How can I extract multipart tar files from the command-line on macOS?

I have multiple 2 GiB gzipped-tar files (.tgz) I downloaded from an online service with Safari. It's a Google Takeout of my entire photos library. As each file downloaded, Safari automatically decompressed them so in the end I had 21 tar files in my Downloads folder. How can I extract the contents of these multiple tar files?