Where is amundsen gulf

Part of the northwestward flowing ice stream was deflected around the Colville Mountains on Victoria Island and rejoined the main ice stream in Amundsen Gulf by way of Prince Albert Sound.

The grounded Amundsen Gulf ice stream extended northwestward to the outer slope in the Beaufort Sea where it was buttressed by Arctic Shelf Ice. Maximum ice stream extent is inferred to have been coincident with the Late Glacial Maximum. Multi-sequence ice-contact sediments and stratigraphic relations with glaciomarine sediments indicate that several ice advances and retreats occurred in the northwestern part of the gulf. Final retreat from the maximum position began prior to 13, cal yr BP and terrestrial dates indicate that the retreating ice front had reached Dolphin and Union Strait by about In all years sampling occurred between the first week of August and mid-September.

During this period there is no polar night complete darkness. Twilight illumination increases at the end of August with daylight decreasing to ca. Zooplankton sampling and CTD casts were conducted in all years along transects that ranged in depth from 20 m to a maximum of m on the lower slope of the Beaufort Shelf. At each station, physical oceanographic data salinity, temperature, and dissolved oxygen were collected with a rosette-mounted Seabird SBE CTD and averaged over 1 m intervals.

Herein we provide chlorophyll a chl a concentrations from to , corresponding to the years of shell dissolution analyses. Total chl a was determined from discrete water samples collected with the rosette. DIC and TA samples were collected from the rosette in ml borosilicate glass bottles and preserved with mercuric chloride following the best practices Dickson et al. The DIC was determined using gas extraction and a coulometric titration with photometric endpoint detection Johnson et al.

The TA was measured by open-cell potentiometric titration with a full curve Gran end-point determination Haradsson et al. All measurements were calibrated using Certified Reference Material supplied by A.

Dickson, Scripps Institute of Oceanography. The vertical distribution of L. All zooplankton sampling was conducted during the daytime hours, ca. The net was hauled vertically and programmed to collect stratified samples from a maximum of five depth strata.

Samples processed in the lab were split using a Folsom splitter , Fisheries and Oceans Canada, Freshwater Institute or beaker method , , Van Guelpen et al. Abundances presented as Ind. In and , L. Individual specimens were carefully picked, without magnification, from fresh samples for dissolution analyses. The individual L.

Such preservation eliminated any potential of shell dissolution during the storage. Limacina helicina shell dissolution was assessed by scanning electron microscopy SEM. Shells were prepared for SEM analysis by, i removal of abiogenic crystals from the shell surface, ii dehydration, iii mounting on the SEM stub, iv removal of the organic layer, and v sputter coating.

Shell size and the distribution of shell damage were recorded. Descriptions of each dissolution category and associated saturation condition from other studies are summarized in Table 1. Table 1. There was at most a 1-month time difference in the start of sea-ice opening during the years when shell dissolution was assessed and In the DOO was earlier relative to , occurring during the week following May 8th and June 26th at the same respective locations.

The sea-ice loss period occurs over a period of weeks in the Dolphin and Union Strait area, with bands of fractured ice persisting in the area. The water masses in Amundsen Gulf, that set the general physical and geochemical conditions, mostly originate from outside the gulf. The three dominant water masses polar mixed layer, Pacific halocline and Atlantic layer were present in each of the three areas where shell dissolution was assessed, and the water column structure was generally similar in and Figure 2.

Deeper waters flow in to the gulf, and extend into the embayments, from the Beaufort continental slope, and from the offshore Beaufort Gyre. The Atlantic-origin bottom waters transitioned to Pacific-origin water Figure 2 around m depth.

Figure 2. Temperature-salinity plots for pteropod shell dissolution focal areas in the Amundsen Gulf in and As is expected for the Arctic Ocean, surface waters in the three areas were generally freshened due to a combination of factors including river water input, ice melt, and the advection and mixing of lower salinity waters.

In the Amundsen Gulf, the direct river inputs are from the relatively small rivers, such as the Hornaday River that flows into Darnley Bay. The large inflow from the Mackenzie River can also have a direct influence when summertime downwelling favorable winds occur on the shelf, pushing Mackenzie River water to the coast where it rapidly flows into the Amundsen Gulf in a boundary current.

In surface water freshening is especially evident at Cape Bathurst salinity as low as 26 where Mackenzie River plume waters are more frequently observed. In , aragonite saturation in the Amundsen Gulf ranged from 0.

Figure 3. Aragonite saturation Omega and Limacina helicina abundance Ind. Chlorophyll a integrated concentrations over the euphotic zone were, on average, four times higher in than at the stations in the Amundsen Gulf.

In the three areas assessed for dissolution, integrated euphotic zone maximum m depth chl a concentrations averaged In , the highest chl a concentrations occurred in the embayments, reaching The abundance and distribution of L. These pteropods were found in all small embayments, i. Shelf waters contained the highest number of individuals in water column integrated abundance, maximum Ind.

In the Amundsen Gulf, L. In , L. The abundance of L. Figure 4. Distribution of Limacina helicina on the Beaufort shelf and in the Amundsen Gulf, — sampling depth integrated abundance indicated by circles, Ind m —2. The diameter of individuals assessed for shell dissolution averaged There was no significant difference in the size of individuals collected in August versus September suggesting limited growth during the study period Figure 5.

Among the individuals assessed for shell dissolution, there were two size classes present. Figure 5. There were no individuals detected without shell dissolution but the shells were not entirely covered with dissolution damage; rather spots of the various Type I—III dissolutions were observed in discrete locations on the shells Figure 7.

The high percentage of Type III dissolution indicates a very high incidence of the most severe dissolution present. Figure 6. Limacina helicina dissolution severity in and Sample size n indicated on each bar.

Figure 7. In panel B , damage on the first whorl is shown in greater detail with the squares indicating deeper-protruding Type III dissolution. Figure 8. Similar to , water depths ca.

The most significant extent of shell dissolution damage occurred on the first whorl Figure 7 across stations and individuals, although smaller extents of dissolution were also scattered around the shell, in particular at the growing edge. In there was evidence of shell structural modification in the adults, but not in juveniles Figure 9. Shell modification was focused around the first whorl, and was evident as a crystalline regrowth overlaid on surface areas of dissolution.

This structural modification in the shape of crystalline regrowth was unstructured and homogenous, and in this, distinctively different than the typical prismatic and underlying cross-lamellar microstructure of pteropod shells Sato-Okoshi et al. Shell modification was evident on few individuals, in particular where the shell dissolution was most severe, and not across all the adults.

In , there was no or extremely limited evidence of shell modification, again only in the adult group, indicating some plastic responses in adults, but not in the juveniles. Figure 9. Shell modification on adult Limacina helicina collected from Minto Inlet in , A observed on recessed area of shell with severe underlying dissolution of the surface shell layer, B the modification on the shell is of crystalline origin, yet it appears unstructured relative to typical pteropod shell microstructure.

The white arrow points to the recessed area A and shell modification layer B. Limacina helicina was widely distributed across the study area including coastal embayments. Although the occurrence of dissolution was severe and consistent in and , L. Highest abundance was observed on the Beaufort shelf Ind.

Despite the sensitivity of polar waters to ocean acidification, dense populations of Limacina spp. During the study period, L. Chlorophyll a integrated concentrations over the euphotic zone were, on average, four-times higher in than at the stations in the Amundsen Gulf. Oceanographic and sea-ice conditions, and shelf upwelling can drive interannual variations in primary production of this order of magnitude in the Canadian Beaufort Sea, with cascading impacts on food availability to zooplankton grazers Tremblay et al.

Despite the higher summer chl a concentrations in , L. However, individuals were on average larger in suggesting that the additional summer resources supported enhanced growth but the later ice opening in may have impeded recruitment, possibly due to a timing mismatch between critical life stages and needed resources. Growth estimates suggest that L. The sea-ice algal bloom provides abundant and critical food Michel et al. The consumption of ice algae specifically by pteropods has been identified through food web studies in the high Arctic and in Antarctica Kohlbach et al.

Pteropods are reported to feed opportunistically, switching from phytoplankton to mobile prey post-bloom Gilmer and Harbison, ; Pasternak et al. Open-water isotopic signatures of L. Ehrman unpublished data , in agreement with evidence of an efficient transfer from primary producers to pelagic grazers in this region Forest et al. Around Cape Parry, L. It is likely that herbivory provides the highest quality diet to support L. The low number and size of adults observed in August indicates a potential mass adult mortality event after spring spawning.

In the study years, the population may have been comprised of a single cohort that overwinters and has a longevity of a single year. The life span of L. Reliance on the sea-ice algal and spring phytoplankton blooms, in the oligotrophic Beaufort Sea, may only support a single cohort which increases the susceptibility of the population to the effects of ocean acidification.

Contingent on key factors such as stratification and mixing which shape the response of primary producers to on-going changes Ardyna et al. We hypothesized that dissolution would be highest in areas of upwelling, a known source of undersaturated waters for shelf environments Feely et al. Amundsen Gulf Limacina is also more impacted than those in regions of known change. The extent of dissolution was positively correlated with salinity, supporting the notion that Pacific-origin waters are a stronger driver of dissolution than the freshened surface water with reduced buffering capacity Yamamoto-Kawai et al.

Water conditions near the surface and around the coast i. Upwelling and downwelling is particularly evident at Cape Bathurst where it is topographically amplified Williams and Carmack, , and undersaturated Pacific-origin water can reach the surface during upwelling events. Due to the large response of the coastal ocean to wind forcing, synoptic, seasonal and inter-annual variation in the winds over Amundsen Gulf and the adjacent Beaufort Shelf and Slope will be strong drivers of coastal conditions, including salinity, dissolved nutrients and aragonite saturation state.

Flow along the coast, continental shelf and slope has the potential to move water from far away to the gulf. For example, surface drifters during a downwelling favorable autumn storm traveled along the coast from the Canadian Beaufort Shelf to Darnley Bay in a few days B. Williams unpublished data. Therefore, pteropods sampled in Amundsen Gulf could have been brought to the gulf by surface oceanic flows and thus conditions experienced on the Beaufort Shelf or slope may have also contributed to their shell dissolution.

In the study area, regions of potential tidal mixing include the continental shelves on either side of the mouth of Amundsen Gulf, including Cape Bathurst, as well as Dolphin and Union Strait McLaughlin et al.

From the s to , the aragonite saturation state has been variable and declining in the upper halocline and deep waters of the Canada Basin and Beaufort Sea Miller et al. Although L. This regular exposure could explain dissolution at the growing edge.

The surface mixed layer represents an important portion of habitat without undersaturated conditions. Consequently, hatching and metamorphosis to the juvenile stage could all occur within the undersaturated Pacific halocline where the corrosive Pacific Winter Water resides Qi et al.

Williams, unpublished data. This study provides evidence of shell modification in adult individuals sampled in A homogenous yet unstructured crystalline layer was deposited in patches over damaged areas on the surface of only the first whorl Figure 9.

The shell modification occurred at locations with the most severe dissolution suggesting that the pteropods may have initiated such a process to build a more mechanically durable shell by reducing the porosity or increasing its thickness. More detailed study of the crystalline layer is required to describe the modifications at the nano- or micro-scale of shell building.

The unstructured and homogenous layer deposited on the pteropod shells may be similar to reduced crystallographic control of shell formation observed for mussels grown under acidification conditions Fitzer et al.

Shell modification as a repair mechanism has been previously documented for L. In this study it is not possible to determine the seasonal timing of the shell modification. It could have occurred during the growth of early life stages, in which case the structurally homogenous crystalline deposition represents a plastic repair response to unfavorable conditions i.

Alternatively, it could have deposited under more favorable conditions later in the summer, in which case the unstructured layer would qualify as shell regrowth. The observed shell modification in , and not in , implies that such deposition is not always feasible and is likely dependent on suitable environmental conditions Seibel et al.

In , summer phytoplankton concentrations may have provided an adequate, accessible energy source to support shell modification in the absence of other metabolic costs such as reproduction. The absence of the unstructured layer on juvenile shells suggests that energy may have been allocated to growth rather than repair. The shell modification may confer some resilience for damaged adults, and as such potentially allows for higher fitness and better reproductive success.

The shell modification appears to be more of a plastic response to the external environmental conditions, rather than an adaptive response. It is evident that the observed depositions on the first whorl do not constitute a process that would have entirely eliminated the shell dissolution apparent at the individual or population level. Given that the shell modification process was only observed in a few adult individuals at spatially limited locations e.

Nevertheless, under future conditions with lower aragonite undersaturation, it is possible that energy devotion to shell modifications may become more common, or necessary, for survival. If shell modifications are not possible in juveniles, future decreases in aragonite undersaturation may lead to death in early life stages with population and ecosystem consequences.

In the Amundsen Gulf, the prevalence and location of dissolution on shells identifies Limacina spp. Longer periods of monitoring are required to use Limacina spp. Due to ongoing anthropogenic contributions of atmospheric CO 2 , it is predicted that Arctic L. Tolerances to current rapid rates of change and cumulative perturbation of marine ecosystems are not well known such that the future survival of Limacina spp. The summer of began with relatively cool temperatures in the Arctic, and the storms and winds that can break up ice were mostly absent, according to NASA ice scientist Walt Meier.

But the long-term thinning of sea ice has made it more susceptible to melting, so the melt season concluded with the sixth-lowest ice extent of the modern satellite era. Even in years with similar ice extents, the line traced around the edge of the sea ice can take on different shapes. Factors like winds and even the topography of the sea floor can affect the location and extent of Arctic ice.

The gulf forms the westernmost section of the Northwest Passage, which opened during the low-ice year of , but remained ice-bound in The close-up view of the ice shows a wide range of sea ice types. Blue ice in the lower right corner is thicker ice that is several years old; it contains fewer and smaller pockets of air that would normally cause ice to reflect blue light. Adjacent to the open water of the Amundsen Gulf is first-year ice, which grows in just one winter.

The dark grey ice is even younger and thinner, and might represent an area of recently open water that refroze. Snow on top of the sea ice accounts for some of the white areas.