KoldeweySeamount
Point of Contact: Kirstin Schulz
Collaborators: Kirstin Schulz, Till Baumann, Morven Muilwijk, Christian Mohn
Resources: poster from the 2nd MOSAiC Science Conference, February 2023
On July 24/25, 2020, at 80°N 1°W, the MOSAiC floe - which was oriented steadily before and after - revolved twice around its own center (Fig. 1). Wind conditions were calm and likely not the cause for this behavior, but the onset of the rotation coincided with the drift passing the around 1000m high Koldewey seamount.
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| Figure 1: Drift track (blue) along the Koldewey Seamount (brown triangle), with measurements from the Polarstern CTD indicated as white squares, and microstructure measurements as white circles. Red arrows indicate the heading of the floe, based on the GPS compass of the long-range ADCP. White stars indicate the start of a new day as indicated. |
According to the GEBCO Undersea Feature Names Gazetteer, the Koldewey Seamount (Summit of 2,059m at 0.9714°W, 80.1912°N in IBCAO v4) was discovered by the German research vessel "Polarstern", in 2004. The seamount was named after Carl Christian Koldewey (1837-1908). Additional Information: This feature has an oval shape and conical form, and is oriented NW to SE. Surveyed during Expeditions ARK-XIII/3, 1997, ARK-XV/2, 1999 and ARK-XVIII/2, 2002 (T. Hartmann). Minimum Depth (m): 2079; Maximum Depth (m): 3600; Total Relief (m): 1521; Dimension/Size: 20 km x 40 km.
We calculate the seamounts width and height, and some non-dimensional numbers which include the stratification strength (Fig. 2).
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| Figure 2: (a) Zonal and meridional cross-section of Koldewey Seamount based on IBCAO v4.2; (b) stratification expressed as buoyancy frequency N. |
Maximum current velocities (depth averaged over the upper 400m) range from ~0.2 ms-1 before and after the floe rotation event, to up to 1 ms-1 during the middle of first rotation, and are still enhanced at ~0.8 ms-1 at the subsequent second rotation. Velocity peaks are semidiurnal, the current is directed near-steadily towards southerly, southwesterly directions (Fig. 3a). Peaks in vertical shear (depth averaged over the upper 400m) are already visible during the onset of the rotation, one semi-diurnal cycle before the mean velocities peaked (Fig 3b).
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| Figure 3: (a) Depth-averaged current velocity (black) and direction (blue dots), and the heading of the floe (blue line). (b) Depth-averaged zonal and meridional shear squared. |
Dead ends:
- ITP94 and ITP111 did not pass the region