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FRINATEK-Fri prosj.st. mat.,naturv.,tek

Topographic control in the Arctic Ocean

Alternative title: Topografisk kontroll av havsirkulasjonen i Arktis

Awarded: NOK 8.1 mill.

Project Number:

314826

Application Type:

Project Period:

2021 - 2024

Location:

The large-scale ocean circulation in the Arctic is much less understood than the circulation in the other world oceans. What we know about currents in the Arctic is that it behaves differently than currents in e.g. the Atlantic Ocean. The reason for this is partially the proximity to Earth's rotation axis (the North Pole!) and partially because of the relatively weak vertical density stratification due to strong heat losses to an icy cold polar atmosphere. The results are ocean currents that are steered by bottom topography to a much greater extent than further south. The large-scale currents primarily follow the continental slope around the polar basin, and therefore the Atlantic Water which brings along heat from the south is also primarily transported along the slopes. The strong topographic steering makes it hard for the Atlantic Water to reach the deep central basins of the Arctic - where the warm water can potentially melt enormous amounts of sea ice. The transport towards the central basins is carried out by so-called mesoscale eddies, a form of ocean turbulence which is influenced by Earth's rotation and in many ways equivalent to atmospheric high and low pressure systems. This 'ocean weather' is also constrained by bottom topography, but it is still able to transport Atlantic Water from the boundary current and into the deep basins. The ambition of this project, called TopArctic, is to improve our fundamental understanding of how bottom topography impacts on both large-scale currents and mesoscale eddies in the Arctic. We will utilize observations and high-resolution numerical models to test hypotheses about topographic control of eddy growth and then about how such eddies in turn control the strength of the larges-scale currents. The research has the potential to improve elementary textbooks on oceanography and also to enhance our ability to model the ocean circulation in the Arctic, today as well as in a future climate.

The Arctic Ocean is still one of the least understood ocean regions on the planet. We essentially lack a basic dynamic 'textbook' theory for how the circulation there is maintained and steered. And complex numerical climate models also have a hard time reproducing the observed hydrography and circulation in the Arctic. This project aims to improve the situation by taking a closer look at the impact of mesoscale eddies (oceanic 'weather') on the large-scale circulation. And to properly understand this impact we are absolutely required to study how bottom topography impacts is eddy field. More than a hundred years ago Nansen and Helland-Hansen reported on how ocean currents in the Arctic are effectively steered by continental slopes and underwater ridge systems. This observation has led to the development of relatively unique theoretical descriptions of the large-scale flow in the Arctic. The theories are nonetheless incomplete in that they completely neglect the role of ocean eddy transport. As it turns out, eddies are almost as constrained by bottom topography as the large-scale flow is. So understanding this topographic impact is absolutely key. This project brings together a diverse team of theoreticians and numerical ocean modelers from Norway and abroad to tackle this research problem. The approach will combine analyses of realistic eddy-permitting models, idealized high-resolution numerical experiments and a study of net effects in budgets of the Arctic Ocean flow. The ambition is to contribute both towards improved eddy parametrizations for use in global numerical climate models and to improve our very basic theories of how the Arctic Ocean works.

Activity:

FRINATEK-Fri prosj.st. mat.,naturv.,tek