Effects of bio-optical factors on the attenuation of ultraviolet and photosynthetically available radiation in the North Water Polynya, nothern Baffin Bay

Recently, the Arctic has experienced a recurrent springtime thinning of the stratospheric ozone layer resulting in increasing ultraviolet-B radiation (UVBR, 280 to 320 nm). However, little is known about the effect of such UVBR enhancement on the Arctic ecosystem. In spring-summer 1998 and fall 1999, 40 stations were investigated in the North Water Polynya (NOW), High Arctic. In the course of this study, 3 periods (pre-bloom, bloom and post-bloom) were distinguished based on chlorophyll a (chl a) concentrations. The attenuation of ultraviolet radiation (UVR) and photosynthetically available radiation (PAR) are reported here. Bio-optical factors, namely particulate organic carbon (POC), dissolved organic carbon (DOC) and chl a concentrations were related to the attenuation coefficient, K-d(lambda), of both UVR and PAR. During the pre-bloom period (9 April to 12 May 1998), all bio-optical factors except chl a concentrations were unrelated to K-d(lambda). However, the absorption of colored dissolved organic matter might prevail. During the bloom period (15 May to 29 June 1998), both chl a and POC were strongly correlated to K-d(lambda). During the post-bloom period (27 August to 25 September 1999), POC contributed from 57 to 83 % of the K-d(lambda). Under stratification conditions, an inverse relationship was observed in the UVR and PAR ranges, between K-d(lambda) and the depth of the subsurface chlorophyll maximum (SCM). This could be a consequence of cell migration below the penetration depth of UVR where they are protected from UVR-induced physiological damages.