Jens Ehn

University of Manitoba | UMN · Centre for Earth Observation Science

In subarctic marine environments, nutrient stocks are replenished through physical and biogeochemical processes in winter, largely setting an upper limit on new primary production for the next growing season. In spring, marine nutrient stocks are modified by freshwater-associated additions, especially in coastal areas. Hydroelectric development of...

Vertical profiles of salinity, and isotopic abundance ratios of hydrogen (δ²H) and oxygen (δ¹⁸O) of 18 landfast ice cores, collected along the northeast coast of James Bay in March 2019, and one ice core collected in Belcher Islands, were used to obtain the winter timeseries of the spatiotemporal evolution of the under-ice plume of La Grande River...

Indigenous-driven and community-partnered research projects seeking to develop salient, legitimate, and credible knowledge bases for environmental decision-making require a multiple knowledge systems approach. When involving partners in addition to communities, diverging perspectives and priorities may arise, making the pathways to engaging in prin...

Thinning sea ice cover and earlier melt in the Arctic impact primary producer (PP) phenology, causing earlier ice algal bloom termination and phytoplankton bloom commencement. However, logistic constraints limit capturing the complete seasonal evolution of PPs and their physical drivers. Here, we combine spectral irradiance data from subsurface oce...

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 Manit...

Numerous studies have been conducted to enhance our understanding of how climate change impacts landfast ice and its break-up in spring or summer. Yet, predictions of break-up timing have proven elusive, and dependent on multiple environmental drivers. In this study, we investigate whether/to what extent snow melt on land adjacent to the coast can...

Sea ice transparency is essential to the ecology of the ice‐covered sea. Research suggests that the diffuse attenuation coefficient of downwelling irradiance () varies with ice temperature (); however, the characteristics of its response are not well understood yet, particularly from a quantitative perspective. In an attempt to fill this gap, three...

River estuaries along western Hudson Bay, Canada, are important summer habitats for beluga whales (Delphinapterus leucus (Pallas, 1776)) and subject to increasing industrial development activities including vessel traffic. The feasibility of establishing a National Marine Conservation Area (NMCA) in western Hudson Bay is under consideration, requir...

The oceanography of the northern Canadian Arctic Archipelago (CAA) remains poorly studied. Here we present a unique set of conductivity–temperature–depth (CTD) and nitrate profiles collected in a fjord system around Axel Heiberg Island in the northern CAA during April–May 2022. The profiles are examined within the context of upstream observations i...

The Hudson Bay Lowlands (HBL) cover a vast area (150-400km wide, ~1300 km long) that has emerged from southern Hudson Bay and James Bay as a result of postglacial isostatic rebound. The cold sub-Arctic climate of HBL has promoted the formation of carbon-rich permafrost peatlands, but the region is now extremely vulnerable to climate warming that is...

While most global coasts suffer from a loss of landmass due to sea-level rise and coastal transgression, the sub-Arctic coastline of Hudson Bay and James Bay witness a reverse phenomenon due to post-glacial rebound. The carbon-rich peatlands Hudson Bay Lowland, that emerged from the retraction of the Tyrell Sea, are witnessing the highest rate of v...

Despite their wide use in past sea-ice reconstructions, the seasonal, habitat and species-based sources of sedimentary sea-ice proxies are poorly understood. Here, we conduct direct observations of the community composition of diatoms, dinoflagellate cysts and highly branched isoprenoid lipids within the sea ice, water column, sediment traps and se...

Climate-driven alterations of the marine environment are most rapid in Arctic and subarctic regions, including Hudson Bay in northern Canada, where declining sea ice, warming surface waters and ocean acidification are occurring at alarming rates. These changes are altering primary production patterns that will ultimately cascade up through the food...

Change in the dispersion pattern of Arctic river plumes due to climate change and hydroelectric regulation is challenging to monitor, calling for synoptic and continuous observation using satellite remote sensing. Algorithms for colored dissolved organic matter (CDOM) and total suspended solids (TSS) were applied to moderate resolution imaging spec...

A large under‐ice plume forms because of the regulated winter discharge from the La Grande River hydroelectric complex (NE James Bay, Canada), which is among the largest winter discharges in the circumpolar north. In 2016–2017, field campaigns were completed to characterize the under‐ice plume's structure, extent, and short‐term dynamics related to...

The ice bridge in Nares Strait is a well-known phenomenon that affects the liquid and solid freshwater flux from the Arctic Ocean through the strait and controls the downstream North Open Water polynya in northern Baffin Bay. Recently, the ice bridge has been in a state of decline, either breaking up earlier in the year or not forming at all and th...

Over the last few decades, there has been an increasing recognition for seagrasses' contribution to the functioning of nearshore ecosystems and climate change mitigation. Nevertheless, seagrass ecosystems have been deteriorating globally at an accelerating rate during recent decades. In 2017, research into the condition of eelgrass (Zostera marina)...

Through analysis of Canadian Ice Service ice charts, we have characterized the temporal and spatial variability of landfast sea ice (or fast ice) surrounding Hudson Bay and James Bay from 2000 to 2019. Over this 19-year period, we observed contrasting changes in fast-ice persistence between the western and eastern sides of Hudson Bay and James Bay....

The ice bridge in Nares Strait is a well-known phenomenon that affects the liquid and solid freshwater flux from the Arctic Ocean through the strait and controlling the downstream North Water polynya in the northern Baffin Bay. Recently, the ice bridge has been in a state of decline, either breaking up earlier or not forming at all, and thereby inc...

Ice bridges are unique features that form when sea ice consolidates and remains immobilized within channels. They form in many locations throughout the Arctic and are typically noted for the polynyas that form on their lee side. However, ice bridges also provide a temporary platform that may be used by both humans and wildlife to cross otherwise im...

Plain Language Summary Hudson Strait is located in northeastern Canada, separating northern Quebec (Nunavik) from Baffin Island, and is seasonally covered by sea ice from December to June. The Strait is a key shipping corridor in the Canadian Arctic, and while most of the shipping occurs during the open water season (July–October), two ice breaking...

The ice bridge that forms seasonally across Nares Strait impedes the southward transport of sea ice from the Lincoln Sea to Baffin Bay and contributes to the maintenance of the North Water Polynya. Previous studies have quantified how the bridge affects ice export and highlighted a long term decline in the duration of the bridge; however, the speci...

Within the dynamic seasonal ice cover of Hudson Bay, the Kivalliq Polynya is a large latent heat polynya that forms throughout winter in the northwest as a result of strong northwesterly offshore surface winds. Polynyas are known to be physically, biologically, and geochemically important and contribute to the regional ice mass balance; however, th...

Hudson Bay (Canada) is the world's largest inland sea, which receives upward of ∼700 km³ of river discharge annually. Cyclonic water circulation transports this riverine water along the coast toward Hudson Strait and into the Labrador Sea. Yearlong observations of the current velocity profile, collected from an array of oceanographic moorings deplo...

Pertinent environmental factors influencing the microalgal bloom during sea-ice breakup in Hudson Bay were investigated in June 2018, producing the first observations of late spring primary production in the offshore waters of this vast inland sea. Phytoplankton production was found to commence at the onset of ice melt, with surface nutrient deplet...

During a research expedition in Hudson Bay in June 2018, vast areas of thick (>10 m), deformed sediment-laden sea ice were encountered unexpectedly in southern Hudson Bay and presented difficult navigation conditions for the Canadian Coast Guard Ship Amundsen. An aerial survey of one of these floes revealed a maximum ridge height of 4.6 m and an av...

Geophysical systems are often assumed to follow Gaussian probability density functions; however, deviations from Gaussian behaviour can shed light on the underlying dynamics. For the large-scale motion of the Arctic sea ice, such deviations have been interpreted as signatures of structure in dynamic flow fields. In this study, we use higher-order m...

The MALINA oceanographic campaign was conducted during summer 2009 to investigate the carbon stocks and the processes controlling the carbon fluxes in the Mackenzie River estuary and the Beaufort Sea. During the campaign, an extensive suite of physical, chemical and biological variables were measured across seven shelf–basin transects (south–north)...

Hudson Bay has so far received little attention during the spring peak of microalgal growth, although it holds 10% of the seasonal ice cover found in the Arctic Ocean and provides a habitat for large populations of migratory birds and marine mammals. Furthermore, Hudson Bay is expected to undergo rapid changes in the timing and distribution of the...

Hudson Bay of northern Canada receives upward of 700 km3 of river discharge annually. Cyclonic water circulation in Hudson Bay transports this massive volume of riverine water along the coast toward Hudson Strait and into the Labrador Sea. However, synoptic, seasonal and interannual variability of the freshwater transport in Hudson Bay remains uncl...

A 2-year-long time series of currents and acoustic backscatter from an acoustic Doppler current profiler, moored over the eastern Beaufort Sea continental slope from October 2003 to September 2005, were used to assess the dynamics and variability of the sound-scattering layer. It has been shown that acoustic backscatter is dominated by a synchroniz...

The MALINA oceanographic campaign was conducted during summer 2009 to investigate the carbon stocks and the processes controlling the carbon Fluxes in the Mackenzie River estuary and the Beaufort Sea. During the campaign, an extensive suite of physical, chemical and biological variables was measured across seven shelf–basin transects (south-north)...

BaySys is a 4-year collaboration among industry partner Manitoba Hydro (Hydro Québec and Ouranos) and the Universities of Manitoba, Northern British Columbia, Québec à Rimouski, Alberta, Calgary, Laval and Trent to conduct oceanographic research in Hudson Bay. The overarching goal of the project is to understand the role of freshwater in Hudson Bay...

A two-year-long time series of currents and acoustic backscatter from an Acoustic Doppler Current Profiler, moored over the eastern Beaufort Sea continental slope from October 2003 to September 2005, were used to assess dynamics and variability of the sound-scattering layer. It has been shown that acoustic backscatter is dominated by a synchronized...

Hudson Bay, along with James Bay, forms a significant section of the Canadian Sub-Arctic basin which experiences an annual event of Land-fast sea ice formation and melt. Here Landfast ice dynamics largely depends on the climatic and oceanographic conditions, along with coastal geomorphology. In this study, we attempt to investigate the annual cycle...

The transmission of ultraviolet (UVR) and photosynthetically available radiation (PAR) through sea ice is a key factor controlling under-ice phytoplankton growth in seasonally ice-covered waters. The increase toward sufficient light levels for positive net photosynthesis occurs concurrently with the sea ice melt progression in late spring when ice...

Hudson Bay is a large seasonally ice-covered Canadian inland sea connected to the Arctic Ocean and North Atlantic through Foxe Basin and Hudson Strait. This study investigates zooplankton distribution, dynamics, and factors controlling them during open-water and ice cover periods (from September 2016 to October 2017) in Hudson Bay. A mooring equipp...

The Hudson Bay system is undergoing climate-driven changes in sea ice and freshwater inflow and has seen an increase in winter river inflow since the 1960s due in part to flow regulation for hydropower production. Southeast Hudson Bay and adjacent James Bay are at the forefront of these changes, with more than 1-month shortening of the season of se...

Recently, we highlighted the presence of a strong west‐east asymmetry in sea ice thickness across Hudson Bay that is driven by cyclonic circulation. Building on this work, we use satellite altimetry and a unique set of in situ observations of ice thickness from three moored upward looking sonars to examine the role of atmospherically driven ice dyn...

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiq...

Hudson Bay is a large, seasonally-ice covered Canadian inland sea, connected to the Arctic Ocean and North Atlantic through Foxe Basin and Hudson Strait. This study investigates zooplankton distribution, dynamics and factors controlling them during open water and ice cover periods (from September 2016 to October 2017) in Hudson Bay. A mooring equip...

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and the fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Q...

Hudson Bay and James Bay combined, form a major section of the large and relatively shallow Canadian Inland Seas. This Sub-Arctic basin experiences a seasonal event of Land-fast sea ice formation and melt. Land-fast sea ice is freezing of sea water with a continuous extent from the shore, extending towards the offshore region. Formation of this fea...

Arctic sea ice is experiencing a shorter growth season and an earlier ice melt onset. The significance of spring microalgal blooms taking place prior to sea ice breakup is the subject of ongoing scientific debate. During the Green Edge project, unique time-series data were collected during two field campaigns held in spring 2015 and 2016, which doc...

Here, we discuss the impact of ice cover on diel vertical migration (DVM) of zooplankton at three locations: Young Sound fjord in Northeast Greenland, northeast of Churchill in Hudson and the Southeastern Beaufort Sea in the Canadian Arctic. At all three locations, we deployed ice-tethered or bottom-anchored moorings equipped with Acoustic Doppler...

The Arctic spring phytoplankton bloom has been reported to commence under a melting sea ice cover as transmission of photosynthetically active radiation (PAR; 400–700 nm) suddenly increases with the formation of surface melt ponds. Spatial variability in ice surface characteristics, i.e., snow thickness or melt pond distributions, and subsequent im...

The particulate beam attenuation coefficient at 660 nm, cp(660), was measured in conjunction with properties of suspended particle assemblages in August 2009 within the Canadian Beaufort Sea continental margin, a region heavily influenced by freshwater and sediment discharge from the Mackenzie River, but also by sea ice melt. The mass concentration...

Past research in seasonally ice‐covered Arctic seas has suggested that ice algae play a role in reducing dissolved inorganic carbon (DIC) during spring, preconditioning surface waters to low dissolved CO2 (pCO2sw), and uptake of atmospheric CO2 during the ice‐free season. The potential role of under‐ice phytoplankton blooms on DIC and pCO2sw has no...

Monthly mean passive microwave-derived sea-ice motion maps for 36 winters (October–April) are used to examine pan-Arctic sea-ice drift speeds and patterns. The mean Arctic Ocean sea-ice motion consists of three well-known primary circulation regimes: the Beaufort Gyre (BG), transpolar drift (TPD), and a motion system from the Kara Sea (KS). The 36-...

A portion of the freshwater transport through Fram Strait consists of low‐salinity Pacific‐derived Arctic water flowing southward along the east coast of Greenland. The pathways of this water are currently unclear. An Ice Tethered Profiler deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected a profile every 3...

A mooring equipped with two acoustic Doppler current profilers (ADCP) and a sediment trap was deployed in September 2016 in Hudson Bay at 59° 58.156’ N 91° 57.144’ W (~190 km north-east from the port of Churchill). The backscatter intensity and vertical velocity time series from the mooring ADCPs showed a pattern typical for the zooplankton diel ve...

During the spring-to-summer transition, the snow cover on Arctic sea ice melts and meltwater pools on the surface to form melt ponds; however, the timing and extent of the ponding vary between years. In Dease Strait (Nunavut), this transition was particularly dramatic in 2014 when on 18 June meltwater had flooded >95% of the surface. In this study,...

The particulate beam attenuation coefficient at 660 nm, cp(660), was measured in conjunction with properties of suspended particle assemblages in August 2009 within the Canadian Beaufort Sea continental margin, a region heavily influenced by sediment discharge from the Mackenzie River. The suspended particulate matter mass concentration (SPM) range...