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Environmental Basics

Physical Environment

The Northern Gulf of Alaska (NGA) is tucked into a corner of the North Pacific. It is a subarctic marine biome that occupies the deep (200-300 m) continental shelf there. This shelf transitions between two distinct physical environments. Inshore, fjords and sounds link the NGA to steep, snow- and ice-clad mountains. Offshore and between sub-marine banks, deep canyons cross-cut the shelf, leading to a deep oceanic trench.

Atmospheric forcing in the NGA is dominated by low pressure systems which sweep the area year-round; however in winter, storms are stronger and more frequent. Winds associated with these systems drive the large-scale, oceanic circulation of the Alaska Gyre – including the Alaskan Stream offshore. Inshore, abundant precipitation in the mountains combine with downwelling winds to drive the coastally-confined Alaska Coastal Current (ACC). These two current systems create a series of quasi-persistent cross-shelf habitats for plankton.

Map of the north Pacific Ocean with major current systems. Blue outlines the NGA site, while orange highlights another relevant LTER site, the California Current Ecosystem

Environmental Drivers

Environmental drivers in the NGA include strongly seasonal conditions like heat, winds, freshwater input, and light. Previous studies such as GLOBEC and GOAIERP have already defined the quasi-predictable effects of these environmental drivers on the biome. However, the primary causes of ecosystem disturbance, which is of key interest to the LTER program, occur on other temporal scales.

At shorter time scales (hours to days), weather events cause the timing and frequency of biological production events to dramatically vary in ways that might depend on location. Also at short time scales, distribution of plankton and production are impacted by other features like:

  • River plumes,
  • Mesoscale eddies, and
  • Mixing zones associated with large, semi-diurnal tides over canyons and banks.

Phenomena with longer time scales are also important. These include multi-decadal fluctuations and trends such as the Pacific Decadal Oscillation (PDO), and millennial excursions of environmental conditions as glaciers retreat and advance.

A glacier entering Prince William Sound during an R/V Tiglax cruise, Spring 2013.
Photo credit: Ana Aguilar-Islas

Ecosystem Characteristics