Genetic analyses of an Antarctic octopus have revealed a startling revelation about the collapse of the West Antarctic Ice Sheet (WAIS) during the Last Interglacial period, approximately 129,000 to 116,000 years ago. This collapse occurred when temperatures were merely about 1 degree Celsius warmer than preindustrial levels. These findings underscore the potential impact of even minimal temperature increases, as projected by the most optimistic climate change mitigation plans, in precipitating the WAIS collapse and subsequent sea-level rise.
Climate change is instigating unprecedented transformations in Earth’s cryosphere, with the West Antarctic Ice Sheet being especially susceptible to rising temperatures. Forecasts suggest it could face irreversible collapse under future climate change trajectories. The critical threshold for the ice sheet may lie within the current global climate targets of 1.5 to 2 degrees Celsius. A total WAIS collapse could have profound global consequences, potentially elevating the average global sea level by an estimated 3 to 5 meters.
Understanding the WAIS’s response to warming climates in the past, such as during the Last Interglacial period when global sea levels were 5 to 10 meters higher and temperatures were around 0.5 to 1.5 degrees Celsius warmer than preindustrial levels, holds the key to determining its fate amid our rapidly warming future. However, uncertainties remain regarding the WAIS’s historical susceptibility to rapid change, with conflicting and inconclusive outcomes from current oceanographic and modeling studies.
In a groundbreaking approach, Sally Lau and colleagues utilized an unexpected dataset – the genetic history of Turquet’s octopus (Pareledone turqueti) – to shed light on this issue. These benthic octopuses inhabit the Weddell, Amundsen, and Ross Seas, with modern populations geographically isolated and divided by the WAIS. Lau et al. sequenced genome-wide single nucleotide polymorphisms in 96 octopuses collected across the Southern Ocean. While the populations displayed genetic distinctiveness, the authors uncovered signs of admixture, indicating historical gene flow between the Ross Sea and the Weddell Sea. Additionally, demographic modeling suggested this mixing occurred during the Last Interglacial.
Lau et al. propose that these enduring signals of gene flow imply the existence of an interior open waterway connecting the Ross Sea and the Weddell Sea during the Last Interglacial, where the current WAIS now sits grounded below sea level. This suggests a complete collapse of the WAIS during that period. Andrea Dutton and Rob DeConto, in a related Perspective, acknowledge the intriguing implications of this analysis and ponder whether this historical scenario could repeat itself given Earth’s current temperature trajectory.