Assessment of Oceanographic Conditions during the North Atlantic EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) Field Campaign
Year: 2023
Type: preprint
Abstract: This manuscript presents an overview of NASA’s EXport Processes in the Ocean from Remote Sensing 2021 Field Campaign in the North Atlantic (EXPORTS NA) and provides quantitative and dynamical descriptions of the physical processes modulating water transformations during the study. A major programmatic goal was to conduct the sampling in a Lagrangian mode so that ocean ecological and biogeochemical changes can be observed independent from physical advective processes. To accomplish this goal, EXPORTS NA conducted a multi-ship, multi-asset field sampling program within a retentive, anticyclonic mode water eddy. Beneath depths of ~100 m, Lagrangian sampling assets remained within the eddy core waters (ECWs) throughout the experiment, demonstrating that the ECWs within the mode water eddy were retentive. However, strong westerly winds from four storm events deepened the mixed layer (ML) of the surface core waters (SCWs) above the eddy’s mode water core by 25-40 m and exchanged some of the SCWs with surface waters outside of the eddy via Ekman transport. Estimates of flushing times ranged from 5-8 days, with surface exchange fractions ranging from 20-75% and were consistent with particle tracking advected by combined geostrophic and Ekman velocities. The relative contributions of horizontal and vertical advection on changes in SCW tracers depend on the horizontal and vertical gradients of that tracer. For example, in the surface waters, horizontal advection played a large role in salinity fluxes, yet vertical entrainment played a larger role in the fluxes of nutrients into the ML. Each storm injected nutrients and low oxygen waters into the ML, after which the surface ocean ecosystem responded by reducing nutrient concentrations and increasing %O2 saturation levels. Overall, SCW values of chlorophyll and POC were the largest at the onset of the field program and decreased throughout the campaign. The analysis presented provides a physical oceanographic context for the many measurements made during the EXPORTS NA field campaign. Illustrated are the many challenges of conducting a production-flux experiment even in a Lagrangian frame and the inherent uncertainties of interpreting biological carbon pump observations that were collected in a Eulerian frame of reference.
Authors: Leah Johnson, David A. Siegel, Andrew F. Thompson, Erik Fields, Zachary K. Erickson, Ivona Cetinic, Craig M. Lee, Eric A. D'Asaro, Norman B. Nelson, Melissa M. Omand, Michaela Sten, Shawnee Traylor, David P. Nicholson, Jason R. Graff, Deborah K. Steinberg, Heidi M. Sosik, Ken O. Buesseler, Mark A. Brzezinski, Inia Soto Ramos, Filipa Carvalho, Stephanie A. Henson
Institutions: University of Washington, University of Washington Applied Physics Laboratory, University of California, Santa Barbara, California Institute of Technology, NOAA Pacific Marine Environmental Laboratory, Goddard Space Flight Center, Morgan State University, University of Rhode Island, Massachusetts Institute of Technology, Woods Hole Oceanographic Institution, Oregon State University, Virginia Institute of Marine Science, National Oceanography Centre
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: green
Awards: G1568901267, G1573210310, G1802316343, G1821804007, G2455452839, G316067346, G3305931967, G3587434657, Marine LTSS: Climate Linked Atlantic Sector Science, G5402437505, G6048969373, PARTICLE SIZE HAS FUNDAMENTAL CONTROL ON THE DISTRIBUTION AND DYNAMICS OF PARTICULATE CARBON IN THE UPPER OCEAN. STOKES LAW STATES THAT PARTICLES WITH LARGER EFFECTIVE DIAMETERS (D) WILL SINK FASTER THAN SMALLER ONES DETERMINING WHETHER PARTICLES ARE EFFECTIVELY SUSPENDED WITHIN THE WATER COLUMN (D<~100 M) OR ARE SINKING (D>~500 M). NET PRIMARY PRODUCTION (NPP) ENTERS PELAGIC ECOSYSTEMS AS SUSPENDED PARTICLES AND THESE PARTICLES (ALONG WITH CDOM) CONTROL THE OCEAN S OPTICAL PROPERTIES. FURTHER SINKING PARTICLES UNDERGO MANY BIOTIC AND ABIOTIC TRANSFORMATIONS IN THEIR SIZE COMPOSITION AND SINKING VELOCITY AS THEY TRANSIT FROM THE SURFACE OCEAN REGULATING CARBON EXPORT AND REMINERALIZATION PROFILES. THIS POINTS TO THE IMPORTANCE OF UNDERSTANDING THE PARTICLE SIZE DISTRIBUTION (PSD) IN PREDICTING THE FATE OF NPP THE CENTRAL GOAL OF EXPORTS. WE PROPOSE TO ANSWER FOUR SCIENCE QUESTIONS TO DEVELOP A PREDICTIVE UNDERSTANDING OF THE PSD FOR BOTH SUSPENDED AND SINKING PARTICLES. 1. HOW DO THE ABUNDANCE COMPOSITION AND PRODUCTIVITY OF PARTICLE SOURCE MATERIALS REGULATE THE PSD FOR SMALLER OPTICALLY RELEVANT PARTICLE SIZES? 2. HOW DO SOURCE PARTICLE CHARACTERISTICS AS WELL AS BIOTIC / ABIOTIC INTERACTIONS ON SINKING PARTICLES REGULATE THE PSD FOR LARGER CARBON EXPORT RELEVANT PARTICLE SIZES? 3. CAN THE COMBINED SIZE DISTRIBUTION FOR SUSPENDED AND SINKING PARTICLES BE MODELED USING OPTICAL DATA AND IN PARTICULAR FROM SATELLITE OCEAN COLOR OBSERVATIONS? 4. HOW DO ENERGY AND CARBON DERIVED FROM PHYTOPLANKTON NPP CASCADE THROUGH THE PARTICLE SIZE SPECTRUM? THESE FOUR SCIENCE QUESTIONS ADDRESS ASPECTS OF MANY OF THE EXPORTS SCIENCE QUESTIONS (SQ) AND ANSWERS SQ1C AND SQ1D DIRECTLY. WE PROPOSE AN INTEGRATED RESEARCH PROGRAM OF IN SITU OPTICAL AND IMAGERY OBSERVATION (SIEGEL NELSON MCDONNELL) AT-SEA CHARACTERIZATION AND EXPERIMENTATION ON COLLECTED AGGREGATES (PASSOW) AND NUMERICAL MODELING (BURD SIEGEL). ADVANCES IN NEARFORWARD ANGLE LIGHT SCATTER (LISST) AND IN SITU IMAGING (UVP) ENABLE HIGH-RESOLUTION PROFILES OF THE PSD FOR BOTH SUSPENDED AND SINKING PARTICULATES. INHERENT OPTICAL AND OCEANOGRAPHIC PROPERTIES WILL BE MONITORED SIMULTANEOUSLY TO CHARACTERIZE SUSPENDED PARTICLE COMPOSITION AND OCEANIC CONTEXT. WE WILL COLLECT SINKING AGGREGATES USING THE MARINE SNOW CATCHER TO CHARACTERIZE THEIR ECOLOGICAL AND BIOGEOCHEMICAL COMPOSITION PHYSICAL PROPERTIES AS WELL AS THEIR DECOMPOSITION RATES ALL OF WHICH ARE NEEDED FOR MODELING. THE ASSEMBLED DATA SET WILL BE THE BASIS OF MECHANISTIC NUMERICAL MODELS THAT TRANSFORM THE COMBINED PSD AS A FUNCTION OF DEPTH AND ECOSYSTEM / CARBON CYCLING STATE. WE WILL TEST RELATIONSHIPS AMONG SOURCE MATERIALS (PHYTOPLANKTON ZOOPLANKTON FECES ETC.) AND BIOTIC (ZOOPLANKTON GRAZING ETC.) AND ABIOTIC (TURBULENCE DENSITY GRADIENTS ETC.) DISRUPTERS OF AGGREGATE DISTRIBUTIONS. DATA AVAILABLE FROM OTHER EXPORTS INVESTIGATIONS (PARTICLE EXPORT&COMPOSITION PHYTOPLANKTON ABUNDANCE&COMPOSITION NPP ETC.) WILL BE INCORPORATED AS NEEDED. FOR EXAMPLE WE WILL ASSESS THE SINKING VELOCITY SIZE SPECTRUM USING COLLECTED TRAP SAMPLES AND OUR PSD MEASUREMENTS AS WELL AS SPATIOTEMPORAL VALIDATED FIELDS OF PARTICLE EXPORT FLUXES AND PSD TRANSFORMATIONS FROM INVERSE MODELING. THESE DATA PRODUCTS AND MODELS WILL BE DISTRIBUTED TO THE EXPORTS SCIENCE TEAM AND BEYOND. OUR PROPOSAL RESPONDS PRIMARILY TO SECTION 3.1.2.2 (COLLECTION&ANALYSIS OF FIELD DATA) OF THE 2016 ROSES A3 SOLICITATION BUT ALSO CONTRIBUTES TO SECTIONS 3.1.2.1 (DEVELOPMENT OF RS DATA PRODUCTS) AND 3.1.2.3 (DEVELOPMENT OF MODELS). LAST THE LEAD-PI (SIEGEL) IS APPLYING TO BE THE EXPORTS SCIENCE LEAD., WE PROPOSE TO IMPLEMENT A MULTI-PLATFORM MULTI-SCALE MULTI-MONTH AUTONOMOUS ARRAY AT TWO EXPORTS SITES TO MEASURE UPPER OCEAN COMMUNITY STRUCTURE SINKING CELLS AGGREGATES AND FECAL PELLETS PHYSICAL EXPORT AND MIGRATING ZOOPLANKTON. THESE OBSERVATIONS WILL COMPLEMENT SHIP-BASED PROGRAMS BY SPANNING A WIDER RANGE OF ECOSYSTEM STATES AND PROVIDING A DIVERSE DATASET FOR EXPORTS MODELING. THE MEASUREMENTS WILL RESOLVE EVOLUTION OF DOMINANT PATHWAYS AND QUANTIFY FLUXES FOR CARBON EXPORT FROM THE EUPHOTIC ZONE TO THE UPPER TWILIGHT ZONE AS WELL AS ATTENUATION FLUX IN THE UPPER TWILIGHT ZONE. THIS EFFORT WILL ALSO DEMONSTRATE THE CAPABILITY TO MEASURE EXPORT FLUXES USING A COMBINATION OF IN SITU MEASUREMENTS AND SATELLITE REMOTE SENSING THUS SERVING AS A PROTOTYPE FOR FUTURE OPERATIONAL SYSTEMS. WE HYPOTHESIZE THAT DOMINANT EXPORT PATHWAYS AND EFFICIENCIES DIFFER BETWEEN ATLANTIC AND PACIFIC SITES BASED ON RELATIVE PHASING OF NET COMMUNITY PRODUCTION (NCP) AND CARBON EXPORT (EZ) FROM THE EUPHOTIC ZONE. IN THE PACIFIC WHERE NCP AND EZ VARY IN PHASE EXPORT WILL BE DOMINATED BY ZOOPLANKTON DIEL MIGRATION AND SLOW-SINKING PELLET FLUXES WITH A SMALLER ROLE FOR PHYSICAL EXPORT AND A WEAKER EXPORT EFFICIENCY. IN CONTRAST DECOUPLING OF NCP AND EZ IN THE ATLANTIC WILL PRODUCE BOTH MORE VARIABLE AND MORE EFFICIENT EXPORT ASSOCIATED WITH FAST-SINKING AGGREGATES PHYSICAL TRANSPORT AND LOW RESPIRATION RATES. SMALL-SCALE PHYSICAL AND ECOSYSTEM VARIATIONS IN THE ATLANTIC WILL ENHANCE SUBMESOCALE EDDY FLUX WHICH MAY CONSTITUTE UP TO HALF OF TOTAL EXPORT DURING SPRINGTIME RESTRATIFICATION. WE PROPOSE THAT SIMILAR IN SITU MEASUREMENTS WILL PERMIT IMPROVED EXPORT PREDICTIONS IN OTHER OCEANIC REGIONS BASED ON REMOTE-SENSING OBSERVATIONS.
OpenAlex ID: W4388599029