Baffin Bay Water Research Articles

Dissolved iron and manganese in the Canadian Arctic Ocean: On the biogeochemical processes controlling their distributions

Dissolved iron (DFe) and manganese (DMn) are essential micronutrients involved in vital phytoplankton physiological pathways, and their deficit can limit primary production in otherwise nutrient-replete surface ocean waters. In this work we present the spatial distributions and biogeochemical cycling of these metals across the Canadian GEOTRACES transect in the Canadian Arctic Ocean during the summer and autumn of 2015. Surface concentrations are dominated by freshwater inputs showing a strong negative correlation with salinity, especially for DMn which behaves more conservatively than DFe. The highest surface concentrations were measured in the Canadian Arctic Archipelago (Fe: 0.401–1.91 and Mn: 4.33–9.54 nmol kg−1) and the Canada Basin (Fe: 0.225–0.479 and Mn: 3.93–7.02 nmol kg−1), regions highly influenced by riverine inputs, whereas the lowest values were found in the Labrador Sea (Fe: 0.106–0.362 and Mn: 0.450–1.09 nmol kg−1) where freshwater inputs diminished and phytoplankton uptake increased. Subsurface and deep water distributions for both metals are largely controlled by a complex balance between sources (advective inputs and organic matter remineralization) and removal processes. The subsurface peaks (∼100–300 m) observed in the Canada Basin (Fe: 0.541 ± 0.060 and Mn: 1.38 ± 0.42 nmol kg−1) and Baffin Bay (Fe: 0.753–1.03 nmol kg−1) were advected from the Chukchi Sea and the Canadian Arctic Archipelago respectively, where DFe and DMn are released from the benthic boundary layer in these shelf-dominated environments. Advective sources associated with the Arctic Circumpolar Boundary Current, rather than vertical fluxes of DFe and DMn in sinking particles, dominate metal distributions in the deep Canada Basin waters (>300 m). In the highly productive Baffin Bay and the Labrador Sea, organic matter remineralization is a notable source of DFe and DMn to deep waters. In the deepest waters (>1000 m), scavenging of DFe and DMn govern their vertical distributions; a pseudo-first order scavenging model explained the continuous removal of DMn in the Canada Basin, where the concentrations reach uniformly low concentrations (0.150 ± 0.004 nmol kg−1) after ∼400 years. Applying this DMn scavenging model we were able to estimate the age (120–190 years) of deep Baffin Bay waters, a topic of discussion for many years.

Evolution of Baffin Bay Water Masses and Transports in a Numerical Sensitivity Experiment under Enhanced Greenland Melt

ABSTRACTWe used a numerical model forced with three different scenarios to analyze Baffin Bay circulation sensitivity to runoff around Baffin Bay, especially the Greenland runoff, for the past (1970–2010) and future (2010–2099). We observed an overall decrease in transport from the Arctic to the North Atlantic for the volume, heat, and freshwater over the time period as well as an augmentation of the freshwater and heat in Baffin Bay. In the early 1990s, the increase in heat in Baffin Bay was consistent with an increase in the West Greenland Irminger Water (WGIW) inflow at Davis Strait while later West Greenland Shelf Water played an important role in the heat import, sustaining the idea that the West Greenland Current might have an impact on the melt of West Greenland tidewater glaciers. The increase in freshwater and later in heat in Baffin Bay leads to changes in the steric height inside Baffin Bay, which leads to changes in the circulation. After 1978, the WGIW reaches the North Water polynya and recirculates into the Baffin Bay gyre where it accumulates over time. In the future experiment, the dynamic changes in Baffin Bay are mainly related to the accumulation of heat inside the gyre.

Modeling Wind-Driven Circulation and Landfast Ice-Edge Processes during Polynya Events in Northern Baffin Bay

AbstractA high-resolution sea ice–ocean numerical model of the North Water polynya has been developed to study the wind-driven circulation during polynya events. An idealized three-layer stratified ocean is used to initialize the model to characterize the baroclinic response to realistic wind and ice conditions. The model general circulation pattern is mainly forced by an along-channel sea level gradient between the Arctic Ocean and Baffin Bay, which determines the magnitude of the southward Baffin Current, and by an across-channel sea level gradient in Baffin Bay, which drives the northward West Greenland Current (WGC). These two currents are found to be anticorrelated to each other in the Smith Sound area. During strong northerly wind events, occurring quite frequently in the winter–spring period in the polynya, nutrient-rich Baffin Bay waters transported by the WGC are forced toward the Greenland shelf, coinciding with upwelling events along the Greenland coast. Whenever an ice bridge is present (i.e., the polynya exists and is substantially open), upwelling also occurs at the landfast ice edge. In such cases, the total upwelling area is increased by an amount that depends on the form of the ice bridge but could easily double during certain years. The baroclinic circulation associated with the upwelling response includes the formation of a cyclonic eddy attached to the ice edge that is generated during strong northerly wind events. Primary production estimations reveal that upwelling during polynya events plays a significant role in the early spring phytoplankton bloom, suggesting that the disappearance of the polynya as a result of climate change may have profound implications for the entire ecosystem.

Le courant du Labrador et quelques-unes de ses conséquences géographiques

Le courant du Labrador et quelques-unes de ses conséquences géographiques

Copepod herbivory rate in a large arctic polynya and its relationship to seasonal and spatial variation in copepod and phytoplankton biomass

Large copepod species (Calanus spp.) overwinter in the North Water Polynya (NOW; ~75 to 79° N, ~68 to 78° W) and, via upward migration, can potentially exert a rapid and important grazing impact on the spring phytoplankton bloom. This study investigated the pattern and factors controlling copepod herbivory in the NOW from April through July 1998. Typically, there was a chlorophyll max- imum between 50 m and the surface. We used incubation experiments to measure weight-specific her- bivory rates (0 to 0.24 µg C µg C -1 d -1 ) representing the average for surface-layer copepod assem- blages at each station, and we quantified 0 to 50 m in situ copepod biomass (20 to 3200 mg C m -2 ). Weight-specific herbivory rate was positively related to initial chlorophyll a concentration in experi- ments (r 2 = 0.54). Maximum in situ copepod herbivory rate and in situ copepod biomass were larger and peaked earlier at stations dominated by Baffin Bay water in the southern and eastern NOW versus stations dominated by silica-rich arctic water in the northern and western NOW. We used a standard scaling model (I = aW b ), where I = maximum daily ingestion rate and W = individual weight, to test the potential effect of size bias on our estimates of total in situ copepod herbivory, because the size struc- tures of experimental and in situ copepod assemblages were often statistically different. Although these calculations found up to ±40% difference in our estimate of total in situ copepod herbivory, this had very little effect on the estimates of copepod impact on daily primary production (±1% PP), be- cause copepod biomass was usually low relative to NOW phytoplankton biomass and productivity. During pre-bloom and spring-bloom conditions, total in situ copepod herbivory was low (<10% of PP). After the spring diatom bloom, we measured higher removal rates (~15 and 55% of PP) at 2 southern stations, where copepod biomass was high and PP was relatively low.

Impact of the large‐scale Arctic circulation and the North Water Polynya on nutrient inventories in Baffin Bay

The distributions of nitrate, phosphate, and silicate in northern Baffin Bay were determined from 90 bottle casts taken between April 11 and July 21, 1998. During late spring, low‐salinity Arctic water entered northern Smith Sound and mixed with Baffin Bay water (BBW) within the North Water Polynya. The Arctic water originated from the Bering Sea and contained high concentrations of phosphate and silicate (referred to as silicate‐rich Arctic water (SRAW)). The distribution of the two water masses was established using a new tracer, Siex, which showed moderate penetration of SRAW into Smith Sound during April and a very strong incursion in May and June, consistent with the intensification of southward current velocities. Biological depletion of macronutrients in BBW began in April and continued until nitrate was exhausted from the upper mixed layer in early June. Beneath the Polynya the deep waters (&gt;450 m) showed a marked increase in nutrient concentration toward the bottom, which was most pronounced in the south and much stronger for silicate than nitrate and phosphate. The silicate enrichment was consistent with dissolution of diatom‐derived biogenic silica in deep waters. The results indicate that the North Water acts as a silicate trap in which the biota differentially transports surface silicate to depth, thereby influencing local and downstream nutrient signatures.

Climatic and oceanic forcing of new, net, and diatom production in the North Water

Abstract New, net, and diatom production in the North Water were estimated during May to July 1998 from in vitro measurements of nitrate uptake and mesoscale temporal changes in the inventories of nitrate, silicate, oxygen, and inorganic carbon (DIC). Sampling stations were divided into two domains according to the position of the dominant water types: the silicate-rich Arctic water (SRAW) and Baffin Bay Water (BBW). BBW dominated in the southeast and was associated with relatively shallow upper mixed layers (UMLs) and weak horizontal advection. A phytoplankton bloom started in late April in BBW and grew slowly over 7 weeks, during which time the build-up of particulate organic nitrogen and carbon accounted for ca. 80% of the nitrate and DIC deficit, respectively. Over half of the new production (1.37 g C m −2 d −1 ) during this period was attributed to wind-driven replenishment of nitrate in the euphotic zone. The bloom culminated when seasonally declining winds and rising temperatures severed the UML from the deep nutrient reservoir. The same change in weather induced ice melt, stratification, and bloom development in northern SRAW, which had previously been characterized by deep UMLs. Collectively, the results imply that the timing and magnitude of blooms in the North Water are controlled by a succession of oceanic and climatic forcings. New C production in the North Water during April to July (1.11 g C m −2 d −1 ) was an order of magnitude higher than in adjacent waters and up to 8 times higher than in the Northeast Water polynya. As much as 80% of this production was mediated by diatoms >5 μm, suggesting potentially high and efficient C transfer to the herbivorous food web and deep waters.

Significance of Labrador Sea and Baffin Bay Waters for growth of the Laurentide Ice Sheet

Global ice-sheet growth from interglacial stage 5e to last glacial maximum stage 2 occurred in two major steps, at the isotope stage 5e/5d and 5a/4 transitions (e.g., Ruddiman et al. 1980). Although we do not know where ice accumulated during these times of increasing oceanic 8’0, one likely location is the Laurentide Ice Sheet (LIS). This paper describes a hypothesis forwarding the possibility that Baffin Bay and the Labrador Sea acted as moisture sources for LIS growth. Then competing interpretations of oceanic sediment cores are evaluated with regard to the potential of these areas as precipitation sources for ice growth at the stage 5a/4 transition. Finally, modelling of the global atmosphere at the stage 2 maximum suggests constraints on the location and timing of ice sheet growth.

Significance of Labrador Sea and Baffin Bay Waters for growth of the Laurentide Ice Sheet

Global ice-sheet growth from interglacial stage 5e to last glacial maximum stage 2 occurred in two major steps, at the isotope stage 5e/5d and 5a/4 transitions (e.g., Ruddiman et al. 1980). Although we do not know where ice accumulated during these times of increasing oceanic 8’0, one likely location is the Laurentide Ice Sheet (LIS). This paper describes a hypothesis forwarding the possibility that Baffin Bay and the Labrador Sea acted as moisture sources for LIS growth. Then competing interpretations of oceanic sediment cores are evaluated with regard to the potential of these areas as precipitation sources for ice growth at the stage 5a/4 transition. Finally, modelling of the global atmosphere at the stage 2 maximum suggests constraints on the location and timing of ice sheet growth.

Relations between the thermocline meso and microzooplankton, chlorophyll a and primary production distributions in Lancaster Sound

Primary productivity in Lancaster Sound was estimated from chlorophyll and light irradiance profiles and light saturation measurments. Mesozooplankton concentrations were measured using an in situ zooplankton counter mounted on a Batfish and with the BIONESS. Microzooplankton concentrations were estimated from samples taken with the BIONESS. The horizontal and vertical distribution of the two groups of zooplankton are described and related to the distribution of chlorophyll primary production and physical features of the Sound. A westward intrusion of Baffin Bay water along the north shore of the sound which mixed with Arctic water flowing easterly resulted in a complex physical environment in the sound. The admixing of these water masses resulted in a highly variable biological structure. The thermocline was the main physical feature that affected the depth of the chlorophyll layer and the levels of primary production, with a shallow thermocline resulting in higher primary production. The admixing of Baffin Bay water with Arctic water at different areas of the sound combined with the different times of appearance of open water resulted in the populations of Calanus hyperboreus and C. glacialis showing different age structures, the youngest being in the Arctic water at the western end of the Sound. Microzooplankton populations were concentrated at various depths depending on the species. Oithona juveniles preferred the upper 10 m when the thermocline was near the surface. Most macrozooplankton were found below the thermocline and the primary production maxium. The largest concentrations of microzooplankton were found at the western end of the Sound in the Arctic water believed to be still in the biological spring.

Neodymium isotopic study of Baffin Bay water: sources of REE from very old terranes

Water samples were collected from Baffin Bay and surrounding areas in order to evaluate this region as a potential source of Nd from old continental material to Atlantic water. The isotopic data ranged from ε Nd(0) = −9.0 to −26 with most of the data around ε Nd(0) = −20 compared with values of North Atlantic Deep Water (NADW) with ε Nd(0) = −13.5 . The concentration of Nd in Baffin Bay waters was as high as 6 × 10 −12 g/g compared with 2.5 × 10 −12 g/g for NADW. The combination of low ε Nd and high Nd concentration indicates that Baffin Bay may be a significant source of Nd from very old crustal material. A simple box model was used to evaluate the contribution to the Nd budget of NADW and it was concluded that a substantial fraction of the Nd from ancient crustal sources that is required to maintain the isotopic composition of NADW could be supplied by Baffin Bay outflow.

Warm water cells in the North Water, Northern Baffin Bay during winter

Sea surface temperatures above the freezing point of seawater (−1.8°C) were observed in the North Water during winter and early spring. The result indicates a possibility of upwelling warm water, presumably of Atlantic origin, brought from lower depths to the surface. The warm water temperatures ranged from −1.7° to −0.1°C. The highest occurrence frequency lay in the temperature interval from −1.0° to −0.8°C. Most warm water cells were found along the Greenland coast in Smith Sound, Lady Ann Strait, and Barrow Strait. They occurred most frequently in Smith Sound, west of Cape Alexander. The highest temperatures of −0.1°C occurred, however, south of Cape Alexander. The occurrence frequency and the total area of warm water patches decreased toward spring. The predominantly northerly wind that is channeled in Smith Sound accounts for a mean ice drift of approximately 17 km d−1. This ice drift causes an ice divergence in Smith Sound and along the Greenland coast. The existence of warm water areas can be explained by the strong northerly wind resulting in a Coriolis force that induces coastal upwelling. The wind‐induced offshore transport of 3.5×105 m3 s−1 in the North Water, compensated by the upwelling of Atlantic Baffin Bay water (0°C) along the Greenland coast, will suffice to keep 10% of the North Water ice free. The combination of ice divergence and forced convection of warm water can be considered as a prime cause of the polynyas in the North Water.

The annual cycle of temperature, salinity, currents and water masses in Disko Bugt and adjacent waters, West Greenland

All available data on bathymetry, temperature, salinity and currents up until and including 1975 are used in describing the seasonal changes and dynamics of the hydrography of Disko Bugt, the Vaigat and adjacent glacier and non glacier fjords. From a winter situation with well mixed -1.75°C cold water in the upper c. 100 m steep halo-and thermoclines develop during the summer between freshened and heated surface water leaving Disko Bugt and deeper more saline water entering from the West Greenland Current. Huge ice bergs have a decisive cooling effect upon the upper 150-200 m affecting the outflowing current as well as the inflowing water which is responsible for the high bottom temperatures and salinities (up to 3.5°C and 34-34.5‰ at 300-500 m) found the year round, and which contributes to raising the temperature in the upper 200 m in the summer, especially in the southern and eastern part of the bay and even into the Vaigat.&#x0D; Surface temperatures reach 12°C in the offshore waters of the bay where salinities may drop to 30‰, and inshore in the more diluted waters of Disko Fjord temperatures may even reach 14°C, whereas in the glacier fjords, where surface salinities come close to zero, 4°C is the highest temperature recorded and subzero temperatures are found even in July. An extensive upwelling of W Greenland water occurs in the northern part of the bay during the summer and fall and similar phenomena occur in Disko Fjord, driven by winds and apparently linked to tidal rhythms. Although TS diagrams show that deep Disko Bugt water and Baffin Bay water is of common origin, no water seems to enter Disko Bugt from Baffin Bay or from the Baffin Current.

On the Origin of Deep Baffin Bay Water

A comparison of the temperature–salinity relationships of waters found in the Arctic Ocean, Baffin Bay and Smith Sound shows that the deep Baffin Bay water originates in the Arctic Ocean rather than through an influx of a mixture of Labrador Sea deep water and Baffin Bay surface water, the salinity of which has been increased sufficiently by freezing to cause the water to sink, as suggested previously by other investigators.