{"id":3534,"date":"2017-09-18T13:09:26","date_gmt":"2017-09-18T13:09:26","guid":{"rendered":"http:\/\/blog.ldeo.columbia.edu\/snowonice\/?page_id=3534"},"modified":"2018-09-28T01:21:49","modified_gmt":"2018-09-28T01:21:49","slug":"locked-in-the-lake","status":"publish","type":"page","link":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/greenlands-holocene-ice-extent\/locked-in-the-lake\/","title":{"rendered":"Locked in the Lake"},"content":{"rendered":"
\"\"<\/a>
Pro-glacial lakes along the edge of the ice sheet.<\/figcaption><\/figure>\n

The stability of the Greenland Ice Sheet through warm interglacial periods has long been under debate. Scientists turn to a number of different indicators including ice from the base of ice cores, sediment samples from Greenland southwestern lakes,\u00a010<\/sup>Be exposure dates from glacial erratics, and more recently 10<\/sup>Be\u00a0<\/sup>dates from rock under the base of the ice sheet to establish ice sheet extent and thickness through time. During our current interglacial, the Holocene, the biggest challenge has been determining the ice extent during the warm Thermal Maximum (~7,400 years ago), a time period that is high priority as the most recent analog to future warming and yet the evidence has\u00a0been overprinted by an expanded ice sheet.<\/p>\n

<\/div>\n

The Snow on Ice<\/strong><\/em> project is using\u00a0continuous sediment sequences collected from the bottom of pro-glacial lakes, created by\u00a0ice sheet meltwater \u00a0and lying along the ice\u00a0perimeter, and matched with new bed machine<\/a> sub-elevation maps created from radar data, to hone in on the ice sheet margin during the Thermal Maximum.<\/p>\n

\"\"
Tubes of sediments cores from Greenland’s pro-glacial lakes are halved and refrigerated for further processing at University at Buffalo<\/a>.<\/figcaption><\/figure>\n

Locked inside the lake sediment is a history of how much\u00a0time the lake spent under ice cover versus\u00a0ice-free. The\u00a0\u00a0lakes selected for coring\u00a0have drainage basins that extend beneath the current ice sheet edge and are fed by the ice sheet meltwater (see top\u00a0image). When the ice sheet covers\u00a0the lake it \u00a0collects mineral-rich glacial sediments from the movement of the ice over the rock. When the ice sheet retreats out of the lake basin the sediment \u00a0transitions to organic-rich mud or gyttja.\u00a0Collecting sediment cores and radiocarbon dating sections of\u00a0 the core where clear shifts in sediment lithology are evident is critical in\u00a0providing a time series of ice\u00a0cover for the area.<\/p>\n

\"\"
The bottom of the pro-glacial lakes are mapped for depth to determine the best place for coring.<\/figcaption><\/figure>\n

A\u00a0careful bathymetric survey of the bottom of each selected lake is the\u00a0preliminary step in sediment coring. If the area has too much accumulation the core will not be able to span the length of time needed for the Holocene. An area with too\u00a0\u00a0little accumulation will not provide the detailed history needed for the glacial expansion and retreat. A map is created to provide a blueprint for working\u00a0in the lake.<\/p>\n

Sediment cores are assessed in the field, and visually described, but the bulk of the analysis will occur back in the lab. Cores will be split, analyzed, and dated. The results\u00a0are matched with sub-ice elevation maps created from radar data that provide the distance the lake drainage basins extend under the existing ice cover. It is the combination of the drainage basin maps and\u00a0the lake sediment dates that provide\u00a0a powerful tool for locating the ice sheet margin during the last Thermal Maximum.<\/p>\n

Read about subglacial mapping, another method used to determine Greenland’s Mid-Holocene ice extent<\/a><\/p>\n

Read about exposure dating, another method used to determine Greenland’s Mid-Holocene ice extent<\/a><\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

The stability of the Greenland Ice Sheet through warm interglacial periods has long been under…<\/p>\n","protected":false},"author":37,"featured_media":0,"parent":3526,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"__cvm_playback_settings":[],"__cvm_video_id":""},"_links":{"self":[{"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/pages\/3534"}],"collection":[{"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/users\/37"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/comments?post=3534"}],"version-history":[{"count":28,"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/pages\/3534\/revisions"}],"predecessor-version":[{"id":4191,"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/pages\/3534\/revisions\/4191"}],"up":[{"embeddable":true,"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/pages\/3526"}],"wp:attachment":[{"href":"https:\/\/blog.ldeo.columbia.edu\/snowonice\/wp-json\/wp\/v2\/media?parent=3534"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}