Net Community Production in the East Coastal waters of the United States from Oxygen to Argon Ratios

Yonghui Gao1, Wei-Jun Cai1, Andrew L Collins2, Bror Jonsson3 and Joseph Salisbury4, (1)University of Delaware, School of Marine Science and Policy, Newark, DE, United States, (2)University of Delaware, School of Marine Science and Policy, Newark, DE, (3)University of New Hampshire, Ocean Processes Analysis Lab, Durham, NH, United States, (4)University of New Hampshire, School of Marine Science and Ocean Engineering
The increase in anthropogenic nutrient input may enhance phytoplankton biomass and their photosynthesis may cause oxygen supersaturation in euphotic zone; while organic matter input from land to sea and decomposition during transportation may lead to oxygen undersaturation. Net community production (NCP) reflects the net outcome between photosynthesis and respiration. Our current understating of NCP mainly relies on bottle incubation and satellite data analysis, which may cause bias in the large area of coastal water. To improve our understanding in the east coast of the United States (25°N to 45 °N) from an integrated perspective, we conducted continuous onboard determination of oxygen (O2) to argon (Ar) ratios in order to separate biological activity from physical mixing effects during June to July 2015 as part of the NOAA East Coast Ocean Acidification (ECOA) investigation. Biological driven O2 supersaturation was derived from difference of O2/Ar in water away from the equilibrium status using equilibrator inlet mass spectrometer. Temperature changed 5°C to 30°C from north to south, and salinity ranged from 20 in the shore region (e.g. inside of Chesapeake Bay) to 36 in offshore water. Photosynthesis (positive NCP) was the dominant process in the Gulf of Maine and in lower Chesapeake Bay due to the re-occurring phytoplankton blooms. In response to large amount of terrestrial organic matter input and quick remineralization at temperature of 20-25°C, respiration (negative NCP) were often observed in the Block Island sound, Delaware Bay mouth and Chesapeake Bay mouth. In the warm subtropics gyre, NCP was slightly negative that may be related to nutrient deficiency and low organic matter input.