Antarctic Elephant Seal Breeding Site Affirms There Was Far Less Sea Ice During Medieval, Roman Periods
DNA evidence suggests the limit of Antarctic sea ice was ~2000 kilometers farther south than it is today 2500 to 1000 years ago.
Elephant seals can only breed in the Southern Ocean’s subantarctic, sea ice free waters. For example, today’s largest colony breeds on Macquarie Island (54.5°S).
Scientists (Wood et al., 2025) have now identified DNA evidence of an elephant seal breeding site at Cape Hallett (72.3°S), with the remains dating to the Roman and Medieval Warm Periods (2500 to 1000 years ago).
Cape Hallett is approximately 2000 kilometers south of the southernmost modern elephant seal breeding grounds. This means Antarctica’s sea ice limits were thousands of kilometers less extensive than today’s back when CO2 concentrations were at “safe” pre-industrial levels (~265 ppm).
Image Source: Wood et al., 2025
A 2019 study indicated Late Holocene elephant seal remains can be found even farther south along the Ross Sea coast than Cape Hallett.
For example, elephant seals occupied breeding sites on Inexpressible Island and Marble Point (77.4°S) from 2000 to 1000 years ago. This means Late Holocene sea ice free latitudes extended 2400 kilometers farther south than today’s.
“…land-fast ice and multi-year sea ice has become much more pronounced in coastal settings over the last millennium.”
