Marine CO2 system variability in a high arctic tidewater-glacier fjord system, Tempelfjorden, Svalbard

Abstract

The marine CO₂ system in Tempelfjorden (Svalbard) was investigated between August 2015 and December 2017 using total alkalinity, pH, temperature, salinity, oxygen isotopic ratio, and nutrient data. Primary production resulted in the largest changes that were observed in the partial pressure of CO₂ (<i>p</i>CO₂, 140 μatm) and the saturation state of aragonite (Ω_Ar, 0.9). Over the period of peak freshwater discharge (June to August), the freshwater addition and air-sea CO₂ uptake (on average 15.5 mmol m⁻² day⁻¹ in 2017) governed the surface <i>p</i>CO₂. About one fourth of the uptake was driven by the freshening. The sensitivity of Ω_Ar to the freshwater addition was investigated using robust regressions. If the effect of air-sea CO₂ exchange was removed from Ω_Ar, a freshwater fraction larger than 50% (lower range of uncertainty) was needed to provide aragonite undersaturated waters. This study shows that Ω_Ar and freshwater fraction relationships that are derived from regression techniques and the interpretation thereof are sensitive to the effect of air-sea CO₂ exchange. Since the freshening in itself only drives a fraction of the air-sea CO₂ uptake, studies that do not account for this exchange will overestimate the impact of freshwater on ΩAr. Finally, in the summer an excess in the salinity normalized dissolved inorganic carbon, corrected for aerobic primary production/respiration, of on average 86 μmol kg⁻¹ was found in the deepest water of the fjord. This excess is suggested to be a result of enhanced CO₂ uptake and brine release during the period of sea ice growth.