Influence of glacial water and carbonate minerals on wintertime sea-ice biogeochemistry and the CO2system in an Arctic fjord in Svalbard

Agneta Fransson,Daiki Nomura,Gernot Nehrke,Mats A Granskog,Melissa Chierici,Tõnu Martma,Svein Kristiansen

doi:10.1017/aog.2020.52

Abstract

AbstractThe effect of freshwater sources on wintertime sea-ice CO2processes was studied from the glacier front to the outer Tempelfjorden, Svalbard, in sea ice, glacier ice, brine and snow. March–April 2012 was mild, and the fjord was mainly covered with drift ice, in contrast to the observed thicker fast ice in the colder April 2013. This resulted in different physical and chemical properties of the sea ice and under-ice water. Data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in April 2012 contained on average 54% of frozen-in glacial meltwater. This was five times higher than in April 2013, where the ice was frozen seawater. In April 2012, the largest excess of sea-ice total alkalinity (AT), carbonate ion ([CO32−]) and bicarbonate ion concentrations ([HCO3−]) relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral-enriched glacial water. In April 2013, the excess of these variables was mainly due to ikaite dissolution as a result of sea-ice processes. Dolomite dissolution increased sea-iceATtwice as much as ikaite and calcite dissolution, implying different buffering capacity and potential for ocean CO2uptake in a changing climate.

Highlights

The Arctic is warming, with the concurrent rapid decline in sea-ice cover and ice thickness, and is one of the most rapidly changing environments on Earth (IPCC, 2019)
Effects of glacial water on sea-ice characteristics In April 2012, both seawater and air temperatures were warmer than in April 2013, more precipitation fell as rain, and the fresh water may have originated from several sources such as rain, snow, glacial meltwater and river runoff
It was obvious that the lowest alkalinity, δ18O and nitrate, and the highest silicate concentrations at the glacier front coincided with the highest freshwater fractions

Summary

Introduction

The Arctic is warming, with the concurrent rapid decline in sea-ice cover and ice thickness, and is one of the most rapidly changing environments on Earth (IPCC, 2019). In Greenland and Svalbard fjords sub-glacial melt releases freshwater, which rises to the surface and brings nutrients and other chemical substances from deeper water layers to the surface (e.g. Straneo and others, 2012; Halbach and others, 2019; Hopwood and others, 2020). Increased nutrient concentrations have been observed near the glacier fronts of several fjords, and promoted primary production and carbon uptake in Greenland (Azetsu-Scott and Syvitski, 1999; Sejr and others, 2011; Straneo and others, 2012; Meire and others, 2015, 2016, 2017) and in Svalbard fjords (e.g. Hodal and others, 2012; Hegseth and Tverberg, 2013; Fransson and others, 2016; Halbach and others, 2019). Increased iron concentrations near glacier fronts have been shown to lead increased primary production in fjords (Statham and others, 2008; Bhatia and others, 2013; Hopwood and others, 2020)

Results

Discussion

Conclusion