Development of under-ice stratification in Himmerfjärden bay, North-Western Baltic proper, and their effect on the phytoplankton spring bloom

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Kari , E , Merkouriadi , I , Walve , J , Leppäranta , M & Kratzer , S 2018 , ' Development of under-ice stratification in Himmerfjärden bay, North-Western Baltic proper, and their effect on the phytoplankton spring bloom ' , Journal of Marine Systems , vol. 186 , pp. 85-95 . https://doi.org/10.1016/j.jmarsys.2018.06.004

Title: Development of under-ice stratification in Himmerfjärden bay, North-Western Baltic proper, and their effect on the phytoplankton spring bloom
Author: Kari, Elina; Merkouriadi, Ioanna; Walve, Jakob; Leppäranta, Matti; Kratzer, Susanne
Contributor: University of Helsinki, Norwegian Polar Institute
University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
Date: 2018-10
Language: eng
Number of pages: 11
Belongs to series: Journal of Marine Systems
ISSN: 0924-7963
URI: http://hdl.handle.net/10138/240217
Abstract: Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.
Subject: Seasonal sea ice
Under-ice plume
Stratification
Phytoplankton spring bloom
Onset
Phytoplankton composition
Baltic Sea
SEA-ICE
FINLAND
HYDROGRAPHY
GULF
TVARMINNE
ESTUARY
VARIABILITY
DISSOLVED ORGANIC-MATTER
ABSORPTION
WATER
1171 Geosciences
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