Atmosphere and Ocean

Downscaling Global Climate Projections with Nested Biophysical Models

Leads: Nicholas Bond, Enrique Curchitser, Katherine Hedstrom
Co-PIs: Georgina Gibson, Albert Herrmann, Jim Overland

We will test these hypotheses:

Climate-induced changes will alter food availability for all trophic levels of the shelf ecosystem through “bottom-up” processes (processes beginning at the bottom of the food web and moving up through trophic levels).
Earlier sea ice retreat expected as a result of warming will result in a later, warm-water spring phytoplankton bloom, increased coupling with zooplankton and greater pelagic secondary productivity. Benthic secondary productivity will decrease.
Reduction in frequency and intensity of summer storms will reduce surface mixing and increase surface insolation. This will increase stratification and lower the supply of nutrients that sustain primary and secondary productivity. The resultant summer and fall conditions will reduce zooplankton and juvenile fish production by reducing their condition (energy density) and over-wintering capability.

Role of Ice Melting in Providing Available Iron to the Surface Water of the Eastern Bering Sea Shelf

Lead: Jingfeng Wu

We will test the hypothesis that melting ice is a significant source of iron for biological growth in Bering Sea shelf water during spring. Initial spring algal growth depletes available iron in the winter-mixed surface water, resulting in a iron limitation of algal growth. The iron input from melting ice relieves this iron limitation and supports a high level of dissolved iron in the stratified shelf surface water for subsequent algal growth when macronutrients are transported inshore from the iron-poor but macronutrient-rich waters of the Aleutian basin.

We will investigate whether iron in the water immediately beneath sea ice cover is depleted before macronutrients are depleted during the initial algal growth in spring in the absence of available iron input from melting sea ice, and will examine whether melting sea ice is an important source of available iron that leads to a persistent excess of iron in the stratified ice-free shelf surface water.

Impact of Changes in Sea Ice on the Physical Forcings of the Eastern Bering Ecosystem

Lead: Jinlun Zhang
Co-PI: Rebecca Woodgate

We will study historical and contemporary changes of Bering Sea ice cover and the impacts of these changes on Bering Sea climate. We will also investigate future changes of the eastern Bering marine environment under global warming scenarios.

Objectives: (1) simulate the historical evolution of the eastern Bering ice-ocean system since 1970; (2) identify key linkages among the atmosphere, sea ice, and ocean in order to understand mechanisms affecting physical processes influencing the ecosystem; (3) examine the interactions between the Bering Sea climate and the Pacific and Arctic climates; and (4) estimate the state of the marine system under different scenarios of climate change.

Stratification on the Bering Shelf and its Consequences for Nutrients and the Ecosystem

Leads: Tom Weingartner, Knut Aagaard

The enormous Bering shelf, containing one of the most productive marine ecosystems in the world, has changed significantly in recent decades, both physically and biologically, and often in concert with regional climate fluctuations. Furthermore, the Bering shelf offers a physical and ecological continuum between the North Pacific and Arctic oceans, and its flow field transmits changes to the northern ecosystems downstream.

We will address the impact of physical variability on the processes and structure of the Bering shelf ecosystem, with special emphasis on how freshwater redistributed by the shelf circulation or introduced from sea ice melt modifies stratification and nutrient distributions. We will ask how changes in sea ice affect advection and mixing; how variable fluxes of low-salinity, nutrient-deficient coastal waters may affect production; how cross-shelf fluxes are established and altered; how these fluxes might respond to climate change; how the seasonal stratification cycle is controlled; and how the buoyant coastal flow evolves.

Examining Summer Hydrographic Structure and Nutrients

Leads: Rolf Sonnerup, Terry Whitledge
Co-PI: Calvin Mordy

We will collect, quality control, analyze, and distribute the core physical and chemical observations collected on the BEST summer cruise as a service component of the larger ecosystem program. We will also examine the persistence of along- and across-shelf gradients of temperature, salinity, fluorescence, oxygen, nutrients and currents by integrating data from summer hydrographic surveys with trajectories from satellite-tracked drifters, data from other cruises, and data from long-term moorings (funded elsewhere).