scholarly journals Ocean carbon cycling during the past 130,000 years – a pilot study on inverse paleoclimate record modelling

2016 ◽  
Author(s):  
Christoph Heinze ◽  
Babette Hoogakker ◽  
Arne Winguth
Keyword(s):  
Carbon Cycle ◽  
Sediment Core ◽  
Ocean Circulation ◽  
General Circulation ◽  
General Pattern ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Last Glacial ◽  
Modelling Studies ◽  
The Last Glacial

Abstract. What role did changes in marine carbon cycle processes and calcareous organisms play for glacial-interglacial variation in atmospheric pCO2? In order to answer this question, we explore results from an ocean biogeochemical ocean general circulation model. We make an attempt to systematically reconcile model results with time dependent sediment core data from the observations. For this purpose, simulated sensitivities of oceanic tracer concentrations to changes in governing carbon cycle parameters are fitted to measured sediment core data.We assume that the time variation of the governing carbon cycle parameters follows the general pattern of the glacial-interglacial deuterium anomaly. Our analysis provides an independent estimate of a maximum mean sea surface temperature drawdown of about 5 °C and a maximum outgassing of the land biosphere by about 430 PgC at the last glacial maximum as compared to preindustrial times. The overall fit of modelled paleoclimate tracers to observations, however, remains quite weak indicating the potential of more detailed modelling studies for full exploitation of the information as stored in the paleo-climatic archive. It can be confirmed, however, that a decline in ocean temperature and a more efficient biological carbon pump in combination with changes in ocean circulation are the key factors for explaining the glacial CO2 drawdown. The analysis suggests that potential changes in the export rain ratio POC:CaCO3 may not have a substantial imprint on the paleo-climatic archive. The use of the last glacial as an inverted analogue to potential ocean acidification impacts thus may be quite limited. A potential strong decrease in CaCO3 export production could contribute to the glacial CO2 decline in the atmosphere but remains hypothetical.

scholarly journals Ocean carbon cycling during the past 130 000 years – a pilot study on inverse palaeoclimate record modelling

2016 ◽  
Vol 12 (10) ◽  
pp. 1949-1978 ◽  
Author(s):  
Christoph Heinze ◽  
Babette A. A. Hoogakker ◽  
Arne Winguth
Keyword(s):  
Carbon Cycle ◽  
Sediment Core ◽  
Ocean Circulation ◽  
General Circulation ◽  
General Pattern ◽  
Circulation Model ◽  
Core Data ◽  
Last Glacial ◽  
Modelling Studies ◽  
The Last Glacial

Abstract. What role did changes in marine carbon cycle processes and calcareous organisms play in glacial–interglacial variation in atmospheric pCO2? In order to answer this question, we explore results from an ocean biogeochemical general circulation model. We attempt to systematically reconcile model results with time-dependent sediment core data from the observations. For this purpose, we fit simulated sensitivities of oceanic tracer concentrations to changes in governing carbon cycle parameters to measured sediment core data. We assume that the time variation in the governing carbon cycle parameters follows the general pattern of the glacial–interglacial deuterium anomaly. Our analysis provides an independent estimate of a maximum mean sea surface temperature drawdown of about 5 °C and a maximum outgassing of the land biosphere by about 430 Pg C at the Last Glacial Maximum as compared to pre-industrial times. The overall fit of modelled palaeoclimate tracers to observations, however, remains quite weak, indicating the potential of more detailed modelling studies to fully exploit the information stored in the palaeoclimatic archive. This study confirms the hypothesis that a decline in ocean temperature and a more efficient biological carbon pump in combination with changes in ocean circulation are the key factors for explaining the glacial CO2 drawdown. The analysis suggests that potential changes in the export rain ratio POC : CaCO3 may not have a substantial imprint on the palaeoclimatic archive. The use of the last glacial as an inverted analogue to potential ocean acidification impacts thus may be quite limited. A strong decrease in CaCO3 export production could potentially contribute to the glacial CO2 decline in the atmosphere, but this remains hypothetical.

scholarly journals Glacial marine carbon cycle sensitivities to Atlantic ocean circulation reorganization by coupled climate model simulations

2011 ◽  
Vol 7 (2) ◽  
pp. 1261-1299 ◽  
Author(s):  
M. O. Chikamoto ◽  
A. Abe-Ouchi ◽  
A. Oka ◽  
R. Ohgaito ◽  
A. Timmermann
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
General Circulation ◽  
Climate Model ◽  
Dissolved Inorganic Carbon ◽  
Circulation Model ◽  
Vertical Gradient ◽  
Ocean General Circulation Model ◽  
Nutrient Utilization ◽  
Atmospheric Pco2

Abstract. A series of Last Glacial Maximum (LGM) marine carbon cycle sensitivity experiments is conducted to test the effect of different physical processes, as simulated by two atmosphere-ocean general circulation model (AOGCM) experiments, on the atmospheric pCO2. One AOGCM solution exhibits an increase in North Atlantic Deep Water (NADW) formation, whereas the other mimics an increase in Antarctic Bottom Water (AABW) associated with a weaker NADW. Due to enhanced gas solubility associated with lower sea surface temperature, both experiments generate a reduction of atmospheric pCO2 by about 20–23 ppm. However, neither a weakening of NADW nor an increase of AABW formation causes a large atmospheric pCO2 change. A marked enhancement in AABW formation is required to represent the reconstructed vertical gradient of dissolved inorganic carbon (DIC) during LGM conditions. The efficiency of Southern Ocean nutrient utilization reduces in response to an enhanced AABW formation, which counteracts the circulation-induced ocean carbon uptake.

scholarly journals Palaeogeographic controls on climate and proxy interpretation

2016 ◽  
Vol 12 (5) ◽  
pp. 1181-1198 ◽  
Author(s):  
Daniel J. Lunt ◽  
Alex Farnsworth ◽  
Claire Loptson ◽  
Gavin L. Foster ◽  
Paul Markwick ◽  
...  
Keyword(s):  
Global Change ◽  
Carbon Cycle ◽  
Ocean Circulation ◽  
General Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Adjustment Factor ◽  
Climate Signal ◽  
Proxy Records ◽  
Global Mean

Abstract. During the period from approximately 150 to 35 million years ago, the Cretaceous–Paleocene–Eocene (CPE), the Earth was in a “greenhouse” state with little or no ice at either pole. It was also a period of considerable global change, from the warmest periods of the mid-Cretaceous, to the threshold of icehouse conditions at the end of the Eocene. However, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. Here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 General Circulation Model simulations covering this period, one simulation per stratigraphic stage. By maintaining atmospheric CO2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the CPE, and explore the underlying mechanisms. We find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. However, there are significant modelled variations on a regional scale. The stratigraphic stage–stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. We also find some control on global mean temperature from continental area and global mean orography. Our results have important implications for the interpretation of single-site palaeo proxy records. In particular, our results allow the non-CO2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. This “adjustment factor” is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. The adjustment factor is illustrated for seven key sites in the CPE, and applied to proxy data from Falkland Plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the CPE. Ultimately, this will enable isolation of the CO2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to CO2 changes during the CPE. Finally, regions where the adjustment factor is constant throughout the CPE could indicate places where future proxies could be targeted in order to reconstruct the purest CO2-induced temperature change, where the complicating contributions of other processes are minimised. Therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies.

Modelling the ocean circulation beneath the Ross Ice Shelf

2003 ◽  
Vol 15 (1) ◽  
pp. 13-23 ◽  
Author(s):  
DAVID M. HOLLAND ◽  
STANLEY S. JACOBS ◽  
ADRIAN JENKINS
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ross Sea ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Shelf Water ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Shelf Water

We applied a modified version of the Miami isopycnic coordinate ocean general circulation model (MICOM) to the ocean cavity beneath the Ross Ice Shelf to investigate the circulation of ocean waters in the sub-ice shelf cavity, along with the melting and freezing regimes at the base of the ice shelf. Model passive tracers are utilized to highlight the pathways of waters entering and exiting the cavity, and output is compared with data taken in the cavity and along the ice shelf front. High Salinity Shelf Water on the western Ross Sea continental shelf flows into the cavity along the sea floor and is transformed into Ice Shelf Water upon contact with the ice shelf base. Ice Shelf Water flows out of the cavity mainly around 180°, but also further east and on the western side of McMurdo Sound, as observed. Active ventilation of the region near the ice shelf front is forced by seasonal variations in the density structure of the water column to the north, driving rapid melting. Circulation in the more isolated interior is weaker, leading to melting at deeper ice and refreezing beneath shallower ice. Net melting over the whole ice shelf base is lower than other estimates, but is likely to increase as additional forcings are added to the model.

The Effect of a Large Freshwater Perturbation on the Glacial North Atlantic Ocean Using a Coupled General Circulation Model

2006 ◽  
Vol 19 (17) ◽  
pp. 4436-4447 ◽  
Author(s):  
C. D. Hewitt ◽  
A. J. Broccoli ◽  
M. Crucifix ◽  
J. M. Gregory ◽  
J. F. B. Mitchell ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Quasi Equilibrium ◽  
Last Glacial ◽  
Proxy Records ◽  
The North ◽  
The North Atlantic ◽  
The Last Glacial

Abstract The commonly held view of the conditions in the North Atlantic at the last glacial maximum, based on the interpretation of proxy records, is of large-scale cooling compared to today, limited deep convection, and extensive sea ice, all associated with a southward displaced and weakened overturning thermohaline circulation (THC) in the North Atlantic. Not all studies support that view; in particular, the “strength of the overturning circulation” is contentious and is a quantity that is difficult to determine even for the present day. Quasi-equilibrium simulations with coupled climate models forced by glacial boundary conditions have produced differing results, as have inferences made from proxy records. Most studies suggest the weaker circulation, some suggest little or no change, and a few suggest a stronger circulation. Here results are presented from a three-dimensional climate model, the Hadley Centre Coupled Model version 3 (HadCM3), of the coupled atmosphere–ocean–sea ice system suggesting, in a qualitative sense, that these diverging views could all have occurred at different times during the last glacial period, with different modes existing at different times. One mode might have been characterized by an active THC associated with moderate temperatures in the North Atlantic and a modest expanse of sea ice. The other mode, perhaps forced by large inputs of meltwater from the continental ice sheets into the northern North Atlantic, might have been characterized by a sluggish THC associated with very cold conditions around the North Atlantic and a large areal cover of sea ice. The authors’ model simulation of such a mode, forced by a large input of freshwater, bears several of the characteristics of the Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP) Project’s reconstruction of glacial sea surface temperature and sea ice extent.

PMIP-carbon: towards a multi-models comparison of climate-carbon interactions at the Last Glacial Maximum

2020 ◽  
Author(s):  
Nathaelle Bouttes ◽  
Ruza Ivanovic ◽  
Ayako Abe-Ouchi ◽  
Hidetaka Kobayashi ◽  
Laurie Menviel ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Carbon Isotopes ◽  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Ice Cores ◽  
Glacial Maximum ◽  
Last Glacial ◽  
Intercomparison Project ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>More and more climate models now include the carbon cycle, but multi-models studies of climate-carbon simulations within the Climate Model Intercomparison Project (CMIP) are limited to present and future time periods. In addition, the carbon cycle is not considered in the simulations of past periods analysed within the Paleoclimate Modelling Intercomparison Project (PMIP). Yet, climate-carbon interactions are crucial to anticipate future atmospheric CO<sub>2</sub> concentrations and their impact on climate. Such interactions can change depending on the background climate, it is thus necessary to compare model results among themselves and to data for past periods with different climates such as the Last Glacial Maximum (LGM).</p><p>The Last Glacial Maximum, around 21,000 years ago, was about 4°C colder than the pre-industrial, and associated with large ice sheets on the American and Eurasian continents. It is one of the best documented periods thanks to numerous paleoclimate archives such as marine sediment cores and ice cores. Despite this period having been studied for years, no consensus on the causes of the lower atmospheric CO<sub>2</sub> concentration at the time (around 180 ppm) has been reached and models still struggle to simulate these low CO<sub>2</sub> values. The ocean, which contains around 40 times more carbon than the atmosphere, likely plays a key role, but models tend to simulate ocean circulation changes in disagreement with proxy data, such as carbon isotopes.</p><p>This new project aims at comparing, for the first time, the carbon cycle representation at the Last Glacial Maximum from general circulation models and intermediate complexity models. We will explain the protocol and present first results in terms of carbon storage in the main reservoirs (atmosphere, land and ocean) and their link to key climate variables such as temperature, sea ice and ocean circulation. The use of coupled climate-carbon models will not only allow to compare changes in the carbon cycle in models and analyse their causes, but it will also enable us to better compare to indirect data related to the carbon cycle such as carbon isotopes.</p>

scholarly journals The Role of Rough Topography in Mediating Impacts of Bottom Drag in Eddying Ocean Circulation Models

2017 ◽  
Vol 47 (8) ◽  
pp. 1941-1959 ◽  
Author(s):  
David S. Trossman ◽  
Brian K. Arbic ◽  
David N. Straub ◽  
James G. Richman ◽  
Eric P. Chassignet ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Turbulence Models ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Wave Drag ◽  
Flat Bottom ◽  
Length Scales ◽  
Barotropic Flow ◽  
Horizontal Length

AbstractMotivated by the substantial sensitivity of eddies in two-layer quasigeostrophic (QG) turbulence models to the strength of bottom drag, this study explores the sensitivity of eddies in more realistic ocean general circulation model (OGCM) simulations to bottom drag strength. The OGCM results are interpreted using previous results from horizontally homogeneous, two-layer, flat-bottom, f-plane, doubly periodic QG turbulence simulations and new results from two-layer, β-plane QG turbulence simulations run in a basin geometry with both flat and rough bottoms. Baroclinicity in all of the simulations varies greatly with drag strength, with weak drag corresponding to more barotropic flow and strong drag corresponding to more baroclinic flow. The sensitivity of the baroclinicity in the QG basin simulations to bottom drag is considerably reduced, however, when rough topography is used in lieu of a flat bottom. Rough topography reduces the sensitivity of the eddy kinetic energy amplitude and horizontal length scales in the QG basin simulations to bottom drag to an even greater degree. The OGCM simulation behavior is qualitatively similar to that in the QG rough-bottom basin simulations, in that baroclinicity is more sensitive to bottom drag strength than are eddy amplitudes or horizontal length scales. Rough topography therefore appears to mediate the sensitivity of eddies in models to the strength of bottom drag. The sensitivity of eddies to parameterized topographic internal lee wave drag, which has recently been introduced into some OGCMs, is also briefly discussed. Wave drag acts like a strong bottom drag in that it increases the baroclinicity of the flow, without strongly affecting eddy horizontal length scales.

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