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2013
Andersson, AJ, Krug LA, Bates NR, Doney SC.  2013.  Sea-air CO2 flux in the North Atlantic subtropical gyre: Role and influence of Sub-Tropical Mode Water formation. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 91:57-70.   10.1016/j.dsr2.2013.02.022   AbstractWebsite

The uptake of atmospheric carbon dioxide (CO2) into the mid-latitudes of the North Atlantic Ocean through the production of wintertime Sub-Tropical Mode Water (STMW) also known as Eighteen Degree Water (EDW) is poorly quantified and constrained. Nonetheless, it has been proposed that the EDW could serve as an important short-term sink of anthropogenic CO2. The objective of the present investigation was to determine sea-air CO2 gas exchange rates and seawater CO2 dynamics during wintertime formation of EDW in the North Atlantic Ocean. During 2006 and 2007, several research cruises were undertaken as part of the CLIMODE project across the northwest Atlantic Ocean with the intent to study the pre-conditioning, formation, and the evolution of EDW. Sea-air CO2 exchange rates were calculated based on measurements of atmospheric pCO(2), surface seawater pCO(2) and wind speed with positive values denoting a net flux from the surface ocean to the atmosphere. Average sea-air CO2 flux calculated along cruise tracks in the formation region equaled -18 +/- 6 mmol CO2 m(-2) d(-1) and -14 +/- 9 mmol CO2 m(-2) d(-1) in January of 2006 and March of 2007, respectively. Average sea-air CO2 flux in newly formed outcropping EDW in February and March of 2007 equaled -28 +/- 10 mmol CO2 m(-2) d(-1). These estimates exceeded previous flux estimates in this region by 40-185%. The magnitude of CO2 flux was mainly controlled by the observed variability in wind speed and Delta pCO(2) with smaller changes owing to variability in sea surface temperature. Small but statistically significant difference (4.1 +/- 2.6 mu mol kg(-1)) in dissolved inorganic carbon (DIC) was observed in two occurrences of newly formed EDW in February and March of 2007. This difference was explained either by differences in the relative contribution from different water masses involved in the initial formation process of EDW or temporal changes owing to sea-air CO2 exchange (similar to 25%) and vertical and/or lateral mixing (similar to 75%) with water masses high in DIC from the cold side of the Gulf Stream and/or from below the permanent thermocline. Based on the present estimate of sea-air CO2 flux in newly formed EDW and a formation rate of 9.3 Sv y (Sverdrup year = 10(6) m(3) s(-1) flow sustained for 1 year), CO2 uptake by newly formed EDW may constitute 3-6% of the total North Atlantic CO2 sink. However, advection of surface waters that carry an elevated burden of anthropogenic CO2 that are transported to the formation region and transformed to mode water may contribute additional CO2 to the total net uptake and sequestration of anthropogenic CO2 to the ocean interior. (c) 2013 Elsevier Ltd. All rights reserved.

2011
Lerman, A, Guidry M, Andersson AJ, Mackenzie FT.  2011.  Coastal Ocean Last Glacial Maximum to 2100 CO(2)-Carbonic Acid-Carbonate System: A Modeling Approach. Aquatic Geochemistry. 17:749-773.   10.1007/s10498-011-9146-z   AbstractWebsite

Using coupled terrestrial and coastal zone models, we investigated the impacts of deglaciation and anthropogenic inputs on the CO(2)-H(2)O-CaCO(3) system in global coastal ocean waters from the Last Glacial Maximum (LGM: 18,000 year BP) to the year 2100. With rising sea level and atmospheric CO(2), the carbonate system of coastal ocean water changed significantly. We find that 6 x 10(12) metric tons of carbon were emitted from the coastal ocean, growing due to the sea level rise, from the LGM to late preindustrial time (1700 AD) because of net heterotrophy and calcification processes. This carbon came to reside in the atmosphere and in the growing vegetation on land and in uptake of atmospheric CO(2) through the weathering of rocks on land. It appears that carbonate accumulation, mainly, but not exclusively, in coral reefs from the LGM to late preindustrial time could account for about 24 ppmv of the 100 ppmv rise in atmospheric CO(2), lending some support to the "coral reef hypothesis". In addition, the global coastal ocean is now, or soon will be, a sink of atmospheric CO(2). The temperature rise of 4-5A degrees C since the LGM led to increased weathering rates of inorganic and organic materials on land and enhanced riverine fluxes of total C, N, and P to the coastal ocean of 68%, 108%, and 97%, respectively, from the LGM to late preindustrial time. During the Anthropocene, these trends have been exacerbated owing to rising atmospheric CO(2), due to fossil fuel combustion and land-use practices, other human activities, and rising global temperatures. River fluxes of total reactive C, N, and P are projected to increase from late preindustrial time to the year 2100 by 150%, 380%, and 257%, respectively, modifying significantly the behavior of these element cycles in the coastal ocean, particularly in proximal environments. Despite the fact that the global shoal water carbonate mass has grown extensively since the LGM, the pH(T) (pH values on the total proton scale) of global coastal waters has decreased from similar to 8.35 to similar to 8.18 and the carbonate ion concentration declined by similar to 19% from the LGM to late preindustrial time. The latter represents a rate of decline of about 0.028 mu mol CO(3) (2-) per decade. In comparison, the decrease in coastal water pH(T) from the year 1900 to 2000 was about 8.18-8.08 and is projected to decrease further from about 8.08 to 7.85 between 2000 and 2100, according to the IS92a business-as-usual scenario of CO(2) emissions. Over these 200 years, the carbonate ion concentration will fall by similar to 120 mu mol kg(-1) or 6 mu mol kg(-1) per decade. This decadal rate of decline of the carbonate ion concentration in the Anthropocene is 214 times the average rate of decline for the entire Holocene. Hence, when viewed against the millennial to several millennial timescale of geologic change in the coastal ocean marine carbon system, one can easily appreciate why ocean acidification is the "other CO(2) problem".