Abstract
Abstract. Sediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic). To study the interannual variability of suspended particulate matter (SPM) dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data), and hydrochemical (nutrients, SPM, stable oxygen isotopes) process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented. The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward shoreward winds, weaker stratification and higher SPM concentration throughout the water column might have severe consequences for the ecosystem on the Laptev Sea shelf.
Highlights
The Arctic Ocean will be seasonally ice-free by the end of this century Larger open
During the summer 2007, the surface salinity over the eastern Laptev Sea shelf exceeded the climatic mean by ∼ 2 standard deviations (Dmitrenko et al, 2010), likely associated with the eastward wind-forced diversion of the Lena River freshwater plume because of a low sea level-pressure cell centered over the central Laptev Sea
Sampling carried out during two Laptev Sea summer expeditions in 2007 and 2008 allows for new insights regarding the role of Lena River freshwater on sediment dynamics on this shelf
Summary
A seapoint turbidity meter connected to a CTD (Conductivity Temperature Depth Meter; SBE19plus, Seabird, USA) was used in order to collect water column turbidity, salinity, and temperature measurements at a total of 177 stations during TRANSDRIFT XII and XIV expeditions in August/September 2007 and 2008. The turbidity meter emits light of 880 nm wavelength with a sampling rate of 10 s−1. It detects light scattered by particles within the water column and generates an output voltage proportional to particles in the water column. A total of 434 water samples of 0.5 L each were collected from different water depths to obtain the SPM concentrations by using the traditional filtering and weighing procedures and to calibrate the optical backscatter. All SPM concentrations obtained from water samples (SPMfilter) ≤ 0.3mg L−1 were set to 0.3 mg L−1, as the elutable portion of the used filters (MILLIPORE Durapore membrane filters ∅ 0.45 microns) is
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