OSNAP

OSNAP
Name	OSNAP
Acronym	OSNAP
Start	2014
Type	International oceanographic observing program
Region	North Atlantic Ocean, Labrador Sea, Irminger Sea, Iceland Basin, Rockall Trough
Partners	National Oceanography Centre (United Kingdom), Woods Hole Oceanographic Institution, University of Washington, Scripps Institution of Oceanography, Dalhousie University, University of Copenhagen, National Oceanic and Atmospheric Administration, British Antarctic Survey, University of Oxford
Methods	Moorings, shipboard hydrography, autonomous floats, gliders, current meters, CTD casts

OSNAP

Introduction

OSNAP is an international, multi-institutional oceanographic observing program focused on the meridional overturning circulation in the subpolar North Atlantic. The program aims to quantify transport variability and water mass transformation across key sections linking the Labrador Sea, Greenland Sea, Irminger Sea, Iceland Basin, and the Rockall Trough. OSNAP brings together researchers from major institutions such as the National Oceanography Centre (United Kingdom), Woods Hole Oceanographic Institution, and Scripps Institution of Oceanography to address questions relevant to the Atlantic Meridional Overturning Circulation, climate variability, and ocean heat transport.

Project Background and Objectives

OSNAP was motivated by prior regional programs including the Overturning in the Subpolar North Atlantic Program origins in observational needs identified after studies like the World Ocean Circulation Experiment and campaigns associated with the Arctic Ocean Fluxes and Processes study. Primary objectives are to provide continuous, trans-basin measurements that resolve the strength and variability of the overturning circulation, quantify heat and freshwater transports, and determine the roles of convection and boundary currents in setting large-scale circulation. The project addresses hypotheses developed from process studies in the Labrador Sea Water formation literature, basin-scale synthesis efforts linked to the Climate Variability and Predictability Program, and modeling work done at centers such as the National Center for Atmospheric Research, Princeton University, and Geophysical Fluid Dynamics Laboratory.

Deployment and Instrumentation

OSNAP employs arrays of moorings, shipboard hydrographic sections, autonomous profiling floats, and gliders deployed across two main trans-basin lines. The western line across the Labrador Sea and the eastern line spanning the Irminger Sea, Iceland Basin, and Rockall Trough utilize instruments including inverted echo sounders, current meters, acoustic Doppler current profilers, and conductivity–temperature–depth sensors used extensively by teams from Dalhousie University, University of Washington, and University of Copenhagen. Repeat hydrographic occupation is carried out on research vessels affiliated with Woods Hole Oceanographic Institution, Scripps Institution of Oceanography, and national research fleets from United Kingdom and United States. Autonomous platforms include Argo-type floats and gliders procured or managed by groups at University of Southampton and University of Plymouth to augment mooring arrays and sample mesoscale variability.

Key Findings and Scientific Impact

OSNAP has demonstrated that overturning variability in the subpolar North Atlantic is dominated by east-west trans-basin changes and boundary current contributions rather than solely by localized convection in the Labrador Sea. Results have shown significant seasonal to interannual modulation of meridional overturning transport, with implications for downstream climate variability tied to studies at Hadley Centre and Met Office. Observational syntheses involving OSNAP data have revised estimates of northward heat transport and freshwater fluxes, informing projections used in assessments by the Intergovernmental Panel on Climate Change and coupled model intercomparison projects coordinated by World Climate Research Programme. OSNAP observations have catalyzed process studies into deep density transformation, invigorated research at facilities such as the University of Oxford and Imperial College London, and influenced numerical experiments at institutions including European Centre for Medium-Range Weather Forecasts and Max Planck Institute for Meteorology.

Data Processing and Availability

Data from OSNAP moorings, shipboard surveys, and autonomous platforms undergo standardized quality control, calibration against hydrographic standards, and archival in community repositories. Processing workflows developed by collaborating teams at National Oceanography Centre (United Kingdom), Woods Hole Oceanographic Institution, and Scripps Institution of Oceanography include sensor drift correction, tidal signal removal, and synthesis with satellite altimetry from missions such as TOPEX/Poseidon and Jason-3. Gridded products and time series are made available through national data centers and international portals used by researchers at National Oceanic and Atmospheric Administration and British Antarctic Survey for model validation, diagnostics, and synthesis with paleoceanographic records from studies at Lamont–Doherty Earth Observatory.

Collaborations and Funding

OSNAP is supported by a consortium of funding agencies and research councils from countries bordering the North Atlantic, with major contributions from the Natural Environment Research Council, National Science Foundation (United States), European Commission research instruments, and national funding bodies in Canada, Denmark, Germany, and Norway. The program is a collaboration among universities and institutes including Dalhousie University, University of Copenhagen, Woods Hole Oceanographic Institution, and National Oceanography Centre (United Kingdom), and engages international projects such as the Global Ocean Observing System and Argo to enhance long-term observing capabilities. OSNAP outputs inform policy-relevant assessments and feed into international synthesis efforts coordinated by organizations like the Intergovernmental Panel on Climate Change and the World Meteorological Organization.

Category:Oceanography