Silicic acid limitation drives bloom termination and potential carbon sequestration in an Arctic bloom

Abstract

The spring diatom bloom in the Arctic Ocean accounts for significant annual primary production leading to the most rapid annual drawdown of water-column p CO 2 . Late-winter waters in the Atlantic Arctic & Subarctic Provinces (AASP) have lower silicic acid concentrations than nitrate, which suggests diatom blooms may deplete Si before N. Here we test a facet of the hypothesis that silicic acid limitation terminates the spring diatom bloom in the AASP and the sinking of the senescent and dead diatoms helps drive carbon sequestration. During a 6-week study, diatoms bloomed and progressively consumed silicic acid to where it limited their growth. The onset of growth limitation was concurrent with the minimum p CO 2 in the surface waters and increases in both the proportion of dead diatoms and the diatom assemblage sedimentation rate. Data reanalysis within the AASP shows a highly significant and positive correlation between silicic acid and p CO 2 in the surface waters, but no significant relationship with nitrate and p CO 2 was observed unless data were smoothed. Therefore, understanding the future of the AASP spring diatom bloom requires models that explicitly consider changes in silicic acid supply as a driver of this process.

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

“…High sinking rates are more often observed at low growth rates and in senescent cells when the energy becomes less sufficient (Smetacek, 1985;Waite et al, 1992;Durkin et al, 2016). Silicic acid limitation terminated the spring diatom bloom and triggered cell death, thus a fast sinking out of the photic layer in the Arctic near Greenland and Svalbard islands (Krause et al, 2019;Agustí et al, 2020). Our data suggests that the low energy availability and cell death due to inefficient photosynthesis under melt stress contributed to the fast sedimentation of some pennate ice diatoms, hence reducing their seeding effect to the open-water bloom.…”

Phosphorus dynamics in the Barents Sea

“…At the Arctic stations silicate remained below the concentration limit (2 μ M) required to support diatom dominated primary production (Egge and Aksnes 1992). Silicate limitation on PP has been reported for subarctic provinces, terminating diatom blooms (Krause et al 2019). Our BEST analysis indicates that silicate and temperature are the dominant factors driving patterns in species distribution across both Atlantic and Arctic waters combined.…”

Arctic (Svalbard islands) active and exported diatom stocks and cell health status

“…Our results reporting fast diatom cell death under aphotic conditions are contrasting with the expectation of high survival capacity of polar diatoms to darkness supported by existing evidence. Recent reports identified fast photosynthetic response to irradiance in diatoms sampled during the dark wintertime around the Svalbard islands (Kvernvik et al, 2018). Phenotypic selection for specific physiological properties allows polar diatoms to acclimate to low light and darkness (Lacour et al, 2019).…”