A pinboard by
Atreya Basu

Ph.D. Student, University of Manitoba


Mass and energy exchange between the freshwater and marine system is the key aspect of physical and biogeochemical processes operating in the coastal waters. Interaction of the solar radiation (light) with the upper water column drives the coastal processes with a significant influence on the biological productivity of the system. Light interacts with optical constituents of the water body viz. the detrital matter (colour dissolved organic matter and inorganic sediments) and the phytoplankton, which are the primary producers of most aquatic system. Along with these, presence of sea ice influence the exchange of light in-between the water column and the atmosphere. My research study involves with the light matter interaction in the upper portion of the water column in Hudson Bay of Canada. Hudson Bay is the largest inland artic sea fed by numerous rivers. This high volume of freshwater input into the Hudson Bay is susceptible to modification, both in terms of water quality and quantity, through exchange processes in the watershed, and through climate forcing of the hydrological cycle both in space and time. A unique aspect of this system is the role that freshwater plays on both sea ice thermodynamic and dynamic processes within Hudson Bay. This freshwater-marine coupling affects all aspects of the Hudson Bay physical, biological and biogeochemical systems through the control which sea ice has on the exchange of light, heat and momentum in the marine system. Therefore, the study of freshwater plume source distinction (between runoff and sea ice melt) and its distribution in the Hudson Bay will directly reflect on the impact of changes in climatic variability on the physical processes of the Bay with its implication on the sea ice cycle. Hudson Bay circulation is critical to the global circulation as it influences the North Atlantic circulation.


Modelling the sea ice-ocean seasonal cycle in Hudson Bay, Foxe Basin and Hudson Strait, Canada

Abstract: The seasonal cycle of water masses and sea ice in the Hudson Bay marine system is examined using a three-dimensional coastal ice-ocean model, with 10 km horizontal resolution and realistic tidal, atmospheric, hydrologic and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation, multi-category elastic-viscous-plastic sea-ice rheology, and two layer sea ice with a single snow layer. Results from a two-year long model simulation between August 1996 and July 1998 are analyzed and compared with various observations. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The model reproduces the summer and winter surface mixed layers, the general cyclonic circulation including the strong coastal current in eastern Hudson Bay, and the inflow of oceanic waters into Hudson Bay. The maximum sea-ice growth rates are found in western Foxe Basin, and in a relatively large and persistent polynya in northwestern Hudson Bay. Sea-ice advection and ridging are more important than local thermodynamic growth in the regions of maximum sea-ice cover concentration and thickness that are found in eastern Foxe Basin and southern Hudson Bay. The estimate of freshwater transport to the Labrador Sea confirms a broad maximum during wintertime that is associated with the previous summer’s freshwater moving through Hudson Strait from southern Hudson Bay. Tidally driven mixing is shown to have a strong effect on the modeled ice-ocean circulation.

Pub.: 04 Aug '04, Pinned: 21 Aug '17

Climate Change Scenarios for the Hudson Bay Region: An Intermodel Comparison

Abstract: General circulation models (GCMs) are unanimous in projecting warmer temperatures in an enhanced CO2 atmosphere, with amplification of this warming in higher latitudes. The Hudson Bay region, which is located in the Arctic and subarctic regions of Canada, should therefore be strongly influenced by global warming. In this study, we compare the response of Hudson Bay to a transient warming scenario provided by six-coupled atmosphere-ocean models. Our analysis focuses on surface temperature, precipitation, sea-ice coverage, and permafrost distribution. The results show that warming is expected to peak in winter over the ocean, because of a northward retreat of the sea-ice cover. Also, a secondary warming peak is observed in summer over land in the Canadian and Australian-coupled GCMs, which is associated with both a reduction in soil moisture conditions and changes in permafrost distribution. In addition, a relationship is identified between the retreat of the sea-ice cover and an enhancement of precipitation over both land and oceanic surfaces. The response of the sea-ice cover and permafrost layer to global warming varies considerably among models and thus large differences are observed in the projected regional increase in temperature and precipitation. In view of the important feedbacks that a retreat of the sea-ice cover and the distribution of permafrost are likely to play in the doubled and tripled CO2 climates of Hudson Bay, a good representation of these two parameters is necessary to provide realistic climate change scenarios. The use of higher resolution regional climate model is recommended to develop scenarios of climate change for the Hudson Bay region.

Pub.: 01 Apr '05, Pinned: 21 Aug '17

Sensitivity of Hudson Bay Sea ice and ocean climate to atmospheric temperature forcing

Abstract: A regional sea-ice–ocean model was used to investigate the response of sea ice and oceanic heat storage in the Hudson Bay system to a climate-warming scenario. Projections of air temperature (for the years 2041–2070; effective CO2 concentration of 707–950 ppmv) obtained from the Canadian Regional Climate Model (CRCM 4.2.3), driven by the third-generation coupled global climate model (CGCM 3) for lateral atmospheric and land and ocean surface boundaries, were used to drive a single sensitivity experiment with the delta-change approach. The projected change in air temperature varies from 0.8°C (summer) to 10°C (winter), with a mean warming of 3.9°C. The hydrologic forcing in the warmer climate scenario was identical to the one used for the present climate simulation. Under this warmer climate scenario, the sea-ice season is reduced by 7–9 weeks. The highest change in summer sea-surface temperature, up to 5°C, is found in southeastern Hudson Bay, along the Nunavik coast and in James Bay. In central Hudson Bay, sea-surface temperature increases by over 3°C. Analysis of the heat content stored in the water column revealed an accumulation of additional heat, exceeding 3 MJ m−3, trapped along the eastern shore of James and Hudson bays during winter. Despite the stratification due to meltwater and river runoff during summer, the shallow coastal regions demonstrate a higher capacity of heat storage. The maximum volume of dense water produced at the end of winter was halved under the climate-warming perturbation. The maximum volume of sea ice is reduced by 31% (592 km³) while the difference in the maximum cover is only 2.6% (32,350 km2). Overall, the depletion of sea-ice thickness in Hudson Bay follows a southeast–northwest gradient. Sea-ice thickness in Hudson Strait and Ungava Bay is 50% thinner than in present climate conditions during wintertime. The model indicates that the greatest changes in both sea-ice climate and heat content would occur in southeastern Hudson Bay, James Bay, and Hudson Strait.

Pub.: 21 Jan '10, Pinned: 21 Aug '17

Mixing and photoreactivity of dissolved organic matter in the Nelson/Hayes estuarine system (Hudson Bay, Canada)

Abstract: This work presents the results of a 4-year study (2009–2012) investigating the mixing and photoreactivity of dissolved organic matter (DOM) in the Nelson/Hayes estuary (Hudson Bay). Dissolved organic carbon (DOC), colored DOM, and humic-like DOM decreased with increasing salinity (r2 = 0.70–0.84). Removal of DOM was noticeable at low to mid salinity range, likely due to degradation and/or adsorption to particles. DOM photobleaching rates (i.e., decrease in DOM signal resulting from exposure to solar radiation) ranged from 0.005 to 0.030 h− 1, corresponding to half-lives of 4.9–9.9 days. Dissolved organic matter from the Nelson and Hayes Rivers was more photoreactive than from the estuary where the photodegradation of terrestrial DOM decreased with increasing salinity. Coincident with the loss of CDOM absorption was an increase in spectral slope S, suggesting a decrease in DOM molecular weight. Marked differences in photoreactivity of protein- and humic-like DOM were observed with highly humidified material being the most photosensitive. Information generated by our study will provide a valuable data set for better understanding the impacts of future hydroelectric development and climate change on DOM biogeochemical dynamics in the Nelson/Hayes estuary and coastal domain. This study will constitute a reference on terrestrial DOM fate prior to building additional generating capacity on the Nelson River.

Pub.: 04 Jun '16, Pinned: 21 Aug '17