Inorganic carbon system dynamics in landfast Arctic sea ice during the early‐melt period

Abstract

We present the results of a 6 week time series of carbonate system and stable isotope measurements investigating the effects of sea ice on air-sea CO 2 exchange during the early melt period in the Canadian Arctic Archipelago. Our observations revealed significant changes in sea ice and sackhole brine carbonate system parameters that were associated with increasing temperatures and the buildup of chlorophyll a in bottom ice. The warming sea-ice column could be separated into distinct geochemical zones where biotic and abiotic processes exerted different influences on inorganic carbon and pCO 2 distributions. In the bottom ice, biological carbon uptake maintained undersaturated pCO 2 conditions throughout the time series, while pCO 2 was supersaturated in the upper ice. Low CO 2 permeability of the sea ice matrix and snow cover effectively impeded CO 2 efflux to the atmosphere, despite a strong pCO 2 gradient. Throughout the middle of the ice column, brine pCO 2 decreased significantly with time and was tightly controlled by solubility, as sea ice temperature and in situ melt dilution increased. Once the influence of melt dilution was accounted for, both CaCO 3 dissolution and seawater mixing were found to contribute alkalinity and dissolved inorganic carbon to brines, with the CaCO 3 contribution driving brine pCO 2 to values lower than predicted from melt-water dilution alone. This field study reveals a dynamic carbon system within the rapidly warming sea ice, prior to snow melt. We suggest that the early spring period drives the ice column toward pCO 2 undersaturation, contributing to a weak atmospheric CO 2 sink as the melt period advances.

Response of the Arctic Marine Inorganic Carbon System to Ice Algae and Under‐Ice Phytoplankton Blooms: A Case Study Along the Fast‐Ice Edge of Baffin Bay

“…Peak ice algae Chl a concentrations in that study were relatively low (~20 mg/m 2 ), but there was a distinct pycnocline at ~50‐m depth, separating the polar mixed layer from underlying Pacific water. Conversely, Brown et al () saw no impact of ice algae on p CO 2sw in the water column through the peak of an intense bottom ice algae bloom near Resolute Bay, Nunavut. Ice algae concentrations in that study were much higher (max ~80 mg/m 2 ), but the water column in that region is typically mixed to the bottom (~150 m) due to strong tidally driven currents (Mundy et al, ).…”

A Model‐Based Analysis of Physical and Biogeochemical Controls on Carbon Exchange in the Upper Water Column, Sea Ice, and Atmosphere in a Seasonally Ice‐Covered Arctic Strait

“…The reference ice concentration is set at 400 mmol C/m 3 , based on observed values of DIC for first‐year landfast sea ice near Resolute (generally in the range of 300–500 mmol C/m 3 ; cf. Brown et al, ; Geilfus et al, ). During ice formation, the average DIC concentration of seawater from which the ice is formed is near 2,100 mmol C/m 3 (Brown et al, ), and hence, is set at 2,100 mmol C/m 3 .…”

“…In the polar oceans, ice cover further complicates the exchanges. Modelers have conventionally treated ice as an inert barrier to the exchange of CO 2 , but recent field work has shown that the growth and melt of sea ice can have a substantial impact on the transport of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the surface polar oceans (e.g., Brown et al, ; Delille et al, ; Geilfus et al ; Miller, Carnat, et al, ; Miller, Papakyriakou, et al, ; Nomura et al, ).…”

“…To determine model parameters and assess performance, we use observations near Resolute Passage in the Canadian Arctic Archipelago (CAA). The location was chosen for this 1‐D study because it has been the site of multiple field campaigns to measure inorganic carbon fluxes and carbonate chemical properties above, in, and below the sea ice in the area (notably Brown et al, ; Geilfus et al, ). This location also has a nearby meteorological station from which atmospheric forcing data were obtained (Environment Canada, http://climate.weather.gc.ca/).…”

Net community production in the bottom of first‐year sea ice over the Arctic spring bloom

“…The overall difference between photosynthesis and respiration represents net community production and describes whether sea ice may be considered as a net autotrophic (O 2 gain) or heterotrophic (O 2 loss) system [Codispoti et al, 2013]. The productive state of the biological community affects gas fluxes between the ice and ocean [Brown et al, 2015], as well as carbon cycling within the Arctic marine system [Matrai and Apollonio, 2013;Michel et al, 2015].…”