Using fluorescent dissolved organic matter to trace and distinguish the origin of Arctic surface waters.

Rafael Gonçalves-Araujo,Kumiko Azetsu-Scott,Mats A Granskog,Colin A Stedmon,Astrid Bracher,Paul A Dodd

doi:10.1038/srep33978

Abstract

Climate change affects the Arctic with regards to permafrost thaw, sea-ice melt, alterations to the freshwater budget and increased export of terrestrial material to the Arctic Ocean. The Fram and Davis Straits represent the major gateways connecting the Arctic and Atlantic. Oceanographic surveys were performed in the Fram and Davis Straits, and on the east Greenland Shelf (EGS), in late summer 2012/2013. Meteoric (fmw), sea-ice melt, Atlantic and Pacific water fractions were determined and the fluorescence properties of dissolved organic matter (FDOM) were characterized. In Fram Strait and EGS, a robust correlation between visible wavelength fluorescence and fmw was apparent, suggesting it as a reliable tracer of polar waters. However, a pattern was observed which linked the organic matter characteristics to the origin of polar waters. At depth in Davis Strait, visible wavelength FDOM was correlated to apparent oxygen utilization (AOU) and traced deep-water DOM turnover. In surface waters FDOM characteristics could distinguish between surface waters from eastern (Atlantic + modified polar waters) and western (Canada-basin polar waters) Arctic sectors. The findings highlight the potential of designing in situ multi-channel DOM fluorometers to trace the freshwater origins and decipher water mass mixing dynamics in the region without laborious samples analyses.

Highlights

Water samples for DOM analysis (CDOM and FDOM) were collected through prerinsed 0.2 μm Millipore Opticap XL filter capsules, except on the EGC2012 cruise precombusted GF/F filters were used
The visible wavelength DOM fluorescence components identified by PARAFAC modeling were correlated to the fraction of meteoric and Pacific water determined using established techniques[17,53]
In 2012 a greater fraction of Pacific waters in the Fram Strait suggests greater contribution of waters from the Canada basin which is reflected in organic matter fluorescence intensities

Summary

Introduction

Water samples for DOM analysis (CDOM and FDOM) were collected through prerinsed 0.2 μm Millipore Opticap XL filter capsules, except on the EGC2012 cruise precombusted GF/F filters (nominal pore size 0.7 μm) were used. The samples were stored in pre-combusted amber glass vials in dark at 4 °C until analysis at the Technical University of Denmark, within two months of collection (Fram and Davis Straits) or analyzed immediately onboard (EGC2012). It should be noted that the optimal situation would be to have all samples 0.2 μm filtered (removing bacteria and colloids) and analyzed immediately onboard logistical constraints and practicalities of collaborative sampling hindered this. An analysis of histograms of the fluorescence properties of DOM from the Fram Strait (sterile filtered and stored) and the EGC (GFF and analyses immediately) indicated no clear systematic bias resulting from the two approach

Objectives

Methods

Results

Discussion

Conclusion