Sea-ice and River Water Inventories Along the Laptev Sea Continental Slope Derived From Stable Oxygen Isotope Composition Within the Water Column

Water masses from the shelf areas are an important contribution to the Arctic Ocean halocline and recent observations have shown that the circulation pattern within the shelf can strongly influence the contribution of river water to the halocline of the Arctic Ocean (e.g. Guay et al. 2001; Dmitrenko et al. 2005). Understanding the processes and the exchange of water masses between the Arctic Ocean basin and the shelf areas are important in respect to halocline stability and potential climatic changes. We use stable oxygen (δ 18O) isotopes of the water to study the exchange of water masses between the Arctic Ocean basin and the shelf areas. The vast Siberian shelf areas are significantly influenced by river runoff and sea-ice processes and δ 18O is an ideal tracer to distinguish between these different freshwater sources. River water can be identified by its highly depleted δ 18O signal relative to marine waters. Sea-ice melting and formation can be identified since salinity is strongly influenced while the δ 18O signal of the remaining water remains nearly unaltered. Considerable inter annual differences are observed between Sea-ice and river water inventory values, which are derived from δ 18O and salinity values in the Eurasian Basin, along the continental margin of the Laptev Sea. Data are from samples taken during NABOS 2005 and 2006 as well as in 1995 (Frank, 1996). Since atmospheric conditions have been shown to be responsible for different transport paths of river water, a simple transport model bases on NCEP wind data is applied. This approach can explain the main features between years with significantly different wind patterns and vorticities. Nevertheless it cannot explain the observed inter annual differences between river water and brine water distributions observed also between years with rather similar vorticities. Also a correlation with annual discharge rates of the contributing rivers cannot account for the differences due to residence times exceeding one year. These results indicate an additional independent and thereby highly complicated system of freshwater storage and release on the continental shelves.