Abstract
Abstract. A general pattern in water mass distribution and potential shelf–basin exchange is revealed at the Laptev Sea continental slope based on hydrochemical and stable oxygen isotope data from the summers 2005–2009. Despite considerable interannual variations, a frontal system can be inferred between shelf, continental slope and central Eurasian Basin waters in the upper 100 m of the water column along the continental slope. Net sea-ice melt is consistently found at the continental slope. However, the sea-ice meltwater signal is independent from the local retreat of the ice cover and appears to be advected from upwind locations. In addition to the along-slope frontal system at the continental shelf break, a strong gradient is identified on the Laptev Sea shelf between 122° E and 126° E with an eastward increase of riverine and sea-ice related brine water contents. These waters cross the shelf break at ~ 140° E and feed the low-salinity halocline water (LSHW, salinity S < 33) in the upper 50 m of the water column. High silicate concentrations in Laptev Sea bottom waters may lead to speculation about a link to the local silicate maximum found within the salinity range of ~ 33 to 34.5, typical for the Lower Halocline Water (LHW) at the continental slope. However brine signatures and nutrient ratios from the central Laptev Sea differ from those observed at the continental slope. Thus a significant contribution of Laptev Sea bottom waters to the LHW at the continental slope can be excluded. The silicate maximum within the LHW at the continental slope may be formed locally or at the outer Laptev Sea shelf. Similar to the advection of the sea-ice melt signal along the Laptev Sea continental slope, the nutrient signal at 50–70 m water depth within the LHW might also be fed by advection parallel to the slope. Thus, our analyses suggest that advective processes from upstream locations play a significant role in the halocline formation in the northern Laptev Sea.
Highlights
Numerous changes are predicted for the Arctic environment in the near future: models suggest that the permanent Arctic sea-ice cover may become seasonal within the few decades (e.g. Overland and Wang, 2013), affecting the perennial sea-ice dynamics on the Arctic shelves
A frontal system is inferred between shelf waters, continental slope waters and basin waters within the Lower Halocline Water (LHW) and low-salinity halocline water (LSHW) along the continental slope of the Laptev Sea (Fig. 6). δ18Oderived signals of river water and sea-ice related brine as well as nutrient ratios (N / P) and signatures from sedimentbottom water denitrification processes (N∗Atl) are found indicative of central Laptev Sea shelf bottom waters and are important for the assignment of shelf, slope and basin water masses of the upper water column along the Laptev Sea continental margin
Instead sea-ice inventories are consistently positive over the continental slope and the summer sea-ice meltwater distribution at the continental margin appears to be influenced by advection from west to east along the Laptev Sea continental slope
Summary
Numerous changes are predicted for the Arctic environment in the near future: models suggest that the permanent Arctic sea-ice cover may become seasonal within the few decades (e.g. Overland and Wang, 2013), affecting the perennial sea-ice dynamics on the Arctic shelves. Precipitation and the freshwater input from rivers may increase (Zhang et al, 2013). Impact of these and other processes related to and defining high-latitude freshwater balances may be critical for the state of the Arctic halocline, which is a ∼ 150 m thick layer with typical temperatures close to freezing and salinities sharply increasing with depth. The halocline insulates the Arctic sea-ice cover from impact of underlying Atlantic Water heat due to its strong stratification, playing a fundamental climatological role In light of climate change and its potential impacts on the Arctic Ocean halocline, further knowledge is needed on its current structure and the processes and regions involved in its formation
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