Effects of sea‐ice and biogeochemical processes and storms on under‐ice water fCO₂ during the winter‐spring transition in the high Arctic Ocean: Implications for sea‐air CO₂ fluxes

Abstract

We performed measurements of carbon dioxide fugacity (fCO2) in the surface water under Arctic sea ice from January to June 2015 during the Norwegian young sea ICE (N‐ICE2015) expedition. Over this period, the ship drifted with four different ice floes and covered the deep Nansen Basin, the slopes north of Svalbard, and the Yermak Plateau. This unique winter‐to‐spring data set includes the first winter‐time under‐ice water fCO2 observations in this region. The observed under‐ice fCO2 ranged between 315 µatm in winter and 153 µatm in spring, hence was undersaturated relative to the atmospheric fCO2. Although the sea ice partly prevented direct CO2 exchange between ocean and atmosphere, frequently occurring leads and breakup of the ice sheet promoted sea‐air CO2 fluxes. The CO2 sink varied between 0.3 and 86 mmol C m−2 d−1, depending strongly on the open‐water fractions (OW) and storm events. The maximum sea‐air CO2 fluxes occurred during storm events in February and June. In winter, the main drivers of the change in under‐ice water fCO2 were dissolution of CaCO3 (ikaite) and vertical mixing. In June, in addition to these processes, primary production and sea‐air CO2 fluxes were important. The cumulative loss due to CaCO3 dissolution of 0.7 mol C m−2 in the upper 10 m played a major role in sustaining the undersaturation of fCO2 during the entire study. The relative effects of the total fCO2 change due to CaCO3 dissolution was 38%, primary production 26%, vertical mixing 16%, sea‐air CO2 fluxes 16%, and temperature and salinity insignificant.

Seasonal Changes in Carbonate Saturation State and Air‐Sea CO2 Fluxes During an Annual Cycle in a Stratified‐Temperate Fjord (Reloncaví Fjord, Chilean Patagonia)

“…In Friday Harbor in the glacially formed San Juan Archipelago (Washington, USA), p CO 2 ranged from ~300 to ~1,100 μatm over a 2‐year period, mostly with high positive Δ p CO 2 , suggesting that the sea is a source for atmospheric CO 2 in this area (Murray et al, ). On the other hand, Kongsfjorden and Tempelfjorden Arctic fjords (Svalbard, Norway) appeared to be less variable systems (in terms of the carbonate dynamics and saturation state of Ω Arag ) and they apparently act as CO 2 sink systems (Fransson et al, , ). In the case of the Godthåbsfjord system (SW Greenland), the input of fresh glacial meltwater produces a strong CO 2 uptake giving a net negative CO 2 flux within this fjord system (Meire et al, ).…”

Atmosphere‐Ice‐Ocean‐Ecosystem Processes in a Thinner Arctic Sea Ice Regime: The Norwegian Young Sea ICE (N‐ICE2015) Expedition

“…The collected time series on sea‐ice physics and biogeochemistry further provided an opportunity to evaluate a state of the art sea‐ice numerical model (Duarte et al, ), showing that physics can be well reproduced given the forcing is realistic, and also giving insights into ice algae dynamics in different types of sea ice. A unique time series quantified the factors that affect surface water CO 2 , showing the importance of transient storm events and ice dynamics for ocean‐atmosphere CO 2 exchange in ice‐covered waters (Fransson et al, ). While Nomura et al () showed that the young new sea ice growing in winter and spring is a source CO 2 to the atmosphere, while in older ice the CO 2 flux is strongly modulated by the snow cover properties.…”

Net Community Production and Carbon Exchange From Winter to Summer in the Atlantic Water Inflow to the Arctic Ocean

“…The characteristics of the Arctic ice cover has changed from thick multi-year sea ice to thinner first-or second-year sea ice (e.g., Serreze et al, 2007;Rabe et al, 2009;Granskog et al, 2016;Rösel et al, 2018). As a result of all these changes, surface-water stratification, primary production, carbon export and ocean CO 2 uptake are expected to change (e.g., ACIA, 2005;AMAP, 2013AMAP, , 2018Slagstad et al, 2015;Fransson et al, 2017).…”