The transition zones between the North Pacific Subtropical Gyre and neighboring ecosystems, notably the North Pacific Subpolar Gyre, exhibit steep changes in environmental conditions (gradients) associated with dramatic changes in the microbial ecosystem. These zones provide suitable venues to understand mechanisms that structure microbial communities and to test ecological theory of how resource supply ratios drive productivity, export, particle size distributions, and elemental stoichiometry. A multidisciplinary team led by Ginger Armbrust is testing three interconnected hypotheses via interrogation of model simulations and direct observations of the transition zone between marine ecosystems.
The hypotheses are:
(1) Enhanced productivity occurs at the transition zone because resources, such as fixed nitrogen and iron, are supplied at close to the optimal ratio for phytoplankton productivity.
(2) Changes in the particle size distribution (PSD) across the front are predictable and related to the community of primary producers and those factors that influence their growth and mortality. The PSD is directly related to enhanced export of sinking particulate carbon at the transition zone and can be used to study non-steady state changes in community structure and productivity in the North Pacific Subtropical Gyre.
(3) Trends in elemental and macro-molecular composition of primary producers vary predictably across the transition zone according to principles of resource ratio competition models.