Multinet on the deck of the R/V Tiglax.
credit: Seth Danielson
Danielson et al., 2016
The Northern Gulf of Alaska is a marine environment along a long and relatively inaccessible coastline. Therefore, our fieldwork is restricted to periodic research cruises and moored instruments that can collect data unattended. Furthermore, to build a more complete picture of the ecosystem, we supplement collected data with modeling studies. The primary elements of our research consist of:
- Regular Observation: Tri-annual cruises will measure parameters along cross-shelf lines between spring and fall. Multi-instrument moorings deployed at selected Seward Line stations will measure parameters year-round. Together, these direct observations will :
- Generate seasonal time series,
- Measure short- and long-term environmental and ecosystem variability, and
- Extend the Seward Line time-series.
Existing collaborations will provide information on higher trophic level such as fish and marine mammals.
- Process Studies: At representative stations during some cruises, we will perform experiments to determine things like the rates of primary production and grazing.
- Modeling Studies: Numerical models will incorporate physical and biogeochemical observations in order to provide frameworks for testing hypotheses. In particular, models will be essential to determining the role of freshwater inputs and for testing what aspects of the food web support resilience.
- Data Management: Data archives and simplified Signature Datasets will share results with LTER colleagues, educators, students, and resource managers.
Specific topics of interest include:
- What regulates and influences the spring bloom?
- What is the role of freshwater inputs (like rivers) in structuring the ecosystem?
- What generates hot spots of high summer primary and secondary production?
- Is there trophic match or mismatch between producers and consumers? Is food available when it is needed?
- What is the distribution and composition of biological communities?
In short, our research team will investigate the features, mechanisms, and processes that drive NGA ecosystem production and foster its resilience.
Decades of previous studies along the Seward Line have revealed the basic structure of the ecosystem in the NGA. Consequently, we can build on this prior knowledge and center our three hypotheses on the characteristics that arise from the NGA ecosystem as a whole — its emergent properties. Our hypotheses are:
- Changes in the hydrologic cycle affect spring bloom production through changes in:
- Cloud cover,
- The vertical balance of stratification and mixing,
- Supplies of macro- and micronutrients, and
- Transport of nutrients and organisms.
- Hot-spots of high summer primary and secondary production result from cross-shelf interactions between water masses. Exchanges between fresher Alaska Coastal Current water and the saline waters that are offshore are assisted by bathymetry and regional winds. Through these interactions, changes in the hydrologic cycle also influence the timing and magnitude of resulting hot spots.
- The nutritional needs and life history of consumers in the NGA minimize trophic mismatch. Thus, ecosystem structure insulates higher trophic levels from the spatial and temporal variability in lower trophic level production. This leads to resilience in the face of long-term climate change.
An exploration of these hypotheses can be found in our 2017 NGA LTER proposal.
Illustration of the Regional Processes
This movie of temperature, iron, primary productivity, salinity, nitrate, and small copepods illustrates the hot spots of productivity in the Gulf of Alaska. A Regional Ocean Modeling System (ROMS) model with embedded nutrient-phytoplankton-zooplankton (GOANPZ) generated these variables.
In March-May, intricate regions of high productivity (upper right) occupy the southeast Alaskan shelf, the western inner shelf between Prince William Sound (PWS), and the area around the Shumagin Islands. In contrast, productivity is lower on the outer shelf between PWS and western Kodiak. Ocean currents distribute iron (upper middle) on the western shelf, which drives this pattern. In addition, changes in iron concentration apparently cause higher simulated productivity on the shelf during the years 2000-2006, relative to 2007-2013. This suggests that data on iron are critical to understanding interannual differences in phytoplankton and zooplankton on the Gulf of Alaska shelf.