Abstract
September open water fraction in the Arctic is analyzed using the satellite era record of ice concentration (1979–2017). Evidence is presented that three breakpoints (shifts in the mean) occurred in the Pacific sector, with higher amounts of open water starting in 1989, 2002, and 2007. Breakpoints in the Atlantic sector record of open water are evident in 1971 in longer records, and around 2000 and 2011. Multiple breakpoints are also evident in the Canadian and Russian halves. Statistical models that use detected breakpoints of the Pacific and Atlantic sectors, as well as models with breakpoints in the Canadian and Russian halves and the Arctic as a whole, outperform linear trend models in fitting the data. From a physical standpoint, the results support the thesis that Arctic sea ice may have critical points beyond which a return to the previous state is less likely. From an analysis standpoint, the findings imply that de-meaning the data using the breakpoint means is less likely to cause spurious signals than employing a linear detrend.
Highlights
In the most recent decade, summer minimum sea ice extent has retreated to levels not seen since the beginning of the satellite record[1]
We look at two different set of halves separately, one set bounded by ocean, the other by land: the Atlantic and Pacific halves, which cover how sea ice might exit the Arctic Ocean and may be of more interest to ice scientists, and the Canadian and Russian halves, which consider possible transit routes from the lower Atlantic to the lower Pacific or vice versa, and so may be of more interest to shipping
The data of record has been obtained from the Nimbus Scanning Multichannel Microwave Radiometer (SMMR: 1979–1987), the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I: 1987–2007) and the Special Sensor Microwave Imager/Sounder (SSMIS: 2008-present)
Summary
In the most recent decade, summer minimum sea ice extent has retreated to levels not seen since the beginning of the satellite record[1]. For the time period from 1960, sources expanded to include aerial surveys, observational re-analyses, operational ice charts, and from 1972, OSI-SAF (Ocean and Sea Ice Satellite Applications Facility) passive microwave retrievals, which is produced using SMMR, SSM/I, SSMIS, and (only in Version 1 of the data set) EMSR from 1972–1979. We show this data from 1953 for context, but our analysis focuses on the period from 1960 onwards, and the satellite era. In processing the ice chart data for this study, any grid cell with ice concentration less than 15% was set to open water to be consistent with the satellite retrievals
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