The Bølling Warming period was the last deglaciation period and occurred about 14,650 years ago. During this time, global sea levels rose about 20 meters in less than 500 years. The source of this meltwater pulse (MWP-1A) and its temporal and causal relationship to the abrupt climate changes of this period remain unclear, but Deschamps et al. (2012) were able to further our understanding of this event. Using coral samples taken from the reefs in Tahiti, the scientists identified a probable total sea level rise between 14 and 18 meters during this time period and an annual sea level rise of 40 millimeters per year. Further, contrary to previous studies, this study concluded that the Antarctic Ice Sheet contributed significantly to global sea level rise during this period. Ultimately, understanding the dynamics of this warming period help scientists understand current warming patterns, as ice sheets today contribute significantly to the global sea level rise and could therefore influence future warming patterns.¾Olivia Jacobs
Deschamps, P., Durand, N., Edouard B., Hamelin, B., Camoin, G., Thomas, A.,
Henderson, G., Okuno, J., Yokoyama, Y. Ice-sheet collapse and sea-level rise at
the Bølling warming 14,600 years ago. Nature 483. 559–564. [GSSS Deschamps
Deschamps et al.(2012) collected coral samples from three distinct areas in reefs near Tahiti during the Integrated Ocean Drilling Program (IODP) Expedition 310. Using U-Th dating and knowledge of the ranges of modern reef environments the scientists were able to map previous sea levels and calculate the change in sea level over the past 16 kyr.
The oldest samples in this study were shallow water coralgal assemblages (± 0.03 kry BP and 16.09 ± 0.04 kry BP. These samples were therefore from before the onset of the Bølling Warming period, and they indicate a Relative Sea Level (RSL) of 117–107 meters below present sea level (m.b.s.l.). The IODP data also revealed a major discontinuity in the Tahiti RSL between 14.28 ±0.02 kry BP and 14.31 ± 0.04 kry BP, thus indicating the start of MWP-1A.
From these and similar data Dechamps et al. inferred a conservative estimate for post-MWP-1A of 88–83 m.b.s.l., which indicates a sea level rise of 14–18 meters during this warming period. The longest possible duration of this sea level jump is about 350 years, which equates to an average sea level rise of about 46 ± 6 mm yr–1 in Tahiti. However, because of uncertainties in the data, the duration of this rise could have been much shorter, and so this estimate is considered a minimum value.
Scientists originally believed that the sea level rise during MWP-1A was caused by partial melting of the Northern Hemisphere ice sheets (NHIS). This would have occurred if a large amount of fresh water were deposited into the North Atlantic, thereby slowing the Atlantic meridional overturning circulation (AMOC) and abruptly ending the Bølling warming period about 14.1 kyr ago. This scenario agrees with previous data in Barbados, which indicate a much later onset of the warming period. However, this study, and other data from reefs in Hawaii and elsewhere, indicate that the Bølling period happened about 500 years earlier than previously believed and it is therefore more likely that the sea level rise coincides with the inception of the Bølling period. Further, the Antarctic Ice Sheet (AIS) probably contributed significantly to the MWP-1A. While uncertainties in the data make it difficult to estimate the relative contribution of the AIS and NHIS to the total SLR, it is probable that the AIS contributed at least half of the eustatic sea level rise during this time period.
These new findings necessitate further investigation, as the initial trigger of the Bølling period is still unknown. However, one of two scenarios is plausible. In the first scenario, the rapid melting of the AIS triggered the intensification of the AMOC, which would have started the Bølling warming in the Northern Hemisphere and melted northern ice sheets. In the second scenario, the AMOC increased first and caused the warming, which led to the melting of the NHIS and subsequently collapsed the AIS. These two scenarios are not mutually exclusive either, as they could have acted together and reinforced one another.
While much is still unknown, the data in this study indicate that the Bølling period occurred much earlier than previously believed, and the AIS contributed greatly to this period of rapid sea level rise. Understanding more about this event may shed light on the dynamics of the current warming period, as ice sheets today contribute greatly to current sea level rise.