This project took advantage of the 2010 transit of the Swedish Research Icebreaker Oden through the eastern Ross Sea (ERS) to investigate a key problem in the physics of air-sea-ice interactions: What processes control the flow of warm Circumpolar Deep Water (CDW) onto the Antarctic continental shelf in the ERS, and how might such incursions change in an evolving polar climate?

It is now widely perceived that in some locations the warmth of CDW drives rapid ice shelf basal melting, which in turn allows grounded ice streams to move more rapidly into the sea. In summer, a sharp transition occurs around the Edward VII Peninsula between a warm region that experiences CDW intrusions and a cold shelf water region that may not. We postulate that a minor shift in the ocean circulation could expose the base of the eastern Ross Ice Shelf to seawater several degrees warmer than today. The ERS lies near the winter residence of the dynamic Amundsen Sea Low on the southern limb of the Ross Gyre, has a nearly perennial sea ice cover, and was devoid of winter measurements.

Goal

To identify key present-day dynamical and thermodynamical mechanisms that control the net onshore transport of warm CDW - or lack thereof - around the Edward VII Peninsula in the Eastern Ross Sea.

Objectives

1. What are the characteristics of the CDW intrusions, meltwater outflows and surface waters in the ERS in reference to those of neighboring regions in the Ross and Amundsen Seas?
2. What are the influences of the atmosphere, sea ice, bathymetry and ice shelves on the ocean circulation in this region?
3. What is the annual cycle of water properties and circulation on the continental shelf of this region?

Funded Components

Of the four original components of the multidisciplinary project proposed to NSF, only two were funded with a reduced scope. They are summarized below.

• Ocean Station Work A series of high-resolution conductivity/temperature/depth (CTD) measurements were made to characterize the summer regional water mass stratification and circulation, the meridional exchange of waters between the oceanic and shelf regimes, and ocean interactions with the local ice shelves, sea ice and atmosphere. CTD data provide the information needed to describe the boundaries and spreading of water masses, to infer their mixing histories and interactions with sea-ice and continental ice, and the spatial framework needed to interpret time series information from the mooring locations. The proposed sampling along and near the planned route onboard the Oden in 2010. Observations of the thermal and density structure along other portions of the Oden track will be made by occupying CTD stations. The number and spacing of stations will be adjusted according to the sea ice conditions and ocean features encountered.
  
  
• Moored Times Series The first long-term (~1-year) time series of current, temperature, salinity (conductivity) and pressure were recorded in the interior of the Little America Troughs, using two short bottom moorings. That record length is adequate to resolve most temporal variability in ocean heat transport at scales from tidal to seasonal. One mooring was deployed off the Ross Ice Shelf, and the other at the outer shelf. The moorings were furnished with two current meters paired with C/T/P recorders and two T/P recorders. Sensors were paired near the bottom and instruments were kept below 300 m to minimize the likelihood of mooring damage from icebergs. Time series were analyzed in combination with data from CTD/LADCP hydrographic stations to compute the baroclinic and total currents at the time of the cruises. Direct current measurements at the bottom were used to estimate barotropic velocity, the unknown constant of integration for the thermal wind component obtained from CTD measurements. The time series of currents and water properties will provide the temporal framework needed to interpret information from the summer snapshots provided by the hydrographic observations.
  
  

2-year Field Program

ERS survey of 2010

The deployment cruise was carried out in early 2010 on the Swedish Icebreaker Oden, sailing from McMurdo, Antarctica to Punta Arenas, Chile. Due to repeated CTD winch failures, only ten CTD stations were occupied.

The two ERS moorings were successfully deployed during this cruise.

To watch a slideshow of ERS CTD operations and mooring deployments on the Oden, click on the image below.

A TAMU REPORT is available here.

CTD is available here.

ERS 1-year Mooring Array of 2010-2011

The two ERS moorings were recovered during the CLIVAR Repeat Hydrography cruise S4P in February 2011 aboard the U.S. R.V.I. Nathaniel B. Palmer. A high-resolution survey of the thermal structure along the shelf break was carried out after mooring recoveries using closely-spaced XBT profiles.

XBT data is available here.

Moored Time Series from SeaBird C/T/D recorders SBE-37, Norterk AQUADOPP and area available here.

Outreach

A documentary video of the ERS moorings recoveries was produced by Juan Botella, a Polar TREC Teacher funded by NSF. To watch the video click on the image below.

Acknowledgements

This project is funded by the National Science Foundation, Office of Polar Programs.