Optical properties of melting landfast sea ice and underlying seawater in Santala Bay, Gulf of Finland

Abstract

[1] In March and early April 2000, spectral irradiance measurements were conducted on 10 occasions above and beneath the landfast sea ice in Santala Bay near the entrance to the Gulf of Finland. The measurements included the spectral albedo and transmittance of the sea ice and the downwelling and upwelling spectral irradiance at different depths in the water column. Spectral albedos integrated over 400-700 nm photosynthetically active radiation (PAR) were in the range of 0.16-0.58, with most common values between 0.33 and 0.42. Maximum transmittances for the ice are found close to 570 nm, decreasing toward shorter and longer wavelengths. Correspondingly, diffuse attenuation coefficients for both seawater and sea ice agree well with earlier measurements in the Baltic Sea and have a PAR attenuation of 0.4-0.7 and 3.1-4.7 m À1 , respectively. During the measurement period the ice reached its maximum thickness of 28 cm and thereafter started to decay. The sea ice was snow free; however, the formation of high-scattering melt/freeze layers above the freeboard largely increased the surface reflectance. Discharged meltwater was retained beneath the sea ice, forming a low-salinity layer which only disappeared as the ice ablated in April. Compared with many parts of the Arctic, the sea ice and seawater in Santala Bay contain higher amounts of dissolved and particulate matter, which are indicated by high absorption at wavelengths below 700 nm and thus potentially increase the melt rate of the sea ice.

The characteristics of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in Antarctic sea ice

“…As mentioned above, the optical properties of CDOM in Baltic sea ice have been shown to differ from that of the under-ice seawater (Ehn et al, 2004;Granskog et al, 2005) as a result of in situ (sympagic) CDOM production (Stedmon et al, 2007). Belzile et al (2000) showed that CDOM was a significant component of the DOM pool attenuating UV light in Arctic first-year sea ice, as did Ehn et al (2004) and Uusikivi et al (2010) for the Baltic Sea.…”

“…As mentioned above, the optical properties of CDOM in Baltic sea ice have been shown to differ from that of the under-ice seawater (Ehn et al, 2004;Granskog et al, 2005) as a result of in situ (sympagic) CDOM production (Stedmon et al, 2007). Belzile et al (2000) showed that CDOM was a significant component of the DOM pool attenuating UV light in Arctic first-year sea ice, as did Ehn et al (2004) and Uusikivi et al (2010) for the Baltic Sea. Scully and Miller (2000) concluded that melting sea ice would be a source of CDOM to the surface ocean in Baffin Bay (Canadian Arctic), and both Kieber et al (2009) and Ortega-Retuerta et al (2010) considered that Antarctic sea ice might be a potential source of CDOM, although this was suggested without direct evidence.…”

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

“…Therefore, surface flooding is rather rare in the Arctic. In the Northern Hemisphere, due to the proximity of pollutant sources, snow falling onto sea ice can result in deposition and accumulation of NO 3 , NH 4 and soot [Ehn et al, 2004;Nomura et al, 2011].…”

Chromophoric dissolved organic matter (CDOM) in first-year sea ice in the western Canadian Arctic

“…In a modeling study on the contribution of CDOM to the heating budget of Arctic seawater, Hill (2008) proposed that ice algae-derived CDOM is the dominant component of the CDOM pool resulting in the increased solar energy trapped in the mixed layer of the Chukchi Sea. Studies in the strongly fluvially impacted subarctic Gulf of Finland have demonstrated the importance of CDOM as a solar UV absorber within the sea ice (Ehn et al, 2004;Uusikivi et al, 2010), the influence of riverine input on the source composition of sea ice CDOM (Granskog et al, 2006), and the distinct optical properties of CDOM in sea ice as compared to that in under-ice seawater (Ehn et al, 2004;Granskog et al, 2005). More recently, surveys have been made on the distribution, photoreactivity (Norman et al, 2011), and fluorescent characteristics (Stedmon et al, 2011b) of DOM and CDOM in Antarctic sea ice in the Weddell Sea and the South Indian Ocean off Wiles Land.…”