Polkinghorne, who has been with the Roar in every season in the Westfield W-League, became the first player to reach 100 appearances in Australia's elite women's club football competition.
She's enjoyed a stellar career in Brisbane since making her debut as a foundation player at the age of 19 and was a key contributor in the Roar's 2008-09 and 2010-11 Championship winning teams'.
Meanwhile, Arnold has also committed her future to Brisbane and continues to enhance her reputation as an integral member of the current squad after joining from Perth Glory last season.
The 23-year-old shot-stopper's recent performances have not gone unnoticed, with Arnold recently being named in the successful Westfield Matildas 2017 Tournament of Nations squad and for the upcoming home series against football powerhouse Brazil.
"To have Clare and Mackenzie as part of our squad for season 2017/18 is great news for our Club," Roar coach Melissa Andreatta said.
"We are excited for what lies ahead and I'm sure both players will have a positive influence on our group once again.
"They are leaders of our team and demonstrate the commitment and passion that we require for the upcoming campaign."
Both Polkinghorne and Arnold will return to Brisbane to begin pre-season training after taking on Brazil on Saturday, September 16 in Penrith and on Tuesday, September 19 in Newcastle.
This article was originally published at: http://www.brisbaneroar.com.au/article/signing-news-w-league-captain--goalkeeper-sign-on/zpd4hjq3doc81fayexw4kqzb3.