Toward a quantitative and empirical dissolved organic carbon budget for the Gulf of Maine, a semienclosed shelf sea

Abstract

A time series of organic carbon export from Gulf of Maine (GoM) watersheds was compared to a time series of biological, chemical, bio-optical, and hydrographic properties, measured across the GoM between Yarmouth, NS, Canada, and Portland, ME, U.S. Optical proxies were used to quantify the dissolved organic carbon (DOC) and particulate organic carbon in the GoM. The Load Estimator regression model applied to river discharge data demonstrated that riverine DOC export (and its decadal variance) has increased over the last 80 years. Several extraordinarily wet years (2006)(2007)(2008)(2009)(2010) resulted in a massive pulse of chromophoric dissolved organic matter (CDOM; proxy for DOC) into the western GoM along with unidentified optically scattering material (<0.2 μm diameter). A survey of DOC in the GoM and Scotian Shelf showed the strong influence of the Gulf of Saint Lawrence on the DOC that enters the GoM. A deep plume of CDOM-rich water was observed near the coast of Maine which decreased in concentration eastward. The Forel-Ule color scale was derived and compared to the same measurements made in 1912-1913 by Henry Bigelow. Results show that the GoM has yellowed in the last century, particularly in the region of the extension of the Eastern Maine Coastal Current. Time lags between DOC discharge and its appearance in the GoM increased with distance from the river mouths. Algae were also a significant source of DOC but not CDOM. Gulf-wide algal primary production has decreased. Increases in precipitation and DOC discharge to the GoM are predicted over the next century.

Microbial Community Response to Terrestrially Derived Dissolved Organic Matter in the Coastal Arctic

“…Several studies suggest that increased freshwater discharge will cause an overall reduction in coastal production (e.g., Balch et al, 2012, 2016; Wikner and Andersson, 2012); however, the present experiment provides evidence that some late season Arctic phytoplankton may benefit from tDOM additions through regenerated nutrients. No such benefit was observed in spring when light levels are low.…”

It’s about time: A synthesis of changing phenology in the Gulf of Maine ecosystem

“…Shifts and variability in the timing of physical events such as seasonal transitions, onset of water column stratification, or seasonal delivery of freshwater, nutrients, and DOC, can have cascading non‐linear and episodic effects on the timing of various coastal processes including ocean surface transparency, phytoplankton productivity (Balch et al, ; Gobler et al, ), episodic hypoxia (Diaz & Rosenberg, ), and acidification (Bauer et al, ; Gledhill et al, ). Projected decreases in DOC export during spring and summer (Huntington et al, ) could influence stream metabolism by reducing labile carbon for heterotrophic bacterial respiration in benthic and pelagic environments (Meyer, Tate, Edwards, & Crocker, ; Volk, Volk, & Kaplan, ).…”

Upper Ocean Cooling in a Coupled Climate Model Due to Light Attenuation by Yellowing Materials

“…The spectral absorption coefficient for these materials from 200 to 700 nm is greatest in the ultraviolet and blue wavelengths, decaying exponentially with increasing wavelength to near zero in the red (Bricaud et al, 1981). Moreover, their abundance in the coastal ocean has been increasing in recent decades as changing precipitation delivers more terrestrial organic material to coastal oceans (e.g., Balch et al, 2016, in the Gulf of Maine). Moreover, their abundance in the coastal ocean has been increasing in recent decades as changing precipitation delivers more terrestrial organic material to coastal oceans (e.g., Balch et al, 2016, in the Gulf of Maine).…”