Climate Variability and Radiocarbon in the CM2Mc Earth System Model

Abstract

The distribution of radiocarbon (14C) in the ocean and atmosphere has fluctuated on time scales ranging from seasons to millennia. It is thought that these fluctuations partly reflect variability in the climate system, offering a rich potential source of information to help understand mechanisms of past climate change. Here, a long simulation with a new, coupled model is used to explore the mechanisms that redistribute 14C within the earth system on interannual to centennial time scales. The model, the Geophysical Fluid Dynamics Laboratory Climate Model version 2 (GFDL CM2) with Modular Ocean Model version 4p1(MOM4p1) at coarse-resolution (CM2Mc), is a lower-resolution version of the Geophysical Fluid Dynamics Laboratory’s CM2M model, uses no flux adjustments, and is run here with a simple prognostic ocean biogeochemistry model including 14C. The atmospheric 14C and radiative boundary conditions are held constant so that the oceanic distribution of 14C is only a function of internal climate variability. The simulation displays previously described relationships between tropical sea surface 14C and the model equivalents of the El Niño–Southern Oscillation and Indonesian Throughflow. Sea surface 14C variability also arises from fluctuations in the circulations of the subarctic Pacific and Southern Ocean, including North Pacific decadal variability and episodic ventilation events in the Weddell Sea that are reminiscent of the Weddell Polynya of 1974–76. Interannual variability in the air–sea balance of 14C is dominated by exchange within the belt of intense “Southern Westerly” winds, rather than at the convective locations where the surface 14C is most variable. Despite significant interannual variability, the simulated impact on air–sea exchange is an order of magnitude smaller than the recorded atmospheric 14C variability of the past millennium. This result partly reflects the importance of variability in the production rate of 14C in determining atmospheric 14C but may also reflect an underestimate of natural climate variability, particularly in the Southern Westerly winds.

Data-based estimates of the ocean carbon sink variability – first results of the Surface Ocean <i>p</i>CO<sub>2</sub> Mapping intercomparison (SOCOM)

“…For MOM4p1-BLING the underlying physical model is GFDL's Modular Ocean Model version 4.1 (Griffies et al, 2004) with 3 • horizontal resolution. The biogeochemical model is Biology Light Nutrient and Gas (BLING; Galbraith et al, 2011). The model was forced at the surface with several reanalysis products, including CORE-II (Large and Yeager, 2009), ERA-40 (Uppala et al, 2005), and NCEP-1 (Kalnay et al, 1996).…”

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

“…The global climate model (GCM) used in this study is CM2Mc, the Geophysical Fluid Dynamics Laboratory's Climate Model version 2 but at lower resolution (3 • ), described in more detail by Galbraith et al (2011) and modified as described by Galbraith and de Lavergne (2018). This includes the Modular Ocean Model version 5, a sea ice module, static land, and static ice sheets, and a module of Biogeochemistry with Light, Iron, Nutrients and Gases (BLINGv1.5; Galbraith et al, 2010).…”

A general framework for aquatic biogeochemical models

“…The setup is based upon the MOM_SIS_BLING test case supplied with MOM5. This is a sea ice/ocean-only version of the coupled climate model CM2Mc (Galbraith et al, 2011), which in turn is a coarse-resolution version of the 1 CM2M earth system model (Delworth et al, 2006) used for the IPCC Fifth Assessment Report (AR5). The MOM_SIS_BLING setup has a nominal resolution of 3 and uses 28 depth levels.…”

“…Coupled hydrodynamic-biogeochemical models are a key tool for analysing and predicting the biogeochemistry and ecology of lakes (Jørgensen, 2010), estuaries (Kim and Khangaonkar, 2012;Robson et al, 2008), shelf seas (Edwards et al, 2012), and oceans (Aumont and Bopp, 2006), and they are an important component of earth system models that describe past, present and future climate (Galbraith et al, 2011;Ridgwell et al, 2007). As coupled models describe many physical, chemical, biological and geological processes, they tend to be interdisciplinary efforts in which individual scientists bring in submodels specifically related to their expertise.…”