Ocean impact on the 79 North Glacier, Northeast Greenland

• Main Author: Schaffer, Janin
• Other Authors: Kanzow, Torsten, Rhein, Monika
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2017
• Subjects: ocean glacier interaction; Nioghalvfjerdsfjorden Glacier; Atlantic Water; Northeast Greenland continental shelf; 500; 500 Science; ddc:500; Greenland; Nioghalvfjerdsfjorden; Nord Gletscher; Fram Strait; glacier; North Atlantic
• Online Access: https://media.suub.uni-bremen.de/handle/elib/1346; https://nbn-resolving.org/urn:nbn:de:gbv:46-00106281-12

The retreat and acceleration of marine-terminating glaciers around the coast of Greenland observed over the last two decades have partly been attributed to a warming of Atlantic Water (AW) circulating around the subpolar North Atlantic. This thesis investigates the impact of the ocean circulation on the 79 North Glacier (79NG), which has Greenland's largest floating ice tongue. One overall hypothesis tested in this thesis is whether a long-term warming of AW in Fram Strait has spread across the continental shelf off Northeast Greenland (NEG) toward the 79NG, which may explain the recent thinning observed at the floating ice tongue. A detailed bathymetry is crucial for studying pathways of AW across the NEG continental shelf. Thus, the first part of this thesis is devoted to an accurate representation of the continental shelf bathymetry and 79NG cavity geometry. Based on a collection of hydrographic data obtained between 1979 and 2016 it is shown that the Norske Trough, the southern branch of the characteristic C-shaped trough system on the continental shelf, is filled up by warm Atlantic Intermediate Water (AIW) exceeding 1 degree Celsius at depths below 200-250 m. Current velocities from moored and lowered ADCPs inside Norske Trough indicate that a boundary current transports warm AIW toward the 79NG. The results show that Norske Trough provides the main pathway for warm AIW from the continental shelf break toward the 79NG. Anomalies in AW temperatures in Fram Strait could reach the 79NG within 1.5 years. A unique data set comprising bathymetric, hydrographic, and current velocity observations obtained during the R/V Polarstern cruise PS100 in front of the 79NG calving front emphasizes the importance of the complex bathymetry for the heat transport into the cavity below the floating ice tongue. A density-driven gravity plume, steered by the bathymetry outside the cavity, transports warm AIW into the subglacial cavity. These findings imply that the AIW layer thickness on the continental shelf plays an important ...