Optical properties in waters around the Mendeleev Ridge related to the physical features of water masses

Abstract

Irradiance profiles were measured during the Korean 2012 summer Arctic Ocean cruise and optical properties were studied. The optical attenuation coefficient in all surface waters was low, as the nutrients in the surface layers became exhausted and phytoplankton growth was only possible at the subsurface where optimal conditions of nutrients and sufficient illumination existed. This high attenuation zone was at about 40–60m. The attenuation properties were categorized to three types. Type-1 waters had weaker maximum attenuation coefficients and were located at the Chukchi Plateau and the north margin of the study region. Type-2 water had an intense maximum of attenuation coefficient up to 0.56/m located on west flank of Mendeleev Ridge and continental slope of East Siberian Sea. Two integral parameters, attenuation depth and optical thickness, were mapped by spatial distribution. The attenuation depth was basically shallower (40m) to the west and deeper to the east (100m). The averaged optical thickness at the level of 30–60m was the main zone of high attenuation. Both the optical attenuation property and the physical features of the water indicated two subsurface water masses: one is the cold shelf water well mixed with river water and transported to the east by a subsurface current along the East Siberian Slope. The other is the warmer water from the Pacific with lower nutrients and transported to the northwest along the north margin of the observed region. A cyclonically re-circulated branch of shelf water passing over the Chukchi Abyssal Plain was described in this study.