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During polar nights in January 2012 and 2017, significantly higher bioluminescence (BL) potential emissions in the upper 50 m were observed in the fjord Rijpfjorden (Svalbard, Norway) in comparison to offshore stations (located on the shelf-break, shelf-slope areas and in the deeper water). The objective of this paper is to better understand why, during two polar nights (separated by 5 years), the values of BL potential in the northern Svalbard fjord are higher than at offshore stations, and what the role of advection is in observed elevated BL potential values in the top 50 m of the fjord. To address the above objective, we applied the same BL potential modeling approach and strategies during polar nights for both 2012 and 2017. For both years, advection of BL potential from offshore (including upwelling along the shelf, shelf-slope) produced an increase of BL potential in the fjord area, in spite of the introduction of mortality in bioluminescent organisms. Observations of BL potential indicated high emissions at depths below 100 m at offshore stations for both polar nights. Our modeling studies demonstrated that these high values of BL potential below 100 m are upwelled and advected to the top 50 m of the fjord. We demonstrated that upwelling and advection of these deep high BL potential values (and therefore, upwelling and advection of corresponding bioluminescent taxa) from offshore areas are dominant factors in observed BL potential dynamics in the top 50 m in the fjord. [ABSTRACT FROM AUTHOR]

Bioluminescence (BL) potential observations registered high BL potential emissions during the polar night of January 2012 at the mouth of a fjord Rijpfjorden (northern Svalbard, Norway). Notably, observations of BL potential at this location were significantly higher in the upper 50 m than observed BL potential at offshore stations located on the shelf-slope areas and in the deeper water off northern Svalbard. In the present paper, we address questions as to why the values of BL potential in the fjord are higher than at offshore stations and what the role of advection is in the observed elevation of BL potential values in the fjord in comparison to offshore stations. We utilized the ensemble approach when changes in BL potential are modeled with the advection-diffusion-source (ADS) model, and the focus is on modeling and predictions of a large ensemble of averaged values of BL potential over a specific domain of interest at the fjord mouth. Results of the modeling have demonstrated increases in ensemble members with BL potential values larger than or equal to the specific threshold in comparison to corresponding ensemble members in the initial distribution. Even when we introduced mortality rates in our simulations (values from 0.1 to 0.3 day−1), increases in ensemble members with higher than the threshold value were more than 3.7 times larger in comparison to ensemble members in the initial distribution. The interpretation of our results is that during the polar night, the fjord represents an area where bioluminescent organisms from offshore aggregate through advection and mixing. [ABSTRACT FROM AUTHOR]