Water mass provenance and mixing in the Fram Strait, Arctic Ocean – Multi-proxy evidence from dissolved Nd isotopes, REEs, Ba, nutrients, and δ18O

Friday, 19 December 2014
Georgi Laukert1, Martin Frank1, Ed C Hathorne1, Dorothea Bauch1, Carolyn Wegner1, Zhimian Cao1, Moritz Zieringer1, Nils Andersen2 and Heidemarie Kassens1, (1)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (2)University of Kiel, Leibniz Laboratory for Radiometric Dating and Stable Isotope Research, Kiel, Germany
Dissolved radiogenic Nd isotopes (εNd), rare earth element (REE), Ba, and nutrient concentrations combined with oxygen isotopes retrieved along a section between Spitsbergen and Greenland at approximately 79°N during the ARK XXVII/1 cruise in 2012 were measured to characterize the origin and mixing of the water masses in the Fram Strait.

Deep waters below 500 m are nearly constant in Nd concentration (CNd) around 16 pmol/kg and εNd signatures range from -9.5±0.2 to -10.9±0.2. The heavy REE to light REE ratio (HREE/LREE) ranges from 4 to 5. Ba concentrations range from 47 to 58 nmol/kg, increasing slightly with depth. These homogeneous signatures do not allow identification of distinct deep water masses.

The upper 500 m of the water column close to the Western Svalbard margin including the shelf is relatively warm and saline (T ≤ 5.5°C, S ≤ 35.1) and shares characteristics of Atlantic Water (AW) including low CNd (~15 pmol/kg) and relatively unradiogenic εNd signatures (-12.2±0.2). This water is also characterized by HREE/LREE around 4 and CBa around 50 nmol/kg.

Low salinity surface waters on the East Greenland shelf have unradiogenic εNd signatures similar to AW (-12.4±0.3) but in contrast to AW high CNd of up to 37 pmol/kg. At the same time the HREE/LREE ratio is relatively low (~3.5) and CBa reaches 73 nmol/kg. This suggests a significant freshwater contribution either from the McKenzie or the Lena rivers. Eastwards of these freshwater-influenced waters (at ~5°W), admixture of a Pacific component characterized by a more radiogenic εNd (-8.8±0.2) and high nutrient concentrations outcropping at surface was detected. Waters of the same origin are present on the East Greenland shelf at about 150 m depth.

Based on these data we use mass balance calculations to determine the fractions of sea ice meltwater, Eurasian run-off, North American run-off, and Arctic seawater and compare these results with our εNd and REE data.