Alexandre Forest

Oceanographic structure drives the assembly processes of microbial eukaryotic communities

Arctic Ocean microbial eukaryote phytoplankton form subsurface chlorophyll maximum (SCM), where much of the annual summer production occurs. This SCM is particularly persistent in the Western Arctic Ocean, which is strongly salinity stratified. The recent loss of multiyear sea ice and increased particulate-rich river discharge in the Arctic Ocean results in a greater volume of fresher water that may displace nutrient-rich saltier waters to deeper depths and decrease light penetration in areas affected by river discharge. Here, we surveyed microbial eukaryotic assemblages in the surface waters, and within and below the SCM. In most samples, we detected the pronounced SCM that usually occurs at the interface of the upper mixed layer and Pacific Summer Water (PSW). Poorly developed SCM was seen under two conditions, one above PSW and associated with a downwelling eddy, and the second in a region influenced by the Mackenzie River plume. Four phylogenetically distinct communities were identified: surface, pronounced SCM, weak SCM and a deeper community just below the SCM. Distance–decay relationships and phylogenetic structure suggested distinct ecological processes operating within these communities. In the pronounced SCM, picophytoplanktons were prevalent and community assembly was attributed to water mass history. In contrast, environmental filtering impacted the composition of the weak SCM communities, where heterotrophic Picozoa were more numerous. These results imply that displacement of Pacific waters to greater depth and increased terrigenous input may act as a control on SCM development and result in lower net summer primary production with a more heterotroph dominated eukaryotic microbial community.

Winter pulses of Pacific-origin water and resuspension events along the Canadian Beaufort slope revealed by a bottom-moored observatory

To assess hydrodynamics and particle transport variability at the Arctic shelf-basin boundary, a bottom-moored marine observatory was maintained from October 2003 to October 2006 over the ca. 300 m isobath on the slope of the Canadian Beaufort Sea (western Arctic Ocean). The mooring line was equipped at ~200 m depth with an oceanographic multi-sensors and a sequential sediment trap. Each winter, an abrupt and brief (<8 days) amplification of the subsurface eastward circulation was recorded when sea ice was covering most of the western Arctic Ocean. Compared to a mean background of 9 cm s-1, the highest daily velocities recorded during the events reached 67, 94 and 62 cm s-1, respectively in 2004, 2005 and 2006. The temperature-salinity signatures of the amplified flows displayed the signal of Pacific-origin shelf waters. The analysis of current components enabled us to propose that we detected the external limit of a submerged eddy formed via baroclinic instability of the shelfbreak current. We suggest that the periodic synchronicity of high atmospheric pressure along with rapid ice formation over the western Arctic Shelf were able to produce such instabilities in the jet. Each winter, the energy carried by the Pacific-origin water pulses was sufficient to erode the upper continental slope, producing marked sediment resuspension. Accordingly, the downward particle flux estimated with the sediment trap reached their annual peak values at the same time as the abrupt current surges were recorded. While the mean daily flux was ~0.1 g m-2 d-1 over the three-year period, the vertical mass flux reached ~0.8 g m-2 d-1 in both January 2004 and February 2006. In January 2005, however, the sediment trap clogged (>10 g m-2 d-1) as a result of the strong water pulse detected during this month. Our study stresses the importance of maintaining long-term marine observatories along the Arctic shelfbreak to better elucidate the links between the changing atmosphere-sea ice-ocean system and biogeochemical fluxes in the Canadian Beaufort Sea.

Assessment of 3D Spatial Interpolation Methods for Study of the Marine Pelagic Environment

Given the volumetric nature of the ocean, 3D spatial modeling and interpolation could be a key to a better understanding of continuous abiotic and biotic phenomena that compose the marine ecosystem, although such techniques are rarely used and their actual performance is poorly studied. Here, we evaluate the performance of 3D spatial interpolation for five pelagic variables derived from a typical oceanographic campaign conducted in the southeastern Beaufort Sea (Canadian Arctic) in 2009. Our main objective is to evaluate and compare the performance of a deterministic interpolation method (inverse distance, IDW) and a geostatistical method (ordinary kriging, OK) with a variation of method input parameters (search neighborhood, weights) for variables with increasing complexity in terms of data anisotropy and sampling configuration. Performance of different 3D interpolation strategies is evaluated by cross-validation and a qualitative comparison of 3D spatial models. Our results show that OK was the optimal method. However, when the complexity of pelagic variables increased in terms of spatial autocorrelation and data variation, the error difference between OK and IDW was reduced. We recommend that recent advances in spatial 3D modeling tools developed primarily for geological modeling should be exploited to extend the usual interpretation of marine pelagic phenomena from a 2D to a 3D environment.

Bridging Time Scales, Disciplines, and Generations to Better Understand the Arctic Marine Ecosystem

Understanding and predicting how ecological and biogeochemical processes in the Arctic Ocean are affected by global changes require an integrated approach. Modifications in the Arctic system may feed back to the Earths climate, and shifts in food web functions could affect the people who depend on marine resources. Connecting information obtained along the circum-Arctic, across disciplines and time scales as well as over generations, is thus key to gaining new insights on the interactions that drive the mechanics of change (Arctic in Rapid Transition Implementation Plan; http://www.iarc.uaf.edu/ART/implementation-plan). Such a framework is needed if the linkages between atmosphere-ice-ocean forcing, land-ocean exchanges, biodiversity, and the productive capacity of the Arctic Ocean are to be properly understood.

Sediment Dynamics from Coast to Slope – Southern Canadian Beaufort Sea

ABSTRACT Osborne, P.D. and Forest, A., 2016. Sediment dynamics from coast to slope – Southern Canadian Beaufort Sea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 537-541. Coconut Creek (Florida), ISSN 0749-0208. Profound changes in cross-shelf sediment fluxes are anticipated in coming decades in the southern Canadian Beaufort Sea where an accelerated increase in temperature could lead to large changes in Arctic river hydrology and coastal-marine geomorphologic processes. In the past decade sediment exported to the Beaufort Shelf has increased while sea level pressure has increased accelerating the Beaufort Gyre, strengthening coastal upwelling and expanding the Mackenzie River plume offshore. Sea-ice extent has decreased while storminess has increased increasing wave action, coastal downwelling, current surge and resuspension and transport on the shoreface and shelf. This paper investigates mechanisms, quantities and rates of sediment transport operating in this cold continental shelf-slope environment. Past studies from more than 2 decades of research are compared with recent measurements to develop improved estimates of sediment sources, pathways, fate and fluxes across the shelf and slope. In particular, we explore connections between data from a long term mooring observatory deployed over the continental shelf and slope during the ArcticNet-Industry Partnership (2009–2011) and Beaufort Regional Environmental Assessment (BREA 2011–2015) to those acquired in studies focusing on nearshore and shoreface. Sediment fluxes from the Mackenzie River and erosion of permafrost coasts are compared with outer shelf-slope measurements of settling particles and near-bottom fluxes. In turn, the role of atmospheric and cryospheric processes in forcing sediment transfer from coast to slope is investigated to assess system response to changing climate and evaluate implications for marine hydrocarbon resource development along the continental margin of the Arctic Ocean.