Swedish Icebreaker Research Articles

Swedish Icebreaker Is the First to Dig Into Greenland’s Remote Victoria Fjord

Data collected aboard Oden will shed light on the dynamics of the Greenland Ice Sheet.

Central Arctic Ocean surface–atmosphere exchange of CO2 and CH4 constrained by direct measurements

Abstract. The central Arctic Ocean (CAO) plays an important role in the global carbon cycle, but the current and future exchange of the climate-forcing trace gases methane (CH4) and carbon dioxide (CO2) between the CAO and the atmosphere is highly uncertain. In particular, there are very few observations of near-surface gas concentrations or direct air–sea CO2 flux estimates and no previously reported direct air–sea CH4 flux estimates from the CAO. Furthermore, the effect of sea ice on the exchange is not well understood. We present direct measurements of the air–sea flux of CH4 and CO2, as well as air–snow fluxes of CO2 in the summertime CAO north of 82.5∘ N from the Synoptic Arctic Survey (SAS) expedition carried out on the Swedish icebreaker Oden in 2021. Measurements of air–sea CH4 and CO2 flux were made using floating chambers deployed in leads accessed from sea ice and from the side of Oden, and air–snow fluxes were determined from chambers deployed on sea ice. Gas transfer velocities determined from fluxes and surface-water-dissolved gas concentrations exhibited a weaker wind speed dependence than existing parameterisations, with a median sea-ice lead gas transfer rate of 2.5 cm h−1 applicable over the observed 10 m wind speed range (1–11 m s−1). The average observed air–sea CO2 flux was −7.6 mmolm-2d-1, and the average air–snow CO2 flux was −1.1 mmolm-2d-1. Extrapolating these fluxes and the corresponding sea-ice concentrations gives an August and September flux for the CAO of −1.75 mmolm-2d-1, within the range of previous indirect estimates. The average observed air–sea CH4 flux of 3.5 µmolm-2d-1, accounting for sea-ice concentration, equates to an August and September CAO flux of 0.35 µmolm-2d-1, lower than previous estimates and implying that the CAO is a very small (≪ 1 %) contributor to the Arctic flux of CH4 to the atmosphere.

Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei.

Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden. We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4–8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol.

Joint Cruise 2-2 2021

The main scientific goal of the Nansen Legacy JC2-2 cruise was to extend the project’s research activities from the northern Barents Sea shelf into the central Arctic Ocean. Specifically, JC2-2 addressed objectives of the research foci RF1, RF2 and RF3 by jointly collecting interdisciplinary samples and data at five process (P) and in-between NLEG stations extending northward from the previously northernmost station P7. We had a special focus on sea ice and the upper ocean as well as connectivity to the mid and deep water column and underlying sediments in early autumn. In addition, JC2-2 explored the role of transport of elements and organisms from the Siberian shelves through the Transpolar Drift in the Amundsen Basin. Experiments were an important part of the cruise and were designed to measure and quantify relevant processes and their rates. This cruise was also a Norwegian contribution to the international Synoptic Arctic Survey (SAS) and took place at the same time as the Swedish icebreaker Oden was on their SAS expedition in the nearby region between Northeast Greenland and the North Pole.

The Holocene dynamics of Ryder Glacier and ice tongue in north Greenland

Abstract. The northern sector of the Greenland Ice Sheet is considered to be particularly susceptible to ice mass loss arising from increased glacier discharge in the coming decades. However, the past extent and dynamics of outlet glaciers in this region, and hence their vulnerability to climate change, are poorly documented. In the summer of 2019, the Swedish icebreaker Oden entered the previously unchartered waters of Sherard Osborn Fjord, where Ryder Glacier drains approximately 2 % of Greenland's ice sheet into the Lincoln Sea. Here we reconstruct the Holocene dynamics of Ryder Glacier and its ice tongue by combining radiocarbon dating with sedimentary facies analyses along a 45 km transect of marine sediment cores collected between the modern ice tongue margin and the mouth of the fjord. The results illustrate that Ryder Glacier retreated from a grounded position at the fjord mouth during the Early Holocene (> 10.7±0.4 ka cal BP) and receded more than 120 km to the end of Sherard Osborn Fjord by the Middle Holocene (6.3±0.3 ka cal BP), likely becoming completely land-based. A re-advance of Ryder Glacier occurred in the Late Holocene, becoming marine-based around 3.9±0.4 ka cal BP. An ice tongue, similar in extent to its current position was established in the Late Holocene (between 3.6±0.4 and 2.9±0.4 ka cal BP) and extended to its maximum historical position near the fjord mouth around 0.9±0.3 ka cal BP. Laminated, clast-poor sediments were deposited during the entire retreat and regrowth phases, suggesting the persistence of an ice tongue that only collapsed when the glacier retreated behind a prominent topographic high at the landward end of the fjord. Sherard Osborn Fjord narrows inland, is constrained by steep-sided cliffs, contains a number of bathymetric pinning points that also shield the modern ice tongue and grounding zone from warm Atlantic waters, and has a shallowing inland sub-ice topography. These features are conducive to glacier stability and can explain the persistence of Ryder's ice tongue while the glacier remained marine-based. However, the physiography of the fjord did not halt the dramatic retreat of Ryder Glacier under the relatively mild changes in climate forcing during the Holocene. Presently, Ryder Glacier is grounded more than 40 km seaward of its inferred position during the Middle Holocene, highlighting the potential for substantial retreat in response to ongoing climate change.

Cold Rush: The Astonishing True Story of the New Quest for the Polar North

Cold Rush: The Astonishing True Story of the New Quest for the Polar North

Meteorological and cloud conditions during the Arctic Ocean 2018 expedition

Abstract. The Arctic Ocean 2018 (AO2018) took place in the central Arctic Ocean in August and September 2018 on the Swedish icebreaker Oden. An extensive suite of instrumentation provided detailed measurements of surface water chemistry and biology, sea ice and ocean physical and biogeochemical properties, surface exchange processes, aerosols, clouds, and the state of the atmosphere. The measurements provide important information on the coupling of the ocean and ice surface to the atmosphere and in particular to clouds. This paper provides (i) an overview of the synoptic-scale atmospheric conditions and their climatological anomaly to help interpret the process studies and put the detailed observations from AO2018 into a larger context, both spatially and temporally; (ii) a statistical analysis of the thermodynamic and near-surface meteorological conditions, boundary layer, cloud, and fog characteristics; and (iii) a comparison of the results to observations from earlier Arctic Ocean expeditions – in particular AOE1996 (Arctic Ocean Expedition 1996), SHEBA (Surface Heat Budget of the Arctic Ocean), AOE2001 (Arctic Ocean Experiment 2001), ASCOS (Arctic Summer Cloud Ocean Study), ACSE (Arctic Clouds in Summer Experiment), and AO2016 (Arctic Ocean 2016) – to provide an assessment of the representativeness of the measurements. The results show that near-surface conditions were broadly comparable to earlier experiments; however the thermodynamic vertical structure was quite different. An unusually high frequency of well-mixed boundary layers up to about 1 km depth occurred, and only a few cases of the “prototypical” Arctic summer single-layer stratocumulus deck were observed. Instead, an unexpectedly high amount of multiple cloud layers and mid-level clouds were present throughout the campaign. These differences from previous studies are related to the high frequency of cyclonic activity in the central Arctic in 2018.

A method for real-time estimation of full-scale global ice loads on floating structures

This paper proposes an algorithm that uses conventional measurements found on-board ships coupled with additional Inertial Measurement Units to estimate the motions and global loads acting on them. The work is motivated by the scarce availability of full-scale load data for sea-ice operations and by the invasive instrumentation of strain gauges used to obtain global loads of all degrees of freedom. Full-scale data are key to a number of design, operational, and research aspects related to sea-ice operations. The proposed algorithm is based on four Inertial Measurement Units (IMUs) that together with position and heading measurements are used to make estimates of dynamic linear and rotational acceleration (acceleration resulting in motion). We show how to use models updated with propulsion and wind measurements to estimate propulsion, hydrodynamic, wind, and ice loads through a setup catering to real-time implementation. A case study with the Swedish icebreaker Oden is presented and discussed. The algorithm effectively yields reasonable ice load history estimations and presents great potential in its further application to real-time global ice load estimations.

A North Pole thermal anomaly? Evidence from new and existing heat flow measurements from the central Arctic Ocean

Constraining the thermal evolution of the Arctic Ocean is hampered by notably sparse heat flow measurements and a complex tectonic history. Previous results from the Lomonosov Ridge in the vicinity of the North Pole, and the adjacent central Amundsen Basin reveal varied values, including those higher than expected considering plate cooling or simple uniform stretching models. Furthermore, in the vicinity of the North Pole an anomalously slow velocity perturbation exists in upper mantle seismic tomography models. However, whether these observations are related to a thermal anomaly in the mantle remains unknown. We present new heat flow results gathered from 17 sediment cores acquired during the “Arctic Ocean 2016” and “SWERUS-C3” expeditions on the Swedish icebreaker Oden. Three sites located on oceanic lithosphere in the Amundsen Basin between 7°W-71E° reveal surface thermal conductivity of 1.07–1.26 W/mK and heat flow in the order of 71–95 mW/m2, in line-with or slightly higher (1–21 mW/m2) than expected from oceanic heat flow curves. These results contrast with published results from further east in the Amundsen Basin, which indicated surface heat flow values up to 2 times higher than predicted from oceanic crustal cooling models. Heat flow of 49–61 mW/m2 was recovered from the Amerasia Basin. Sites from the submerged continental fragments of the Lomonosov Ridge and Marvin Spur recovered heat flow in the order of 53–76 and 51–69 mW/m2 respectively. When considering the additional potential surface heat flux from radiogenic heat production in the crust, these variable measurements are broadly in line with predictions from uniform extension models for continental crust. A seismically imaged upper mantle velocity anomaly in the central Arctic Ocean may arise from a combination of compositional and thermal variations but requires additional investigation. Disentangling surface heat flow contributions from crustal, lithospheric and mantle processes, including variable along-ridge rifting rates and timing, density and phase changes, conductive and advective dynamics, and regional tectonics, requires further analysis.

Potential source regions and processes of aerosol in the summer Arctic

Abstract. Sub-micrometer particle size distributions measured during four summer cruises of the Swedish icebreaker Oden 1991, 1996, 2001, and 2008 were combined with dimethyl sulfide gas data, back trajectories, and daily maps of pack ice cover in order to investigate source areas and aerosol formation processes of the boundary layer aerosol in the central Arctic. With a clustering algorithm, potential aerosol source areas were explored. Clustering of particle size distributions together with back trajectories delineated five potential source regions and three different aerosol types that covered most of the Arctic Basin: marine, newly formed and aged particles over the pack ice. Most of the pack ice area with < 15% of open water under the trajectories exhibited the aged aerosol type with only one major mode around 40 nm. For newly formed particles to occur, two conditions had to be fulfilled over the pack ice: the air had spent 10 days while traveling over ever more contiguous ice and had traveled over less than 30% open water during the last 5 days. Additionally, the air had experienced more open water (at least twice as much as in the cases of aged aerosol) during the last 4 days before arrival in heavy ice conditions at Oden. Thus we hypothesize that these two conditions were essential factors for the formation of ultrafine particles over the central Arctic pack ice. In a comparison the Oden data with summer size distribution data from Alert, Nunavut, and Mt. Zeppelin, Spitsbergen, we confirmed the Oden findings with respect to particle sources over the central Arctic. Future more frequent broken-ice or open water patches in summer will spur biological activity in surface water promoting the formation of biological particles. Thereby low clouds and fogs and subsequently the surface energy balance and ice melt may be affected.

Persistent organic pollutants in biota samples collected during the Ymer-80 expedition to the Arctic

During the expedition with the Swedish ice-breaker HMS Ymer to the Arctic in 1980 samples of a number of vertebrate species were collected for determination of persistent organic pollutants (POPs). Specimens of Arctic char (Salvelinus alpinus), glaucous gull (Larus hyperboreus), common eider (Somateria mollissima), Brünnich's guillemot (Uria lomvia), ringed seal (Phoca hispida), and polar bear (Ursus maritimuDuring the 1980 expedition to the Arctic with the icebreaker Ymer, a number of vertebrate species were sampled for determination of persistent organic pollutants. Samples of Arctic char (Salvelinus alpinus, n=34), glaucous gull (Larus hyperboreus, n=8), common eider (Somateria mollissima, n=10), Brünnich’s guillemot (Uria lomvia, n=9), ringed seal (Pusa hispida, n=2) and polar bear (Ursus maritimus, n=2) were collected. With the exception of Brünnich’s guillemot, there was a marked contamination difference of birds from western as compared to eastern/northern Svalbard. Samples in the west contained a larger number of polychlorinated biphenyl (PCB) congeners and also polychlorinated terphenyls, indicating local sources. Brünnich’s guillemots had similar pollutant concentrations in the west and east/north; possibly younger birds were sampled in the west. In Arctic char, pollutant profiles from lake Linnévatn (n=5), the lake closest to the main economic activities in Svalbard, were similar to profiles in Arctic char from the Shetland Islands (n=5), but differed from lakes to the north and east in Svalbard (n=30). Arctic char samples had higher concentrations of hexachlorocyclohexanes (HCHs) than the marine species of birds and mammals, possibly due to accumulation via snowmelt. Compared to the Baltic Sea, comparable species collected in Svalbard had lower concentrations of PCB and dichlorodiphenyltrichloroethane (DDT), but similar concentrations indicating long-range transport of hexachlorobenzene, HCHs and cyclodiene pesticides. In samples collected in Svalbard in 1971, the concentrations of PCB and DDT in Brünnich’s guillemot (n=7), glaucous gull (n=2) and polar bear (n=2) were similar to the concentrations found in 1980.Keywords: Polar bear; ringed seal; glaucous gull; Brünnich’s guillemot; common eider; Arctic char.(Published: 26 October 2015)To access the supplementary material for this article, please see supplementary files in the column to the right (under Article Tools).Citation: Polar Research 2015, 34, 21129, http://dx.doi.org/10.3402/polar.v34.21129

Effect of dynamic bending of level ice on ship's continuous-mode icebreaking

This paper focuses on the influences of the dynamic effects of ship–ice–water interaction on ship performance, ship motions, and ice resistance. The effects of the dynamic bending of ice wedges and ship speeds are especially investigated. The study is carried out using a numerical procedure simulating ship operations in level ice with ship motions in six degrees of freedom (DOFs). A case study is conducted with the Swedish icebreaker Tor Viking II. The 3-D hull geometry of the ship is modeled based on the lines drawing. The predicted performance of the ship is compared with data from full-scale ice trials.

The Arctic summer atmosphere: an evaluation of reanalyses using ASCOS data

Abstract. The Arctic has experienced large climate changes over recent decades, the largest for any region on Earth. To understand the underlying reasons for this climate sensitivity, reanalysis is an invaluable tool. The Arctic System Reanalysis (ASR) is a regional reanalysis, forced by ERA-Interim at the lateral boundaries and incorporating model physics adapted to Arctic conditions, developed to serve as a state-of-the-art, high-resolution synthesis tool for assessing Arctic climate variability and monitoring Arctic climate change. We use data from Arctic Summer Cloud-Ocean Study (ASCOS) to evaluate the performance of ASR and ERA-Interim for the Arctic Ocean. The ASCOS field experiment was deployed on the Swedish icebreaker Oden north of 87° N in the Atlantic sector of the Arctic during August and early September 2008. Data were collected during the transits from and to Longyearbyen and the 3-week ice drift with Oden moored to a drifting multiyear ice floe. These data are independent and detailed enough to evaluate process descriptions. The reanalyses captures basic meteorological variations coupled to the synoptic-scale systems, but have difficulties in estimating clouds and atmospheric moisture. While ERA-Interim has a systematic warm bias in the lowest troposphere, ASR has a cold bias of about the same magnitude on average. The results also indicate that more sophisticated descriptions of cloud microphysics in ASR did not significantly improve the modeling of cloud properties compared to ERA-Interim. This has consequences for the radiation balance, and hence the surface temperature, and illustrate how a modeling problem in one aspect of the atmosphere, here the clouds, feeds back to other parameters, especially near the surface and in the boundary layer.

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

Abstract. Unique measurements of vertical size-resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from on board the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Within the lowermost couple hundred metres, transport from the marginal ice zone (MIZ), condensational growth and cloud processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore long-range transport plumes are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, such plumes can influence the radiative balance of the planetary boundary layer (PBL) by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles could be in biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary-layer transport of precursor gases from the MIZ, are considered to constitute the origin of cloud condensation nuclei (CCN) particles and thus be of importance for the formation of interior Arctic low-level clouds during summer, and subsequently, through cloud influences, for the melting and freezing of sea ice.

A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model

ABSTRACTEnhancement of number concentrations of particles with sizes less than 25 nm diameter has been frequently observed in the boundary layer over the central Arctic Ocean during summer. The sectional aerosol dynamics model for Marine Aerosol Formation (MAFOR) was applied to evaluate the capability of different nucleation mechanisms to reproduce nucleation events observed during three expeditions (1996, 2001 and 2008) onboard the Swedish icebreaker Oden. Model calculations suggest that a source rate of a condensable organic vapour (OV) of about 2×105 cm−3 s−1 is required to reproduce observed growth of nucleation mode particles. Nucleation rates predicted by the newly proposed combined sulphuric acid nucleation mechanism, which best described new particle formation in the Arctic, ranged from 0.04 to 0.1 cm−3 s−1. This mechanism additively combines ion-mediated nucleation and cluster activation, and treats condensation of OV without correction of the Kelvin effect. In several events, the simultaneous number enhancement of particles in the 20–50 nm size range remained unexplained by the nucleation mechanisms. This lends support to alternative theories such as the fragmentation of marine gels (≈200–500 nm diameter in size) by physical or chemical processes.

Ethological analysis of the trace fossil Zoophycos: hints from the Arctic Ocean

The distribution of the trace fossil Zoophycos in Quaternary marine sediments from the Arctic Ocean was studied in twelve piston and gravity cores retrieved during the Swedish icebreaker expedition ...

Local Design Pressures for Structures in Ice: Analysis of Full-Scale Data

The design of structures for ice conditions requires knowledge of local ice pressures to allow for appropriate levels of structural strengthening. Full-scale field data are keys to enhancing our understanding and modeling of ice behavior. Data collected during icebreaker ramming events represent an important source of information for use in design load estimation, and the evaluation of design methodologies. This paper examines several ship-ice interaction data sets using the ‘event-maximum’ method of local pressure analysis developed by Jordaan and et al. (1993, “Probabilistic Analysis of Local Ice Pressures,” ASME J. Offshore Mech. Arct. Eng., 115, pp. 83–89). In this method, the local pressure is obtained from a normalized curve, which contains two parameters α and x0. The parameter α is a function of the area, well represented by the curve α=CaD, where a is the local area of interest, and C and D are constants. The parameter x0 is assumed a constant for a given design scenario. An alternative approach, the up-crossing rate method, is presented in a companion paper (2009, “Estimation of Local Ice Pressure Using Up-Crossing Rate,” Proceedings of the OMAE 2009, Honolulu, HI). Local pressure analysis results for data from the USCGS Polar Sea, CCGS Terry Fox, CCGS Louis St. Laurent, and Swedish Icebreaker Oden are presented. A discussion of panel exposure, event duration, and the effects of these factors on x0 is given. New design curves are included. For all data considered, the calculated values of α fall below the design curve. For the design, it is recommended that α is calculated using a C value based on the impact data collected under ice conditions similar to those for the design scenario; D may be treated as a constant having a value of −0.7. A design value of x0 may be determined based on the analysis of appropriate data sets. The treatment of exposure is described for data analysis and design. The effects of exposure must be removed during data analysis to provide a design curve based on single panel exposure. For the design, estimates from the design curves must be adjusted to properly reflect the design exposure.

Circumpolar measurements of speciated mercury, ozone and carbon monoxide in the boundary layer of the Arctic Ocean

Abstract. Using the Swedish icebreaker Oden as a platform, continuous measurements of airborne mercury (gaseous elemental mercury (Hg0), divalent gaseous mercury species HgIIX2(g) (acronym RGM) and mercury attached to particles (PHg)) and some long-lived trace gases (carbon monoxide CO and ozone O3) were performed over the North Atlantic and the Arctic Ocean. The measurements were performed for nearly three months (July–September 2005) during the Beringia 2005 expedition (from Göteborg, Sweden via the proper Northwest Passage to the Beringia region Alaska – Chukchi Penninsula – Wrangel Island and in-turn via a north-polar transect to Longyearbyen, Spitsbergen). The Beringia 2005 expedition was the first time that these species have been measured during summer over the Arctic Ocean going from 60° to 90° N. During the North Atlantic transect, concentration levels of Hg0, CO and O3 were measured comparable to typical levels for the ambient mid-hemispheric average. However, a rapid increase of Hg0 in air and surface water was observed when entering the ice-covered waters of the Canadian Arctic archipelago. Large parts of the measured waters were supersaturated with respect to Hg0, reflecting a strong disequilibrium. Heading through the sea ice of the Arctic Ocean, a fraction of the strong Hg0 pulse in the water was transferred with some time-delay into the air samples collected ~20 m above sea level. Several episodes of elevated Hg0 in air were encountered along the sea ice route with higher mean concentration (1.81±0.43 ng m−3) compared to the marine boundary layer over ice-free Arctic oceanic waters (1.55±0.21 ng m−3). In addition, the bulk of the variance in the temporal series of Hg0 concentrations was observed during July. The Oden Hg0 observations compare in this aspect very favourably with those at the coastal station Alert. Atmospheric boundary layer O3 mixing ratios decreased when initially sailing northward. In the Arctic, an O3 minimum around 15–20 ppbV was observed during summer (July–August). Alongside the polar transect during the beginning of autumn, a steady trend of increasing O3 mixing ratios was measured returning to initial levels of the expedition (>30 ppbV). Ambient CO was fairly stable (84±12 ppbV) during the expedition. However, from the Beaufort Sea and moving onwards steadily increasing CO mixing ratios were observed (0.3 ppbV day−1). On a comparison with coeval archived CO and O3 data from the Arctic coastal strip monitoring sites Barrow and Alert, the observations from Oden indicate these species to be homogeneously distributed over the Arctic Ocean. Neither correlated low ozone and Hg0 events nor elevated concentrations of RGM and PHg were at any extent sampled, suggesting that atmospheric mercury deposition to the Arctic basin is low during the Polar summer and autumn.

Long‐baseline acoustic navigation for under‐ice autonomous underwater vehicle operations

AbstractThe recent Arctic GAkkel Vents Expedition (AGAVE) to the Arctic Ocean's Gakkel Ridge (July/August 2007) aboard the Swedish icebreaker I/B Oden employed autonomous underwater vehicles (AUVs) for water‐column and ocean bottom surveys. These surveys were unique among AUV operations to date in requiring georeferenced navigation in proximity to the seafloor beneath permanent and moving ice cover. We report results for long‐baseline (LBL) acoustic navigation during autonomous under‐ice surveys near the seafloor and adaptation of the LBL concept for several typical operational situations including navigation in proximity to the ship during vehicle recoveries. Fixed seafloor transponders were free‐fall deployed from the ship for deep positioning. The ship's helicopter collected acoustic travel times from several locations to georeference the transponders' locations, subject to the availability of openings in the ice. Two shallow beacons suspended from the ship provided near‐surface spherical navigation in ship‐relative coordinates. During routine recoveries, we used this system to navigate the vehicles into open water near the ship before commanding them to surface. In cases in which a vehicle was impaired, its position was still determined acoustically through some combination of its acoustic modem, the fixed seafloor transponders, the ship‐deployed transponders, and an onboard backup relay transponder. The techniques employed included ranging adapted for a moving origin and hyperbolic navigation. © 2008 Wiley Periodicals, Inc.

Transports of Nordic Seas water masses and excess SF 6 through Fram Strait to the Arctic Ocean

To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean – 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoride (SF 6) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF 6 into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF 6 was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south.