NGA Phase 2 Process Studies

Transitioning from the first funding cycle of an LTER site (phase 1) to the second come with a lot of considerations and opportunities. Phase 1 has largely focused on survey and monitoring work where the emphasis was clearly on maintaining and expanding existing time series (e.g., Sewardline). While there were some process studies, those activities that try to interrogate the flows of energy and interactions between members of the ecosystem, they were generally quite resource limited and short on time (2-4 days). As someone that comes from a process study background (for reference, the California Current Ecosystem LTER site has entire 30-35 day cruises focused entirely on processes), I knew I wanted to advocate for expanded process work in Phase 2.

With lots of input and help from my colleagues, I think we came up with an exciting plan.

Outline of one process study. Summer cruises would entail 2-3 such studies.

Here is a schematic sketch of some of the core components of the new process studies. For Phase 2 we are interesting in learning more about how fronts shape the ecosystem and the biogeochemistry of the Gulf of Alaska. While there are many fronts in the region, several are disproportionally important and are more predictable than others: the ACC front and the shelf-break front.

In the figure I’ve sketched the ACC front moving along the coast as it’s steered bathymetric features and powered by buoyant freshwater additions.

The process study would entail:

  1. Local synoptic survey with the Deep-focus Particle Imager (DPI), a towed instrument outfitted with a multitude of sensors.
  2. Deployment of a buoy array that will be used to monitor the relative motion of waters inside and adjacent to the front over the course of the study.
  3. A series of ~24h intensive stations where the majority of the work will be conducted. The focus here will be on establishing rate measurements and to look at how biomass/biogeochemical stocks are changing over time. Likely 4 of these Lagrangian stations will be occupied, with the order shown above.
  4. A final DPI survey may be conducted; and the buoys recovered.

Adaptive and intensive studies like this will be essential to address questions about how the ecosystem responds to short-term environmental forcings–aspects that our current snapshots of the ecosystem (survey work) is ill-equipped to address.

A quick look at the spatial and temporal variability without our system makes the argument easily. This image of satellite-derived chlorophyll highlights the fine scale structure imposed by circulation and mixing within our region. Moreover it is not difficult to imagine how boon and bust cycles of ecosystem productivity over short time scales hampers our ability to interpret field data: where these measurements collected at steady state? Where they measured at a decline? An increase? We often have no clear context for such an assessment–a gap that can be filled by the proposed process studies above.

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