Abstract
Snow cover on sea ice is the most important factor controlling light availability for sea ice algae, but it is predicted by climate models to become more variable and stochastic. Here, we document effects of a sudden, complete loss of the entire snow cover on first-year sea ice at Kangerlussuaq Fjord, West Greenland, due to a natural Föhn wind event that caused a ca. 17 °C air temperature increase over 36 h. We applied Imaging-PAM fluorometry to examine effects of snow cover on algal distribution and photobiology and observed a rapid decrease in algal biomass associated with loss of the skeletal ice crystal layer on the underside of the ice that had supported most of the visible algae. Furthermore, the remaining algae were photobiologically stressed, as seen in a significant decrease in the dark-acclimated fluorescence yield (ΦPSII_max) from 0.55 before snow loss to 0.41 after. However, recovery in the dark suggested that non-photosynthetic quenching was successfully dissipating excess energy in the community and that there was little photodamage. An observed decrease in the photosynthetic efficiency α from 0.22 to 0.16 µmol é m−2 s−1 is therefore likely to be due to photoacclimation and the change in community composition. Centric diatoms and flagellates were the main taxa lost in the snow loss event, whereas the sea ice specialist Nitzschia frigida increased in numbers. These observations are similar to those seen in artificial snow-clearing experiments and consistent with snow clearing being a useful approach for investigating the complex interactions between snow cover, irradiance fluctuations, and ice algal performance.
Highlights
Primary production in seasonally ice-covered polar oceans is driven by ice-associated and planktonic algae
Spectral composition was dominated by blue-green wavelengths, with maximum transmittance close to 480 nm but with a higher absorption in the red part of the spectrum with snow cover, consistent with how peak irradiance absorption by snow occurs at ca. 670 nm (Figure 3C)
The fortuitous weather event documented in this paper has allowed us to explore how theused results such experiments against a natural
Summary
Primary production in seasonally ice-covered polar oceans is driven by ice-associated and planktonic algae. There are generally two approaches for studying effects of snowmelt on the ice algae community: first, manipulative field experiments involving complete or partial artificial snow removal, following effects from a subsequent time series [12,20], and second, measurement of selected parameters such as biomass or primary production as a function of natural variation in snow depth over space or time [21–23] The limitations of these two approaches for understanding large-scale, rapid increases in irradiance in response to sudden snowmelt are evident. We are able to present a fortuitous account of a sudden weather-driven warming and large-scale snow loss event impacting an ice algal community on an entire fjord during the spring growth season at Kangerlussuaq, a Greenland fjord This is, to the authors’ knowledge, the first study of its kind, addressing the photobiological consequences of a rapid, wholesale natural loss of the snow cover over an entire fjord system. The specific objectives were to study the effects on the photophys iology of ice algae following sudden snow loss, as well as the role of a ca. 17 °C air of temperature increase within 36 h
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