Enhancement of rates of net community production and gross primary production at the shelfbreak front

Frannie Adams1, Alice Choe2, Erin Kim1, Lumi Kinjo3, Arshia Mehta1, Zoe Sandwith4, Dennis Joseph McGillicuddy Jr5 and Rachel Stanley1, (1)Wellesley College, Wellesley, MA, United States, (2)Wellesley College, Wellesley, United States, (3)Wellesley College, Chemistry, Wellesley, United States, (4)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (5)Woods Hole Oeanographic Institution, Woods Hole, MA, United States
Abstract:
Upwelling associated with the shelfbreak front can bring nutrient-rich water to the
surface, potentially enhancing biological productivity. However, observational and modeling
studies over the past decade have shown mixed results as to whether shelfbreak fronts truly
increase biomass; in particular, a mean enhancement of chlorophyll is not observed despite
local enhancements being measured. The Shelfbreak Productivity Interdisciplinary Research
Operation at the Pioneer Array (SPIROPA) Project carried out three research cruises designed
to address the issue of whether there is indeed a mean enhancement of productivity at the
shelfbreak front and which conditions promote such an enhancement. Here, we present rates of
net community production (NCP, photosynthesis minus community respiration) and gross
primary production (GPP, total photosynthesis rate) measured as part of SPIROPA on the
continental shelf and shelfbreak of the Middle Atlantic Bight during two springs (2018 and 2019)
and one summer (2019). In particular, oxygen-argon ratios, as measured by a shipboard
equilibrator inlet mass spectrometer, are used to quantify the rate of NCP in the surface ocean
at kilometer-scale resolution. Triple oxygen isotopes are used to quantify the rate of GPP. The
NCP/GPP ratio is a measure of carbon cycling efficiency. We found enhancement of rates of
productivity at the front in many conditions. Additionally, we saw a tight coherence between
changes in sea surface temperature and changes in NCP, suggesting physical controls on
upper ocean biogeochemistry.