PHYTOPLANKTON PLAY KEY ROLES AS THE BASE OF THE MARINE FOOD WEB AND AS A CRUCIAL COMPONENT IN THE EARTH'S CARBON CYCLE. UNDERSTANDING HOW OCEAN DYNAMICS INFLUENCE PLANKTON ECOLOGY WILL ADD TO BASIC KNOWLEDGE AND INFORM STUDIES OF HIGHER-LEVEL MARINE ORGANISM HABITAT. HERE WE PROPOSE TO EXAMINE HOW OCEAN DYNAMICS ACROSS AN UNPRECEDENTED RANGE OF SCALES (FROM BASIN-SCALE GYRE CIRCULATION TO FRONTS EDDIES FILAMENTS AND LONG INTERNAL WAVES) SET TRANSPORT AND RE-ORGANIZE PHYTOPLANKTON COMMUNITIES. WE WILL USE A COMBINATION OF SATELLITE DATA EXTENSIVE FLOW CYTOMETRY OBSERVATIONS OTHER EXISTING IN-SITU MEASUREMENTS AND MODELING TO ACHIEVE THESE GOALS. OUR PROPOSAL BRINGS TOGETHER AN INTERDISCIPLINARY TEAM WITH EXPERTISE IN PHYSICAL OCEANOGRAPHY PHYSICAL OCEAN MODELS ECOLOGY MARINE ECOSYSTEM MODELS SATELLITE OCEANOGRAPHY BIOLOGICAL OCEANOGRAPHY COMPUTATION AND DATA ANALYTICS. WE PROPOSE TO STUDY: (1) THE COMBINATION OF PHYSICAL MECHANISMS ON SCALES FROM 1 TO 1000S KM THAT CONTROL THE DYNAMIC PHYTOPLANKTON COMMUNITY BIOGEOGRAPHY; (2) THE OBSERVABLE SIGNATURES OF THESE MULTISCALE BIOGEOGRAPHICAL PATTERNS IN SATELLITE AND IN-SITU DATA; (3) THE CONSEQUENCES OF PHYSICAL PROCESSES OF DIFFERENT SCALES ON BIOGEOGRAPHY BIOGEOCHEMISTRY HIGHER TROPHIC LEVELS AND IMPLICATION FOR VULNERABILITY OF ECOSYSTEMS; (4) WHAT IS MISSED WHEN THE VARIOUS SCALES ARE NOT RESOLVED IN OBSERVATIONS AND MODELS; AND (5) HOW OBSERVABLE SIGNATURES CAN BE SYSTEMATICALLY EXPLOITED TO BEST MONITOR THE TRANSPORT AND REORGANIZATION OF MARINE PHYTOPLANKTON BIOGEOGRAPHY NOW AND IN THE FUTURE.