SEATTLE – After nearly a month at sea aboard a 274-foot-long research vessel studying how iron affects microscopic marine plant life, Bill Caddigan was ecstatic Thursday afternoon.

“It’s been an awesome ride,” said the SAD 44 Telstar Middle School science teacher from Bethel, the first teacher from Maine to participate in a full oceanographic research cruise through the University of Maine’s School of Marine Sciences in Orono.

“The trip has been a hands-on job shadowing experience in oceanography,” Caddigan said via e-mail Thursday from aboard the Thomas G. Thompson, a U.S. Navy ship operated by the University of Washington.

On Friday, he was back in Seattle at the University of Washington where the cruise began on May 12, and expects to return to Telstar on Tuesday, June 14.

Caddigan was selected from several applicants in late March by UM oceanography professor Mark Wells, who initiated the search for a teacher to join the research cruise.

“It is important to me that students become more aware of current science, in general, and oceanography in particular,” Wells said via e-mail from aboard the ship about 1,000 miles offshore of Vancouver, B.C. and about 775 miles south of Anchorage, Alaska.

“Having a teacher participate in our work provides students a direct window to these activities and, hopefully, will provide them (with) a better understanding of our world. (Caddigan) provided the best overview of how he intended to use the opportunity for enhancing the experiences of his students,” Wells said of why he chose Caddigan.

Throughout the trip, Caddigan posted daily logs, photographs and links to scientific information pertinent to the research being conducted on his Teacher At Sea Web site, http://teacheratsea.mainelearns.org/.

“I responded via e-mail to hundreds of questions from Maine students who asked sound scientific questions,” said Caddigan, who had 85 students in his seventh-grade class this year.

The purpose of the trip, Wells said, was to explore how small variations in iron and copper affect the growth of larger phytoplankton.

“Ocean life will not affect how cold or warm it will be next winter, but it might have measurable impacts over decades and centuries. It is the plankton that will cause this impact. Growth and death of the larger phytoplankton results in carbon removal from surface waters, and thus, draw down of atmospheric carbon dioxide,” Wells said.

“It is this increase in mainly carbon dioxide that is causing warming of the planet, that, in turn, is affecting the distribution of heat (energy) and, ultimately, our weather,” Wells said.

Oceanographic research, he added, is like assembling a complicated puzzle with many pieces, but no final picture to help in the assembly.

Caddigan said he gained a better understanding of oceanography from the physical aspects of deploying a water sampling device and filtering sea water samples, to the scientific reasoning behind why scientists monitor the condition of oceans.

He also celebrated his 50 birthday on Tuesday, watching hundreds of Dall porpoises surf in the ship’s wake.

“It was an incredible sight. (I) never dreamed of being 50, let alone celebrating it in the north Pacific Ocean, surfing with porpoise” and a purpose, he added.