Cabot Strait Research Articles

Long-term changes in size–depth distributions of urophycis tenuis white hake in the southern gulf of st lawrence and cabot strait

the body length–water depth distribution of urophycis tenuis white hake (pisces, gadidae) in the southern gulf of st lawrence (1971–1975, 1981–1985, 1991–1995 and 2001–2002) and cabot strait (1994–1997) was examined. contrary to expectation, linear regression analyses indicated 13 of 17 years had negative slopes with larger fish being found in shallower water. length–depth relationships were statistically significant for five of 17 years (negative slopes: 1971, 1972, 1975, 1981; positive slope: 2002). regression slopes generally increased from 1971 to 2002 indicating the length–depth relationship changed from negative in the early 1970s and 1980s, to negative and positive in the early 1990s, and finally to positive in 2001–2002. in the cabot strait, a significant positive relationship was observed for fish length and water depth indicating large u. tenuis generally occurred in deeper water. we propose that slopes of the length–depth relationship became positive in the 1990s and early 2000s due to the loss of large u. tenuis taken in a seasonal fishery in the southern gulf of st lawrence that targeted highly aggregated spawning and post-spawning shoals of fish in shallow water during summer.

A seventy-two-year record of diminishing deep-water oxygen in the St. Lawrence estuary: The northwest Atlantic connection

Oxygen concentrations in the bottom waters of the Lower St. Lawrence estuary (LSLE) decreased from 125 µmol L™1 (37.7% saturation) in the 1930s to an average of 65 µmol L™1 (20.7% saturation) for the 1984-2003 period. A concurrent 1.65°C warming of the bottom water from the 1930s to the 1980s suggests that changes in the relative proportions of cold, fresh, oxygen-rich Labrador Current Water (LCW) and warm, salty, oxygen-poor North Atlantic Central Water (NACW) in the water mass entering the Laurentian Channel probably played a role in the oxygen depletion. We estimate that about one half to two thirds of the oxygen loss in the bottom waters of the LSLE can be attributed to a decreased proportion of LCW. This leaves between one third and one half of the oxygen decrease to be explained by causes other than changes in water mass composition. An increase in the along-channel oxygen gradient from Cabot Strait to the LSLE over the past decades, combined with data from sediment cores, suggests that increased sediment oxygen demand may be partly responsible for the remainder of the oxygen decline. In July 2003, approximately 1,300 km2 of seafloor in the LSLE was bathed in hypoxic water (<62.5 µmol L−1).

Ice Conditions in the Gulf of St.Lawrence and Cabot Strait (with particular reference to the Sydney Bight Area)

Les glaces qui, au printemps, se trouvent dans le détroit de Cabot et tout particulièrement dans la région de la baie Sydney, gênent souvent les traversées des bateaux passeurs entre Port-aux-Basques, Terre-Neuve et North Sydney, Nouvelle-Ecosse. Des données sur les principaux relevés des glaces dans le golfe Saint-Laurent et le détroit de Cabot ont été recueillis et étudiées en tenant compte de ce problème. Les relations qui existent entre les nuances de température, les vents et l'étendue des glaces ont été étudiées à la lumière de la statistique. La somme des températures de décembre et janvier correspond assez bien aux principales étendues des glaces qui se trouvaient dans le golfe et le détroit durant ces deux mois. L'étude des vents indique un véritable mouvement de la glace à partir du golfe en direction du détroit durant les années où des observations ont été faites. Si l'on additionne les températures et les vents et les exprime en termes de glace de dérive, on découvre que ces deux éléments sont très étroitement liés l'un à l'autre.

Sea level and surface current variability in the Gulf of St Lawrence from satellite altimetry

Sea level and surface current variability in the Gulf of St Lawrence have been investigated primarily using seven years of TOPEX/Poseidon altimeter data. An orthogonal response analysis is used to derive an annual cycle from 1-s altimetric data along satellite ground tracks, while simultaneously removing aliased residual tides and dynamic signals at alias tide frequencies. An examination of tidal-frequency variability points to the need for a better tide model for detiding altimetric data in order to study shorter (than seasonal) period processes in the Gulf of St Lawrence. Annual sea level amplitudes and phase fields are constructed from the along-track analysis results using a linear interpolation procedure. The altimetric annual harmonic has a magnitude of 2-5 cm in amplitude and is highest in fall. The altimetric sea level results agree well with independent tide-gauge data at coastal stations and can be accounted for mainly by steric height. Geostrophic surface current anomalies derived from the altimetric annual sea level anomalies are then discussed in conjunction with numerical solutions from a regional hydrodynamic model. Interannual sea level change in the Gulf of St Lawrence is also investigated from both altimetry and tide-gauge data, indicating a prominent gulf-wide sea level drop around 1997, with exact timing dependent on location. The interannual sea level variability is thought to be primarily associated with the Labrador Current transport variability (via both the Strait of Belle Isle and Cabot Strait) and the south-north fluctuation of the Gulf Stream position (via Cabot Strait).

Distribution des kystes du type Alexandrium excavatum dans les sédiments récents et postglaciaires des marges est-canadiennes

Des analyses palynologiques ont été réalisées dans des échantillons de sédiments de surface de l'Atlantique Nord et de ses bassins adjacents afin de retracer la distribution des kystes des taxons toxiques du type Alexandrium excavatum . La présence de kystes le long des marges sud-scandinaves et au large des côtes sud-est canadiennes indique une préférence pour les milieux néritiques où sont enregistrées des conditions tempérées fraîches (15-17 °C en août) et des salinités relativement faibles (~32 ‰) dans les eaux de surface. Dans le secteur du golfe du Saint-Laurent, l'abondance des kystes augmente de l'estuaire vers les marges atlantiques (détroit de Cabot). L'analyse de séquences postglaciaires du golfe du Saint-Laurent révèle un maximum d'abondance des kystes du type Alexandrium excavatum autour de 9 000 ans BP, soit au début du présent interglaciaire. Cet acmé est marqué par des concen-trations particulièrement élevées (jusqu'à 104 kystes.cm -3 ) à l'embouchure du golfe du Saint-Laurent (région du détroit de Cabot). La distribution actuelle et postglaciaire des kystes du type Alexandrium excavatum laisse supposer un ensemencement régional du golfe du Saint-Laurent à partir des marges nord-atlantiques adjacentes.

Summer Transports of Nutrients in the Gulf of St. Lawrence Estimated by Inverse Modelling

In this paper, we use an inverse methodology to parameterize box models of the Estuary and Gulf of St. Lawrence (GSL) to study carbon, oxygen and nutrient exchanges and transports during the summer period. Three models were developed and compared: a purely physical model A1 and two models including biogeochemical processes (new production, particle sedimentation, remineralization, and burial): a ‘high-flux’ model A2 and a ‘low-flux’ model A3, named in reference to shallow particle flux measurements. Even though the best fits for oxygen, phosphate, and nitrate mass balances were obtained with the low-flux model A3, our results show that a model based only on advection and diffusion fluxes gives a good representation of all the nutrient patterns in summer. However, the use of nutrient and other biogeochemical processes improved the water, heat, and salt balances relative to using only physical data. Moreover, the use of biogeochemical processes allows model A3 more flexibility to reproduce oxygen and nutrient patterns in the deep layer. Without the biogeochemical processes, the deep circulation along the Laurentian Channel and the upward fluxes into the upper layers were reduced below expected values due to the incapacity of the model to balance deep inflows of nutrients with surface outflows through Cabot Strait. The low-flux model A3 estimated higher velocities in the deep layer since the deep nutrient inflows could then be balanced by biological removal in the upper layers. The resulting flow pattern indicated that the St. Lawrence system can be characterized by two main regions: the western region (Estuary, Gaspé Current and Northwestern Gulf), where high biological production is associated with a cyclonic and upwelling circulation, and the eastern region (Laurentian Channel Central, Jacques Cartier Passage, Esquiman Channel and Cabot Strait), where low production is associated with an anticyclonic and downwelling circulation. The Southern Gulf or Magdalen Shallows is mainly influenced by the Gaspé Current, which transports nutrients and production towards Cabot Strait.

Delineating stocks of Atlantic cod (Gadus morhua) in the Gulf of St Lawrence and Cabot Strait areas using vertebral number

Cod ( Gadus morhua ) from several populations overwinter in the Cabot Strait area at the entrance to the Gulf of St Lawrence. We examined the utility of vertebral number for estimating the stock composition of cod aggregations in this overwintering area. Stock-specific mean vertebral numbers were estimated using samples obtained in the 1994–1997 spring (spawning) and summer (feeding) seasons when the populations were geographically separated. Mean vertebral number was significantly lower in the southern Gulf population than in each other population (northern Gulf, southern Newfoundland, Sydney Bight, eastern Scotian Shelf), but did not differ significantly among the other populations. Stock-specific vertebral counts were stable over the study period and, for three of the five stocks (including the large migratory Gulf of St Lawrence stocks), over several year classes. Stock composition of the overwintering aggregations was estimated using samples obtained from synoptic bottom-trawl surveys of the Cabot Strait area in January of 1996 and 1997. In both years, mean vertebral number was significantly lower along the south flank of the Laurentian Channel in NAFO (Northwest Atlantic Fisheries Organization) Divisions 4T and 4Vn than in areas on the north side of the Channel, suggesting that the south side of the Channel was dominated by southern Gulf cod. Maximum likelihood estimates of stock composition based on vertebral number indicated that cod in overwintering aggregations in the 4T–4Vn area were almost entirely (98%) from the southern Gulf stock while southern Gulf cod were almost entirely absent (<0.1%) from the aggregations on the north side of the Laurentian Channel. Bootstrapping indicated that the precision of these estimates was high. Simulations indicated that their bias was negligible. These results suggest that there is virtually no stock mixing across the Laurentian Channel during the overwintering period despite the aggregation of cod from several populations in this small area each year. We conclude that vertebral number provides a useful complement to other types of characters (microsatellite DNA markers, chemical composition of otoliths) that have been used to delineate these cod stocks.

The influence of local and remote winds on the synoptic sea level variability in the Gulf of Saint Lawrence

The influence of local and remote winds on sea level and circulation variability in the synoptic band in the Gulf of Saint Lawrence is examined. We use two years of winter sea level data from the Gulf of Saint Lawrence, a statistical regression model and a linear, barotropic, depth-averaged numerical model to separate the effect of local and remote forcing. The boundary conditions of the numerical model are determined using an adjoint data assimilation technique. The results show that the influence of the local wind on sea level is negligible over the study period. Most of the variability is introduced through the open boundaries of the Gulf of Saint Lawrence, notably Cabot Strait. The remote forcing can be related to the large-scale wind fields over the adjacent Newfoundland and Labrador Shelves. The numerical model results provide a basis for operational modelling of the synoptic variability in the Gulf of Saint Lawrence.

MIXED-STOCK ANALYSIS OF ATLANTIC COD NEAR THE GULF OF ST. LAWRENCE BASED ON MICROSATELLITE DNA

The collapse of various stock complexes of cod (Gadus morhua) in the northwest Atlantic has prompted a clarification of relationships among stock components. Here we examine the genetic composition of >2300 cod collected during 1994–1997 in the Gulf of St. Lawrence and its approaches to determine whether: (1) stock components can be genetically identified; (2) population structure is temporally stable; (3) components are always separated and, if not, where and when are they mixed; and (4) component contributions to mixtures can be estimated. We use polymorphism at six microsatellite DNA loci from cod collected on or near their spring and summer spawning grounds to examine structure and then employ maximum likelihood analyses to estimate contributions of each component to mixtures overwintering near the entrance to the Gulf. Estimates of genetic structure (FST and RST) reveal significant differences among cod populations during stock-separated periods, and the structure appears to be temporally stable. Multidimensional scaling analysis of estimates of genetic distance (DA) suggest that the structure results from differences among cod collected within the Gulf of St. Lawrence and those collected near the entrance to the Gulf on either side of the Laurentian Channel in the Cabot Strait, as well as among cod collected south of Newfoundland along the north side of the Channel. Weak genetic heterogeneity among seven regional mixed-stock collections during the overwintering period suggests that cod aggregations characteristically found in the overwintering region represent population mixtures that differ in the proportion of cod contributed to them by the various stock components. Maximum likelihood estimates indicate no significant temporal changes in component contributions to the mixed-stock samples between 1996 and 1997 when all of the winter mixed-stock samples were pooled. The combined contribution of cod from the southern and northern Gulf of St. Lawrence to the mixed-stock samples ranged between 46% and 71% (expected 64%). More precise estimates of contributions from these two regions are precluded by the weak genetic differentiation detected in our samples. The contribution by cod from the Cape Breton Island region was small and estimated at 3%. Contributions by cod from the eastern Scotian Shelf, southwest Newfoundland and south-central Newfoundland were in the range of 13–14%, 4%, and 8%, respectively. Contributions by inshore cod from Placentia and Fortune Bays in south Newfoundland were small to negligible (∼3% each). The results indicate that future management could be designed around the spatial and temporal scale of the stock structure identified during the stock-separated period and around the spatially varying contributions to the overwintering mixed-stock fishery.

Late Paleozoic to Cenozoic history of the offshore Sydney Basin, Atlantic Canada

The Sydney Basin covers a large offshore area south of Newfoundland, with a well-exposed outcrop belt on Cape Breton Island. The geological history of the poorly known offshore area is interpreted using an industry seismic grid and Lithoprobe line 86-5, tied to outcrops and two wells. The mid-Devonian to Upper Carboniferous - Permian basin fill is 6-7 km thick and represents three extensional phases with intervening and succeeding compressive phases. The mid-Devonian McAdams Lake Formation was deposited in a local half-graben during early post-Acadian extension. Following deformation, a suite of Early Carboniferous extensional basins filled mainly with Horton Group conglomerates developed on northeast-trending and southeast-dipping master faults. Some faults developed along Acadian terrane boundaries. The Windsor Group extends over the master faults to onlap basement as a result of thermal sag and Visean eustatic rise. Mid-Carboniferous deformation, linked to the Alleghanian orogeny, reactivated faults and caused basin inversion and a basinwide unconformity. Upper Carboniferous to ?Permian coal measures and redbeds were subsequently deposited in a broad basin that developed over the Early Carboniferous basins. Subsidence may reflect extension on major faults in the Cabot Strait coupled with thermal sag and (or) continued sag on an underlying mid-crustal detachment. After coalification, Acadian terrane boundaries and other lineaments were reactivated during a compressive tectonic episode, probably during the Permian. The basin's polycyclic history, with repeated subsidence and inversion phases, has important implications for hydrocarbon systems.

Dissolved organic carbon in the Gulf of St. Lawrence

Dissolved organic carbon in the Gulf of St. Lawrence was measured throughout the water column by high-temperature catalytic oxidation during and after the 1994 spring phytoplankton bloom. DOC ranged from 28 to 111 μM. Except for the waters near the Magdalen Islands, the DOC in the euphotic zone was higher after the bloom (84.2–99.1 μM) than during the bloom (81–83 μM). Lowest euphotic zone DOC occurred near the Magdalen Islands (49 μM) where it was nearly as low as the deep-water DOC (35–50 μM) in the Anticosti Channel and Cabot Strait. In the deep water below 150 m the DOC levels in the inner regions of the Gulf were higher during the bloom than after it. These results along with the results of phytoplankton, bacteria, and ocean chemistry analyses were subjected to multiple regression, Spearman Rank, and principal component analyses to elucidate the role of DOC in transferring carbon between planktonic components of the Gulf of St. Lawrence pelagic ecosystem. The analyses showed a relationship between DOC and phytoplankton primary production in the euphotic zone during the bloom and a relationship between DOC and bacterial production in the euphotic zone after the bloom. A diel study showing DOC production in the morning and DOC degradation in the evening implicated phytoplankton in generating DOC during the day.

Trophic structure of macrobenthos in the Gulf of St. Lawrence and on the Scotian Shelf

The Gulf of St. Lawrence and Scotian Shelf provide a diversity of oceanographic conditions in a continental margin setting. Climate is markedly seasonal, and bathymetry and hydrodynamic conditions cover a broad range, significantly influencing the patterns of organic matter sedimentation and, potentially, benthic community dynamics. Samples for analysis of benthic macrofauna and sediment microorganisms were collected at six stations in the Gulf of St. Lawrence (GSL) and the Scotian Shelf during winter and summer cruises, as part of the Canadian Joint Global Ocean Flux Study. Multivariate analyses indicate significant site-related trends in trophic guilds, benthic assemblages, and microbial activity, some of which are related to geomorphological characteristics (bathymetry, topography, and substratum). Macrofaunal trophic guild data show that the stations with relatively deep settling basins (Cabot Strait and Emerald Basin), dominated by surface deposit feeders, were distinct from stations with sloping bottoms (Anticosti Gyre and Anticosti Channel), where subsurface deposit feeders dominated or surface and subsurface deposit feeders were equally abundant. Deposit feeders (surface and subsurface trophic groups) made up >60% of the benthic communities, except at the Scotian slope station where they represented 44% of the total benthic abundances. Based on the data collected in both the water column and the sediment at three deep stations in the GSL, we hypothesize that the proportion of surface and subsurface deposit feeders, and thus the nature of bioturbation activity, is related to the magnitude and pattern of organic matter supply from the euphotic zone.

Late quaternary paleohydrology of the Gulf of St. Lawrence (Québec, Canada) based on diatom analysis

Postglacial sediments from three cores raised from the Gulf of St. Lawrence along the path of the Laurentian Channel, were analyzed for diatoms. A sequence of four distinct zones was defined from oldest to youngest: 1. Characterized by low diatom concentrations, this zone is mainly represented by heavily silicified species Delphineis surirella, Stephanopyxis turris, Coscinodiscus radiatus and Paralia ornata that were probably deposited by glacial drift in a glaciomarine environment from about 18 000 to 14 000 years BP. 2. This postglacial sedimentation zone deposited around 13 000 years BP, is marked by high diatom concentrations with cold-water marine species, Thalassiosira antarctica resting spores and Porosira glacialis. The upper part of the zone suggests a gradual warming with the appearance of temperate water species, Bacterosira bathyomphala and Chaetoceros spp., both resting spores and vegetative cells. 3. An important cooling of surface temperatures is noticed by the resurgence of cold species, Porosira glacialis, Thalassiosira antarctica resting spores and Thalassiosira hyalina. This zone is associated with the Younger Dryas chronozone dated from 10 800 to 10 300 years BP. This interval is also characterized by two marked freshwater pulses, coming from the outflow of Laurentide Ice Sheet meltwater, on the surface layer of the Goldthwait Sea. Although well-defined in the northwestern Gulf area (core 90-031-015), the influence of this meltwater decreases considerably or even disappears in Cabot Strait (core 89-007-111) and offshore (core 90-031-044). Evidence of reduced postglacial glacial runoff on surface water supports the conclusion that it could not have generated the Younger Dryas cooling episode. 4. The diatom assemblages from 10 000 years BP through Recent correspond to the progressive establishment of modern-like surface water conditions.

Distribution of Calanus spp. on and around the Nova Scotia Shelf in April: evidence for an offshore source of Calanus finmarchicus to the central and western regions

Observations of hydrography and Calanus spp. abundance were made at stations on lines across the central and eastern Scotian Shelf (SS) in April 1995 and 1997 and on additional lines on the western SS and across Cabot Strait (CS) and the Laurentian Channel (LC) in 1997. Calanus finmarchicus was more abundant on the central and western SS than in the east, and Calanus hyperboreus was concentrated in the east and in areas influenced by the Nova Scotia Current. Calanus spp. on the eastern SS probably originated mainly from populations overwintering in the Gulf of St. Lawrence. High abundances of C. finmarchicus occurred at or beyond the shelf break when warm slope water was present, suggesting that they derived from a population overwintering in the deep water south of the SS. In both years, slope water was present in the near-surface layers at shelf stations of the Halifax Line (HL), but in 1997 the degree of intrusion was greater. Calanus finmarchicus abundances were also substantially higher at shelf stations of the HL in 1997, implying contribution from the offshore population to the populations in central and western SS regions. Consistent with the suggested difference in their origins, C. finmarchicus on the western SS belonged primarily to the new year's generation, whereas those on the eastern SS belonged mainly to that of the previous year.

Late glacial stratigraphy and history of the Gulf of St. Lawrence, Canada

The three-dimensional configuration of the Quaternary sediments in the Gulf of St. Lawrence is described based on analysis of 8000 km of high-resolution seismic reflection data complemented by analysis of seven piston cores. Till and or ice-contact deposits, glaciomarine sediments, postglacial basinal muds, and bank-top lagoonal sediments grading to sands and gravels make up the stratigraphic succession. Numerous thick accumulations of ice-contact - morainal deposits and "till tongues" indicate the position of former ice margins. The sequence of breakup of the last glacial ice in the gulf has been interpreted on the basis of these data and associated accelerator mass spectroscopy 14C dates. Grounded ice extended beyond Cabot Strait before 14.3 ka and retreated rapidly to north of Anticosti Island by 13.7 ka. Local residual piedmont lobes of glacial ice within the Cape Breton Channel and Baie des Chaleurs persisted longer, until about 12.2 ka. Ancestral hanging valleys formed the Cape Breton Channel and Baie des Chaleurs and served as conduits for ice lobes that flowed into the deeper Laurentian Channel. As many as four superimposed (Late Wisconsinan) glaciogenic sequences, up to 190 m in composite thickness, occur at the mouths of these (hanging) valleys. The thickest glacial sections were deposited on the southwestward slope of the Laurentian Channel. The surface of the till - ice-contact sediments between 440 and 100 m below present sea level has been extensively modified by iceberg scouring. The deeper limit (440 m) marks the maximum draft of icebergs, which was in large part determined by the thickness of the calving ice front. The disappearance of iceberg scour marks at 100 m is interpreted to have resulted from erosion of the glacial deposits by a Late Wisconsinan transgression whose low stand is suggested by a well-developed terrace on parts of the Magdalen Plateau at a present water depth of 110 m. A piston core that penetrated sediments overlying the uppermost (Late Wisconsinan) till in the Cape Breton Channel is interpreted to represent a deposit of lagoonal or shallow-marine sediments with localized deposits in excess of 65 m thickness. The depositional style of the postglacial deposits suggests sufficient bottom currents to erode sediments on the Magdalen Plateau.

Distribution of &lt;i&gt;Calanus&lt;/i&gt; spp. on and around the Nova Scotia Shelf in April: evidence for an offshore source of &lt;i&gt;Calanus finmarchicus&lt;/i&gt; to the central and western regions

Observations of hydrography and Calanus spp. abundance were made at stations on lines across the central and eastern Scotian Shelf (SS) in April 1995 and 1997 and on additional lines on the western SS and across Cabot Strait (CS) and the Laurentian Channel (LC) in 1997. Calanus finmarchicus was more abundant on the central and western SS than in the east, and Calanus hyperboreus was concentrated in the east and in areas influenced by the Nova Scotia Current. Calanus spp. on the eastern SS probably originated mainly from populations overwintering in the Gulf of St. Lawrence. High abundances of C. finmarchicus occurred at or beyond the shelf break when warm slope water was present, suggesting that they derived from a population overwintering in the deep water south of the SS. In both years, slope water was present in the near-surface layers at shelf stations of the Halifax Line (HL), but in 1997 the degree of intrusion was greater. Calanus finmarchicus abundances were also substantially higher at shelf stations of the HL in 1997, implying contribution from the offshore population to the populations in central and western SS regions. Consistent with the suggested difference in their origins, C. finmarchicus on the western SS belonged primarily to the new year's generation, whereas those on the eastern SS belonged mainly to that of the previous year.

Seasonal variation in the habitat associations of Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) from the southern Gulf of St. Lawrence

We compared habitat associations of southern Gulf of St. Lawrence Atlantic cod (Gadus morhua) and American plaice (Hippoglossoides platessoides) between the summer feeding season on the Magdalen Shallows and the overwintering period in the Cabot Strait. Data were from bottom trawl surveys conducted in September 1993, 1994, and 1995 and January 1994, 1995, and 1996. Both species occupied much deeper, warmer water in winter than in summer. The effect of cod age on temperature distribution reversed between the two seasons, with younger cod occupying warmer water than older cod in summer and colder water in winter. Selection of both depth and temperature by cod tended to be more significant in September than in January. The reduced statistical significance of habitat selection by cod in winter was associated with a more aggregated distribution in this season. The contrast between seasons in habitat associations was particularly strong for plaice. The median habitats occupied by plaice were 58-67 m and -0.1 to 0.3°C in September and 374-426 m and 5.2-5.4°C in January. Habitat selection by plaice was significant in both seasons, but significance tended to be greater in January. Degree of aggregation in plaice distribution was similar between the two seasons. Female plaice occupied significantly warmer water than males in September but not in January. The ecological and practical implications of this striking seasonal variation in habitat associations are discussed.

Comparative diagenesis at three sites on the Canadian continental margin

Diagenesis of carbon, oxygen, nitrogen, and manganese at three sites on the Canadian continental margin is quantitatively compared and contrasted using results from a computer code (CANDI) published by Boudreau (1996a), The data at Station 3 (Cabot Strait) are well explained by the steady state output from CANDI, assuming a porewater balance created by diffusion and reaction only, whereas the data from Stations 4 (Emerald Basin-Scotia Shelf) and 5 (Scotia Slope) are not consistent, in one way or another, with this simple model. The deviations between model and data at Station 4 are best explained by nonsteady-state diagenesis. Model fits to the Station 5 ΣCO 2 observations are improved dramatically by adding some irrigation at this site, but the ΣNH 3 distribution appears to be subject to an additional anomalous transport to the O 2 zone and subsequent oxidation to NO 3 . The mechanism for this latter phenomena is unknown and in need of future research. In addition, the O 2 and ΣCO 2 profiles at all sites require the existence of at least two reactive organic matter types; furthermore, the initial amounts of these OM types at each station is strongly dependent on the intensity of particle bioturbation. Ammonia is preferentially regenerated at Station 3 at a high ratio of about 25 N to 106 C. The net kinetics of the deeper removal of Mn 2+ appear to be fractional-order with respect to the concentration of this species, suggesting multiple removal processes, Finally, an oxidant balance, assuming steady state, indicates a considerable difference in the use of oxidants at each station even though the O 2 fluxes are similar.

Simultaneous measurement of O2, Mn, Fe, I−, and S(—II) in marine pore waterswith a solid‐state voltammetric microelectrode

A solid‐state Au/Hg voltammetric microelectrode was used to measure, simultaneously and with millimeter spatial resolution, the vertical distributions of O2, Mn2+, Fe2+, HS−, and I− in the pore water of sediments from the Canadian continental shelf and slope. The electrode was used shipboard to analyze undisturbed sediment cores and in a sediment mesocosm to determine the three‐dimensional distribution of redox species in the sediment surrounding an actively irrigated worm burrow. In cores from Emerald Basin and Cabot Strait, O2 disappeared and Mn2+, Fe2+, and HS− appeared in the vertical sequence predicted on the basis of thermodynamics. In a core from the Scotian slope, O2 disappeared at ~14‐mm depth but Mn2+ was not detected over the 50‐mm depth examined with the probe. In all three cores, I− was detected in the pore water below the oxygen‐penetration depth. In none of the cores did the distributions of O2 and Mn2+ overlap. The thickness of the layer within which neither O2 nor Mn2+ could be detected ranged from 8 to 40 mm; we suggest that nitrate, not oxygen, is used to oxidize Mn2+. The upwarddirected Mn2+ gradients of 3.5 and 10 mol mm4 in the Emerald Basin and Cabot Strait sediments, respectively, drive manganese fluxes that are more than one order of magnitude lower than the O2 fluxes, which are estimated at 4‐S mmol mm−2 d−1. The three‐dimensional distributions of solutes in the pore water in the sediment surrounding an irrigated worm burrow demonstrate that both the O2‐penetration depth and the depth where Mn2+ is first detected are deeper in the vicinity of the worm burrow than away from it. This is consistent with the notion that irrigation brings oxygenated water into the worm tube, allowing oxygen to diffuse across the burrow wall into the sediment and react with Mn2+ and other reduced porewater constituents. Three‐dimensional heterogeneity in porewater composition cannot be detected by conventional one‐dimensional coring and slicing techniques. Because these latter techniques average the porewater composition in a large volume of sediment, they may indicate that the distributions of individual species overlap when in fact they do not.

Deferring to Vichy in the Western Hemisphere: The St Pierre and Miquelon Affair of 1941

a week of the fall of France in June 1940, the Canadian, British, and Newfoundland governments were looking anxiously towards the tiny islands of St Pierre and Miquelon,1 situated in the Cabot Strait, twelve nautical miles off the south coast of Newfoundland, and the sole remnant of France's former colonial possessions in North America. After protracted discussions within St Pierre and Miquelon's administrative council, the executive administrator, Gilbert de Bournat, recognized in July the legitimacy of the French parliament's transfer of power to the government of Marshal Philippe Petain. The ninety-six square miles of St Pierre and Miquelon thus became territory loyal to the new regime at Vichy. Although de Bournat, in the months following the French armistice with Germany, was still in communication with the French ministry of colonies, he would have to rely on Admiral Georges Robert, governor of the proVichy French West Indies and based at Martinique, for the islands' defence. Although Canada and Newfoundland faced a potentially hostile territory almost within sight of their shores, St Pierre's loyalty to Vichy did not pose a direct military threat. Under the terms of the Anglo-French treaty of Paris of 1763, St Pierre and Miquelon had been demilitarized. Despite the removal of this stipulation from the treaty of Versailles of 1783, the islands possessed in 1940 neither fortifications nor a garrison.2 The only weapons