Arctic Ice Least for 3000 years

Arctic ice at multi-millennium low: researchers

June 3, 2010
Courtesy of Ohio State University
and World Science staff

Less ice co­vers the Arc­tic to­day than at any time in the past few thou­sand years. So says an in­terna­t­ional group of re­search­ers that has com­piled what they call the first com­pre­hen­sive his­to­ry of Arc­tic ice.

For dec­ades, sci­en­tists have strived to col­lect sed­i­ments from the difficult-to-access Arc­tic Ocean floor, to find out what the Arc­tic was like in the past. Their most re­cent goal: to br­ing a long-term per­spec­tive to the ice loss we see to­day.

Arc­tic sea ice ex­tent in Au­gust 2009 – the ar­ea of the Arc­tic Ocean cov­ered by float­ing ice – as meas­ured by NA­SA satel­lites. It was the third low­est ex­tent since sat­el­lite mea­sure­ments were first made in 1979. (Cour­te­sy NA­SA)
Now, in an up­com­ing is­sue of the jour­nal Quar­ternary Sci­ence Re­views, a team led by Ohio State Uni­vers­ity has re-ex­am­ined the da­ta from nearly 300 past and on­go­ing stud­ies and com­bined them to form a big-pic­ture view of the pole's cli­mate his­to­ry.

"The ice loss that we see to­day—the ice loss that started in the early 20th Cen­tu­ry and sped up dur­ing the last 30 years—ap­pears to be un­matched over at least the last few thou­sand years," said Le­o­nid Polyak, a re­search sci­ent­ist at Byrd Po­lar Re­search Cen­ter at Ohio State Uni­vers­ity. Polyak is lead au­thor of the pa­per and a pre­ced­ing re­port that he and his coau­thors pre­pared for the U.S. Cli­mate Change Sci­ence Pro­gram.

Satel­lites can pro­vide de­tailed meas­ures of how much ice is co­vering the pole right now, but sed­i­ment co­res are like fos­sils of the ocean's his­to­ry, he ex­plained. A sed­i­ment co­re is a pole-shaped sam­ple of sed­i­ments ob­tained by push­ing a hol­low tube in­to the sed­i­ment and then pulling it out. This al­lows sci­en­tists to ex­am­ine many lay­ers of sed­i­ment cor­re­spond­ing to dif­fer­ent time pe­ri­ods.

"Sed­i­ment co­res are es­sen­tially a rec­ord of sed­i­ments that set­tled at the sea floor, lay­er by lay­er, and they rec­ord the con­di­tions of the ocean sys­tem dur­ing the time they set­tled," said Polyak. "When we look care­fully at var­i­ous chem­i­cal and bi­o­log­i­cal com­po­nents of the sed­i­ment, and how the sed­i­ment is dis­tribut­ed—then, with cer­tain skills and luck, we can re­con­struct the con­di­tions at the time the sed­i­ment was de­posit­ed."

For ex­am­ple, sci­en­tists can search for a bio­chem­i­cal mark­er that is tied to cer­tain spe­cies of al­gae that live only in ice. If that mark­er is in the sed­i­ment, then that loca­t­ion was likely co­vered in ice at the time. Sci­en­tists call such mark­ers "prox­ies" for the thing they ac­tu­ally want to mea­sure—in this case, the ge­o­graph­ic ex­tent of the ice in the past.

While know­ing the loss of sur­face ar­ea of the ice is im­por­tant, Polyak said that this work can't yet re­veal an even more im­por­tant fact: how the to­tal vol­ume of ice—thick­ness as well as sur­face ar­e­a—has changed over time. "Un­derneath the sur­face, the ice can be thick or thin. The new­est sat­el­lite tech­niques and field ob­serva­t­ions al­low us to see that the vol­ume of ice is shrink­ing much faster than its ar­ea to­day. The pic­ture is very trou­bling. We are los­ing ice very fast," he said.

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