Abstract

Abstract. Climate change significantly impacts Arctic shelf regions in terms of air temperature, ultraviolet radiation, melting of sea ice, precipitation, thawing of permafrost and coastal erosion. Direct consequences have been observed on the increasing Arctic river flow and a large amount of organic carbon sequestered in soils at high latitudes since the last glacial maximum can be expected to be delivered to the Arctic Ocean during the coming decade. Monitoring the fluxes and fate of this terrigenous organic carbon is problematic in such sparsely populated regions unless remote sensing techniques can be developed and proved to be operational. The main objective of this study is to develop an ocean colour algorithm to operationally monitor dynamics of suspended particulate matter (SPM) on the Mackenzie River continental shelf (Canadian Arctic Ocean) using satellite imagery. The water optical properties are documented across the study area and related to concentrations of SPM and particulate organic carbon (POC). Robust SPM and POC : SPM proxies are identified, such as the light backscattering and attenuation coefficients, and relationships are established between these optical and biogeochemical parameters. Following a semi-analytical approach, a regional SPM quantification relationship is obtained for the inversion of the water reflectance signal into SPM concentration. This relationship is reproduced based on independent field optical measurements. It is successfully applied to a selection of MODIS satellite data which allow estimating fluxes at the river mouth and monitoring the extension and dynamics of the Mackenzie River surface plume in 2009, 2010 and 2011. Good agreement is obtained with field observations representative of the whole water column in the river delta zone where terrigenous SPM is mainly constrained (out of short periods of maximum river outflow). Most of the seaward export of SPM is observed to occur within the west side of the river mouth. Future work will require the validation of the developed SPM regional algorithm based on match-ups with field measurements, then the routine application to ocean colour satellite data in order to better estimate the fluxes and fate of SPM and POC delivered by the Mackenzie River to the Arctic Ocean.

Highlights

  • The Arctic Ocean is strongly influenced by direct river inputs

  • The content was shown to vary from one extreme to another, i.e. from the mineral-rich particles at the river mouth (POC : suspended particulate matter (SPM) ratio of 2 % on average) to organic-rich particles away from the river plume (POC : SPM ratio in the range 10–45 %)

  • The river plume waters appeared as a complex transition zone with mixed mineral and organic particles and a particulate organic carbon (POC) : SPM ratio typically increasing with decreasing SPM concentration

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Summary

Introduction

The Arctic Ocean is strongly influenced by direct river inputs (freshwater, nutrients, terrigenous suspended and dissolved substances). Polar amplification of climate change significantly impacts the Arctic Ocean with repercussions on both the regional and global carbon cycles (www.acia.uaf.edu). The melting of ice and permafrost, increasing precipitation and hydrological processes at high latitudes are changing freshwater discharge and the amount of terrestrial organic and inorganic matter that is delivered to the ocean (Peterson et al, 2002; Frey and McClelland, 2009). D. Doxaran et al.: Optical characterisation of suspended particles presumably highly refractory terrigenous particulate organic carbon (POCter), expected to be resistant to degradation in coastal waters until burial in marine sediments, is quite uncertain (Hedges et al, 1997; Schlunz and Schneider, 2000) and warrants careful monitoring in coming years

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