Tracing of submarine groundwater discharge in the Siberian Arctic coastal zone: the case study in the Buor-Khaya Bay, Laptev Sea.

Abstract:

That is suggested and widely accepted that a significant portion of the Great Siberian Rivers discharge comes to the Arctic ocean via submarine groundwater discharge (SGD). However, that statement was never proofed by observations. When groundwater discharges from the coastal aquifer to the ocean, the radium isotopes are transported with the groundwater, and they can be measured to trace and quantify SGD, and the flux of constituents associated with SGD. The primary goal of this study is to use radium isotopes to proof that SGD is existing in the Laptev Sea coastal zone close to the Lena River delta, which supposed to be characterized by continuous permafrost with thickness up to 600-800m. If so, we supposed to quantify methane fluxes to the coastal ocean through SGD. Discrete seawater, and Lena river water samples

were collected from different horizons from the holes made in fast ice using submerged pump and Niskin bottle in the western part of Buor- Khaya Bay in March-April 2014 and 2015. We identified and traced SGD using short-lived radium (²²⁴Ra and ²²³Ra) and radon (²²²Rn) isotopes in complex with geophysical (electromagnetic technique) , geological (sediment core results from 16 boreholes), hydrological (temperature, salinity), and hydrochemical (total alkalinity, dissolved methane and oxygen) data. It was found that the SGD is controlled by the processes associated with changing state of the subsea permafrost. Thus, this technique can give an unique information about the location of SGD “leakage” sites across the East Siberian Arctic Shelf, which represents > 80% of subsea permafrost existing in the entire Arctic ocean.