is high demand for complete satellite SST maps (or L4 SST analyses) of the Arctic regions to monitor the rapid environmental changes occurring at high latitudes. Although there are a plethora of L4 SST products to choose from, satellite-based products evolve constantly with the advent of new satellites and frequent changes in SST algorithms, with the intent of improving absolute accuracies. The constant change of these products, as reflected by the version product, make it necessary to do periodic validations against in situ data. Eight of these L4 products are compared here against saildrone data from two 2019 campaigns in the western Arctic, as part of the MISST project. The accuracy of the different products is estimated using different statistical methods, from standard and robust statistics to Taylor diagrams. Results are also examined in terms of spatial scales of variability using auto- and cross-spectral analysis. The three products with the best performance, at this point and time, are used in a case study of the thermal features of the Yukon–Kuskokwim delta. The statistical analyses show that two L4 SST products had consistently better relative accuracy when compared to the saildrone subsurface temperatures. Those are the NOAA/NCEI DOISST and the RSS MWOI SSTs. In terms of the spectral variance and feature resolution, the UK Met Office OSTIA product appears to outperform all others at reproducing the fine scale features, especially in areas of high spatial variability, such as the Alaska coast. It is known that L4 analyses generate small-scale features that get smoothed out as the SSTs are interpolated onto spatially complete grids. However, when the high-resolution satellite coverage is sparse, which is the case in the Arctic regions, the analyses tend to produce more spurious small-scale features. The analyses here indicate that the high-resolution coverage, attainable with current satellite infrared technology, is too sparse, due to cloud cover to support very high resolution L4 SST products in high latitudinal regions. Only for grid resolutions of ~9–10 km or greater does the smoothing of the gridding process balance out the small-scale noise resulting from the lack of high-resolution infrared data. This scale, incidentally, agrees with the Rossby deformation radius in the Arctic Ocean (~10 km).

Arctic Ocean Water Mass Structure and Circulation

The Arctic Ocean is the smallest of the world oceans, yet one whose currents and water masses extend globally. It is an advection-dominated ocean in that currents import distinct waters from both the North Atlantic and the North Pacific that interact and layer vertically by density. Further modified by river inputs and the freezing and melting of sea ice, the Arctic Ocean exports modified waters back into the North Atlantic, thus impacting the global thermohaline circulation. This physical system forms the backdrop for almost all chemical, biological, and geological processes within the Arctic Ocean, all of which are expected to change in a warming Earth. To anticipate the effects of such changes in external and advective forcing, it is necessary to understand how they interact and are manifested in the observed hydrographic structures. The aim of this review is thus to present and discuss the processes responsible for these structures.

Atlantic Ocean Circulation as the Driving Force for the Holocene Thermal Maximum and Millennial Scale Climatic Variability

The aim of this meta-study is to provide an understanding of the Atlantic Ocean Circulation as the driving force for the Holocene Thermal Maximum (HTM) and Millennial Scale Climatic Variability. In addition to continental ice sheets, during the Great Ice Age (GIA) there was also a 900-m thick floating ice shelf (FIS) in the Arctic Ocean. Below the FIS, it was likely freshwater. It is plausible that around 11,700 BP the Gulf Stream established the present flow route. Until around 10,800 BP the Grand Banks of Newfoundland (GBN) diverted part of the Gulf Stream flow west towards the north-eastern American coast, where the HTM existed between ca. 11,600 and 10,800 BP. Soon after the Gulf Stream was able to flow over the GBN, the HTM started in Ireland ca. 10,700 BP. By ca. 10,000 BP, the Gulf Stream arrived on the coast of Norway, which diverted the outflow south through the English Channel for approximately 2,000 years. In Northern and Central Europe, the HTM existed between ca. 9,500 and 7,000 BP. Due to the melting of ice, the outflow turned brackish, and was mainly surface currents, having a temperature of around 0℃. The formation of descending salty water (DSW), which creates the suction of the Gulf Stream, was low. Between ca. 6,000 and 4,500 BP, there was Mid-Holocene cooling. Then the Arctic Ocean water was salinated by double diffusive convection (DDC). When DSW formation increased to its present-day volume, the Neoglacial period started ca. 4,500 BP. Since then, outflow has taken place mainly through cold (approximately –2℃) undercurrents. At this time, the intensive millennial scale cycling of warmer and colder periods also started. When increasingly larger areas in Arctic Ocean are covered by insulating multi-year ice (MYI), DSW formation and the suction of the Gulf Stream decrease, and vice versa. The amplitude of the cycle is approximately 750 to 800 years.

Arctic Cyclones and Their Interactions With the Declining Sea Ice: A Recent Climatology

AbstractIn this study, we applied a cyclone tracking algorithm to multiple reanalyses and categorized the detected cyclones based on season, intensity, and sea ice state to provide an Arctic cyclone climatology with emphasis on cyclone‐sea ice interactions over the Arctic Ocean and adjacent waters. Our study period is from 1979 to 2015 and the reanalyses we are using are ERA‐Interim, ERA5, and CFSR. As for our intensity variable, we use Accumulated Cyclone Energy (ACE), which has commonly been used as an intensity metric in the tropics but has not been utilized for high latitudes before. ACE has the advantage that it relates the cyclone intensity to the kinetic energy of the cyclone and therefore better represents the cyclone impact/interaction with the surface. We performed comparisons with the other more commonly used intensity metrics to assess the use of the ACE metric in the Arctic. Our main findings include increased cyclone counts with higher trends toward the end of the study period. Cold season cyclone counts were also found to be related to decreased sea ice concentration throughout the year. We also show that there is a relationship between the cyclone intensity measured by ACE and the surface state. Less sea ice was shown to be related to higher cyclone intensities. Comparisons between the the three reanalysis data sets are also presented.

Distribution of rorquals and Atlantic cod in relation to their prey in the Norwegian high Arctic

Recent warming in the Barents Sea has led to changes in the spatial distribution of both zooplankton and fish, with boreal communities expanding northwards. A similar northward expansion has been observed in several rorqual species that migrate into northern waters to take advantage of high summer productivity, hence feeding opportunities. Based on ecosystem surveys conducted during August–September in 2014–2017, we investigated the spatial associations among the three rorqual species of blue, fin, and common minke whales, the predatory fish Atlantic cod, and their main prey groups (zooplankton, 0-group fish, Atlantic cod, and capelin) in Arctic Ocean waters to the west and north of Svalbard. During the surveys, whale sightings were recorded by dedicated whale observers on the bridge of the vessel, whereas the distribution and abundance of cod and prey species were assessed using trawling and acoustic methods. Based on existing knowledge on the dive habits of these rorquals, we divided our analyses into two depth regions: the upper 200 m of the water column and waters below 200 m. Since humpback whales were absent in the area in 2016 and 2017, they were not included in the subsequent analyses of spatial association. No association or spatial overlap between fin and blue whales and any of the prey species investigated was found, while associations and overlaps were found between minke whales and zooplankton/0-group fish in the upper 200 m and between minke whales and Atlantic cod at depths below 200 m. A prey detection range of more than 10 km was suggested for minke whales in the upper water layers.

Set sustainable goals for the Arctic gateway coordinated international governance is required to resist yet another tipping point.

Global warming is reducing the Arctic sea-ice and causing energetic stress to marine key predatory species such as polar bears and narwhals contributing to the ongoing pollution already threatening the biodiversity and indigenous people of the vulnerable region. Now, the opening of the Arctic gateway and in particular the increase in shipping activities causes further stress to marine mammals in the region. These shipping activities are foreseen to happen in the Northwest and Northeast Passage, Northern Sea Route and Transpolar Sea Route in the Arctic Ocean, which could be yet another step towards a crucial tipping point destabilizing global climate, including weathering systems and sea-level rise. This calls for international governance through the establishment of Arctic International National Parks and more Marine Protected Areas through the Arctic Council and UN's Law of the Sea to ensure sustainable use of the Arctic Ocean and adjacent waters.

Economic and environmental aspects of the development possibilities for the northern sea route

Sea transport is an important part of the international transport system. Its development is especially important for the Arctic, which is an important energy region with easy access to the sea for the transportation of crude oil, liquefied natural gas and other resources. This investment area is a priority for Russia and a number of other countries, including China, since it promotes interests in energy and shipping field. Tankers with icebreaking capabilities delivering crude oil and natural gas from the Far East to Western markets account for about 45% of shipping on the Northern Sea Route (NSR). The rest of the transportation is carried out within the framework of the large Russian project “Yamal LNG” by ice-class tankers from the Sabetta port to Europe. However, the volume of sea traffic in the Arctic Ocean waters remains insignificant. In this regard, the article analyzes the economic and environmental aspects of possible expanding of using the NSR as an alternative route from Europe to Asia. Although the NSR is a direct route, the absence of transshipment points and transit ports complicates the conditions for transit goods carriage, and some route sections are too shallow for large container carriers. There are a number of other important operational constraints, including extreme climatic conditions and environmental issues: ships emissions, oil spills on ice. It is concluded that the pace of the Arctic projects implementation will directly determine traffic volume. To overcome barriers and restrictions that prevent the NSR’s transformation into a transport corridor for both Russia and international transit flows, it is necessary to implement projects for the Arctic support zones creation and development, as well as the modernization and expansion of the nuclear icebreaker fleet capacities. A method is proposed for calculating the time of cargo delivery, considering the multi-range of logistics chains based on the NSR.

Changes in Circulation and Particle Scavenging in the Amerasian Basin of the Arctic Ocean over the Last Three Decades Inferred from the Water Column Distribution of Geochemical Tracers.

Since the 1980–1990s, international research efforts have augmented our knowledge of the physical and chemical properties of the Arctic Ocean water masses, and recent studies have documented changes. Understanding the processes responsible for these changes is necessary to be able to forecast the local and global consequences of these property evolutions on climate. The present work investigates the distributions of geochemical tracers of particle fluxes and circulation in the Amerasian Basin and their temporal evolution over the last three decades (from stations visited between 1983 and 2015). Profiles of 230‐thorium (230Th) and 231‐protactinium (231Pa) concentrations and neodymium isotopes (expressed as εNd) measured in the Amerasian Basin prior to 2000 are compared to a new, post‐2000s data set. The comparison shows a large scale decrease in dissolved 230Th and 231Pa concentrations, suggesting intensification of scavenging by particle flux, especially in coastal areas. Higher productivity and sediment resuspension from the shelves appear responsible for the concentration decrease along the margins. In the basin interior, increased lateral exchanges with the boundary circulation also contribute to the decrease in concentration. This study illustrates how dissolved 230Th and 231Pa, with εNd support, can provide unique insights not only into changes in particle flux but also into the evolution of ocean circulation and mixing.

The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

This study aims to perform the results of the investigation of the Kara Sea carbonate system (CS) changes and the factors that determine it. The important feature of the Kara Sea water structure is strong stratification caused mainly by the Ob’ and Yenisey rivers discharge which is estimated as 81% of the total continental runoff to sea. Occurring climate changes, as an increase in the total volume of the Arctic Ocean water (due to melting of glaciers, sea ice decline and river runoff increase), air temperature and CO2 concentration growth should affect greatly the Kara Sea CS. However, riverine water influence seems to be the main driver of future acidification of the Kara Sea water due to permafrost thawing as it stores a great amount of buried carbon. An increase of carbon (mainly inorganic) flow to the sea will lead to carbonate equilibrium shift, oxidation of organic matter and release of CO2 that ultimately leads to a decrease in pH and therefore acidification. The area of the riverine plume depends on the amount of freshwater flowing into the sea and the conditions of the wind forcing. According to the data from Shirshov Institute cruises within the plume area aragonite saturation is below 1 that shows its state as acidified. Prevalence of pCO2 values in the freshened surface layer over the atmospheric shows that atmospheric carbon dioxide, apparently, cannot serve as the main driver for the acidification of the surface waters of the Kara Sea. At the shallow shelf to the north of the Ob′ Inlet mouth we observe acidification of the whole water column from surface to the bottom layer due to elevated riverine discharge and increase of flowing terrestrial carbon.

Deep ocean 14C ventilation age reconstructions from the Arctic Mediterranean reassessed

The present-day ocean ventilation in the Arctic Mediterranean (Nordic Seas and Arctic Ocean), via transformation of northward inflowing warm Atlantic surface water into cold deep water, affects regional climate, atmospheric circulation and carbon storage in the deep ocean. Here we study the glacial evolution of the Arctic Mediterranean circulation and its influence on glacial climate using radiocarbon reservoir-age reconstructions on deep-sea cores from the Fram Strait that cover the late glacial period (33,000–20,000 yr ago; 33–20 ka). Our results show high Benthic-Planktic 14C age differences of ∼1500 14C years 33–26.5 ka suggesting significant water column stratification between ∼100–2600 m water depth, and reduction and/or shoaling of deep-water formation. This phase was followed by break-up of the stratification during the Last Glacial Maximum (LGM; 26–20 ka), with Benthic-Planktic 14C age differences of ∼250 14C years, likely due to enhanced upwelling. These ocean circulation changes potentially contributed to the final intensification phase of glaciation via positive cryosphere-atmosphere-ocean circulation-carbon cycle feedbacks. Our data also do not support ‘extreme aging’ of >6000 14C years in the deep Arctic Mediterranean, and appear to rule out the proposed outflow of very old Arctic Ocean water to the Nordic Seas during the LGM and to the subpolar North Atlantic Ocean during the deglacial period.

Marine and terrestrial influences on ice nucleating particles during continuous springtime measurements in an Arctic oilfield location

Abstract. Aerosols that serve as ice nucleating particles (INPs) have the potential to modulate cloud microphysical properties and can therefore impact cloud radiative forcing (CRF) and precipitation formation processes. In remote regions such as the Arctic, aerosol–cloud interactions are severely understudied yet may have significant implications for the surface energy budget and its impact on sea ice and snow surfaces. Further, uncertainties in model representations of heterogeneous ice nucleation are a significant hindrance to simulating Arctic mixed-phase cloud processes. We present results from a campaign called INPOP (Ice Nucleating Particles at Oliktok Point), which took place at a US Department of Energy Atmospheric Radiation Measurement (DOE ARM) facility in the northern Alaskan Arctic. Three time- and size-resolved aerosol impactors were deployed from 1 March to 31 May 2017 for offline ice nucleation and chemical analyses and were co-located with routine measurements of aerosol number and size. The largest particles (i.e., ≥ 3 µm or “coarse mode”) were the most efficient INPs by inducing freezing at the warmest temperatures. During periods with snow- and ice-covered surfaces, coarse mode INP concentrations were very low (maximum of 6 × 10−4 L−1 at −15 ∘C), but higher concentrations of warm-temperature INPs were observed during late May (maximum of 2 × 10−2 L−1 at −15 ∘C). These higher concentrations were attributed to air masses originating from over open Arctic Ocean water and tundra surfaces. To our knowledge, these results represent the first INP characterization measurements in an Arctic oilfield location and demonstrate strong influences from mineral and marine sources despite the relatively high springtime pollution levels. Ultimately, these results can be used to evaluate the anthropogenic and natural influences on aerosol composition and Arctic cloud properties.