About SCOPE-Gradients

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.

The SCOPE-Gradients vision is to mechanistically predict ocean ecosystem structure and function. To achieve this vision, field campaigns are designed to cross steep environmental gradients that separate biogeochemically distinct ecosystems. Thus far, three spring cruises span nearly 20° of latitude, from the warm, nutrient-limited North Pacific Subtropical Gyre to the colder, more productive subpolar gyre. Continuous underway observations of surface water properties (e.g., organisms, environmental conditions, productivity) are strategically punctuated by depth profiles from select stations to connect surface processes to those in waters well below the mixed layer. Observations are interpreted within the context of large-scale physical forcing, obtained via both satellite remote sensing and atmospheric and ocean circulation models. Data are also reinforced by long-term in situ observations derived from Argo profiling floats and drifters. Conceptual and mathematical models are an integral component of the program, as they underlie both experimental design and data interpretation; in turn, new observations motivate simplified theories and numerical simulations. Interpretations are further facilitated through data compilation within Simons CMAP, an open-source data service designed for retrieval, visualization and analysis of oceanic datasets, including in situ observations, multidecade global satellite remote sensing and model outputs. With the increasing amounts of available observations within Simons CMAP, data-driven models are becoming an important complement to mechanistic models. A defining feature of the SCOPE-Gradients program is a highly collaborative environment that enables powerful intellectual bridges between modelers and observationists, and between those that work at the molecular scale and those that work at the larger, more integrative scale. The SCOPE-Gradients field program is synergistic to the SCOPE-ALOHA focus on furthering our mechanistic understanding of microbial ecology in time and space in the North Pacific Subtropical Gyre.

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