Variability of pathways of deep water transport to the Denmark Strait

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) contributes to the large-scale transport of heat and salt by water in the North Atlantic Ocean. In this project, we investigated the pathways and sources of the Denmark Strait Overflow Water (DSOW). The DSOW is the dense water which flows through the Denmark Strait (DS) over a sill. Model data described by Köhl et al. [2007] is used to investigate these pathways and corresponding hydrographic properties. Virtual particles are released using a particle tracking simulation called OceanParcels [Delandmeter and van Sebille, 2019] and resulting trajectories are investigated.

The results show the connection between the DSOW and the East Greenland Current (EGC), but do not show a stable main pathway over time between these. Both the North Icelandic Jet (NIJ) and the East Iceland Current (EIC) appear to be connected with the EGC. Moreover, it appears that the warmer path of the DSOW originates from the EGC, and the colder path from the NIJ. Some particles from the EIC may return near the Iceland shelf and flow back to the east side of the Kolbeinsey Ridge (KR). However, no differences in temperature between the east and west side of the KR are recognizable in the results of the trajectories. Additionally, no clear connection between the DSOW and the Iceland Sea gyre is found.

However, trajectories are found to be strongly fluctuating on a monthly time scale rather than inter-annual time scale. For this reason, mesoscale eddies and their influence are investigated in more detail in two locations by using an eddy tracking system of Nencioli et al. [2010]. First, the area around the DS is investigated, where relatively many anticyclonic eddies are found compared to the entire study area. The intermittent occurrence of eddies shows a strong relation with volume transport to the DS, as shown by potential vorticity and potential density. Second, a smaller area near the Spar Fracture Zone (SFZ) is investigated. The strengthening of an eddy, which is locked due to the topography, is found to be related to the diversion from the EGC into the EIC. To investigate if eddies are likely to be one of the responsible mechanisms for the variability of the sources and pathways into the DS, a confirmation by observational research is recommended, as well as further research into the possible mechanisms behind these eddies.