Project Funding: 2017 - 2020

NRA: 2016 NASA: Carbon Cycle Science   

Funded by NASA

Abstract:
Carbon cycling within coastal continental margins is fundamentally important to the global carbon cycle. Coastal oceans contribute about 1/3 of the total marine productivity across the globe (or ~ 16 Pg (1Pg =1E15g)). They receive ~1Pg from terrestrial discharge via rivers. They contribute about half of the total global ocean new production (3.6Pg). These are big numbers—yet we still do not know whether coastal margins are net sources or sinks for carbon. There are four components of the carbon cycle—particulate organic carbon (POC), particulate inorganic carbon (PIC), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC). The first three carbon fractions (POC, PIC, and DOC) can be estimated using optical proxies while the fourth (DIC, associated with ocean acidification) is best measured chemically. There are few coastal time series that assess all of these components. This proposal is a successor proposal for the Gulf of Maine North Atlantic Time Series (GNATS), an 18-year transect time series across the Gulf of Maine (GoM) using ferries, small research vessels, and gliders to measure all four parts of the carbon cycle. During several anomalously wet years, GNATS documented some fundamental shifts in the GoM such as significant drops in primary production (associated with POC and PIC production) and the appearance of unexpected highly scattering particles <0.2um diameter (hence DOC), well out to sea. We have also observed winter DIC concentrations across the GoM, low enough that the entire GoM can show low aragonite saturation values < 1.6—levels that are known to be inhibitory to calcification by certain marine organisms. Here we are proposing to (a) continue the GNATS for three years with eight cruises per year (six aboard a commercial ferry and two aboard a small research vessel) focusing on the four parts of the GoM carbon cycle, (b) further validate satellite ocean-color sensors for radiance and other products in this complex optical environment, (c) make GNATS into an experimental observatory by testing a range of hypotheses on changing productivity and the source of submicron scattering particles, (d) construct carbon cycle models of the GoM based on biogeochemical fluxes and allometric scaling—performing model intercomparison and hypothesis testing using the models, and (e) continue a collaboration in which we are deploying an above-water LIDAR (light detection and ranging) from the GNATS, assessing the LIDAR’s ability to profile optical properties deeper than one optical depth. We include previous results demonstrating that we can track water masses using temperature and salinity, then document co-varying changes in POC (based on an optical proxy to particle backscattering), oxygen, and chlorophyll in these water masses; these allow the estimation of net primary production (NPP) and net community production. We also show how allometric scaling models can contribute to these estimations. We are requesting funds to upgrade one of our Slocum gliders to carry a SUNA nitrate sensor that will allow us to more accurately estimate nitrate depletion and NPP. These glider results will allow us to better discern and quantify whether the GoM is a net source or sink for carbon. Along with a whole host of environmental variables, GNATS provides critical insights about the major processes affecting all aspects of the carbon cycle in thistemperate coastal region: changes in productivity, hydrography, phytoplankton functional groups, land–sea carbon transport caused by major riverine flood events and droughts, plus potential changes due to ocean acidification. Such results will provide insights to other temperate coastal zones around the globe. Simply put, a sustained, combined measurement and modeling approach, such as the kind we are proposing here, is the optimal way for NASA to predict changes to all four parts of the marine carbon cycle as a function of long-term climate change in this complex coastal zone.

Publications:

Balch, W. M., Bowler, B. C., Drapeau, D. T., Lubelczyk, L. C., Lyczkowski, E. 2018. Vertical Distributions of Coccolithophores, PIC, POC, Biogenic Silica, and Chlorophyll a Throughout the Global Ocean. Global Biogeochemical Cycles. 32(1), 2-17. DOI: 10.1002/2016GB005614

Collister, B. L., Zimmerman, R. C., Sukenik, C. I., Hill, V. J., Balch, W. M. 2018. Remote sensing of optical characteristics and particle distributions of the upper ocean using shipboard lidar. Remote Sensing of Environment. 215, 85-96. DOI: 10.1016/j.rse.2018.05.032

Hopkins, J., Balch, W. M. 2018. A New Approach to Estimating Coccolithophore Calcification Rates From Space. Journal of Geophysical Research: Biogeosciences. 123(5), 1447-1459. DOI: 10.1002/2017JG004235

More details may be found in the following project profile(s):

• NASA Ocean Biology & Biogeochemistry (OBB) Project Profile