COMPASS: Climate-relevant Ocean Measurements and Processes on the Antarctic continental Shelf and Slope

Project Information

COMPASS

Grant agreement ID: 741120

DOI

10.3030/741120

Project closed

EC signature date 5 May 2017

Start date 1 September 2017

End date 29 February 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 3 499 269,98

EU contribution

€ 3 499 269,98

Coordinated by

UNIVERSITY OF EAST ANGLIA
United Kingdom

Periodic Reporting for period 5 - COMPASS (COMPASS: Climate-relevant Ocean Measurements and Processes on the Antarctic continental Shelf and Slope)

Reporting period: 2023-09-01 to 2024-02-29

Summary of the context and overall objectives of the project

Physical processes on the continental shelf and slope all around Antarctica are crucially important for determining future sea level rise, for setting the properties and volume of dense bottom water exported globally, and for regulating the carbon cycle. Yet our ability to model and predict these processes over future decades is still rudimentary. This deficiency in understanding originates in a lack of observations in this inaccessible region. COMPASS has advanced understanding of the most critical mechanisms by which the ocean interacts with the atmosphere, sea-ice and ice shelves. It is vital that we improve our understanding of these processes, so that we can increase our confidence in future climate predictions.

The overall goal of COMPASS was to advance our understanding of the climate-relevant oceanographic processes on the continental shelf and slope of Antarctica. We harnessed new technology to make measurements in parts of the ocean that are data-sparse and poorly understood, used novel approaches to data analysis to tease out the mechanisms driving the phenomena we observe, assessed to what extent these processes occur in numerical models (both high-resolution ocean models, and coupled climate models), and deduced what steps are needed for the future (both for Antarctic marine observing strategies, and for numerical modelling development).

Ocean gliders enable us to collect the high resolution microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, epsilon, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. We report the first detailed estimates of epsilon from a Seaglider.

Meltwater content and pathways determine the impact of Antarctica's melting ice shelves on ocean circulation and climate. Using ocean glider observations, we quantifed meltwater distribution and transport within the Bellingshausen Sea's Belgica Trough. The observations and simulations reveal meltwater retention, likely to promote climactically important feedbacks on circulation and future melting.

Strong density gradients across the fronts indicate the presence of a frontal jet and are thought to modulate the southward heat transport across the front. A front in the Weddell Sea was surveyed for the first time in high resolution over 2 months with underwater gliders occupying a transect across the front. The five transects show significant, transient (a few weeks) variability of the southern boundary and its frontal jet in location, strength and width.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The major task achieved was the planning, design and purchase of an autonomous ocean surface vehicle with the capability for deploying a profiling glider.

We were fortunate to be invited to collaborate with another ERC project, Eurec4a, in a large ocean-atmosphere field campaign off Barbados in 2020. We installed meteorological sensors on Caravela so that we could calculate air-sea fluxes of heat and momentum. The team travelled to Barbados where we deployed Caravela, carrying a Seaglider. Caravela carried the Seaglider to the study site where the glider was successfully released. Simultaneous measurements of the upper ocean and sea surface were made for several weeks. The gliders were recovered from research vessel Meteor, and Caravela returned under her own wave-propulsion to Barbados for recovery.

In parallel with the development of Caravela, we undertook experiments in the Roland von Glasow sea ice chamber to test various different anti-icing coatings.

COMPASS has undertaken a series of deployments of ocean gliders around Antarctica. This has included deployments in the Amundsen Sea in 2019 and 2022, Bellingshausen Sea in 2020, Weddell Sea in 2019, 2020, 2021 and 2024, and Ross Sea in 2022-2023. Analysis of the data from these glider deployments is completed and published, or is underway. A review paper on Antarctic slope front processes has been published. An assessment of the contributions of gliders to ocean observing systems was published. Significant effort has been devoted in COMPASS into developing analysis and data quality approaches to glider microstructure data.

Analysis of ocean and climate model output was pursued through COMPASS, in particular an assessment of the seasonal cycle in climate models, and of the connectivity between the Weddell, Belingshausen and Amundsen Seas. High resolution ocean models were assessed against observations in the Amundsen and Bellingshausen Seas, and used to study the spatial and temporal context of the glider campaigns.

The results of COMPASS have been disseminated at a very large number of international conferences and workshops over the 6.5 years (too numerous to recall).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The most exciting and novel aspect of COMPASS has been the development and successful field campaign of Caravela - using one robot to deploy another. This has not been done before, and has attracted a good deal of attention. There are many potential applications of such a technique - for example enabling a timely deployment of a glider at a particular time and place (e.g. immediately prior to a hurricane, or after a volcanic eruption). She is the only ASV we are aware of that can deliver and deploy an ocean glider to a remote location. The vessel has involved close collaboration with industrial partners.

One of the exciting achievements was the COMPASS Bellingshausen glider deployment (described by Sheehan et al. 2023 and Flexas et al. recently accepted). This was a collaboration with colleagues in the US. We achieved a long deployment of several months with one UEA glider and one CalTech glider. The study region was the shelf and slope of the Bellingshausen, a relatively little studied area. Sheehan et al. (2023) described the meltwater pathways and were able to distinguish for the first time the signatures of meltwater from different ice shelf cavities. This offers exciting possibilities for future monitoring of ice shelf melting. These papers stimulated novel experiments putting tracers into ice shelf cavities in a high-resolution model.

Our Ross Sea glider deployment is one of the most exciting. The gliders were deployed from fast ice adjacent to the Ross Ice Shelf into marine mammal breathing holes. One of the gliders disappeared for several days after deployment. When it reappeared, we discovered that it had been on an unauthorised foray beneath the ice shelf. Whilst there have been some very limited measurements under the ice shelf previously from moorings, our glider gave the first measurements in the 5 metres immediately below the ice, as the glider repeatedly came up trying to surface. We document for the first time the boundary layer beneath the ice and the heat transfer across it.

A major achievement is the successful measurement of turbulent microstructure on our Seagliders. Ocean mixing and the processes that cause it are of major concern to ocean and climate scientists, as they influence nutrient fluxes, heat fluxes, air-sea interaction, sea surface temperature (and hence weather forecasting). These techniques have been applied to a more extensive Amundsen Sea data set. We are not aware of any previous papers from microstructure turbulence measurements on Seagliders.

Recovery of a COMPASS glider in the sea ice in the Amundsen Sea, February 2019

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Caravela prior to first science campaign, deploying from Barbados