RONNE POLYNYA EXPERIMENT (ROPEX)

ROPEX Information
Articles from ROPEX

HMS Endurance During ROPEX

Please contact Dr. Laurie Padman at ESR for more information



BACKGROUND


The Ronne Polynya Experiment (ROPEX) was carried out in the southern Weddell Sea in January and February 1998, using the Royal Navy ice-strengthened hydrographic vessel HMS Endurance. The experiment focused on the southern shelf of the Weddell Sea (see Figure 1).



Figure 1. ROPEX operations area in the southern Weddell Sea. Water less that 500 m deep is shaded. Small dots indicate the cruise track. Larger dots indicate CTD stations. Open squares indicate mooring locations (see Table). The Ice Front for the Ronne and Filchner Ice Shelves is shown schematically.


The ship departed from the Falkland Islands on January 14 and returned on February 20, operating in the southern Weddell Sea for the period January 21 to February 12 (Figure 1). Over one hundred conductivity-temperature-depth ("CTD") stations were collected in the region of the Filchner overflow, and near and north of the Ronne ice front. Bathymetry data were obtained over the southwestern continental shelf, a region for which no prior data existed. Five European current meter moorings were recovered, three from the Ronne ice front and two from the Filchner Depression. Four new European/US moorings were deployed in a region where dense water modified by the inclusion of potentially supercooled Ice Shelf Water first flows down the continental slope after leaving the Filchner Depression.

The primary goal of the program was to obtain oceanographic, sea-ice, and atmospheric measurements to improve our understanding of the physical processes coupling the southern Weddell Sea to the circulation and properties of the global ocean and atmosphere. In the southern Weddell Sea (Figure 1), four elements strongly interact with each other: the ocean over the continental shelf; the polar atmosphere; sea-ice (when it is present); and the massive floating glacial ice shelves, which are the oceanic termination of continental ice as it flows off the Antarctic continent.

Therefore, the primary research tasks for the cruise were:

Sea ice conditions during the cruise were very favourable (Plate 2 and Plate 3), allowing the ship to survey a large area north of the Ronne Ice Front (Figure 1). No previous oceanographic or even bathymetric data have been obtained from this region.

 

Our data will be integrated with other programs in the region, including measurements obtained under the Ronne Ice Shelf (Nicholls, 1996). This study will improve our ability to model the Weddell Seas role in such processes as the global fresh water budget and the generation of Antarctic Bottom Water, the latter being a fundamental component of the Global Ocean Conveyor Belt (Broecker, 1991).

The primary institution responsible for the ROPEX cruise is the British Antarctic Survey (BAS). Other participating institutions are:

 

The scientific party is shown in Plate 1.

 

For another view of ROPEX on the web, check out: http://gnarly.lanl.gov/Pop/eclare/Antarctic/antarctic.html

 

Acknowledgements: The US component of this research was supported by the National Science Foundation grant OPP-9615525. We gratefully acknowledge the assistance of Captain T. Barton, the officers and crew of HMS Endurance, for providing an excellent platform for ROPEX.




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PRINCIPAL RESULTS


Oceanography

Moorings: In total, five moorings belonging to Alfred-Wegener Institute (AWI) and the Institute of Geophysics, University of Bergen, were recovered, three from near the Ronne Ice Front, and two in the northern Filchner Depression (Figure 1). These moorings, consisting of five Neil-Brown Acoustic and eleven Aanderaa current meters (see Table), had been deployed in early 1995: previous attempts to recover them had failed due to heavy ice conditions. The recovered instruments contained up to 2.5 years of current, temperature, and conductivity data. The current meters recovered from the Ronne Ice Front more than double the amount of data from this region.

Four new moorings were deployed across the continental slope just to the west of the Filchner Depression (Figure 1). These moorings (see Table) support instruments from AWI, the British Antarctic Survey, the University of Bergen, and Earth & Space Research. The moorings are intended to measure the overflow of dense water that contains a component of Ice Shelf Water (ISW) originating in processes under the Filchner-Ronne Ice Shelves (FRIS). High-salinity shelf water flows into the cavity under the floating glacial ice shelves and is modified by incorporation of the fresh and cold glacial ice. The resultant ISW is potentially supercooled, i.e., it is colder than the surface freezing temperature for its salinity. ISW is believed to play a significant role in the creation of the dense waters of the Weddell Sea (Foldvik and Gammelsrød, 1988). The new moorings will monitor the time-dependence of the efflux of this dense water from the Filchner Depression, the presumed main drainage trough to the deep Weddell Basin from the FRIS.

CTD: Over one hundred CTD profiles were collected in two primary study areas, the northern Filchner Depression and overflow region, and the area near and north of the Ronne Ice Front (Figure 1). The measurements in the former area were made with an emphasis on locating dense outflows of shelf water and ISW prior to the new mooring deployments (see Figure 2). The profiles collected in the Ronne Depression region were designed to study the distributions of high-salinity shelf water and ISW in this area for which no prior CTD data exist (other than in a narrow strip along the polynya region just north of the Ronne ice front). Data were obtained with a Seabird SBE-911 plus CTD, with a Carousel Water Sampler containing twelve, twelve-liter bottles. In addition, water samples were collected for subsequent analysis of salinity (for checking the CTD calibration), and for d 18O, the latter being useful particularly for estimating the fraction of glacial ice melt that has been incorporated into the seawater. Work is still in progress on final calibration of these data.

Bathymetry: One of HMS Endurances primary functions is the collection of high-quality bathymetric data in its operating area. During ROPEX, ice conditions and program scheduling allowed the ship to collect data from regions of the southern Weddell Sea (in particular, the southwestern corner) that had not previously been explored (see Figure 1). These new data improve our understanding of potential drainage paths for dense shelf water to the deep Weddell Sea. Significantly, these data also radically improve our ability to model tides in this region. Tides have been shown to be energetic, and play a critical role in water mass production and transformation processes in the Weddell Sea, yet modeled tidal currents are very sensitive to the quality of bathymetric information (Robertson, Padman, and Egbert, 1998; Padman, Kottmeier, and Robertson, 1998).



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Atmospheric Measurements:

  This section under construction

 

 

 

Sea Ice Observations and Sampling:

Sea ice conditions during the ROPEX cruise are shown in Plate 3.

A preliminary report of the sea ice conditions during the cruise has been prepared by S.F. Ackley and E.C. Hunke.

Sea ice conditions in the Weddell Sea, Jan-Feb 1998
url: http://gnarly.lanl.gov/Pop/eclare/Antarctic/prelim.html


 

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REFERENCES

Broecker, W.S. 1991. The Great Ocean Conveyor. Oceanography, 4, 79-89.

Foldvik, A., and T. Gammelsrød. 1988. Notes on Southern Ocean Hydrography, Sea-Ice, and Bottom Water Formation. Palaeogeography, Paleaoclimatology, and Palaeoecology, 67, 3-17.

Nicholls, K. 1996. Temperature Variability Beneath Ronne Ice Shelf, Antarctica, From Thermistor Cables. Journal of Geophysical Research, 101(C1), 1199-1210.

Padman, L., C. Kottmeier, and R. Robertson. 1998. Tidal Ice Motion in the Weddell Sea. Submitted to the Journal of Geophysical Research.

Robertson, R., L. Padman, and G. D. Egbert. 1998. Tides in the Weddell Sea, in Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margin, Antarctic Research Series, Vol 75 , edited by S. Jacobs and R. Weiss, pp 341-369, American Geophysical Union, Washington, DC.

 


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REPORTS FROM ROPEX


A.J.U.S. Report


Click here for a downloadable copy of a four-page summary on the oceanography components of ROPEX (available in postscript or Acrobat PDF form). This report was prepared for publication in the Antarctic Journal of the United States.


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FRISP Report


Click here for a downloadable copy (2.6 MB, in Acrobat PDF form) of a nine-page discussion on the effect of adding ROPEX depth data to the existing bathymetric data base for the Weddell Sea. This report was prepared for publication in the Filchner-Ronne Ice Shelf Program (FRISP) Report No. 12 (1998).


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