scholarly journals Simulating low frequency changes in atmospheric CO<sub>2</sub> during the last 740 000 years

2006 ◽  
Vol 2 (2) ◽  
pp. 57-78 ◽  
Author(s):  
P. Köhler ◽  
H. Fischer
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ice Core ◽  
Low Frequency ◽  
Ice Cores ◽  
Deep Ocean ◽  
Natural Variability ◽  
Delayed Response ◽  
Marine Biota ◽  
Frequency Changes

Abstract. Atmospheric CO2 measured in Antarctic ice cores shows a natural variability of 80 to 100 ppmv during the last four glacial cycles and variations of approximately 60 ppmv in the two cycles between 410 and 650 kyr BP. We here use various paleo-climatic records from the EPICA Dome C Antarctic ice core and from oceanic sediment cores covering the last 740 kyr to force the ocean/atmosphere/biosphere box model of the global carbon cycle BICYCLE in a forward mode over this time in order to interpret the natural variability of CO2. Our approach is based on the previous interpretation of carbon cycle variations during Termination I (Köhler et al., 2005a). In the absense of a process-based sediment module one main simplification of BICYCLE is that carbonate compensation is approximated by the temporally delayed restoration of deep ocean [CO32−]. Our results match the low frequency changes in CO2 measured in the Vostok and the EPICA Dome C ice core for the last 650 kyr BP (r2≈0.75). During these transient simulations the carbon cycle reaches never a steady state due to the ongoing variability of the overall carbon budget caused by the time delayed response of the carbonate compensation to other processes. The average contributions of different processes to the rise in CO2 during Terminations I to V and during earlier terminations are: the rise in Southern Ocean vertical mixing: 36/22 ppmv, the rise in ocean temperature: 26/11 ppmv, iron limitation of the marine biota in the Southern Ocean: 20/14 ppmv, carbonate compensation: 15/7 ppmv, the rise in North Atlantic deep water formation: 13/0 ppmv, the rise in gas exchange due to a decreasing sea ice cover: −8/−7 ppmv, sea level rise: −12/−4 ppmv, and rising terrestrial carbon storage: −13/−6 ppmv. According to our model the smaller interglacial CO2 values in the pre-Vostok period prior to Termination V are mainly caused by smaller interglacial Southern Ocean SST and an Atlantic THC which stayed before MIS 11 (before 420 kyr BP) in its weaker glacial circulation mode.

scholarly journals Proposing a mechanistic understanding of changes in atmospheric CO<sub>2</sub> during the last 740 000 years

2006 ◽  
Vol 2 (1) ◽  
pp. 1-42 ◽  
Author(s):  
P. Köhler ◽  
H. Fischer
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Atmospheric Carbon Dioxide ◽  
Ice Core ◽  
Ice Cores ◽  
Global Carbon Cycle ◽  
Natural Variability ◽  
Marine Biota ◽  
Glacial Cycles ◽  
Global Carbon

Abstract. Atmospheric carbon dioxide (CO2) measured in Antarctic ice cores shows a natural variability of 80 to 100 ppmv during the last four glacial cycles and variations of approximately 60 ppmv in the two cycles between 410 and 650 kyr BP. We here use dust and the isotopic temperature proxy deuterium (δD) from the EPICA Dome C Antarctic ice core covering the last 740 kyr together with other paleo-climatic records to force the ocean/atmosphere/biosphere box model of the global carbon cycle BICYCLE in a forward mode over this time in order to reconstruct the natural variability of pCO2. Our simulation results covered by our proposed scenario are based on process understanding gained previously for carbon cycle variations during Termination I. These results match the pCO2 measured in the Vostok ice core well (r2=0.80) and we predict prior to Termination V significantly smaller amplitudes in pCO2 variations mainly based on a reduced interglacial ocean circulation and reduced interglacial Southern Ocean sea surface temperature. These predictions for the pre-Vostok period match the new pCO2 data from the EPICA Dome C ice core for the time period 410 to 650 kyr BP equally well (r2=0.79). This is the first forward modelling approach which covers all major processes acting on the global carbon cycle on glacial/interglacial time scales. The contributions of different processes (terrestrial carbon storage, sea ice, sea level, ocean temperature, ocean circulation, CaCO3 chemistry, marine biota) are analysed.

scholarly journals High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core

2013 ◽  
Vol 9 (6) ◽  
pp. 2789-2807 ◽  
Author(s):  
S. Schüpbach ◽  
U. Federer ◽  
P. R. Kaufmann ◽  
S. Albani ◽  
C. Barbante ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ross Sea ◽  
Transport Model ◽  
Mineral Dust ◽  
Ice Core ◽  
Ice Cores ◽  
Last Interglacial ◽  
The Holocene ◽  
Proxy Records

Abstract. In this study we report on new non-sea salt calcium (nssCa2+, mineral dust proxy) and sea salt sodium (ssNa+, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa2+ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa2+ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data. The availability of multiple East Antarctic nssCa2+ records also allows for a revision of a former estimate on the atmospheric CO2 sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO2 increase during T1. During the last interglacial, ssNa+ levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean. In contrast, Holocene ssNa+ flux in Talos Dome is about the same as during the last interglacial, indicating that there was similar ice cover present in the Ross Sea area during MIS 5.5 as during the Holocene.

scholarly journals Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks

2020 ◽  
Vol 117 (9) ◽  
pp. 4498-4504 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Eun Young Kwon ◽  
Tobias Friedrich
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Sea Ice ◽  
General Circulation ◽  
Deep Ocean ◽  
General Circulation Models ◽  
Ice Dynamics ◽  
Carbon Cycle Model ◽  
Ocean Stratification ◽  
Ocean Ventilation

The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here, we use a transient run of an intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of 10. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared with the current climate. Sensitivity tests with a steady-state carbon cycle model indicate that the two mechanisms combined can reduce atmospheric carbon by 40 ppm, with ocean stratification acting early within a glacial cycle to amplify the carbon cycle response.

scholarly journals Temporal Variations in the Deep Ice-Core Chemistry Record from Dye 3, Greenland (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 209-209
Author(s):  
C.C. Langway ◽  
K. Goto-Azuma
Keyword(s):  
Chemical Constituents ◽  
Ice Core ◽  
Low Frequency ◽  
Ice Cores ◽  
Temporal Variations ◽  
Atmospheric Composition ◽  
Data Sets ◽  
Core Samples ◽  
Core Profile ◽  
Polar Snow

Measurements of the chemical constituents in polar-snow deposits translate into chronological records representing a history of atmospheric composition for the periods involved. The 2037 m deep continuous and undisturbed ice core recovered at Dye 3, Greenland between 1979 and 1981 contains a temporal record of sequential snow deposits for the past 9 × 104 a B.P. (Dansgaard and others 1985). The upper 90 m of the deep core were unsuitable for chemistry studies, but stratigraphic continuity with present-day accumulation was obtained by hand-excavating a 5.4 m deep pit and augering two shallow cores to 138 and 113 m depths. The pit and shallow cores represent the last two centuries of snow precipitation.To date, over 6000 individual samples of the pit, shallow and deep ice cores have been measured by ion chromatography for Cl−, NO3−, and SO42− in the field and laboratory (Herron and Langway 1985, Finkel and Langway 1985, Finkel and others 1986), under clean-room conditions. All pit and shallow-core samples were prepared in a continuous sequence of eight samples per year, as identified by other stable and radioactive isotope-dating methods. The deep ice-core samples were selected and prepared from core intervals spaced over the 2037 m profile from time units which showed evidence of abrupt or transitory periods in climate change or volcanic disturbances, as defined by stable isotopes (Dansgaard and others 1985), atmospheric gases (Oeschger and others 1985) and dust (Hammer and others 1985).Approximately 1700 new measurements from the Dye 3 samples are included in this study. Variability in the chemical constituents and their concentration levels is present and meaningful on a short-term and long-term basis. The time units measured represent seasons, years, decades, centuries and longer geological periods. Particular attention is given to two new high- and low-frequency detailed chronological data sets from (1) a continuous 26 m core profile, representing 3000 years, extending from the Holocene/Wisconsin boundary back into the late Wisconsin and (2) measurements made on 106 samples spaced every 2 m over the Wisconsin-age ice from 1786 to 2008 m.

Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks over the last eight glacial cycles

2020 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Eun Young Kwon ◽  
Tobias Friedrich
Keyword(s):  
Carbon Sequestration ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Sea Ice ◽  
Deep Ocean ◽  
Glacial Cycles ◽  
Ice Dynamics ◽  
Ocean Stratification ◽  
Ocean Ventilation ◽  
The Impact

&lt;p class=&quot;p1&quot;&gt;&lt;span class=&quot;s1&quot;&gt;The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here we use a transient run of the LOVECLIM intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea-ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of ten. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared to the current climate. The impact of the two mechanisms on carbon sequestration was then tested within a steady-state carbon cycle. The two mechanisms combined can reduce atmospheric carbon by 40 ppm, of which approximately 30 ppm is due to ocean stratification. Moreover, ocean stratification from increased SO sea ice production acts early within glacial cycles to amplify the carbon cycle response.&lt;/span&gt;&lt;/p&gt;

scholarly journals Iron in ice cores from Law Dome, East Antarctica: implications for past deposition of aerosol iron

1998 ◽  
Vol 27 ◽  
pp. 365-370 ◽  
Author(s):  
R. Edwards ◽  
P. N. Sedwick ◽  
Vin Morgan ◽  
C. F. Boutron ◽  
S. Hong
Keyword(s):  
Southern Ocean ◽  
Late Holocene ◽  
Ice Core ◽  
Iron Concentration ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Iron Deposition ◽  
Past Century ◽  
Preliminary Estimate

Total-dissolvable iron has been measured in sections of three ice cores from Law Dome, East Antarctica, and the results used to calculate atmospheric iron deposition over this region during the late Holocene and to provide a preliminary estimate of aerosol iron deposition during the Last Glaciol Maximum I LGM). Ice-core sections dating from 56-2730 BP (late Holocene) and ~18000 BP (LGM) were decontaminated using trace-metal clean techniques, and total-dissolvable iron was determined in the acidified meltwatcrs by flow-injection analysis. Our results suggest that the atmospheric iron flux onto the Law Dome region has varied significantly over time-scales ranging from seasonal to Glaciol-interglaciol. The iron concentrations in ice-core sections from the past century suggest (1) a 2 4-fold variation in the atmospheric iron flux over a single annual cycle, with the highest flux occurring during the spring and summer, and (2) a nearly 7-fold variation in the annual maximum atmospheric iron flux over a 14 year period. The average estimated atmospheric iron flux calculated from our late-Holocene samples is 0.056-0.14 mg m a−1, which agrees well with Holocene flux estimates derived from aluminium measurements in inland Antarctic ice cores and a recent order-of-magnitude estimate of present-day atmospheric iron deposition over the Southern Ocean. The iron concentration of an ice-corc section dating from the LGM was more than 50 times higher than in the late-Holocene ice samples. Using a snow-accumulation rate estimate of 130 kg m −2 a−1 for this period, we calculate 0.87 mgm −2 a−1 as a preliminary estimate of atmospheric iron deposition during the LGM, which is 6-16 times greater than our average late-Holocene iron flux. Our data are consistent with the suggestion that there was a significantly greater flux of atmospheric iron onto the Southern Ocean during the LGM than during then Holocene.

scholarly journals Ice-core dating and chemistry by direct-current electrical conductivity

1992 ◽  
Vol 38 (130) ◽  
pp. 325-332 ◽  
Author(s):  
Kenorick Taylor ◽  
Richard Alley ◽  
Joe Fiacco ◽  
Pieter Grootes ◽  
Gregg Lamorey ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Ice Core ◽  
Low Frequency ◽  
Ice Cores ◽  
Quantitative Comparison ◽  
Quantitative Interpretation ◽  
Conductivity Measurements ◽  
Temperature Variations ◽  
The Core ◽  
Ice Core Dating

AbstractAlthough quantitative interpretation of the low-frequency electrical conductivity of ice cores from central Greenland is complicated by temperature variations of the measured core, annual layers can be recognized in sections of the core that are not impacted by non-seasonal features. Ambiguities in counting of annual layers can be minimized by comparing the electrical conductivity measurements to measurements of dust concentration and visual stratigraphy. A non-linear relationship between applied voltage and the current measured across two electrodes complicates the quantitative comparison of measurements made with different equipment, but does not affect the overall shape of the observed features.

scholarly journals Climatic information archived in ice cores: impact of intermittency and diffusion on the recorded isotopic signal in Antarctica

2019 ◽  
Author(s):  
Mathieu Casado ◽  
Thomas Münch ◽  
Thomas Laepple
Keyword(s):  
Time Scales ◽  
Signal To Noise Ratio ◽  
Ice Core ◽  
Ice Cores ◽  
Reanalysis Data ◽  
Climatic Conditions ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Frequency Changes ◽  
Isotopic Signal

Abstract. The isotopic signal (δ18O and δD) imprinted in ice cores from Antarctica is not solely generated by the temperature sensitivity of the isotopic composition of precipitation but also contains the signature of the intermittency of precipitation patterns as well as of post-deposition processes occurring at the surface and in the firn. This leads to a proxy signal recorded by the ice cores that may not be representative of the local climatic variations. Due to precipitation intermittency, the ice cores only record brief snapshots of the climatic conditions, resulting in aliasing of the climatic signal, and thus a large amount of noise which reduces the minimum temporal resolution at which a meaningful signal can be retrieved. The analyses are further complicated by isotopic diffusion which acts as a low pass filter that dampens any high frequency changes. Here, we use reanalysis data (ERA-Interim) combined with satellite products of accumulation to evaluate the spatial distribution of the transfer function that describes the formation of the isotopic signal across Antarctica. The minimum time scales at which the signal-to-noise ratio exceeds unity range from less than a year at the coast to a thousand years further inland. Based on solely physical processes, we were thus able to define a lower bound for the time scales at which climate variability can be reconstructed from ice core water isotopic compositions.

scholarly journals Antarctic and Southern Ocean dust transport pathways: Forward-trajectory modeling and rare earth element source constraints from the RICE ice core

2021 ◽  
Author(s):  
◽  
Peter David Neff
Keyword(s):  
Rare Earth ◽  
New Zealand ◽  
South America ◽  
Southern Ocean ◽  
Mineral Dust ◽  
Ice Core ◽  
Ice Cores ◽  
Potential Contribution ◽  
Anthropogenic Aerosols ◽  
Dust Transport

<p>Mineral dust fertilization of Southern Ocean surface waters, and mixing with Antarctic deep-water, influences oceanic uptake of carbon dioxide and draws down global atmospheric concentrations during glacial periods. Quantifying modern variability in dust source and transport strength, especially with respect to high- and low-latitude climate phenomena (e.g. the Southern Annular Mode, El Niño Southern Oscillation), will improve understanding of this important aspect of the global carbon cycle. Using high-order geochemical provenance techniques can also reveal in greater detail what aspects of dust transport are recorded in Antarctic ice core records, allowing for better interpretation of glacial-interglacial dust records at individual sites.  First, using forward trajectories and climate reanalysis data, this work explores modern variability (1979-2013) in atmospheric transport of mineral dust from Southern Hemisphere potential source areas (PSA)—primarily Australia, southern South America and southern Africa. Estimates of the relative source and transport strength of New Zealand are also discussed, and compared with other dust PSA to evaluate New Zealand’s potential contribution to Southern Ocean and Antarctic dust deposition. Extra-Antarctic dust PSA distributions are detailed for individual ice core sites, including the newly recovered Roosevelt Island Climate Evolution (RICE) ice core (79.36ºS, 161.71ºW, 550 m a.s.l.). This approach—applicable to many types of aerosol—reveals persistent, strong transport from New Zealand and Patagonia to the southern high-latitudes during all seasons. It also demonstrates that southward transport of air masses from pan-Pacific dust sources is affected by circulation variability initiated in the central tropical Pacific Ocean.  High-resolution discrete sampling of the RICE core allows for unprecedented analysis of trace elements at sub-annual to annual scales. The rare earth elements (REE, lanthanide elements Lanthanum to Lutetium) can preserve the signature of their original source material and thus provide provenance constraints for dust preserved in Antarctic snow and ice. While challenging, measurements of REE concentration to the single femtogram per gram (10-15 g g-1) level have been made by combining efficient sample introduction and a jet-interface sector-field inductively coupled plasma mass spectrometer. The methodology and fidelity of these measurements are presented, in addition to results for other low-concentration elements associated with natural and anthropogenic aerosols.  REE data from the RICE ice core are then used to explore possible modern sources of dust in the Ross Sea sector of Antarctica, testing hypothesized trajectory model distributions. Twentieth-century and late-Holocene (2.3 ka – present) REE data from the RICE ice core represent the first measurements of this kind from the Pacific sector of Antarctica. RICE data are compared with Holocene REE data from the Drønning Maud Land and Dome C ice cores, with consideration of REE signatures in dust samples from PSA. Data from the RICE ice core indicate fewer than 5% contributions of dust from South America, and show strong negative trends in crustal-normalized REE signatures suggesting contributions from local Antarctic dust.</p>

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