Residents the Boothbay area have undoubtedly been to the ocean and noticed the color of the water.

In shallow areas, it can appear clear, but as one wades out into the deep, opacity increases and it appears blue, green, gray or a mixture of those colors.

As John Cullen, a professor at Dalhousie University, explained Wednesday night at the Boothbay Harbor Opera House, it is the volume of phytoplankton in the water that causes oceans to appear the colors they are, and it was only in the last 40 years that scientists began to truly understand that relationship.

Cullen, the penultimate speaker for this year's series of Bigelow Laboratory-sponsored Café Scientifique talks at the Opera House, began his presentation, "Light, life, and the oceans: Charles S. Yentsch and the transformation of ocean science over 40+ years," by describing his own journey through the field of oceanography.

He moved from research cruises in Monterey Bay in the 1970s to working at the Scripps Institute of Oceanography in the latter part of that decade. From there, in the 1980s, he transferred to the Bedford Institute of Oceanography, and by 1982, he was on to Port Aransas, Texas.

He eventually made his way to Dalhousie, and along his travels through various institutions, organizations and states, he studied the impact of phytoplankton, the emerging fields of bio-optical oceanography and various other technologies that made it possible to study the ocean from within its depths and from the emptiness of space.

He downplayed his own contribution to the field, however, in favor of describing the giants' shoulders he has stood on all these years. Scientists such as Father Pietro Angelo Secchi, who invented the Secchi Disk, a device that measures ocean transparency, and Gordon Riley, who performed studies on phytoplankton with relatively crude methods that involved the manual collection of large vials of water.

"The foundations were developed through precious few data points," Cullen said. "(Riley) made fantastic descriptions to make observations that had almost no resolution."

Cullen's work was the equivalent of a man traversing the ocean in a single boat who is attempting to determine marine life and oceanic patterns through the contents of a handful of water bottles. His work may have been tireless — and to Cullen it appeared precious — but was but a blip on the screen of work that was to come.

A chemist named J.Y. Buchanan, Cullen said, related ocean color to the abundance of phytoplankton in the late 1800s, but his observations went unnoticed by others. The observations came before their time, and it was not until a scientist named Charles Yentsch arrived on the scene that modern oceanographic techniques would begin to take shape.

"Charlie made the connection at the right time," Cullen said.

Yentsch was the man who forwarded the idea that phytoplankton levels were directly related to the color of the ocean. He worked with NASA to explain the connection and develop techniques that would allow satellites to survey phytoplankton levels from Earth orbit.

Phytoplankton absorbs light for photosynthesis, so hyperspectral satellite imaging can detect phytoplankton levels on a global scale by analyzing the resulting ocean color. This breakthrough allowed scientists to move from an extremely small number of data points to countless data points. But it did not end there.

Technology has also improved in such a way, Cullen pointed out, that torpedo-shaped drones can autonomously scour beneath the ocean for signs of life. Scientists can also use advanced methods of ocean analysis such as flow cytometry, which uses lasers to count and sort chemical characteristics of the water at thousands of particles per second, to quickly analyze oceanic contents.

Cullen said Yentsch's vision made possible what is happening throughout oceanographic research today. Yentsch observed the relationship between phytoplankton and ocean color at the right time, and he was bold enough to help spread the idea throughout the world. Now, automated, underwater observations can work in tandem with satellite imagery to present a complete picture of both ocean color and all other ocean characteristics.

Cullen indicated that the observations scientists are making can impact many other related fields such as physics and geology. It helps describe phenomena such as global warming and shows an abundance of life that, for many years, humans did not know about nor could possibly understand its relationship with the ocean as a whole.

To close, Cullen quoted Yentsch who commented about the future of the study of oceanography: "In this time in history, we are lucky to have the support of government agencies (and other financial backers) ... otherwise we would all be priests or out of work."

He said the future of oceanography depends on the vision of scientists such as Yentsch. Without his help, science would have not have progressed to where it is today, and without the vision of scientists now working in the field, oceanography will not be able to progress into the territory of tomorrow.