Elephant Seals Breeding In The Ross Sea Up To 1000 years Ago – Now It’s Too Cold
By Paul Homewood
I was tipped off about this paper (sorry, forgot who!), which casts an interesting light on climate changes around the Ross Sea, in the Antarctic.
Environmental change drives demographic and evolutionary processes that determine diversity within and among species. Tracking these processes during periods of change reveals mechanisms for the establishment of populations and provides predictive data on response to potential future impacts, including those caused by anthropogenic climate change. Here we show how a highly mobile marine species responded to the gain and loss of new breeding habitat. Southern elephant seal, Mirounga leonina, remains were found along the Victoria Land Coast (VLC) in the Ross Sea, Antarctica, 2,500 km from the nearest extant breeding site on Macquarie Island (MQ). This habitat was released after retreat of the grounded ice sheet in the Ross Sea Embayment 7,500–8,000 cal YBP, and is within the range of modern foraging excursions from the MQ colony. Using ancient mtDNA and coalescent models, we tracked the population dynamics of the now extinct VLC colony and the connectivity between this and extant breeding sites. We found a clear expansion signal in the VLC population ∼8,000 YBP, followed by directional migration away from VLC and the loss of diversity at ∼1,000 YBP, when sea ice is thought to have expanded. Our data suggest that VLC seals came initially from MQ and that some returned there once the VLC habitat was lost, ∼7,000 years later. We track the founder-extinction dynamics of a population from inception to extinction in the context of Holocene climate change and present evidence that an unexpectedly diverse, differentiated breeding population was founded from a distant source population soon after habitat became available.
Put simply, it shows that the climate was much warmer 8000 years ago, before cooling maybe 1000 years ago. The paper notes:
Today the region is mostly enclosed by year round land-fast sea ice, and is therefore unsuitable for southern elephant seal breeding. Elephant seals are not found along the VLC today.
Put this together with evidence of a much colder climate in the Ross Sea during the Little Ice Age, and the fact that Antarctic glaciers began retreating again in the 19thC, and we can begin to see current climatic conditions there in a proper perspective.