Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation

Abstract

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr−1). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr−1) is considerable and represents almost a third of the atmospheric CO2 uptake in the region.

Dissolved Organic Nitrogen Production and Export by Meridional Overturning in the Eastern Subpolar North Atlantic

“…This transit time sets the upper limit for the age of the DON produced in the eSPNA at <3 years. This is consistent with several previous studies reporting important remineralization of DOM in the deep North Atlantic Ocean between polar and tropical latitudes (Carlson et al, 2010;Fontela et al, 2016;Hansell et al, 2012). The transit time is thus too short for the locally produced semirefractory DON to fully decay before being exported.…”

“…Previous studies addressing the role of DOM in the biological carbon pump quantified either the contribution of DOC to net organic carbon export from the photic layer (Romera-Castillo et al, 2016;Roshan & DeVries, 2017) or to oxygen consumption in the dark ocean (Arístegui et al, 2002;Carlson et al, 2010;Fontela et al, 2016). All these studies found a consistent contribution of 17-40% of DOC to the carbon export from the surface or the respiration in the deep ocean.…”

“…Subsequent to this Red (upper) and blue (lower) arrows and numbers represent the circulation in the density levels corresponding to the upper and lower limbs of the Atlantic Meridional Overturning Circulation, limited by the 1 = 32.15-kg/m 3 isopycnal. export, removal of the semirefractory fraction of this DOM has been documented in the deep North Atlantic Ocean (Carlson et al, 2010;Hansell et al, 2012;Fontela et al, 2016). DSOW and ISOW are the Denmark Strait and Iceland Strait overflows.…”

“…NAC, IC, and EGC represent the North Atlantic, Iceland, and East Greenland Currents. However, these studies did not discuss the role of the SPNA as a source or sink of DOM (Carlson et al, 2010;Hansell et al, 2012), or they considered that the DOM imported from the thermocline waters of subtropical origin does not suffer significant biogeochemical transformations in the SPNA and it is only passively transported to the deep ocean by the MOC (Fontela et al, 2016). R.R.…”

Understanding the predictability of the Arctic climate

“…This can reduce northward heat transfer, which might counter the warming to some extent, but can cause more warming in other parts of the world (ACIA, 2004). Also, the carbon uptake of the ocean can decrease due to a decreasing AMOC, resulting in higher carbon dioxide levels in the atmosphere (Fontela et al 2016). …”