Abstract
Abstract. Bio-optical measurements and sampling were carried out in the delta of the Lena River (northern Siberia, Russia) between 26 June and 4 July 2011. The aim of this study was to determine the inherent optical properties of the Lena water, i.e., absorption, attenuation, and scattering coefficients, during the period of maximum runoff. This aimed to contribute to the development of a bio-optical model for use as the basis for optical remote sensing of coastal water of the Arctic. In this context the absorption by CDOM (colored dissolved organic matter) and particles, and the concentrations of total suspended matter, phytoplankton-pigments, and carbon were measured. CDOM was found to be the most dominant parameter affecting the optical properties of the river, with an absorption coefficient of 4.5–5 m−1 at 442 nm, which was almost four times higher than total particle absorption values at visible wavelength range. The wavelenght-dependence of absorption of the different water constituents was chracterized by determining the semi logarithmic spectral slope. Mean CDOM, and detritus slopes were 0.0149 nm−1(standard deviation (stdev) = 0.0003, n = 18), and 0.0057 nm−1 (stdev = 0.0017, n = 19), respectively, values which are typical for water bodies with high concentrations of dissolved and particulate carbon. Mean chlorophyll a and total suspended matter were 1.8 mg m−3 (stdev = 0.734 n = 18) and 31.9 g m−3 (stdev = 19.94, n = 27), respectively. DOC (dissolved organic carbon) was in the range 8–10 g m−3 and the total particulate carbon (PC) in the range 0.25–1.5 g m−3. The light penetration depth (Secchi disc depth) was in the range 30–90 cm and was highly correlated with the suspended matter concentration. The period of maximum river runoff in June was chosen to obtain bio-optical data when maximum water constituents are transported into the Laptev Sea. However, we are aware that more data from other seasons and other years need to be collected to establish a general bio-optical model of the Lena water and conclusively characterize the light climate with respect to primary production.
Highlights
The Lena River with its extensive delta is the pathway for transport of large amounts of organic and inorganic material, in diverse forms of carbon, from its huge catchment area of about 2 486 000 km2 into the Arctic Ocean, into the Laptev Sea (Kattner et al, 1999)
Of all water constituents CDOM is the main source of absorption in the visible wavelength range in the Lena River
The major pigments, which we found in phytoplankton of the Lena River during our campaign, were chlorophyll a, fucoxanthin, and chlorophyll b (Chl b)
Summary
The Lena River with its extensive delta is the pathway for transport of large amounts of organic and inorganic material, in diverse forms of carbon, from its huge catchment area of about 2 486 000 km into the Arctic Ocean, into the Laptev Sea (Kattner et al, 1999). It has an annual fresh water discharge of around 500 km (Dmitrenko et al, 2008; http://www.feow.org/ecoregion_details.php?eco= 608).
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