I like this data:

https://gcmd.nasa.gov/KeywordSearch/Metadata.do?Portal=amd&K...

And from there:

https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/...

And a Wiki article discussing it:

https://en.wikipedia.org/wiki/File_talk:Vostok_Petit_data.sv...

Where this chart is interesting:

https://en.wikipedia.org/wiki/File_talk:Vostok_Petit_data.sv...