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Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used to project future environmental changes. However, their slow adjustment time also hinders effective use of ESMs because of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here, a solution to this spin-up problem based on sequence acceleration, is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a black box fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panel on Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrial models can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improved estimates of metrics such as climate sensitivity, and higher model resolution than currently feasible. 

OSU-UVic Climate Model of Intermediate Complexity with Model of Ocean Biogeochemistry and Isotopes (MOBI2.2). New features in this release include Nathaniel Fillman's carbon and C13 decomposition code and Samar Khatiwala's Pa/Th code. 

Abstract Ocean geochemical tracers such as radiocarbon, protactinium and thorium isotopes, and noble gases are widely used to constrain a range of physical and biogeochemical processes in the ocean. However, their routine simulation in global ocean circulation and climate models is hindered by the computational expense of integrating them to a steady state. Here, a new approach to this long‐standing “spin‐up” problem is introduced to efficiently compute equilibrium distributions of such tracers in seasonally‐forced models. Based on “Anderson Acceleration,” a sequence acceleration technique developed in the 1960s to solve nonlinear integral equations, the new method is entirely “black box” and offers significant speed‐up over conventional direct time integration. Moreover, it requires no preconditioning, ensures tracer conservation and is fully consistent with the numerical time‐stepping scheme of the underlying model. It thus circumvents some of the drawbacks of other schemes such as matrix‐free Newton Krylov that have been proposed to address this problem. An implementation specifically tailored for the batch HPC systems on which ocean and climate models are typically run is described, and the method illustrated by applying it to a variety of geochemical tracer problems. The new method, which provides speed‐ups by over an order of magnitude, should make simulations of such tracers more feasible and enable their inclusion in climate change assessments such as IPCC. 

Gas exchange between the atmosphere and ocean interior profoundly impacts global climate and biogeochemistry. However, our understanding of the relevant physical processes remains limited by a scarcity of direct observations. Dissolved noble gases in the deep ocean are powerful tracers of physical air-sea interaction due to their chemical and biological inertness, yet their isotope ratios have remained underexplored. Here, we present high-precision noble gas isotope and elemental ratios from the deep North Atlantic (~32°N, 64°W) to evaluate gas exchange parameterizations using an ocean circulation model. The unprecedented precision of these data reveal deep-ocean undersaturation of heavy noble gases and isotopes resulting from cooling-driven air-to-sea gas transport associated with deep convection in the northern high latitudes. Our data also imply an underappreciated and large role for bubble-mediated gas exchange in the global air-sea transfer of sparingly soluble gases, including O 2 , N 2 , and SF 6 . Using noble gases to validate the physical representation of air-sea gas exchange in a model also provides a unique opportunity to distinguish physical from biogeochemical signals. As a case study, we compare dissolved N 2 /Ar measurements in the deep North Atlantic to physics-only model predictions, revealing excess N 2 from benthic denitrification in older deep waters (below 2.9 km). These data indicate that the rate of fixed N removal in the deep Northeastern Atlantic is at least three times higher than the global deep-ocean mean, suggesting tight coupling with organic carbon export and raising potential future implications for the marine N cycle. 

Abstract Ocean warming patterns are a primary control on regional sea level rise and transient climate sensitivity. However, controls on these patterns in both observations and models are not fully understood, complicated as they are by their dependence on the “addition” of heat to the ocean’s interior along background ventilation pathways and on the “redistribution” of heat between regions by changing ocean dynamics. While many previous studies attribute heat redistribution to changes in high-latitude processes, here we propose that substantial heat redistribution is explained by the large-scale adjustment of the geostrophic flow to warming within the pycnocline. We explore this hypothesis in the University of Victoria Earth System Model, estimating added heat using the transport matrix method. We find that throughout the midlatitudes, subtropics, and tropics, patterns of added and redistributed heat in the model are strongly anticorrelated (R≈ −0.75). We argue that this occurs because changes in ocean currents, acting across pre-existing temperature gradients, redistribute heat away from regions of strong passive heat convergence. Over broad scales, this advective response can be estimated from changes in upper-ocean density alone using the thermal wind relation and is linked to an adjustment of the subtropical pycnocline. These results highlight a previously unappreciated relationship between added and redistributed heat and emphasize the role that subtropical and midlatitude dynamics play in setting patterns of ocean heat storage. Significance StatementThe point of our study was to better understand the geographic pattern of ocean warming caused by human-driven climate change. Warming patterns are challenging to predict because they are sensitive both to how the ocean absorbs heat from the atmosphere and to how ocean currents change in response to increased emissions. We showed that these processes are not independent of one another: in many regions, changes in ocean currents reduce regional variations in the build-up of new heat absorbed from the atmosphere. This finding may help to constrain future projections of regional ocean warming, which matters because ocean warming patterns have a major influence on regional sea level rise, marine ecosystem degradation, and the rate of atmospheric warming.