R. Grant Ingram

Vertical Flux of Biogenic Carbon in the Ocean: Is There Food Web Control?

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.

Abundance of larval rainbow smelt (Osmerus mordax) in relation to the maximum turbidity zone and associated macroplanktonic fauna of the middle St. Lawrence estuary

We tested the hypothesis that the distribution and retention of larval smelt (Osmerus mordax) in the middle estuary of the St. Lawrence River is related to the maintenance of other planktonic organisms in the maximum turbidity zone (MTZ). We documented the horizontal and vertical distribution of larval smelt, macrozooplankton, and suspended particulate matter over four tidal cycles at each of three stations located along the major axis of the turbid upstream portion of the middle estuary. During summer, the turbid, warm, and low salinity waters of the two upstream stations were characterized byNeomysis americana, Gammarus sp. (principallyG. tigrinus), larval smelt,Mysis stenolepsis, andCrangon septemspinosus. The more stratified and less turbid waters of the downstream station were characterized by a coastal marine macrozooplanktonic community and the almost total absence of smelt larvae. Within the MTZ, the distribution ofN. americana coincided with the zone of longest average advective replacement times (null zone). Smelt larvae were distributed further upstream within the MTZ thanN. americana. Overall, larger larvae were distributed further upstream than smaller larvae. The relationship between turbidity and larval density at a specific time was weak (due to resuspension of sediments but not larvae), but the mechanism responsible for producing higher residence times for both sediment and larvae on a longer term basis appears the same. The daily movement and skewed nature of the null zone (due to the general cyclonic circulation of the middle estuary) defines a geographic zone over which the larval smelt population oscillates and remains despite the mean downstream velocities over the water column.

Interannual variability of sea‐ice cover in Hudson bay, Baffin bay and the Labrador sea

Abstract The spatial and temporal relationships between subarctic Canadian sea‐ice cover and atmospheric forcing are investigated by analysing sea‐ice concentration, sea‐level pressure and surface air temperature data from 1953 to 1988. The sea‐ice anomalies in Hudson Bay, Baffin Bay and the Labrador Sea are found to be related to the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO). Through a spatial Students i‐test and a Monte Carlo simulation, it is found that sea‐ice cover in both Hudson Bay and the Baffin Bay‐Labrador Sea region responds to a Low/Wet episode of the SO (defined as the period when the SO index becomes negative) mainly in summer. In this case, the sea‐ice cover has a large positive anomaly that starts in summer and continues through to autumn. The ice anomaly is attributed to the negative anomalies in the regional surface air temperature record during the summer and autumn when the Low/Wet episode is developing. During strong winter westerly wind events of the NAO, th...

An overview of physical processes in the North Water

The presence of a polynya strongly affects biological processes by influencing underwater light levels, water-column stratification, the upwelling of nutrients, and the timing of production cycles. An overview of the existing literature on the oceanography, meteorology and sea-ice conditions of the North Water, a large recurring polynya in northern Baffin Bay, is presented. The North Water is influenced by a cold inflow of Arctic Ocean water from the north and, in some areas, a warmer inflow of Atlantic water from the south. Earlier observations and modeling studies suggested that both wind and ocean advection of sea ice, as well as heat input to the surface waters by either upwelling or mixing, were responsible for the formation and maintenance of the polynya. Recent data indicate the North Water to be primarily generated by the southward drift of ice by winds and currents, as opposed to melting ice by sensible heat input over large areas. Localized sensible heat effects occur in fall, winter and spring along the Greenland side of the polynya.

Water column structure and circulation under the North Water during spring transition: April-July 1998

Abstract The North Water is a large recurring polynya in northern Baffin Bay. Over 400 hydrographic CTD profiles taken over a grid of stations between April and July 1998 were analysed to understand the water-column structures underlying the polynya during spring transition. In the North Water, imported and dissimilar water masses converge over a complex bathymetry: Northern assembly (NA) waters are derived from inflows through Nares Strait and Jones Sound; Southern assembly (SA) waters are derived from a northern-moving branch of the West Greenland Current (WGC). NA and SA waters mix primarily over the north–south Smith Sound Canyon, between 76.5°N and 77°N latitude, to form a distinct, relatively thick halocline layer (termed ‘North Water assembly’, NWA), characterised by density-compensating thermohaline intrusions. In the southern portion of the North Water, a sharp front between NWA waters and SA waters roughly aligns with the 500-m isobath. Flow patterns, deduced from potential temperature vs. salinity (θ−S) diagrams and from minima in stability frequency (N) profiles, indicate that this front results from the convergence of NWA waters and a branch of the WGC that is cyclonically re-directed as it approaches Smith Sound Canyon. Not all SA waters are immediately re-directed south towards the front, as a second branch follows the Greenland coast toward Smith Sound. While θ−S signatures show some evidence of upwelling along the Greenland coast (e.g. outcropping of isopycnal surfaces), no surfacing of warm Atlantic-derived water was observed during the sampling period (1998), suggesting that mechanical removal of ice by winds and currents is the primary mechanism by which the North Water forms. Some sensible heat exchange associated with brine rejection and penetrative convection may occur, but only during periods of active ice formation.

Nitrogenous nutrition of sea-ice microalgae

SummaryThere are indications that the final biomass attained by sea-ice microalgae in southeastern Hudson Bay is nitrogen limited. The present study investigates the possibility that the rate at which the final yield is approached is also nitrogen limited. Nutrient data suggest that nitrogen was actively taken up by the microalgae, and periodically replenished by mixing processes related to fortnightly tides. High molar C:N ratios (>15), typical of nitrogen-deficient cells, have been observed at times of low dissolved inorganic nitrogen. Absolute transport rates of nitrogen were estimated from natural changes in dissolved inorganic and particulate organic nitrogen. Cell losses and nitrogen uptake rates were highest during periods of maximum current speed, suggesting that the rate of biological production at the ice-water interface could be limited by the accumulated biomass. These results suggest (1) that the sea-ice microalgae in southeastern Hudson Bay are nitrogen limited in their natural environment, and (2) that nutrient replenishment and perhaps losses of biomass governed by fortnightly tidal mixing periodically enhance the growth of microalgae at the ice-water interface.

A three-dimensional numerical simulation of Hudson Bay summer ocean circulation: topographic gyres, separations, and coastal jets

Abstract The summer ocean circulation in Hudson Bay is studied numerically using the Blumberg-Mellor model with a 27.5 km × 27.5 km horizontal grid and a realistic bottom topography. In the control run 1) monthly climatological forcing fields of wind stress, oceanic inflow/outflow, and salt and heat fluxes are used. In addition, results are presented for a number ot sensitivity experiments: 2) no topography (otherwise conditions are identical to the control run), 3) no wind forcing, 4) no oceanic inflow/outflow, 5) no heat and salt fluxes, 6) no temperature and salinity variations, and 7) without the nonlinear terms. While the overall simulated circulation in Hudson Bay is cyclonic, the strong steering of the flow by the bathymetry is particularly noticeable. Mesoscale topographic gyres are simulated, and the separation of the coastal current due to topographic bumps occurs in several locations. The simulated circulation also has well-developed vorticity features and narrow, density-driven coastal jets al...

Characteristics of the turbulent oceanic boundary layer under sea ice. Part 1: A review of the ice-ocean boundary layer

Abstract A number of experimental studies in polar regions over the past decade have helped us to better understand the structure of the ice-ocean boundary layer. This work reviews the ice-water drag coefficientss compiled from various experiments and our understanding of the turbulent characteristics of the ice-ocean boundary layer, which in turn leads to consideration of the density structure in the upper ocean. Surface intrusions of freshwater from rivers and buoyancy effects caused by surface freezing or ice melt are found to play an important role in modifying turbulent processes in coastal regions

Fronts and Mesoscale Features in the St. Lawrence Estuary

Mesoscale features found in the St. Lawrence estuary range from those encountered in much smaller estuaries to those occuring on continental shelves. The influence of freshwater input, wind forcing and tidal processes on the distribution of temperature, salinity and current fields are discussed. Mechanisms responsible for variability of frontal phenomena, eddy formation and coastal jet dynamics are considered as a function of seasonal changes in the forcing variables. Comparisons of features in the St. Lawrence and in similar regions elsewhere are presented

Variation of Upper Layer Dynamics During Breakup of the Seasonal Ice Cover in Hudson Bay

The present study describes circulation and stratification changes associated with the melt and breakup of the seasonal ice cover in the coastal waters of southeast Hudson Day. Field work was carried out at a station located 25 km north of the Great Whale River. Buoyancy fluxes and dissipation rates were calculated as well as changes in potential energy. Surface velocity data were partitioned into frequency bands and complex demodulated. Throughout the sampling period, most of the current energy was found to be in the semi-diurnal tidal band. After ice breakup, however, low frequency and inertial motions became relatively more important in response to direct wind forcing at the sea surface. Changes in amplitudes and phases of the major tidal constituents occurred and are related to the presence of the sea ice cover. Between early April and mid-June, semi-diurnal current amplitude doubled while its phase shifted by 45 to 60 degrees. In early June, the ice cover was sufficiently dispersed to allow the surface turbulence to overcome the buoyancy flux and mix the upper water column.