Deglaciation Timing of Millennial-Scale Climate Change in Antarctica and Greenland During the Last Glacial Period Thomas Blunier and Edward Brook, 2001 Interhemispheric Atlantic Seesaw Response During the Last Deglaciation Stephen Barker et al, 2009 Jesse Senzer

Pleistocene Epoch 2.8 mya to 10,000 ya

Dansgaard-Oeschger Events Dansgaard-Oeschger (D-O) events were first reported in Greenland ice cores by scientists Willi Dansgaard and Hans Oeschger. Each of the 25 observed D-O events consist of an abrupt warming to near- interglacial conditions that occurred in a matter of decades, and was followed by a gradual cooling. NOAA National Climatic Data Center

Blunier’s Hypothesis Millennial-scale temperature variability is characterized by abrupt changes in Greenland, and more gradual fluctuations in Antarctica. This offset pattern is thought to be a direct result of oceanic thermohaline circulation patterns, and results in the “bipolar seesaw” phenomenon. Schuttenhelm, 2011

Atlantic Meridional Overturning Circulation (AMOC) “The Great Ocean Conveyor” Saundry, 2012

Blunier’s Evidence Contrasted the timing of climate events using isotopic data in the Greenland Ice Sheet Project 2 (GRISP2) ice core from Summit, Greenland with the Byrd ice core from Byrd Station, Antarctica. Used atmospheric methane from GRIP in Greenland and Byrd and Vostok in Antarctica as a correlation. National Science Foundation Lowell, 2011

(A) Isotope data from GISP2, Greenland(B) Isotope data from Byrd Station, Antarctica (C) Methane data from GISP2 and GRIP(D) Methane data from Byrd Station

Blunier’s Take Home Message Understanding climate dynamics and forcing is an evolving science. The bipolar seesaw has been a persistent feature of glacial climate. As seen in the Richard Kerr article, North Atlantic deep water and the AMOC are part of a continuous, interrelated system that is not fully understood. Saundry, 2011

Heinrich Stadials HS1-6 Related to some of the coldest intervals between D-O events were six distinctive periods, named after paleoclimatologist Hartmut Heinrich. They represent an increase in icebergs discharged from the Laurentide ice sheet in North America and a southward extension of cold, polar waters. NOAA National Climatic Data Center

Younger Dryas (YD) The Younger Dryas occurred during the transition from the last glacial period into the present interglacial (the Holocene). About 14,500 years ago, the Earth's climate began to shift from a cold glacial world to a warmer interglacial state. Partway through this transition, temperatures in the Northern Hemisphere suddenly returned to near-glacial conditions. This near-glacial period is called the Younger Dryas, named after a flower (Dryas octopetala) that grows in cold conditions and became common in Europe during this time. NOAA National Climatic Data Center

Barker et al’s Hypothesis The bipolar seesaw is a key component not only for millennial-scale climate variability, but also for changes on glacial- interglacial timescales. 1) GISP2 2)Marine core 3)Marine core 4)Marine core 5)Marine core TNO57-21 (this study) 6)Antarctic ice core

Matt’s time to shine

Key Fig 2. Concepts Polar species decline mirrors Antarctic temperature increase and N. Atlantic SST decrease. Direct link between abrupt changes at high northern latitudes and similarly abrupt variations in the geometry of the ACC. Mg/Ca ratios in planktonic forams show warming generally occurs during intervals of reduced polar species.

Key Fig 3. Concepts Surface ocean productivity associated with warmer SST found by analyzing abundance of benthic forams. Intensification of the ACC during HS1 might have promoted the release of carbon dioxide by increasing the rate of vertical mixing within the Southern Ocean.

Barker et al’s Take Home Message Increasing our understanding of the physical links between north and south at millennial timescales is critical for understanding the potential role of such variability as a feedback on global climate change.

Questions

Works Cited Barker, S. et al, 2009, Interhemispheric Atlantic Seesaw Response During the Last Deglaciation, Nature, v. 457, p Blunier, T. and Brook, E.J., 2001, Timing of Millennial-Scale Climate Change in Antarctica and Greenland During the Last Glacial Period, Science, v. 291, p Heinrich and Dansgaard-Oeschger Events, NOAA National Climatic Data Center, (October 15, 2012) Lowell, T., 2011, Chasing Greenland’s Melting Ice in Search of Climate Clues, Northwestern University, (October 14, 2012) National Science Foundation, US Antarctic Program, , (October 14, 2012) Raymo, M. and Huybers, P., 2008, Unlocking the Mysteries of the Ice Ages, Nature, v. 451, p Saundry, P., 2012, Atlantic Meridional Overturning Circulation, The Encyclopedia of Earth, (October 16, 2012) Schuttenhelm, R., 2011, New Evidence for Bipolar Seesaw Link Between Greenland and Antarctica- and Abrupt Climate Variability, Bits of Science, antarctica-climate-variability-3124/ (October 14, 2012)