Global- and regional paleoclimate reconstructions from greenhouse gas and borehole temperature of polar ice cores

Seminar by Dr. Ji-Woong Yang from Seoul National University

01 January 2019
15:00 — 16:00

According to IPCC report, the Earth’s climate has been warming rapidly since the 20thcentury, and the current warming trend is expected to continue in the upcoming decades. Therefore, the “paleoclimatologists” are searching for hints from the history of the Earth’s climate. The paleoclimate proxy archives have recorded the temporal evolution of the climate and environment in local to global scale. Using the proxy archives, the paleoclimatologists have revealed that numerous abrupt climate change events occurred in the past, providing invaluable information on analogues of the rapid warming in present days, or how the Earth’s climate would respond to the abrupt events. Among the various proxy archives, polar ice core is the unique archive that preserves the ancient atmosphere within the bubbles, allowing us to analyze directly the composition of past atmosphere. In this talk, I’ll provide a brief introduction of my researches on paleoclimate reconstruction using polar ice cores.

First topic is atmospheric methane (CH4) variability during the early Holocene. CH4is a potent greenhouse gas, whose atmospheric mixing ratio has been increased more than 2.5 times since the Industrial Revolution. Thus understanding control mechanisms of atmospheric CH4is essential to better project the future climate warming. Despite a numerous CH4time series has been reconstructed for the last millennia, a significant contribution of anthropogenic emission makes the CH4budget complicated. However, as the human activity and populations during the early Holocene were negligible compared to the late Holocene, the early Holocene CH4was dominantly controlled by natural processes. This study aims to provide insights into natural CH4control mechanisms under Holocene interglacial boundary condition. The new early Holocene CH4records exhibit four abrupt CH4drops in quasi 1000-year spacing. Each event occurred in similar timings with abrupt cooling in Greenland, southward shift of ITCZ, and reduction of Asian- and Indian monsoon intensity. Comparing with Greenland ice core CH4records, the inter-polar difference of CH4(IPD) shows a gradual increase from the onset of the Holocene to around 9500 years before 1950 AD, implying the extension of boreal CH4 source regions following deglaciation.

The ice cores itself provide plenty of insights into the Earth’s climate, but also the boreholes after drilling the ice cores allow to measure the thermal state of the glacier and/or ice sheet that preserve regional surface temperature in the past. As the satellite and AWS observations revealed that the global warming trends are not homogeneous over the Antarctica, it is important to understand the temperature controls at each area. Despite of importance in global climate system, the surface temperature in the northern Victoria Land is not well constrained due to lack of long-term observation and complex topography. So far, paleoclimate reconstructions in this region has entirely relied on water stable isotope thermometry, but the slope is not constant temporally and spatially. Therefore, an independent temperature history is necessary. The second topic is the surface temperature history at Styx Glacier, northern Victoria Land (Antarctica) inferred from borehole temperature. The colleagues and I inversed the borehole temperature data to infer the past temperature history. Resulting temperature history exhibits a warming signal between the 16th–18thcentury and the mid-20thcentury, while no recent warming is found since the mid-20thcentury. Using the annual-mean surface temperature data, the composite differences with Southern Annular Mode (SAM) index, center pressure and position of Amundsen-Bellingshausen Sea Low show a significant negative correlation with annual mean SAM index. 

In the third topic, I’ll shortly introduce my future research plan. This project aims to reconstruct the terrestrial and oceanic biological productivity using ice cores over the abrupt climate changes during the last glacial period. Together with simulations of AOGCM capable of modelling the oxygen cycles, this project will contribute to better understand of global productivity response to abrupt climate change.