Lincoln Sea Research Articles

Novel observations of Atlantic walruses (Odobenus rosmarus rosmarus) in Archer Fjord, northern Ellesmere Island, Nunavut, Canada

In Canada and West Greenland, Atlantic walruses (Odobenus rosmarus rosmarus) are commonly found in productive shallow water areas with their latitudinal range extending from the Ontario coast of Hudson Bay ( ~ 53°N) to southern Kane Basin ( ~ 79°N). Most sightings information of Atlantic walruses in Kane Basin come from late-nineteenth and early-twentieth century Arctic expeditions with aerial surveys seldom being performed in this area and none being conducted to date in waters around northern Ellesmere Island—a largely understudied area overall. We conducted photographic and visual aerial surveys in the Canadian jurisdiction of northern Nares Strait and Lincoln Sea in August 2018. We documented novel photographic and observational evidence of several Atlantic walruses in Archer Fjord, Nunavut—a fjord that extends westward from Lady Franklin Bay. The least cost path of travel between the northern distribution limit of the high-Arctic Atlantic walrus population and the entrance to Lady Franklin Bay is approximately 255 km. Coupled with a previous observation of Atlantic walruses in northern Kane Basin in 2009 and one adult male in Archer Fjord in 2010, the observation of eight Atlantic walruses in Archer Fjord in 2018, indicates a possible update to the northern range of high-Arctic Atlantic walrus to Archer Fjord. Little is known of the physical-biological dynamics of northern Ellesmere Island; therefore, this is a priority study area to obtain baseline ecological data for the last Arctic area predicted to retain multi-year sea ice to inform Arctic conservation and management.

Seafloor Kinematics of the Near-Greenland Region of the Eurasian Basin

The Lincoln Sea floor evolved during stretching of a segment of the continental Greenland –Barents Sea shelf. Prior to the onset of extension, the continental shallow-water Morris Jesup Rise and the Yermak Plateau were a single unit. During rifting, this single continental plateau broke apart, initiating propagation of the Gakkel mid-ocean ridge toward the Atlantic. The breakup continued for ~1.5 Ma, 35.3–33.7 Ma ago. The emplacement of numerous mafic dikes during rifting could have caused the high-amplitude magnetic anomalies on the single plateau. For the first time, the fracture geometry involved in the breakup of the continental crust has been reconstructed, the Euler poles and angle of rotation describing its kinematics have been determined, and the paleobathymetry on the flanks of the fracture have been reconstructed.

Airborne Observations of Summer Thinning of Multiyear Sea Ice Originating From the Lincoln Sea.

To better understand recent changes of Arctic sea ice thickness and extent, it is important to distinguish between the contributions of winter growth and summer melt to the sea ice mass balance. In this study we present a Lagrangian approach to quantify summer sea ice melt in which multiyear ice (MYI) floes that were surveyed by airborne electromagnetic thickness sounding within Nares Strait during summer were backtracked, using satellite imagery, to a region in close proximity (3–20 km) to spring ice thickness surveys carried out in the Lincoln Sea. Typical modal total MYI thicknesses, including ~0.4‐m snow, ranged between 3.9 and 4.7 m in the Lincoln Sea during April. Ice‐only modal thicknesses were between 2.2 and 3.0 m in Nares Strait during August. Total thinning including snow and ice was 1.3 ± 0.1 m including 0.4 ± 0.09 m of snow melt and 0.9 ± 0.2 m of ice melt. This translates to a seasonal net heat input of 305 ± 69 MJ/m2 (262 ± 60 MJ/m2 for ice only) and seasonal net heat flux of 57 ± 13 W/m2 (45 ± 10 W/m2 for ice only), which is unlikely to be explained by solar radiation fluxes alone. Furthermore, our approach provides an improvement on traditional ice mass balance buoy estimates because it integrates melt over larger spatial scales, where melt can be highly variable due to differential melt experienced between melt ponds, bare ice, hummocks, and ridges.

Deglacial to postglacial history of Nares Strait, Northwest Greenland: a marine perspective from Kane Basin

Abstract. A radiocarbon-dated marine sediment core retrieved in Kane Basin, central Nares Strait, was analysed to constrain the timing of the postglacial opening of this Arctic gateway and its Holocene evolution. This study is based on a set of sedimentological and geochemical proxies of changing sedimentary processes and sources that provide new insight into the evolution of ice sheet configuration in Nares Strait. Proglacial marine sedimentation at the core site initiated ca. 9.0 cal ka BP following the retreat of grounded ice. Varying contributions of sand and clasts suggest unstable sea ice conditions and glacial activity, which subsisted until ca. 7.5 cal ka BP under the combined influence of warm atmospheric temperatures and proglacial cooling induced by the nearby Innuitian (IIS) and Greenland (GIS) ice sheets. An interval rich in ice-rafted debris (IRD) is interpreted as the collapse of the ice saddle in Kennedy Channel ca. 8.3 cal ka BP that marks the complete opening of Nares Strait and the initial connection between the Lincoln Sea and northernmost Baffin Bay. Delivery of sediment by icebergs was strengthened between ca. 8.3 and ca. 7.5 cal ka BP following the collapse of the buttress of glacial ice in Kennedy Channel that triggered the acceleration of GIS and IIS fluxes toward Nares Strait. The destabilisation in glacial ice eventually led to the rapid retreat of the GIS in eastern Kane Basin at about 8.1 cal ka BP as evidenced by a noticeable change in sediment geochemistry in our core. The gradual decrease in carbonate inputs to Kane Basin between ∼8.1 and ∼4.1 cal ka BP reflects the late deglaciation of Washington Land. The shoaling of Kane Basin can be observed in our record by the increased winnowing of lighter particles as the glacio-isostatic rebound brought the seabed closer to subsurface currents. Reduced iceberg delivery from 7.5 to 1.9 cal ka BP inferred by our dataset may be linked to the retreat of the bordering ice sheets on land that decreased their number of marine termini.

The Early Collapse of the 2017 Lincoln Sea Ice Arch in Response to Anomalous Sea Ice and Wind Forcing

AbstractOne of the most dramatic indicators of climate change is the reduction in the extent and thickness of Arctic sea ice that has resulted in an increase in wind‐driven sea ice mobility. During April and May 2017, satellite observations indicated that the ice arch that forms between Nares Strait and the Lincoln Sea collapsed. Typically, this collapse occurs in July or August allowing multiyear ice to exit the Arctic through Nares Strait. Here we show that the period of the collapse was associated with the presence of a polynya in northern Nares Strait, thin ice in the Lincoln Sea, and an unusual wind regime characterized by strong northerly flow. We propose that these anomalous conditions resulted in the arch's early collapse. If the ice in the region continues to thin, early collapses may occur more frequently with implications for the regional as well as the downstream climate and ecosystems.

Sea-ice drag as a function of deformation and ice cover: Effects on simulated sea ice and ocean circulation in the Arctic

Many state-of-the-art coupled sea ice-ocean models use atmospheric and oceanic drag coefficients that are at best a function of the atmospheric stability but otherwise constant in time and space. Constant drag coefficients might lead to an incorrect representation of the ice-air and ice-ocean momentum exchange, since observations of turbulent fluxes imply high variability of drag coefficients. We compare three model runs, two with constant drag coefficients and one with drag coefficients varying as function of sea-ice characteristics. The computed drag coefficients range between 0.88 ×10−3 and 4.68 ×10−3 for the atmosphere, and between 1.28 ×10−3 and 13.68 ×10−3 for the ocean. They fall in the range of observed drag coefficients and illustrate the interplay of ice deformation and ice concentration in different seasons and regions. The introduction of variable drag coefficients improves the realism of the model simulation. In addition, using the average values of the variable drag coefficients improves simulations with constant drag coefficients. When drag coefficients depend on sea-ice characteristics, the average sea-ice drift speed in the Arctic basin increases from 6.22 cm s−1 to 6.64 cm s−1. This leads to a reduction of ice thickness in the entire Arctic and particularly in the Lincoln Sea with a mean value decreasing from 7.86 m to 6.62 m. Variable drag coefficients lead also to a deeper mixed layer in summer and to changes in surface salinity. Surface temperatures in the ocean are also affected by variable drag coefficients with differences of up to 0.06 °C in the East Siberian Sea. Small effects are visible in the ocean interior

Increasing Mobility of High Arctic Sea Ice Increases Marine Hazards Off the East Coast of Newfoundland

AbstractHeavy ice conditions along Canada's east coast during spring 2017 presented hazardous conditions for the maritime industry and required the Canadian Coast Guard to pull its research icebreaker, CCGS Amundsen, off its scientific cruise to provide ice escort services and conduct search and rescue operations along Newfoundland's northeast coast. Greater ice concentrations and a thicker ice pack than are typical of this area created the anomalous ice cover. Within this paper we present in situ observations of the ice cover, confirming that pieces of multiyear sea ice from the high Arctic were present within the ice cover, and subsequently examine the transport pathway that connects the export of thick multiyear sea ice from the Lincoln Sea and Canadian Arctic Archipelago to coastal communities in Newfoundland. We conclude with a discussion on how an increasingly mobile Arctic sea ice cover may increase these ice hazards in the south.

A Meteoric Water Budget for the Arctic Ocean

AbstractA budget of meteoric water (MW = river runoff, net precipitation minus evaporation, and glacial meltwater) over four regions of the Arctic Ocean is constructed using a simple box model, regional precipitation‐evaporation estimates from reanalysis data sets, and estimates of import and export fluxes derived from the literature with a focus on the 2003–2008 period. The budget indicates an approximate/slightly positive balance between MW imports and exports (i.e., no change in storage); thus, the observed total freshwater increase observed during this time period likely resulted primarily from changes in non‐MW freshwater components (i.e., increases in sea ice melt or Pacific water and/or a decrease in ice export). Further, our analysis indicates that the MW increase observed in the Canada Basin resulted from a spatial redistribution of MW over the Arctic Ocean. Mean residence times for MW were estimated for the Western Arctic (5–7 years), Eastern Arctic (3–4 years), and Lincoln Sea (1–2 years). The MW content over the Siberian shelves was estimated (∼14,000 km3) based on a residence time of 3.5 years. The MW content over the entire Arctic Ocean was estimated to be ≥44,000 km3. The MW export through Fram Strait consisted mostly of water from the Eastern Arctic (3,237 ± 1,370 km3 yr−1) whereas the export through the Canadian Archipelago was nearly equally derived from both the Western Arctic (1,182 ± 534 km3 yr−1) and Lincoln Sea (972 ± 391 km3 yr−1).

Ice and Snow Thickness Variability and Change in the High Arctic Ocean Observed by In Situ Measurements

AbstractIn April 2017, we collected unique, extensive in situ data of sea ice and snow thickness. At 10 sampling sites, located under a CryoSat‐2 overpass, between Ellesmere Island and 87.1°N mean and modal total ice thicknesses ranged between 2 to 3.4 m and 1.8 to 2.9 m, respectively. Coincident snow thicknesses ranged between 0.3 to 0.47 m (mean) and 0.1 to 0.5 m (mode). The profile spanned the complete multiyear ice zone in the Lincoln Sea, into the first‐year ice zone farther north. Complementary snow thickness measurements near the North Pole showed a mean thickness of 0.31 m. Compared with scarce measurements from other years, multiyear ice was up to 0.75 m thinner than in 2004, but not significantly different from 2011 and 2014. We found excellent agreement with a commonly used snow climatology and with published long‐term ice thinning rates. There was reasonable agreement with CryoSat‐2 thickness retrievals.

Regional crustal architecture of Ellesmere Island, Arctic Canada

Abstract New deep seismological data from Ellesmere Island and the adjacent Arctic continental margin provide new information about the crustal structure of the region. These data were not available for previous regional crustal models. This paper combines and redisplays previously published results – a gravity-derived Moho map and seismological results –to produce new maps of the Moho depth, the depth to basement and the crystalline crustal thickness of Ellesmere Island and contiguous parts of the Arctic Ocean, Greenland and Axel Heiberg Island. Northern Ellesmere Island is underlain by a thick crustal block (Moho at 41 km, c. 35 km crust). This block is separated from the Canada–Greenland craton in the south by a WSW–ENE-trending channel of thinned crystalline crust (Moho at 30–35 km, <20 km thick crust), which is overlain by a thick succession of metasedimentary and younger sedimentary rocks (15–20 km). The Sverdrup Basin in the west and the Lincoln Sea in the east interrupt the crustal architecture of central Ellesmere Island, which is interpreted to be more representative of its initial post-Ellesmerian Orogen structure, but with a later Sverdrup Basin and Eurekan overprint.

Pan-Arctic sea ice-algal chl a biomass and suitable habitat are largely underestimated for multiyear ice.

There is mounting evidence that multiyear ice (MYI) is a unique component of the Arctic Ocean and may play a more important ecological role than previously assumed. This study improves our understanding of the potential of MYI as a suitable habitat for sea ice algae on a pan-Arctic scale. We sampled sea ice cores from MYI and first-year sea ice (FYI) within the Lincoln Sea during four consecutive spring seasons. This included four MYI hummocks with a mean chl a biomass of 2.0mg/m2 , a value significantly higher than FYI and MYI refrozen ponds. Our results support the hypothesis that MYI hummocks can host substantial ice-algal biomass and represent a reliable ice-algal habitat due to the (quasi-) permanent low-snow surface of these features. We identified an ice-algal habitat threshold value for calculated light transmittance of 0.014%. Ice classes and coverage of suitable ice-algal habitat were determined from snow and ice surveys. These ice classes and associated coverage of suitable habitat were applied to pan-Arctic CryoSat-2 snow and ice thickness data products. This habitat classification accounted for the variability of the snow and ice properties and showed an areal coverage of suitable ice-algal habitat within the MYI-covered region of 0.54million km2 (8.5% of total ice area). This is 27 times greater than the areal coverage of 0.02million km2 (0.3% of total ice area) determined using the conventional block-model classification, which assigns single-parameter values to each grid cell and does not account for subgrid cell variability. This emphasizes the importance of accounting for variable snow and ice conditions in all sea ice studies. Furthermore, our results indicate the loss of MYI will also mean the loss of reliable ice-algal habitat during spring when food is sparse and many organisms depend on ice-algae.

Ekman circulation in the Arctic Ocean: Beyond the Beaufort Gyre

AbstractData derived from satellite‐based observations, with buoy‐based observations and assimilations, are used to calculate ocean Ekman layer transport and evaluate long‐term trends in the Arctic Ocean over the period 1979–2014. The 36 year mean of upwelling (downwelling) is 3.7 ± 2.0 (–4.0 ± 2.2) Sv for the entire Arctic Basin, with ∼0.3 Sv net downwelling contributed mostly by the Canadian region. With regard to long‐term trends, the annual mean upwelling (downwelling) over the entire Arctic Basin is increasing at a linear rate of 0.92 (–0.98) Sv/decade. The Canada/Alaska coasts and Beaufort and Laptev Seas are regions of greatest Ekman transport intensification. The central Arctic Ocean and Lincoln Sea also have an increasing trend in transport. The Canadian and Eurasian regions each account for about half the total vertical Ekman variations in the Arctic Basin.

Snow depth on Arctic sea ice derived from radar: In situ comparisons and time series analysis

AbstractThe snow radar being flown on NASA's Operation IceBridge, ongoing aircraft campaigns to the Arctic and the Antarctic are providing unique observations of the depth of snow on the sea ice cover. In this paper, we focus on the radar‐derived snow depth results from the 2009–2012 Arctic campaigns. We develop and evaluate the use of a distinct snow layer tracker to measure snow depth based on a Support Vector Machine (SVM) supervised learning algorithm. The snow radar is designed to detect both the air‐snow and snow‐ice interfaces using ultrawideband frequencies from 2 to 8 GHz. The quality, errors, and repeatability of the snow radar snow depth estimates are examined, based on comparisons with in situ data obtained during two separate sea ice field campaigns, the GreenArc 2009 and the CryoVEx 2011 campaigns off Greenland in the Lincoln Sea. Finally, we analyze 4 years (2009–2012) of three annually repeated sea ice flight lines obtained in early spring, located off Greenland and the Canadian Arctic. We examine the annual variations of snow depth differences between perennial and seasonal ice when available. Overall, the snow layer tracker produced consistent, accurate results for snow depths between 0.10 and ∼0.60 m. This was confirmed with comparisons with the two data sets from the in situ measurement campaigns as well as with the time series analysis, and is consistent with other published results.

Comparing springtime ice-algal chlorophyll a and physical properties of multi-year and first-year sea ice from the Lincoln Sea.

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.

Three-dimensional localization of transient acoustic sources using an ice-mounted geophone

This paper presents an approach to three-dimensional (3D) localization of ocean acoustic sources using a single three-component geophone on Arctic sea ice. Source bearing is estimated by maximizing the radial signal power as a function of horizontal look angle, applying seismic polarization filters to suppress shear waves with transverse particle motion. The inherent 180° ambiguity is resolved by requiring outgoing (prograde) particle motion in the radial-vertical plane. Source range and depth estimates and uncertainties are computed by Bayesian inversion of arrival-time differences of the water-borne acoustic wave and ice seismic waves, including the horizontally-polarized shear wave and longitudinal plate wave. The 3D localization is applied to geophone recordings of impulsive sources deployed in the water column at a series of ranges (200 to 1000 m) and bearings (0° to 90°) for three sites in the Lincoln Sea characterized by smooth annual ice, rough/ridged annual ice, and thick multi-year ice. Good bearing estimates are obtained in all cases. Range-depth localization is successful for ranges over which ice seismic arrivals could be reliably detected, approximately 200 m on rough ice, 500 m on smooth ice, and 800 m on multi-year ice. Effects of environmental uncertainty on localization are quantified by marginalizing over unknown environmental parameters.

On the waters upstream of Nares Strait, Arctic Ocean, from 1991 to 2012

The Lincoln Sea is a bifurcation point, where waters from the Canadian and Eurasian Basins flow to Nares or Fram Strait. Mechanisms that control which waters are found in the Lincoln Sea, and on its continental shelves, are unknown. Using conductivity–temperature–depth (CTD; from hydrographic and ice-tethered profiler surveys), nutrient, and mooring data with the DRAKKAR global 3-D coupled ocean/sea-ice model, the Lincoln Sea was examined from 1991 to 2012. Although both Pacific and Atlantic waters were observed on the North Ellesmere and North Greenland shelves, Atlantic water was shallower on the North Greenland shelf. Thus, deeper than 125m, water was warmer and saltier on the North Greenland shelf than the North Ellesmere shelf. Three different water types were identified on the North Ellesmere shelf – waters from the Canadian Basin were observed 1992, 1993, 1996, 2005, and 2012, waters from both the Canadian and Eurasian Basins were observed in 2003, 2004, and 2008, and waters with no temperature minima or maxima below the surface mixed layer were observed in 1991, 2006, 2009, and 2010. Mixing with vertical advection speeds of 1×10−4ms−1 were observed on the continental slope and this mixing could cause the disappearance of the temperature maxima. Model results suggest that currents on the North Ellesmere shelf were weak (less than 10cms−1), baroclinic, and directed away from Nares Strait while currents on the North Greenland shelf were stronger (less than 15cms−1), and primarily directed towards Nares Strait. CTD, mooring, and model results suggest that the water advected to Nares Strait is primarily from the North Greenland shelf while water on the North Ellesmere shelf is advected westward.

New aero‐gravity results from the Arctic: Linking the latest Cretaceous‐early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean

The tectonic history of the Arctic Ocean remains poorly resolved and highly controversial. Details regarding break up of the Lomonosov Ridge from the Barents‐Kara shelf margins and the establishment of seafloor spreading in the Cenozoic Eurasia Basin are unresolved. Significantly, the plate tectonic evolution of the Mesozoic Amerasia Basin is essentially unknown. The Arctic Ocean north of Greenland is at a critical juncture that formed at the locus of a Mesozoic three‐plate setting between the Lomonosov Ridge, Greenland, and North America. In addition, the area is close to the European plate, resulting in complicated interactions between all these areas that are difficult to resolve. In 2009, the 550,000 km2 LOMGRAV aero‐geophysical survey produced the first collocated gravity and magnetic measurements over the area, significantly increasing the data coverage. We present an interpretation of a new free‐air gravity compilation, which reveals a regionally consistent structural grain across the Lomonosov Ridge, the Ellesmere and Lincoln Sea shelves, and the Alpha Ridge. We interpret the grain as evidence of latest Cretaceous (∼80 Ma) regional extension in response to the northward propagation of Atlantic and Labrador Sea opening into the Arctic, west of Greenland. This interpretation is consistent with coincident alkaline volcanic activity evident in the borderlands of the Lincoln Sea. We further suggest that Eurekan crustal shortening contributed to the formation of the distinct Lomonosov Ridge plateau against an important fault zone north of Greenland. Our results provide new constraints for Cretaceous–Cenozoic plate reconstructions of the Arctic.

Hydrographic changes in the Lincoln Sea in the Arctic Ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010

Hydrographic data from the Arctic Ocean show that freshwater content in the Lincoln Sea, north of Greenland, increased significantly from 2007 to 2010, slightly lagging changes in the eastern and central Arctic. The anomaly was primarily caused by a decrease in the upper ocean salinity. In 2011 upper ocean salinities in the Lincoln Sea returned to values similar to those prior to 2007. Throughout 2008–2010, the freshest surface waters in the western Lincoln Sea show water mass properties similar to fresh Canada Basin waters north of the Canadian Arctic Archipelago. In the northeastern Lincoln Sea fresh surface waters showed a strong link with those observed in the Makarov Basin near the North Pole. The freshening in the Lincoln Sea was associated with a return of a subsurface Pacific Water temperature signal although this was not as strong as observed in the early 1990s. Comparison of repeat stations from the 2000s with the data from the 1990s at showed an increase of the Atlantic temperature maximum which was associated with the arrival of warmer Atlantic water from the Eurasian Basin. Satellite‐derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the Canadian Archipelago shelf as far as the Lincoln Sea, causing a strong flow toward Nares Strait and likely Fram Strait. The total volume of anomalous freshwater observed in the Lincoln Sea and exported by 2011 was close to , approximately 13% of the total estimated FW increase in the Arctic in 2008.

The Effect of Climate Change on the Sea Ice and Hydrography in Nares Strait

A three-dimensional coupled ocean (Hybrid Coordinate Ocean Model; HYCOM) and sea-ice (Community Ice Code; CICE) model were used to simulate the ice cover and hydrography in the Lincoln Sea, Nares Strait and Baffin Bay for the period 1952 to 2080. The first eight years were used to spin up the model. The last 120 years were divided into four-year sub-periods, which have been evaluated and compared in order to estimate the simulated changes. The modelled oceanic volume flux and freshwater fluxes compare well with observations in the present day scenario. The annual volume flux varies, but the 10-year average is approximately 0.8 Sv (1 Sv = 106m3s−1) without any long-term trend. It should be noted that 5 cm were added to the sea surface height in Baffin Bay and Lancaster Sound during the entire simulation. This was done in order to control the volume flux of the control period without changing the variabillity. The freshwater flux increases from approximately 27 mSv in the control scenario to 73 mSv in the future scenario, mainly due to a fresher surface. The magnitude of the annual ice area flux through Nares Strait is higher than expected compared with results from satellite images. This is because the ice arch formed in the southern part of Kane Basin is less stable in the model simulation. The result is a sea-ice area flux of about 100 . This is approximately the same sea-ice area flux as observed in 2007 when the ice arch did not form. The sea-ice area flux from 2040 increases by around 50% because of a lowering of the sea-ice concentration which causes a large reduction in the internal sea-ice strength. The sea-ice volume flux is reduced during the entire period from approximately 200 to around 125 . The simulated sea-ice cover decreases throughout the entire period. The area is still fully ice covered during winter, but the duration of the sea-ice coverage becomes shorter. This leads to a fresher sea surface and a temperature increase of up to 0.5 °C at depths of approximately 200 m. The opening of the North Water Polynya in spring is limited by the reduced lifetime of the ice arch in Kane Basin. However, during some years when the ice arch is stable the polynya opens as expected both in time and place.

Comparison of coincident snow-freeboard and sea ice thickness profiles derived from helicopter-borne laser altimetry and electromagnetic induction sounding

[1] Sea ice thickness plays a critical role in global climate change, but it cannot be measured directly from space. Alternatively, sea ice freeboard is measured and converted to sea ice thickness with assumptions made for snow depth and snow/ice densities. This paper investigates the relationship between snow-freeboard (ice-freeboard plus snow) and total thickness (ice thickness plus snow) and addresses the uncertainties that arise from the unknown snow depth and snow/ice densities. A unique data set of coincident measurements of snow-freeboard and total thickness was collected in the Arctic and Antarctic. Snow-freeboard was determined by laser altimetry, and total thickness was determined by electromagnetic induction with a helicopter-borne instrument. Obtained total thickness/snow-freeboard ratios range from 2 to 12 in the Arctic and from 2 to 8 in the Antarctic. The principal finding is that the ratios vary greatly within each region, and a fixed ratio per profile should not be used, as this can induce incorrect ice thicknesses. The ratio uncertainties can induce a relative thickness error of 5.4% and 4.9% in the first-year and multiyear ice mode. Additionally, the coincident measurements allow the calculation of snow depth that can be used to densify existing in situ measurements. To assess accuracy, calculated snow depths were compared to in situ measurements and agree within ±5 cm. This increases if measurements and calculations differ spatially. The method of deriving snow-freeboard from laser altimetry is briefly described, and the variability of the total thickness/snow-freeboard ratio is shown for one profile in the Lincoln Sea and one in the Weddell Sea.