Longhurst biogeographical provinces

Longhurst biogeographical provinces
Name	Longhurst biogeographical provinces
Area	Global oceans
Established	1998
Founder	Alan Longhurst
Type	Biogeographical provincialization
Classification	Marine provinces

Longhurst biogeographical provinces are a global scheme dividing the World Ocean into ecological provinces based on physical, chemical, and biological attributes. Designed for consistent comparison of pelagic ecosystems, the provinces support analyses of marine productivity, biogeochemical cycles, and fisheries across regions such as the North Atlantic Ocean, South Pacific Ocean, and Indian Ocean. The framework links oceanographic features like currents and fronts to ecological patterns observed by researchers at institutions including the Scripps Institution of Oceanography, the Woods Hole Oceanographic Institution, and the National Oceanic and Atmospheric Administration.

Overview

Longhurst provinces partition the pelagic realm into coherent units intended to reflect recurring patterns in phytoplankton and zooplankton distribution, nutrient dynamics, and light regimes. The scheme complements other spatial frameworks such as the Marine Ecoregions of the World, the Large Marine Ecosystem approach, and the Exclusive Economic Zone mapping used by the Food and Agriculture Organization. By aligning provinces with features like the Gulf Stream, the Kuroshio Current, and the Antarctic Circumpolar Current, the framework facilitates cross-disciplinary research by teams at the National Science Foundation, the European Space Agency, and the Intergovernmental Oceanographic Commission.

History and development

The provincialization was formalized by oceanographer Alan R. Longhurst in the late 20th century, building on observations from expeditions associated with the Challenger expedition legacy and twentieth-century programs such as the International Geophysical Year and the Joint Global Ocean Flux Study. Early data sources included time-series from the Bermuda Atlantic Time-series Study, the HOT (Hawaii Ocean Time-series), and collections housed at the Smithsonian Institution. The approach evolved alongside satellite missions like SeaWiFS and MODIS Aqua that provided basin-scale chlorophyll patterns and with modeling advances at centers such as the National Center for Atmospheric Research and the Met Office Hadley Centre.

Classification and criteria

Provinces were delineated using criteria that integrate physical forcing (currents, stratification), chemical gradients (nutrient regimes), and biological signals (primary production, community structure). The method synthesizes datasets from platforms including research vessels of the Albatross lineage, autonomous floats from the Argo program, and remote sensing from ERS-1. Classification relied on expert interpretation of features like upwelling zones associated with the California Current and oligotrophic gyres exemplified by the North Pacific Gyre. The schema is hierarchical, grouping provinces into broader biomes analogous to frameworks used by the International Union for Conservation of Nature and the Convention on Biological Diversity.

List of provinces and provinces map

Longhurst identified approximately 56 provinces initially, later refined to about 64–70 units depending on mapping resolution, each named for geographic or oceanographic landmarks such as the North Atlantic Drift, Benguela Current, Equatorial Pacific, and Western Indian Ocean. The province map has been visualized in atlases produced by publishers like Elsevier and disseminated via projects at the Plymouth Marine Laboratory and the National Aeronautics and Space Administration. Researchers often overlay province boundaries with datasets from the Global Ocean Observing System, the Sea Around Us project, and the Global Biodiversity Information Facility for analyses of species distributions, fisheries catch, and biogeochemical fluxes.

Ecological and oceanographic characteristics

Each province is characterized by distinct regimes of light availability, mixed-layer depth, nutrient supply, and trophic pathways that influence communities from pico-plankton to large pelagic fishes managed under agreements like the United Nations Convention on the Law of the Sea. Provinces capture phenomena such as seasonal bloom dynamics comparable to those documented in the North Sea time-series and persistent features like the Eddy fields associated with the South Atlantic Gyre. The framework has been used to interpret patterns in satellite-derived chlorophyll, in situ nutrient profiles collected aboard vessels like the RV Knorr, and biogeochemical measurements from initiatives including the Gulf of Mexico Research Initiative.

Applications in marine research and management

Scientists apply Longhurst provinces to stratify analyses of global primary production, to standardize reporting in multinational programs such as the Global Ocean Ship-based Hydrographic Investigations Program and to inform management by agencies like the International Commission for the Conservation of Atlantic Tunas and regional bodies including the Pacific Islands Forum. The provinces aid ecological niche modeling performed by groups at the Max Planck Institute for Meteorology and the Plymouth Marine Laboratory, support climate change impact studies that use outputs from the Coupled Model Intercomparison Project ensembles, and guide conservation planning by organizations such as BirdLife International when linking seabird foraging to ocean provinces.

Criticisms and limitations

Critiques note that provinces are static delineations that may not capture mesoscale variability generated by features like mesoscale eddies and transient events such as El Niño–Southern Oscillation. Others point to scale mismatches with management units like Exclusive Economic Zone boundaries and call for integration with dynamic products from the Global Drifter Program and real-time satellite feeds from the Copernicus Programme. Methodological debates reference alternatives including data-driven clustering used by teams at the Lamont–Doherty Earth Observatory and the need for improved linkage to biological databases hosted by the Ocean Biogeographic Information System.

Category:Oceanography Category:Biogeography