scholarly journals Warm ocean processes and carbon cycling in the Eocene

2013 ◽  
Vol 371 (2001) ◽  
pp. 20130099 ◽  
Author(s):  
Eleanor H. John ◽  
Paul N. Pearson ◽  
Helen K. Coxall ◽  
Heather Birch ◽  
Bridget S. Wade ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Column ◽  
Carbon Isotope ◽  
General Circulation ◽  
Middle Eocene ◽  
General Circulation Models ◽  
Individual Species ◽  
Elevated Water ◽  
Burial Rates ◽  
Using Data

Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.5–33.7 Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.

scholarly journals A new method for evaluating the impact of vertical distribution on aerosol radiative forcing in general circulation models

2013 ◽  
Vol 13 (7) ◽  
pp. 18809-18853
Author(s):  
M. R. Vuolo ◽  
M. Schulz ◽  
Y. Balkanski ◽  
T. Takemura
Keyword(s):  
Vertical Distribution ◽  
Radiative Forcing ◽  
General Circulation ◽  
Cloud Amount ◽  
General Circulation Models ◽  
Individual Species ◽  
Clear Sky ◽  
Atmospheric Column ◽  
Aerosol Forcing ◽  
The Impact

Abstract. The quantification and understanding of direct aerosol forcing is essential in the study of climate. One of the main issues that makes its quantification difficult is the lack of a complete comprehension of the role of the aerosol and clouds vertical distribution. This work aims at reducing the incertitude of aerosol forcing due to the vertical superposition of several short-lived atmospheric components, in particular different aerosols species and clouds. We propose a method to quantify the contribution of different parts of the atmospheric column to the forcing, and to evaluate model differences by isolating the effect of radiative interactions only. Any microphysical or thermo-dynamical interactions between aerosols and clouds are deactivated in the model, to isolate the effects of radiative flux coupling. We investigate the contribution of aerosol above, below and in clouds, by using added diagnostics in the aerosol-climate model LMDz. We also compute the difference between the forcing of the ensemble of the aerosols and the sum of the forcings from individual species, in clear-sky. This difference is found to be moderate on global average (14%) but can reach high values regionally (up to 100%). The non-additivity of forcing already for clear-sky conditions shows, that in addition to represent well the amount of individual aerosol species, it is critical to capture the vertical distribution of all aerosols. Nonlinear effects are even more important when superposing aerosols and clouds. Four forcing computations are performed, one where the full aerosol 3-D distribution is used, and then three where aerosols are confined to regions above, inside and below clouds respectively. We find that the forcing of aerosols depends crucially on the presence of clouds and on their position relative to that of the aerosol, in particular for black carbon (BC). We observe a strong enhancement of the forcing of BC above clouds, attenuation for BC below clouds, and a moderate enhancement when BC is found within clouds. BC forcing efficiency amounts to 44, 171, 333 and 178 W m-2 per unit optical depth for BC below, within, above clouds and for the 3-D BC distribution, respectively. The different behaviour of forcing nonlinearities for these three components of the atmospheric column suggests that, an important reason for differences between cloudy-sky aerosol forcings from different models may come from different aerosol and clouds vertical distributions. Our method allows to evaluate the contribution to model differences due to aerosol and clouds radiative interactions only, by reading 3-D aerosol and cloud fields from different GCMs, into the same model. This method avoids differences in calculating optical aerosol properties and forcing to enter into the discussion of inter-model differences. It appears that the above and in-cloud amount of BC is larger for SPRINTARS (190 compared to 179), increasing its cloudy-sky forcing efficiency with respect to LMDz, being thus potentially an important factor for inter-model differences.

scholarly journals Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

2009 ◽  
Vol 5 (5) ◽  
pp. 2115-2156 ◽  
Author(s):  
M. Widmann ◽  
H. Goosse ◽  
G. van der Schrier ◽  
R. Schnur ◽  
J. Barkmeijer
Keyword(s):  
Data Assimilation ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Weather Forecasting ◽  
General Circulation Models ◽  
Last Millennium ◽  
Proxy Data ◽  
Using Data

Abstract. Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode.

Characterization and degradation process of sludge profiles inside a facultative pond (Patagonia, Argentina)

2011 ◽  
Vol 64 (11) ◽  
pp. 2239-2245 ◽  
Author(s):  
M. Faleschini ◽  
J. L. Esteves
Keyword(s):  
Organic Matter ◽  
Surface Layer ◽  
Water Column ◽  
Phytoplankton Bloom ◽  
Degradation Process ◽  
Core Sample ◽  
Temperate Climate ◽  
Sediment Layer ◽  
Organic Matter Concentration ◽  
Elevated Water

To investigate the characteristics and degradation process in sludge profile, three sampling sessions were made in three different places inside the primary facultative pond of Puerto Madryn city, which was located in a region with a temperate climate in coastal Patagonia (Argentina). The sludge showed an extremely negative redox potential (between −441 and −282 mV) and elevated water content and organic matter concentration, ranging from 83.3 to 97.1% for porosity and from 22.5 to 64.4% for organic matter. The surface layer at the Outlet station during the summer showed the greatest concentration of pigments, reaching a maximum value of 10.6 mg/g for chlorophyll-a and 40.9 mg/g for phaeophytin, and a fast diminution with sediment depth. The important concentration of pigment in the surface layer, coincident with phytoplankton bloom in the water column, could support the importance of nitrogen removal via uptake and organic sedimentation in the water column. In warm months the degradation rate was clear, as reflected in a decrease in sediment layer, and even part of the clay bottom was captured inside an 8 cm core sample, registering extremely low concentrations of pigments, carbohydrates, proteins and lipids. The season and the degree of treatment have an influence on sludge characteristics and the organic matter degradation process.

scholarly journals Beyond the Fe-P-redox connection: preferential regeneration of phosphorus from organic matter as a key control on Baltic Sea nutrient cycles

2011 ◽  
Vol 8 (6) ◽  
pp. 1699-1720 ◽  
Author(s):  
T. Jilbert ◽  
C. P. Slomp ◽  
B. G. Gustafsson ◽  
W. Boer
Keyword(s):  
Organic Matter ◽  
Baltic Sea ◽  
Water Column ◽  
Water Depth ◽  
P Availability ◽  
Biogeochemical Models ◽  
Reducing Conditions ◽  
Basin Scale ◽  
Burial Rates ◽  
The Baltic

Abstract. Patterns of regeneration and burial of phosphorus (P) in the Baltic Sea are strongly dependent on redox conditions. Redox varies spatially along water depth gradients and temporally in response to the seasonal cycle and multidecadal hydrographic variability. Alongside the well-documented link between iron oxyhydroxide dissolution and release of P from Baltic Sea sediments, we show that preferential remineralization of P with respect to carbon (C) and nitrogen (N) during degradation of organic matter plays a key role in determining the surplus of bioavailable P in the water column. Preferential remineralization of P takes place both in the water column and upper sediments and its rate is shown to be redox-dependent, increasing as reducing conditions become more severe at greater water-depth in the deep basins. Existing Redfield-based biogeochemical models of the Baltic may therefore underestimate the imbalance between N and P availability for primary production, and hence the vulnerability of the Baltic to sustained eutrophication via the fixation of atmospheric N. However, burial of organic P is also shown to increase during multidecadal intervals of expanded hypoxia, due to higher net burial rates of organic matter around the margins of the deep basins. Such intervals may be characterized by basin-scale acceleration of all fluxes within the P cycle, including productivity, regeneration and burial, sustained by the relative accessibility of the water column P pool beneath a shallow halocline.

scholarly journals Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

2010 ◽  
Vol 6 (5) ◽  
pp. 627-644 ◽  
Author(s):  
M. Widmann ◽  
H. Goosse ◽  
G. van der Schrier ◽  
R. Schnur ◽  
J. Barkmeijer
Keyword(s):  
Data Assimilation ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Weather Forecasting ◽  
General Circulation Models ◽  
Last Millennium ◽  
Proxy Data ◽  
Using Data

Abstract. Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode.

scholarly journals A data-driven multi-cloud model for stochastic parametrization of deep convection

2013 ◽  
Vol 371 (1991) ◽  
pp. 20120374 ◽  
Author(s):  
J. Dorrestijn ◽  
D. T. Crommelin ◽  
J. A. Biello ◽  
S. J. Böing
Keyword(s):  
Markov Chains ◽  
General Circulation ◽  
Large Scale ◽  
Cloud Model ◽  
Deep Convection ◽  
General Circulation Models ◽  
Data Driven ◽  
Persistent Problem ◽  
Spatial Coupling ◽  
Using Data

Stochastic subgrid models have been proposed to capture the missing variability and correct systematic medium-term errors in general circulation models. In particular, the poor representation of subgrid-scale deep convection is a persistent problem that stochastic parametrizations are attempting to correct. In this paper, we construct such a subgrid model using data derived from large-eddy simulations (LESs) of deep convection. We use a data-driven stochastic parametrization methodology to construct a stochastic model describing a finite number of cloud states. Our model emulates, in a computationally inexpensive manner, the deep convection-resolving LES. Transitions between the cloud states are modelled with Markov chains. By conditioning the Markov chains on large-scale variables, we obtain a conditional Markov chain, which reproduces the time evolution of the cloud fractions. Furthermore, we show that the variability and spatial distribution of cloud types produced by the Markov chains become more faithful to the LES data when local spatial coupling is introduced in the subgrid Markov chains. Such spatially coupled Markov chains are equivalent to stochastic cellular automata.

scholarly journals Variable C : N : P stoichiometry of dissolved organic matter cycling in the Community Earth System Model

2014 ◽  
Vol 11 (6) ◽  
pp. 9071-9101 ◽  
Author(s):  
R. T. Letscher ◽  
J. K. Moore ◽  
Y.-C. Teng ◽  
F. Primeau
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
General Circulation ◽  
General Circulation Models ◽  
Ocean Model ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Organic C ◽  
Community Earth System Model

Abstract. Dissolved organic matter (DOM) plays an important role in the ocean's biological carbon pump by providing an advective/mixing pathway for ~ 20% of export production. DOM is known to have a stoichiometry depleted in nitrogen (N) and phosphorus (P) compared to the particulate organic matter pool, a~fact that is often omitted from biogeochemical-ocean general circulation models. However the variable C : N : P stoichiometry of DOM becomes important when quantifying carbon export from the upper ocean and linking the nutrient cycles of N and P with that of carbon. Here we utilize recent advances in DOM observational data coverage and offline tracer-modeling techniques to objectively constrain the variable production and remineralization rates of the DOM C / N / P pools in a simple biogeochemical-ocean model of DOM cycling. The optimized DOM cycling parameters are then incorporated within the Biogeochemical Elemental Cycling (BEC) component of the Community Earth System Model and validated against the compilation of marine DOM observations. The optimized BEC simulation including variable DOM C : N : P cycling was found to better reproduce the observed DOM spatial gradients than simulations that used the canonical Redfield ratio. Global annual average export of dissolved organic C, N, and P below 100 m was found to be 2.28 Pg C yr−1 (143 Tmol C yr−1), 16.4 Tmol N yr−1, and 1 Tmol P yr−1, respectively with an average export C : N : P stoichiometry of 225 : 19 : 1 for the semilabile (degradable) DOM pool. DOC export contributed ~ 25% of the combined organic C export to depths greater than 100 m.

scholarly journals Wave–turbulence interaction-induced vertical mixing and its effects in ocean and climate models

2016 ◽  
Vol 374 (2065) ◽  
pp. 20150201 ◽  
Author(s):  
Fangli Qiao ◽  
Yeli Yuan ◽  
Jia Deng ◽  
Dejun Dai ◽  
Zhenya Song
Keyword(s):  
Water Column ◽  
Ocean Circulation ◽  
General Circulation ◽  
Climate Models ◽  
Theoretical Calculations ◽  
Critical Role ◽  
Vertical Mixing ◽  
General Circulation Models ◽  
Wave Turbulence ◽  
Coupled Models

Heated from above, the oceans are stably stratified. Therefore, the performance of general ocean circulation models and climate studies through coupled atmosphere–ocean models depends critically on vertical mixing of energy and momentum in the water column. Many of the traditional general circulation models are based on total kinetic energy (TKE), in which the roles of waves are averaged out. Although theoretical calculations suggest that waves could greatly enhance coexisting turbulence, no field measurements on turbulence have ever validated this mechanism directly. To address this problem, a specially designed field experiment has been conducted. The experimental results indicate that the wave–turbulence interaction-induced enhancement of the background turbulence is indeed the predominant mechanism for turbulence generation and enhancement. Based on this understanding, we propose a new parametrization for vertical mixing as an additive part to the traditional TKE approach. This new result reconfirmed the past theoretical model that had been tested and validated in numerical model experiments and field observations. It firmly establishes the critical role of wave–turbulence interaction effects in both general ocean circulation models and atmosphere–ocean coupled models, which could greatly improve the understanding of the sea surface temperature and water column properties distributions, and hence model-based climate forecasting capability.

Effective Radius of Ice Cloud Particle Populations Derived from Aircraft Probes

2006 ◽  
Vol 23 (3) ◽  
pp. 361-380 ◽  
Author(s):  
Andrew J. Heymsfield ◽  
Carl Schmitt ◽  
Aaron Bansemer ◽  
Gerd-Jan van Zadelhoff ◽  
Matthew J. McGill ◽  
...  
Keyword(s):  
Water Content ◽  
General Circulation ◽  
General Circulation Models ◽  
Effective Radius ◽  
Radiative Properties ◽  
Regional Study ◽  
Cloud Particle ◽  
Ice Cloud ◽  
Direct Measurements ◽  
Using Data

Abstract The effective radius (re) is a crucial variable in representing the radiative properties of cloud layers in general circulation models. This parameter is proportional to the condensed water content (CWC) divided by the extinction (σ). For ice cloud layers, parameterizations for re have been developed from aircraft in situ measurements 1) indirectly, using data obtained from particle spectrometer probes and assumptions or observations about particle shape and mass to get the ice water content (IWC) and area to get σ, and recently 2) from probes that derive IWC and σ more directly, referred to as the direct approach, even though the extinction is not measured directly. This study compares [IWC/σ] derived from the two methods using datasets acquired from comparable instruments on two aircraft, one sampling clouds at midlevels and the other at upper levels during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) field program in Florida in 2002. A penetration by one of the aircraft into a cold midlatitude orographic wave cloud composed of small particles is further evaluated. The σ and IWC derived by each method are compared and evaluated in different ways for each aircraft dataset. Direct measurements of σ exceed those derived indirectly by a factor of 2–2.5. The IWC probes, relying on ice sublimation, appear to measure accurately except when the IWC is high or the particles too large to sublimate completely during the short transit time through the probe. The IWC estimated from the particle probes are accurate when direct measurements are available to provide constraints and give useful information in high IWC/large particle situations. Because of the discrepancy in σ estimates between the direct and indirect approaches, there is a factor of 2–3 difference in [IWC/σ] between them. Although there are significant uncertainties involved in its use, comparisons with several independent data sources suggest that the indirect method is the more accurate of the two approaches. However, experiments are needed to resolve the source of the discrepancy in σ.

IDF curves for future climate scenarios in a locality of the Tapajós Basin, Amazon, Brazil

2019 ◽  
Vol 11 (3) ◽  
pp. 760-770
Author(s):  
Carlos Eduardo Aguiar de Souza Costa ◽  
Claudio José Cavalcante Blanco ◽  
José Francisco de Oliveira-Júnior
Keyword(s):  
General Circulation ◽  
Climate Changes ◽  
Global Climate ◽  
General Circulation Models ◽  
Future Climate ◽  
Climate Policies ◽  
Rcp 8.5 ◽  
Idf Curves ◽  
Using Data ◽  
The Impact

Abstract Changes in the global climate are attributed to the levels of greenhouse gases. Thus, future scenarios (Representative Concentration Pathways – RCPs) have been developed to explore the impact of different climate policies on the world. The RCPs are essential tools for General Circulation Models (GCMs) to simulate future climate changes. Curves that associate Intensity, Duration and Frequency (IDF) are used in forecasts and are fundamental for the design of hydraulic projects and risk management. The objective of this study was to design IDF curves for the RCP 4.5 and 8.5, using data from the HadGEM2-ES, CanESM2 and MIROC5 models. The Equidistance Quantile Matching Method was used to design the IDF curves. The simulated curves presented differences when related to the existing curve. The largest differences were for the MIROC5 (146% in RCP 8.5) and the smallest differences were for the CanESM2 (−20.83% for RCP 8.5). This result demonstrates that the method incorporates changes in future climate variability. The spatial resolutions of each model influenced their IDF curves, which led the CanESM2 curves to not present satisfactory results that are different from the MIROC5 curves, which were the ones that best represented the possible future differences.

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