Water mass circulation and weathering inputs in the Labrador Sea based on coupled Hf–Nd isotope compositions and rare earth element distributions

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Filippova, Alexandra, Frank, Martin, Kienast, Markus, Rickli, Jörg, Hathorne, Ed, Yashayaev, Igor M., Pahnke, Katharina
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2017
• Subjects: Greenland; Newfoundland; Denmark Strait; Labrador Sea; North Atlantic; North East Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/35504/; https://oceanrep.geomar.de/id/eprint/35504/1/Filippova.pdf; https://doi.org/10.1016/j.gca.2016.11.024

The Labrador Sea is one of the key areas for deep water formation driving the Atlantic thermohaline circulation and thus plays an important role in Northern Hemisphere climatic fluctuations. In order to better constrain the overturning processes and the origins of the distinct water masses, combined dissolved Hf–Nd isotopic compositions and rare earth element (REE) distribution patterns were obtained from four water depth profiles along a section across the Labrador Sea. These were complemented by one surface sample off the southern tip of Greenland, three shallow water samples off the coast of Newfoundland, and two deep water samples off Nova Scotia. Although light REEs are markedly enriched in the surface waters off the coast of Newfoundland compared to north Atlantic waters, the REE concentration profiles are essentially invariant throughout the water column across the Labrador Sea. The hafnium concentrations of surface waters exhibit a narrow range between 0.6 and 1 pmol/kg but are not significantly higher than at depth. Neodymium isotope signatures (ɛNd) vary from unradiogenic values between −16.8 and −14.9 at the surface to more radiogenic values near −11.0 at the bottom of the Labrador Sea mainly reflecting the advection of the Denmark Strait Overflow Water and North East Atlantic Deep Water, the signatures of which are influenced by weathering contributions from Icelandic basalts. Unlike Nd, water column radiogenic Hf isotope signatures (ɛHf) are more variable representing diverse weathering inputs from the surrounding landmasses. The least radiogenic seawater ɛHf signatures (up to −11.7) are found in surface waters close to Greenland and near the Canadian margin. This reflects the influence of recirculating Irminger Current Waters, which are affected by highly unradiogenic inputs from Greenland. A three to four ɛHf unit difference is observed between Denmark Strait Overflow Water (ɛHf ∼ −4) and North East Atlantic Deep Water (ɛHf ∼ −0.1), although their source waters have essentially the same ɛNd ...