anberry15

Thank you for these great suggestions!

Hi there,
I'm also in the Boston area. There are plenty of academic labs here that accept undergraduate volunteers, and as a candidate with a degree already in hand, I'm sure you would be very desirable. I am unfamiliar with oceanography departments around here, but try looking at the websites of Tufts, Harvard, MIT, Suffolk (pretty small department, probably does not encompass your research interests), UMass Boston, Northeastern, BU, Brandeis, and Boston College to name a few. Just look on the biology department faculty pages.
In contacting professors that suit your particular interests, I would suggest attaching a CV and resume. Write a bit about yourself, your research interests, future goals, and why their lab sticks out to you. Try to be concise, and ask them if they would like to speak with you further as a potential volunteer. You will probably have to email a few at a time, because I remember applying to biochemistry labs as a wee undergrad and only getting 3/7 responses (in which only 2 said they were willing to accept new students). If you don't get any responses, feel free to politely prod them again in a week or so, because it's easy for the first message to accidentally slip through the cracks.

So one thing I think you could easily do is try to find a volunteer research position or other entry level research positions (field technician and other temporary or seasonal positions). These are often advertised on places such as Texas A&M job board (see link below) - which is not only for jobs based out of Texas or that university, usually the ads are on the national or international level. If you do some searching you might be able to find some other list services that could list positions you might be able to apply to.
https://wfscjobs.tamu.edu/job-board/
Another thing you could do is try looking at universities in your area (which if you are in Boston area there should be plenty) and try to find a lab/professor who is doing stuff that you would like to have experience in. Then you could reach out by email to that professor and ask if there are any volunteer positions available in their lab or upcoming. If they have grad students in their lab needing field hands they may very well take you up on that and get you some opportunities volunteering. I had a volunteer in my lab during my Master's that did exactly what I suggest you do and helped volunteer with several different things in the lab.
The only thing in any case you will need to do is be up front that you do have a job and let them know how much that limits your availability/what flexibility that job allows you. This is especially true for positions that are advertised since I believe a lot of those do require you to have quite a bit of availability.

Seasonal field assistant/technician jobs are great for post-bac experience. The paid positions are easier to get if you have some relevant experience, but if you apply for a bunch and/or know someone connected to one then you can still get one. There are also volunteer/internship positions that usually expect less experience, if you can afford that.
I worked a couple in the year between undergrad and grad school. I gained a bunch of skills so that I could hit the ground running with my grad school research. 
The TAMU job board is a nice resource for finding these positions: http://wfscjobs.tamu.edu/job-board/