Sea Ice CO₂ Dynamics Across Seasons: Impact of Processes at the Interfaces

Abstract

• First long-term monitoring of both pCO2 and CO2 fluxes at sea ice interfaces in McMurdo Sound (Antarctica) from late winter to summer • Large biomass build-up is strikingly associated with transient heterotrophy and nitrate plus nitrite accumulation • New conceptual approach involving biofilm formation can explain observed inconsistencies: accumulation of nitrate plus nitrite and CaCO3

Sources and sinks of methane in sea ice

“…With these combinations of parameters, the d 13 C value at steady state reached -10 ‰, which is a good approximation of our most enriched d 13 C signature. The occurrence of CH 4 production despite the aerobic conditions encountered in sea ice (van der Linden et al, 2020), and from a 13 C-enriched pool as suggested by the model, points toward a different pathway than the classical anaerobic ones reported in Whiticar (1999;Figure 5). Although most of the phytoplankton and microbial species involved in aerobic CH 4 production identified to date (Table 1) are not sympagic, Pseudomonas, a microbial genus that contains seawater members capable of the C-P lyase pathway, and Phaeocystis spp.…”

“…CH 4 produced from bacterial degradation of methyl phosphonate (MPn) esters, which are part of the semilabile dissolved organic matter (DOM) pool, is characterized by a d 13 C of -39 ‰ (Repeta et al, 2016). DOM was not measured in these ice cores but can be approximated by the POC concentrations (Figure 12) reported in Van der Linden et al (2020). The vertical profiles of POC reach 2,890 mM at the ice bottom but show little variation in the ice interior, with concentrations lower than 35 mM, except for 2 local peaks, on September 19 at 103.5-cm depth (165 mM) and on October 18 at 47-cm depth (343 mM).…”

“…The water column depth at the sampling site was approximately 86 m. Noteworthy features of the study site include its location near the flanks of an active volcano, Mount Erebus, and in the vicinity of the Ross Ice Shelf. A thorough description of the study site, the sampling procedure, and sea-ice physicochemical properties can be found in Carnat et al (2014) and Van der Linden et al (2020).…”

Nutrient Distribution in East Antarctic Summer Sea Ice: A Potential Iron Contribution From Glacial Basal Melt

“…The ice platelets can eventually be incorporated onto the base of the ice shelf (marine ice) via buoyant accumulation (Oerter et al., 1992), or be carried out from the ice shelf cavity and deposited beneath neighboring sea ice (subice platelet layers; Langhorne et al., 2015; Tison et al., 1998). Under sea ice, in‐situ growth can continue, creating a porous and friable subice platelet layer from which the highest concentrations of sea‐ice algae (up to 374 mg C L −1 and 6.5 mg Chl a L −1 ) have been reported (Arrigo et al., 2010; Bombosch, 2013; Smetacek et al., 1992; van der Linden et al., 2020). The origin of marine ice Fe is often associated with highly reactive glacial flour produced from subglacial physical and chemical weathering (Wadham et al., 2010).…”

Landfast sea ice in the Bothnian Bay (Baltic Sea) as a temporary storage compartment for greenhouse gases

“…The resulting chemical activity of these impurities within sea ice influences the exchange of greenhouse gases (GHGs), including carbon dioxide (CO 2 ), methane (CH 4 ), and N 2 O (notable GHGs), across the ocean-sea ice-atmosphere interface (Lannuzel et al, 2020). During winter, sea ice acts as a source of CO 2 with high brine partial pressure of CO 2 due to increased brine concentrations and associated ikaite precipitation (Rysgaard et al, 2011;Geilfus et al, 2013;Fransson et al, 2015;Geilfus et al, 2016), whereas in spring and summer, sea ice shifts to become a sink for atmospheric CO 2 due to brine freshening, ikaite dissolution, and the biological carbon pump (Rysgaard et al, 2011;Geilfus et al, 2012;Van der Linden et al, 2020).…”