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Variability in the ocean carbon sink: Drivers and challenges to detection of change

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Wednesday, 29 November 2017, 2:00

Wednesday, November 29, 2017. 2:00PM. Variability in the ocean carbon sink: Drivers and challenges to detection of change. Galen A. McKinley, Lamont Doherty Earth Observatory of Columbia University. Sponsored by Geophysical Fluid Dynamics Laboratory. More information here.


Cumulatively since preindustrial times, the ocean has absorbed 41% of all fossil fuel emissions; the remaining emissions have almost entirely remained in the atmosphere. Variability in the ocean carbon sink is substantial and poorly understood. Improved understanding of the driving physical and biogeochemical mechanisms is critical, and has increasingly important international policy implications. In this talk, I will present three studies using models and observations that elucidate the drivers and consequences of this variability. First, using a North Atlantic regional model, we show that decadal timescale circulation changes associated with the Atlantic Multidecadal Oscillation (AMO) have significant impacts on the natural component of surface ocean pCO2. With positive AMO, a slowing subpolar gyre and associated reduced mixed layer depths leads to more carbon being retained at depth. AMO-related warming only partially compensates by increasing pCO2. Second, we address the degree to which the biological pump may be a first-order driver of CO2 flux variability. Using co-located observations of surface ocean pCO2 and satellite chlorophyll, our global analysis supports the long-held assumption that the carbon cycle is most strongly driven by the biological pump at high latitudes, particularly in the Southern Ocean. Third, we note that detection of expected long-term growth in the ocean carbon sink will require filtering out variability. Large ensemble climate model simulations indicate that the forced trend in carbon uptake should be largest, and thus most quickly detectable, in the high latitudes. Surface ocean pCO2 observations over the past 35 years indicate a pattern consistent with this prediction in the North Pacific; but elsewhere, variability continues to be the dominant signal.

 

Location  NOAA GFDL, Smagorinsky Seminar Room, Princeton, NJ.