Solar Forcing Recorded by Aerosol Concentrations in Coastal Antarctic Glacier Ice, McMurdo Dry Valleys

Ice-core chemistry data from Victoria Lower Glacier, Antarctica, suggest, at least for the last 50 years, a direct influence of solar activity variations on the McMurdo Dry Valleys (MDV) climate system via controls on air-mass input from two competing environments: the East Antarctic ice sheet and the Ross Sea. During periods of increased solar activity, when total solar irradiance is relatively high, the MDV climate system appears to be dominated by air masses originating from the Ross Sea, leading to higher aerosol deposition. During reduced solar activity, the Antarctic interior seems to be the dominant air-mass source, leading to lower aerosol concentration in the ice-core record. We propose that the sensitivity of the MDV to variations in solar irradiance is caused by strong albedo differences between the ice-free MDV and the ice sheet

Developing community-based scientific priorities and new drilling proposals in the southern Indian and southwestern Pacific oceans

An International Ocean Discovery Program (IODP) workshop was held at Sydney University, Australia, from 13 to 16 June 2017 and was attended by 97 scientists from 12 countries. The aim of the workshop was to investigate future drilling opportunities in the eastern Indian Ocean, southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern Ocean. The overlying regional sedimentary strata are underexplored relative to their Northern Hemisphere counterparts, and thus the role of the Southern Hemisphere in past global environmental change is poorly constrained. A total of 23 proposal ideas were discussed, with ~12 of these deemed mature enough for active proposal development or awaiting scheduled site survey cruises. Of the remaining 11 proposals, key regions were identified where fundamental hypotheses are testable by drilling, but either site surveys are required or hypotheses need further development. Refinements are anticipated based upon regional IODP drilling in 2017/2018, analysis of recently collected site survey data, and the development of site survey proposals. We hope and expect that this workshop will lead to a new phase of scientific ocean drilling in the Australasian region in the early 2020s.The organizers gratefully acknowledge generous and critically important funding for participants’ travel to the workshop. Funding came from the Australian and New Zealand IODP Consortium (ANZIC), the US Science Support Program (USSSP), the Magellan-Plus Workshop Program of the European Consortium for Ocean Research Drilling (ECORD), the Japan Drilling Earth Consortium (J-DESC), the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), IODP-India, and the home institutions of numerous scientists

Antarctic Climate Change and the Environment: A Decadal Synopsis and Recommendations for Action

Scientific evidence is abundantly clear and convincing that due to the current trajectory of human-derived emissions of CO2 and other greenhouse gases, the atmosphere and ocean will continue to warm, the ocean will continue to acidify, atmospheric and ocean circulation patterns will be altered, the cryosphere will continue to lose ice in all forms, and sea level will rise

Reassessing the post-Last Glacial Maximum retreat history from the Southwest Ross Sea

Constraining the timing of the retreat of the Last Glacial Maximum (LGM) Antarctic Ice Sheet in the Ross Sea provides insights into the processes controlling marine-based ice sheet retreat. The over-deepened Ross Sea continental shelf is an ideal configuration for marine ice-sheet instability, and this region was thought to be one of the largest Antarctic contributors to post-LGM sea level rise. However, the chronology and pattern of retreat of the LGM ice sheet in the Ross Sea is largely constrained by coastal records along the Transantarctic Mountain front in the Western Ross Sea. Although these offer more reliable dating techniques than marine sediment cores, they may be influenced by local glaciers derived from East Antarctic outlet glaciers. Consequently, these coastal records may be ambiguous in the broader context of retreat in the central regions of the Ross Sea. However, previous studies have inferred that records in this region retreated in a north to south pattern, and was fed by ice sourced from the central Ross Sea – with the implication that broader ice sheet retreat in the central Ross Sea occurred as late as the mid Holocene. We present two lines of evidence that counter this established interpretation of the pattern of retreat in the Ross Sea: 1) a sedimentary facies succession and foraminifera-based radiocarbon chronology from within the Ross Sea embayment that indicates glacial retreat and open marine conditions to the east of Ross Island was already in place before 8.6 cal ka BP, at least 1 kyr earlier than indicated by terrestrial records in McMurdo Sound; and 2) a new multibeam swath bathymetry data that identifies well-preserved glacial features indicating thick (>700m) marine-based ice derived from the East Antarctic Ice Sheet (EAIS) coastal outlet glaciers dominated the ice sheet input into the southwestern Ross Sea during the last phases of glaciation – and thus may have acted independent of any ice in the central Ross Sea embayment. Comparing these data to new modelling experiments, we hypothesize that marine-based ice sheet retreat was triggered by oceanic forcings along most of the Pacific Ocean coastline of Antarctica, but continued early Holocene retreat into the inner shelf region of the Ross Sea occurred primarily as a consequence of marine ice sheet instability. Keywords: Ross Sea, deglaciation, Last Glacial Maximum, Holocen

Antarctic Cryosphere Evolution Project (AnCEP): New IODP proposal for transect drilling in the Southern Ocean

第3回極域科学シンポジウム　横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月26日（月） 国立国語研究所 ２階講

The Eocene-Oligocene boundary climate transition: An Antarctic perspective

Antarctica underwent a complex evolution over the course of the Cenozoic, which influenced the history of the Earth’s climate system. The Eocene-Oligocene boundary is a divide of this history when the ice-free ‘greenhouse world’ transitioned to the ‘icehouse’ with the glaciation of Antarctica. Prior to this, Antarctica experienced warm climates, peaking during Early Eocene when tropical-like conditions existed at the margins of the continent where geological evidence is present. Climate signals in the geological record show that the climate then cooled, but not enough to allow the existence of significant ice until the latest Eocene. Glacial deposits from several areas around the continental margin indicate that ice was present by the earliest Oligocene. This matches the major oxygen isotope positive shift captured by marine records. On land, vegetation was able to persist, but the thermophylic plants of the Eocene were replaced by shrubby vegetation with the southern beech Nothofagus, mosses and ferns, which survived in tundra-like conditions. Coupled climate–ice sheet modelling indicates that changing levels of atmospheric CO2 controlled Antarctica’s climate and the onset of glaciation. Factors such as mountain uplift, vegetation changes, ocean gateway opening and orbital forcing all played a part in cooling the polar climate, but only when CO2 levels reached critical thresholds was Antarctica tipped into an icy glacial world

Preparation for deep sea drilling proposal in the Indian Sector of the Southern Ocean: Conrad Rise and off Enderby Land

第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月16日（水） 国立国語研究所　2階フロ