The eastern North Pacific Ocean is home to a staggering diversity of marine life, built upon a rich ocean climate and an abundance of available nutrients. These “bottom-up” processes – the set of environmental conditions that make life possible – are countered by “top-down” processes, in which predators of all sizes control the populations of their prey.

Global temperature image showing the Northern Gulf of Alaska study area
(above) with enlarged insert (right) showing an example of monthly water
temperature.

Some ecosystems are simpler and easier to study. But in the complex eastern North Pacific system, the combination of top-down and bottom-up processes acts simultaneously and with different intensities on all species. Studying these processes in detail is a formidable task, and researchers are constrained both by scale – the relative size of the study area and the duration of the study – and by poor, often incomplete descriptions of the state of the ocean.

To this end, researchers Edward Gregr and Ryan Coatta, of the University of British Columbia, have published several datasets of spatial information on temperature, chlorophyll-a and other environmental parameters for the eastern North Pacific. Their goal: To enable their own work and that of fellow researchers studying the same region by sharing data.

Building the Dataset
“We conducted a series of analyses investigating the relationship between Steller sea lions, their prey, and various indicators of their physical habitat,” the authors write. “We conducted these studies for two different spatial extents, at two spatial resolutions, and three temporal scales.”

The areas studied included the Gulf of Alaska, which was divided into grid cells of 3x3 km² (3.5 sq mi), and a larger study area encompassing the range of the western stock of Steller sea lions within U.S. waters using grid cells measuring 9x9 km² (31.6 sq mi). The researchers built a collection of physical oceanographic data from satellite-borne remote sensors and output from an ocean circulation model, developed by Al Hermann and colleagues at the Pacific Marine Environmental Laboratory in Seattle Washington.

“This collection of monthly, physical oceanographic data is suitable for a range of oceanographic analyses at the temporal scale of months and seasons,” the authors advise. “The spatial scale of 9x9 km² is suitable for monthly studies, and could be aggregated if seasonal or long-term temporal averages were desired.”

Current velocity at mixed layer depth

Further, Gregr and Coatta note that the data collection for the 3x3 km² northern Gulf of Alaska study area, by integrating remote sensing data with water column properties, represents one of the best physical data sets ever assembled for this region. Although the circulation model output limits the data to a single year (2001), the data offers a breadth of variables that should provide a fertile background for further research into relationships between species and their habitat.

Enabling Marine Research
Gregr and Coatta also comment on the recent development of general distribution maps of marine species, based on average ocean conditions. They note that such analyses are suitable for tracking population trends and managing fisheries. However, studies at this broad scale do not necessarily reflect the ecology of a particular species, which responds to subtle interactions between species and to environmental changes from season to season and year to year. Data applicable to a variety of scales is essential to grasp the nuances of ecology.

“These data can thus support analyses in the North Pacific and Bering Sea across a range of temporal and spatial scales,” the authors conclude. “We hope this collection will be useful to marine scientists interested in species distributions, habitat description, marine classification, and protected area designation.”

Datasets:

To see more maps and obtain copies of the spatial datasets for the Bering Sea and Eastern North Pacific, click here.

Publication:
Environmental data for the eastern North Pacific and Bering Sea. Gregr, E.J. and R. Coatta. 2008. Fisheries Centre Research Reports Vol 16 pp. 79 abstract As part of our investigations into Steller sea lion habitat use and fisheries economics, we have prepared a collection of physical oceanographic data for the eastern North Pacific and the Bering Sea. Data include rectified grids of chlorophyll-a concentrations, sea surface temperature, slope of sea surface temperature, sea level anomaly, wind speed, current velocity and direction, mixed layer depth, and bathymetry. Geographic Information System-compatible raster (gridded) data were created from available on-line sources as both monthly and long-term averages. Monthly averages were produced for all available years for each sensor at a spatial scale of 9x9 km2 for the Gulf of Alaska and Bering Sea. We prepared long-term averages (climatologies) at 3x3 km2 for the northern Gulf of Alaska, and for the entire eastern North Pacific we prepared each source data set at its native resolution. We evaluated the sea surface temperature data at the 9x9 km2 scale using available quality data, and improved the data provided by interpolating through low quality pixels. Considerable processing was required to create a continuous North Pacific perspective, and to ensure that the data sets were correctly aligned at the different spatial scales. We also present 2-week averaged data from the output of a Regional Ocean Modelling System (ROMS) implemented for the northern Gulf of Alaska (3x3 km2) for the year 2001. These data provide a representation of the changing, vertical structure of the ocean. Given the significant investment to create a rectified data collection, we have prepared the data for distribution to interested researchers. The ROMS data are provided in MS Access format, and the remote sensing data as binary float files. Federal Geographic Data Committee (FGDC)-compatible metadata have been prepared. The data described herein are available from the Marine Mammal Research Unit web site or on request.

September 2, 2008