Satellite records go back to 1979 [https://www.theguardian.com/world/2020/oct/22/alarm-as-arcti...], but there appear to be ground based observations from earlier years that corroborate the abnormality of the current year.

Interesting, the wiki page notes:

> The sea has a severe climate with temperatures below 0 °C (32 °F) over more than nine months per year, low water salinity

Given the low salinity and below 0 °C for so long, you would expect it to be frozen most of the time.

I was curious too, came across this graphic showing records since they began in 1979 (original source NOAA) https://mobile.twitter.com/ZLabe/status/1318913839568662529/...

This article refers to a 1981-2010 Median:

http://nsidc.org/arcticseaicenews/2020/07/laptev-sea-lapping...

Edit: Another graph goes back to 1979.

The first record in the graph used by the hn-linked article is from 1978.

If I'm not wrong this should be the point from which frequent reliable measurements had been taken. (It also roughly matches with my memory about that topic).

NSIDC records began in 1979 for the arctic sea ice. Earlier records have to be intuited from proxy sources, such as anecdotal accounts or early photos.