PhD DEFENSE | SHANNON MCCLISH | RESOLVING SEASONAL TO ANNUAL MARINE NET COMMUNITY PRODUCTION USING BIOGEOCHEMICAL ARGO FLOAT OBSERVATIONS
Abstract: Net community production (NCP) is the net production of organic carbon by phytoplankton minus community respiration. Annual net community production (ANCP) is the flux of biologically produced organic carbon from the surface ocean each year and provides a metric of the magnitude of the biological carbon pump. Changes in the environment and ecosystem interactions impact NCP on a variety of scales, and how ANCP will change in the future remains uncertain. This dissertation uses biogeochemical observations from robotic profiling floats to investigate NCP on seasonal and annual timescales. The first study focuses on the impact of Southern Ocean seasonal sea ice on the timing of phytoplankton blooms and associated NCP. Phytoplankton biomass increases and nutrient drawdown begins when sea ice first begins to break up, but before sea ice fully retreats. The majority of seasonal NCP occurs under sea-ice cover and is missed in previous estimates derived from satellite observations. The second study investigates how the magnitude of seasonal NCP relates to ANCP in the Southern Ocean. A variable fraction of organic carbon produced during seasonal blooms is respired above the winter mixed layer depth and is re-entrained, decoupling seasonal and ANCP. The amount of respired and re-entrained carbon is controlled by both respiration rates and the maximum mixed layer depth. The third study characterizes the fraction of carbon respired and re-entrained and ANCP in ten global open ocean biomes, and reveals that differences in the fraction respired and re-entrained are related to the ratio of the euphotic depth to the maximum mixed layer depth. ANCP in subpolar seasonally stratified and subtropical permanently stratified biomes is similar despite large seasonal blooms in subpolar biomes because of the fraction respired and re-entrained.
Location: MSB 100
Date & Time: Monday, August 18, 2025 at 3:00pm
You can also connect via Zoom:
https://hawaii.zoom.us/j/88640772631
Meeting ID: 886 4077 2631
Passcode: 854798
