Minnesotans were subjected to more than $40 million of television and radio ads during the election that ended last week, according to a Star Tribune analysis.

The cost of the ads to blast political messages to voters will continue to rise; final reports are not yet available from campaigns, and TV stations had yet to make public all the advertising spending information from late October.

But the volume of political noise is clear from the preliminary analysis. During the final weeks, nearly every moment of prime-time television advertising time was snatched up by campaigns desperate to put their candidates over the top.

Using data from television stations, the Center for Public Integrity and the state and federal campaign finance agencies, the Star Tribune found that Democratic U.S. Sen. Al Franken was the state's top spender.

His campaign alone spent an estimated $7 million on TV ads, according to the Center for Public Integrity. No other group comes close to that amount, and his campaign made up more than half of the total ad spending in the U.S. Senate race.

Franken began his aggressive ad campaign in May of this year, well before most others were running political advertisements, and never let up. Most of Franken's ads showed the senator in a positive light, rather than putting down challenger Mike McFadden.

The strategy worked: Franken's job approval rating actually rose over the course of this year, and he won re-election with 53 percent of the vote.

Despite Franken's big spending, the U.S. Senate race was not the most expensive contest to litter the airwaves.

That distinction belongs to the U.S. House race in northern Minnesota's Eighth Congressional District.

According to Federal Election Commission records, parties, independent groups and the candidates vying for that territory spent almost $14 million on TV advertisements over the past year. That far surpasses the advertising dollars spent on previous U.S. House races in that district, and this year's numbers will grow. Democratic U.S. Rep. Rick Nolan and Republican challenger Stewart Mills have yet to file their final spending reports with the federal campaign agency.

In the end, the voters of that district narrowly decided they did not want a change in the U.S. House and re-elected Nolan for another two-year term.

Despite big spending in the western Seventh Congressional District, voters there widely backed their incumbent Democratic U.S. Rep. Collin Peterson over Republican Torrey Westrom. In recent years, Peterson's races attracted almost no advertising spending.

But this year, viewers along Minnesota's western border were barraged with more than $9 million in television ads. The vast majority of the ad cash came from just two groups — the National Republican Congressional Committee, which backed Westrom, and the Democratic Congressional Campaign Committee, which defended Peterson.

The governor's race

Compared with those federal races, which focused on just a sliver of the state's voters, Minnesota's governor's race was cheap when it came to the ad game.

To woo the state's more than 3 million voters, DFL Gov. Mark Dayton, Republican Jeff Johnson and their allies spent just under $9 million, according to data from the Minnesota Campaign Finance and Public Disclosure Board and the Center for Public Integrity.

In that contest, the biggest spenders were the Democratic-supporting Alliance for a Better Minnesota and Dayton's campaign. According to the data, the Alliance, which has backing from unions and wealthy Minnesotans, spent at least $2.7 million on the governor's race, while Dayton spent about $2 million.

Dayton was elected to his post with just over 50 percent of the vote, making him the first governor elected with a pure majority of the vote in a generation.

Rachel E. Stassen-Berger • Twitter: @RachelSB