Spatial and Temporal Heterogeneity in Net Community Production in the Crossshelf Direction of the Atlantic Northeastern Shelf

The ocean, via physical and biological processes, absorbs 25% of anthropogenic CO2 emissions. Climate change, however, hampers the ocean’s ability to sequester carbon. The Northeast U.S. Shelf Long-Term Ecological Research (NES-LTER) project works to understand how warmer temperatures and increased environmental variability, caused by climate change, affects planktonic food webs and the productivity of the Northeast U.S. Continental Shelf ecosystem. Gas tracers, such as O2/Ar ratios and triple oxygen isotopes, are used to quantify productivity in the form of Net Community Production (NCP) and Gross Oxygen Production (GOP), respectively. NCP represents the total amount of photosynthesis minus community respiration, whereas GOP is the total amount of oxygen produced from photosynthesis. Summer and winter data from eight NES-LTER cruises between 2018-2021 enables the analysis of spatial heterogeneity and small-scale variability in productivity rates on seasonal and annual timescales . Data reveals that NCP rates are highest at mid-shelf latitudes and are smaller than expected in coastal nearshore waters of the NES. We examine temperature, salinity, transport of deeper slope waters, benthic respiration consuming oxygen, phytoplankton community structure, GOP rates, and nutrient availability to better understand cross-shelf variability in NCP. We find that, in winter, respiration from the benthic component is likely to have lowered NCP in nearshore waters, resulting in the observed peaks at mid-shelf latitudes. In summer, patterns of NCP closely follow phytoplankton biovolume, suggesting that the mid-shelf peak in NCP is related to changes in phytoplankton community abundance or structure.