Benthic foraminifera as tracers of brine production in Storfjorden sea ice factory

• Main Authors: Fossile, Eleonora, Nardelli, Maria Pia, Jouini, Arbia, Lansard, Bruno, Pusceddu, Antonio, Moccia, Davide, Michel, Elisabeth, Péron, Olivier, Howa, Hélène, Mojtahid, Meryem
• Format: Text
• Language: English
• Published: 2019
• Subjects: Arctic; Storfjordrenna; Svalbard; Svalbard Archipelago; Foraminifera*; glacier; North Atlantic; Sea ice; Storfjorden
• Online Access: https://doi.org/10.5194/bg-2019-405; https://www.biogeosciences-discuss.net/bg-2019-405/

The rapid response of benthic foraminifera to environmental factors (e.g., organic matter quality and quantity, salinity, pH) and their high fossilisation potential make them promising bio-indicators for the intensity and recurrence of brine formation in Arctic seas. Such approach, however, requires a thorough knowledge of their modern ecology in such extreme settings. To this aim, seven stations along a N–S transect across the Storfjorden (Svalbard archipelago) have been sampled using an interface multicorer. This fjord is an area of intense sea ice formation characterised by the production of Brine-enriched Shelf Waters (BSW) as a result of a recurrent latent-heat polynya. Living (Rose Bengal stained) foraminiferal assemblages were analysed together with geochemical and sedimentological parameters in the top five centimetres of the sediment. Three major biozones were distinguished: (i) the <q>inner fjord</q> dominated by typical glacier proximal calcareous species which opportunistically respond to fresh organic matter inputs; (ii) the <q>deep basins and sill</q> characterised by glacier distal agglutinated faunas. These latter are either dominant because of the mostly refractory nature of organic matter and/or the brine persistence that hampers the growth of calcareous species and/or causes their dissolution. (iii) The <q>outer fjord</q> characterised by typical North Atlantic species due to the intrusion of the North Atlantic water in the Storfjordrenna. The stressful conditions present in the <q>deep basins and sill</q> (i.e. acidic waters and low food quality) result in a high agglutinated/calcareous ratio (A / C). This supports the potential use of the A / C ratio as a proxy for brine persistence and overflow in Storfjorden.