Project 2 R Mac Neil

Project 2 - Antarctic Ocean Mechanics

This project investigates interactions between the ocean and atmosphere in order to determine how the present Ross Sea operates in terms of transport and energetics, test this knowledge on a past Ross Sea under warmer conditions, and suggest how a future Ross Sea might operate.

Why this research project, and what do we plan to do?

New understanding is needed of Antarctica’s climate and ice sheet configuration during previous warm periods, to compare with present-day trends and predict ice sheet behaviour in a +2°C (Paris Agreement), or warmer, world.

Research Questions:

  1. How are oceanic and atmospheric heat transports changing?
  2. When will we see the emergence of the anthropogenic signal from the natural variability?

Research Activities:

  1. determine the role of the atmosphere in driving ocean boundary conditions and cycling and transport of energy
  2. sensitivity analysis of oceanic response to various conditions
  3. investigate the influence of westerlies, easterlies and katabatic flow in influencing ocean conditions
  4. examine oceanic fluxes of heat and salt at the continental shelf-break region (where a warming ocean is forced up onto the continental shelf and onwards into the Ross Ice Shelf Cavity)
  5. explore the fate and influence of meltwater
  6. better characterise the Ross Ice Shelf Polynya to better identify the relationships between atmospheric drivers and ocean response – as well as the coupling between ocean and cavity
  7. better describe the range of variability on the ocean circulation system using past conditions and then extend towards a future with a changing ocean and boundary conditions

The project focuses on the Ross Sea ocean-atmosphere system with a particular focus on atmospheric and oceanic processes. Our research connects across several scales, addressing climate, regional and mechanistic processes to detect, quantify and project an emerging anthropogenic signal in a complex ocean-atmosphere system.

Objective 1: Heat and salt transport in the ocean-atmosphere-ice system

Objective Leader: Denise Fernandez

Goal: develop an analysis of a heat, salt and energetics for the present ocean-ice-atmosphere system, and use the resulting tools to model future predictions.

Research Activities:

  • examine modelling veracity and quantify the sensitivity of modelling to discretization, mixing parameterization and other componentry, such as topography
  • develop and examine questions relating to mechanics and transport in the region (e.g. variation in wind, pathways for heat and salt, sources and fate of meltwater, pathways and fluxes involved in cavity-cavity connectivity)
  • test simulation-derived hypotheses about how the exchange of water between the Ross Sea and the Southern Ocean depends on air-sea heat fluxes, winds, and the links to sea ice formation, location of the density front on the shelf, and formation of high salinity shelf water at the edge of the Ross Sea
  • examine future Ross Sea configurations, such as the effects of sea ice or an ice shelf free Ross Sea, major iceberg intrusions, and loss of a significant glacier tongue
P2 Schematic

Figure: The Ross Sea system and past, present and proposed activity. A) RSO moorings, B) Cape Adare/Robertson Bay, C) Terra Nova Bay, D) Haskell Strait, E) HWD2, F) HWD1 and G) IODP Exp. 374 sites. Proposal objectives (O1-4) examine multiple aspects of this system as indicated on the map. The dotted circles are pending, subject to future work and/or mooring recovery. The purple circle is the site of RISIPE polynya experiment (Objective 4).

Objective 2: Paleoceanographic insights into large-scale changes

Objective Leader: Christina Riesselman

Goal: to reconstruct conditions during past warm periods, including sea surface temperature (SST), salinity (melt water), ocean currents and circulation, mixing, stratification, and sea ice.

Research Activities:

  • develop novel proxies (using existing surface sediment and water column particle samples, augmented by sediment trap samples and environmental data); validate and test against existing records
  • developing calibrations to deconvolve physical influences and biological influences from existing and new sediment core records
  • apply established and emerging calibrations and proxies to warm climate intervals in new and existing sediment cores
  • examine the structure, behaviour, and interaction of water masses along the West Antarctic margin during Pliocene and Pleistocene warm climate intervals and transitions
  • track water mass evolution along the path of the Antarctic Slope Current, providing insights into cavity-cavity connection during warm climate intervals
  • reconstruct the dynamics of the Southern Ocean frontal system, and evaluate sea ice, the polar front and Pacific Antarctic Circumpolar Current dynamics under warmer climates
Objective 2 Sea ice cracks I Mc Gregor

Objective 3: Continental shelf-slope mechanics

Objective Leader: Melissa Bowen

Goal: to monitor heat and salt transport of the Ross Sea shelf-slope system as an interface for Antarctic Bottom Water (AAWB) export and modified Circumpolar Deep Water (mCDW) import.

Research Activities:

  • moored array recoveries and deployments every two years in Ross Sea outflow and in-shelf sites
  • distinguish between changes in the flow rate and shifting of the current on the slope
  • analysis of transport and water properties of the time series
  • investigate links between exchange and allied measurements of water properties, sea ice and atmospheric fluxes in the Ross Sea
  • measure changes in high-salinity shelf water that may be contributing to deep water properties of the outflow
  • identify the return pathways for CDW getting up onto shelf/and or pathways into the RIS cavity
Objective 3 Moored equipment T Haskell

Objective 4: Polynya and Ice-Edge Processes

Objective Leader: Craig Stewart

Goal: to quantify mechanics of the Ross Ice Shelf Polynya (RISP) and the cavity edge, an ice-ocean-atmosphere nexus whose influence on both sea ice production and global ocean circulation extends to the north and south.

Research Activities:

  • evolve long term ocean moorings/voyages
  • study the mechanics of the RISP, which generates 28% of Antarctic polynya sea ice production yet is significantly under-explored
  • seek to capture substantial wind- and convection-driven mixing, shelf frontal melt rates and turbulence data for the Ross Ice Shelf frontal region, helping to dramatically improve our ability to predict the ocean behaviour
  • examine the cavity boundary conditions and termination mechanics, focusing on the seaward end of the ice shelf and how this interacts with the polynya, open ocean/sea ice and influences cavity circulation
P2 schematic 2

Figure: The RISIPE polynya experiment (Objective 4) designed to look at critical transfers at the ice-ocean-atmosphere boundary. Polynya are remarkable geophysical phenomena, especially around Antarctica. Despite their relatively small size in global terms, they provide a localized connection between the atmosphere, cryosphere and ocean that has implications at local, regional and global scales.