Abstract
In this study, we present unique data collected with a Surface and Under-Ice Trawl (SUIT) during five campaigns between 2012 and 2017, covering the spring to summer and autumn transition in the Arctic Ocean, and the seasons of winter and summer in the Southern Ocean. The SUIT was equipped with a sensor array from which we retrieved: sea-ice thickness, the light field at the underside of sea ice, chlorophyll a concentration in the ice (in-ice chl a), and the salinity, temperature, and chl a concentration of the under-ice water. With an average trawl distance of about 2 km, and a global transect length of more than 117 km in both polar regions, the present work represents the first multi-seasonal habitat characterization based on kilometer-scale profiles. The present data highlight regional and seasonal patterns in sea-ice properties in the Polar Ocean. Light transmittance through Arctic sea ice reached almost 100 in summer, when the ice was thinner and melt ponds spread over the ice surface. However, the daily integrated amount of light under sea ice was maximum in spring. Compared to the Arctic, Antarctic sea-ice was thinner, snow depth was thicker, and sea-ice properties were more uniform between seasons. Light transmittance was low in winter with maximum transmittance of 73. Despite thicker snow depth, the overall under-ice light was considerably higher during Antarctic summer than during Arctic summer. Spatial autocorrelation analysis shows that Arctic sea ice was characterized by larger floes compared to the Antarctic. In both Polar regions, the patch size of the transmittance followed the spatial variability of sea-ice thickness. In-ice chl a in the Arctic Ocean remained below 0.39 mg chl a m�2, whereas it exceeded 7 mg chl a m�2 during Antarctic winter, when water chl a concentrations remained below 1.5 mg chl a m�2, thus highlighting its potential as an important carbon source for overwintering organisms. The data analyzed in this study can improve large-scale physical and ecosystem models, habitat mapping studies and time series analyzed in the context of climate change effects and marine management.
Highlights
IntroductionBesides playing an essential role in global ocean circulation (e.g., Schmitz, 1995; Ferrari et al, 2014) and in regulating Earth’s climate and weather (e.g., Liu, 2012; Dethloff et al, 2019), sea ice is crucial for the Arctic and Antarctic polar food webs (e.g., Eicken, 1992; McMinn et al, 2010; Meyer and Auerswald, 2014)
Sea ice is one of the Earth system components most sensitive to climate change
The latter had higher under-ice water chl a, higher mean under-ice water temperature (−1.54 ± 0.13 ◦C compared to −1.77 ± 0.05 ◦C) and lower mean salinity (33.70 ± 0.43 compared to 34.13 ± 0.23)
Summary
Besides playing an essential role in global ocean circulation (e.g., Schmitz, 1995; Ferrari et al, 2014) and in regulating Earth’s climate and weather (e.g., Liu, 2012; Dethloff et al, 2019), sea ice is crucial for the Arctic and Antarctic polar food webs (e.g., Eicken, 1992; McMinn et al, 2010; Meyer and Auerswald, 2014). Due to changes from complete darkness to 24 h daylight, and extreme natural variations in water temperature in high latitudes, the concentration of primary production in both the sea ice and the water column undergoes a seasonal cycle, which has a major impact on food availability and life cycle of animals living in polar regions (Swadling et al, 1997; Brierley and Thomas, 2002). Knowledge of sea ice and under-ice environmental properties as drivers of large-scale patterns in the abundance and distribution of seaice algae and phytoplankton, and, of zooplankton and nekton, is essential for understanding ecosystem functioning and predicting possible consequences of climate change for the ecosystems (Flores et al, 2011, 2019; David et al, 2015, 2016; Ehrlich et al, 2020)
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