Hudson Bay Complex Research Articles

An overview of the NEMO modelling for the BaySys project

This article is intended as an introduction to discuss the development of a modelling framework to examine simulated climate change and river discharge regulation and their combined impact on marine conditions in the Hudson Bay Complex as a contribution to BaySys, a collaborative project between Manitoba Hydro, Hydro-Quebec, the University of Manitoba, the University of Alberta, Université Laval and Ouranos. In support of this work, a sea ice and oceanographic model was improved and then used to further study the effects of freshwater loading and ice cover on the circulation of Hudson Bay. This modelling perspective is based on the Nucleus for European Modelling of the Ocean (NEMO) ocean general circulation model coupled to version 2 of the Louvain-la-Neuve sea ice model (LIM2). The goal of the modelling was to provide a framework and tool for simulating projected changes in marine state and dynamic variables, while also enabling an integration of observations and numerical analyses. A key aspect of this work was the climate-hydrologic-ocean model integration aspect. The inclusion of a biogeochemical model and explicit tidal forcing to examine the evolution of a Canadian marginal sea with century-long integrations was also a novel aspect of the work. Overall, this work examines the NEMO modelling configuration used in BaySys, how it is set up and the experiments carried out. A broader picture evaluation of the model output is made including the BaySys mooring observations, showing that the modelling framework is suitable to examine the posed questions on the role of climate change and river regulation.

Protected and conserved coastal areas in Canada: insights with respect to Target 3 of the Kunming-Montreal Global Biodiversity Framework

Despite coastal area being recognised as an important subcomponent in protected and conserved areas targets for over a decade, it has been orphaned in both national and international reporting. In this paper, we provide the first progress report on protected and conserved coastal area in Canada. While 13.6 per cent of Canada’s coastal area is protected and conserved, there is substantial variation across Canada’s three oceans and Great Lakes, jurisdictional authorities, and marine/terrestrial ecosystems. Importantly, Manitoba (37.3 per cent) and the Yukon (45.1 per cent) have already achieved the 30 per cent coastal protection target of the Kunming-Montreal Global Biodiversity Framework (KM-GBF). However, Newfoundland and Labrador (7 per cent) and the Northwest Territories (8 per cent) currently fall significantly short. Very poor protection is evident in several marine bioregions and terrestrial ecozones, including across the Arctic, the Newfoundland and Labrador Shelves (0.7 per cent) and the Hudson Bay Complex (5.1 per cent). The Great Lakes require urgent and focused conservation attention, with lakes Ontario (3.6 per cent) and Erie (3.7 per cent) exhibiting a dismal amount of coastal protected and conserved area. Our results highlight the importance of explicitly reporting on the status of coastal area protection and we outline several considerations that can be used by the global conservation community to support more effective coastal protection, accounting and reporting vis-à-vis Target 3 of the KM-GBF

Sources of seasonal sea-ice bias for CMIP6 models in the Hudson Bay Complex

AbstractThe seasonal ice-free period in the Hudson Bay Complex (HBC) has grown longer in recent decades in response to warming, both from progressively earlier sea-ice retreat in summer and later sea-ice advance in fall. Such changes disrupt the HBC ecosystem and ice-based human activities. In this study, we compare 102 simulations from 37 models participating in phase 6 of the Coupled Model Intercomparison Project to the satellite passive microwave record and atmospheric reanalyses. We show that, throughout the HBC, models simulate an ice-free period that averages 30 d longer than in satellite observations. This occurs because seasonal sea-ice advance is unrealistically late and seasonal sea-ice retreat is unrealistically early. We find that much of the ice-season bias can be linked to a warm bias in the atmosphere that is associated with a southerly wind bias, especially in summer. Many models also exhibit an easterly wind bias during winter and spring, which reduces sea-ice convergence on the east side of Hudson Bay and impacts the spatial patterns of summer sea-ice retreat. These results suggest that, for many models, more realistic simulation of atmospheric circulation would improve their simulation of HBC sea ice.

Understanding the Physical Forcings Behind the Biogeochemical Productivity of the Hudson Bay Complex

AbstractMultiple factors influence the spatial and temporal chlorophyll‐a concentration of marine systems. The Hudson Bay Complex has historically been seen as a large, low‐production inland sea situated in the north of Canada. However, recent field campaigns, for the BaySys project, have provided new data on primary production in the bay. Due to the Hudson Bay complex's positioning, it experiences seasonal sea‐ice cover and has many rivers draining into it, resulting in a unique estuarine‐like environment. We use the biogeochemical model BLINGv0 + DIC, coupled to the online regional physical oceanographic and sea‐ice models, NEMOv3.6 and LIM2, respectively, forced with two bias‐corrected Coupled Model Intercomparison Project 5 climate forcings (MIROC5 and MRI) to simulate the base of the ecosystem. The simulations were evaluated with chlorophyll‐a satellite imagery and observations collected in 2018 and analyzed with Empirical Orthogonal Functions to understand the underlying physical forcings and key areas of chlorophyll‐a concentration distribution. The evaluation showed that both simulations successfully reproduced the sea‐ice melt, from west to east and formation, from north to south and correlated well with spatial bloom patterns. The main drivers of phytoplankton growth are the seasonal light and nutrient levels (48% and 54%), the mixed layer depth dynamics (18% and 14%), nutrient supply from rivers (13% and 8%), and sea ice production (7%) for the MIROC5 and MRI simulations, respectively. The sea‐ice dynamics and river runoff played a significant role in the system's productivity. Therefore, with future climate change and increased river regulation projects, up to 20% of overall chlorophyll‐a may be negatively impacted.

Content in fatty acids and carotenoids in phytoplankton blooms during the seasonal sea ice retreat in Hudson Bay complex, Canada

The Hudson Bay complex (HBC) is home to numerous indigenous communities that traditionally have relied heavily on its marine resources. The nutritional quality and stocks of the entire HBC food web depend in large part on the phytoplankton production of bioactive molecules (long chain polyunsaturated fatty acids and carotenoids) and their transfer through trophic levels. The purpose of this study was thus to determine which molecules were produced during spring phytoplankton blooms, as well as the environmental factors driving this production. We investigated 21 stations in 5 sub-regions of the HBC. At the time of sampling, the sub-regions studied had different environmental settings (e.g., ice cover, nutrients, seawater salinity and temperature) conditioning their bloom stages. Pre- and post-bloom stages were associated with relatively low concentrations of bioactive molecules (either fatty acids or carotenoids). In contrast, the highest concentrations of bioactive molecules (dominated by eicosapentaenoic acid and fucoxanthin) were associated with the diatom bloom that typically occurs at the ice edge when silicates remain available. Interestingly, the large riverine inputs in eastern Hudson Bay led to a change in protist composition (larger contribution of Dinophyceae), resulting in lower while more diverse content of bioactive molecules, whether fatty acids (e.g., α-linolenic acid) or carotenoids (e.g., peridinin). As greater stratification of the HBC is expected in the future, we suggest that a mixotrophic/heterotrophic flagellate-based food web would become more prevalent, resulting in a smaller supply of bioactive molecules for the food web.

Simulated impacts of relative climate change and river discharge regulation on sea ice and oceanographic conditions in the Hudson Bay Complex

In this analysis, we examine relative contributions from climate change and river discharge regulation to changes in marine conditions in the Hudson Bay Complex using a subset of five atmospheric forcing scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5), river discharge data from the Hydrological Predictions for the Environment (HYPE) model, both naturalized (without anthropogenic intervention) and regulated (anthropogenically controlled through diversions, dams, reservoirs), and output from the Nucleus for European Modeling of the Ocean Ice-Ocean model for the 1981–2070 time frame. Investigated in particular are spatiotemporal changes in sea surface temperature, sea ice concentration and thickness, and zonal and meridional sea ice drift in response to (i) climate change through comparison of historical (1981–2010) and future (2021–2050 and 2041–2070) simulations, (ii) regulation through comparison of historical (1981–2010) naturalized and regulated simulations, and (iii) climate change and regulation combined through comparison of future (2021–2050 and 2041–2070) naturalized and regulated simulations. Also investigated is use of the diagnostic known as e-folding time spatial distribution to monitor changes in persistence in these variables in response to changing climate and regulation impacts in the Hudson Bay Complex. Results from this analysis highlight bay-wide and regional reductions in sea ice concentration and thickness in southwest and northeast Hudson Bay in response to a changing climate, and east-west asymmetry in sea ice drift response in support of past studies. Regulation is also shown to amplify or suppress the climate change signal. Specifically, regulation amplifies sea surface temperatures from April to August, suppresses sea ice loss by approximately 30% in March, contributes to enhanced sea ice drift speed by approximately 30%, and reduces meridional circulation by approximately 20% in January due to enhanced zonal drift. Results further suggest that the offshore impacts of regulation are amplified in a changing climate.

A baseline evaluation of oceanographic and sea ice conditions in the Hudson Bay Complex during 2016–2018

In this paper, we examine sea surface temperatures (SSTs) and sea ice conditions in the Hudson Bay Complex as a baseline evaluation for the BaySys 2016–2018 field program time frame. Investigated in particular are spatiotemporal patterns in SST and sea ice state and dynamics, with rankings of the latter to highlight extreme conditions relative to the examined 1981–2010 climatology. Results from this study show that SSTs in northwestern Hudson Bay from May to July, 2016–2018, are high relative to the climatology for SST (1982–2010). SSTs are also warmer in 2016 and 2017 than in 2018 relative to their climatology. Similarly, unusually low sea ice cover existed from August to December of 2016 and July to September of 2017, while unusually high sea ice cover existed in January, February, and October of 2018. The ice-free season was approximately 20 days longer in 2016 than in 2018. Unusually high ice-drift speeds occurred in April of 2016 and 2017 and in May of 2018, coinciding with strong winds in 2016 and 2018 and following strong winds in March 2017. Strong meridional circulation was observed in spring of 2016 and winter of 2017, while weak meridional circulation existed in 2018. In a case study of an extreme event, a blizzard from 7 to 9 March 2017, evaluated using Lagrangian dispersion statistics, is shown to have suppressed sea ice deformation off the coast of Churchill. These results are relevant to describing and planning for possible future pathways and scenarios under continued climate change and river regulation.

A baseline evaluation of atmospheric and river discharge conditions in the Hudson Bay Complex during 2016–2018

In this article, we examine atmospheric and river discharge conditions within the Hudson Bay Complex for the BaySys 2016–2018 field program time frame. Investigated in particular is a subset of European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis - Interim (ERA-Interim) atmospheric forcing variables, namely 2-m surface temperature, 10-m surface winds, precipitation, and sea-level pressure, in addition to river discharge. Results from this assessment show that 2016 was characterized by unusually warm conditions (terrestrial and marine) throughout the annual cycle; 2017 by strong cyclone activity in March and high precipitation in January, October, and November; and 2018 by cold and windy conditions throughout the annual cycle. Evaluation of terrestrial conditions showed higher than normal land surface temperatures (the Hudson Bay physical watershed) for all of the 2016–2018 period (excluding a colder than normal spell August–November 2018), particularly in January (2016 and 2017), higher than normal precipitation in October (2016 and 2017), and higher than normal terrestrial discharge to the Hudson Bay Complex in March (2016 and 2017), with drier than average June through October (2016–2018).

Screening for High-Risk Marine Invaders in the Hudson Bay Region, Canadian Arctic

The Canadian Arctic is receiving increased ship traffic, largely related to non-renewable resource exploitation and facilitated by climate change. This traffic, much of which arrives in ballast, increases opportunities for the spread of aquatic invasive species (AIS). One of the regions at greatest risk is the Hudson Bay Complex. A horizon scanning exercise was conducted using the semi-quantitative Canadian Marine Invasive Screening Tool (CMIST) to identify AIS of potential concern to the region. This screening-level risk assessment tool, uses documented information to answer questions related to the likelihood and impact of invasion. Species were analyzed by ecological categories (zoobenthos, zooplankton, phytobenthos) and taxonomic groups, with 14 species (out of 31) identified as being of highest relative risk. Crabs, mollusks, macrozooplankton and macroalgae were the taxonomic groups with the highest overall risk scores, through a combination of higher likelihood of invasion and impact scores relative to other taxa. Species that may pose the highest AIS risk are currently mainly distributed on the east and west coasts of the North Atlantic Ocean. Their distributions coincide with source ports and shipping pathways that are well connected to the Hudson Bay Complex. This first horizon scan to identify potential high-risk AIS for the Canadian Arctic incorporated two novel approaches into the CMIST analysis: i) use of the tool to assess two new ecological categories (phytobenthos and zooplankton), and ii) use of averaged CMIST results to interpret general risk patterns of ecological categories. This study is also the first to use CMIST scores to highlight common source regions and connected ports for the highest risk species. In a scenario of climate change and increasing ship traffic, this information can be used to support management actions such as the creation of watch lists to inform adaptive management for preventing AIS establishment, and mitigating associated environmental and economic impacts.

Modelling the advection of pollutants in the Hudson Bay complex

The Hudson Bay Complex is a system of semi-enclosed waterbodies in the eastern Canadian sub-Arctic with limited communication to the Arctic Ocean via Fury and Hecla Strait, and to the North Atlantic Ocean via Hudson Strait. There has been a significant increase in ship traffic in the Hudson Bay Complex as it provides a maritime link to Eurasia, known as the Arctic Bridge, and the southern route of the Northwest Passage, connecting the ports in the North Atlantic Ocean and Pacific Ocean. The increasing ship traffic could promote a higher risk of accident, especially when considering the higher mobility of sea ice due to the warming over the polar region . In this study, we used a high-resolution numerical model to highlight the circulation pathways of pollutants due to ocean advection . We released Lagrangian particles at 9 sites, located along the Arctic Bridge and the southern Northwest Passage, every 10 days through the operating season (June–October) for 12 years (2004–2015), to determine when and over which sites the accidental spill of pollutant would have the greatest negative impact. We characterized three circulation pathways with respect to the oceanic circulation regime of where the particles were initially seeded, and computed the following parameters to numerically describe the spreading of particles: area occupied, distance travelled, and the depths of particles. We conclude that the particles released in eastern Hudson Strait exhibited the largest spreading area rapidly below the surface layer, posing a challenge for recovery operations and a threat to the environment. • Circulation pathways of pollutants in Hudson Bay due to ocean advection are studied. • This study is based on an ocean-sea ice coupled high-resolution model and Lagrangian particle tracking scheme. • The particles exhibited three main pathways with respect to oceanic circulation regime. • Particles released in the eastern Hudson Strait exhibited the largest spreading area with highest variability.

Changing surface radiation and energy budgets of the Hudson Bay Complex using the North American regional reanalysis (NARR) model

Monthly and annual component fluxes of the surface radiation and energy budgets for the two-decade period from 1997 to 2016 are compared with the climate normal period (1981–2010) for the marine system consisting of James Bay, Hudson Bay, Hudson Strait and Foxe Basin using estimates from the North American regional reanalysis model. Reflected solar radiation has declined unevenly, primarily offshore of major rivers, in polynyas and along shore leads, both during earlier melt and later freeze up. Annually, net radiation increases are driven by albedo decreases during the summer. Over 94% of the increases in ocean heat gain during the melt season are due to increases in absorbed sunlight. Large enhanced oceanic heat losses in the late fall are almost entirely consumed by intensified convective losses of both sensible and latent heat. All the seas within the Hudson Bay Complex show a reduced rate of ocean warming over the past two decades. This outcome can be partially reconciled with the observation that all water bodies are experiencing enhanced losses of energy during extended ice-free winters that exceed enhanced gains of energy during the extended ice-free summers. The implications of seasonal changes in ice cover for future climate are discussed.

“Sensitivity of freshwater dynamics to ocean model resolution and river discharge forcing in the Hudson Bay Complex” [J. Mar. Syst. 196, August 2019, Pages 48–64

“Sensitivity of freshwater dynamics to ocean model resolution and river discharge forcing in the Hudson Bay Complex” [J. Mar. Syst. 196, August 2019, Pages 48–64

Sensitivity of freshwater dynamics to ocean model resolution and river discharge forcing in the Hudson Bay Complex

Abstract Hydroelectric development and regulation have modified the temporal and spatial distribution of runoff entering the Hudson Bay Complex (HBC). To understand the impacts and future of regulation in this region, the numerical ocean model, NEMO, run with the Arctic and Northern Hemispheric Atlantic (ANHA) configuration, is used to model present day freshwater dynamics associated with river runoff and sea ice melt. The present work establishes the freshwater budget in each subregion of the HBC, in addition to evaluating the sensitivity to model resolution and estimates of river discharge forcing. It is shown that the annually averaged HBC freshwater budget is mainly a balance between river discharge and freshwater advected out of the region, while surface fluxes (ice melt and growth, and precipitation and evaporation) are the dominant term on seasonal time scales. Runoff forcing is found to impact the long term mean volume and freshwater fluxes out of the HBC, while increased resolution has minimal effect on these fluxes, with the exception of the Southampton–Baffin Island gate. Quantitative estimates of turbulent, mean, and Ekman components of freshwater exchange between the interior and boundary regions of Hudson Bay are also presented. We use offline Lagrangian passive tracers to estimate the HBC runoff residence time, which is as long as 32 years.

Revisiting the Circulation of Hudson Bay: Evidence for a Seasonal Pattern

AbstractThe Hudson Bay Complex is the outlet for many Canadian rivers, receiving roughly 900 km3/year of river runoff. Historically, studies found a consistent cyclonic flow year‐round in Hudson Bay, due to the geostrophic boundary current induced by river discharge and cyclonic wind forcing that was supported by available observations at that time. Using a high‐resolution ocean general circulation model, we show that in summer, the mean circulation is not cyclonic but consists of multiple small cyclonic and anticyclonic features, with the mean flow directed through the center of the bay. Absolute Dynamic Topography and velocity observations also show this seasonal flow pattern. We find that this summer circulation is driven by geostrophic currents, generated by steric height gradients, which are induced by increased river discharge during the spring freshet, and reinforced by anticyclonic seasonal wind patterns.

Modelling Sea Surface Temperature (SST) in the Hudson Bay Complex Using Bulk Heat Flux Parameterization: Sensitivity to Atmospheric Forcing, and Model Resolution

ABSTRACTSea surface temperature (SST) from four Nucleus for European Modelling of the Ocean (NEMO) model simulations is analyzed to study the bulk flux parameterization to compute SST over the Hudson Bay Complex (HBC) for the summer months (August and September) from 2002 to 2009. The NEMO simulation was forced with two atmospheric forcing sets with different resolutions: the Coordinated Ocean-ice Reference Experiment, version 2 (COREv2), as the lower resolution and the Canadian Meteorological Centre’s Global Deterministic Prediction System Reforecasts (CGRF) as the higher resolution. The CGRF forcing is also implemented in the third and fourth runs using different runoff data and different NEMO resolutions (1/12° versus 1/4°). Results show that all four modelled SSTs followed observed SST patterns, with regional differences in SST bias between simulations with different atmospheric forcing. The SST differences are small between simulations forced with the same atmospheric forcing but with different model resolution or runoff. This implies that the model resolution and runoff have a small effect on the simulated SST in the HBC. Moreover, to better capture the effect of near-surface temperature (Tair) on simulated SST, we conducted three analyses using the Haney flux linearization formula. Results from these assessments did not indicate any direct influence on the model-simulated SSTs by Tair. Looking at the heat flux as a signature for SST showed that both averaged spatial distribution and time series of net heat flux produced by the three CGRF forcing simulations were higher than the net heat flux generated by the CORE 2 simulation. This was generally true for all four components of the total heat flux (sensible, latent, shortwave, and longwave) individually as well. Total heat flux in summer is governed by the shortwave heat flux, with values up to 120 W m−2 in August, and the longwave heat flux is the main contributor to the total heat flux differences. These heat flux differences lead to corresponding colder model SSTs for the CGRF runs and warmer SSTs for the CORE 2 simulations.

Impacts of 1.5 and 2.0 °C Warming on Pan‐Arctic River Discharge Into the Hudson Bay Complex Through 2070

AbstractDischarge projections into the Hudson Bay Complex to 2070 are investigated for global mean temperature warming levels of 1.5 and 2.0 °C. Median precipitation increases from 1986–2005, ranging from 2% during summer to 19% during winter, are projected to increase discharge in all seasons except summer. The rise in discharge is greatest furthest north, into Foxe Basin, Ungava Bay, and Hudson Strait, exceeding 10% above historical annual means. A 2.0 °C warming results in higher discharge than 1.5 °C warming owing to greater precipitation (e.g., 6.5% greater spring discharge increase); however, summer discharge for 2.0 °C warming is lower due to enhanced evaporation and lower precipitation increase from historical (4.0% lower summer discharge increase). Extreme daily high flows are projected to be greater than historical, more so for 2.0 °C warming than 1.5 °C warming, and this is greatest in the eastern and northern regions. These projections suggest continued increasing river discharge into pan‐Arctic coastal oceans.

Sea ice thickness in the Eastern Canadian Arctic: Hudson Bay Complex & Baffin Bay

Past observations of sea ice thickness in the Eastern Canadian Arctic (ECA) have generally been restricted to drill-hole measurements at a few local sites on landfast ice. Here we use data from the laser altimeter ICESat and the radar altimeter Cryosat-2 to present a 14-year record (2003–2016) of high-resolution and spatially extensive ice thickness observations for the ECA and identify 12 sub-regions with distinct patterns. The mean sea ice growth rate within the seasonally ice-covered ECA from November to April is 23cmmo−1 (565km3mo−1), with the fastest increase in thickness occurring through strong ice convergence and deformation in eastern Hudson Bay and Foxe Basin. Our results demonstrate characteristically asymmetrical distributions of sea ice thickness in both Hudson Bay and Baffin Bay, but in opposing directions. In Hudson Bay the spring ice cover is 40cm thicker in the eastern region compared to the northwestern region, whereas in Baffin Bay the ice is 20cm thicker in the western half of the bay compared to the eastern half. In Hudson Bay we find that years with strong and positive ice drift vorticity (i.e. cyclonic and convergent conditions) correlate with increasingly asymmetrical sea ice covers, with the level of west-east asymmetry varying from 2 to 11cm per 100km. However, in Baffin Bay the ice drift vorticity is typically negative (i.e. anticyclonic and divergent) with no obvious link to the asymmetry of the spring ice cover. Finally, we estimate that large interannual variations in spring sea ice volume within the ECA lead to ±15% variations in the volume of freshwater available at the ocean surface during summer.

IceMap250—Automatic 250 m Sea Ice Extent Mapping Using MODIS Data

The sea ice cover in the North evolves at a rapid rate. To adequately monitor this evolution, tools with high temporal and spatial resolution are needed. This paper presents IceMap250, an automatic sea ice extent mapping algorithm using MODIS reflective/emissive bands. Hybrid cloud-masking using both the MOD35 mask and a visibility mask, combined with downscaling of Bands 3–7 to 250 m, are utilized to delineate sea ice extent using a decision tree approach. IceMap250 was tested on scenes from the freeze-up, stable cover, and melt seasons in the Hudson Bay complex, in Northeastern Canada. IceMap250 first product is a daily composite sea ice presence map at 250 m. Validation based on comparisons with photo-interpreted ground-truth show the ability of the algorithm to achieve high classification accuracy, with kappa values systematically over 90%. IceMap250 second product is a weekly clear sky map that provides a synthesis of 7 days of daily composite maps. This map, produced using a majority filter, makes the sea ice presence map even more accurate by filtering out the effects of isolated classification errors. The synthesis maps show spatial consistency through time when compared to passive microwave and national ice services maps.

Natural history museum data on Canadian Arctic marine benthos

Natural history museum’s collection data remain an underutilized resource that can help answer important questions, such as those related to the understanding of the spatial patterns of Arctic marine diversity. The present study compiles historical museum records from the Canadian Museum of Nature (6,002 records) and from the US National Museum of Natural History – Smithsonian Institution (240 records) on marine benthic taxa collected in the Canadian Arctic. This information is used to explore museum collection history and to examine the geographic distribution of collection records within five regions of the Canadian Arctic. The present museum datasets together cover a total of 774 taxa collected over 100 years with most of the specimens being collected between the 1920s and 1980s in the Hudson Bay Complex and Eastern Arctic regions. To better represent the overall Canadian Arctic diversity of marine benthos in museum collections, future specimen acquisition efforts could be directed towards certain taxonomic groups (e.g., polychaetes) and regions (e.g., Arctic Basin). Museum records significantly complement published reviews on benthic diversity and are critical for generating a comprehensive and accurate baseline status on benthic species distribution and diversity across the Canadian Arctic regions. We therefore stress the urgency for natural history museums holding Arctic marine benthic data to make their collection data accessible and informative.

Circumpolar Genetic Structure and Recent Gene Flow of Polar Bears: A Reanalysis.

Recently, an extensive study of 2,748 polar bears (Ursus maritimus) from across their circumpolar range was published in PLOS ONE, which used microsatellites and mitochondrial haplotypes to apparently show altered population structure and a dramatic change in directional gene flow towards the Canadian Archipelago—an area believed to be a future refugium for polar bears as their southernmost habitats decline under climate change. Although this study represents a major international collaborative effort and promised to be a baseline for future genetics work, methodological shortcomings and errors of interpretation undermine some of the study’s main conclusions. Here, we present a reanalysis of this data in which we address some of these issues, including: (1) highly unbalanced sample sizes and large amounts of systematically missing data; (2) incorrect calculation of FST and of significance levels; (3) misleading estimates of recent gene flow resulting from non-convergence of the program BayesAss. In contrast to the original findings, in our reanalysis we find six genetic clusters of polar bears worldwide: the Hudson Bay Complex, the Western and Eastern Canadian Arctic Archipelago, the Western and Eastern Polar Basin, and—importantly—we reconfirm the presence of a unique and possibly endangered cluster of bears in Norwegian Bay near Canada’s expected last sea-ice refugium. Although polar bears’ abundance, distribution, and population structure will certainly be negatively affected by ongoing—and increasingly rapid—loss of Arctic sea ice, these genetic data provide no evidence of strong directional gene flow in response to recent climate change.