Ecosystems Projects » Seward Line

Seward Line

Location of the Data

Data from the Seward Line (now part of the Northern Gulf of Alaska Long-Term Ecological Research project) can be found on the AOOS Ocean Data Explorer.

The Need

The Seward Line is a sustained ship transect and time series that is now part of the northern Gulf of Alaska Long Term Ecological Research (NGA LTER). The northern Gulf of Alaska is a highly productive biological community, with the lower levels of the food chain (phytoplankton and zooplankton) supporting Alaska’s iconic fish, crabs, seabirds, and marine mammals. Large increases in phytoplankton during the spring and sustained production during the summer support zooplankton that transfer energy up the food chain. Substantial amounts of this organic matter also sink to feed animals on the sea bottom.

The purpose of the Seward Line, and the NGA LTER research, is to develop an understanding of the response of this marine ecosystem to climate variability. Sampling along the Seward Line is obtaining a multi-year dataset that will lead to a better understanding of the seasonal cycle and the interannual variability in the physical-chemical structures and biological productivity of the Gulf of Alaska shelf.

Multi-disciplinary monitoring of the Gulf of Alaska ecosystem has occurred every May and again in late summer (August or September) since 1998. Fisheries managers and research scientists can make informed assessments of Alaska marine ecosystem health and status because of these measurements. Preserving core physical, nutrient, chemistry, phytoplankton and zooplankton data at these stations is a high priority for NGA LTER scientists.

The North Pacific Research Board (NPRB), the Alaska Ocean Observing System (AOOS), and the Exxon Valdez Oil Spill Trustee Council (EVOS) via the GulfWatch Alaska program all provide additional funding that make this time series possible.

Map of the sampling stations that are part of the Northern Gulf of Alaska Long-term Ecological Research program, which includes the Seward Line.


Project Location

The Seward Line is a series of stations along a 150 nautical mile long transect, starting with the GAK1 location near the entrance of Resurrection Bay on the eastern side of the Kenai Peninsula in southcentral Alaska. This transect stretches from GAK1 into oceanic waters well past the continental shelf break. Data from this transect have been critical in defining the oceanic current systems that characterize the system.

The Seward Line complements the other NGA LTER transects: the Kodiak Island Line, Middleton Island Line, and Cape Suckling Line. Additional sampling locations are located in western Prince William Sound. 

Project Details

UAF oceanography professor Dr. Thomas C. Royer established the Seward Line and GAK1 in December, 1970. Dr. Royer continued sampling over the years, and starting in fall 1997, sampling in the NGA area expanded to include chemistry and biology during 6-7 cruises per year as part of the U.S. Global Ocean Ecosystem Dynamics (GLOBEC) program. This sampling was continued from 2005-2009 by the North Pacific Research Board with reduction to two cruises annually. This program is now funded by a consortium of NPRB, AOOS,  EVOS and most recently NSF.

The Seward Line cruises on the Gulf of Alaska shelf determine the physical and chemical oceanographic structure, the primary production and the distribution and abundance of zooplankton. The seasonal and inter-annual variations in these measurements are examined, and the results distributed to the NOAA Fisheries for inclusion in Gulf of Alaska Ecosystem Status Reports. At present, cruises are conducted each spring (May), early summer (June/July) and late summer (mid September).

Project Highlights

2021 Research Highlight  Massive algae bloom in the Gulf of Alaska could be good for marine life, researchers say. Read more here.

2020 Field Season Complete  Despite challenges and restrictions due to COVID-19, the NGA LTER was able to complete their 2020 field operations. These operations included four planned research cruises, and redeployment of several moorings.

To enable this, we shortened cruise lengths, reduced the number of participating scientist, and transferred on cruise to a different vessel. In the end, the NGA team pulled off the core Gulf of Alaska sampling and so maintained the long-term time series datasets. Read more here.

Successful Seward Line Cruise Completed! – Despite only having three scientists aboard and working around 2 gales, the Spring 2020 cruise succeeded! That means all the cruise objectives were met during the May 4 – 10, 2020 cruise, thanks to the efforts of the entire team, including marine technicians and the whole crew of the R/V SikuliaqRead the Post-Cruise Update here

Alaska Public Media, May 2020  With the impact of COVID-19 on research during the summer of 2020, the Seward Line cruise shows how science can adapt during the time of COVID-19. Before the cruise departed, Alaska Public Media’s Casey Grove spoke to LTER Lead PI Russ Hopcroft. Dr Hopcroft explained why sampling this spring was necessary to understand measurements that might be more easily made later in the year, and how springtime measurements enable connections to be made between years. LISTEN: Pared down Sikuliaq sailing in Gulf of Alaska maintains research streak


There have been over 150 peer-reviewed publications since 1975 that have used data from the Seward Line and GAK1. Publications for this project can be found on the Northern Gulf of Alaska Long Term Ecological Research website.

Principal Investigators

Many more personnel are involved in the NGA LTER research, including the Seward Line. Find more information here.

Russell Hopcroft

Department of Oceanography, UAF