DOVER — Gov. Jack Markell signed a bill Thursday decriminalizing small amounts of marijuana. The signing came less than an hour after the Senate passed the bill 12-9, on party lines.

Once House Bill 39 goes into effect in six months, anyone arrested for possessing an ounce or less or cannabis would face only a civil penalty of $100 rather than criminal charges.

An individual who carries more than one ounce or uses marijuana in public would still face criminal charges, as would anyone under 21 found to be possessing cannabis.

After meeting with legal counsel and the bill’s chief sponsors, Gov. Markell, a Democrat, signed the proposal into law behind closed doors.

“The governor remains committed to reducing the number of people entering the criminal justice system and refocusing resources where they are needed most and House Bill 39 supports these efforts,” a spokeswoman for the governor said Thursday night.

After initially not taking a public stance on the issue, Gov. Markell announced his support for the bill in March.

Fourteen states have decriminalized cannabis, and four others have passed laws legalizing it.

Like the House earlier this month, the Senate vote fell along party lines.

Supporters have said punishments for marijuana possession are disproportionate to the act itself. They’ve also argued penalties are unfairly applied along racial lines and can severely impact a person’s job or college prospects.

“Many young people are hindered with getting financial aid, for example, to go to college because they might have smoked marijuana,” Sen. Margaret Rose Henry, D-Wilmington, said.

But opponents see the bill as something that could lead to more minors using drugs and to more drug dealers in Delaware.

“This is not, ‘I’m having a beer,’ because that has a spectrum,” Sen. Colin Bonini, R-Dover, said. “And comparing this to alcohol is, in my opinion, I don’t think that’s a fair comparison. I have one alcoholic beverage, I am not impaired.”

Echoing statements made by a representative of the Police Chiefs’ Council the day before, Sen. Brian Pettyjohn, R-Georgetown, said he believes one ounce is too large an amount.

Acknowledging on the floor he expected the legislation to pass, Sen. Bonini said he felt the vote was one the state is “going to really, really regret.”

After just 10 minutes of discussion in the chamber, lawmakers took a vote, passing the bill.

Despite protestations from Republicans, the bill does not legalize cannabis. Rep. Helene Keeley, D- Wilmington, has insisted it is not intended as a step toward that and a representative from the Marijuana Policy Project said he was not thinking about legalization.

“We think it’s a good policy change for the state of Delaware,” said Robert Capecchi, deputy director of state policies for the Marijuana Policy Project. “Absolutely thrilled that the governor saw fit to sign it right away so that this policy change happens as soon as possible.

“It’ll be good for Delaware law enforcement to be able to stop making arrests and taking people to booking and wasting all that time for simply possessing something that’s safer than alcohol. We still need penalties. No one should go think this is a depenalization measure, so there’s still a penalty for possessing and using marijuana, but at least Delaware will no longer be saddling people with criminal records for doing that.”