Early spring subglacial discharge plumes fuel under-ice primary production at a Svalbard tidewater glacier

Abstract

Abstract. Subglacial upwelling of nutrient-rich bottom water is known to sustain elevated summer primary production in tidewater-glacier-influenced fjord systems. However, the importance of subglacial upwelling during the early spring season has not been considered yet. We hypothesized that subglacial discharge under sea ice is present in early spring and that its flux is sufficient to increase phytoplankton primary productivity. We evaluated the effects of the submarine discharge on primary production in a seasonally fast-ice covered Svalbard fjord (Billefjorden) influenced by a tidewater outlet glacier in April and May 2019. We found clear evidence for subglacial discharge and upwelling. Although the estimated bottom-water entrainment factor (1.6) and total fluxes were lower than in summer studies, we still observed substantial impact on the fjord ecosystem and primary production at this time of the year. The subglacial discharge leads to a salinity-stratified surface water layer and sea ice formation with low bulk salinity and permeability. The combination of the stratified surface layer, a 2-fold higher under-ice irradiance due to thinner snow cover, and higher N and Si concentrations at the glacier front supported phytoplankton primary production 2 orders of magnitude higher (42.6 mg C m−2 d−1) compared to a marine reference site at the fast-ice edge. Reciprocal transplant experiments showed that nutrient supply increased phytoplankton primary production by approximately 30 %. The brackish-water sea ice at the glacier front with its low bulk salinity contained a reduced brine volume, limiting the inhabitable brine channel space and nutrient exchange with the underlying seawater compared to full marine sea ice. Microbial and algal communities were substantially different in subglacial-influenced water and sea ice compared to the marine reference site, sharing taxa with the subglacial outflow water. We suggest that with climate change, the retreat of tidewater glaciers in early spring could lead to decreased under-ice phytoplankton primary production. In contrast, sea ice algae production and biomass may become increasingly important, unless sea ice disappears first, in which case spring phytoplankton primary production may increase.

Reply on RC1

“…Vonnahme et al (2021) found evidence for upwelling movement at the southern part of the Nordenskiöldbreen terminus, despite the shallow waters. Such inflow was as well found during the spring period when the adjacent area is covered by sea ice, even though the flow was considerably lower than during the summer period (Vonnahme et al, 2021). We argue that spring inflow of meltwater originated probably without contact with the subglacial environment as no visual evidence of sediment inflow was observed.…”

Fifty Years of Tidewater Glacier Surface Elevation and Retreat Dynamics along the South-East Coast of Spitsbergen (Svalbard Archipelago)

“…Tidewater glaciers do not only represent a dominant landscape feature on the eastern coast of Svalbard, but also constitute one of the most important ecological hotspots where the marine ecosystem is fed by nutrients and other compounds from the terrestrial environment [4,5,61]. The subglacial meltwater discharge also modifies the general circulation of water in front of the glacier terminus, usually leading to water upwelling and increased mixing of the fjord water [62,63].…”

“…Many animal species rely heavily on this element of the ecosystem, typically marine mammals or birds in Svalbard [3]. The inflow of nutrients also supports primary production near glacier calving fronts [4,5].…”

Rubisco in high Arctic tidewater glacier‐marine systems: A new window into phytoplankton dynamics

“…Across the Arctic, nitrate delivery by tidewater glacial marine systems has been tied to higher primary production using in situ chlorophyll a (Chl a ) measurements, carbon fixation rate estimates, and remote sensing analyses (Meire et al 2017; Vonnahme et al 2021; Dunse et al 2022), but there have been very few studies evaluating the impact of tidewater glaciers on marine phytoplankton community dynamics (Kanna et al 2022; Maselli et al 2023). Despite the high density of tidewater glaciers across Nunavut in the Canadian Arctic Archipelago, there have been no comprehensive studies investigating interactions between phytoplankton and glaciers in this region.…”