Easily measured call attributes can detect vocal differences between Weddell seals from two areas (Casey and Davis).

Underwater vocalisations of Weddell seals were recorded at Casey (1997) and Davis (1992 and 1997) Antarctica.  The goal of the study was to determine if it would be possible to identify geographic variations between the Casey and Davis seals using easily measured, narrow bandwidth calls (and not broadband or very short duration calls).  Two observers measured the starting and ending frequency (Hz), duration (msec) and number of elements (discrete sounds) of four categories of calls; long duration trills, shorter descending frequency whistles, ascending frequency whistles and constant frequency mews.  The statistical analyses considered all calls per base, single and multiple element calls, and individual call types.  Except for trills, discriminant function analysis indicated less variation between the call attributes from Davis in 1992 and 1997 than between either of the Davis data sets and Casey 1997. The data set contains measures from 2966 calls; approximately 1000 calls per base and year.  Up to 100 consecutive calls were measured from each recording location per day of recording so the data set indicates the relative occurrence of each of the call types per base and year.  There were very few ascending whistles at Casey. All of the trills and mews contained a single element. This data set was published in Bioacoustics 11: 211-222.
The fields in this dataset are:
Observer
Station
Location
Time
Call Number
Call Type
Frequency
Duration
Elements
Overlap
In 2011, another download file was added to this record, providing recording locations made during the project in 2010.
Furthermore:
In 1997 Daniela Simon made some opportunistic recordings for the project near Casey.  The recording locations were:
Berkley Island  110 38'E,  66 12' 40"S
Herring Island  110 40'E,  66 25'S
O'Brien Bay     110 31'E,  66 18' 30"S
Eyres Bay       110 32'E,  66 29" 20"S
The Davis sites:
IN 1990 THERE WAS ONLY ONE RECORDING SITE - 78 12.5' E,  68 31.6' S
IN 1997 RECORDINGS WERE MADE AT THE FOLLOWING SITES
EAST SIDE OF WEDDELL ARM - 78 07.55' E  68 32.17' S PARTIZAN ISLAND - 78 13.66' E  68 29.57' S LONG FJORD - 78 18.95' E  68 30.24' S TOPOGRAV ISLAND - 78 12.40' E  68 29.33'S OFFSHORE - 77 58.73'E  68 26.35'S TRYNE BAY - 78 26.25'E  68 24.87'S LUCAS ISLAND - 77 57.00'E  68 30.36'S WYATT EARP ISLANDS - 78 31.51'E  68 21.31'S
The attached document is "a listing of the Weddell seal breeding locations near Mawson where Patrick Abgrall in 2000 and Phil Rouget in 2002 made underwater recordings".  The sound recording effort in 2000 was not as high as it was in 2002, hence fewer locations are listed.
The Abgrall sites are referred to in the paper 'Variation of Weddell seal underwater vocalizations over mesogeographic ranges' that Abgrall, Terhune Burton co-authored, published in Aquatic mammals in 2003.
This paper also refers to the Casey and Davis sites above.
The Rouget sites relate to the metadata record 'Weddell Seal underwater calling rates during the winter and spring near Mawson Station, Antarctica'
Entry ID: ASAC_1132-1
In general the seals can create breathing holes in areas where tide cracks form, namely close to grounded icebergs, the shoreline and islands.  I doubt that they could/would create breathing holes through solid 2 m ice.

Tags: AMD, AMD/AU, CALL NUMBER, CALL TYPE, CEOS, CONTINENT > ANTARCTICA > Casey, CONTINENT > ANTARCTICA > Davis, DURATION, EARTH SCIENCE > BIOLOGICAL CLASSIFICATION > ANIMALS/VERTEBRATES, EARTH SCIENCE > BIOLOGICAL CLASSIFICATION > ANIMALS/VERTEBRATES > MAMMALS, ELEMENTS, FIELD SURVEYS, FREQUENCY, GEOGRAPHIC REGION > POLAR, GEOGRAPHIC VARIATION, HYDROPHONES, LEPTONYCHOTES WEDDELLII, LOCATION, METHODOLOGY, OBSERVER, OCEAN > SOUTHERN OCEAN, OVERLAP, STATION, TIME, VOCALISATIONS, WEDDELL SEAL
Organization: Australian Ocean Data Network