The global pact to conserve biodiversity on the high seas was finally agreed in March and formally adopted by the United Nations in June.
It is seen as a crucial tool to meet a target agreed last year to protect 30% of the earth's land and sea by 2030, known as "30 by 30".
At least 60 countries are expected to sign the agreement at the annual United Nations General Assembly on Wednesday.
Mads Christensen, interim executive director of Greenpeace International, described the signings as a "powerful signal" and help maintain momentum to meet the "30 by 30" target.
"Now politicians must bring the treaty home and ensure it is ratified in record time."
Persons:
Borja Suarez, Mads Christensen, Jessica Battle, David Stanway, Stephen Coates
Organizations:
El, Recovery, Gran Canaria, REUTERS, United Nations, United Nations General Assembly, Greenpeace International, International Union for, Worldwide Fund, Nature, Thomson
Locations:
El Burrero Beach, Gran, Spain, Singapore