MOOS Upper-water-column Science Experiment (MUSE)

The MOOS Upper-Water-Column Science Experiment (MUSE) coordinated (within the framework of MOOS) a number of upper-water-column science projects, culminating in a large-scale, multi-institute, multi-disciplinary, field experiment in Monterey Bay in August, 2000. This coordination effort involved broadening the scope of the MBARI natural iron enrichment experiment to incorporate additional science projects and additional observational assets, including AUVs, drifters, aircraft, gliders, and small boats. The goal of the natural iron enrichment project to track the evolution of biological communities across nutrient-rich upwelling fronts encompassed the goals of several other MBARI science projects, such as monitoring of picoplankton, physics and biology of ocean fronts, biogeochemical response to climate and ocean variability, and bioluminescence measurements.

As the first phase of the MOOS Implementation Plan, MUSE exemplified the process of converting a set of science problems into a coordinated interdisciplinary field experiment from which a set of engineering requirements emerges. These engineering requirements, which include platforms, instrumentation, and data management, will form the basis of a MOOS core system specification.

The natural iron enrichment problem, which represents the core science problem behind MUSE, seeks to assess the processes that control the transformation of resuspended iron into iron available to phytoplankton. These processes occur to a measurable extent across sediment-rich upwelling fronts. That iron is important to phytoplankton growth is well known, but to date only two experiments have tracked (albeit at limited resolution) the evolution of biogeochemical properties during iron-induced phytoplankton blooms. 

The MUSE project involved three ships, two aircraft, two satellites, two AUVs, several drifters, nine moorings, six gliders, and a host of small boats. The weather cooperated in the second week of August to produce a remarkable upwelling event (Figure 1). High-resolution (in time and space) surveys with AUVs and gliders revealed previously unnoticed details of the complex coastal circulation system during the fertilization event. Iron concentrations increased from ambient values near one nanomole, while the system was in a relaxed state prior to onset of upwelling favorable winds, to values greater than six nanomoles in the core of the upwelled plume. Iron was lost at a rate of about 40 percent per day. This iron loss rate is similar to that observed in the deliberate iron fertilization experiment created in the equatorial Pacific during the IRONEX II experiment in 1995. Underway mapping of algal species, using DNA probes and the Environmental Sample Processing (ESP) system developed at MBARI, revealed a major bloom of Pseudo-nitzschia australis, a diatom that produces toxic domoic acid (Figure 2). The toxic species were found in waters low in iron suggesting that perhaps they had sequestered this element from other species.

The information on circulation, chemistry, and biological consequences was combined to create a conceptual model for what occurred in Monterey Bay. As the upwelling-favorable northwesterly winds intensified, a cold filament tended south-southeast across the mouth of the bay from the upwelling center near Point A๑o Nuevo. The aircraft surveys found a warm, dry, atmospheric jet of comparable scale, previously unobserved, blowing off the Santa Cruz mountains directly above the filament. The leading edge of the cold filament was high in iron and, as it entered the bay, it appeared to squeeze out water that was high in phytoplankton and low in dissolved inorganic nitrogen. The phytoplankton from the bay acted as seed for the next set of blooms. 

Sufficient iron was supplied by these events such that algae consumed all of the dissolved inorganic nitrogen in the coastal zone, but offshore and in areas where the coastal topography is not conducive to sediment resuspension, phytoplankton exhibited signs of iron stress. Residual dissolved inorganic nitrogen was found in these areas. During relaxation and reversal of the upwelling-favorable winds, warmer oceanic water moved shoreward, resulting in accumulation of phytoplankton in the bay. The cycle was restarted when the upwelling favorable winds returned.

MUSE provided tantalizing observations pertinent to the understanding of coastal upwelling systems. MUSE was only the first step as MBARI embarks on a plan to build a network of coordinated long-term ocean observatories and assimilate the physical, chemical, biological, and geological information into coupled ocean-atmosphere models. This long-term effort will take several years to complete, but as individual components become available, they will be demonstrated in coordinated multi-discipinary experiments patterned after the MUSE model.

Participating MBARI Groups

  • Chavez/Johnson— natural iron enrichment in ocean fronts
  • Chavez— biogeochemical response to coastal upwelling
  • Scholin/DeLong— monitoring of picoplankton in ocean fronts
  • Robison/Hamner— physics and biology of ocean fronts
  • Barry/Buck— benthic community production under upwelling zones
  • Matthews/Davis— sampling, estimation, detection of episodic events
  • Paull— iron from seafloor venting
  • Ryan/Chavez— frontal processes and vertical flux along filaments
  • Haddock/Moline/Widder— zooplankton/phytoplankton contribution to bioluminescence

Participating AOSN/ICON Groups

  • Paduan/Shulman (NPS/MSU)— modeling of ocean fronts
  • Bellingham (MIT/MBARI)— AUV development
  • Davis (SIO)— glider development
  • Eriksen (UW)— glider development
  • Frye/Singh (WHOI)— AUV docking
  • Preisig/Johnson (WHOI)—acoustic communications
  • Phoha/Greley (PSU/ARL)— data processing
  • Chao/Howden (JPL/Goddard)— airborne salinity measurements
Data Index Aircraft AUV CODAR
Drifters Moorings Satellites Ships