Patterns of suspended particulate matter across the continental margin in the Canadian Beaufort Sea during summer

• Main Authors: J. K. Ehn, R. A. Reynolds, D. Stramski, D. Doxaran, B. Lansard, M. Babin
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-04-01
• Series: Biogeosciences
• Online Access: https://www.biogeosciences.net/16/1583/2019/bg-16-1583-2019.pdf

<p>The particulate beam attenuation coefficient at 660&thinsp;nm, <span class="inline-formula"><i>c</i>_p(660)</span>, was measured in conjunction with properties of suspended particle assemblages in August 2009 within the Canadian Beaufort Sea continental margin, a region heavily influenced by freshwater and sediment discharge from the Mackenzie River, but also by sea ice melt. The mass concentration of suspended particulate matter (SPM) ranged from 0.04 to 140&thinsp;g&thinsp;m<span class="inline-formula">⁻³</span>, its composition varied from mineral to organic dominated, and the median particle diameter determined over the range 0.7–120&thinsp;<span class="inline-formula">µ</span>m varied from 0.78 to 9.45&thinsp;<span class="inline-formula">µ</span>m, with the fraction of particles <span class="inline-formula">&lt;1</span>&thinsp;<span class="inline-formula">µ</span>m in surface waters reflecting the degree influenced by river water. Despite this range in particle characteristics, a strong relationship between SPM and <span class="inline-formula"><i>c</i>_p(660)</span> was found and used to determine SPM distributions across the shelf based on measurements of <span class="inline-formula"><i>c</i>_p(660)</span> taken during summer seasons of 2004, 2008, and 2009. SPM spatial patterns on the stratified shelf reflected the vertically sheared two-layer estuarine circulation and SPM sources (i.e., fluvial inputs, bottom resuspension, and biological productivity). Along-shelf winds generated lateral Ekman flows, isopycnal movements, and upwelling or downwelling at the shelf break. Cross-shelf transects measured during three summers illustrate how sea ice meltwater affects river plume extent, while the presence of meltwater on the shelf was associated with enhanced near-bottom SPM during return flow of upwelled Pacific-origin water. SPM decreased sharply past the shelf break with further transport of particulate matter occurring near the bottom and in interleaving nepheloid layers. These findings expand our knowledge of particle distributions in the Beaufort Sea controlled by river discharge, sea ice, and wind, each of which is sensitive to weather and climate variations.</p>