Changes in Arctic sea ice result in increasing light transmittance and absorption

Abstract

.[1] Arctic sea ice has declined and become thinner and younger (more seasonal) during the last decade. One consequence of this is that the surface energy budget of the Arctic Ocean is changing. While the role of surface albedo has been studied intensively, it is still widely unknown how much light penetrates through sea ice into the upper ocean, affecting seaice mass balance, ecosystems, and geochemical processes. Here we present the first large-scale under-ice light measurements, operating spectral radiometers on a remotely operated vehicle (ROV) under Arctic sea ice in summer. This data set is used to produce an Arctic-wide map of light distribution under summer sea ice. Our results show that transmittance through first-year ice (FYI, 0.11) was almost three times larger than through multi-year ice (MYI, 0.04), and that this is mostly caused by the larger melt-pond coverage of FYI (42 vs. 23%). Also energy absorption was 50% larger in FYI than in MYI. Thus, a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems. Citation: Nicolaus, M., C. Katlein,

Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

“…The Arctic sea-ice cover is declining rapidly, with reductions in the summer minimum extent by more than 50%, a decline in mean thickness by over 60%, and a 30-60% decrease in snow on ice thickness since the 1970s (Stroeve et al 2012;Webster et al 2014;Lindsay and Schweiger 2015). These changes in sea-ice allow for more light penetration and longer growing seasons (Wassmann and Reigstad 2011;Nicolaus et al 2012), potentially increasing Arctic Ocean primary production (Arrigo et al 2008). Enhanced thermal stratification and freshening due to sea-ice melt and increasing river discharge may alter the light regime in the shallower upper mixed layer (Peterson et al 2002;Steinacher et al 2010).…”

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…Novel and emerging technologies and methods, including the use of Remotely Operated Vehicles (ROV) and Autonomous Underwater Vehicles (AUV) instrumented with up-ward looking sonars and optical sensors, promise measurements of physical (e.g., under-ice topography) and biological (e.g., transmitted under-ice irradiance used as proxy for ice algal biomass) parameters on ecological and biogeochemical relevant scales [Mundy et al, 2007;Nicolaus et al, 2012;Williams et al, submitted].…”

“…Melt ponds efficiently transmit light to the underlying ocean, with transmission values typically an order of magnitude higher than bare ice [Frey et al, 2011]. Therefore, substantial melt pond coverage changes the ocean's surface energy budget [Nicolaus et al, 2012] and stimulates under-ice primary productivity [e.g., Arrigo et al, 2012]. Melt ponds also host their own planktonic communities [Horner et al, 1985], but their contribution in the large-scale carbon cycle is likely limited [Lee et al, 2012].…”

Nutrient availability limits biological production in Arctic sea ice melt ponds

“…Serreze et al 2000;Haas et al 2008), leading to the replacement of most of the multiyear ice with first-year ice (Maslanik et al 2007;Comiso 2012). These changes have increased the total areal coverage of melt ponds during the Arctic summer (Nicolaus et al 2012;Rösel and Kaleschke 2013). The temporal evolution in melt pond coverage is mainly determined by the increasing atmospheric Abstract Every spring and summer melt ponds form at the surface of polar sea ice and become habitats where biological production may take place.…”